The Corelatus Blog
E1/T1 and SDH/SONET telecommunications

Erlang example code for GTH

Posted February 1st 2009

Years ago, I wrote a few bits of example code to help customers get started with controlling a GTH. If you were kind, you'd call them minimal, e.g. the Erlang one was about 20 lines long.

None of our customers that use Erlang were very impressed by that, so I'd hand out part of the code we use to do API testing (a cut-down XML parser and a little library to handle sockets) along with sternly issued instructions that this was just example code and that live systems needed something more robust. Not great, but I had other things to do.

I finally got around to completing and releasing a proper native Erlang API for the GTH. No (visible) XML. It's a gen_server, so it's well-behaved and simple enough so that you can do almost anything from the Erlang shell, e.g. to turn on an E1:

1> {ok, A} = gth:start_link("").
{ok, <0.44.0>}
2> gth:set(A, "pcm1B", [{"status", "enabled"}]).

and put an audio file on a timeslot:

3> {ok, Bin} = file:read_file("/tmp/resample_q_alaw.raw").
4> {ok, _ID, P_socket} = gth:new_tcp_player(A, "1B", 2).
5> gen_tcp:send(P_socket, Bin).
6> flush().

There's a direct mapping between GTH commands and function names in the gth.erl module, e.g. the XML <set> command becomes gth:set(). While writing the gth.erl module, I also rewrote our entire API test suite (60 modules, 30kloc) to use the gth.erl interface. It ended up under 20kloc. I'd guess half of that reduction comes from gth.erl being nicer to use and the other half comes from cleaning up "while I was at it".

The code, with examples:

While writing gth.erl, I had a go at doing something similar in Python. But that's another story.

Permalink | Tags: erlang, GTH