Quantum and Evolution Series Installation and Operating Handbook
8-61
8.15 Sat-ABIS
Sat-ABIS
is an embedded optimiser in the modem for GSM Abis traffic.
It is used in symmetric point-to-point links for cellular backhaul, saving up to 50%
bandwidth. It combines and optimises Abis traffic on four T1/E1 interfaces (using either
CRC4, FAS, ESF or D4 framing) into a single carrier and supports up to 256 Abis voice
channels.
Compressed data is converted to HDLC-framed packets for transmission over satellite.
Sat-ABIS interoperates with GSM equipment from major manufacturers including Alcatel,
Nokia, Ericsson, Siemens and Motorola. The modems with Sat-ABIS sit between the BTS
and BSC.
Sat-ABIS supports 1:1 redundancy with no external hardware. Four Ethernet ports for
future growth.
In relation to compression, Sat-ABIS:
•
Removes silence (idle speech) frames.
•
Removes idle data frames (channels not assigned to calls).
•
Performs (LAPD) signalling optimization, including compression of repetitive data
patterns such as idle flags between HDLC control messages on signal channels.
‘Drop and Insert’ of timeslots is provided, thereby supporting fractional T1/E1 links.
Abis implementations vary with manufacturer and therefore the modem allows each
timeslot (and 16kbps portions of timeslots) – see picture overleaf - to be allocated to
either voice or signalling, thereby allowing the correct compression techniques to be
applied to each portion of the data.
