IBM OPTIONS ATM OC-3c, User Manual

Page: 21 / 140

Asynchronous Transfer Mode (ATM) Layer 2-9
ATM is Service Transparent
ATM allows for the high speed transfer of a wide range
of user traffic, including voice, video and other data.
The cell format means that more than one service
(traffic type) can be
multiplexed over the same
physical line, see Figure 2-4.
Figure 2-4 Service Processing
Cells are de-multiplexed at the other end of the
connection and forwarded to the correct service
destination.
Multi-service processing promotes scalability by
significantly reducing the number of changes needed
to add new service traffic types to your network.
ATM is Connection-oriented
ATM is a connection-oriented transport service that
requires a communication channel to be set up
between the ATM source and destination end-systems
before ATM cells can pass between them.
Before a direct data connection can be set up
between two end-systems, a number of control
connections are set up. These control connections are
beyond the scope of this guide. If you require further
information about control connections, refer to the
ATM Forum’s “LAN Emulation Over ATM” document.
Figure 2-5 shows the logical structure of a
communication channel.
Figure 2-5 Communication Channels
Several communication channels can operate over the
same physical link. Each
Virtual Path Connection (VPC)
contains several communication channels known as
Virtual Channel Connections (VCCs) .
The ATM Module only manages Virtual Channel
Connections (VCC).