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DiffServ: Differentiated Service Architecture in IP Network
DiffServ defines an architecture for implementing scalable service differentiation in the Internet. A "Service" defines some significant characteristics of packet transmission in one direction across a set of one or more paths within a network. These characteristics may be specified in quantitative or statistical terms of throughput, delay, jitter, and/or loss, or may otherwise be specified in terms of some relative priority of access to network resources. Service differentiation is desired to accommodate heterogeneous application requirements and user expectations, and to permit differentiated pricing of Internet service.
DiffServ architecture is composed of a number of functional elements implemented in network nodes, including a small set of per-hop forwarding behaviors, packet classification functions, and traffic conditioning functions including metering, marking, shaping, and policing. Differentiated Service architecture achieves scalability by implementing complex classification and conditioning functions only at network boundary nodes, and by applying per-hop behaviors to aggregates of traffic which have been appropriately marked using the DS field in the IP (IPv4 or IPv6 ) headers [DSFIELD]. Per-hop behaviors are defined to permit a reasonably granular means of allocating buffer and bandwidth resources at each node among competing traffic streams. Per-application flow or per-customer forwarding state need not be maintained within the core of the network.
The differentiated services architecture is based on a simple model where traffic entering a network is classified and possibly conditioned at the boundaries of the network, and assigned to different behavior aggregates. Each behavior aggregate is identified by a single DS codepoint. Within the core of the network, packets are forwarded according to the per-hop behavior associated with the DS codepoint. In this section, we discuss the key components within a differentiated services region, traffic classification and conditioning functions, and how differentiated services are achieved through the combination of traffic conditioning and PHB-based forwarding.
Protocol Structure - DiffServ: Differentiated Service ArchitectureIn DiffServ, a replacement header field, called the DS field, is defined, which is intended to supersede the existing definitions of the IPv4 TOS octet and the IPv6 Traffic Class octet. The format of the header as follows:
DSCP - differentiated services codepoint to select the PHB a packet experiences at each node.
CU - currently unused
IP , IPv6
DiffServ architecture is defined by IETF (http://www.ietf.org ) RFC 2474 and 2475.
http://www.javvin.com/protocol/rfc2474.pdf : An Architecture for Differentiated Services
http://www.javvin.com/protocol/rfc2475.pdf : Differentiated Services Field