IISP - Interim Inter-Switch Signaling Protocol

ATM Forum specification for interswitch signalling using UNI 3.1 (or optionally, but not preferrably, UNI 3.0 if both switches can be configured to use it). The current specification (as of 95-07-05) is Version 1.0, released by the ATM Forum in December 1994.

Since no routing information is exchanged among switches that implement IISP, manual configuration of the following is required:

• Whether the switches on each end of an IISP link are to assume the "user" or the "network" roles of a UNI connection. One side of an IISP link must be configured as "network" and the other side "user," but it doesn't matter which side assumes which role.
• Next hop routing tables in each switching system (i.e. ATM switch).

These tables consist of the following triplet:

 <ATM address, address length, interface over which call should be routed>

The address length is used to provide a means by which route destinations can be summarized (in a heirarchical topology) using a "longest match" mechanism.

IISP was formerly referred to as P-NNI Phase 0.