Mobile Computing COE 446 Network Operation Tarek Sheltami

Mobile Computing COE 446 Network Operation Tarek Sheltami KFUPM CCSE COE http: //faculty. kfupm. edu. sa/coe/tarek/coe 446. htm Principles of Wireless Networks K. Pahlavan and P. Krishnamurth 9/26/2020 1

Outline § Mobile management § § Location Updates Paging Location Information Dissemination Handoff management 9/26/2020 2

Mobile Management 1. 2. 3. § Mobility and location management § § Knowledge of where the destination is (location) 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 How to reach the destination (route) 9/26/2020 3

Mobile Management. . § Location Management § § Involves tracking of the location of MT § 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 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 9/26/2020 4

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: 1. 2. 3. 9/26/2020 Location Updates Paging Location Information Dissemination 5

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 § Whethere 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 § 9/26/2020 The network have to page the MT in such group of cells 6

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 9/26/2020 7

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 9/26/2020 8

Mobile Management. . § Location Management. . § Location Update Algorithms § § Two types: Static and Dynamic § 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 9/26/2020 In static location updates, the topology of the cellular network decides when the location updated needs to be initiated 9

9/26/2020 10

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 9/26/2020 11

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: 9/26/2020 1. Upon powering up, it compares the location area identity 2. 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 3. 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 12

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 9/26/2020 13

9/26/2020 14

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 9/26/2020 15

Mobile Management. . § Location Management. . § Location Update Algorithms § 9/26/2020 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 16

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 § 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 It is quite impossible to determine location accurately, especially if the location update cost has to be kept low 9/26/2020 17

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) 9/26/2020 18

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 9/26/2020 19

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 § § Visiting database keeps track of the MTs in its service area 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 The home and visiting database communicate with each other to authenticated and update each other 9/26/2020 20

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 9/26/2020 21

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 9/26/2020 22

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 Qo. S § 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) 9/26/2020 23

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 9/26/2020 24

Mobile Management Handoff Management § Handoff decision time are types of algorithms, metrics used by algorithms, and performance evaluation methodologies 9/26/2020 25

Important issues involved in the handoff mechanism 9/26/2020 26

Two basic actions during handoff 9/26/2020 27