QoS Application Classes

Cisco pioneered a QoS baseline for DSCP markings in 2002. The DSCP decimal value and per hop behavior (PHB) for each of the 11 identified application classes is as follows: Application PHB DSCP Routing CS6 48 Voice EF 46 Interactive Video AF41 34 Streaming Video CS4 32 Mission-Critical Data AF31 26 Call Signalling CS3 24 Transactional Data AF21 18 Network Management CS2 16 Bulk Data AF11 10 Best Effort default 0 Scavenger CS1 8 The IETF formally standardized their recommendations for QoS markings in RFC4594. The RFC is very close, but there are some differences that are explained in detail in the QoS section of the Telepresence 2.0 SRND. Links to these documents are in the references section at the bottom of this blog. We will not delve into some of the details of the application classes. The routing application class (layer 3 control protocols) is the application class used to identify and mark routing protocols (RIP, OSPF, EIGRP, BGP, etc.). Most routing protocols are marked as CS6 by default by Cisco routers that originate routing protocol traffic. Routers internally prioritize IGP routing protocols through a process known as PAK PRIORITY. BGP routing protocol traffic is not internally prioritized by this mechanism. More information can be found at the link in the references section of this blog. The voice application class includes only voice media application (RTP) and follows the expedited forwarding model (RFC3246). Voice media application is normally mapped to the priority queue to guarantee low latency servicing. The next blog will continue our coverage of application classes. REFERENCES Enterprise QoS SRND 3.3: http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book.html Configuration Guidelines for Diffserv Service Classes (RFC 4594): http://www.ietf.org/rfc/rfc4594.txt?number=4594 Cisco Telepresence SRND: http://www.cisco.com/en/US/docs/solutions/Enterprise/Video/TP-Book.html PAK Priority http://www.cisco.com/en/US/tech/tk543/tk544/technologies_tech_note09186a0080094612.shtml