CoS Priority and ToS Rewrite

The two parameters configurable for CoS priority are 802.1p and Type of Service (ToS). Each CoS can be mapped to an 802.1p priority and a ToS rewrite value. The 802.1p parameter is:

The ToS parameter is:

Assigning and Marking Traffic with a Priority displays the relationship between your application, priority level, 802.1p, and ToS assignments (shown here using DSCP terminology).

QoS priority/ToS configuration:

The ICMP protocol, used for error messaging, has a low bandwidth requirement, with a high tolerance for delay and jitter, and is appropriate for a low priority setting. HTTP and FTP protocols, used respectively for browser-generated and file transfer traffic, have a medium to high bandwidth requirement, with a medium to high tolerance for delay and jitter, and are appropriate for a medium priority level. Voice (VoIP), used for voice calls, has a low bandwidth requirement, but is very sensitive to delay and jitter and is appropriate for a high priority level.

See RFC 1349 for further details on ToS. See RFCs 2474 and 2475 for further details on DSCP.