TCP/IP Tutorial and Technical Overview - IBM Redbooks

MPLS also provides the ability to analyze fields outside the IP packet header
when determining the explicit route for a data packet. For example, the network
administrator can develop traffic flow policies based on how or where a packet
entered the network. In a traditional network, this information is only available at
the ingress point. The additional analysis provides the administrator with a higher
level of control, resulting in a more predictable level of service.
Quality of service routing
QoS routing is the ability to choose a route for a particular data stream so that the
path provides a desired level of service. These levels of service can specify
acceptable levels of bandwidth, delay, or packet loss in the network. This
provides the intelligence to deliver different levels of service based on overall
network policies.
Providing a network path delivering a desired QoS often requires the use of
explicit routing. For example, it is straightforward to allocate a path for a
particular stream requiring a specific bandwidth allocation. However, it is
possible that the combined bandwidth of multiple streams may exceed existing
capacity. In this scenario, individual streams, even those between the same
ingress and egress nodes, might need to be individually routed. This requires a
finer level of granularity than that provided by standard traffic engineering.
There are two approaches to providing QoS routing in an MPLS environment:
► The MPLS label contains class of service (CoS) information. As traffic flows
through the network, this information can be used to intelligently prioritize
traffic at each network hop.
► The MPLS network can provision multiple paths between ingress and egress
devices. Each path is engineered to provide a different level of service. Traffic
is then intelligently assigned to an appropriate path as it enters the network.
These approaches simply classify packets into a class of service category. Local
network administration policies determine the service provided to each category.
Multiprotocol support
The Multiprotocol Label Switching standard provides support for existing
network-layer protocols, including IPv4, IPv6, IPX, and AppleTalk. The standard
also provides link layer support for Ethernet, token ring, FDDI, ATM, frame relay,
and point-to-point links. Activities continue to extend this standard to other
protocols and network types.
MPLS is not limited to a specific link layer technology; it can function on any
media over which network layer packets can pass.
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