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 One
of the key benefits of ATM is that it operates over
existing transport technologies such as the widely deployed
PDH and SDH networks. Any test strategy should start
with building confidence in the physical transmission
medium. Once this requirement has been confidently completed,
you can begin to test higher layers in the protocol
stack until you have confidence in the end-to-end transmission
of the services that generate the revenue for the carrier.
A typical broadband network might carry internet TCP/IP
data over Frame Relay links, aggregated through AAL-5
onto a high speed ATM backbone, carried on an underlying
SONET/SDH transmission network. At each of these network
layers, a distinct protocol operates to manage the flow
of data from one end to the other.
However, these protocols operate independently from
each other. Any one of them could stop the flow of data,
although the cause will not be immediately apparent
to an observer looking at only one or two of the protocol
layers.
The limitation of many test tools is that they are
optimized for looking at one specific protocol layer:
for example ATM layer, service layer, or physical layer.
A better approach is to correlate measurements across
multiple layers in order to fully understand how they
interact.
This application note focuses on the ATM Forum Traffic
Management Specification Version 4.0 (TM4.0) which includes
- Service Categories (Traffic Classes)
- ATM Quality of Service (QoS) parameters (I.356)
- Connection Admission control (CAC)
- Usage Parameter Control (UPC)
- Generic Cell Rate Algorithm (GCRA) for Policing
and Shaping (I.371)
Other issues examined are
- TM4.0 Contract Verification
- OAM Functional Testing and In-Service QoS Measurements
- Adaptation Layer QoS Testing
- Adaptation Layer Performance Testing
- Automated Testing
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