Corelatus probes extract signalling or voice data from E1 and T1 G.703 PCM links (2 or 1.5Mbit/s) in fixed, GSM and 3G UMTS mobile mobile telephone networks. The probes connect to E1/T1 links, decode layer 1 and layer 2 of the protocol stack and then forward the monitored data to an external server over TCP/IP.
Probes are permanently installed in the SS7 network, on GSM Gb, Abis, A, C, D, E and F links and on 3G Iub, Iucs and Iups links. The monitored data can be used for real-time billing, fraud detection, network supervision and lawful interception. It can also be used to create new services, for instance SMS welcome.
Monitoring probes have an extra-sensitive receiver designed for use with a non-intrusive tap which allows sniffing the signal directly from an interconnection cable (a -20dB protected monitor point, as specified in ITU-T G.772). The probes are also compatible with -30dB monitor points used by some operators.
In installations using a digital cross-connect, the E1/T1 link can be normally terminated.
The probe is rate synchronised to the telephone network via a user-selectable E1/T1 interface. Absolute time, for timestamps, is maintained via NTP.
For applications requiring unprocessed access to the data, for instance error analysis or voice channel monitoring, the probe can forward the links to an external application without any L2 processing.
Data may be forwarded as separate 64kbit/s timeslots, or as a complete 2Mbit/s (1.5Mbit/s) span, using TCP/IP for the transport.
In-band signalling (DTMF, CAS MFC R2, SS5) can also be applied to voice timeslots.
When monitoring signalling, the monitoring probe takes care of layer 2: the packets are delimited, unstuffed, checked and time-stamped before forwarding to the external application. Statistics counters keep track of the number and type of packets for each signalling link.
| Protocol | Performance (per module) | Standards |
|---|---|---|
| ISDN LAPD | 64 channels | ITU-T Q.921 |
| SS7 MTP-2 (56/64 kbit/s) | 64 channels | ITU-T Q.703 ANSI T1.111.2 |
| SS7 MTP-2 (Nx64 kbit/s) | up to 64 channels up to 8Mbit/s |
ITU-T Q.703 Annex A ANSI T1.111.2 |
| Frame Relay | up to 64 channels up to 16Mbit/s |
ITU-T Q.922 |
| HSSL (ATM-AAL5 based) | 6 channels, 12 Mbit/s | ITU-T I.361 ITU-T I.363.5 ANSI T1.111.2A |
| HSSL (ATM-AAL0 based) | 6 channels, 12 Mbit/s | ITU-T I.361 |