Fw: Developing SMS-based Services in erlang

Sean Hinde <>
Mon Nov 4 13:23:59 CET 2002

> It depends on what you want to do. The welcome service referred to was
> presented at last year's Erlang conference. That particular system
> works by monitoring all (many? some?) internal #7 links to figure out
> what the user is up to:
>   http://www.erlang.se/euc/01/Hinde2001/sld004.htm
> I don't know how they do it, but I can guess: they've probably
> written a PDU decoder in Erlang. It's probably specific to extracting
> the location-update and insert-subscriber-data packets, so it's
> relatively simple. 

Indeed. We monitor all of our international signalling links. The PDU
decoder (unrolled version) is attached in case anyone is interested. We also
made a node whose job is to correlate ISD and LU messages based on TCAP
Transaction ID, which then sends these joined up messages to another node
which does the Welcome SMS logic/database and sends out messages to one of
our SMSCs.

The main problem we had was that we were persuaded to make a load balancing
and failover mechanism between multiple SMSCs, which ended up with a bug in
it's restart logic. We only had two weeks to make the whole system (between
2 of us) so I guess that wasn't too bad.

We have no intention of implementing any active c7 nodes ourselves in
Erlang. Our approach normally is to find a company which gives us a simple
TCP/IP based API to e.g. INAP messages and not take on any of the trauma of
trying to write any part of a c7 stack ourselves.


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