Mobile Computing COE 446 Network Operation

1. Mobile Computing COE 446Network Operation Tarek Sheltami KFUPM CCSE COE http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm Principles of Wireless Networks K. Pahlavan and P. Krishnamurth

2. Outline • Mobile management • Location Updates • Paging • Location Information Dissemination • Handoff management

3. Mobile Management • Mobility and location management • Radio resources and power management • Security • Tetherless access user has the ability to move around while connected to the network and continuously possesses the ability to the service provider • Knowledge of where the destination is (location) • How to reach the destination (route)

4. Mobile Management.. • Location Management • Involves tracking of the location of MT • When a call is made to a mobile number, a dedicated channel has to be set up from the calling party to the called party for the conversation to proceed • It has to be set up over the fixed part of the network and a pair of radio channels have to be allocated to the MT for the voice conversation, this is before the actual conversation takes place • If the MT moves during the course of a conversation, the step taken to handle the continuity of conversation is called handoff • Routers will use the destination address to deliver the packet

5. Mobile Management.. • Location Management.. • Required steps to determine location of the destination are done before the packet is routed to the dest • The status of the MT should be determined by the routing process • Location management has three parts: • Location Updates • Paging • Location Information Dissemination

6. Mobile Management.. • Location Management.. • Location updates are messages sent by the MT regarding its location to the fixed network • Each time the MT makes an update to reflect its new location, a database in the fixed part of the network has to be updated to reflect the new location • Whether there is a change in the location, the update message will be transmitted to the fixed network • Updates are periodic there will be some uncertainty in the location of MT to something around a group of cells • Paging is used by the network to deliver an incoming message to the MT • The network have to page the MT in such group of cells

7. Mobile Management.. • Location Management.. • The paged terminal will respond through the point of access that is providing coverage in its cell, which will enable the network to locate accurately the MT • In order to initiate paging, the calling party or incoming message should trigger a location request from some fixed network entity • The fixed network entity will access some kind of database that will contain the most current location related to the particular MT and use this information to generate the paging request as well as deliver the message or set up a channel

8. Mobile Management.. • Location Management.. • Location information dissemination refers to the procedures that are required to store and distribute the location information related to MTs served by the network • Location management is the tradeoff between the cost of the nature, number and frequency of location updates and the cost of paging

9. Mobile Management.. • Location Management.. • Location Update Algorithms • Two types: Static and Dynamic • In static location updates, the topology of the cellular network decides when the location updated needs to be initiated • In dynamic location updates, the mobility of the user and call patterns is used in initiating location updates • Most cellular networks use static location update, which is a group of cell assigned a location area (LA) identifiers • Each BS in the LA broadcasts this identification number periodically over some control channels

11. Mobile Management.. • Location Management.. • Location Update Algorithms • An MT is required to continually listen to the control channel for the LA identifier • When LA changes, MT will make an update to the location by transmitting a message with new identifier to the databases containing the location information • If there is an incoming message, paging is performed in the group of cells corresponding to the location identifier stored in the database • The MT usually responds and communication can be established

12. Mobile Management.. • Location Management.. • Location Update Algorithms • In GSM, an LA consists of a group of cells controlled by a base station controller (BSC) • An MT performs the location under the circumstances: • Upon powering up, it compares the location area identity • When the MT crosses the boundary of the a location area, because the BS broadcasts the LA identity, which an MT is required to monitor and compares it with the stored value • After a period of time predetermined by the network, because update mechanism might be costly if MT does not leave an LA for long periods of time

13. Mobile Management.. • Location Management.. • Location Update Algorithms • The primary problem with static LA identifier approach is that if an MT is frequently crossing the boundary of two LAs, there will be a ping-pong effect of continually switching between two LAs • One suggested solution is to employ a dwell timer that persists without location updates for sometime to ensure that location update is worthwhile • Distance-based, where the location update is performed after crossing a certain number of cells • Timer-based, where a location update is performed after a certain time elapse

15. Mobile Management.. • Location Management.. • Location Update Algorithms • Variation of the pervious two schemes take into account the signaling load on control channels and the location and velocity of the MT • Example of dynamic location update schemes are state-base and user-profile-based • State-based location update, the MT makes decision on when to perform an update based on its current state information, includes time elapsed, distance traveled, the number of LAs crossed and number of calls received that could be changed based on the user mobility and call patterns

16. Mobile Management.. • Location Management.. • Location Update Algorithms • User-profile-based location update, maintains a sequential list of LAs that the MT may be located in at different points of time based on the history of the MT

17. Mobile Management Paging Schemes • Broadcasting a message in a cell or a group of cells to obtain a response from the MT for which a call or a message is incoming • Paging only the cell in which the MT is located reduces the cost • It is quite impossible to determine location accurately, especially if the location update cost has to be kept low • Blanket Paging refers to paging the MT in all the cells with LA simultaneously • Closest-Cell-First, first paging the cell where the MT was last seen, then subsequent rings of cells that are equidistant from this cell in each paging cycle

18. Mobile Management Paging Schemes • If there are delay constraints, several rings may be polled simultaneously in a paging cycle • In general, if the first location estimate is not correct, the next page should be performed so that the probability of locating the mobile is the next largest and so on • Paging is performed according to location updates and then subsequent pages based on other parameters (history, distance, …) • A timer is used to declare that the MT as unreachable in a particular cycle (sequential paging)

19. Mobile Management Paging Schemes • Results indicate that blanket polling provides the lowest delay at small load, whereas sequential paging can sustain a higher paging request rate especially when there are several incoming calls to a certain area Location Dissemination • When there is an incoming call to the MT, there is a need for at least one fixed network entity, whose location and address is known, which can be reached to obtain information about the MT (anchor) • The anchor has some information regarding the location and routing information of the MT

20. Mobile Management Location Dissemination • Multiple anchor points are usually employed to avoid congestion and call failure • Every MT is associated with home network and home database • The home database keeps track of the profile of the MT • The location of MT is maintained in terms of a visiting network, where the MT is located • Visiting database keeps track of the MTs in its service area • The home and visiting database communicate with each other to authenticated and update each other

21. Mobile Management Location Dissemination • In GSM, the home and visiting database are call home location register (HLR) and visiting location register (VLR) • When a MT observes a change in the LA identity, it transmits a location update message through its BS to an MSC • The MSC contacts its VLR with the location update, which contacts its HLR via location registration message only if it has no info about the MT • The HLR authenticates and acknowledges the location registration, updates its own database, and sends a message to the old VLR to cancel the registration there

22. Mobile Management Location Dissemination • When a call is made to a mobile phone, the anchor entity contacts the MSC associated with the HLR of the MT • The HLR contacts the VLR that is associated with the MT and enable call setup Handoff Management • Ping-Pong effect refers to several handoffs that occur back and forth between two BSs • This has a severe charge on the both the user’s quality perception and the network load • One way to eliminate the Ping-Pong effect is to persist with a BS for as long as possible

23. Mobile Management Handoff Management • If the handoff is delayed, a weak signal reception persist unnecessarily, resulting in a lower voice quality, increasing the probability of call drops and degrading QoS • Handoff involves a sequence of events in the backbone network that include rerouting the connection and reregistering to the new point of access (additional load) • Handoff has an impact on traffic matching and traffic density for individual BSs • We can consider handoff as consisting of two different steps • In the first step, the handoff management process determines that a handoff is required (handoff decision and initiation)

24. Mobile Management Handoff Management • In the second step, the rest of the network is made aware of the handoff and the connection is restructured to reflect the new location of the MT • An anchor in the fixed part must be involved in the handoff management process in a manner similar to location management • Several issues arise during the handoff management, which are divided into two categories: architectural issues and handoff decision time algorithms • Architectural issues are those related to methodology, control and software/hardware elements

25. Mobile Management Handoff Management • Handoff decision time are types of algorithms, metrics used by algorithms, and performance evaluation methodologies

26. Important issues involved in the handoff mechanism

27. Two basic actions during handoff