computer science

Network switching subsystem

Network switching subsystem is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Network switching subsystem rather than just read about it. In short: Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mobile phone operators and allows mobile devices to communicate with each other and telephones in the wider public switched telephone network (PSTN).

Key takeaways

Network switching subsystem belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Network switching subsystem to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Network switching subsystem from memory before moving on to harder problems.

Reference excerpt

Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mobile phone operators and allows mobile devices to communicate with each other and telephones in the wider public switched telephone network (PSTN). The architecture contains specific features and functions which are needed because the phones are not fixed in one location. The NSS originally consisted of the circuit-switched core network, used for traditional GSM services such as voice calls, SMS, and circuit switched data calls. It was extended with an overlay architecture to provide packet-switched data services known as the GPRS core network. This allows GSM mobile phones to have access to services such as WAP, MMS and the Internet.

Mobile switching center (MSC)

Description The mobile switching center (MSC) is the primary service delivery node for GSM/CDMA, responsible for 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 subsystems (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 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 Release 4.

Mobile switching center server (MSC-Server, MSCS or MSS)

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 (MGW) makes it possible to cross-connect circuit-switched calls switched by using IP, ATM AAL2 as well as 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 telecommunication networks. MSS software may run on generic computers or virtual machines in cloud environment.

Other GSM core network elements connected to the MSC The MSC connects to the following elements:

The home location register (HLR) for obtaining data about the SIM and mobile services ISDN number (MSISDN; i.e., the telephone number). The base station subsystems (BSS) which handles the radio communication with 2G and 2.5G mobile phones. The UMTS terrestrial radio access network (UTRAN) which handles the radio communication with 3G mobile phones. The visitor location register (VLR) provides subscriber information when the subscriber is outside its home network. Other MSCs for procedures such as hand over.

Procedures implemented Tasks of the MSC include:

Delivering calls to subscribers 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.

Home location register (HLR) The home location register (HLR) is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM core network. There can be several logical, and physical, HLRs per public land mobile network (PLMN), though one international mobile subscriber identity (IMSI)/MSISDN pair can be associated with only one logical HLR (which can span several physical nodes) at a time. The HLRs store details of every SIM card issued by the mobile phone operator. Each SIM has a unique identifier called an IMSI which is the primary key to each HLR record. Another important item of data associated with the SIM are the MSISDNs, which are the telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the number used for making and receiving voice calls and SMS, but it is possible for a SIM to have other secondary MSISDNs associated with it for fax and data calls. Each MSISDN is also a unique key to the HLR record. The HLR data is stored for as long as a subscriber remains with the mobile phone operator. Examples of other data stored in the HLR against an IMSI record is:

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Network switching subsystem

Start with the simplest possible case. Write down what Network switching subsystem claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Network switching subsystem before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Network switching subsystem ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Network switching subsystem

In research: Network switching subsystem appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Network switching subsystem in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Network switching subsystem is common in secondary-school and first-year university syllabi. It links to neighbouring topics GSM standard, Telecommunications infrastructure, so understanding it makes those chapters shorter.
In everyday life: Look for Network switching subsystem outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Network switching subsystem in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Network switching subsystem means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Network switching subsystem out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Network switching subsystem in simple terms?

Why does Network switching subsystem matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Network switching subsystem?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Network switching subsystem.