![]() To preserve backward-compatibility with any IP precedence scheme currently in use on the network, DiffServ has defined a DSCP value in the form xxx000, where x is either 0 or 1. Also, if a packet arrives at a DS-compliant node, and the DSCP value is not mapped to any other PHB, the packet will get mapped to the default PHB. The default PHB essentially specifies that a packet marked with a DSCP value of 000000 (recommended) receives the traditional best-effort service from a DS-compliant node (that is, a network node that complies with all of the core DiffServ requirements). In other words, a PHB refers to the packet scheduling, queueing, policing, or shaping behavior of a node on any given packet belonging to a BA, as configured by a service level agreement (SLA) or a policy map. Packets from multiple sources or applications can belong to the same BA. With the ability of the system to mark packets according to DSCP setting, collections of packets with the same DSCP setting that are sent in a particular direction can be grouped into a BA. RFC 2475 defines PHB as the externally observable forwarding behavior applied at a DiffServ-compliant node to a DiffServ Behavior Aggregate (BA). The value of the CU bits is ignored by DS-compliant interfaces when determining the PHB to apply to a received packet. A currently unused 2-bit (CU) field is reserved for explicit congestion notification (ECN). Six bits of the DS field are used as the DSCP to select the Per-Hop Behavior (PHB) at each interface. The DS field supersedes the existing definitions of the IP version 4 (IPv4) type of service (ToS) octet (RFC 791) and the IPv6 traffic class octet. DS Field DefinitionĪ replacement header field, called the DS field, is defined by Differentiated Services. Typically, Differentiated Services is appropriate for aggregate flows because it performs a relatively coarse level of traffic classification. ![]() The network uses the QoS specification to classify, mark, shape, and police traffic and to perform intelligent queueing.ĭifferentiated Services is used for several mission-critical applications and for providing end-to-end QoS. This specification can occur in different ways, for example, using the 6-bit differentiated services code point (DSCP) setting in IP packets or source and destination addresses. With Differentiated Services, the network tries to deliver a particular kind of service based on the QoS specified by each packet. Information About Differentiated Servicesĭifferentiated Services is a multiple service model that can satisfy differing QoS requirements. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module. For the latest caveats and feature information, seeīug Search Tool and the release notes for your platform and software release. Your software release may not support all the features documented in this module. Cisco IOS QoS software supports three types of service models: best-effort services, Integrated Services (IntServ), and Differentiated Services. End-to-end QoS is the ability of the network to deliver service required by specific network traffic from one end of the network to another. DiffServ is a set of end-to-end quality of service (QoS) capabilities. This module contains an overview of implementing Differentiated Services (DiffServ) on your network. Overview of DiffServ for Quality of Service ![]() DiffServ Implementation Troubleshooting Logs.Benefits of Implementing Differentiated Services.Information About Differentiated Services.Overview of DiffServ for Quality of Service. ![]()
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