Queuing methods
Issue 3.4.1 June 2005
321
Round-robin
Round-robin (sometimes called custom) queuing sorts data into queues, and services each
queue in order. An administrator manually configures which type of traffic enters each queue,
the queue depth, and the amount of bandwidth to allocate to each queue.
Round-robin queuing is not particularly suited to IP Telephony. It does not ensure strict enough
priority to voice packets, so they may still wait behind other traffic flows in other queues. Latency
and jitter can be at unacceptable levels.
CB-WFQ / LLQ / CBQ
Class-Based Weighted Fair Queuing (CB-WFQ) with Low-Latency Queuing (LLQ), which is
sometimes called Class-Based Queuing (CBQ), combines the above-mentioned queuing
mechanisms. Generally, there is one strict-priority queue, several round-robin queues, and
weighted fair queuing for the remainder. This queuing mechanism works very well for
converged networks. IP Telephony bearer and signaling packets receive the priority they need,
while there remains an equitable mechanism for distributing remaining bandwidth. In addition,
limits can be set on the high-priority queue to prevent it from using more than a specified
amount of bandwidth. Bandwidth that is reserved for the high-priority queue will be given to
other queues if insufficient traffic enters the high-priority queue.
RED / WRED
Although they are not queuing methods per se, Random Early Detection (RED) and Weighted
Random Early Detection (WRED) are important queue management techniques. RED and
WRED work by randomly discarding packets from a queue. RED takes advantage of the
congestion control mechanism of TCP. By randomly dropping packets prior to periods of high
congestion, RED causes the packet source to decrease its transmission rate. Assuming that the
packet source is using TCP, it will decrease its transmission rate until all the packets reach their
destination, which indicates that the congestion is cleared. Some implementations of RED,
called Weighted Random Early Detection (WRED), combines the capabilities of the RED
algorithm with IP Precedence. This combination provides for preferential traffic handling for
higher-priority packets. It can selectively discard lower-priority traffic when the interface begins
to get congested, and provide differentiated performance characteristics for different classes of
service.
RED and WRED are useful tools for managing “data” traffic, but should not be used for “voice.”
Because IP Telephony traffic runs over UDP, because IP Telephony protocols do not retransmit
lost packets, and because IP Telephony transmits at a constant rate, the IP Telephony queue
should never be configured for WRED. WRED only adds unnecessary packet loss, and
consequently reduces voice quality.
Содержание Application Solutions
Страница 1: ...Avaya Application Solutions IP Telephony Deployment Guide 555 245 600 Issue 3 4 1 June 2005 ...
Страница 20: ...About This Book 20 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 21: ...Issue 3 4 1 June 2005 21 Section 1 Avaya Application Solutions product guide ...
Страница 22: ...22 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 74: ...Avaya Application Solutions platforms 74 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 106: ...Call processing 106 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 124: ...Avaya LAN switching products 124 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 139: ...Issue 3 4 1 June 2005 139 Section 2 Deploying IP Telephony ...
Страница 140: ...140 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 186: ...Traffic engineering 186 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 204: ...Security 204 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 214: ...Voice quality network requirements 214 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 228: ...Avaya Integrated Management 228 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 239: ...Reliability Issue 3 4 1 June 2005 239 Figure 69 S8700 Media Server in a high reliability configuration ...
Страница 274: ...Reliability and Recovery 274 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 275: ...Issue 3 4 1 June 2005 275 Section 3 Getting the IP network ready for telephony ...
Страница 276: ...276 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 350: ...Implementing Communication Manager on a data network 350 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 356: ...Network recovery 356 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 366: ...Network assessment offer 366 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 367: ...Issue 3 4 1 June 2005 367 Appendixes ...
Страница 368: ...Appendixes 368 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 394: ...Access list 394 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 414: ...DHCP TFTP 414 Avaya Application Solutions IP Telephony Deployment Guide ...