The various entities in the GSM network are connected to one another through signalling networks.
Signalling is used for example, for subscriber mobility, subscriber registration, call establishment,
etc. The connections to the various entities are known as ‘reference points’. Examples include:
• A interface – the connection between MSC and BSC;
• Abis interface – the connection between BSC and BTS;
• D interface – the connection between MSC and HLR;
• Um interface – the radio connection between MS and BTS.
Various signalling protocols are used over the reference points. Some of these protocols for GSM
are the following:
• mobile application part (MAP) – MAP is used for call control, subscriber registration, short
message service, etc.; MAP is used over many of the GSM network interfaces;
• base station system application part (BSSAP) – BSSAP is used over the A interface;
• direct transfer application part (DTAP) – DTAP is used between MS and MSC; DTAP is carried
over the Abis and the A interface. DTAP is specified in GSM TS 04.08 [49];
• ISDN user part (ISUP) – ISUP is the protocol for establishing and releasing circuit switched
calls. ISUP is also used in landline Integrated Services Digital Network (ISDN). A circuit is the
data channel that is established between two users in the network. Within ISDN, the data channel
is generally a 64 kbit/s channel. The circuit is used for the transfer of the encoded speech or
other data. ISUP is specified in ITU-T Q.763 [137].
When it comes to call establishment, GSM makes a distinction between signalling and payload.
Signalling refers to the exchange of information for call set up; payload refers to the data that is
transferred within a call, i.e. voice, video, fax etc. For a mobile terminated GSM call, the signalling
consists of exchange of MAP messages between GMSC, HLR and visited MSC (VMSC). The
payload is transferred by the ISUP connection between GMSC and VMSC. It is a continual aim
to optimize the payload transfer through the network, as payload transfer has a direct cost aspect
associated with it. Some network services are designed to optimize the payload transfer. One
example is optimal routing.
1 comments:
If you're trying to lose fat then you need to start following this totally brand new custom keto meal plan.
To produce this service, certified nutritionists, fitness trainers, and cooks have united to develop keto meal plans that are effective, convenient, cost-efficient, and delightful.
From their grand opening in early 2019, 1000's of clients have already completely transformed their figure and well-being with the benefits a proper keto meal plan can give.
Speaking of benefits: in this link, you'll discover eight scientifically-confirmed ones provided by the keto meal plan.
Post a Comment