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How AAL1 helped converge networks

Sep 07, 20042 mins

* The operational efficiency of AAL1

As we saw last week, one trend is clear: As raw bandwidth has become less expensive over the past two decades, the emphasis on using every possible bit-per-second of that bandwidth has likewise diminished. Instead, other considerations that relate more to the overall efficiency of network operations have taken precedence.

A first example of this comes from the development of ATM Adaptation Layer 1 (AAL1).

AAL1 was designed for the transport of information in which there is an exact timing relationship that must be maintained between the source and the receiver. This traffic tends to be constant-bit-rate, connection-oriented traffic. Of course, the most obvious example of a type of traffic that fits this description is traditional, pulse code modulation voice. But why, especially in a pre-VoIP era, was this even considered?

Network efficiency. The traditional WAN was a TDM network designed originally for transporting voice conversations. For years, we shoehorned data onto this network until the first broadband packet ATM-based networks were deployed. This resulted in parallel networks that were inefficient no matter how you define efficiency.

At the same time, it was recognized that it would take a long time for traditional voice nets to go away. Consequently, while AAL1 was extremely inefficient from the perspective of bandwidth utilization, having the capability to run traditional voice over the newer data-centric networks provided great “network efficiency” in terms of maintaining a single network. So while there’s an extent to which bandwidth efficiency is important, operational efficiency clearly won out.

Next time we’ll wrap up this discussion with an even more extreme example of operational efficiency.