1、1,Wireless Communication and Network,Chapter 7 Location/Mibility Management,2,Why do we need location/mobility management? What is location/mobility management? Types of mobility management Handoff management Location management Location Management in GSM Concept of Location area Location update pro
2、cedure Call delivery procedure Other location management strategies Location update Paging Database management Mobile IP management,What we will learn in this chapter:,3,Why mobility management?,In wireline networks, there is a fixed relationship between a terminal and its physical locations In cont
3、rast, mobile terminals (MTs) are free to travel and thus its network access point changes as it moves around the network coverage area The ID of an MT no longer provides the current location information of the MT. How to keep track of mobile terminals?,4,Why mobility management?,An example: cellular
4、 network Callers telephone tunes to the strongest signal. Callers request includes both her and Callees telephone numbers. BS relays the request to the switch. The switch commands several BSs to transit paging messages containing Callees number. Callees phone responds to the paging message by inform
5、ing the system of its location. The switch commands Callers phone to tune to channel X and Callees phone to channel Y. The cellular phone conversation starts. During the conversation, Callee moves to a new cell. The system rearranges itself to maintain the conversation.,Where is 13520899790?,Send br
6、oadcast messages from every base station?,5,What is mobility management?,Mobility management is one of the most important and challenging problems The objective is for the network to determine the location of the MT at any time for both message delivery and maintaining connections as the MT is movin
7、g into a new area Maintain location information as MTs power-on, move, or power-off A function at network layer and above,6,Types of mobility management,Handoff management (keep the connection) Maintain a users connection as the MT continues to move and change its access point to the network. Trigge
8、red by user mobility / roaming, signal strength deterioration(弱化), traffic load management, etc Location management (establish the communication) Tracking the changes of locations of MTs. Discovering the current location of the MT for call / message delivery.,7,Handoff management,Three stages Initia
9、tion Either the user, a network agent, or changing network conditions identify the need for handoff New connection generation The network find resources for the handoff connection and perform any additional routing operations Data-flow control The network must maintain the delivery of the data from
10、the old connection path to the new connection path according to agreed-upon(意见一致) service guarantees,8,Location management,Every mobile network manages location information differently depending on several factors: type of offered service (calls, messages, etc) subscriber density traffic of mobile t
11、erminal calls / messages Two main methods used for mobility management: methods without location updating methods using location areas,9,Without location updating,Network does not know where the MT is located Whenever an incoming message or call arrives, sends searching messages all over the covered
12、 areas. The advantage is simplicity Disadvantages: Limited capacity for incoming calls Limited subscriber density population,10,Using location areas,Location area (LA) consists of a certain number of cells or subnets. MT reports its current location area from time to time - location update Network a
13、lways knows in which location area the MT is located (via location updating), but it does not know precisely what cell. Upon the arrival of an incoming message, the MT is searched only inside the location area. Limits the cost of resource utilization due to limiting the searching to the location are
14、a. GSM uses this method.,11,Location management,Two stages Location update (registration) MT notifies the network of its new access point (e.g., when it is powered on, or moving into new area) Network authenticates the MT and revises the MTs location. Need location information storage. Message deliv
15、ery Network is queried for the MTs location profile and the current position of the MT is found. Message / call is delivered to the found location.,12,Two Major Components,Location Update The mobile terminal informs the system its current location. Paging The system sends messages (from one or more
16、base stations) to find a particular user.,13,Two Extreme Cases,Location never update (no cost). Need to page every cells (high cost).,Location updates for every cell crossing (high cost). Need to page only one cell (low cost).,Location update,14,Partition the region into different location areas.,Lo
17、cation Area,15,Location Update,LA-1,LA-2,Location update,No location update,Location update is performed when there is a boundary crossing.,How to determine the size of a LA?,16,Location Databases,Home Database Every MS is permanently associated with a home database Keep track of the profile of the
18、MS Mobile ID, authentication keys, location, etc. Visiting Database Keeps track of the MSs in its service area.,These two databases communicate with each other to authenticate and update each other about the location of an MS.,GSM Terminology: Home Location Register (HLR) Visitor Location Register (
19、VLR),17,MSC,MSC,(1),(2),(3),(4),(6),(5),GSM Example: Location Update,Mobile Switching Center,18,Location Update Procedures,MS transmits a LU to the new BS The BS forwards the LU to the MSC MSC sends LU to the HLR and updates VLR HLR does the following: authenticate the MS record the ID of the new VL
20、R send an ACK to the new VLR HLR sends a registration cancellation message to the old VLR The old VLR removes the record of the MS and returns an ACK to HLR,19,GSM Example: Call Delivery,20,Call Delivery Procedure,Calling MS sends a call initiation signal to MSC through BS. MSC sends a location requ
21、est to HLR of the called MS HLR determines serving VLR of called MS and sends a route request message to it. MSC allocates a temporary ID to MS and sends this ID to HLR HLR forwards the ID to MSC of the calling MS Calling MSC requests a call set up to the called MSC Paging messages are sent to cells
22、 within the LA.,21,Other Location Management Strategies,22,Ping-Pong Effect,LA-1,A lot of location updates may be generated if a user crosses LA boundary frequently.,23,Other Location Update Algorithms,Time Based Each user periodically updates his location (e.g. every hour) Movement Based Each user
23、counts the number of boundary crossings between cells. Updates his location when this number reaches a predefined value, N. Distance Based Each user tracks the distance he has moved (in number of cells) since the last update. Updates his location when the distance reaches a predefined value, N.,24,M
24、ovement Based (N = 2),Location update,Suppose location update is performed when entering this cell.,25,Distance Based (N = 2),Location update,Suppose location update is performed when entering this cell.,26,Page every cells within the LA.,Blanket(地毯) Paging,27,Page the cells sequentially until the u
25、ser is found.,Sequential Paging,1,2,3,4,8,7,6,5,9,10,28,How to determine paging order?,Method 1: Shortest Distance First Pages the user starting from the cell where he last updated his location. Move outward in a shortest-distance-first order. Ties are broken arbitrarily. Example: (in a highway),Las
26、t Location Update,1,2,3,4,5,29,How to determine paging order?,Method 2: Based on Location Probability Estimate the probability that a user is located in each cell within the current LA. Page the cells in decreasing order of probability. Example: (in a highway),Last Location Update,A,B,C,D,E,Suppose
27、Prob. Distribution is:0.05, 0.2, 0.4, 0.25, 0.1 Paging order: C, D, B, E, A,30,Paging Delay,In our previous example, the expected delay is E D = 0.41 + 0.252 + 0.23 + 0.14 + 0.051= 1.95 (paging cycles)Worst-case delay is 5 paging cycles.The expected number of cells to be paged is also 1.95. Worst-ca
28、se: 5 cells.,31,Blanket Paging vs. Sequential Paging,Sequential group paging may be used if there is a constraint on paging delay,32,Page groups of cells sequentially until the user is found.,Sequential Group Paging,1,2,2,2,3,3,3,3,4,4,Worst case delay is 4 cycles.,33,Database Management,Location Up
29、date Involves the updating of location databases Call Delivery Involves the querying of location databases The cost is very high if the MS is located far away from its HLR. e.g. if the MS is roaming in USA and its HLR is in Beijing.,34,Database Management,Three Enhancement Methods: Per User Location
30、 Caching User Profile Replication Forwarding Pointers,35,Per-User Location Caching,Every time user x is called, xs locaton is cached at the VLR in the callers LA.Any subsequent call to x originated from that LA can reuse this information. No need to contact user xs HLR.,36,Cache Invalidation,Eager C
31、aching Whenever a user moves to a new LA, all cache entries for this users location are updated. Location update cost increases if a user moves frequently. Lazy Caching Cache update is not performed. Two cases can occur: a hit or a miss In case of a miss, contact the HLR there is an additional cost,
32、 since the cached VLR must be visited first.,37,User Profile Replication,Observation: Each user usually communicates frequently with a small number of sources. How can we make use of this observation? User profiles are replicated at selected databases to reduce the cost of querying the HLR.,38,User
33、Profile Replication,When a call is initiated from a certain LA, the corresponding MSC determines if a replication of the called MSs user profile is available locally. If available, no HLR query is needed. When the MS moves to another location, the network updates all replications.,39,Pointer Forward
34、ing,Each time a user moves to a new LA, a forwarding pointer is set up to its pervious VLR to point to the new VLR. Calls to the user will first query the HLR to determine the first VLR and then follow the chain to reach the current VLR. The length of the pointer chain is limited to a maximum value
35、N. This method can reduce the cost of updating the HLR.,40,Mobile IP,41,Outline,How to support Internet mobility? by Mobile IP.Our discussion will be based on IPv4 (the current version).,42,IP Address,IP address is a 32-bit number assigned to each network interface of a node. Nodes (such as routers)
36、 with multiple network interfaces have multiple IP addresses.,IP Address in Dotted-Decimal Notation,43,Network Prefix; Host Portion,An IP address has two components Network prefix Identifying a link Identical for all nodes attached to the same link Host portion Identifying a specific host or router
37、connected to that link Example: 129.61.18.26, prefix length = 24 Network prefix = 129.61.18 Host portion = 26,44,Motivations:,Without specific support, message delivery is not possible for mobile hosts (MHs) away from its home IP subnet: IP routing is based on the network prefix and destination IP a
38、ddress: Example: 129.61.18.26, prefix length = 24 Network prefix = 129.61.18 Host portion = 26 MT cannot change IP address on moving to new IP-subnet otherwise not able to delivery messages.,45,Routing Table,a,Router A,Router B,Router C,Host 1,Host 1s routing table,Host 1 wants to forward a packet t
39、o 7.7.7.1,Rules for Routing: 1. Compare the left-most Prefix-Length bits of each Target with the IP destination address. 2. Choose the matching route with the largest Prefix-Length.,Default route,46,1.0.0.1,1.0.0.2,1.0.0.254,3.0.0.254,a,a,a,c,3.0.0.253,3.0.0.252,c,c,2.0.0.253,2.0.0.3,b,2.0.0.4,4.0.0
40、.5,4.0.0.252,b,b,b,b,Host 1,Host 2,Host 3,Host 4,Host 5,Router A,Router B,Router C,A Routing Example: 1.0.0.1 2.0.0.4,Host 1s routing table,Ethernet A Network Prefix = 1.0.0,High-Speed Fiber Backbone Network Prefix = 3.0.0,Ethernet B Network Prefix = 2.0.0,Ethernet C Network Prefix = 4.0.0,47,1.0.0.
41、1,1.0.0.2,1.0.0.254,3.0.0.254,a,a,a,c,3.0.0.253,3.0.0.252,c,c,2.0.0.253,2.0.0.3,b,2.0.0.4,4.0.0.5,4.0.0.252,b,b,b,b,Host 1,Host 2,Host 3,Host 4,Host 5,Router A,Router B,Router C,A Routing Example: 1.0.0.1 2.0.0.4,Router As routing table,Ethernet A Network Prefix = 1.0.0,High-Speed Fiber Backbone Net
42、work Prefix = 3.0.0,Ethernet B Network Prefix = 2.0.0,Ethernet C Network Prefix = 4.0.0,48,1.0.0.1,1.0.0.2,1.0.0.254,3.0.0.254,a,a,a,c,3.0.0.253,3.0.0.252,c,c,2.0.0.253,2.0.0.3,b,2.0.0.4,4.0.0.5,4.0.0.252,b,b,b,b,Host 1,Host 2,Host 3,Host 4,Host 5,Router A,Router B,Router C,A Routing Example: 1.0.0.
43、1 2.0.0.4,Router Bs routing table,Ethernet A Network Prefix = 1.0.0,High-Speed Fiber Backbone Network Prefix = 3.0.0,Ethernet B Network Prefix = 2.0.0,Ethernet C Network Prefix = 4.0.0,49,1.0.0.1,1.0.0.2,1.0.0.254,3.0.0.254,a,a,a,c,3.0.0.253,3.0.0.252,c,c,2.0.0.253,2.0.0.3,b,2.0.0.4,4.0.0.5,4.0.0.25
44、2,b,b,b,b,Host 1,Host 2,Host 3,Host 4,Host 5,Router A,Router B,Router C,A Routing Example: 1.0.0.1 2.0.0.4,Router Bs routing table,Ethernet A Network Prefix = 1.0.0,High-Speed Fiber Backbone Network Prefix = 3.0.0,Ethernet B Network Prefix = 2.0.0,Ethernet C Network Prefix = 4.0.0,?,50,Problem,The p
45、acket is undeliverable Host 4 is not connected to Ethernet B. Router B will then send a Host Unreachable error message back to Host 1.Q: How to solve it?,51,Solution 1: Host-Specific Route,Place host-specific routes in the routing tables of Router A, B, and C as follows:,Router A,Router B,Router C,Q
46、: Is this a good solution?,52,Solution 2: Change IP Address,Simply change the IP address of host 4, as it moves from Ethernet B to Ethernet C. For example, Dynamic Host Configuration Protocol (DHCP) can be used to acquire a new IP address. 这是我们通常使用的方式！ Q: Is this a good solution?,53,Solution 3: Mobi
47、le IP,A standard proposed to solve the problem of Internet mobility. It allows the mobile node to use two IP addresses: a fixed home address a care-of address that changes at each new point of attachment,54,引入移动IP的原因,主机移动 接入位置的变化 IP变化 无法路由到原来的主机地址上 连接中断,55,移动IP的设计目标,移动节点在改变数据链路层接入点后，应能够保持与Internet上其
48、它节点的连续通信 移动节点无论连接到任何接入点，应该能够用原来的IP地址进行通信 移动节点应该能够与不具有移动IP的其它节点进行通信，并且不需要修改这些节点的协议 移动节点不应该比Internet上的其它节点面临更多的安全危险,56,移动IP的功能实体,移动节点（Mobile Node） 家乡代理（Home Agent） 外地代理（ Foreign Agent）,57,Mobile IP Terminology & Func.,MN,HA,FA,CN,Internet,MN, Mobile Node An IP host that maintains network connectivity using its “home” IP address, regardless of which subnet (or network) it is connected to,
