Little Phone Cards

MPLS is widely recognized as the most modern approach to providing the network functionality required by VoIP and other real-time applications. MPLS combines layer 2 and layer 3 technologies to support a mix of services. From the lower-layer ATM and PSTN technologies, MPLS has borrowed the concepts of simple label lookup-based packet forwarding, a-priori out-ofband forwarding path allocation, and service-time resource commitment. From the layer 3 IGP and Differentiated Services QoS framework, MPLS borrows the concept of advertising network topology and link attributes and providing multiservice forwarding paths to mitigate network complexity and enhance scale.

Traffic Engineered MPLS technologies have been designed from the start to address the complexities and high availability requirements of carrier-grade VoIP and other premium services. Fast re-route, auto-bandwidth provisioning, and virtual path TE tunnels are some of the MPLS capabilities that guarantee the high level of quality and reliability that we expect from telephony services.

MPLS defines label-switched paths, which are simple uni-directional forwarding paths constructed by wrapping ATM, IP, and other transport protocols packets in MPLS frames. MPLS identifies each frame with a label. The ingress label edge router (LER) provisions the labels and distributes them to label switching routers (LSR) using a signaling protocol such as LDP or Resource Reservation Protocol-traffic engineering (RSVP-TE) prior to enabling transport across the path. The label distribution process involves an automated sequence of resource requests and acknowledgements that create a path between two points in the network. When using RSVP-TE, QoS parameters may be specified as a requirement to each LSR. When acknowledged, these QoS parameters represent an agreement to provide that level of QoS, or FEC, to packets forwarded along the path.

Service providers can construct customized LSPs that support specific application requirements. Network managers can design LSPs to minimize the number of hops, meet certain bandwidth requirements, support precise performance requirements, bypass potential points of congestion, direct traffic away from the default path selected by the IGP, or simply force traffic across certain links or nodes in the network.

An important benefit of the label-swapping forwarding algorithm is its ability to take any type of user traffic, associate it with an FEC, and map the FEC to an LSP that has been specifically designed to satisfy the FEC’s requirements. Adding DSCP support to the MPLS network allows the network to populate a single LSP with multiple FECs.

The MPLS-TE approach also enables network administrator to provision MPLS fast reroute (FRR) paths for LSPs and associated backup paths while minimizing physical LSR overlap between primary and backup paths. FRR limits path outage times to milliseconds by pre-negotiating resource borrowing from LSR neighbors and localizing the event signaling that implements the FRR operation.

Deploying technologies based on label-swapping forwarding techniques offers network administrators precise control over traffic flow in their networks. This unprecedented level of control results in a network that operates more efficiently and provides more predictable service.

Source: Juniper Networks, Inc. White Paper