available to the CCDP. Some methods are established, whereas other practices are continually
evolving as technology becomes more sophisticated.
patterns that are variable in terms of information rate. Simply stated, ATM standards are tailor-
made for the requirements of voice. The range of standards now available allows a variety of
voice networking applications to be addressed. If you include VoATM in the design of the
modern multiservice network, a complete range of voice and data services can be merged into
a single network.
possible traffic types for VoATM. Different ATM adaptation types have been developed for
different traffic types, each with its benefits and detriments. ATM Adaptation Layer 1 (AAL1)
is the most common adaptation layer used with constant bit-rate services.
common method of supporting a full E1 byte stream from end to end. The trade-off with this
method is that a full E1 may be sent, regardless of the actual number of voice channels in use.
Structured AAL1 contains a pointer in the payload that allows the DS0 structure to be
maintained in subsequent cells. This allows the network to be more efficient by not using
bandwidth for unused DS0s. The remapping option allows the ATM network to terminate
structured AAL1 cells and remap DS0s to the proper destinations. This eliminates the need for
PVCs between every possible source and destination. The big change with this method is that
a PVC is not built from edge to edge.
time traffic and are suitable for guaranteeing a certain level of service in a voice network. CBR,
in particular, allows the amount of bandwidth, end-to-end delay, and delay variation to be
specified during the call setup. The method of transporting voice channels through an ATM
network is dependent on the nature of the traffic.
transparently over the signaling virtual circuit (VC) from end station to end station. Second,
coordination between the end systems allows the selection of a VC to carry the voice
communication between end stations. The ATM network is generally transparent with regard to
interpreting the signaling that takes place between end stations. However, some products
understand CAS signaling and can prevent the sending of empty voice cells when the end
stations are on-hook. A signaling request from an end station causes the ATM network to create
a switch virtual circuit (SVC) with the appropriate QoS to the desired end station. The creation