![]() The DSCP maps to a per-hop-behavior (PHB) that defines an associated service class. Specific service classifications are identified by a DSCP, essentially a numeric index. ![]() IETF RFC 2475, An Architecture for Differentiated Services ( ).ĭS provides a mechanism to define and deliver multiple and unique service classifications that can be offered by a service provider. IETF RFC 2474, Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers ( ) Release S-CX6.4.0M3 adds the capability to mark DNS and ENUM queries.įor basic information about DS, refer to:ĪCLI Configuration Guide Realm-Based Packet Marking topic in the Realms and Nested Realms chapter, which provides information on currently supported DS marking of SIP and RTP packets Previous software releases provided the capabilities to mark standard SIP and Real-Time Protocol (RTP) messages. This mandate requires that network elements function as a DS marker - that is as a device that sets the Distributed Services Codepoint (DSCP) in the Differentiated Services field of the IP header. In the next blog, we will learn QoS models for using markings for different application classes.Oracle Communications Session Border Controller can mark DNS/ENUM packets with a configurable differentiated services code point (DSCP).Ĭertain service providers mandate support for Differentiated Services (DS) on all traffic streams exiting any network element. Although you can mark a ping with a ToS value of 184, the ICMP (ping) traffic will probably not be mapped to the proper application class. The ToS byte value for EF is as follows: 128 64 32 16 8 4 2 1 1 0 1 1 1 0 0 0 A DSCP value of 46 results in a ToS byte value of 184. IP accounting shows the entire ToS byte, while Netflow shows the ToS byte in hexadecimal format. Sniffer Pro LAN and Wire Shark sniffers show the entire ToS field as well. An extended ping from a Cisco router will also allow administrators to see the entire ToS byte. A ping –V from a Microsoft operating system requires setting the entire ToS byte. Many network management utilities will only allow administrators to configure or display the entire ToS byte. Notice the two least significant zeros that were added to the 101110 binary pattern. The EF pattern discussed above, will becomes 10111000 when considering the entire octet. The ToS byte uses all eight bits, while the DSCP is only using the leading six digits. It is good to know how to convert a DSCP decimal value to an entire ToS octet (byte) values as well. The DSCP binary pattern of 101110 (46) uses six digits or binary values-32 16 8 4 2 1. The binary digits of 4 2 1 are used to factor the 101 binary pattern when only three digits are under consideration. Jitter (delay variation) The three most significant bits of 101 are only considered if IP Precedence was being used.The priority queue guarantees three critical services: All EF traffic is normally mapped to the priority queue (PQ) on Cisco switches and routers. Cisco IP Phones mark signaling packets (SCCP or SIP) to CS3 (24), while media (RTP) is marked to EF (DSCP 46) by default. The EF model is used for voice over IP media traffic (RTP) by default in most vendors phones. Please do NOT think that the 11 means high drop preference. DSCP 46 is backward compatible with an IP Precedence value of 5 as seen in the following binary pattern: 101110 = DSCP 46 The EF marking of 46 does NOT follow the drop preference rules of the assured forwarding model. The Expedited Forwarding (EF) model is used to provide resources to latency (delay) sensitive real-time, interactive traffic. The assured forwarding (AF) model is used to provide priority values to different data applications.
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