 NAMASTHI, welcome to the video lecture on GSM call procedure and GSM hand-off learning outcome. At the end of this session, students will be able to explain GSM call procedure. Students will be able to explain GSM hand-off procedure. These are the contents of this video lecture. There are three mechanisms of call establishment which are embedded in all voice oriented cellular communication network that allow a mobile subscriber to establish and maintain a connection with the network. These mechanisms are registration of the mobile subscriber, call establishment and hand-off procedure. Registration takes place as soon as the mobile subscriber unit is switched off. Call establishment process occurs when the mobile subscriber initiates or receives a call. Hand-off mechanism enables the mobile subscriber to change its communication link from one part of the network to another part. Before starting GSM call process and GSM hand-off process, we must know all the equipments which are involved in GSM architecture. So as an interesting part, you can draw GSM architecture. You can pause the video for two minutes and you can draw GSM architecture. So this is GSM architecture. Here you can see all the equipments which are involved in GSM. And each equipment has a role in call initiate process or call establishment process. So we must know each equipment before starting the GSM call procedure and GSM hand-off procedure. So let us start with the registration process. For an MS to operate in an MSC, it must be registered by accessing the base station. The MSC Assigns a TMSI number to the MS updates the information in VLR and HLR. Whenever the MS is switched on, there is a need to possibly establish a new registration with the cellular network. Sometimes a mobile subscriber is required to connect to the cellular network at different locations through the base station. That may not be owned by a home service provider. Similarly speaking, the MS passively synchronizes to the frequency bit and frame timings of the nearest base station to get ready for information exchange. The MS receives the cell identity and the system parameters determine its location in the cellular network. The mobile subscriber registration process is described by the action taken and signal part. We made two lists action taken and signal part. We can see action, for example MS request a channel. So signal flow or the message flow is from the MS who initiates a channel request. MS initiates a channel request and it transmits request to the base station and base station forwards that request to the base station. So we can see each and every action file registration process and path for that particular action or message flow to execute that action. First action is MS request a channel, second action channel activation response, acknowledgement for activation, assignment of channel, location update request for authentication. Now let us discuss next part of GSM call process that is mobile to network call. The mobile subscriber monitors the BCS that is broadcast channel and gets synchronized to the nearest base station. By receiving BCCS broadcast control channel, FCCS that is frequency correction channel and SCS that is synchronization channel messages, the mobile subscriber is locked on to the system to initiate a call. The mobile subscriber first dial the called subscriber number and press the send button on the GSM mobile phone. The mobile subscriber transmits a burst of RACS data on the same ARFCN that is absolute radio frequency channel number as the base station. The base station then responds with the AGCH message that is access grant channel message on the CCS common control channel which assigns the mobile subscriber to a new channel for SDCCS that is standalone dedicated channel. The mobile subscriber receives its ARFCN and time slot assignment from the AGCH on TS0 of BCH. Now again we can see action taken in mobile to network call and signal path. There are number of actions which are involved in mobile to network call procedure and its equivalent message path is shown in front of action taken. The last part is network to mobile call. To make a call from landline telephone subscriber the call request information is processed through the gateway MSC to the destination MSC. After getting the information from the HLR of the called mobile then the called mobile subscriber is contacted through the base station. The base station broadcasts a PCS that is paging channel message on the BCS broadcast message. The mobile subscriber looks on to the same ARFCN decodes its page and responds with the RACS message. The base station then uses the AGCH on the CCS that is common control channel to assign the mobile subscriber you need to a new channel for connection to the SDCCS and SACCH that is standalone dedicated channel. And slow associated dedicated channel and slow associated channel. While the network and the serving base station are connected once the subscriber establishes timing advance and authentication on the SDCCS. The base station assigns the TCS. Now last part of this video lecture is GSM handoff procedure. So basically what is handoff and when it takes place. Handoff is usually initiated because of signal strength weakening at the age of a sale boundary. Handoff in GSM is divided into four major categories. Generally base station monitors the signal strength received by mobile subscriber and when the signal strength decreases below the threshold it initiates a handoff procedure. There are four major categories which are involved in GSM handoff procedure. The handoff can be intra sale come intra base station handoff. This type of handoff is necessary when high interference occurs during the call. The channel for the connection is changed within the sale by moving to another frequency of the same sale or another time slot of the same frequency. The handoff process is initiated by the base station. Next category is inter sale come intra base station controller handoff. That is inter sale come intra base station handoff. In this type of handoff the change in the radio channel between two sales that are served by the same base station. Initially the handoff request is initiated by the serving base station to the base station. The MSC transmits the handoff request to the destination base station. After receiving acknowledgement the MSC gives the handoff command. The mobile subscriber transmits a handoff complete message to the base station which relays it to the MSC for releasing the earlier occupied channel. Now next category which is called inter base station controller or inter base station come intra MSC handoff. A call connection is changed between two sales that are served by the different BSEs but operate in the same MSC. When the measured value of the received signal strain at the mobile subscriber is lower than threshold value it informs the serving BSE which initiates the handoff command to the MSC of that area. The MSC relays the handoff request to the BSE which sends channel activation request through the BTS. It is then possible for the handoff call to be handled in the new MSC. The BTS provides the MS with the list of available channel neighbouring sale via the BCCH that is broadcast channel. The mobile subscriber monitors the received signal strain from the BCCH of these neighbouring sales reports these measured data to the MSC using SSCS. This is called mobile assisted handoff. The BTS also monitors the received signal strain from the mobile subscriber to make a handoff decision. The MSC negotiates a new channel with the new BSE and indicates to the mobile subscriber that a handoff should be made using a handoff command. Upon completion of the handoff the mobile subscriber confirms with the handoff complete message to the MSC. Now last category inter-MSC handoff. Connection is changed between two sales that are in different MSCs. This situation occurs in case of roaming. This handoff occurs where the home MSC is notified of the handoff condition through the PSTN and at the home MSC sends the necessity data to the new MSC through PSTN again. These are references. Thank you.