Misplaced Pages

#135864

55-412: The base transceiver station , or BTS, contains the equipment for transmitting and receiving radio signals ( transceivers ), antennas , and equipment for encrypting and decrypting communications with the base station controller (BSC). Typically a BTS for anything other than a picocell will have several transceivers (TRXs) which allow it to serve several different frequencies and different sectors of

110-411: A Gaussian low-pass filter prior to being fed to a frequency modulator , which greatly reduces the interference to neighboring channels ( adjacent-channel interference ). Antenna combiners are implemented to use the same antenna for several TRXs (carriers), the more TRXs are combined the greater the combiner loss will be. Up to 8:1 combiners are found in micro and pico cells only. Frequency hopping

165-511: A regular pulse excited-long term prediction (RPE-LTP) coder for voice data between the mobile device and the BSS, but pulse-code modulation ( A-law or μ-law standardized in ITU G.711 ) upstream of the BSS. RPE-LPC coding results in a data rate for voice of 13 kbit/s where standard PCM coding results in 64 kbit/s. Because of this change in data rate for the same voice call , the transcoder also has

220-756: A BTS vary depending on the cellular technology used and the cellular telephone provider. There are vendors in which the BTS is a plain transceiver which receives information from the MS (mobile station) through the Um air interface and then converts it to a TDM (PCM) based interface, the Abis interface, and sends it towards the BSC. There are vendors which build their BTSs so the information is preprocessed, target cell lists are generated and even intracell handover (HO) can be fully handled. The advantage in this case

275-454: A base station, each pointing in different directions, it is possible to sectorise the base station so that several different cells are served from the same location. Typically these directional antennas have a beamwidth of 65 to 85 degrees. This increases the traffic capacity of the base station (each frequency can carry eight voice channels) whilst not greatly increasing the interference caused to neighboring cells (in any given direction, only

330-443: A buffering function so that PCM 8-bit words can be recoded to construct GSM 20 ms traffic blocks. Although transcoding (compressing/decompressing) functionality is defined as a base station function by the relevant standards, there are several vendors which have implemented the solution outside of the BSC. Some vendors have implemented it in a stand-alone rack using a proprietary interface. In Siemens ' and Nokia 's architecture,

385-455: A full switching center, as well as an SS7 node with connections to the MSC and serving GPRS support node (SGSN) (when using GPRS ). It also provides all the required data to the operation support subsystem (OSS) as well as to the performance measuring centers. A BSC is often based on a distributed computing architecture, with redundancy applied to critical functional units to ensure availability in

440-410: A rule, these are stolen or lost devices. Mobile operators rarely use EIR capabilities to block devices on their own. Usually blocking begins when there is a law in the country, which obliges all cellular operators of the country to do so. Therefore, in the delivery of the basic components of the network switching subsystem (core network) is often already present EIR with basic functionality, which includes

495-462: A small number of frequencies are being broadcast). Typically two antennas are used per sector, at spacing of ten or more wavelengths apart. This allows the operator to overcome the effects of fading due to physical phenomena such as multipath reception . Some amplification of the received signal as it leaves the antenna is often used to preserve the balance between uplink and downlink signal. The base station controller (BSC) provides, classically,

550-400: A smaller number of connections towards the mobile switching center (MSC) (with a high level of utilisation). Overall, this means that networks are often structured to have many BSCs distributed into regions near their BTSs which are then connected to large centralised MSC sites. The BSC is undoubtedly the most robust element in the BSS as it is not only a BTS controller but, for some vendors,

605-446: A specific service number, sending SMS to a specific service number, and all Internet traffic is redirected to a specific landing page. This is achieved by the fact that EIR can send commands to several MNO systems (HLR, PCRF , SMSC , etc.). The most common suppliers of individual EIR systems (not as part of a complex solution) are the companies BroadForward, Mahindra Comviva, Mavenir, Nokia, Eastwind. Connected more or less directly to

SECTION 10

#1733086031136

660-529: 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

715-611: A ‘whitelisted’ response to all CheckIMEI and the ability to fill IMEI blacklist, which will be given a ‘blacklisted’ response. When the legislative framework for blocking registration of devices in cellular networks appears in the country, the telecommunications regulator usually has a Central EIR ( CEIR ) system, which is integrated with the EIR of all operators and transmits to them the actual lists of identifiers that must be used when processing CheckIMEI requests. In doing so, there may be many new requirements for EIR systems that are not present in

770-567: Is a database of the MSs ( Mobile stations ) that have roamed into the jurisdiction of the Mobile Switching Center (MSC) which it serves. Each main base transceiver station in the network is served by exactly one VLR (one BTS may be served by many MSCs in case of MSC in pool), hence a subscriber cannot be present in more than one VLR at a time. The data stored in the VLR has either been received from

825-499: Is a late addition to the GSM standard. It performs some of the processing tasks of the BSC, but for packet data. The allocation of channels between voice and data is controlled by the base station, but once a channel is allocated to the PCU, the PCU takes full control over that channel. The PCU can be built into the base station, built into the BSC or even, in some proposed architectures, it can be at

880-465: Is allowed to attach and proceed with GSM services. After successful authentication, the MSC sends the encryption key K c to the base station controller (BSC) so that all communications can be encrypted and decrypted. Of course, the mobile phone can generate the K c itself by feeding the same RAND supplied during authentication and the K i into the A8 algorithm. The AuC is usually collocated with

935-470: Is also referred to as the transcoder and rate adaptation unit ( TRAU ). Some networks use 32 kbit/s ADPCM on the terrestrial side of the network instead of 64 kbit/s PCM and the TRAU converts accordingly. When the traffic is not voice but data such as fax or email, the TRAU enables its rate adaptation unit function to give compatibility between the BSS and MSC data rates. The packet control unit (PCU)

990-465: Is an additional form of identification check performed on the serial number of the mobile phone described in the EIR section below, but this is not relevant to the AuC processing. Proper implementation of security in and around the AuC is a key part of an operator's strategy to avoid SIM cloning . The AuC does not engage directly in the authentication process, but instead generates data known as triplets for

1045-412: 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. The MSC connects to the following elements: Tasks of

1100-413: Is less load on the expensive Abis interface. The BTSs are equipped with radios that are able to modulate layer 1 of interface Um; for GSM 2G+ the modulation type is Gaussian minimum-shift keying (GMSK), while for EDGE -enabled networks it is GMSK and 8-PSK . This modulation is a kind of continuous-phase frequency-shift keying . In GMSK, the signal to be modulated onto the carrier is first smoothed with

1155-454: Is often used to increase overall BTS performance; this involves the rapid switching of voice traffic between TRXs in a sector. A hopping sequence is followed by the TRXs and handsets using the sector. Several hopping sequences are available, and the sequence in use for a particular cell is continually broadcast by that cell so that it is known to the handsets. A TRX transmits and receives according to

SECTION 20

#1733086031136

1210-468: 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: The HLR is a system which directly receives and processes MAP transactions and messages from elements in

1265-430: 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

1320-563: Is the trisector, also known as clover, in which there are three sectors served by separate antennas. Each sector has a separate direction of tracking, typically of 120° with respect to the adjacent ones. Other orientations may be used to suit the local conditions. Bisectored cells are also implemented. These are most often oriented with the antennas serving sectors of 180° separation to one another, but again, local variations do exist. Network and Switching Subsystem#Description Network switching subsystem ( NSS ) (or GSM core network )

1375-434: Is used to authenticate the customer and generate a key for encrypting voice and data traffic, as defined in 3GPP TS 43.020 (03.20 before Rel-4). Development of A3 and A8 algorithms is considered a matter for individual GSM network operators, although example implementations are available. To encrypt Global System for Mobile Communications (GSM) cellular communications A5 algorithm is used. The Visitor Location Register (VLR)

1430-531: The Home Location Register (HLR) , or collected from the MS. In practice, for performance reasons, most vendors integrate the VLR directly to the V-MSC and, where this is not done, the VLR is very tightly linked with the MSC via a proprietary interface. Whenever an MSC detects a new MS in its network, in addition to creating a new record in the VLR, it also updates the HLR of the mobile subscriber, apprising it of

1485-529: The GSM standards, which specify eight TDMA timeslots per radio frequency. A TRX may lose some of this capacity as some information is required to be broadcast to handsets in the area that the BTS serves. This information allows the handsets to identify the network and gain access to it. This signalling makes use of a channel known as the Broadcast Control Channel (BCCH). By using directional antennas on

1540-480: The Internet . 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

1595-492: The gsm core network (typically when the phone is powered on). Once the authentication is successful, the HLR is allowed to manage the SIM and services described above. An encryption key is also generated that is subsequently used to encrypt all wireless communications (voice, SMS, etc.) between the mobile phone and the GSM core network. If the authentication fails, then no services are possible from that particular combination of SIM card and mobile phone operator attempted. There

1650-563: The intelligence behind the BTSs. Typically a BSC has tens or even hundreds of BTSs under its control. The BSC handles allocation of radio channels, receives measurements from the mobile phones, and controls handovers from BTS to BTS (except in the case of an inter-BSC handover in which case control is in part the responsibility of the anchor MSC ). A key function of the BSC is to act as a concentrator where many different low capacity connections to BTSs (with relatively low utilisation) become reduced to

1705-462: The network management system (NMS), and manages operational states of each TRX, as well as software handling and alarm collection. The basic structure and functions of the BTS remains the same regardless of the wireless technologies. A BTS is usually composed of: Directional antennas reduce LoRa (long-range) interference. If not sectorised, the cell will be served by an omnidirectional antenna , which radiates in all directions. A typical structure

Base station subsystem - Misplaced Pages Continue

1760-490: The BSC. This data is obtained directly from radio planning engineering which involves modelling of the signal propagation as well as traffic projections. The transcoder is responsible for transcoding the voice channel coding between the coding used in the mobile network, and the coding used by the world's terrestrial circuit-switched network, the Public Switched Telephone Network . Specifically, GSM uses

1815-452: The EIR response to determine whether or not to allow the device to register or re-register on the network. Since the response of switching equipment to ‘greylisted’ and ‘unknown equipment’ responses is not clearly described in the standard, they are most often not used. Most often, EIR uses the IMEI blacklist feature, which contains the IMEI of the devices that need to be banned from the network. As

1870-764: The GSM core network are many other functions. The billing center is responsible for processing the toll tickets generated by the VLRs and HLRs and generating a bill for each subscriber. It is also responsible for generating billing data of roaming subscriber. The multimedia messaging service center supports the sending of multimedia messages (e.g., images, audio , video and their combinations) to (or from) MMS-bluetooth. The voicemail system records and stores voicemail. According to U.S. law, which has also been copied into many other countries, especially in Europe, all telecommunications equipment must provide facilities for monitoring

1925-532: 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

1980-408: The GSM network, for example, the location update messages received as mobile phones roam around. The HLR connects to the following elements: The main function of the HLR is to manage the fact that SIMs and phones move around a lot. The following procedures are implemented to deal with this: The authentication center (AuC) is a function to authenticate each SIM card that attempts to connect to

2035-488: The HLR, although this is not necessary. Whilst the procedure is secure for most everyday use, it is by no means hack proof. Therefore, a new set of security methods was designed for 3G phones. In practice, A3 and A8 algorithms are generally implemented together (known as A3/A8, see COMP128 ). An A3/A8 algorithm is implemented in Subscriber Identity Module (SIM) cards and in GSM network Authentication Centers. It

2090-427: The MSC include: 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

2145-508: The MSC to use during the procedure. The security of the process depends upon a shared secret between the AuC and the SIM called the K i . The K i is securely burned into the SIM during manufacture and is also securely replicated onto the AuC. This K i is never transmitted between the AuC and SIM, but is combined with the IMSI to produce a challenge/response for identification purposes and an encryption key called K c for use in over

2200-587: The MSC. When a particular IMSI requests access to the GSM core network, the MSC sends the RAND part of the triplet to the SIM. The SIM then feeds this number and the K i (which is burned onto the SIM) into the A3 algorithm as appropriate and an SRES is calculated and sent back to the MSC. If this SRES matches with the SRES in the triplet (which it should if it is a valid SIM), then the mobile

2255-663: The SGSN site. In most of the cases, the PCU is a separate node communicating extensively with the BSC on the radio side and the SGSN on the Gb side. Base transceiver station A base transceiver station ( BTS ) or a baseband unit (BBU) is a piece of equipment that facilitates wireless communication between user equipment (UE) and a network. UEs are devices like mobile phones (handsets), WLL phones, computers with wireless Internet connectivity, or antennas mounted on buildings or telecommunication towers. The network can be that of any of

Base station subsystem - Misplaced Pages Continue

2310-405: The air communications. The AuC connects to the following elements: The AuC stores the following data for each IMSI: When the MSC asks the AuC for a new set of triplets for a particular IMSI, the AuC first generates a random number known as RAND . This RAND is then combined with the K i to produce two numbers as follows: The numbers ( RAND , SRES, K c ) form the triplet sent back to

2365-456: The cell (in the case of sectorised base stations). A BTS is controlled by a parent BSC via the "base station control function" (BCF). The BCF is implemented as a discrete unit or even incorporated in a TRX in compact base stations. The BCF provides an operations and maintenance (O&M) connection to the network management system (NMS), and manages operational states of each TRX, as well as software handling and alarm collection. The functions of

2420-447: The event of fault conditions. Redundancy often extends beyond the BSC equipment itself and is commonly used in the power supplies and in the transmission equipment providing the A-ter interface to PCU. The databases for all the sites, including information such as carrier frequencies , frequency hopping lists, power reduction levels, receiving levels for cell border calculation, are stored in

2475-481: The functioning of BTS. Typically a BTS will have several transceivers (TRXs) which allow it to serve several different frequencies and different sectors of the cell (in the case of sectorised base stations). A BTS is controlled by a parent base station controller via the base station control function (BCF). The BCF is implemented as a discrete unit or even incorporated in a TRX in compact base stations. The BCF provides an operations and maintenance (O&M) connection to

2530-413: 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

2585-419: The legacy EIR: Other functions may be required in individual cases. For example, Kazakhstan has introduced mandatory registration of devices and their binding to subscribers. But when a subscriber appears in the network with a new device, the network operation is not blocked completely, and the subscriber is allowed to register the device. To do this, there are blocked all services, except the following: calls to

2640-531: 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

2695-500: 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

2750-476: The new location of that MS. If VLR data is corrupted it can lead to serious issues with text messaging and call services. Data stored include: The primary functions of the VLR are: EIR is a system that handles real-time requests to check the IMEI (checkIMEI) of mobile devices that come from the switching equipment (MSC, SGSN , MME ). The answer contains the result of the check: The switching equipment must use

2805-455: 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 mobile phones to have access to services such as WAP , MMS and

SECTION 50

#1733086031136

2860-408: 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 . The mobile switching center server is a soft-switch variant (therefore it may be referred to as mobile soft switch, MSS) of

2915-425: The transcoder is an identifiable separate sub-system which will normally be co-located with the MSC. In some of Ericsson 's systems it is integrated to the MSC rather than the BSC. The reason for these designs is that if the compression of voice channels is done at the site of the MSC, the number of fixed transmission links between the BSS and MSC can be reduced, decreasing network infrastructure costs. This subsystem

2970-457: The wireless communication standards, it is generally associated with mobile communication technologies like GSM and CDMA . In this regard, a BTS forms part of the base station subsystem (BSS) developments for system management. It may also have equipment for encrypting and decrypting communications, spectrum filtering tools (band pass filters) and so on. Antennas may also be considered as components of BTS in general sense as they facilitate

3025-464: The wireless communication technologies like GSM , CDMA , wireless local loop , Wi-Fi , WiMAX or other wide area network (WAN) technology. BTS is also referred to as the node B (in 3G networks) or, simply, the base station (BS). For discussion of the LTE standard the abbreviation eNB for evolved node B is widely used, and GNodeB for 5G . Though the term BTS can be applicable to any of

#135864