192 APPENDIX C: G UIDELINES FOR CONNECTING REMOTE AUDIO DEVICESCommunicationLatencyRequirementsThe interconnect latency requirements can be broken into two maincategories: large packet latency and small packet latency. Depending onthe configuration of the interconnection mechanism, these latencies canbe quite different, often due to the interconnection device applyingcompression to the packets. The compression function can increaseexponentially with packet size, resulting in very long delays for largepackets.Large Packet Latency The round-trip latency on large packets, 300 bytes to full MTU, must beless than 450 ms. The system will support an occasional packet delay of450 to 900 ms, but each such delay will cause retries and thus affectbandwidth and performance. If delays in excess of 450 ms occur at a“high rate” (more than one such delay every three seconds) then systemdegradation can occur, resulting in problems initializing (downloadingdevices) as well as sluggish performance of system features.Small Packet Latency The round-trip latency on small packets, from 64 bytes up to the largepacket size, should be less than 150 ms, to maintain a high performancelevel (this is especially significant in the quality of user conversations).Longer latency will not cause system failure but can result in “talk-over”situations within a conversation. Additionally, the longer latency cancause the system to appear sluggish during user interaction (dialing,answering, etc.).
