3Com 3C10111C - NBX 100 - Modular Exp Base, Руководство по установке, Страница: 192 / 210

192 A
PPENDIX
C: G
UIDELINES FOR
C
ONNECTING
R
EMOTE
A
UDIO
D
EVICES
Communication
Latency
Requirements
The interconnect latency requirements can be broken into two main
categories: large packet latency and small packet latency. Depending on
the configuration of the interconnection mechanism, these latencies can
be quite different, often due to the interconnection device applying
compression to the packets. The compression function can increase
exponentially with packet size, resulting in very long delays for large
packets.
Large Packet Latency The round-trip latency on large packets, 300 bytes to full MTU, must be
less than 450 ms. The system will support an occasional packet delay of
450 to 900 ms, but each such delay will cause retries and thus affect
bandwidth and performance. If delays in excess of 450 ms occur at a
“high rate” (more than one such delay every three seconds) then system
degradation can occur, resulting in problems initializing (downloading
devices) as well as sluggish performance of system features.
Small Packet Latency The round-trip latency on small packets, from 64 bytes up to the large
packet size, should be less than 150 ms, to maintain a high performance
level (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 can
cause the system to appear sluggish during user interaction (dialing,
answering, etc.).