 Namaste, Welcome to the video lecture on GSM Identifiers, Channels and Frame Structure. Learning Outcome At the end of this session, students will be able to explain use of identifiers, students will be able to classify GSM channel, students will be able to explain GSM frame structure. These are the contents of this video lecture. GSM treats the users and the equipment in different ways. GSM numbers, subscribers and equipments identifiers are some of the known ones. There are many other identifiers that have been well defined which are required for Subscribers Mobility Management and for addressing the remaining network element. First Identifier International Mobile Subscriber Identity i.e. IMSI number Every registered user has an original International Mobile Subscriber Identity i.e. IMSI stored in this Subscriber Identity module i.e. SIM. Size of IMSI number is of 15 digits or less. When an IMSI attempts a call, it needs to contact base station. The base station offers service only if it identifies IMSI as a valid subscriber. For that, IMSI needs to store certain values uniquely defined for IMSI like country code, network type, subscriber id and so on. IMSI number has three parts. First part is called mobile country code. Next identifier is IMAI number, International Mobile Station Equipment Identity number. The International Mobile Station Equipment Identity i.e. IMAI looks more like a serial number which distinctively identifies a mobile station internationally. This is allocated by the equipment manufacturer and registered by the network operator who stores it in the entrepreneurs in residence. By means of IMAI, one recognizes absolute stolen or non-functional equipment. Next identifier is IMSI's DN number i.e. Mobile Subscriber I's DN number. The authenticated telephone number of a mobile station is the Mobile Subscriber I's DN number i.e. IMSI's DN number. Based on the SIM, a mobile station can have many IMSI's DN number as each subscriber is assigned with a separate IMSI's DN to its SIM card. Listed below is the structure followed by IMSI's DN categories as they are defined based on International I's DN number plan. There are three parts in IMSI's DN number. First part is called country code. Up to three decimal places, for example, 9-1 is country code of India. National Destination Code i.e. NDC number. Typically, two or three decimal places are required to store national decimal number. And last part is called subscriber number. Maximum 10 decimal places are required to store subscriber number. All these parts contribute total 15 digits for IMSI's DN number. Now interesting part of this video lecture, you can pause the video for two minutes and list any five countries code used in IMSI's DN identifier. I think two minutes are over. Next identifier is MSRN i.e. Mobile Station Roaming Number. Mobile Station Roaming Number is an interim location dependent IMSI's DN number, assigned to a mobile station by regionally responsible visitor location register i.e. VLR. Using MSRN, the incoming calls are channeled to the MS. The difference is MSRN is used when MS is roaming in other network. Now next identifier i.e. Location Area Identity. Within a PLMN, a location area identifies its own authentic location area identity. The LAI hierarchy is based on international standard and structured in a unique format as mentioned below. Now last identifier, Temporary Mobile Subscriber Identity i.e. TMSI number. Temporary Mobile Subscriber Identity i.e. TMSI number can be assigned by the VLR which is responsible for the current location of a subscriber. The TMSI need to have only local significance in the area handled by the VLR. This is stored on the network side only in the VLR and is not passed to the home location register i.e. HLR. Now next part of this video lecture is GSM channel. In communication, channel can be physical and logical connection. When MS and BTS communicate, they use a specific pair of channels which are denoted by ARFCN i.e. Absolute Radio Frequency Channel Number. The data whether user traffic or signaling information are mapped on to the physical channels by defining a number of logical channels. A logical channel will carry information of a specific type and a number of the channels may be combined before being mapped on to the same physical channel. Logical channels divided into two categories. First category is called traffic channels and next category is called signaling channel. Traffic channel can be of two types. First type is called full-rate traffic channel and next type is called half-rate traffic channel. Traffic channel carries information at a rate of 22.8 kbps and half-rate traffic channel carries information at a rate of 11.34 kbps. Control channels or signaling channels carry signaling information between an MS and BTS. There are several forms of control channels in GSM and they can generally be divided into three categories. First type is called broadcast control channel, second type is called common control channel and third type is called dedicated control channel. Broadcast control channel. Broadcast control channels are transmitted in downlink direction only. Only transmitted by base station, the broadcast channels are used to broadcast synchronization and general network information to all the MS within a cell such as location, area identity and maximum output power. It has three types, frequency, correction channel, synchronization channel and broadcast control channel. Let us discuss frequency correction channel. For the frequency correction synchronization of mobile station, the repeated transmission of frequency burst is called FCCH. This serves two purposes. One is to make sure this is the BCCH carrier. The other is to allow MS to synchronize to the frequency. Next channel is called synchronization channel, allows the mobile station to synchronize time-wise with the base station. Repeated broadcast of synchronization burst is called SCH. Now, last channel in this category which is called BCCH that is broadcast control channel is used to broadcast control information to every MS within a cell. This information includes details of control channel configuration used at the base station. A list of BCCH carrier frequency used at the neighboring base station and a number of parameters that are used by the MS when accessing the base station. Now, next group is called common control channels. The common control channels are used by the MS during the paging and access procedure. Common control channels are of three types. First is called PCH, next one is called RACH and last one is called AGC, PCH that is paging channel. Within a certain time interval the MS will listen to the paging channel, PCH to see if the network wants to get in contact with the MS. The reason could be an incoming call or an incoming short message. Next channel is called RACH. If listening to the PCH the MS will realize it is being paged, the MS answers requesting a signal in channel on the random access channel that is RACH. RACH can also be used if MS wants to get in contact with the network. To operate the mobile in particular physical channel time slot or ARFCM, AGCH is used by the network to grant or deny an MS access to the network by supplying it with a detail of dedicated channel. Now last group that is dedicated control channels. Signaling information is carried between MS and BTS using associated and dedicated control channels during or not during a call. There are three types of dedicated control channels. First one is called SDCCH that is standalone dedicated control channel. Next one is called SSCH that is low associated control channel and last one is called FACCH that is fast associated control channel. First one that is SSCH. Non urgent information example transmitter output power is transmitted using the slow associated control channel. On the uplink MS sends average the measure on own base station and neighboring base station on the downlink the MS receives the system information with transmitting power what timing advance to use it is transmitted at 13 frame of TCH fast associated control channel. More urgent information example handover command is sent using the time slot which are stolen from the traffic channel. Last one is SDCCH in some situations signaling information must flow between the network and a call is not in progress during a location update. This could be accommodated by allocating either a full rate or half rate traffic channel and using either in SSCH or FACCH to carry the information. This would however be west of the limited radio resources so a low data rate channel above one eighth of TCH is defined also used in call set up process. Last part is called GSM frame. In GSM frequency band of 25 MHz is divided into 200 kHz of small band each carry one RF carrier this gives 125 carriers as one carrier is used as a guard channel between GSM and other frequency bands and 24 carriers are useful as a RF channel. This division of frequency pool is called FDMA. Now each RF carrier will have 8 times slot this division time wise is called TDMA. In designing an appropriate frame structure in TDMA the following requirements are generally considered. Frequency band of operation, number of logical channels or number of time slots in TDMA frame, channel bandwidth, maximum cell radius, maximum vehicle speed, maximum delay spread, maximum coding delay. Here each RF carrier frequency shared between 8 users in GSM system the basic radio resources is a time slot with duration of about 577 microsecond and each time slot has 15 divided by 26 that is 0.577 millisecond of time duration. This time slot carries 156.25 bits which leads to bit rate 270.833 kbps. We can see normal burst format. GSM hyper frame is group of packet of 2048 super frame and super frame is formed by combining either 51 traffic multi frames or 26 control multi frames. Each frame has 8 time slots and each time slot is having 577 microsecond duration. These are references. Thank you.