PDF of this tutorial- network layer (IP) routing protocols
- edge of network layer forwarding
- core network label-based switching
- label schematics and granularity
- signaling protocol for label distribution
- traffic engineering
- compatibility with various Layer-2 forwarding paradigms (ATM, frame relay, PPP)
Figure 8 depicts the protocols that can be used for MPLS operations. The routing module can be any one of several popular industry protocols. Depending on the operating environment, the routing module can be OSPF, BGP, or ATM’s PNNI, etc. The LDP module utilizes transmission control protocol (TCP) for reliable transmission of control data from one LSR to another during a session. The LDP also maintains the LIB. The LDP uses the user datagram protocol (UDP) during its discovery phase of operation. In this phase, the LSR tries to identify neighboring elements and also signals its own presence to the network. This is done through an exchange of hello packets.
Figure 8. MPLS Protocol Stack
The IP Fwd is the classic IP–forwarding module that looks up the next hop by matching the longest address in its tables. For MPLS, this is done by LERs only. The MPLS Fwd is the MPLS forwarding module that matches a label to an outgoing port for a given packet. The layers, shown in the box with the broken line, can be implemented in hardware for fast, efficient operation.
MPLS Applications
MPLS addresses today's network backbone requirements effectively by providing a standards-based solution that accomplishes the following:
- Improves packet-forwarding performance in the network
- MPLS enhances and simplifies packet forwarding through routers using Layer-2 switching paradigms.
- MPLS is simple, which allows for easy implementation.
- MPLS increases network performance because it enables routing by switching at wireline speeds.
- Supports QoS and CoS for service differentiation
- MPLS uses traffic-engineered path setup and helps achieve service-level guarantees.
- MPLS incorporates provisions for constraint-based and explicit path setup.
- Supports network scalability
- MPLS can be used to avoid the N2 overlay problem associated with meshed IP–ATM networks.
- Integrates IP and ATM in the network
- MPLS provides a bridge between access IP and core ATM.
- MPLS can reuse existing router/ATM switch hardware, effectively joining the two disparate networks.
- Builds interoperable networks
- MPLS is a standards-based solution that achieves synergy between IP and ATM networks.
- MPLS facilitates IP–over-synchronous optical network (SONET) integration in optical switching.
- MPLS helps build scalable VPNs with traffic-engineering capability.
