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Benefits of CoS

IP routers normally forward packets independently, without controlling throughput or delay. This type of packet forwarding, known as best-effort service, is as good as your network equipment and links allow. Best-effort service is sufficient for many traditional IP data delivery applications, such as e-mail or Web browsing. However, newer IP applications such as real-time video and audio (or voice) require lower delay, jitter, and packet loss than simple best-effort networks can provide.

CoS features allow a Juniper Networks device to improve its processing of critical packets while maintaining best-effort traffic flows, even during periods of congestion. Network throughput is determined by a combination of available bandwidth and delay. CoS dedicates a guaranteed minimum bandwidth to a particular service class by reducing forwarding queue delays. (The other two elements of overall network delay, serial transmission delays determined by link speeds and propagation delays determined by media type, are not affected by CoS settings.)

Normally, packets are queued for output in their order of arrival, regardless of service class. Queuing delays increase with network congestion and often result in lost packets when queue buffers overflow. CoS packet classification assigns packets to forwarding queues by service class.

Because CoS must be implemented consistently end-to-end through the network, the CoS features on the Juniper Networks device are based on IETF Differentiated Services (DiffServ) standards to interoperate with other vendors’ CoS implementations.