There is common confusion about the distinction between ATM and broadband ISDN (BISDN) -- in fact, the terms are sometimes used synonymously. The latter is a set of services being defined for the transport of all types of data at speeds starting at about 150 Mbps. The transport backbone for BISDN will be an optical time-division-multiplexed network based on synchronous-optical-network (SONET) technology in the United States and on synchronous-digital-hierarchy (SDH) technology in Europe.
It is based on fiber and provides much higher capacities than the current copper equivalent, as well as having a greatly reduced average bit error rate. The SONET/SDH backbone will provide the transport for services in m
uch the same way existing facilities provide the fundamental structure for packet-switching systems today.
BISDN comprises synchronous and asynchronous transfer modes.
Synchronous
here refers to a constant stream of data, as is associated with time division multiplexing and circuit switching.
Asynchronous
refers to a discontinuous stream of data, as is found with statistical multiplexing and packet switching.
ATM has come to refer to cell-based packetized data transfer, usually below the speeds dictated by BISDN. As the meaning of X.25 has been expanded to represent both technologies and services, the terms
frame relay
and
ATM
represent both the services and the technology used to implement the services. For example, in the future, ATM will run in the network but not as a service to the end user. Frame relay services will be offered to users, and the underlying transport will be ATM.
BISDN Protocol Reference Model
illustration_link (15 Kbytes)
ATM has been chosen as the underlying transport technology within the broadband ISDN protocol stacks. The BISDN reference model is divided into multiple planes and layers. The User plane provides for the transfer of application information. The Control plane protocols deal with call establishments. The Management plane defines a platform to exchange information between User and Control planes.
Broadband ISDN
