Corelatus probes extract signalling or voice data from E1 and T1 G.703 PCM links (2 or 1.5Mbit/s) in fixed and mobile telephone networks. The probes handle the electrical connection to the telephone network, timeslot selection, and the timing-sensitive protocol stack layers. The extracted data is sent to an external server over TCP/IP.
Probes are typically used for real-time billing, network supervision, logging, fraud detection, to fulfil CALEA requirements and for network trouble-shooting.
| Key Characteristics | |
| Size | 1U in a standard 19" rack. Up to three modules fit in a single 1U chassis. |
| Interfaces | 16 E1/T1 receivers per module |
| 2x 10/100Mbit Ethernet per module | |
| MTP-2 (Q.703) | 64 simultaneous timeslots per module (i.e. capable of monitoring both directions of 32 MTP-2 links) |
| LAPD (Q.921) | 64 simultaneous timeslots per module |
| Frame Relay | Up to 16Mbit/s (256 timeslots) in up to 64 channels per module |
| HSSL (ATM over E1) | Up to 12Mbit/s (196 timeslots) in six channels per module |
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 or CAS MFC R2) 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 timestamped before forwarding to the external application. Statistics counters keep track of the number and type of packets for each signalling link.
| Protocol | Standard | Notes |
| ISDN LAPD | ITU-T Q.921 | |
| SS7 MTP-2 | ITU-T Q.703 ANSI T1.111.2 |
Optional removal of duplicate FISU and LSSU signal units. 2Mbit/s high speed link (HSSL) national option and non-standard Nx64kbit/s MTP-2 also available. |
| Frame Relay | ITU-T Q.922 | |
| HSSL (ATM-based) | ITU-T I.361 ITU-T I.363.5 ANSI T1.111.2A |
Monitoring is possible at either the raw cell level (ATM AAL0) or at the CPCS sublayer of ATM AAL5 |