Chapter Summary and Review

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The concept of processing transmitted communication by label is not new; it has been implemented successfully for the U.S. Postal Service, Federal Express, and many other package-handling systems. In networking, this process has been used in Frame Relay and ATM. What is new is that the ubiquitous and uncontrolled Internet Protocol (IP) is now operating under a new set of rules where it can be classified, managed, and policed across any type of network.

The nice feature of MPLS is that setting up for it does not involve a fork-like modification of networking hardware. In some cases, only software-based modifications to existing IP routers are required to accommodate MPLS. For a fraction of the expense incurred in installing a dedicated network, MPLS allows IP traffic to be classified, marked, and policed-while consistently providing a method by which Layers 2 and 3 can exchange data.

MPLS does not replace IP; rather, it supplements IP, so that traffic can be marked, classified, and policed. With the use of MPLS, end-to-end quality of service can finally be achieved.

MPLS highlights include the following:

• MPLS allows for the marriage of IP to Layer 2 technologies (such as ATM) by overlaying a protocol on top of IP networks.

• Network routers that are equipped with special MPLS software work by processing MPLS labels contained within the shim header.

• Raw IP traffic is presented to the LER, where labels are pushed; these packets are forwarded over the LSP to the LSR, where labels are swapped.

• At the egress to the network, the LER removes the MPLS labels and marks the IP packets for delivery.

• If traffic crosses several networks, it can be tunneled across the networks by use of stacked labels.

Knowledge Review 

Answer the following true/false questions.

1. MPLS is like ATM, the LSPs are like ATM, and a VCI with a label is like a VPI.

2. MPLS allows engineering of IP traffic.

3. MPLS labels can be stacked.

4. MPLS LSRs pop labels.

5. In MPLS, packets are assigned labels like ZIP codes, and they remain the same throughout the network.

Answers: 1: true; 2: true; 3: true; 4: false; 5: false.

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