Why multiple ATM addressing schemes

Questions about ATM addressing schemes

Question: Why are there multiple ATM addressing schemes?

Answer: According to the ATM UNI 3.x and RFC 1577, there are three structures of ATM Address that can identify an end station.

1) E.164
2) NSAP
3) Both

The multiple addressing schemes exist because the various companies representing switch and service providers could not reach an agreement on one format, split, more or less, along public network vs atm lan lines. The way to tell what format to use is to ask your vendor (whether network service or equipment vendor). Assumptions are risky...

During the ISDN meetings of 1984-1988 there was much discussion in ITU and ISO regarding NSAPs and E.164. As near as I recall it came down to the idea that E.164 does not (by itself) constitute an NSAP, but can be part of the NSAP.

So, if you are just operating on a LAN you would use NSAP but probably not E.164. If you are operating on an ATM network and only addressing end-stations (and could care less about OSI) you would be OK with E.164 addressing. Finally, if you are dealing with OSI based end stations on an ATM network you would use both, the E.164 bit gets you to the end-station and the NSAP add-on finds the SAP at Transport Layer.

Question: Where to find info on the encoding of E.164 addresses in NSAP address?

Answer: In general, the best place to look for answers is ISO 8348, which is the defining standard for NSAP addresses. Annex A contains the relevant information, section A.5.3 especially. Some information can also be found in section 3.1.1.3 of UNI 4.0 as well.

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Maintained by Carl Symborski
Last Changed 14 June 1997