Editing Network switching subsystem (section)

==Mobile switching center (MSC)==
<!-- This section is linked from [[Short message service]] -->

===Description===
The '''mobile switching center''' (MSC) is the primary service delivery node for GSM/CDMA, responsible for [[routing in the PSTN|routing]] voice calls and SMS as well as other services (such as conference calls, FAX, and circuit-switched data).

The MSC sets up and releases the '''end-to-end connection''', handles mobility and hand-over requirements during the call and takes care of charging and real-time prepaid account monitoring.

In the GSM mobile phone system, in contrast with earlier analogue services, fax and data information is sent digitally encoded directly to the MSC. Only at the MSC is this re-coded into an "analogue" signal (although actually this will almost certainly mean sound is encoded digitally as a [[pulse-code modulation]] (PCM) signal in a 64-kbit/s timeslot, known as a [[DS0]] in America).

There are various different names for MSCs in different contexts which reflects their complex role in the network, all of these terms though could refer to the same MSC, but doing different things at different times.

The '''gateway MSC''' (G-MSC) is the MSC that determines which "visited MSC" (V-MSC) the subscriber who is being called is currently located at. It also interfaces with the PSTN. All mobile to mobile calls and PSTN to mobile calls are routed through a G-MSC. The term is only valid in the context of one call, since any MSC may provide both the gateway function and the visited MSC function. However, some manufacturers design dedicated high capacity MSCs which do not have any [[base station subsystem]]s (BSS) connected to them. These MSCs will then be the gateway MSC for many of the calls they handle.

The '''visited MSC''' (V-MSC) is the MSC where a customer is currently located. The [[Network_switching_subsystem#Visitor_location_register_(VLR)|visitor location register]] (VLR) associated with this MSC will have the subscriber's data in it.

The '''anchor MSC''' is the MSC from which a [[handover]] has been initiated. The '''target MSC''' is the MSC toward which a handover should take place. A [[mobile switching center server]] is a part of the redesigned MSC concept starting from [[3GPP#Standards|3GPP Release 4]].

===Mobile switching center server (MSC-Server, MSCS or MSS)===
{{main article|Mobile switching centre server}}

The '''mobile switching center server''' is a soft-switch variant (therefore it may be referred to as mobile soft switch, MSS) of the mobile switching center, which provides circuit-switched calling mobility management, and GSM services to the mobile phones [[roaming]] within the area that it serves. The functionality enables split control between (signaling ) and user plane (bearer in network element called as media gateway/MG), which guarantees better placement of network elements within the network.

MSS and [[Media Gateway|media gateway]] (MGW) makes it possible to cross-connect circuit-switched calls switched by using IP, ATM AAL2 as well as [[Time-division multiplexing|TDM]]. More information is available in 3GPP TS 23.205.

The term [[Circuit switching]] (CS) used here originates from traditional telecommunications systems. However, modern MSS and MGW devices mostly use generic [[Internet]] technologies and form [[Next-generation network|next-generation telecommunication networks]]. MSS software may run on generic computers or [[virtual machine]]s in [[Cloud computing|cloud]] environment.

===Other GSM core network elements connected to the MSC===
The MSC connects to the following elements:
* The [[Network switching subsystem#Home location register (HLR)|home location register]] (HLR) for obtaining data about the [[Subscriber Identity Module|SIM]] and [[MSISDN|mobile services ISDN]] number (MSISDN; i.e., the telephone number).
* The [[Base Station Subsystem|base station subsystems]] (BSS) which handles the radio communication with [[2G]] and [[2.5G]] mobile phones.
* The [[UTRAN|UMTS terrestrial radio access network]] (UTRAN) which handles the radio communication with [[3G]] mobile phones.
* The [[Network switching subsystem#Visitor location register (VLR)|visitor location register]] (VLR) provides subscriber information when the subscriber is outside its home network.
* Other MSCs for procedures such as [[handoff|hand over]].

===Procedures implemented===
Tasks of the MSC include:
* [[GSM services#Call set up process for incoming calls|Delivering calls to subscribers]]{{Broken anchor|date=2024-07-22|bot=User:Cewbot/log/20201008/configuration|target_link=GSM services#Call set up process for incoming calls|reason= The anchor (Call set up process for incoming calls) [[Special:Diff/8922898|has been deleted]].}} as they arrive based on information from the VLR.
* Connecting outgoing calls to other mobile subscribers or the PSTN.
* Delivering SMSs from subscribers to the [[short message service center]] (SMSC) and vice versa.
* Arranging handovers from BSC to BSC.
* Carrying out handovers from this MSC to another.
* Supporting [[supplementary services]] such as conference calls or call hold.
* Generating billing information.