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The GSM data and fax services are part of the GSM "bearer" services defined by the GSM governing body called the MoU, or "Memo of Understanding". The GSM MoU defines an internationally accepted digital cellular telephony standard which has more than 300 GSM mobile networks in Europe, the US, Asia, Africa and Australia and the data and fax capabilities of the two networks are an enhancement of the original Phase 1 voice-only GSM specification. The "data over cellular" bearer services are part of the Phase 2 implementation of GSM. A GSM network’s data transfer facility allows the digital equivalent of modem transmissions - known as data streaming - at data speeds of up to 9,600 bits per second (bps) and fax speeds of up to 9,600 bps, which is of course a lot slower and two generations older than the analogue v.90 56kbps across standard PSTN lines. The data and fax components support all the international data and fax standards like Group 3 fax, v.32 and v.27 ter. The key though to delivering these enhanced services is something called SS 7 (Signaling System Number 7), a robust set of techniques or protocols designed to provide fast, efficient, reliable transfer and delivery of signaling information across the GSM network and to support both switched voice and non-voice applications. SS 7 is essentially the multimedia specification of GSM, proving data (data/fax capabilities), sound (voice mail) and images (fax mail) to the user. The SS 7 protocol enables extremely fast data connections among mobile switching centres (MSCs), so fast that the networks can obtain enhanced services data while the call is being connected. The SS 7.05 subset of the protocol defines SMS, or short message services, whereby text messages of up 160 characters can be passed to and between GSM mobiles.
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