hereafter , the terminology “ station ” ( sta ) includes but is not limited to a user equipment , a wireless transmit / receive unit ( wtru ), a fixed or mobile subscriber unit , a pager , or any other type of device capable of operating in a wireless environment . when referred to hereafter , the terminology “ mesh point ” includes but is not limited to a node - b , a base station , a site controller , an access point or any other type of interfacing device in a wireless environment . the present invention is applicable to any wireless mesh networks including , but not limited to , ieee 802 . 11 , ieee 802 . 11s , ieee 802 . 15 , ieee 802 . 15 . 5 . fig1 is a diagram of an exemplary mesh wlan 100 comprising eight ( 8 ) mesh points 104 1 - 104 8 . in this example , mesh point 104 4 is an imp for the sta 102 and mesh point 104 2 is an emp for the data sent by the sta 102 . data sent by the sta 102 is routed from one mesh point 104 4 to another mesh point 104 2 through the intermediate mesh points in the mesh wlan 100 for the internet access . multiple data paths can be established within the mesh wlan 100 . as an example , two different data paths from the imp mesh point 104 4 to the emp mesh point 104 2 are illustrated by the solid lines designated “ a ” and “ b ” in fig1 . as aforementioned with reference to fig2 , a drawback with the prior art 802 . 11 mac frame format is that the imp address is not included in the mac frame in a multi - hop transmission . the present invention solves this problem by including the imp address in the mac frame 400 . referring to fig4 , a diagram of a mesh mac frame 200 in accordance with the present invention is shown . the mac frame 200 includes a mac header 204 , a frame body 212 and a frame check sequence ( fcs ) field 214 . this aspect of the mac frame format is same to the one in prior art , which guarantees backward compatibility . the mac header 204 includes a frame control , a duration / id , address 1 , address 2 , address 3 , a sequence control and address 4 . these elements are well known to those of skill in the art . in accordance with the present invention , however , the mac header 204 further includes a mesh control field 202 . the mesh control field 202 comprises an imp address field 206 and an emp address field 208 . the receiving mesh point recognizes the imp 104 4 and the emp 104 2 with the mesh control field 202 and may send an ack to the imp 104 4 or other intermediate mesh point in accordance with the imp address field 206 . it should be noted that the mac frame format in fig4 is provided as an example and the mesh control field 202 may be included in any location in the mac frame 200 and the length of the imp and emp address fields may vary . a routing function is available in each mesh point , which allows the mesh point , based on the emp address included in the mesh control field 202 , to know which path used to route the data . when the imp 104 4 receives an ack , the imp 104 4 can discard the related data in its queue . if the imp 104 4 receives a non - acknowledgement ( nack ), the imp 104 4 re - transmits the data . to avoid any buffer overflow , the imp 104 4 should discard the data from its queue after a certain amount of time ( time - out ) if the imp 104 4 does not receive ack nor nack from the emp 104 2 . fig3 is a signaling diagram for transmission along data path “ b ” of a data packet and an ack between an imp ( in this example mesh point 104 4 ), an emp ( in this example mesh point 104 2 ) and intermediate mesh points 104 7 , 104 8 , 104 6 , 104 3 , ( not all of which are shown in fig3 for convenience ), in accordance with the present invention . the data packet is forwarded from the imp 104 4 to the emp 104 2 through the intermediate mesh points 104 7 , 104 8 , 104 6 , 104 3 . as will be explained in detail hereinafter , the mac frame 200 contains both imp 104 4 and emp 104 2 addresses in the imp address field 206 and the emp address field 208 . when the intermediate mesh points 104 7 , 104 8 , 104 6 , 104 3 and the emp 104 2 receive a data packet successfully , the intermediate mesh points 104 7 , 104 8 , 104 6 , 104 3 and the emp 104 2 send an ack to either the preceding intermediate mesh point or the imp 104 4 . it should be noted that fig3 is an example and zero or any number of intermediate mesh points may exist between the imp 104 4 and the emp 104 2 . additionally , the intermediate mesh points used to send the ack may be same mesh points via which the data packet is forwarded or may be different mesh points . the acknowledgement mechanism of the present invention supports both single and multiple - hop data delivery over a mesh wlan . the acknowledgement mechanism operates in four modes : 1 ) emp - to - imp data acknowledgement for more reliable data transfer , ( e . g ., ftp , http ); 2 ) single - hop data acknowledgement for reliable data transfer ; 3 ) combined emp - to - imp and single - hop data acknowledgement for very - reliable data transfer , ( e . g ., signaling ); and 4 ) no acknowledgement for high - throughput , packet - loss resilient , delay sensitive data transfer , ( e . g ., video / audio streaming ). in the first mode , ( emp - to - imp acknowledgement ), the acknowledgement is done through all the paths . whenever the emp receives a packet sent by the imp , the emp sends back an ack to the originator using the imp address included in the received packet . in the second mode , ( single hop acknowledgement ), the acknowledgement is done at every hop between the transmitting mesh point and the next immediate receiving mesh point . the third mode , ( combined emp - to - imp acknowledgement and single hop acknowledgement ), combines the first mode and the second mode . in the fourth mode , no acknowledgement is required between the imp and the emp . although this impacts the reliability of the data delivery , it reduces the delay in transmission . a new frame subtype for the frame subtype information element in the frame control field 210 ( shown in fig4 ) is also defined for indicating that the mac frame 200 includes the imp address field 206 and the emp address field 208 . the frame control field 210 may also inform which acknowledgement mode among the four modes stated above is to be used for this data packet . for the first and third mode among the four modes stated above , the mac frame format allows for an emp - to - imp ack to be transmitted through another path different from the one used for transmission of the data packet . to reduce the delay of transmission , the sender does not need to wait for the ack to be received before sending the next frame , ( i . e ., sending and acknowledging can be asynchronous ). in this case the bulk ack can be used to reduce traffic on the network . an ack can also be sent purposely via different paths depending on the traffic level in order to reduce contention of acks with data . this mechanism could be used for delay sensitive and error tolerant applications such as voice application . fig5 is a flow diagram of a process 300 for sending an ack to the imp in accordance with the present invention . a mac frame is generated by attaching a mac header to a data packet ( step 302 ). the mac header includes fields for an imp address and an emp address . the mac frame is forwarded to the emp either directly or via one or more intermediate mesh points ( step 304 ). the intermediate mesh point , if there is any , and the emp sends an ack for successful reception of the data packet to the imp ( step 306 ). although the features and elements of the present invention are described in the preferred embodiments in particular combinations , each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention .