October 31, 2010 by Isybel Harto
Basic telecommunication services fall into:
- Bearer Services
Teleservices enable subscribers to communicate with each other. Teleservices consist of speech services, short message services, and fax services.
I. Speech Services
Speech services consist of telephony calls and emergency calls.
- Telephony calls
Telephony calls enable mobile subscribers to communicate with PSTN subscribers, ISDN subscribers, and PLMN subscribers.
- Emergency calls
When a subscriber presses the emergency key or dials the number of an emergency service center, the call is connected to the nearest emergency center. An emergency call can be made without a SIM card. The network operator can decide whether to charge subscribers for such calls.
II. Short Message Services
Short message services (SMS) consists of point-to-point (PP) SMS and point-to-multipoint SMS. Point-to-point SMS consists of short message mobile originated service (MO/PP) and short message mobile terminated service (MT/PP).
Point-to-multipoint service refers to short message cell broadcast service:
- Short message MO/PP
A mobile subscriber sends a short message to a short message center (SMC).
- Short message MT/PP
The SMC sends a short message to a mobile subscriber.
- Short message cell broadcast
III. Fax Services
Fax service allows the connection of group 3 fax apparatus to the mobile stations of GSM PLMN. Fax connection may be set up between the PSTN/ISDN and the GSM PLMN or inside the GSM PLMN. The following two types of faxes are supported:
- Automatic fax group 3
The Teleservice supports fax group 3 automatic call/automatic answer function.
- Alternate speech/fax group 3
When both the speech and fax services are needed, the M900/M1800 MSC/SSP/IP supports the communication of speech followed by fax.
2. Bearer Services
Data communication (especially Internet) has become more and more popular. Data service is a major service provided by GSM operators. Bearer service enables transmission of information between the terminal access reference points. This capability includes some low-layer functions, corresponding to layers 1–3 of the OSI reference model.
According to access modes, bearer services fall into the following categories:
- 3.1 kHz audio
The PSTN provides subscribers with a channel capable of transmitting 3.1 kHz analog speech signals, while in the GSM PLMN, the signals transmitted between the mobile terminals and the networks are all digitized. Therefore, a special audio Modem is needed at the connection point between the GSM PLMN and the PSTN to fulfill this conversion. For the data communication between PLMN subscribers and PSTN subscribers, only 3.1 kHz audio mode can be adopted. While for the data communication between PLMN subscribers and ISDN subscribers, 3.1 kHz audio mode or unrestricted digital information (UDI) mode can be used. This mode supports multiple subscriber data rates at 300 bit/s, 1200 bit/s, 1200/75 bit/s, 2400 bit/s, 4800 bit/s, and 9600 bit/s.
- PAD (Packet assembly/disassembly)
The MSC provides an asynchronous connection to the PAD equipment. This enables PLMN subscribers to access a packet network (PSPDN/ISDN).This mode supports multiple subscriber rates, including 300 bit/s, 1200 bit/s, 1200/75 bit/s, 2400 bit/s, 4800 bit/s, and 9600 bit/s.
Basic packet access provides a synchronous connection that enables PLMN subscribers to access a packet network (PSPDN/ISDN). In this case, the mobile subscriber can only be a calling party.This mode supports multiple subscriber rates, including 1200 bit/s, 2400 bit/s, 4800 bit/s, and 9600 bit/s.
According to transmission modes, bearer services fall into the following categories:
- Transparent transmission mode (T-mode)
In T-mode, error correction is completed using the forward error correction mechanism provided by the radio interface transmission scheme. The available throughput and transmission delay is fixed. T-mode does not use the Radio Link Protocol (RLP).
- Non-transparent transfer mode (NT-mode)
NT-mode adopts RLP. On the basis of forward error correction mechanism provided by the radio interface transmission scheme, messages can be resent if the peer end does not receive the message correctly. In this mode, the throughput varies with the basic transmission quality and transmission delay (the higher the error probability is, the lower the throughput will be). Measured by residual error codes, the transmission quality in the NT-mode is much better than that in the T-mode.
According to service codes, bearer services fall into the following categories:
- Asynchronous circuit bearer services (BS2X)
BTS2X provides asynchronous data transmission at various rates, and supports both 3.1 kHz audio and PAD access. The PLMN can interconnect with the PSPDN with the PSTN/ISDN as the transmission network. The communication between the PLMN and the PSTN can be done only through 3.1 kHz audio, while the communication between the PLMN and the ISDN can be done in various modes including 3.1 kHz audio.
- Basic packet bearer services (BS3X)
BS3X provides full-duplex circuit-switched synchronous data transmission at various rates for data exchange among packet terminals. BS3X supports:
– Communication between mobile subscribers and packet terminals in the PSTN/ISDN
– Access of the PLMN to the access unit (AU) of the PSPDN through the PSTN
– Access of the PLMN to the packet handler (PH) of the PSPDN through the ISDN,or directly to the PSPDN through the PH of the ISDN.
- Dedicated PAD access (BS4X)
BS4X allows a simple terminal to communicate with the X.25 terminals on the PSPDN through dedicated PAD. Compared with BS2X, BS4X does not need the ISDN or PSTN. BS4X only supports mobile originated calls.
- Dedicated packet bearer services (BS5X)
BS5X provides the packet bearer services for which the PLMN directly connects to the PSPDN through the PH. The communication between the MSC and the PH
When the MSC serves as a GMSC, it does not have subscribers, but provides processing when obtaining route information through the HLR if the mobile subscriber subscribes to certain supplementary services such as CFU and CFNRc. When the subscriber has CAMEL subscription data and subscribes to CFU/CFNRc services, the GMSC performs the MOC procedure. A supplementary service modifies or enhances a basic teleservice. A supplementary service must be offered together or in association with a basic teleservice. A supplementary service may be offered by several different teleservices. The M900/M1800 digital cellular mobile switching system provides supplementary
services such as:
- Line identification
- Call forwarding
- Call barring
- Call completion
- Multiparty service
- Community of interest
- Advice of charge
- Unstructured supplementary service
In addition, the MSC provides self-defined services to meet
Line identification services include CLIP, CLIR, COLP, and COLR.
- Calling line identification presentation (CLIP)
CLIP is a supplementary service provided for the called party. When a mobile subscriber receives a call, the network does not display the calling number.
- Calling line identification restriction (CLIR)
CLIR is a supplementary service provided for the calling party. When a mobile subscriber makes a call, the network does not display the calling number to the called party.
- Connected line identification presentation (COLP)
COLP is a supplementary service provided for the calling party. When a mobile subscriber makes a call, the connected subscriber may not be the called party because the called party activates the call forwarding service. In this case, the network displays the connected number to the calling subscriber.
- Connected line identification restriction (COLR)
COLR is a supplementary service provided for the called party. When a subscriber who signed up for this service receives the call, the network does not display his number to the calling subscriber
Call forwarding services include CFU, CFB, CFNRy, and CFNRc.
- Call forwarding unconditional (CFU)
When a mobile subscriber is called, he can forward all calls to a pre-selected third party unconditionally by activating this service. The third party can be a subscriber of the PLMN, PSTN, and ISDN, or service stations such as voice mailbox.
- Call forwarding on mobile subscriber busy (CFB)
When a mobile subscriber is engaged in a call and a new call is coming, the new call is forwarded to a pre-selected third party.
- Call forwarding on mobile subscriber no reply (CFNRy)
When a mobile subscriber is alerted for a long time and does not answer the call, the call is forwarded to a third party after the expiry of no reply timer.
- Call forwarding on mobile subscriber not reachable (CFNRc)
When the radio channel connection between the network and the MS is interrupted, the call to this MS will be forwarded to a third party. The “unreachable” conditions include no response to paging, radio channel assignment failure, and MS power-off.
Call completion services include call waiting (CW) and call hold (HOLD).
- Call waiting (CW)
The CW service permits a mobile subscriber to be notified of an incoming call (as per basic call procedures) although the traffic channel is unavailable for the incoming call and the mobile subscriber is engaged in an active or held call. Subsequently, the subscriber can accept, reject, or ignore the incoming call.
- Call hold (HOLD)
The HOLD service allows a mobile subscriber to suspend an ongoing call so as to initiate a new call or switch over to another call being held, and then, if desired, resume the call just interrupted. When a call is on hold, the MS temporarily being disconnected will hear prompt tone and music.
The multiparty (MPTY) service allows a multi-connection call for mobile subscribers, that is, a simultaneous communication with more than one party. As a prerequisite, mobile subscribers have to register the HOLD service
Community of Interest
The community of interest services include closed user group (CUG) service. A CUG can be a single subscriber or several subscribers with the same attributes. The CUG service allows one subscriber to join different CUGs (a maximum of 10). The CUG service can meet the demands of either small groups of a few members or large organizations with thousands of subscribers. The CUG can use all teleservices except emergency call, short message, dedicated PAD access, and dedicated packet access.
The CUG service has the following options:
- CUG calls only
Subscribers with this function can originate calls to or receive calls from other
members of the same group.
- Incoming calls barred within a CUG (icb)
Subscribers with this function cannot receive calls but can make calls to other
members in the group.
- Outgoing calls barred within a CUG (ocb)
Subscribers with this function cannot originate calls but can receive calls from
other members in the group.
- Incoming and outgoing calls barred within a CUG
Subscribers with this function cannot make calls to or receive calls from other
members in the group.
- CUG with outgoing access (OA)
Subscribers with this function can make calls to subscribers outside this CUG.
- CUG with incoming access (IA)
Subscribers with this function can receive calls from subscribers outside this CUG.
- CUG with IA and OA:
Subscribers with this function can make calls to and receive calls from other
Advice of Charge
The charging supplementary services consist of two services, advice of charge (information) and advice of charge (charging).
- Advice of charge, information (AoCI)
AoCI allows immediate display of charges on the termination of the call. If the subscriber registers the AoCI service, the network sends the charging rate to the MS that automatically calculates and displays the charge amount for each call.
- Advice of charge, charging (AoCC)
In addition to the functions of AoCI, AoCC also supports leased MS service and PPS. These services require the MS to support the Phase 2 standards and a special SIM card.
The call barring services defined in the GSM specifications consists of barring of incoming calls and barring of outgoing calls.
Barring of incoming calls falls into the following two types:
- Barring of all incoming calls (BAIC)
With this service, the calls to a subscriber are barred.
- Barring of incoming calls when roaming outside the home PLMN country
With this service, the calls to a subscriber are barred when he is roaming outside
his home PLMN country.
Barring of outgoing calls falls into the following three types:
- Barring of all outgoing calls (BAOC)
With this service, all calls made by a subscriber are barred except the emergency
- Barring of outgoing international calls (BOIC)
With this service, all international calls made by a subscriber are barred.
- Barring of outgoing international calls except those directed to the home PLMN
This barring service allows calls towards a party in the country of subscription.
When the subscriber is roaming in the home PLMN country, calls to subscribers in
other countries are barred. When the subscriber is roaming outside the home
PLMN country, only the calls to subscribers of local country and home country are
Unstructured Supplementary Service
Unstructured supplementary service mainly refers to unstructured supplementary service data (USSD). The USSD service provides information to subscribers in the interaction mode. It is implemented in two modes: one is that the GSM network provides information services concerning subscribers; another is that the GSM network is the bearer network and information services are provided by a special information center called “USSD center.” Subscriber can send certain service request to the network by entering supplementary service operation commands on the MS, or the network side initiates USSD commands to perform certain operations. USSD service may be provided by the GSM network, or provided by other networks with the GSM network as the bearer for transparent transmission. The USSD center can provide the following information:
- Flight schedule or other information
- Foreign exchange
- Sports news
- Ticket booking
- Bank account
The USSD service can also be used for the query and management of subscriber service data in the mobile network. For example, Subscribers can use the USSD service to manage intelligent services once the
MSC is connected to the WIN.
Subscribers can query data in the VLR and HLR (such as the query of the subscriber MSISDN number)
The USSD service facilitates the creation and provisioning of new services
Explicit Call Transfer (ECT)
ECT is a call forwarding service determined by mobile subscribers. The subscriber who has registered the ECT service can temporarily end an ongoing call and originate a new call through the HOLD function. After the new call is successfully connected, thesubscriber can trigger the ECT service to enable the conversation between the party involved in the original call and the called party in the new call. At the same time, he quits the service himself. To implement the ECT service, the mobile subscriber must have subscribed to HOLD service
Operator-determined barring (ODB) means that the PLMN operator can regulate the subscriber’s access to certain GSM services. It is fulfilled through management of the data in the HLR. ODB applies to all subscriber services and bearer services except emergency calls. It takes precedence over the supplementary services described previously. When there is a conflict between ODB and a supplementary service, the supplementary service is restricted. ODB is similar to call barring, but different in the following aspects:
Firstly, the service state of ODB subscribers is controlled by the network operator, but for the call barring service, the state can be controlled by either the subscriber or the operator. Secondly, ODB service is activated once it is provided, but call barring service must be activated by the subscriber after being provided.
The MSC supports the following ODB services:
- Barring outgoing calls
- Barring outgoing international calls
- Barring outgoing international calls except those directed to the home PLMN country
- Barring of outgoing calls when roaming outside the home PLMN country
- Barring incoming calls
- Barring incoming calls when roaming outside the home PLMN country
- Barring of roaming outside the home PLMN country
- Barring of outgoing premium rate calls (information)
- Barring of outgoing premium rate calls (entertainment)
- Barring of supplementary services management
Enhanced Multilevel Precedence and Preemption (eMLPP)Service
The enhanced multilevel precedence and preemption (eMLPP) service allows classification of mobile subscribers according to a specific subscriber priority. Precedence means assigning a priority to a point-to-point call, group call, or broadcast call in combination with a fast call setup. Preemption means high priority calls can seize the resources, such as radio channels, which are used by low priority calls, when the network offers no idle resources. The eMLPP service is implemented in the PLMN as a GSM supplementary service according to GSM Recommendations 02.67, 03.67 and 04.67. It is applicable to those subscribers with teleservices 1x, 6x, and all bearer services of the GSM network where the eMLPP service is provided
Self-Defined Supplementary Services
To meet specific customer requirements, the MSC also provides some self-defined supplementary services, including subscriber roaming area restriction, LA-dependant roaming area restriction, and subscriber roaming restriction.
- Roaming area restriction (through zone code)
Zone code is a kind of subscription data in the HLR. It can be used to restrict the roaming area of the subscriber. The MSC can define the location areas (LAs) contained in each zone code. In this way, the area that allows mobile subscriber roaming can be set flexibly.
- LA-dependant roaming area restriction
The MSC can provide roaming restriction function based on LA without the cooperation of the HLR. For this type of roaming restriction, subscriber group and area number (one area number may correspond to one or more LAs) must be defined first. The relationship between the subscriber group and area number must be defined, so that the area in which roaming is forbidden for this subscriber group can be decided.
- Subscriber roaming restriction (through VLR table)
The VLR table contains a kind of subscription data in the HLR. It defines the roaming area of the subscriber with the unit of VLR area. The MSC enables this roaming restriction with the cooperation of HLR.
The MSC provides location service (LCS).
LCS refers to the location-related services provided for the mobile subscriber by the mobile network operator who determines the geographical location of the mobile station by use of specialized mobile location techniques. The location services locate the mobile terminal to the cell level. LCS finds wide use in different fields, ranging from security to charging and from
information service to tracing management.
LCS benefits the following services:
- Public security services (for example, emergency services and emergency alarm
- Location-based charging and tracing services
- Location-based information services (for example, navigation, sightseeing, broadcast to designated areas, and mobile yellow page)
The MSC also provides virtual roaming service (VRS). If a subscriber, Mobile V for example, signs up for the VRS, he owns one MSISDN respectively in each network of two countries/regions. The VRS is implemented through a special service procedure: When a subscriber in country/area A calls Mobile V, he only needs to dial mobile V’s MSISDN in the network of country/area A. Likewise, when a subscriber in country/area B calls Mobile V, he only needs to dial Mobile V’s MSISDN in the network of country/region B.