marking at Layer 2 takes place in the 3-bit User Priority field called the Class of Service (CoS), which resides inside an Ethernet header. The CoS field only exists inside Ethernet frames when trunking (either 802.1Q or Inter-Switch Link [ISL]) is used. The field can be used to set eight different binary values, which the classification features of other QoS tools can use
Layer 2 switches perform QoS features based on the CoS field within the Ethernet headers without regard for the markings within the IP header
The two most popular marking fields for QoS are the IP Precedence and IP DSCP fields that were introduced in QoS tools frequently use these two fields in part because the IP packet header exists from endpoint to endpoint in a network
DSCPs use the same 3 bits as IP Precedence and combine these with the next 3 bits of the ToS byte to provide a 6-bit field for QoS marking. Thus, DSCP values range from 0 (000000) to 63 (111111). This range provides unprecedented richness in marking granularity.
DSCP values can be expressed in numeric form or by special keyword names, called per-hop behaviors (PHB). Three defined classes of DSCP PHBs exist: Best-Effort (BE or DSCP 0), Assured Forwarding (AFxy), and Expedited Forwarding (EF). In addition to these three defined PHBs, Class-Selector (CSx) codepoints have been defined to be backward compatible with IP Precedence (in other words, CS1 through CS7 are identical to IP Precedence values 1 through 7). The RFCs describing these PHBs are 2547, 2597, and 3246
SIP traces provide key information in troubleshooting SIP Trunks, SIP
endpoints and other SIP related issues. Even though these traces are in
clear text, these texts can be gibberish unless you understand fully
what they mean. This document attempts to br...
Please find the attached HTML document, download and open it on your PC.
This provides an easy to use form where you simply answer a few
questions and it will render the proper jabber-config.xml file for you
to copy/paste. There is built in logic to verif...
[toc:faq]CUCM Database Replication is an area in which Cisco customers
and partners have asked for more in-depth training in being able to
properly assess a replication problem and potentially resolve an issue
without involving TAC. This document discusse...