CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation-in-part of U.S. application Ser. No. 10/732,671, filed on Dec. 9, 2003, entitled “Method for Channel Congestion Management,” the content of which is incorporated herein by reference in its entirety.  
         [0002]     The following U.S. provisional and continuation-in-part patent applications, including the present application, are being filed concurrently and the disclosure of every other application is incorporated by reference in the present application in its entirety for all purposes: 
        U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Adaptive Use of Satellite Uplink Bands” (Attorney Docket No. 017018-008000US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 by Mark Dankberg, Mark Miller, Steve Hart, Kristi Jaska, and Bob Wilson for “Frequency Re-use for Service and Gateway Beams” (Attorney Docket No. 017018-008300US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Satellite Architecture” (Attorney Docket No. 017018-008500US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Piggy-back Satellite Architecture” (Attorney Docket No. 017018-008600US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Placement of Gateways Away from Service Beams” (Attorney Docket No. 017018-008800US)     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Multi-Service Provider Subscriber Authentication” (Attorney Docket No. 017018-007700US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 “Large Packet Concatenation in Satellite Communication System” (Attorney Docket No. 017018-008200US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 “Upfront Delayed Concatenation In Satellite Communication System” (Attorney Docket No. 017018-010500US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Map-Trigger Dump Of Packets In Satellite Communication System” (Attorney Docket No. 017018-010600US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Web/Bulk Transfer Preallocation Of Upstream Resources In A Satellite Communication System” (Attorney Docket No. 017018-010700US);     U.S. Continuation in Part Patent Application No. ______, filed Nov. 3, 2006 for “Code Reuse Multiple Access For A Satellite Return Link” (Attorney Docket No. 017018-001212US);     U.S. Continuation in Part Patent Application No. ______, filed Nov. 3, 2006 for “Method for Congestion Management” (Attorney Docket No. 017018-006110US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Aggregate Rate Modem” (Attorney Docket No. 017018-008900US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Packet Reformatting for Downstream Links” (Attorney Docket No. 017018-009000US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Downstream Waveform Modification” (Attorney Docket No. 017018-009100US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Upstream Resource Optimization” (Attorney Docket No. 017018-009200US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Upstream MF-TDMA Frequency Hopping” (Attorney Docket No. 017018-009300US);     U.S. Provisional Patent Application No. ______,filed Nov. 3, 2006 for “Downstream Virtual Channels Multiplexed on a Per Symbol Basis” (Attorney Docket No. 017018-009400US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Modified Downstream Waveform” (Attorney Docket No. 017018-010800US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Adapted DOCSIS Circuit for Satellite Media” (Attorney Docket No. 017018-009500US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Satellite Downstream Virtual Channels” (Attorney Docket No. 017018-009700US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Satellite Broadband with Less than One Country of Coverage” (Attorney Docket No. 017018-010300US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Multi-User Detection in Satellite Return Link” (Attorney Docket No. 017018-010100US)     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Multi-rate Downstreaming in Multiple Virtual Channel Environment” (Attorney Docket No. 017018-010200US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Satellite Upstream Load Balancing” (Attorney Docket No. 017018-009900US);     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Satellite Upstream/Downstream Virtual Channel Architecture” (Attorney Docket No. 017018-010000US); and     U.S. Provisional Patent Application No. ______, filed Nov. 3, 2006 for “Virtual Downstream Channel Load Balancing” (Attorney Docket No. 017018-009800US).       
 
     
    
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0030]     NOT APPLICABLE  
       REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK.  
       [0031]     NOT APPLICABLE  
       BACKGROUND OF THE INVENTION  
       [0032]     This invention relates to management of bandwidth resources in a packet telecommunication network, particularly at the datalink layer of a wireless network involving Multiple User Multiple Simultaneous Access (MUMSA) channels via a satellite communication network.  
         [0033]     There are various bandwidth management schemes known for attempting to control traffic load, particularly at the datalink layer and the physical layer. Single simultaneous user traffic management is known in the random multiple access services environment for a Multiple User Single Simultaneous Access (MUSSA) channel. However, the known traffic management schemes are deficient when applied to MUMSA applications because a so-called multi-user channel of the current art allows only single simultaneous user access. As load is increased, collisions between two or more transmissions decrease efficiency. Examples relevant to the present invention are described in a paper presented at IEEE INFOCOM 2001 by Zohar Naor and Hanoch Levy, entitled “A Centralized Dynamic Access Probability Protocol for Next Generation Wireless Networks,” IEEE INFOCOM 2001  The Conference on Computer Communications , No. 1, April 2001, pp. 767-775. In this paper, the channel load in a conventional ALOHA channel access protocol system is estimated by a measurement at the hub, then the hub sets a probability of access for the network and broadcasts that probability for use as a control or channel access restriction parameter to the network through a control channel or in a control timeslot. This protocol is not directly applicable to a multiple-simultaneous-user environment.  
         [0034]     There are many multiple-user, single-channel protocols, but almost all such protocols rely on a central control to dole out channel access to a subset of the general user population. For example, in the well-known Code Division Multiple Access (CDMA) systems, a central authority allocates individual spreading codes to a number of users, one at a time. Thus, the random access on this MUMSA channel is accomplished by only a strictly controlled subset of the user population.  
         [0035]     Code Reuse Multiple Access (CRMA) is an example of the MUMSA channel in which the entire user population is free to broadcast randomly. Here there is a true multiple-user, multiple simultaneous access environment, but it lacks sufficient control mechanisms to optimize channel utilization.  
         [0036]     Consumer broadband satellite services are gaining traction in North America with the start up of star network services using Ka band satellites. While such first generation satellite systems may provide multi-gigabit per second (Gbps) per satellite overall capacity, the design of such systems inherently limits the number of customers that may be adequately served. Moreover, the fact that the capacity is split across numerous coverage areas further limits the bandwidth to each subscriber.  
         [0037]     While existing designs have a number of capacity limitations, the demand for such broadband services continues to grow. The past few years have seen strong advances in communications and processing technology. This technology, in conjunction with selected innovative system and component design, may be harnessed to produce a novel satellite communications system to address this demand.  
         [0038]     What is needed is a system for control of access to MUMSA channels that maximizes the channel utilization under all load conditions while minimizing the amount of overhead, and maintaining the low delay of a random access approach.  
       SUMMARY OF THE INVENTION  
       [0039]     According to the invention, a method for managing data traffic in a multi-user multiple-simultaneous-access (MUMSA) environment, for example in a code reuse multiple access (CRMA) environment or other physical environment having true random access with more than one transmission present at the same time, the method including steps of providing a mechanism for estimating channel load for multiple users, then using the estimate of channel load to calculate a congestion threshold (CT) on an ongoing basis (which may be a probability of access), selecting a current congestion threshold, and then at each terminal performing an experiment using that congestion threshold value and a random number generator to determine if a packet is eligible to be transmitted, thus throttling the random transmission of packets so that the transmitted load from the terminal has a rate of packet transmission that is less than or equal to the congestion threshold times the offered load (from the user), where the congestion threshold value is related to the probability of a globally successful transmission of a number of simultaneously transmitted packets. In addition, the terminal may include a quality of service (QOS) factor to control the throttling of the transmitted load, allowing predictable data rates, latency and packet error rates. The experiment performed at the user terminal with congestion threshold value and the random number generator output as parameters determines whether the packet is actually transmitted or discarded. A basic load detection technique is disclosed for determining actual loads at the hub.  
         [0040]     Further according to the invention, in an environment where there are virtual downstream channels for packets, where the upstream packet streams are not directly affiliated with any of the downstream packet streams and where the upstream packet streams can be associated independently through common CRMA channels, channel congestion can be mitigated using CMRA techniques. In particular, when a virtual downstream channel becomes congested, the related upstream channels can each be throttled separately, so that their request function is suppressed, thereby mitigating against the clogging of the virtual downstream channel and the channel load is balanced. In another alternative or in addition, the users of the virtual downstream channel can be assigned to another virtual downstream channel to which the downstream packet streams have been transferred. The motivation for throttling and channel switching is on the basis of not only the downstream (data capacity) requirements but also upstream (data capacity) requirements.  
         [0041]     In a first embodiment, an upstream channel is associated with a single virtual downstream channel. (One to one). In that embodiment, each virtual downstream channel would throttle its own affiliated upstream channels. In another embodiment, upstream channels are unaffiliated with a downstream channel or can be pooled. (One to many). Because of the advantages of pooling large numbers of terminals in random access channels, terminals of multiple virtual downstream channels may by served by common random upstream channels. Preferably, terminals of all virtual downstream channels are pooled into a single common random upstream channel. In practice the terminals are grouped by capability, level of service, frequency band, speed of transmission and the like to effect the creation a group of upstream channels unaffiliated with any downstream channel, such that a mechanism, such as herein disclosed, is useful for managing the operation of the terminals. Control can be individually or by upstream channel.  
         [0042]     The invention will be better understood by reference to the following detailed description in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0043]      FIG. 1  is a use-case diagram of a Code Reuse Multiple Access (CRMA) Channel Access Protocol (CCAP).  
         [0044]      FIG. 2  is a diagram of operation of a method of the prior art.  
         [0045]      FIG. 3A  is a high level flow diagram for illustrating load estimate techniques at a network controller of the prior art.  
         [0046]      FIG. 3B  is a high level flow diagram for illustrating load estimate techniques at a terminal of the prior art.  
         [0047]      FIG. 3C  is a diagram for illustrating load estimate techniques at a network controller.  
         [0048]      FIG. 4A  is a diagram of operation of a method according to the invention.  
         [0049]      FIG. 4B  is a high level flow chart of operation related to quality of service at the network controller.  
         [0050]      FIG. 4C  is a high level flow chart of operation related to quality of service at a user terminal.  
         [0051]      FIG. 5  is a diagram for illustrating a basic apparatus for performing a load estimation technique.  
         [0052]      FIG. 6  is a timing diagram showing the computation of a congestion threshold and its application to congestion control.  
         [0053]      FIG. 7  is a flow chart of a technique for determining and disseminating a congestion threshold value.  
         [0054]      FIG. 8  is a flow chart illustrating how a local portion of the access protocol is performed at each terminal.  
         [0055]      FIG. 9  is a flow chart illustrating the algorithm for setup and teardown of virtual circuits at the network terminal for each request from a subscriber terminal.  
         [0056]      FIG. 10  is a flow chart for the handling of a packet according to a local MUMSA-CAP-QOS at a subscriber terminal. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0057]      FIG. 1  is an overview in a Use-Case diagram  10  which illustrates schematically each of the components of the invention and each of the cases in which the components or “actors” participate.  
         [0058]     The actors include:  
         [0059]     Network Operator  12 : The Network Operator  12  is the entity including the people and business concerns of a service provider (SP) that set the service policies (including quality of service (QOS) parameters) including the services of setting of operating parameters  14  and entering service agreements  16  for users of user devices  18  and subscriber terminals  20 .  
         [0060]     Network Controller  22 : The Network Controller  22  is the service in the form of computer software which computes a congestion threshold (CT) using parameters set by the Network Operator  12  and based on the measurements taken by a Network Hub  26 .  
         [0061]     Network Hub  26 : The Network Hub  26  comprises the communications equipment (antennas, radios, modems and software) which transmits packets  28  and receives packets  30  from subscriber terminals  20  and measures the network load  32 , that is, the amount of traffic being presented to the network. In general, any or even all of the subscriber terminals can perform the network load measurement, so long as they can receive the shared channel.  
         [0062]     Subscriber Terminal  20 : The Subscriber Terminal  20  comprises the communication equipment at the user premises that has the functions of transmitting data to  34  and receiving data from  36  the Network Hub  26  and performs the local portion of the channel access protocol  38  as herein explained.  
         [0063]     User Device  18 : The User Device  18  is the local computer (or other network device) located at the customer premises where the network traffic originates and terminates. It has the function of exchanging packets  40  with the subscriber terminal  20 .  
         [0064]     The basic embodiment of the CRMA Channel Access Protocol (CCAP) provides for robust access to the shared CRMA channel according to a best-efforts (BE) services standard. BE services provide no guarantees of minimum throughput or delay. According to the invention, the CRMA CAP services are extended by providing network services with a guaranteed quality of service (QOS). This extension is explained further herein.  
         [0065]     It is useful to examine prior art Multiple User Single Simultaneous Access ((MUSSA) channel configurations for comparison. Referring to  FIG. 2 , a MUSSA channel  102  of the prior art is divided into time slots  104 - 111  that can accommodate exactly one user at a time. In this example, User  1  and User  2  transmit successfully in adjacent time slots  104 ,  105 , but User  3  and User  4  both attempt to use the same time slot  109 , and both are unsuccessful, an event known as a collision. User  5  then transmits successfully in timeslot  111 . For maximum throughput in such channels, the channel usage must be limited so that, on average, only a small fraction of the slots are used. As a result of this limitation, the collisions that do occur are almost always between exactly two users. In this example, the other three users were able to transmit successfully, while the two colliding transmissions were lost and would require a further attempt, thus reducing ultimate channel throughput.  
         [0066]     Referring to  FIG. 3A , at a high level, the network controller  22  of the prior art estimates load (Step  100 ), generates a congestion threshold value or equivalent (Step  110 ) and broadcasts the congestion threshold value to all subscriber terminals (Step  120 ). Referring to  FIG. 3B , at each subscriber terminal  20  in the prior art, the congestion threshold value is received (Step  130 ), performs a random experiment using the received congestion threshold (Step  140 ), and broadcasts the packet to the hub  26 ) if the experiment is a success (Step  150 ).  
         [0067]     Referring to  FIG. 3C , according to the prior art, various techniques are employed to estimate load at the hub  26 , which has a preamble detector  122  to detect from the incoming channel, and it has a traffic demodulator  124  to provide data output. The incoming modulated channel can be sampled to determine whether it is idle or non-empty during the sampling interval. After the preamble detector, the data can be monitored for idle, successful packet transmission or collision. After the traffic demodulator  124  the data stream can be monitored for packet arrival.  
         [0068]     Referring to  FIG. 4A , a Multiple User Multiple Simultaneous Access (MUMSA) channel  112  of the invention is depicted. The MUMSA channel  112  is not divided into time slots. Successful transmissions from a number of users can overlap in time, made possible by use of Pseudo Noise (PN) spreading sequences. Each transmission is not time aligned with the other transmissions and the transmissions can also vary in length, as opposed to the fixed length, slotted transmissions of the channel  102  of  FIG. 2 . Here, the number of active users on the channel can vary instantaneously while always taking on integer values. Although not shown in this example, a rough analog of the MUSSA collision will occur when the instantaneous number of active users exceeds the maximum number of transmissions that the channel can support. In this MUMSA collision, by definition, a large number of transmissions are lost, as opposed to the two transmissions typically lost in a MUSSA collision. As the number of simultaneous users increases, however, the statistical behavior of the channel can be more accurately predicted upon which the present invention capitalizes.  
         [0069]     Referring to  FIG. 4B , according to a specific embodiment of the invention, a combination of congestion threshold and quality of service activities are performed at the hub  26  which are used to estimate load (Step  132 ), and the hub  26  broadcasts the load (Step  134 ), whereupon the terminal  20  ( FIG. 4C B) receives the load (Step  136 ), calculates a congestion threshold value, specifically a probability of access based on load and quality of service, as described (Step  138 ), then performs a random experiment (Step  142 ) with the locally-calculated congestion threshold and broadcasts the packet if the experiment is a success (Step  144 ). Each subscriber terminal enjoys this autonomy.  
         [0070]     In accordance with the invention, and referring to  FIG. 5 , in order to allow a number of active load estimates to proceed autonomously and with greater versatility, a controller  152  senses the rate of preamble detections at the output of a preamble detector  122 , and further senses the number of active traffic demodulators  124 ,  224 ,  324 ,  424 . The controller  152  alternatively senses the received power into the preamble detector and/or tests for packet arrivals at their outputs to the network. These tests can be combined. These options provide for a finer resolution estimate of the instantaneous load of the network.  
         [0071]     The CCAP with extensions according to the invention are performed by the network controller  22  and by the subscriber terminals  20 . The basic sequence of this protocol is shown in  FIG. 6 . The Network Hub  26  measures the network load by a process not directly germane to this invention (Step A) and reports with a Network Load Update to the Network Controller  22  (Step B). The Network Controller  22  conveys a new congestion threshold to the Subscriber Terminal  20  (Step C) in preparation for receipt of the next packet for transmission from the User Device  18  (Step D). The local access protocol (Step E) is invoked at the Subscriber Terminal  20  for the packet received for transmission whereupon the decision is made as to whether the packet is to be transmitted (Step F). If so, it is transmitted to the Network Hub  26  (Step G). If not, the packet is dropped (Step H).  
         [0072]      FIG. 7  is a flow chart for computation of the congestion threshold at the Network Controller  22 . First a desired access level (DAL) is computed, as hereinafter explained (Step K). An initial value of the congestion threshold is set or preset to 100% (CT=1) (Step L). An iterative process begins with each new network load measurement to establish a channel load CL from zero (CL=0) to 100% (CL=1) (Step M). An adjustment value AV is set as the desired access level divided by channel load (DAL/CL) or more precisely, the desired access level divided by the maximum of the channel load or 0.001 (where 0.001 is set to avoid a division by zero) (Step N). Hysteresis is applied to the adjustment value (AV) so that when AV&gt;1, it goes up at ¼ slope (Step O). Thereafter, the new congestion threshold is set to be the old congestion threshold multiplied by the adjustment value up to a value of 100%, or more precisely, the minimum of 1 and CT*AV (Step P). This new congestion threshold is then broadcast to all subscriber terminals (Step Q), and the iteration repeats (Step R).  
         [0073]     The desired access level (DAL) is computed based on the capacity of the system (in terms of number of possible simultaneous transmissions without degradation) and the quality requirements (in terms of packet error rates).  
         [0074]     Below is a depiction of the process for determining the probability P of access for a given network capacity:  
         [0075]     Assuming a Poisson process and a given access rate “r” the probability of exactly “k” accesses is:  
         P   ⁢           ⁢     access   ⁡     (     r   ,   k     )         :=         r   k     ·     ⅇ     -   r         k         
 
         [0076]     Determine the percentage of time that it is acceptable for the number of transmissions to exceed multiple access threshold (P excess ). For a given network capacity, expressed as the Multiple Access Threshold M, and a given rate of transmissions we know  
           ∑     k   =     M   +   1       ∞     ⁢     P   ⁢           ⁢     access   ⁡     (     r   ,   k     )           =     P   excess         
 
         [0077]     So, just find the maximum rate “r” such that:  
           ∑     k   =   1     M     ⁢     P   ⁢           ⁢     access   ⁡     (     r   ,   k     )           &lt;     1   -     P   excess           
 
         [0078]     The Congestion Threshold (CT) is used by each subscriber terminal in the network to perform the local portion of the CCAP, as explained in connection with  FIG. 8 . Between the network controller  22  and a representative Subscriber Terminal (ST)  20 , the first step is to process a packet for transmission (Step AA), then determine whether it is a control packet (Step BA), and if not, to transmit the packet (Step CA) then end (Step DA) to prepare to repeat the process. If it is a control packet, then a (pseudo-)random number is generated Step EA) and tested against a threshold (Step FA) established by policy or default. If the threshold is not met, the packet is transmitted (Step CA), otherwise it is dropped (Step GA) and the process is ended (Step DA) to be prepared to repeat.  
         [0079]     The quality of services (QOS) extensions to this invention allow the network to offer services with a guaranteed QOS in terms of a guaranteed minimum data rate and guaranteed maximum packet error rate. This is accomplished by the addition of a mechanism to admit QOS services into the network and by modification of the processes undertaken in the Network Controller to set the Congestion Threshold (CT) and the algorithm in the Subscriber Terminal to perform the Local CCAP.  
         [0080]     A Service Admission Protocol (SAP) for the QOS extensions is shown in  FIG. 9 . After setup (Step SA), service types are determined (Step TA), and all Best Effort (BE) services are automatically admitted (Step AB), since no guarantees are made for these services. QOS extensions are provided on a virtual circuit basis: a terminal may have one or more virtual circuits. The QOS extensions fall into two categories: Permanent Virtual Circuits (PVCs) (Step BB) and Switched Virtual Circuits (SVCs) (Step CB). PVCs are allocated on a long-term basis and must always be admitted (Step EB). SVCs are allocated on request and are admitted (Step GB) if the resources are available to meet the service level agreement of the request (Step FB). It is thus important that safeguards be built into the service management system to prevent over-commitment of PVCs. These safeguards are the subject to the service provider&#39;s policies, which will rely on the capacity provided by the subject invention.  
         [0081]     The network controller also uses the algorithm of  FIG. 9  to maintain a running tally of the committed information rate (Total_CIR) (Steps DB, HB, IB). This is used in a modified version of the Congestion Threshold (CT) calculation, as follows:  
         [0082]     Compute BE_Load=max(CL−Total_CIR,1)  
         [0083]     Compute BE_DAL=DAL−Total_CIR  
         [0084]     Compute BE_Load=max(CL−Total_CIR,1)  
         [0085]     Compute BE_DAL=DAL−Total_CIR  
         [0086]     AV=BE_DAL/BE_Load  
         [0087]     Apply Hysteresis to AV, AV&gt;1, go up at ¼ slope  
         [0088]     Set CT=min(1, CT*AV)  
         [0089]     The Subscriber Terminal then uses a modified version of the Local CCAP (herein Local CCAP—QOS) for handling each packet. This is shown in  FIG. 10 . The control packets are identified (Step AC), bypass the QOS process and are transmitted (Step BC). Packets not intended for the QOS circuit are identified (Step CC), a random number is generated (Step DC) and compared with the congestion threshold (EC). If less than the congestion threshold the packet is dropped (Step FC) rather than transmitted.  
         [0090]     The packet is tested to determine if the packet is intended for the QOS circuit (Step GC), whereupon it is placed in the QOS transmission queue (Step HC) and not immediately transmitted. The packets is then processed according to the QOS transmission queue handling procedures. If not, then a circuit setup request is sent to the network controller (Step IC).  
         [0091]     The QOS packets which have been placed in a QOS Transmission Queue are handled as noted in Step HC, wherein, according to the invention, packets must be transmitted at least at a rate provided by the service agreement CIR. The terminal may also transmit packets at rates beyond the CIR, assuming there is network capacity. For transmission of the excess packets, the subscriber terminal simply applies the standard CCAP algorithm.  
         [0092]     When the transmission queue is empty for a sufficient length of time, or when the service is terminated via a higher layer protocol, the Subscriber Terminal must send a request to tear-down the virtual circuit.  
         [0093]     The invention has been explained with reference to specific embodiments. Other embodiments will be evident to those of ordinary skill in the art. For example, while the invention has been explained with reference to operation where traffic through a hub is measured, the invention has broader applications. Therefore it is not intended that the invention be limited, except as indicated by the appended claims. Appendix A provides background information.  
         [0094]     The following information is given as background in order to understand the environment of high-speed satellite communication, particularly as employed to service subscribers accessing high speed networks.  
         [0095]      FIG. 1A  is a block diagram of an exemplary satellite communications system  100  configured according to various embodiments of the invention. The satellite communications system,  100  includes a network  120 , such as the Internet, interfaced with a gateway  115  that is configured to communicate with one or more subscriber terminals  130 , via a satellite  105 . A gateway  115  is sometimes referred to as a hub or ground station. Subscriber terminals  130  are sometimes called modems, satellite modems or user terminals. As noted above, although the communications system  100  is illustrated as a geostationary satellite  105  based communication system, it should be noted that various embodiments described herein are not limited to use in geostationary satellite based systems, for example some embodiments could be low earth orbit (LEO) satellite based systems.  
         [0096]     The network  120  may be any type of network and can include, for example, the Internet, an IP network, an intranet, a wide-area network (“WAN”), a local-area network (“LAN”), a virtual private network, the Public Switched Telephone Network (“PSTN”), and/or any other type of network supporting data communication between devices described herein, in different embodiments. A network  120  may include both wired and wireless connections, including optical links. Many other examples are possible and apparent to those skilled in the art in light of this disclosure. As illustrated in a number of embodiments, the network may connect the gateway  115  with other gateways (not pictured), which are also in communication with the satellite  105 .  
         [0097]     The gateway  115  provides an interface between the network  120  and the satellite  105 . The gateway  115  may be configured to receive data and information directed to one or more subscriber terminals  130 , and can format the data and information for delivery to the respective destination device via the satellite  105 . Similarly, the gateway  115  may be configured to receive signals from the satellite  105  (e.g., from one or more subscriber terminals) directed to a destination in the network  120 , and can format the received signals for transmission along the network  120 .  
         [0098]     A device (not shown) connected to the network  120  may communicate with one or more subscriber terminals, and through the gateway  115 . Data and information, for example IP datagrams, may be sent from a device in the network  120  to the gateway  115 . The gateway  115  may format a Medium Access Control (MAC) frame in accordance with a physical layer definition for transmission to the satellite  130 . A variety of physical layer transmission modulation and coding techniques may be used with certain embodiments of the invention, including those defined with the DVB-S2 and WiMAX standards. The link  135  from the gateway  115  to the satellite  105  may be referred to hereinafter as the downstream uplink  135 .  
         [0099]     The gateway  115  may use an antenna  110  to transmit the signal to the satellite  105 . In one embodiment, the antenna  110  comprises a parabolic reflector with high directivity in the direction of the satellite and low directivity in other directions. The antenna  110  may comprise a variety of alternative configurations and include operating features such as high isolation between orthogonal polarizations, high efficiency in the operational frequency bands, and low noise.  
         [0100]     In one embodiment, a geostationary satellite  105  is configured to receive the signals from the location of antenna  110  and within the frequency band and specific polarization transmitted. The satellite  105  may, for example, use a reflector antenna, lens antenna, array antenna, active antenna, or other mechanism known in the art for reception of such signals. The satellite  105  may process the signals received from the gateway  115  and forward the signal from the gateway  115  containing the MAC frame to one or more subscriber terminals  130 . In one embodiment, the satellite  105  operates in a multi-beam mode, transmitting a number of narrow beams each directed at a different region of the earth, allowing for frequency re-use. With such a multibeam satellite  105 , there may be any number of different signal switching configurations on the satellite, allowing signals from a single gateway  115  to be switched between different spot beams. In one embodiment, the satellite  105  may be configured as a “bent pipe” satellite, wherein the satellite may frequency convert the received carrier signals before retransmitting these signals to their destination, but otherwise perform little or no other processing on the contents of the signals. A variety of physical layer transmission modulation and coding techniques may be used by the satellite  105  in accordance with certain embodiments of the invention, including those defined with the DVB-S2 and WiMAX standards. For other embodiments a number of configurations are possible (e.g., using LEO satellites, or using a mesh network instead of a star network), as evident to those skilled in the art.  
         [0101]     The service signals transmitted from the satellite  105  may be received by one or more subscriber terminals  130 , via the respective subscriber antenna  125 . In one embodiment, the antenna  125  and terminal  130  together comprise a very small aperture terminal (VSAT), with the antenna  125  measuring approximately 0.6 meters in diameter and having approximately 2 watts of power. In other embodiments, a variety of other types of antennas  125  may be used at the subscriber terminal  130  to receive the signal from the satellite  105 . The link  150  from the satellite  105  to the subscriber terminals  130  may be referred to hereinafter as the downstream downlink  150 . Each of the subscriber terminals  130  may comprise a single user terminal or, alternatively, comprise a hub or router (not pictured) that is coupled to multiple user terminals. Each subscriber terminal  130  may be connected to consumer premises equipment (CPE)  160  comprising, for example computers, local area networks, Internet appliances, wireless networks, etc.  
         [0102]     In one embodiment, a Multi-Frequency Time-Division Multiple Access (MF-TDMA) scheme is used for upstream links  140 ,  145 , allowing efficient streaming of traffic while maintaining flexibility in allocating capacity among each of the subscriber terminals  130 . In this embodiment, a number of frequency channels are allocated which may be fixed, or which may be allocated in a more dynamic fashion. A Time Division Multiple Access (TDMA) scheme is also employed in each frequency channel. In this scheme, each frequency channel may be divided into several timeslots that can be assigned to a connection (i.e., a subscriber terminal  130 ). In other embodiments, one or more of the upstream links  140 ,  145  may be configured with other schemes, such as Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Code Division Multiple Access (CDMA), or any number of hybrid or other schemes known in the art.  
         [0103]     A subscriber terminal, for example  130 -a, may transmit data and information to a network  120  destination via the satellite  105 . The subscriber terminal  130  transmits the signals via the upstream uplink  145 -a to the satellite  105  using the antenna  125 -a. A subscriber terminal  130  may transmit the signals according to a variety of physical layer transmission modulation and coding techniques, including those defined with the DVB-S2 and WiMAX standards. In various embodiments, the physical layer techniques may be the same for each of the links  135 ,  140 ,  145 ,  150 , or may be different. The link from the satellite  105  to the gateway  115  may be referred to hereinafter as the upstream downlink  140 .  
         [0104]     Turning to  FIG. 1B , a block diagram is shown illustrating an alternative embodiment of a satellite communication system  100 . This communication system  100  may, for example, comprise the system  100  of  FIG. 1A , but is in this instance described with greater particularity. In this embodiment, the gateway  115  includes a Satellite Modem Termination System (SMTS), which is based at least in part on the Data-Over-Cable Service Interface Standard (DOCSIS). The SMTS in this embodiment includes a bank of modulators and demodulators for transmitting signals to and receiving signals from subscriber terminals  130 . The SMTS in the gateway  115  performs the real-time scheduling of the signal traffic through the satellite  105 , and provides the interfaces for the connection to the network  120 .  
         [0105]     In this embodiment, the subscriber terminals  135  use portions of DOCSIS-based modem circuitry, as well. Therefore, DOCSIS-based resource management, protocols, and schedulers may be used by the SMTS for efficient provisioning of messages. DOCSIS-based components may be modified, in various embodiments, to be adapted for use therein. Thus, certain embodiments may utilize certain parts of the DOCSIS specifications, while customizing others.  
         [0106]     While a satellite communications system  100  applicable to various embodiments of the invention is broadly set forth above, a particular embodiment of such a system  100  will now be described. In this particular example, approximately 2 gigahertz (GHz) of bandwidth is to be used, comprising four 500 megahertz (MHz) bands of contiguous spectrum. Employment of dual-circular polarization results in usable frequency comprising eight 500 MHz non-overlapping bands with 4 GHz of total usable bandwidth. This particular embodiment employs a multi-beam satellite  105  with physical separation between the gateways  115  and subscriber spot beams, and configured to permit reuse of the frequency on the various links  135 ,  140 ,  145 ,  150 . A single Traveling Wave Tube Amplifier (TWTA) is used for each service link spot beam on the downstream downlink, and each TWTA is operated at full saturation for maximum efficiency. A single wideband carrier signal, for example using one of the 500 MHz bands of frequency in its entirety, fills the entire bandwidth of the TWTA, thus allowing a minimum number of space hardware elements. Spotbeam size and TWTA power may be optimized to achieve maximum flux density on the earth&#39;s surface of −118 decibel-watts per meter squared per megahertz (dbW/m 2 /MHz). Thus, using approximately 2 bits per second per hertz (bits/s/Hz), there is approximately 1 Gbps of available bandwidth per spot beam.  
         [0107]     With reference to  FIG. 12A , an embodiment of a forward link distribution system  1200  is shown. The gateway  115  is shown coupled to an antenna  110 , which generates four downstream signals. A single carrier with 500 MHz of spectrum is used for each of the four downstream uplinks  135 . In this embodiment, a total of two-frequencies and two polarizations allow four separate downstream uplinks  135  while using only 1 GHz of the spectrum. For example, link A  135 -A could be Freq 1U (27.5-28.0 GHz) with left-hand polarization, link B  135 -B could be Freq 1U (27.5-28.0) GHz with right-hand polarization, link C could be Freq 2U (29.5-30 GHz) with left-hand polarization, and link D could be Freq 2U (29.5-30 GHz) with left-hand polarization.  
         [0108]     The satellite  105  is functionally depicted as four “bent pipe” connections between a feeder and service link. Carrier signals can be changed through the satellite  105  “bent pipe” connections along with the orientation of polarization. The satellite  105  converts each downstream uplink  135  signal into a downstream downlink signal  150 .  
         [0109]     In this embodiment, there are four downstream downlinks  150  that each provides a service link for four spot beams  205 . The downstream downlink  150  may change frequency in the bent pipe as is the case in this embodiment. For example, downstream uplink A  135 -A changes from a first frequency (i.e., Freq 1U) to a second frequency (i.e., Freq ID) through the satellite  105 . Other embodiments may also change polarization between the uplink and downlink for a given downstream channel. Some embodiments may use the same polarization and/or frequency for both the uplink and downlink for a given downstream channel.  
         [0110]     Referring next to  FIG. 12B , an embodiment of a return link distribution system is shown. This embodiment shows four upstream uplinks  145  from four sets of subscriber terminals  125 . A “bent pipe” satellite  105  takes the upstream uplinks  145 , optionally changes carrier frequency and/or polarization (not shown), and then redirects them as upstream downlinks  140  to a spot beam for a gateway  115 . In this embodiment, the carrier frequency changes between the uplink  145  and the downlink  140 , but the polarization remains the same. Because the feeder spot beams to the gateway  115  is not in the coverage area of the service beams, the same frequency pairs may be reused for both service links and feeder links.  
         [0111]     Turning to  FIGS. 2A and 2B , examples of a multi-beam system  200  configured according to various embodiments of the invention are shown. The multi-beam system  200  may, for example, be implemented in the network  100  described in  FIGS. 1A and 1B . Shown are the coverage of a number of feeder and service spot beam regions  225 ,  205 . In this embodiment, a satellite  215  reuses frequency bands by isolating antenna directivity to certain regions of a country (e.g., United States, Canada or Brazil). As shown in  FIG. 2A , there is complete geographic exclusivity between the feeder and service spot beams  205 ,  225 . But that is not the case for  FIG. 2B  where there may in some instances be service spot beam overlap (e.g.,  205 -c,  205 -d,  205 -e), while there is no overlap in other areas. However, with overlap, there are certain interference issues that may inhibit frequency band re-use in the overlapping regions. A four color pattern allows avoiding interference even where there is some overlap between neighboring service beams  205 .  
         [0112]     In this embodiment, the gateway terminals  210  are also shown along with their feeder beams  225 . As shown in  FIG. 2B , the gateway terminals  210  may be located in a region covered by a service spotbeam (e.g., the first, second and fourth gateways  210 - 1 ,  210 - 2 ,  210 - 4 ). However, a gateway may also be located outside of a region covered by a service spotbeam (e.g., the third gateway  210 - 3 ). By locating gateway terminals  210  outside of the service spotbeam regions (e.g., the third gateway  210 - 3 ), geographic separation is achieved to allow for re-use of the allocated frequencies.  
         [0113]     There are often spare gateway terminals  210  in a given feeder spot beam  225 . The spare gateway terminal  210 - 5  can substitute for the primary gateway terminal  210 - 4  should the primary gateway terminal  210 - 4  fail to function properly. Additionally, the spare can be used when the primary is impaired by weather.  
         [0114]     Referring next to  FIG. 8 , an embodiment of a downstream channel  800  is shown. The downstream channel  800  includes a series of superframes  804  in succession, where each superframe  804  may have the same size or may vary in size. This embodiment divides a superframe  804  into a number of virtual channels  808 ( 1 -n). The virtual channels  808 ( 1 -n) in each superframe  804  can be the same size or different sizes. The size of the virtual channels  808 ( 1 -n) can change between different superframes  804 . Different coding can be optionally used for the various virtual channels  808  ( 1 -n). In some embodiments, the virtual channels are as short as one symbol in duration.  
         [0115]     With reference to  FIG. 9 , an embodiment of an upstream channel  900  is shown. This embodiment uses MF-TDMA, but other embodiments can use CDMA, OFDM, or other access schemes. The upstream channel  900  has 500 MHz of total bandwidth in one embodiment. The total bandwidth is divided into m frequency sub-channels , which may differ in bandwidth, modulation, coding, etc. and may also vary in time based on system needs.  
         [0116]     In this embodiment, each subscriber terminal  130  is given a two-dimensional (2D) map to use for its upstream traffic. The 2D map has a number of entries where each indicates a frequency sub-channel  912  and time segment  908 ( 1 - 5 ). For example, one subscriber terminal  130  is allocated sub-channel m  912 -m, time segment one  908 - 1 ; sub-channel two  912 - 2 , time segment two  908 - 2 ; sub-channel two  912 - 2 , time segment three  908 - 3 ; etc. The 2D map is dynamically adjusted for each subscriber terminal  130  according to anticipated need by a scheduler in the SMTS.  
         [0117]     Referring to  FIG. 13 , an embodiment of a channel diagram is shown. Only the channels for a single feeder spot beam  225  and a single service spot beam  205  are shown, but embodiments include many of each spot beam  225 ,  205  (e.g., various embodiments could have  60 ,  80 ,  100 ,  120 , etc. of each type of spot beam  225 ,  205 ). The forward channel  800  includes n virtual channels  808  traveling from the gateway antenna  110  to the service spot beam  205 . Each subscriber terminal  130  may be allocated one or more of the virtual channels  808 . m MF-TDMA channels  912  make up the return channel  900  between the subscriber terminal (ST) antennas  125  and the feeder spot beam  225 .  
         [0118]     Referring next to  FIG. 3 , an embodiment of a ground system  300  of gateways  115  is shown in block diagram form. One embodiment could have fifteen active gateways  115  (and possibly spares) to generate sixty service spot beams, for example. The ground system  300  includes a number of gateways  115  respectively coupled to antennas  110 . All the gateways  115  are coupled to a network  120  such as the Internet. The network is used to gather information for the subscriber terminals. Additionally, each SMTS communicates with other SMTS and the Internet using the network  120  or other means not shown.  
         [0119]     Each gateway  115  includes a transceiver  305 , a SMTS  310  and a router  325 . The transceiver  305  includes both a transmitter and a receiver. In this embodiment, the transmitter takes a baseband signal and upconverts and amplifies the baseband signal for transmission of the downstream uplinks  135  with the antenna  110 . The receiver downconverts and tunes the upstream downlinks  140  along with other processing as explained below. The SMTS  310  processes signals to allow the subscriber terminals to request and receive information and schedules bandwidth for the forward and return channels  800 ,  900 . Additionally, the SMTS  310  provides configuration information and receives status from the subscriber terminals  130 . Any requested or returned information is forwarded via the router  325 .  
         [0120]     With reference to  FIG. 11 , an embodiment of gateway receiver  1100  is shown. This embodiment of the receiver  1100  processes four return channels  900  from four different service spot beams  205 . The return channels  900  may be divided among four pathways using antenna polarization and/or filtering  1104 . Each return channel is coupled to a low-noise amplifier (LNA)  1108 . Down conversion  1112  mixes down the signal into its intermediate frequency. Each of the upstream sub-channels  912  is separated from the signal by a number of tuners  1116 . Further processing is performed in the SMTS  310 .  
         [0121]     Referring next to  FIG. 10 , an embodiment of a gateway transmitter  1000  is shown. The downstream channels  800  are received at their intermediate frequencies from the SMTS  310 . With separate pathways, each downstream channel  800  is up-converted  1004  using two different carrier frequencies. A power amplifier  1008  increases the amplitude of the forward channel  900  before coupling to the antenna  110 . The antenna  110  polarizes the separate signals to keep the four forward channels  800  distinct as they are passed to the satellite  105 .  
         [0122]     With reference to  FIG. 4 , an embodiment of a SMTS  310  is shown in block diagram form. Baseband processing is done for the inbound and outbound links  135 ,  140  by a number of geographically separated gateways  115 . Each SMTS  310  is generally divided into two sections, specifically, the downstream portion  305  to send information to the satellite  105  and the upstream portion  315  to receive information from the satellite  105 .  
         [0123]     The downstream portion  305  takes information from the switching fabric  416  through a number of downstream (DS) blades  412 . The DS blades  412  are divided among a number of downstream generators  408 . This embodiment includes four downstream generators  408 , with one for each of the downstream channels  800 . For example, this embodiment uses four separate 500 MHz spectrum ranges having different frequencies and/or polarizations. A four-color modulator  436  has a modulator for each respective DS generator  408 . The modulated signals are coupled to the transmitter portion  1000  of the transceiver  305  at an intermediate frequency. Each of the four downstream generators  408  in this embodiment has J virtual DS blades  412 .  
         [0124]     The upstream portion  315  of the SMTS  310  receives and processes information from the satellite  105  in the baseband intermediate frequency. After the receiver portion  1100  of the transceiver  305  produces all the sub-channels  912  for the four separate baseband upstream signals, each sub-channel  912  is coupled to a different demodulator  428 . Some embodiments could include a switch before the demodulators  428  to allow any return link sub-channel  912  to go to any demodulator  428  to allow dynamic reassignment between the four return channels  908 . A number of demodulators are dedicated to an upstream (US) blade  424 .  
         [0125]     The US blades  424  serve to recover the information received from the satellite  105  before providing it to the switching fabric  416 . The US scheduler  430  on each US blade  424  serves to schedule use of the return channel  900  for each subscriber terminal  130 . Future needs for the subscriber terminals  130  of a particular return channel  900  can be assessed and bandwidth/latency adjusted accordingly in cooperation with the Resource Manager and Load Balancer (RM/LB) block  420 .  
         [0126]     The RM/LB block  420  assigns traffic among the US and DS blades. By communication with other RM/LB blocks  420  in other SMTSes  310 , each RM/LB block  420  can reassign subscriber terminals  130  and channels  800 ,  900  to other gateways  115 . This reassignment can take place for any number of reasons, for example, lack of resources and/or loading concerns. In this embodiment, the decisions are done in a distributed fashion among the RM/LB blocks  420 , but other embodiments could have decisions made by one master MR/LB block or at some other central decision-making authority. Reassignment of subscriber terminals  130  could use overlapping service spot beams  205 , for example.  
         [0127]     Referring next to  FIG. 5 , an embodiment of a satellite  105  is shown in block diagram form. The satellite  105  in this embodiment communicates with fifteen gateways  115  and all STs  130  using sixty feeder and service spot beams  225 ,  205 . Other embodiments could use more or less gateways/spot beams. Buss power  512  is supplied using a power source such as chemical fuel, nuclear fuel and/or solar energy. A satellite controller  516  is used to maintain attitude and otherwise control the satellite  105 . Software updates to the satellite  105  can be uploaded from the gateway  115  and performed by the satellite controller  516 .  
         [0128]     Information passes in two directions through the satellite  105 . A downstream translator  508  receives information from the fifteen gateways  115  for relay to subscriber terminals  130  using sixty service spot beams  205 . An upstream translator  504  receives information from the subscriber terminals  130  occupying the sixty spot beam areas and relays that information to the fifteen gateways  115 . This embodiment of the satellite can switch carrier frequencies in the downstream or upstream processors  508 ,  504  in a “bent-pipe” configuration, but other embodiments could do baseband switching between the various forward and return channels  800 ,  900 . The frequencies and polarization for each spot beam  225 ,  205  could be programmable or preconfigured.  
         [0129]     With reference to  FIG. 6A , an embodiment of an upstream translator  504  is shown in block diagram form. A Receiver and Downconverter (Rx/DC) block  616  receives all the return link information for the area defined by a spot beam  205  as an analog signal before conversion to an intermediate frequency (IF). There is a Rx/DC block  616  for each service spot beam area  205 . An IF switch  612  routes a particular baseband signal from a Rx/DC block  616  to a particular upstream downlink channel. The upstream downlink channel is filled using an Upconverter and Traveling Wave Tube Amplifier (UC/TWTA) block  620 . The frequency and/or polarization can be changed through this process such that each upstream channel passes through the satellite  105  in a bent pipe fashion.  
         [0130]     Each gateway  115  has four dedicated UC/TWTA blocks  620  in the upstream translator  504 . Two of the four dedicated UC/TWTA blocks  620  operate at a first frequency range and two operate at a second frequency range in this embodiment. Additionally, two use right-hand polarization and two use left-hand polarization. Between the two polarizations and two frequencies, the satellite  105  can communicate with each gateway  115  with four separate upstream downlink channels.  
         [0131]     Referring next to  FIG. 6B , an embodiment of a downstream translator  508  is shown as a block diagram. Each gateway  115  has four downstream uplink channels to the satellite  105  by use of two frequency ranges and two polarizations. A Rx/DC block  636  takes the analog signal and converts the signal to an intermediate frequency. There is a Rx/DC block  636  for all sixty downstream uplink channels from the fifteen gateways  115 . The IF switch  612  connects a particular channel  800  from a gateway  115  to a particular service spot beam  205 . Each IF signal from the switch  628  is modulated and amplified with a UC/TWTA block  632 . An antenna broadcasts the signal using a spot beam to subscriber terminals  130  that occupy the area of the spot beam. Just as with the upstream translator  504 , the downstream translator  508  can change carrier frequency and polarization of a particular downstream channel in a bent-pipe fashion.  
         [0132]      FIG. 7  comprises a block diagram illustrating a set of subscriber equipment  700  which may be located at a subscriber location for the reception and transmission of communication signals. Components of this set of subscriber equipment  700  may, for example, comprise the antenna  125 , associated subscriber terminal  130  and any consumer premises equipment (CPE)  160 , which may be a computer, a network, etc.  
         [0133]     An antenna  125  may receive signals from a satellite  105 . The antenna  125  may comprise a VSAT antenna, or any of a variety other antenna types (e.g., other parabolic antennas, microstrip antennas, or helical antennas). In some embodiments, the antenna  125  may be configured to dynamically modify its configuration to better receive signals at certain frequency ranges or from certain locations. From the antenna  125 , the signals are forwarded (perhaps after some form of processing) to the subscriber terminal  130 . The subscriber terminal  130  may include a radio frequency (RF) frontend  705 , a controller  715 , a virtual channel filter  702 , a modulator  725 , a demodulator  710 , a filter  706 , a downstream protocol converter  718 , an upstream protocol converter  722 , a receive (Rx) buffer  712 , and a transmit (Tx) buffer  716 .  
         [0134]     In this embodiment, the RF frontend  705  has both transmit and receive functions. The receive function includes amplification of the received signals (e.g., with a low noise amplifier (LNA)). This amplified signal is then downconverted (e.g., using a mixer to combine it with a signal from a local oscillator (LO)). This downconverted signal may be amplified again with the RF frontend  705 , before processing of the superframe  804  with the virtual channel filter  702 . A subset of each superframe  804  is culled from the downstream channel  800  by the virtual channel filter  702 , for example, one or more virtual channels  808  are filtered off for further processing.  
         [0135]     A variety of modulation and coding techniques may be used at the subscriber terminal  130  for signals received from and transmitted to a satellite. In this embodiment, modulation techniques include BPSK, QPSK, 8PSK, 16APSK, 32PSK. In other embodiments, additional modulation techniques may include ASK, FSK, MFSK, and QAM, as well as a variety of analog techniques. The demodulator  710  may demodulate the down-converted signals, forwarding the demodulated virtual channel  808  to a filter  706  to strip out the data intended for the particular subscriber terminal  130  from other information in the virtual channel  808 .  
         [0136]     Once the information destined for the particular subscriber terminal  130  is isolated, a downstream protocol converter  718  translates the protocol used for the satellite link into one that the DOCSIS MAC block  726  uses. Alternative embodiments could use a WiMAX MAC block or a combination DOCSIS/WiMAX block. A Rx buffer  712  is used to convert the high-speed received burst into a lower-speed stream that the DOCSIS MAC block  726  can process. The DOCSIS MAC block  726  is a circuit that receives a DOCSIS stream and manages it for the CPE  160 . Tasks such as provisioning, bandwidth management, access control, quality of service, etc. are managed by the DOCSIS MAC block  726 . The CPE can often interface with the DOCSIS MAC block  726  using Ethernet, WiFi, USB and/or other standard interfaces. In some embodiments, a WiMax block  726  could be used instead of a DOCSIS MAC block  726  to allow use of the WiMax protocol.  
         [0137]     It is also worth noting that while a downstream protocol converter  718  and upstream protocol converter  722  may be used to convert received packets to DOCSIS or WiMax compatible frames for processing by a MAC block  726 , these converters will not be necessary in many embodiments. For example, in embodiments where DOCSIS or WiMax based components are not used, the protocol used for the satellite link may also be compatible with the MAC block  726  without such conversions, and the converters  718 ,  722  may therefore be excluded.  
         [0138]     Various functions of the subscriber terminal  130  are managed by the controller  715 . The controller  715  may oversee a variety of decoding, interleaving, decryption, and unscrambling techniques, as known in the art. The controller may also manage the functions applicable to the signals and exchange of processed data with one or more CPEs  160 . The CPE  160  may comprise one or more user terminals, such as personal computers, laptops, or any other computing devices as known in the art.  
         [0139]     The controller  715 , along with the other components of the subscriber terminal  130 , may be implemented in one or more Application Specific Integrated Circuits (ASICs), or a general purpose processor adapted to perform the applicable functions. Alternatively, the functions of the subscriber terminal  130  may be performed by one or more other processing units (or cores), on one or more integrated circuits. In other embodiments, other types of integrated circuits may be used (e.g., Structured/Platform ASICs, Field Programmable Gate Arrays (FPGAs) and other Semi-Custom ICs), which may be programmed in any manner known in the art. The controller may be programmed to access memory unit (not shown). It may fetch instructions and other data from the memory unit, or write data to the memory-unit.  
         [0140]     As noted above, data may also be transmitted from the CPE  160  through the subscriber terminal  130  and up to a satellite  105  in various communication signals. The CPE  160 , therefore, may transmit data to DOCSIS MAC block  726  for conversion to the DOCSIS protocol before that protocol is translated with an upstream protocol converter  722 . The slow-rate data waits in the Tx buffer  716  until it is burst over the satellite link.  
         [0141]     The processed data is then transmitted from the Tx buffer  716  to the modulator  725 , where it is modulated using one of the techniques described above. In some embodiments, adaptive or variable coding and modulation techniques may be used in these transmissions. Specifically, different modulation and coding combinations, or “modcodes,” may be used for different packets, depending on the signal quality metrics from the antenna  125  to the satellite  105 . Other factors, such as network and satellite congestion issues, may be factored into the determination, as well. Signal quality information may be received from the satellite or other sources, and various decisions regarding modcode applicability may be made locally at the controller, or remotely. The RF frontend  705  may then amplify and upconvert the modulated signals for transmission through the antenna  125  to the satellite.  
         [0142]     The following information is given as background in order to understand the environment of high-speed satellite communication, particularly as employed to service subscribers accessing high speed networks.  
         [0143]      FIG. 1A  is a block diagram of an exemplary satellite communications system  100  configured according to various embodiments of the invention. The satellite communications system  100  includes a network  120 , such as the Internet, interfaced with a gateway  115  that is configured to communicate with one or more subscriber terminals  130 , via a satellite  105 . A gateway  115  is sometimes referred to as a hub or ground station. Subscriber terminals  130  are sometimes called modems, satellite modems or user terminals. As noted above, although the communications system  100  is illustrated as a geostationary satellite  105  based communication system, it should be noted that various embodiments described herein are not limited to use in geostationary satellite based systems, for example some embodiments could be low earth orbit (LEO) satellite based systems.  
         [0144]     The network  120  may be any type of network and can include, for example, the Internet, an IP network, an intranet, a wide-area network (“WAN”), a local-area network (“LAN”), a virtual private network, the Public Switched Telephone Network (“PSTN”), and/or any other type of network supporting data communication between devices described herein, in different embodiments. A network  120  may include both wired and wireless connections, including optical links. Many other examples are possible and apparent to those skilled in the art in light of this disclosure. As illustrated in a number of embodiments, the network may connect the gateway  115  with other gateways (not pictured), which are also in communication with the satellite  105 .  
         [0145]     The gateway  115  provides an interface between the network  120  and the satellite  105 . The gateway  115  may be configured to receive data and information directed to one or more subscriber terminals  130 , and can format the data and information for delivery to the respective destination device via the satellite  105 . Similarly, the gateway  115  may be configured to receive signals from the satellite  105  (e.g., from one or more subscriber terminals) directed to a destination in the network  120 , and can format the received signals for transmission along the network  120 .  
         [0146]     A device (not shown) connected to the network  120  may communicate with one or more subscriber terminals, and through the gateway  115 . Data and information, for example IP datagrams, may be sent from a device in the network  120  to the gateway  115 . The gateway  115  may format a Medium Access Control (MAC) frame in accordance with a physical layer definition for transmission to the satellite  130 . A variety of physical layer transmission modulation and coding techniques may be used with certain embodiments of the invention, including those defined with the DVB-S2 and WiMAX standards. The link  135  from the gateway  115  to the satellite  105  may be referred to hereinafter as the downstream uplink  135 .  
         [0147]     The gateway  115  may use an antenna  110  to transmit the signal to the satellite  105 . In one embodiment, the antenna  110  comprises a parabolic reflector with high directivity in the direction of the satellite and low directivity in other directions. The antenna  110  may comprise a variety of alternative configurations and include operating features such as high isolation between orthogonal polarizations, high efficiency in the operational frequency bands, and low noise.  
         [0148]     In one embodiment, a geostationary satellite  105  is configured to receive the signals from the location of antenna  110  and within the frequency band and specific polarization transmitted. The satellite  105  may, for example, use a reflector antenna, lens antenna, array antenna, active antenna, or other mechanism known in the art for reception of such signals. The satellite  105  may process the signals received from the gateway  115  and forward the signal from the gateway  115  containing the MAC frame to one or more subscriber terminals  130 . In one embodiment, the satellite  105  operates in a multi-beam mode, transmitting a number of narrow beams each directed at a different region of the earth, allowing for frequency re-use. With such a multibeam satellite  105 , there may be any number of different signal switching configurations on the satellite, allowing signals from a single gateway  115  to be switched between different spot beams. In one embodiment, the satellite  105  may be configured as a “bent pipe” satellite, wherein the satellite may frequency convert the received carrier signals before retransmitting these signals to their destination, but otherwise perform little or no other processing on the contents of the signals. A variety of physical layer transmission modulation and coding techniques may be used by the satellite  105  in accordance with certain embodiments of the invention, including those defined with the DVB-S2 and WiMAX standards. For other embodiments a number of configurations are possible (e.g., using LEO satellites, or using a mesh network instead of a star network), as evident to those skilled in the art.  
         [0149]     The service signals transmitted from the satellite  105  may be received by one or more subscriber terminals  130 , via the respective subscriber antenna  125 . In one embodiment, the antenna  125  and terminal  130  together comprise a very small aperture terminal (VSAT), with the antenna  125  measuring approximately 0.6 meters in diameter and having approximately 2 watts of power. In other embodiments, a variety of other types of antennas  125  may be used at the subscriber terminal  130  to receive the signal from the satellite  105 . The link  150  from the satellite  105  to the subscriber terminals  130  may be referred to hereinafter as the downstream downlink  150 . Each of the subscriber terminals  130  may comprise a single user terminal or, alternatively, comprise a hub or router (not pictured) that is coupled to multiple user terminals. Each subscriber terminal  130  may be connected to consumer premises equipment (CPE)  160  comprising, for example computers, local area networks, Internet appliances, wireless networks, etc.  
         [0150]     In one embodiment, a Multi-Frequency Time-Division Multiple Access (MF-TDMA) scheme is used for upstream links  140 ,  145 , allowing efficient streaming of traffic while maintaining flexibility in allocating capacity among each of the subscriber terminals  130 . In this embodiment, a number of frequency channels are allocated which may be fixed, or which may be allocated in a more dynamic fashion. A Time Division Multiple Access (TDMA) scheme is also employed in each frequency channel. In this scheme, each frequency channel may be divided into several timeslots that can be assigned to a connection (i.e., a subscriber terminal  130 ). In other embodiments, one or more of the upstream links  140 ,  145  may be configured with other schemes, such as Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Code Division Multiple Access (CDMA), or any number of hybrid or other schemes known in the art.  
         [0151]     A subscriber terminal, for example  130 -a, may transmit data and information to a network  120  destination via the satellite  105 . The subscriber terminal  130  transmits the signals via the upstream uplink  145 -a to the satellite  105  using the antenna  125 -a. A subscriber terminal  130  may transmit the signals according to a variety of physical layer transmission modulation and coding techniques, including those defined with the DVB-S2 and WiMAX standards. In various embodiments, the physical layer techniques may be the same for each of the links  135 ,  140 ,  145 ,  150 , or may be different. The link from the satellite  105  to the gateway  115  may be referred to hereinafter as the upstream downlink  140 .  
         [0152]     Turning to  FIG. 1B , a block diagram is shown illustrating an alternative embodiment of a satellite communication system  100 . This communication system  100  may, for example, comprise the system  100  of  FIG. 1A , but is in this instance described with greater particularity. In this embodiment, the gateway  115  includes a Satellite Modem Termination System (SMTS), which is based at least in part on the Data-Over-Cable Service Interface Standard (DOCSIS). The SMTS in this embodiment includes a bank of modulators and demodulators for transmitting signals to and receiving signals from subscriber terminals  130 . The SMTS in the gateway  115  performs the real-time scheduling of the signal traffic through the satellite  105 , and provides the interfaces for the connection to the network  120 . In this embodiment, the subscriber terminals  135  use portions of DOCSIS-based modem circuitry, as well. Therefore, DOCSIS-based resource management, protocols, and schedulers may be used by the SMTS for efficient provisioning of messages. DOCSIS-based components may be modified, in various embodiments, to be adapted for use therein. Thus, certain embodiments may utilize certain parts of the DOCSIS specifications, while customizing others.  
         [0153]     While a satellite communications system  100  applicable to various embodiments of the invention is broadly set forth above, a particular embodiment of such a system  100  will now be described. In this particular example, approximately 2 gigahertz (GHz) of bandwidth is to be used, comprising four 500 megahertz (MHz) bands of contiguous spectrum. Employment of dual-circular polarization results in usable frequency comprising eight 500 MHz non-overlapping bands with 4 GHz of total usable bandwidth. This particular embodiment employs a multi-beam satellite  105  with physical separation between the gateways  115  and subscriber spot beams, and configured to permit reuse of the frequency on the various links  135 ,  140 ,  145 ,  150 . A single Traveling Wave Tube Amplifier (TWTA) is used for each service link spot beam on the downstream downlink, and each TWTA is operated at full saturation for maximum efficiency. A single wideband carrier signal, for example using one of the 500 MHz bands of frequency in its entirety, fills the entire bandwidth of the TWTA, thus allowing a minimum number of space hardware elements. Spotbeam size and TWTA power may be optimized to achieve maximum flux density on the earth&#39;s surface of −118 decibel-watts per meter squared per megahertz (dbW/m 2 /MHz). Thus, using approximately 2 bits per second per hertz (bits/s/Hz), there is approximately 1 Gbps of available bandwidth per spot beam.  
         [0154]     With reference to  FIG. 12A , an embodiment of a forward link distribution system  1200  is shown. The gateway  115  is shown coupled to an antenna  110 , which generates four downstream signals. A single carrier with 500 MHz of spectrum is used for each of the four downstream uplinks  135 . In this embodiment, a total of two-frequencies and two polarizations allow four separate downstream uplinks  135  while using only 1 GHz of the spectrum. For example, link A  135 -A could be Freq 1U (27.5-28.0 GHz) with left-hand polarization, link B  135 -B could be Freq 1U (27.5-28.0) GHz with right-hand polarization, link C could be Freq 2U (29.5-30 GHz) with left-hand polarization, and link D could be Freq 2U (29.5-30 GHz) with left-hand polarization.  
         [0155]     The satellite  105  is functionally depicted as four “bent pipe” connections between a feeder and service link. Carrier signals can be changed through the satellite  105  “bent pipe” connections along with the orientation of polarization. The satellite  105  converts each downstream uplink  135  signal into a downstream downlink signal  150 .  
         [0156]     In this embodiment, there are four downstream downlinks  150  that each provides a service link for four spot beams  205 . The downstream downlink  150  may change frequency in the bent pipe as is the case in this embodiment. For example, downstream uplink A  135 -A changes from a first frequency (i.e., Freq 1U) to a second frequency (i.e., Freq 1D) through the satellite  105 . Other embodiments may also change polarization between the uplink and downlink for a given downstream channel. Some embodiments may use the same polarization and/or frequency for both the uplink and downlink for a given downstream channel.  
         [0157]     Referring next to  FIG. 12B , an embodiment of a return link distribution system is shown. This embodiment shows four upstream uplinks  145  from four sets of subscriber terminals  125 . A “bent pipe” satellite  105  takes the upstream uplinks  145 , optionally changes carrier frequency and/or polarization (not shown), and then redirects them as upstream downlinks  140  to a spot beam for a gateway  115 . In this embodiment, the carrier frequency changes between the uplink  145  and the downlink  140 , but the polarization remains the same. Because the feeder spot beams to the gateway  115  is not in the coverage area of the service beams, the same frequency pairs may be reused for both service links and feeder links.  
         [0158]     Turning to  FIGS. 2A and 2B , examples of a multi-beam system  200  configured according to various embodiments of the invention are shown. The multi-beam system  200  may, for example, be implemented in the network  100  described in  FIGS. 1A and 1B . Shown are the coverage of a number of feeder and service spot beam regions  225 ,  205 . In this embodiment, a satellite  215  reuses frequency bands by isolating antenna directivity to certain regions of a country (e.g., United States, Canada or Brazil). As shown in  FIG. 2A , there is complete geographic exclusivity between the feeder and service spot beams  205 ,  225 . But that is not the case for  FIG. 2B  where there may in some instances be service spot beam overlap (e.g.,  205 -c,  205 -d,  205 -e), while there is no overlap in other areas. However, with overlap, there are certain interference issues that may inhibit frequency band re-use in the overlapping regions. A four color pattern allows avoiding interference even where there is some overlap between neighboring service beams  205 .  
         [0159]     In this embodiment, the gateway terminals  210  are also shown along with their feeder beams  225 . As shown in  FIG. 2B , the gateway terminals  210  may be located in a region covered by a service spotbeam (e.g., the first, second and fourth gateways  210 - 1 ,  210 - 2 ,  210 - 4 ). However, a gateway may also be located outside of a region covered by a service spotbeam (e.g., the third gateway  210 - 3 ). By locating gateway terminals  210  outside of the service spotbeam regions (e.g., the third gateway  210 - 3 ), geographic separation is achieved to allow for re-use of the allocated frequencies.  
         [0160]     There are often spare gateway terminals  210  in a given feeder spot beam  225 . The spare gateway terminal  210 - 5  can substitute for the primary gateway terminal  210 - 4  should the primary gateway terminal  210 - 4  fail to function properly. Additionally, the spare can be used when the primary is impaired by weather. Referring next to  FIG. 8 , an embodiment of a downstream channel  800  is shown. The downstream channel  800  includes a series of superframes  804  in succession, where each superframe  804  may have the same size or may vary in size. This embodiment divides a superframe  804  into a number of virtual channels  808 ( 1 -n). The virtual channels  808 ( 1 -n) in each superframe  804  can be the same size or different sizes. The size of the virtual channels  808 ( 1 -n) can change between different superframes  804 . Different coding can be optionally used for the various virtual channels  808  ( 1 -n). In some embodiments, the virtual channels are as short as one symbol in duration.  
         [0161]     With reference to  FIG. 9 , an embodiment of an upstream channel  900  is shown. This embodiment uses MF-TDMA, but other embodiments can use CDMA, OFDM, or other access schemes. The upstream channel  900  has 500 MHz of total bandwidth in one embodiment. The total bandwidth is divided into m frequency sub-channels, which may differ in bandwidth, modulation, coding, etc. and may also vary in time based on system needs.  
         [0162]     In this embodiment, each subscriber terminal  130  is given a two-dimensional (2D) map to use for its upstream traffic. The 2D map has a number of entries where each indicates a frequency sub-channel  912  and time segment  908 ( 1 - 5 ). For example, one subscriber terminal  130  is allocated sub-channel m  912 -m, time segment one  908 - 1 ; sub-channel two  912 - 2 , time segment two  908 - 2 ; sub-channel two  912 - 2 , time segment three  908 - 3 ; etc. The 2D map is dynamically adjusted for each subscriber terminal  130  according to anticipated need by a scheduler in the SMTS.  
         [0163]     Referring to  FIG. 13 , an embodiment of a channel diagram is shown. Only the channels for a single feeder spot beam  225  and a single service spot beam  205  are shown, but embodiments include many of each spot beam  225 ,  205  (e.g., various embodiments could have  60 ,  80 ,  100 ,  120 , etc. of each type of spot beam  225 ,  205 ). The forward channel  800  includes n virtual channels  808  traveling from the gateway antenna  110  to the service spot beam  205 . Each subscriber terminal  130  may be allocated one or more of the virtual channels  808 . m MF-TDMA channels  912  make up the return channel  900  between the subscriber terminal (ST) antennas  125  and the feeder spot beam  225 .  
         [0164]     Referring next to  FIG. 3 , an embodiment of a ground system  300  of gateways  115  is shown in block diagram form. One embodiment could have fifteen active gateways  115  (and possibly spares) to generate sixty service spot beams, for example. The ground system  300  includes a number of gateways  115  respectively coupled to antennas  110 . All the gateways  115  are coupled to a network  120  such as the Internet. The network is used to gather information for the subscriber terminals. Additionally, each SMTS communicates with other SMTS and the Internet using the network  120  or other means not shown.  
         [0165]     Each gateway  115  includes a transceiver  305 , a SMTS  310  and a router  325 . The transceiver  305  includes both a transmitter and a receiver. In this embodiment, the transmitter takes a baseband signal and upconverts and amplifies the baseband signal for transmission of the downstream uplinks  135  with the antenna  110 . The receiver downconverts and tunes the upstream downlinks  140  along with other processing as explained below. The SMTS  310  processes signals to allow the subscriber terminals to request and receive information and schedules bandwidth for the forward and return channels  800 ,  900 . Additionally, the SMTS  310  provides configuration information and receives status from the subscriber terminals  130 . Any requested or returned information is forwarded via the router  325 .  
         [0166]     With reference to  FIG. 11 , an embodiment of gateway receiver  1100  is shown. This embodiment of the receiver  1100  processes four return channels  900  from four different service spot beams  205 . The return channels  900  may be divided among four pathways using antenna polarization and/or filtering  1104 . Each return channel is coupled to a low-noise amplifier (LNA)  1108 . Down conversion  1112  mixes down the signal into its intermediate frequency. Each of the upstream sub-channels  912  is separated from the signal by a number of tuners  1116 . Further processing is performed in the SMTS  310 .  
         [0167]     Referring next to  FIG. 10 , an embodiment of a gateway transmitter  1000  is shown. The downstream channels  800  are received at their intermediate frequencies from the SMTS  310 . With separate pathways, each downstream channel  800  is up-converted  1004  using two different carrier frequencies. A power amplifier  1008  increases the amplitude of the forward channel  900  before coupling to the antenna  110 . The antenna  110  polarizes the separate signals to keep the four forward channels  800  distinct as they are passed to the satellite  105 . With reference to  FIG. 4 , an embodiment of a SMTS  310  is shown in block diagram form. Baseband processing is done for the inbound and outbound links  135 ,  140  by a number of geographically separated gateways  115 . Each SMTS  310  is generally divided into two sections, specifically, the downstream portion  305  to send information to the satellite  105  and the upstream portion  315  to receive information from the satellite  105 .  
         [0168]     The downstream portion  305  takes information from the switching fabric  416  through a number of downstream (DS) blades  412 . The DS blades  412  are divided among a number of downstream generators  408 . This embodiment includes four downstream generators  408 , with one for each of the downstream channels  800 . For example, this embodiment uses four separate 500 MHz spectrum ranges having different frequencies and/or polarizations. A four-color modulator  436  has a modulator for each respective DS generator  408 . The modulated signals are coupled to the transmitter portion  1000  of the transceiver  305  at an intermediate frequency. Each of the four downstream generators  408  in this embodiment has J virtual DS blades  412 .  
         [0169]     The upstream portion  315  of the SMTS  310  receives and processes information from the satellite  105  in the baseband intermediate frequency. After the receiver portion  1100  of the transceiver  305  produces all the sub-channels  912  for the four separate baseband upstream signals, each sub-channel  912  is coupled to a different demodulator  428 . Some embodiments could include a switch before the demodulators  428  to allow any return link sub-channel  912  to go to any demodulator  428  to allow dynamic reassignment between the four return channels  908 . A number of demodulators are dedicated to an upstream (US) blade  424 .  
         [0170]     The US blades  424  serve to recover the information received from the satellite  105  before providing it to the switching fabric  416 . The US scheduler  430  on each US blade  424  serves to schedule use of the return channel  900  for each subscriber terminal  130 . Future needs for the subscriber terminals  130  of a particular return channel  900  can be assessed and bandwidth/latency adjusted accordingly in cooperation with the Resource Manager and Load Balancer (RM/LB) block  420 .  
         [0171]     The RM/LB block  420  assigns traffic among the US and DS blades. By communication with other RM/LB blocks  420  in other SMTSes  310 , each RM/LB block  420  can reassign subscriber terminals  130  and channels  800 ,  900  to other gateways  115 . This reassignment can take place for any number of reasons, for example, lack of resources and/or loading concerns. In this embodiment, the decisions are done in a distributed fashion among the RM/LB blocks  420 , but other embodiments could have decisions made by one master MR/LB block or at some other central decision-making authority. Reassignment of subscriber terminals  130  could use overlapping service spot beams  205 , for example.  
         [0172]     Referring next to  FIG. 5 , an embodiment of a satellite  105  is shown in block diagram form. The satellite  105  in this embodiment communicates with fifteen gateways  115  and all STs  130  using sixty feeder and service spot beams  225 ,  205 . Other embodiments could use more or less gateways/spot beams. Buss power  512  is supplied using a power source such as chemical fuel, nuclear fuel and/or solar energy. A satellite controller  516  is used to maintain attitude and otherwise control the satellite  105 . Software updates to the satellite  105  can be uploaded from the gateway  115  and performed by the satellite controller  516 .  
         [0173]     Information passes in two directions through the satellite  105 . A downstream translator  508  receives information from the fifteen gateways  115  for relay to subscriber terminals  130  using sixty service spot beams  205 . An upstream translator  504  receives information from the subscriber terminals  130  occupying the sixty spot beam areas and relays that information to the fifteen gateways  115 . This embodiment of the satellite can switch carrier frequencies in the downstream or upstream processors  508 ,  504  in a “bent- 7 pipe” configuration, but other embodiments could do baseband switching between the various forward and return channels  800 ,  900 . The frequencies and polarization for each spot beam  225 ,  205  could be programmable or preconfigured.  
         [0174]     With reference to  FIG. 6A , an embodiment of an upstream translator  504  is shown in block diagram form. A Receiver and Downconverter (Rx/DC) block  616  receives all the return link information for the area defined by a spot beam  205  as an analog signal before conversion to an intermediate frequency (IF). There is a Rx/DC block  616  for each service spot beam area  205 . An IF switch  612  routes a particular baseband signal from a Rx/DC block  616  to a particular upstream downlink channel. The upstream downlink channel is filled using an Upconverter and Traveling Wave Tube Amplifier (UC/TWTA) block  620 . The frequency and/or polarization can be changed through this process such that each upstream channel passes through the satellite  105  in a bent pipe fashion.  
         [0175]     Each gateway  115  has four dedicated UC/TWTA blocks  620  in the upstream translator  504 . Two of the four dedicated UC/TWTA blocks  620  operate at a first frequency range and two operate at a second frequency range in this embodiment. Additionally, two use right-hand polarization and two use left-hand polarization. Between the two polarizations and two frequencies, the satellite  105  can communicate with each gateway  115  with four separate upstream downlink channels.  
         [0176]     Referring next to  FIG. 6B , an embodiment of a downstream translator  508  is shown as a block diagram. Each gateway  115  has four downstream uplink channels to the satellite  105  by use of two frequency ranges and two polarizations. A Rx/DC block  636  takes the analog signal and converts the signal to an intermediate frequency. There is a Rx/DC block  636  for all sixty downstream uplink channels from the fifteen gateways  115 . The IF switch  612  connects a particular channel  800  from a gateway  115  to a particular service spot beam  205 . Each IF signal from the switch  628  is modulated and amplified with a UC/TWTA block  632 . An antenna broadcasts the signal using a spot beam to subscriber terminals  130  that occupy the area of the spot beam. Just as with the upstream translator  504 , the downstream translator  508  can change carrier frequency and polarization of a particular downstream channel in a bent-pipe fashion.  
         [0177]      FIG. 7  comprises a block diagram illustrating a set of subscriber equipment  700  which may be located at a subscriber location for the reception and transmission of communication signals. Components of this set of subscriber equipment  700  may, for example, comprise the antenna  125 , associated subscriber terminal  130  and any consumer premises equipment (CPE)  160 , which may be a computer, a network, etc.  
         [0178]     An antenna  125  may receive signals from a satellite  105 . The antenna  125  may comprise a VSAT antenna, or any of a variety other antenna types (e.g., other parabolic antennas, microstrip antennas, or helical antennas). In some embodiments, the antenna  125  may be configured to dynamically modify its configuration to better receive signals at certain frequency ranges or from certain locations. From the antenna  125 , the signals are forwarded (perhaps after some form of processing) to the subscriber terminal  130 . The subscriber terminal  130  may include a radio frequency (RF) frontend  705 , a controller  715 , a virtual channel filter  702 , a modulator  725 , a demodulator  710 , a filter  706 , a downstream protocol converter  718 , an upstream protocol converter  722 , a receive (Rx) buffer  712 , and a transmit (Tx) buffer  716 .  
         [0179]     In this embodiment, the RF frontend  705  has both transmit and receive functions. The receive function includes amplification of the received signals (e.g., with a low noise amplifier (LNA)). This amplified signal is then downconverted (e.g., using a mixer to combine it with a signal from a local oscillator (LO)). This downconverted signal may be amplified again with the RF frontend  705 , before processing of the superframe  804  with the virtual channel filter  702 . A subset of each superframe  804  is culled from the downstream channel  800  by the virtual channel filter  702 , for example, one or more virtual channels  808  are filtered off for further processing.  
         [0180]     A variety of modulation and coding techniques may be used at the subscriber terminal  130  for signals received from and transmitted to a satellite. In this embodiment, modulation techniques include BPSK, QPSK, 8PSK, 16APSK, 32PSK. In other embodiments, additional modulation techniques may include ASK, FSK, MFSK, and QAM, as well as a variety of analog techniques. The demodulator  710  may demodulate the down-converted signals, forwarding the demodulated virtual channel  808  to a filter  706  to strip out the data intended for the particular subscriber terminal  130  from other information in the virtual channel  808 . Once the information destined for the particular subscriber terminal  130  is isolated, a downstream protocol converter  718  translates the protocol used for the satellite link into one that the DOCSIS MAC block  726  uses. Alternative embodiments could use a WiMAX MAC block or a combination DOCSIS/WiMAX block. A Rx buffer  712  is used to convert the high-speed received burst into a lower-speed stream that the DOCSIS MAC block  726  can process. The DOCSIS MAC block  726  is a circuit that receives a DOCSIS stream and manages it for the CPE  160 . Tasks such as provisioning, bandwidth management, access control, quality of service, etc. are managed by the DOCSIS MAC block  726 . The CPE can often interface with the DOCSIS MAC block  726  using Ethernet, WiFi, USB and/or other standard interfaces. In some embodiments, a WiMax block  726  could be used instead of a DOCSIS MAC block  726  to allow use of the WiMax protocol.  
         [0181]     It is also worth noting that while a downstream protocol converter  718  and upstream protocol converter  722  may be used to convert received packets to DOCSIS or WiMax compatible frames for processing by a MAC block  726 , these converters will not be necessary in many embodiments. For example, in embodiments where DOCSIS or WiMax based components are not used, the protocol used for the satellite link may also be compatible with the MAC block  726  without such conversions, and the converters  718 ,  722  may therefore be excluded.  
         [0182]     Various functions of the subscriber terminal  130  are managed by the controller  715 . The controller  715  may oversee a variety of decoding, interleaving, decryption, and unscrambling techniques, as known in the art. The controller may also manage the functions applicable to the signals and exchange of processed data with one or more CPEs  160 . The CPE  160  may comprise one or more user terminals, such as personal computers, laptops, or any other computing devices as known in the art.  
         [0183]     The controller  715 , along with the other components of the subscriber terminal  130 , may be implemented in one or more Application Specific Integrated Circuits (ASICs), or a general purpose processor adapted to perform the applicable functions. Alternatively, the functions of the subscriber terminal  130  may be performed by one or more other processing units (or cores), on one or more integrated circuits. In other embodiments, other types of integrated circuits may be used (e.g., Structured/Platform ASICs, Field Programmable Gate Arrays (FPGAs) and other Semi-Custom ICs), which may be programmed in any manner known in the art. The controller may be programmed to access memory unit (not shown). It may fetch instructions and other data from the memory unit, or write data to the memory-unit. As noted above, data may also be transmitted from the CPE  160  through the subscriber terminal  130  and up to a satellite  105  in various communication signals. The CPE  160 , therefore, may transmit data to DOCSIS MAC block  726  for conversion to the DOCSIS protocol before that protocol is translated with an upstream protocol converter  722 . The slow-rate data waits in the Tx buffer  716  until it is burst over the satellite link.  
         [0184]     The processed data is then transmitted from the Tx buffer  716  to the modulator  725 , where it is modulated using one of the techniques described above. In some embodiments, adaptive or variable coding and modulation techniques may be used in these transmissions. Specifically, different modulation and coding combinations, or “modcodes,” may be used for different packets, depending on the signal quality metrics from the antenna  125  to the satellite  105 . Other factors, such as network and satellite congestion issues, may be factored into the determination, as well. Signal quality information may be received from the satellite or other sources, and various decisions regarding modcode applicability may be made locally at the controller, or remotely. The RF frontend  705  may then amplify and upconvert the modulated signals for transmission through the antenna  125  to the satellite.
A method for managing data traffic in a multi-user multiple-simultaneous-access (MUMSA) environment, for example in a code reuse multiple access (CRMA) environment or other physical environment having true random access with more than one transmission present at the same time, the method including estimating channel load for multiple users, then using the estimate of channel load to calculate a congestion threshold on an ongoing basis, at each terminal performing an experiment using that congestion threshold value and a random number generator to determine if a packet is eligible to be transmitted, transferring downstream virtual channel traffic and redistributing user terminals to affiliate with the proper downstream virtual channel.