So what is MPLS?

Multi-Protocol Layer Switching (MPLS) introduces an additional mechanism to improve quality. (The protocol gets its name from the fact that it works with a number of protocols: IP, ATM, and Frame Relay.) Without MPLS, routers must perform a lookup on the header of each packet that enters the router. However, with MPLS, a label is applied at the edge router to each packet in a flow and any subsequent routers along the path simply forward the packets along a predetermined path without having to waste time examining the full packet header. This process is carried out at a lower or less sophisticated level of the router’s execution and uses up fewer processing cycles – In short, it is faster. The labels, of course, are similar to those proposed in DiffServ.

MPLS can be combined with another device known as a packet shaper, which has knowledge of specific applications (SAP, Voice, Video, HTML, email, etc.) and of individuals and organizations. By defining packet shaping policies that link to the MPLS labels in the routers, voice traffic can be assigned capacity on route paths such that the voice quality is maintained no matter what other types of traffic are being generated on the network. In summary, QoS must be evaluated based on a user’s perception of the quality of the call. The quality is influenced by codec selection, echo cancellation and silence suppression. In addition, latency above 100ms will sound uncomfortable for both parties. Network delay on the WAN introduces additional delay. Simply throwing lots of bandwidth at the problem will not necessarily eliminate quality problems. For this reason protocols like MPLS, as well as packet shaping solutions, should be evaluated for high traffic links.

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