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Labeled BGP in Seamless MPLS Architecture

MPLS across networks

Multiprotocol Label Switching (MPLS) protocol provides a range of services in a very robust and efficient manner and supports a variety of access technologies such as T1/E1, ATM, Frame Relay, DSL.  MPLS also supports newer services including L2/L3 VPNs and traffic engineering that have made it the de-facto choice for scalability with service providers and enterprise networks.

Unified MPLS for Mobile Transport (UMMT) has encouraged the use of Unified MPLS which provides an architecture that allows for:

  • Unified models: Extending the labeled Border Gateway Protocol (BGP) control plane to access plane
  • Enhanced synchronization distribution models
  • End-to-end ATM/TDM circuit transport

The UMMT System enables a unified L3 MPLS/IP transport extending end-to-end from the mobile core to the access. It simplifies the control plane by providing seamless MPLS Label Distribution Protocols (LDP) across access, pre-aggregation, aggregation/distribution, and core domains of the network.

The sheer size of the routing and MPLS label information in the control plane and forwarding plane will easily overwhelm the technical scaling limits on the smaller nodes (CSGs, preaggregation nodes). Unified MPLS elegantly solves this problem with a divide-and-conquer strategy of isolating the access, aggregation and core network layers into independent and isolated Interior Gateway Protocol (IGP) domains. LDP is used for setting up Layered Service Providers (LSP) within these domains and RFC-3107 BGP-labeled unicast is used for setting up LSPs across domains.

LDP is confined to a single area establishing intra-area LSP, whereas RFC-3107 (labeled BGP) is across Area Border Routers (ABR) to establish an end-to-end LSP path. RFC-3107 is useful in the cases where the MPLS network must scale. This technique helps the deployment of Unified MPLS in the core and aggregation networks by providing end-to-end LSP across multiple routing protocol domains.  It defines procedures for BGP to allocate labels to establish seamless LSP path across BGP boundaries that enables scale MPLS networks with hierarchical LSPs.

MPLS across networks

Three stack-labeled architecture for seamless MPLS across network, RFC 3107 BGP peers

In the typical deployment scenario shown above, the provider edge router allocates two labels to the unlabeled incoming packet. The outermost label is used to switch the packet across the core between RFC- 3107 BGP peers. The second (middle) label is used to direct the packet towards the final edge device in the LSP (once it exits the core network), and the third (now innermost) label is the MPLS service label. Each region communicates using end-to-end transport tunnel setup by carrying label information in BGP (RFC-3107). BGP can also be used to handle boundary control with its ability to use policies and communities to control the loopback propagation.

In a large service provider network, there could be an IGP running along with LDP within a single area. However in case of scalability where Seamless/Unified MPLS is intended, Labeled BGP (RFC-3107) can provide the PE reachability. IGP routes would not be propagated from aggregation to core and it is confined within that area. BGP labels will be used by Labeled BGP PEs and ABRs to reach labeled PEs in remote networks, thus helping to build hierarchical LSP across domains.

Hierarchical LSPs enable complete visibility of deployed business services across WANs, allowing the BSS and OSS systems to support easy deployment of optimized operations and multiple topologies. Velankani is at the forefront of developing these next generation applications which provide unified views of mobile and fixed converged networks.

Velankani Communications Technologies, Inc., has provided solutions for telecommunications equipment manufacturers and service providers for more than 25 years. Velankani delivers carrier-grade solutions that are deployed in large networks and then upgraded through multiple releases. We understand real network behaviors and possess the subject matter expertise needed to make the appropriate technology, design and tool choices.

For more information, contact   or Rekha Poosala ().


Venkatesha Murthy

Venkatesha Murthy, Director- Engineering, Velankani Communications Technologies Inc.

Sanja Kulur

Sanjay Kulur, Technical Manager, Velankani Communications Technologies Inc.

Indhu Ganesan

Indhu Ganesan, Java Design Lead, Velankani Communications Technologies Inc.

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