 नमस्ते, welcome to the video lecture on GSM architecture and signalling protocol architecture. Learning Outcome At the end of this session, students will be able to identify different entities in GSM architecture and students will be able to describe the GSM architecture. These are the contents of the video lecture. GSM stands for Global System for Mobile Communication. It is a digital cellular technology used for transmitting mobile voice and data services. The concept of GSM emerged from a cell-based mobile radio system at bail laboratories in early 1970s. It is a second-generation digital mobile telephone standard. Time-division multiple access is used with frequency-division multiple access. And GSM also provides 9.6 kbps data connection. Separate uplink and downlink frequencies are used in GSM. Features which are included telephone fax SMS. These are new features which are included in GSM architecture or second-generation standard. Second-generation GSM standard. Pause video for 2 minutes and list all frequency bands which are used for GSM network. I think 2 minutes are over. I should tell answer of this. GSM operates on the mobile communication band 900 MHz and 1800 MHz in most parts of the world. In US, GSM operates in the band 850 MHz and 1900 MHz. The band for the GSM which is used in US is different from rest of the world. GSM system architecture consists of 3 major subsystems. First subsystem is bell station subsystem. Second one is network and switching subsystem. And last one, operation switching subsystem. The GSM technical specifications define the different elements within the GSM network architecture. It defines the different elements and the ways in which they interact to enable the overall system operation to be maintained. We can observe detail architecture of GSM. Let us see function of each element in architecture. First element that is bell station subsystem. Again the bell station subsystem has 3 different elements. The bell station subsystem section of GSM network architecture that is fundamentally associated with communicating with the mobiles on the network. It consists of first one mobile station, bell station and bell trans receiver station. First element of BSS that is mobile station. Mobile stations, mobile equipment, they are most widely known as sale or mobile phones. Are section of a GSM network that the user sees and operates. There are number of elements to the cell phone. Although the two main elements are the main hardware and the sim. It also contains a number known as the international mobile equipment identity number that is IMA number. This is installed in the phone at a manufacturer and cannot be changed. The sim or subscriber identity model contains information that provides the identity of the user to the network. It contains variety of information including a number known as the international mobile subscriber identity number that is IMS number. BTS, bell trans receiver station. The BTS used in a GSM network comprises the radio transmitter receiver and their associated antennas. They transmit and receive to directly communicate with the mobiles. The BTS is the defining element for each cell. The bell station trans receiver communicates with the mobiles and the interface between the two is known as the UEM interface with the associated protocols. BSC that is bell station controller. The function of BSC is the BSC forms the next stage back into the GSM network. It controls a group of BTS and is often co-located with one of the BTS in its group. It manages the radio resources and controls items such as handover within the group of BTS, allocates channels and like. It communicates with the BTS that is bell station trans receiver or what is termed the AB's interface. The BSC forms the next stage back into the GSM network. It controls a group of bell station. It manages the radio resources and controls items such as handover within the group. It allocates channels and communicates with the best trans receiver stations or what is termed as the AB's interface. Next subsystem is NSS that is network and switching subsystem. The GSM system architecture contains a variety of different elements and is often termed as core network. It provides the main control and interfacing for the whole mobile network. The major elements within the core network include MSC that is mobile switching center, HLR that is home location register, VLR that is visitor location register, AUC that is authentication center, EIR that is equipment identity register. The first element within a network subsystem is MSC that is mobile switching center. The main element within the core network area of the overall GSM network architecture is the mobile switching center. The MSC acts like a normal switching node within the PSTN or ISDN but also provides additional functionality to enable the requirements of a mobile user to be supported. These include registration, authentication, call location, inter-MSC handover and call routing to the mobile subscriber. It also provides an interface to the PSTN so that calls can be routed from the mobile networks to a phone connected to a landline. Interfaces to other MSC's are also provided to enable calls to be made to mobiles on different networks. HLR, home location register. This database contains all the administrative information about each subscriber along with their last known location. In this way, the GSM network is able to route calls to the relevant base station for the MSC. When a user switches on their phone, the phone registers with the network, incoming call can be routed appropriately. Even when the phone is not active or it is switched off, it re-registers periodically to ensure that the network is aware of its latest position. There is one HLR per network, although it may be distributed across various sub-centers for operational reasons. VLR, visitor location register. This contains selected information from the HLR that enables the selected services for the individual subscriber to be provided. The VLR cannot be implemented as separate entity but it is commonly realized as an integral part of the MSC. Rather than a separate entity, in this way access is made faster and more convenient. Few part of the database is also stored in VLR like a TMSI number or roaming number. When mobile station visits another location, the temporary database is formed in a VLR. AUC, that is authentication center. Function of this component from NSS is to provide authentication for verification of the subscriber identity, ensures confidentiality of each cell and protect from fraud call. EIR, that is Equipment Identity Register. The EIR is the entity that decides whether a given mobile equipment may be allowed onto the network. Each mobile equipment has a number known as the International Mobile Equipment Identity. This number, as mentioned above, is installed in the equipment and is checked by the network during the registration. Dependent upon the information held in the EIR, the mobile may be allocated on of three states, allowed onto the network bed access or monitored in case its problem. OSS, operation and support subsystem. The OSS or operation support subsystem is an element within the overall GSM network architecture that is connected to components of the NSS and the BSC. It is used to control and monitor the overall GSM network and it is also used to control the traffic load of the base station. It must be noted that as the number of base stations increases within the scaling of the subscriber population, some of the maintenance task transform to the base stations, allowing saving in the cost of the ownership of the system. Now last part of this video lecture, Signalling Protocol Architecture. GSM architecture is a layered model that is designed to allow communications between two different systems. The lower layer assures the service of the upper layer protocol. Each layer passes suitable notifications to ensure the transmitted data has been formatted and received accurately. Based on the interface, the GSM Signalling Protocol is assembled into three general layers. Layer 1, the physical layer, it uses the channel structures over the air interface. Layer 2, the data link layer. Across the UM interface, the data link layer is a modified version of the link access protocol for the D-channel protocol used in ISDN. Called link access protocol on the DM channel. Across the A interface, a message transfer part that is MTP layer 2 of SS7 is used. Layer 3, GSM Signalling Protocol's third layer is divided into three sub-layer. First layer is Radio Resource Management also called as RR layer. Mobility management also called as MM layer. Connection management also called as CM layer. These are references. Thank you.