Rules of the road
- By Paul Korzeniowski
- May 28, 2001
Here are some of the key standards behind network quality-of-service (QOS) capabilities:
Differentiated services (diffserv) — Diffserv is an Internet Engineering Task Force (IETF) standard for adding QOS to IP networks. Operating at Layer 3 of the standard seven-layer networking model, diffserv uses the IP type of service field as the diffserv byte to identify and prioritize traffic. Diffserv is supported in most of the new networking products purchased by large enterprises, such as government agencies. Multiprotocol label switching (MPLS) — Another IETF Layer 3 switching specification, MPLS uses labels that contain forwarding information to prioritize traffic. The labels are attached to IP packets by a router that sits at the edge of the network, known as a label-edge router. This enables routers in the core of the network, known as label-switch routers, to examine the labels more quickly than if they had to look up destination addresses in a routing table. Resource reservation setup protocol (RSVP) — RSVP is the first attempt to address QOS concerns. RSVP is based on a sophisticated per-connection signaling system that requires routers in the network to agree to a specific level of service. After initial usage, vendors found it complex and not easily scaled, so adoption has ebbed. Common open policy service (COPS) — A complement to RSVP, COPS describes how policy information on a network is communicated between servers and clients. Because RSVP is a policy client (a user requesting resources over a network), COPS is used to relay that information to the policy servers on a network. Adoption has been hindered by complexity and scaling issues.