E-Content of
INTERNET TECHNOLOGY AND WEB DESIGN
Chapter : 4.10 ATM
Topic : 4.10.1 Asynchronous Transfer Mode (ATM)
Asynchronous Transfer Mode (ATM)
• Asynchronous Transfer Mode (ATM) is a streamlined packet transfer
interface. ATM also is a connection-oriented network.
• ATM uses packets of fixed size for the communication of data. These
packets are called as ATM cells.
• ATM is used for efficient data transfer over high-speed data networks.
• ATNI provides real time and non-real time services.
• The services provided are
Synchronous TDM streams such as T-1.
Services using the constant bit rates.
Compressed voice and video.
Traffic with specific quality requirement using the non-real time
variable bit rate.
IP based services using available bit rate (ABR) and unspecified bit rate
(UBR) services.
• The ATM needs an adaption layer for supporting the information transfer
protocols that are not based on ATM.
• Cell Relay
ATM is also known as cell relay.
It has advantages of better reliability and fidelity, which allows
faster packet switching than X.25.
• Applications
ATM was developed as a part of work on ISDN.
But now it is used in non-ISDN system where the data rates are very high.
ATM Protocol Architecture (ATM Reference Model)
• ATM is a streamlined protocol. It has minimal error and flow control capabilities.
E-Content of
INTERNET TECHNOLOGY AND WEB DESIGN
• Hence the number of overhead bits required with each cell is reduced which
enables ATM to operate at high data rates.
• Also, due to the ATM cells of fixed size, the processing required at each node is
simplified. This also supports the use of ATM at high data rates.
• FIG 4.31 shows the ATM protocol architecture for an interface between user and
network.
FIG 4.32: ATM Protocol Architecture
• Layers in the ATM protocol model are
Physical layer
ATM layer
ATM Adaption layer (AAL)
• Physical Layer
The physical layer of the protocol involves the specification of a transmission
medium and signal-encoding scheme.
The data rates specified at this layer are between 25.6 Mbps and 622.08
Mbps, but data rates higher and lower than these are possible.
• ATM Layer
This layer is common to all the services that provide the packet transfer
capabilities.
E-Content of
INTERNET TECHNOLOGY AND WEB DESIGN
This layer defines the transmission of data in fixed size cells and it also
defines the use of logical connections.
• ATM Adaption Layer (AAL)
This layer is a service dependent layer. It is used for supporting the
information transfer protocol not based on ATM.
The AAL maps the higher layer information onto the ATM cell and cell is
transported over the ATM network.
• Planes in the ATM protocol model are
User plane
Control plane
Management plane
• User plane
It is used for transferring user information along with associated controls such
as flow control, error control etc.
• Control plane
It is supported to perform the call control and connection control functions.
• Management plane
It includes the plane management.
The management plane performs management functions related to a system.
They include,
Provision of coordination between all planes.
Layer management.
Management function relating to resources and parameters residing in its
protocol entities.
