DiffServ Definition


Defined by the IETF in RFC 2474 (1998) as a framework for enabling the deployment of scalable service discrimination in the Internet. DiffServ operates at the Network Layer (Layer 3) to assign relative priorities to packets on the basis of an 8-bit code point in the Differentiated Services (DS) field in the IP header.The DS field occupies the same position as the IPv4 Type of Service (ToS) octet or the IPv6 Traffic Class field. At the ingress to each node, the DS field is analyzed and a routing table is consulted in order to determine queuing considerations at the packet's output interface on that node, which considerations reflect the differential level of treatment to be afforded that packet in accordance with a policy that may be based on application, customer, traffic type, or as expressed in a Service Level Agreement (SLA). Such policy criteria might include time of day, source and destination address pair, and port number (i.e., application identifier).There are two primary types of per-hop behaviors (PHBs), representing two service levels, or forwarding classes. Expedited Forwarding (EF) provides minimal delay, jitter, and loss.Assured Forwarding (AF) comprises four classes, each of which contains three drop precedences and allocates certain amounts of buffer space and bandwidth. DiffServ operates on a packet-by-packet and hop-by-hop basis, which explains why it ultimately did not scale up well to the size of the Internet. See also AF, bandwidth, buffer, EF, header, hop, IETF, Internet, IPv4, IPv6, jitter, node, packet, routing, and SLA.

Webster's New World Telecom

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