lecture 09 location management 第 9 讲 移动位置管理
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Lecture 09 Location Management第 9 讲 移动位置管理
§9.1 LM Basics
§9.2 LM in Cellular Networks
§9.3 LM in Ad Hoc Networks
§9.4 Mobile IP
What’s It?
Location is usefulCommunication: call forwarding , data forwardingLocation based services
Location is?Geographical coordinateCell IDIP addr…
Location management.The maintenance of the binding between the logical identifier and physical location of the user.
LBS App.
Location Management
Localization Module
Geographic Information
System
A special kind of data value in a mobile data management system.A data item whose value changes with respect to time.
Key Issues in Location Management
A mobile user creates uncertainty of his/her exact location. How to know the current location?
From localization/positioning system
Where to store the location information?Location database
What to do for new location?Location update
Who to maintain and provide location information?Location server, with cooperation from clients
Location Services
Location services are provided by a location server. Location server manages a location database, which holds
user location.It receives user position updates and stores into the location database.
Location database (also called moving object database) contains location information about mobile users.
Mobile users or moving objects have their identity.
Current user locations are stored in multiple databases or replicated databases.
Location information is queried by different agency at different places to achieve their functionality, e.g. location-based services.
Locating Moving Objects
Moving objects:Mobile devices, Mobile users, Mobile software
Two extremes to find their current location:Store everywhere: Cost of location update is very high.
Full replication of location
Allow search to be performed locally (fast).
Search everywhere: No cost of updateNo location information is stored anywhere.
Searching is performed on demand everywhere (expensive).
One should balance between search and update costs.Perform location update to certain key places
Search within some area
Locating Moving Objects
Availability
Nowhere
At all sites
At selected sites (e.g., at frequently calling cells)
Occurrence
Never update
Always update (at each movement)Preci
sion
Exact location
The whole network
Set of locations
Periodic update
Locating Moving Objects
Three design issues:Where: availability
At all sites, at selected (frequently visited) sites or at no site.When: occurrence
Stored location is always updated, updated periodically, or never updated.What: precision
Exact location, within a set of possible locations, or any location within network.
Two basic operations:Paging
Search initiated by system to find the mobile unit.Server broadcasts a search message and target replies via uplink channel.
UpdateImpose an upper bound on the location uncertainty.Mobile unit sends update message via uplink channel.
Cost of Location Management
Cost of Location Management System (LMS) includes Number of database updatesNumber of messages, size of messages and distance the messages need to travel.
Major parameters Relative frequency of the move.Call operations of each user.
Call to Mobility Ratio (CMR):the number of calls made to a user during a period / the number of location updates generated by the user.High CMR “always update”Low CMR “paging” is better.
Paging
To locate a mobile user by querying/searchingLook up the location database if it is accurate.
Simultaneous pagingTo page simultaneously in the cells where the user may be located.
Short response time
Sequential pagingPaging cells in the order of descending probability
Low paging cost
A hierarchical solutionGroup related or neighboring cells within the area served by the Message Service Center (MSC) into location areas.
Simultaneous in one area, sequential among areas
Location Update
Observation: it is not necessary to always update, since an object is likely to be near its last location.The vicinity of the last update information gives the most probable location of the mobile user.
Static scheme vs. Dynamic schemePredefined update occurrenceDynamic decided update occurrence
Location Update
Static update scheme: global information is needed.
Group cells into location areas as before.All location areas contain non-overlapping groups of cells.
Mobile user sends update when it crosses a location area boundary.
Advantage: low update cost.
Disadvantage: accuracy is only to location area.
Selection of designated reporting cells.Mobile user must send in updates when they enter some designated cells.
Advantage: optimal set of reporting cells can be computed.
Disadvantage: determining the optimal set is expensive.
Location Update
Dynamic update scheme: update based on local information and initiated by client, i.e., the place where the update takes place is dynamic, as determined by client.Distance-based
Update when the Euclidean distance (or Manhattan distance) to the previously updated location exceeds a threshold.
Movement-basedUpdate when the number of cell boundaries crossed since last reporting reaches a threshold.
Time-basedUpdate when the time to the previous update exceeds a threshold (i.e., periodic updates).
§9.2 LM in Cellular Networks
General scheme Location Management Architecture
Two-tier.
Hierarchical
Centralized Techniques for Efficiency
Caching
Replication
Forwarding pointer
Location Management in GSM
The Mobility Management layer (MM) is built on top of the Radio Resources Management (RR) layer.
MM handles the functions due to mobility of subscriber and authentication and security aspects.
A mobile phone that is powered on is informed of an incoming call by a paging message sent over the PAGCH channel of a cell.
Paging vs. update:Page each cell in the network for each call
Costly paging, suitable for few call but much movement
Page exactly one cell but requires the mobile phone to send updates each time it changes cell:
Costly update, suitable for many calls but little movement
Location Management in GSM
Compromised solution used in GSM is to group cells into location areas.
A location area is a collection of adjacent cells.
Update required only when moving between location areas.
To search, mobile units are paged in the cells of their current location area.
HLR: home location register VLR: visitor location register
AuC- Authentication CenterEIR – Equipment Identity Register
Location Management in GSM
HLR (Home Location Register) Maintains the current location of a user as part of the user’s profile.
At a network location pre-specified for each user U (the home zone).
When U moves from zone A to zone B, the HLR for U is updated.
To locate a user U, the HLR for U is queried to get U’s current location.
VLR (Visitor Location Register) Holds information about a visiting user who moves out of its home zone.
VLR contains a copy of the profile of a visiting user V.
(To reduce the expensive querying cost at remote HLR)
When V moves from zone A to zone B, Entry for V will be removed from the VLR at zone A and
The corresponding entry will be inserted to the VLR at zone B.
Location Update in GSM
When mobile phone moves to a new location area:
Location update msg is sent to new MSC/VLR via base station.
If mobile phone is authorized in the new MSC/VLR, it determines the subscriber’s HLR from the mobile identification number.
HLR sends reg. ack. msg to new MSC/VLR and
sends reg. cancellation msg to old MSC/VLR to cancel its VLR entry
Periodic location updating
After the updating time period, if the mobile phone has not registered, it is then deregistered.
Call Delivery in GSM
Calling phone sends call initiation signal to MSC via a base station.
MSC determines address of HLR of called phone and sends it a location req. msg.
HLR sends a route req. msg to the MSC/VLR currently serving the phone.
MSC/VLR allocates a temporary local directory number to the called phone and replies HLR with this number.
HLR forwards this info. to the MSC of calling phone. The MSC of calling phone requests a call setup to the MSC of
called phone.
MSC 1
To otherMSCs
HL
R VL
R
MSC 2
MSC2
CURRLOC
A
INFO
USER
A
INFOUSER
VLR
A
INFOUSER
VLR
HLR
Fixed Network
HL
R VL
R
MSC 3
HL
R VL
R
Change from MSC2 to MSC3on second movement
Location Management in GSM
IMSI: international mobile subscriber identity TMSI: temporary mobile subscriber identity
Location Management in 3G
Besides HLR and VLR, there is GLR Gateway Location Register:
Between HLR and VLR, like the agent in the CAS model.GLR contains roamer’s profile and location information. GLR can interact with multiple VLR in the visitor network.
GLR handles location update from VLR by behaving like HLR. Local location update: at GLR
Location Management Architecture
Two-tier.Only HLR and VLR.HLR contains actual location of user.To search, contact VLR first. If not found, ask HLR.
Hierarchical.Inserts multiple layers between HLR and VLR.HLR contains actual location of user (direct or indirect).To search, contact leaf. If not found, traverse up the tree.
Centralized database.A single location database containing all location info.
Two-Tier Scheme
HLR
VLR
MSCHLR
VLR
MSC
VLR
MSC
VLR
MSC
Two-Tier Scheme
Advantage:Simple architecture and management.A maximum of 2 operations for each lookup.Only 3 operations for each update.
Disadvantage:Does not support locality.
Searching in nearby locations is impossible.Always need to register with HLR at a possibly far distance upon a move, even if the move is just to a neighboring cell.
Home Location Register is permanent.Resettlement is not supported: users who had moved to new region permanently still contact old HLR.Does not scale well to larger distributed systems since HLR is always contacted.
Hierarchical Scheme
To avoid contacting remote HLR and to serve neighboring search, multiple registers are used.
A hierarchy of location databases is maintained.
Internal node contains information about user registered in the set of zones in its subtree.Leaf node contains actual location of objects in its coverage.Internal node contains information about users registered and their location, which are covered by the children nodes.Two types of schemes:
Pointers to lower level database (e.g., find X via pointers to 12).Actual location of each object (find Y directly at 16).
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X 12 Y 16
Y 16
Y 16
Y 16pointer scheme location scheme
Hierarchical Scheme
Let LCA(i, j) denote the least common ancestor of nodes i and j.
To search for object Y which is currently at node i (i.e., 16) initiated by a user at node j (e.g., 19).
Go up the tree from j until LCA(i, j) is reached, where Y is found, with its actual location at 16.
To lookup for object X at node i (i.e., 12) initiated by a user at node j (e.g., 8).
Go up the tree from j to LCA(i, j) is reached, where X is found.
Follow the pointer for X until X is really found at 12.
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LCA(8,12)LCA(19,16)
Hierarchical Scheme
With pointer, to update X from i to j:Databases along path i, …, LCA(i, j), …, j are to be updated.
Entries for X from i to the node just below LCA(i, j) are deleted.Entries for X are created from the node just below LCA(i, j) to j, each pointing to the proper child.Entries for X at LCA(i, j) is updated to point to the proper child.
For example X moves from 12 to 14. With location, to update Y from i to j:
Databases from i to LCA(i, j) and from root to j are to be updated.
Entries for X from i to the node just below LCA(i, j) are deleted.Entries for X are created from the node just below LCA(i, j) to point to j.Entries for X from root to LCA(i, j) are updated to point to j.
For example Y moves from 16 to 17.18 19 20
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Hierarchical Scheme
AdvantageMobile object is not bound to HLR.
Locality of moves and lookups is possible.
It is fast to search for a user nearby.
DisadvantageSeemingly increased number of communication messages.
Increased load and storage requirements for intermediate databases.
Intermediate databases store location information (actual location or a pointer) for all objects covered by its children.
Root database stores location information for ALL objects.
Centralized Database
To simplify location query and update, a centralized database can be assumed to contain the location of all objects.
Centralized database solution is often adopted for simplicity if the object moves continuously, reporting its location.
Recall in previous schemes, location of object is only accurate up to the cell.
A spatial database is often used to store an object location for fast querying, with additional features for moving objects.
Additional operations supported include nearest neighbor search (find the closest gas station), range query (find restaurants within 5 minutes drive), and k-nearest neighbors.
Recall that in the centralized database, there could be numerous objects. Cost of full scan is prohibitive and update is expensive.
Specially designed databases are needed for that purpose.
Centralized Database
To reduce update cost, object movement can be predicted.Predicting object movement, then an object that does not deviate from its predicted location does not need to send in an update.
Trade off can be made with respect to the frequency of updates for lower accuracy.
Send an update only when distance, movement, or time elapsed exceed certain threshold.
Group-based approach:A group of objects that stay close to one another can have their aggregated location reported together via the group leader.
Safe-region approach:As long as an object stays within its safe region, no update is needed, since server knows that object is within that safe region.Size of safe region may be adjusted dynamically according to actual query need (an object seldom interested should update location less).
Centralized Database
Time-based, movement-based and combined updating example.
a b c
hg
f e
d
a b c
hg
f e
d
Centralized Database
Distance-based example.
4
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85
6
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35
7
Location a b c d c b d g f e f g d b a
Distance-based (D=3)
a b - d - b d g f e f g d b a
Distance-based (D=4)
a b - - - - - g f e f g d - a
Distance-based (D=6)
a - c - - - - g - e f - d - a
Centralized Database
Group-based example with 3 groups.There are algorithms to form and maintain the group membership.
Techniques for Efficiency
One may perform caching of location of moving object to reduce need to send in query.
Cache the moving object location (e.g. callee’s location) at the caller site.This is effective with large CMR.
One may extend caching into replication with multiple copies of the location.
Replicate location of a moving object at its frequent callers.This is also effective with large CMR.
Forwarding pointers is used to reduce updates to VLR and HLR.
Do not update VLR and HLR.Just leave a forwarding pointer from old VLR to new VLR.This is effective with small CMR.
Caching
To locate a user U, the cache at the VLR of caller’s zone is queried first, before contacting U ’s HLR.
In two-tier scheme, caching enhances VLR and HLR.If user U at L1 is called by user A at L2. VLR at L1contains U.
Cache at L2 can then indicate that U is at L1.
Subsequent calls originated from L2 can directly contact U without having to look for U’s HLR.
Two caching schemes:Eager caching: when a user is moved to a new location, all cache entries for this user’s location are updated.
Lazy caching: a move operation does not automatically translate to a cache update.
With lazy caching, during a lookup, either user is still in indicated location (cache hit) or has moved out (cache miss).
Replication
One can create copies about this information at selected sites (e.g., at hubs).
Improve lookup response time.
Reduce network load during lookup.
Generate additional overhead during location update.
Replication should be made judiciously for high CMR.More precisely, if Local CMR (LCMRi,j), i.e., number of lookups for user X in zone i from zone j during a period / number of location updates of X is greater than a threshold ( = cost of update / cost saving with local lookup).
Replication may also be performed to indicate the approximate user location (e.g., current partition).
Replication
Working set replication is applicable to two-tier scheme.
For each user X, replicas are kept at frequent callers of X. This is called the working set of X.
Ensure that for all j, LCMRi,j for X in zone i from zone j cost of update / cost saving with local lookup.
When a call to X is made from zone k:If k is in working set, no update is needed.If k is not in working set but the above inequality holds for k, k is added to the set.
When X moves, the inequality is evaluated for each member k in the working set of X:
If it does not hold for k, k is removed. Performance is affected by CMR.
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X1
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X
(2, 3) are in working set.
Y (at 6) queries X (at 1).
6 is added to working set if inequality is true.
Now X moves to 5. The working set (2, 3,
6) needs updating.
VLRi-X|HLRi…
VLR…|HLR-X
VLRk-X|HLRk…VLRi…|HLRi…VLRi-X |HLRi…
VLR…|HLR-X
VLRk-X |HLRk…
Forwarding Pointers
Invalidation to caching and replication can be expensive, with low CMR (e.g., CMR < 0.5).
One can provide forwarding pointers to point to the potential current location (ProbLoc). This reduces communication overhead and query load at remote HLR.
In two-tier scheme, when X moves from i to k, a pointer is added at VLR at i to point to VLR at k without informing HLR.
During lookup if no information on X is found at current VLR, HLR of X is queried for proper VLR and follow the forwarding pointers.
Chain of pointers should not exceed a length of K. Typical value of K < 5.
VLRn-X|HLRn…
X moves from i to k.
Instead of changing HLR for X, setup forwarding pointer at i to k.
Now X moves to n again, and forwarding pointer is added to k.
Forwarding Pointers
Forwarding pointers can be used also in hierarchical scheme.
Recall how a location update is done: entries along path from old cell to LCA then new cell, plus those coming from root need to be updated.
Use similar idea as bypass pointers in caching, create forwarding pointers to point to new location.
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LCA(12,15)
X moves from 12 to 15 without forwarding.
Forwarding Pointers
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Example that X moves from 12 to 15 with pointer and location schemes.
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Pointer Purging
There is a need to purge the forwarding pointers.Save storage.Avoid storing stale information.Improve lookup efficiency by compressing forwarding chain.
User X moves from 11 to 18 to 26 then to 14. Pointers in 11, 18, 26 can be purged. Pointers in interior nodes leading to these nodes can be purged.
Other Issues
Concurrency controlLocation and pointer updates occur asynchronously. It is possible that a user has moved but a caller follows the old pointer down (and cannot reach the user).Transactions for update are too expensive (lock too many entries).
RecoveryNodes may crash, and information should be restored upon node recovery. This demands periodic checkpointing of information at HLR and paging for mobile users by VLR.
Precision, currency and performance tradeoffFiner location granularity within cell is possible, with more frequent reporting from client. Both translate into higher update cost.Server can keep a predication of the client location/trajectory, and client detects whether it is within allowable distance from the predication. Update/paging is only sent when deviation is too large.
Service discoveryServices provided by a host are similar to its location, i.e., can be registered with service (location) database for lookup. In mobile computing, host providing services may move. Calls (e.g., remote procedure calls) need to be routed to the moving host.
§9.3 LM in Ad Hoc Networks
Location in Mobile Ad Hoc NetworksUsed as basic of routing protocol
Location based services (LBS)
Location dependent applicationsE.g. data collection
Major IssuesDistributed location data storage
Distributed query
Failure resilience
Scalability
Categorization of LM in Ad Hoc Networks
Proactive LM: periodically exchange location informationSome-for-some
Some-for-all
All-for-someHome region based
Quorum node based
All-for-all Location dissemination
Reactive LM: discover location on demand
Host Region based Approach
Similar to HLR/VLR in cellular networks Region: a rectangle or a circle area Nodes Region location server Location initialization
Broadcast or mapping function Trigger of update
timer-based (i.e., periodic updates), distance-based (i.e., moved more than a threshold) predictive distance-based
Threshold of difference between predication and actual location
Location updateSend update to nodes in home regionVia a geographical forwarding protocolProblems
?
Quorum-based Approach
Quorum?The minimum number of votes that a distributed transaction has to obtain in order to be allowed to perform an operation – Wikipedia
Quorum for location managementUpdate: to what nodes to send location update
Query: to what nodes to query location information
There must be intersection between the nodes get the update and the nodes be queried.
Please Give a naive example of quorum.
Uniform Quorum System (UQS)
Quorum constructionA subset of the network nodes are chosen that best serve as the network's virtual backbone
Quorums are then defined as subsets of the VB nodes, such that any two quorums intersect.
Location updateSends new location information to the nearest VB node
The VB node forward the update to a quorum of nodes Location query
Similar to update
Column/Row Quorum
A node's column All the nodes to the north and south of the node's current location
The thickness of the column can be configured A node’s row
Similar to column, but in west and east direction Update
To the column nodes Query
To the row nodes
Column/Row Quorum
The void region problem: special mechanism to address it.
Grid Location Service (GLS)
The set of location servers is determined by a predefined geographic grid and the ordering of node id.
Key issuesLocation server selection,
Location query request, and
Location server update
Location Server Selection in GLS
Hierarchical grids
Order-1
Order-2
Order-3
Location Server Selection in GLS
A node x choose three servers in each grid order
The node that has the least ID greater than x in that order square.
Location Query Request in GLS
Query request is forwarded to a node with ID the least greater than or equal to the destination ID, within the order-2 and then higher square
using geographic forwarding
Location Server Update in GLS
When a node moves a given threshold, it must send an update packet to all of its location servers.
To avoid excessive update traffic, the update frequency is calculated using a threshold distance and the location servers' square order
Location query failures when? How to handle it?
Doubling Circles
Similar to GLS Arranges the network into circles of increasing size
centered on a node's location; The radius of each subsequent circle is one meter
larger than the radius of the previous circle.
Location Info. Dissemination Approach
LEAP, Legend Exchange and Augmentation Protocol Two location tables
Local table at each node
Legend, token like table Two messages
Hello: exchange location info. between neighbors
Legend: traverse the networkWith list of locations collected
To collect location info.
To disseminate location info.
Reactive LM
A location table at each node To locate a node
Check the location table, then
Ask neighbors in a specific scope (with TTL), then
Flood request packet in the entire network.
§9.4 Mobile IP
IP assumes end hosts are in fixed physical locationsWhat happens if we move a host between networks?
IP addresses enable IP routing algorithms to get packets to the correct network
Each IP address has network part and host partThis keeps host specific information out of routers
DHCP is used to get packets to end hosts in networksThis still assumes a fixed end host
What if a user wants to roam between networks?
IP Routing Breaks Under Mobility
Why this hierarchical approach? Answer: Scalability!Millions of network addresses, billions of hosts!
137.30.2.*
.50 .52 .53
router
router
139.20.3.*
.200
Mobile IP Basics
To allow a mobile host to move about without changing its permanent IP address
StandardsMobile IPv4: IETF RFC 5944, IETF RFC 4721
Mobile IPv6: RFC 6275
Mobile IP Entities
Mobile Node (MN)The entity that may change its point of attachment from network to network in the Internet
Detects it has moved and registers with “best” FA
Assigned a permanent IP called its home address to which other hosts send packets regardless of MN’s location
Since this IP doesn’t change it can be used by long-lived applications as MN’s location changes
Home Agent (HA)This is router with additional functionalityLocated on home network of MNDoes mobility binding of MN’s IP with its COAForwards packets to appropriate network when MN is away
Does this through encapsulation
Mobile IP Entities
Foreign Agent (FA)Another router with enhanced functionalityIf MN is away from HA the it uses an FA to send/receive data to/from HAAdvertises itself periodicallyForward’s MN’s registration requestDecapsulates messages for delivery to MN
Care-of-address (COA)Address which identifies MN’s current locationSent by FA to HA when MN attachesUsually the IP address of the FA
Correspondent Node (CN)End host to which MN is corresponding (eg. a web server)
Mobile IP Operations
1. MN travels to a foreign network and gets a new CoA.2. MN performs a binding update to HA (new CoA registered ). 3. A CN wants to contact the MN. HA intercepts packets.4. The HA then tunnels all packets to the MN5. MN answers the CN
Mobile IP Support Services
Agent DiscoveryTo determine where a MN is
RegistrationTo registers MN’s COA with its HA
TunnelingTo tunnel the data between CN and MN
Agent/Location Discovery
Each mobile node is responsible for ongoing discovery process.
Must determine if it is attached to its home network or a foreign network.
FA Periodically broadcasts the ICMP Router Discovery Protocol (IRDP) message
MNListens for agent advertisement messages.
…Compares the network portion of the router's IP address with the network portion of the home address.
Agent Advertisement
Agent Advertisement
IRDP :Type 9 = Agent Advertisement, 10 = Agent Solicitation
Code 0 = Advertising Agent is a fully capable router. 16 = only a Mobile IP agent
Num Addrs The number of router addresses advertised in this message
Addr Entry Size The number of 32-bit words of information per each router address
LifetimeThe maximum number of seconds that the router addresses may be considered valid.
Router Address[i]The sending router's IP address (es) on the i = 1..Num Addrs interface from which this message is sent.
Preference Level[i] The preferability of each Router Address[i]Mobility Adv. Ext. :Type 16 (Mobility Advertisement Extension)
Length6+4*#COAs (6 = the sequence number, Registration Lifetime, Flags, and Reserved fields + another 4 bytes per each COA)
Sequence Number The count of Agent Adv. messages sent since the agent was initialized.
Registration LifetimeThe longest lifetime in seconds that the Registration Request will be accepted by this agent. 0xffff = infinity.
Agent Solicitation
Foreign agents are expected to issue agent advertisement messages periodically.
„If a mobile node needs the agent information immediately, it can issue an ICMP router solicitation message.
…Any agent receiving this message will then issue an agent advertisement.
Care-of Addresses
The address to forward data between MN and CN/HA Two choices
The address of the FA
Foreign agent delivers packets forwarded from home agent to mobile host
Co-located addressIP address obtained by the MN on the foreign network
Temporary IP address obtained through an Internet service, e.g. DHCP
… May be owned by the mobile node as a long-term address for roaming
Home agent tunnels packets directly to the temporary IP address
Regardless, care-of address must be registered with home agent
Move Detection
How can a MN detect it has moved away? Algorithms to detect move:
Use of lifetime fielda mobile node uses the lifetime field as a timer for agent advertisements.
…Use of network prefixa mobile node checks if any newly received agent advertisement messages are on the same network as the node's current care-of address.
Registration
Via UDP, port 434
Registration Messages
Registration Procedure Security
Mobile IP is designed to resist attacks:A node pretending to be a foreign agent sends a registration request to a home agent to divert the mobile node’s traffic to itself.
An agent replays an old registration messages to cut the �mobile node from the network.
The registration request and reply contain an authentication extension
Fields = type, length, security parameter index (SPI), authenticator
Registration Procedure Security
Type 31 = Mobile-Home, 33 = Mobile-Foreign, 34 = Foreign-Home
Length 4 plus the number of bytes in the Authenticator
Security parameter index (SPI)
Identifies the Security Association (SA) for datagrams between two nodes. SPI selects the authentication algorithm and secret keys either shared or public to compute the Authenticator
AuthenticatorA code used to authenticate the message. (variable length)Default is 128-byte keyed MD5
A random number (64 bits) for avoid replay attacks
Tables Maintained on Routers
Mobility Binding TableMaintained on HA of MN
Visitor ListMaintained on FA
IP Tunneling
HA intercepts all packets destined for MNThis is simple unless sending application is on or near the same network as the MN
HA masquerades as MN HA forwards these packets to FA
IP tunneling FA decapsulates packets addressed to MN and forwards them
via hardware addressMN can perform FA functions if co-CoA is used
Bidirectional communications require tunneling in each direction
IP Tunneling
IP-in-IP TunnelingNot support IP fragmentationPath MTU discovery must be enabled
Generic Routing Encapsulation (GRE)
Routing Inefficiency
home agentcorrespondent host
Mobile host and correspondent hostmight even be on the same network!!
Route Optimizations
Possible Solution:Home agent sends current care-of address to correspondent host
Correspondent host caches care-of address
Future packets tunneled directly to care-of address
But!An instance of the cache consistency problem arises...
Cached CoA becomes stale when the mobile host moves
Potential security issues with providing CoA to CN
Possible Route Optimization
Other Mobile IP Problems
Single HA model is fragilePossible solution – have multiple HA
Frequent reports to HA if MN is movingPossible solution – support of FA clustering
SecurityConnection hijacking, snooping…
Many open research questions
Mobility in IPv6
Route Optimization is a fundamental part of Mobile IPv6 Mobile IPv4 it is an optional set of extensions that may not be supported by all nodes
Foreign Agents are not needed in Mobile IPv6MNs can function in any location without the services of any special router in that location
SecurityNodes are expected to employ strong authentication and encryption
Other details…
A Summary
Concept of location management Key issues in LM LM in cellular networks LM in ad hoc networks LM via MIP
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