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E1/T1 Monitoring Probes

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.

Corelatus Hardware

Probes are typically used for real-time billing, network supervision, logging, fraud detection, to fulfil CALEA requirements and for network trouble-shooting.

Carrier-grade hardware

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

Connection to the E1/T1 lines

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.

Synchronisation

The probe is rate synchronised to the telephone network via a user-selectable E1/T1 interface. Absolute time, for timestamps, is maintained via NTP.

In-band Modes

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.

Out-of-band Signalling Modes

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 LAPDITU-T Q.921
SS7 MTP-2ITU-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 RelayITU-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