ATM Dictionary - UNI - User-to-Network Interface

UNI - User-to-Network Interface

UNI (You-Knee) - The interface between any of:

User ATM equipment (e.g. hosts) and private or public ATM network equipment (e.g. ATM switches)
CPE (Customer Premises Equipment, e.g. private ATM switch) and public network equipment (e.g. provider ATM switch)

The ATM Forum has defined two contexts in which the UNI appears:

Public UNI, connecting ATM equipment within a private network--either hosts or switches--with public network provider (carrier) networks.
Private UNI, used exclusively to connect hosts to switches where both are managed by the same administrative entity.

Note that switch-to-switch interconnection is defined by the NNI (Network-to-Network Interface) in the case where the interconnection is not between a private and public network (i.e. the interconnection resides wholly within either a private or a public network).

These concepts are illustrated below:

              Private                      Public
                UNI                         UNI
    ATM-User-----------Private ATM Switch---------Public ATM Network
                                                    /
                                                   /
    ATM-User-----------Public UNI-----------------/

Specification of the ATM Forum private and public UNIs involves ITU (International Telecommunications Union) B-ISDN Protocol Reference Model (B-ISDN PRM) layers one, two, and three; i.e. the physical media (Layer 1) over which the ATM protocol layer (Layer 2) is carried, and the signaling AAL (SAAL layer 3) necessary to implement the UNI.

The first published ATM Forum UNI specification was version 3.0. A new version (3.1) appeared to align version 3.0 with current ITU work involving Q.2931. The ATM Forum is currently working on version 4.0 of the UNI