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.

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.

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.

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

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.

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).

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.

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

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)

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.