841776279-Handoff-in-GSM-Networks-1.pptx

841776279-Handoff-in-GSM-Networks-1.pptx

1. Handoffs in GSM Networks By Dr. Kosgiker G. M.

2. INTRODUCTION TO HANDOFF Signal Degradation Network Congestion A cell may sometimes get overloaded, handling a large number of calls. This congestion may be alleviated by handing off mobiles to less congested nearby cells. Handoff occurs during an active call when a mobile device changes its association from one base station to another ensuring seamless connection without interruption A handoff between base stations results not only in the mobile transmitting/receiving to/from a new base station but also in the rerouting of the ongoing call from a switching point within the network to the new base station There may be several reasons for handoff to occur such as: The signal between the current base station and the mobile may have deteriorated to such an extent that the call is in danger of being dropped Handoff ensures a seamless transition to a cell with a stronger signal, preserving call continuity.

3. Handoff Process Between Base Stations in GSM Networks This diagram illustrates the handoff process in GSM Networks The steps involved when a base station does decide to handoff a mobile user are: Step 1- Handoff Initiation : Old base station (BS) informs the visited MSC of the need for a handoff and potential new BS. Step 2- Path Setup : The visited MSC allocates resources and initiates communication with the new BS for handoff.

4. Step 3- Channel Activation : The new BS activates a radio channel for the mobile device. Step 4- Path Confirmation : The new BS informs the MSC and old BS about the established path and provides the required details for the mobile. Step 5- Mobile Notification: The mobile is notified to perform a handoff, unaware of the preparations beforehand. Step 6- Channel Activation Completion: The mobile exchanges messages with the new BS to activate the new channel. Step 7- Handoff Completion : The mobile sends a "handoff complete" message, and the visited MSC reroutes the ongoing call to the new BS. Step 8- Resource Release: Resources associated with the old BS are released.

5. Anchor MSC The first MSC (Mobile Switching Center) visited by the mobile when a call begins. The anchor MSC remains fixed throughout the duration of the call, regardless of the number of inter-MSC handoffs. It serves as a permanent intermediary for routing the call. Inter-MSC Handoff When a mobile moves to a new Base Station (BS) associated with a different MSC than the current one The anchor MSC updates the call path to reroute to the new visited MSC . At any point in time, call management involves only three MSCs: Home MSC Anchor MSC Visited MSC

6. Before Handoff : The call is routed from the correspondent to the mobile via the home network, anchor MSC, and the visited MSC. After Handoff : When the mobile moves to a new MSC, the anchor MSC reroutes the call to the new visited MSC via updated routing table while maintaining continuity. Call Routing in GSM (Using Anchor MSC) Calls are routed through the following sequence: From the Home MSC (where the mobile is registered) to the Anchor MSC . From the Anchor MSC to the Visited MSC (current location of the mobile). Even when the mobile moves to a new MSC’s area during an ongoing call, the routing path is rerouted from the anchor MSC to the new MSC where the mobile is located.

7. MSC Chaining (Alternative Approach) Instead of rerouting through the anchor MSC: A chaining approach can be used. Here, the old MSC forwards the ongoing call to the new MSC every time the mobile moves to a new area. Challenges of MSC Chaining: This approach may increase the path's length and complexity due to multiple forwarding hops. Path Minimization in IS-41 Cellular Networks: IS-41 networks use optional path minimization steps to simplify routing. These steps remove unnecessary MSCs between the anchor MSC and the current MSC to optimize call routing.

8. Comparison of Mobility management in GSM and Mobile IP Aspect GSM Mobility Management Mobile IP Scope of Mobility Designed for mobility within cellular networks (local mobility). Designed for global mobility across multiple IP networks or subnets. Handoff Process Involves handoff between base stations within the same cellular network. Involves updating the IP address and using home and foreign agents to route packets as the device moves. Address Management Uses temporary identifiers (temporary IMSI) for routing calls in cells, which change as the user moves. Maintains a constant IP address (home address) while moving between different networks. Location Update Location updates occur when the device moves to a new location area or cell, handled by the GSM network. Location is updated when the mobile device moves to a new foreign network , informing the home agent for proper routing. Protocols and Standards Relies on GSM-specific protocols (e.g., Location Area Update, Paging). Uses Mobile IP protocols (e.g., Registration Request, Binding Update) to manage mobility at the IP layer.

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