This blog now uses chronicle to compile the blog.

Before, I used Wordpress. Wordpress is OK and mostly 'just works'. But, after a year, I wanted something which followed my normal workflow, i.e. edit-compile-test-checkin-publish. It's easier for me to write posts in emacs, build the blog with a Makefile, version-control with git and publish via scp.

I've made all comments go via mail, comment spam was getting overwhelming.

This post is for people who want to use C to control a GTH. Other languages (e.g. Erlang, Java, Python and Perl) are easier to work with, but in some applications you want the complete control that C gives you.

Corelatus provides a C API for GTH. The C API lets you control a GTH using plain C function calls---all of the XML wire format is taken care of.

Here's an example of how to use it to record speech on an E1/T1 timeslot, something you'd typically do in a voicemail system:

#include "gth_apilib.h"
...

  GTH_api api;                     // GTH_api represents one GTH API connection
  int result;
  int data_socket;
  char buffer[2000];
  char job_id[MAX_JOB_ID];
  int octet_count;

  result = gth_connect(&api, "172.16.1.10");    // Assuming the default GTH IP 
  assert(result == 0);

  // We want to record audio on the E1/T1 called "1A", on timeslot 3.
  data_socket = gth_new_recorder(api, "1A", 3, job_id);

  while ( (octet_count = recv(data_socket, buffer, sizeof buffer, 0)) ) {
    // do whatever you want with the received data
  }

...

The recording above happens in the 'while' loop. It continues forever (i.e. until you abort it). The audio data is bit-for-bit identical to what was on the E1/T1 timeslot, so this can be used for recording both voice and signalling.

Further examples

The C API code includes further examples to:

• Record audio or signalling from a timeslot to a .wav file
• Play back previously recorded files
• Install (upgrade) the firmware on a GTH
• Monitor (sniff) SS7 MTP-2 and save the signalling to a wireshark (PCAP) compatible file.
• Monitor CAS R2 signalling.

Standalone Parser

Aside: the C API code includes a standalone parser for the XML responses the GTH emits. You can use the parser without using the rest of the API library, if you want to.