Differentiated Services

1. Differentiated Services • IntServ is too complex • More focus on services than deployment • Functionality similar to ATM, but at the IP layer • Per flow QoS guarantee: per flow signaling, resource reservation, packet scheduling at IP level. • Not scalable • Focus on end to end • Cannot be deployed incrementally.

2. Differentiated Services: • Less focus on services more focus on deployment. • Resource allocation for aggregated traffic • Distinguish a small number of classes • Forward class recorded in the packet header, no per flow classification and scheduling is needed. • Traffic policing on the edge and class-based forwarding in the core • Edge router is usually lower speed and can put more functionality • Core router is usually higher speed – make it simple.

3. Differentiated Services: • Define forwarding behaviors not services • opposite to IntServ • Forwarding behaviors are much easier to enforce than services (local .vs. global) • QoS guarantee by provisioning rather than reservation • QoS by ‘IP + admission control’ • QoS for aggregate traffic, not individual flows. • Emphasis on service level agreements rather than dynamic signaling • Service level agreement can be monitor by the edge router • Signaling needs other things: authentication • Focus on a single domain, not end to end • DS domain.

4. Service & Forwarding treatment • Related, but not one-to-one mapping. • Per-Hop Behaviors (PHBs) • Externally observable forwarding treatments at a single node are described by PHBs. • Each PHB is represented by a 6-bits value called Differentiated Services CodePoint (CSCP). • All packets with the same codepoint are referred as a behavior aggregate. • PHB may describe the forwarding treatments in either relative or absolute terms. • Minimal bandwidth • Proportional allocation of link bandwidth

5. Per-Hop Behaviors (PHBs) • A set of PHBs may for a PHB group. A PHB group may describe resource allocation in relative terms among than self. • Multiple PHB groups may coexist in the same DS domain. • PHBs are typically implemented by means of buffer management and packet scheduling • WFQ may be used, it does not have to be.

6. Service: • A service describes the overall treatment of a customer’s traffic within a DS domain. • Customers see services not PHBs. • To support a service, many components must work together: • Mapping of service to PHBs, traffic conditioning, network provisioning, PHB-based forwarding. • Services in the DiffServ architecture is defined in the form of Service Level Agreement (SLA).

7. Service: • SLA includes traffic conditioning agreement (TCA): • Traffic profile • Performance metrics • Actions for nonconformant packets • Additional marking and shaping services. • Service can be defined in either quantitative or qualitative terms. • Service may have scopes.

8. Differentiated Services Field • IP TOS field XXX D T R 0 0 • DS Field: DSCP(6 bits) CU (2 bits) • 32 standardized codepoints xxxxx 0 • 16 experimental codepoints xxxx11 • 16 experimental, but may be standarized xxxx 0 1

9. Differentiated Services Field • Historical codepoint definition • Provides limited backward compatibility • Default PHB codepoint (000000) • Backward compatibility with the current best effort forwarding treatment • Class selector codepoints (xxx 000) • Backward compatibility with some known current use of IP precedence field. • At least two forwarding classes • Larger numerical value should have better or equal forwarding treatment • (111000) and (110000) must be better than (000000)

10. Differentiated Services Field • Current codepoint allocation • Two new standardized PHBs: assure forwarding (AF) and expedited forwarding (EF). • Table 3.3. Summarize the current codepoint allocation.