 Hello friends, myself, Darshan Pandit, Assistant Professor, Department of Computer Science and Engineering from Walton Institute of Technology, Solapur. So, today we are going to discuss about handover in GSM. So, at the end of the session, student can differentiate between intra-cell, inter-cell, inter-BSC and inter-MSC handovers. So, basically we are having four types of handover, intra-cell, inter-cell, intra-BSC handover, inter-BSC, intra-MSC handover, inter-MSC handover. So, before going for these types, so let us see what do you mean by handover. So, handover is a process of transferring an ongoing call or a data session from one cell to another cell in order to avoid call termination when the phone gets outside the range of first cell. So, you can see in the figure when phone is moving away from area covered by one cell and entering the area covered by another cell, the call is transferred to the second cell. So that is the call is transferred from first base station to second base station. So, basically the base station is responsible for forming the cell. So, in cellular system, we require handover procedure as single cell do not cover whole service area. So, because of this, the smaller the cell size, the faster the movement of mobile session through the cell. So, we can have 250 kilometer per hour for GSM. So, this is why we require more and more handover of ongoing cell. So, however, so in this procedure, handover should not cause a cutoff or a call drop. So, in this GSM aims at maximum handover duration of 60 milliseconds. So, there are basic two reasons for handover when the mobile session moves out of the range of BTS or a certain antenna of BTS. So, the received signal decreases continuously until it falls below the minimum requirement of communication. The error rate may grow due to interference. The distance of BTS may be too high, that is more than 35 kilometers as per the cell size, the quality of radio link or a radio transmission is impossible in near future. So, these are the handover due to load balancing. So, these all are the various factor for which we require handover. So, another reason for handover is the wired infrastructure of MSC, BSE may decide that traffic in one cell is too high and shift some mobile session to another cell with a lower load. So, this may also cause handover due to load balancing. So, let us see types of handover. So, first is intra cell handover. So, this is the handover within a cell, a narrow band interference could make transmission at a certain frequency impossible. So, the BSE could then decide the change of carrier frequency. So, such kind of handover is performed to optimize the traffic load in a cell or to improve quality of connection by changing the carrier frequency. So, this type of handover is known as intra cell handover. So, second type is inter cell intra BSE handover. So, in this type the mobile session moves from one cell to another cell, but stays within the control of same BSE. So, the BSE then performs handover that is it assigns a new radio channel to new cell and releases the old one. So, you can see in the scenario 2. So, in scenario 3 it is known as inter BSE intra MSE handover. So, in this BSE only controls the limited number of cell. So, GSM also has to perform handover between cells controlled by different BSE. BSE is nothing, but base station controller. So, this handover then has to be controlled by MSE. So, last handover type is that is scenario 4 inter MSE handover. A handover that could be required between 2 cells belonging to different MSE. MSE is nothing, but mobile switching center. So, in this case both MSE perform handover together. So, just think and write which type of handover is required when a mobile user moves from one cell to another cell. So, that is inter cell handover. So, when to make handover decision? So, that is so handover decision is made upon the weak signal. So, the weak signal is identified by periodic measurement that is periodic measurement of mobile station and BTS is done based on uplink and downlink of mobile station and base station. So, we can see in the figure 3 which shows handover decision depending upon the received signal. So, received signal is measured based on uplink and downlink of BTS and MS. So, whenever MS moves away from one BTS that is known as BTS old and when it moves closer to new one that is new BTS. So, the handover decision does not depend upon actual value of the received signal, but on average value. So, the BSE collects all values that is bit error rate and signal level from uplink and downlink from BTS and MS and then calculates the average value. So, these values are then compared with the threshold that is handover margin which includes some hysteresis that is to avoid a ping pong effect. So, that is without hysteresis we can get a short term interference like shadowing due to building and it may cause handover. So, because of this we require some hysteresis. So, still even with the HOMargin the ping pong effect can occur in GSM that is a value which is too high could cause cutoff or handover and a value which is too low may cause handover. So, basically ping pong effect occur when MS is handed over from one cell to another cell, but quickly handed back to the original cell. So, this causes unnecessary signaling from UM interface or it may be from ABs or A interface and can give a indication of incorrect handover parameter settings or a dominance problem in the area. So, this figure shows intra MSC handover. So, figure 4 so, you can see in the figure on signal flow during inter BSE intra MSC handover. So, in which MS that is mobile station sends its periodic measurement report after that BTS old forward this report to BTS old along with its own measurement. After that based on these values that is current traffic condition the BSE old may decide to perform handover and sends the message handover required to MSC. Then MSC then comprises the request of the resources needed for handover from new BSE that is BSE new. So, this BSE checks if enough resources are available and activates a physical channel at BTS new to prepare the arrival of MS. After that the BTS new acknowledges the successful channel activation then BSE new acknowledges the handover request after that MSC then issues a handover command that is forwarded to MS. So, now MS breaks its old radio link and access the new BTS. So, this include establishment of a link with new BTS and release the resources of old BSE and BTS. So, to signal successful handover using handover and clear complete messages. So, this is how handover is performed in intra MSC. So, these are the references which are used to create this video. Thank you.