User-To-Network Interface (Uni; Atm Data Transmission - Nortel BayStack 450-24T Using Manual

User-to-Network Interface (UNI)

The user-to-network interface (UNI) represents the interface between an end point
of an ATM network and the switch (the user connection).
The UNI can also be the interface between an end point of an ATM network and a
switch or between a switch and a router.
There are two types of UNI interfaces:
•
•
For more information about UNI 3.0 and UNI 3.1, refer to ATM User-Network
Interface (UNI) Specification, Version 3.0 and ATM User-Network Interface
Interface (UNI) Specification, Version 3.1.

ATM Data Transmission

Data transmission (also called cell switching) through the ATM network relies on
the establishment of logical connections between ATM entities. ATM is a
connection-oriented service. This means that an ATM entity cannot transmit
information until it establishes a connection with a receiving entity. These
connections consist of virtual channels, virtual paths, and transmission paths
(Figure D-2).
A virtual channel is a logical connection between two communicating ATM
entities. Each virtual channel may carry a different protocol or traffic type. The
virtual channel transports cells that have a common identifier. The identifier is
called the virtual identifier (VCI) and is part of the cell header. You can establish
permanent virtual channels or you can set them up as dynamic virtual channels,
which allows the network to adjust to the traffic demand.
A virtual path is a set of virtual channels between a common source and
destination. The virtual channels in a virtual path logically associate to a common
identifier. This identifier is called the virtual path identifier (VPI) and is part of the
cell header. You can base cells on either the VPI alone, or on a combination of the
VPI and the VCI.
309978-D Rev 01
Private UNI -- interface between an end point device and a private network
switch
Public UNI -- interface between an end point device and the public switched
network
ATM Overview
D-5