ADTRAN AOS Version R10.1.0 Command Reference Manual page 3283

Command Reference Guide
According to RFC 791, the ToS field contains the following bits:
The 3-bit IP precedence values (0 through 7) are specified as:
111 Network Control Packets
110 Internetwork Control Packets
101 Critical Traffic
100 Flash Override
011 Flash
010 Immediate Servicing
001 Priority Traffic
000 Routine Data
The IP precedence values provide network routers with information about what kind of traffic is contained
in the IP packet. Based on the IP precedence values, some networks (when supported) can offer special
handling to certain packets. In addition, providing IP precedence values to critical traffic (such as route
information) ensures that critical packets will always be delivered regardless of network congestion. This
traffic is often critical to network and internetwork operation. In general, the higher the IP precedence
value, the more important the traffic and the better handling it should receive in the network. It is important
to remember that not all equipment in the public IP network will be configured to recognize and handle IP
precedence values. While it is a good idea to set the values for important traffic, it does not guarantee
special handling.
In addition to the precedence values, RFC 791 specifies bits for delay, throughput, and reliability to help
balance the needs of particular traffic types when traveling on the IP network infrastructure. When these
bits are set to 0, they are handled with normal operation. When set to 1, each bit specifies premium
handling for that parameter. For example, a 1 in the delay position indicates that the traffic is delay
sensitive and care should be taken to minimize delay. A 1 in the throughput position indicates that the
traffic has higher bandwidth requirements that should be met. A 1 in the reliability position indicates that
the traffic is sensitive to delivery issues and care should be taken to ensure proper delivery with all packets
of this type. These extra bits are rarely used because they are quite difficult to balance the cost and
benefits of each parameter (especially when more than one bit is set to 1).
60000CRG0-35E
0 1 2 3
Precedence
Delay
Throughput
Copyright © 2012 ADTRAN, Inc.
Quality of Service Map Command Set
4 5 6 7
Unused
Reliability
3283