title: implementing ack over UDP?
body: <p>We have a system (built in C) in place that performs communication over UDP.  Recently we have found a necessity to guarantee delivery of packets.  My question is: what would be the minimum additions to a UDP based system to ensure delivery using ack packets?  Also, ideally without having to manipulate the packet headers.  We have application level control over the packets including sequence numbers and ack/nack flags.  I am wondering if this is a lost cause and anything we attempt to do will basically be a flawed and broken version of TCP.  Basically, is there a minimalist improvement we can make to achieve guaranteed delivery (we do not need many features of TCP such as congestion control etc.).  Thanks!</p>