Lecture 09 Location Management ?9? ??????

1
Lecture 09 Location Management?9? ??????

• 9.1 LM Basics
• 9.2 LM in Cellular Networks
• 9.3 LM in Ad Hoc Networks
• 9.4 Mobile IP

2
Whats It?

• Location is useful
• Communication call forwarding , data forwarding
• Location based services
• Location is?
• Geographical coordinate
• Cell ID
• IP addr
• Location management.
• The maintenance of the binding between the
  logical identifier and physical location of the
  user.

A special kind of data value in a mobile data
management system. A data item whose value
changes with respect to time.
3
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

4
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.

5
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 update
• No 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

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Locating Moving Objects
At all sites
Availability
At selected sites (e.g., at frequently calling
cells)
The whole network
Nowhere
Set of locations
Exact location
Occurrence
Never update
Periodic update
Precision
Always update (at each movement)
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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.
• Update
• Impose an upper bound on the location
  uncertainty.
• Mobile unit sends update message via uplink
  channel.

8
Cost of Location Management

• Cost of Location Management System (LMS) includes
  
• Number of database updates
• Number 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.

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Paging

• To locate a mobile user by querying/searching
• Look up the location database if it is accurate.
• Simultaneous paging
• To page simultaneously in the cells where the
  user may be located.
• Short response time
• Sequential paging
• Paging cells in the order of descending
  probability
• Low paging cost
• A hierarchical solution
• Group related or neighboring cells within the
  area served by the Message Service Center (MSC)
  into location areas.
• Simultaneous in one area, sequential among areas

10
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 scheme
• Predefined update occurrence
• Dynamic decided update occurrence

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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.

12
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-based
• Update when the number of cell boundaries crossed
  since last reporting reaches a threshold.
• Time-based
• Update when the time to the previous update
  exceeds a threshold (i.e., periodic updates).

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9.2 LM in Cellular Networks

• General scheme
• Location Management Architecture
• Two-tier.
• Hierarchical
• Centralized
• Techniques for Efficiency
• Caching
• Replication
• Forwarding pointer

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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

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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 Center EIR Equipment
Identity Register
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Location Management in GSM

• HLR (Home Location Register)
• Maintains the current location of a user
  as part of the users 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 Us 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.

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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 subscribers 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.

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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.

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MSC 1
MSC 2
VLR
To other MSCs
HLR
Fixed Network
Change from MSC2 to MSC3 on second movement
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Location Management in GSM

• IMSI international mobile subscriber identity
• TMSI temporary mobile subscriber identity

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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 roamers 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

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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.

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Two-Tier Scheme
MSC
HLR
HLR
MSC
VLR
VLR
MSC

• Network 1

MSC

• Network 2

VLR
VLR
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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.

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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).

1
location scheme
pointer scheme
2
3
7
6
5
4
18
19
20
15
16
17
12
13
14
8
9
10
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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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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.

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Hierarchical Scheme

• Advantage
• Mobile object is not bound to HLR.
• Locality of moves and lookups is possible.
• It is fast to search for a user nearby.
• Disadvantage
• Seemingly 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.

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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.

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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).

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Centralized Database

• Time-based, movement-based and combined updating
  example.

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Centralized Database

• Distance-based example.

2
4
5
3
2
7
8
5
3
5
6
Location a b c d c b d g f e f g d b a
Distance-based (D3) a b - d - b d g f e f g d b a
Distance-based (D4) a b - - - - - g f e f g d - a
Distance-based (D6) a - c - - - - g - e f - d - a
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Centralized Database

• Group-based example with 3 groups.
• There are algorithms to form and maintain the
  group membership.

• Group-based

• Individual-based

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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. callees
  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.

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Caching

• To locate a user U, the cache at the VLR of
  callers 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 Us HLR.
• Two caching schemes
• Eager caching when a user is moved to a new
  location, all cache entries for this users
  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).

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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).

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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.

X
5
1
4
2
6
8
7
3
9

• (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.

38
Forwarding Pointers

• Invalidation to caching and replication can be
  expensive, with low CMR (e.g., CMR lt 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 lt 5.

• 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.

VLRn-XHLRn
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Forwarding Pointers

• X moves from 12 to 15 without forwarding.

• 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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Forwarding Pointers

• Example that X moves from 12 to 15 with pointer
  and location schemes.

?
41
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.

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Other Issues

• Concurrency control
• Location 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).
• Recovery
• Nodes 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 tradeoff
• Finer 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 discovery
• Services 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.

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9.3 LM in Ad Hoc Networks

• Location in Mobile Ad Hoc Networks
• Used as basic of routing protocol
• Location based services (LBS)
• Location dependent applications
• E.g. data collection
• Major Issues
• Distributed location data storage
• Distributed query
• Failure resilience
• Scalability

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Categorization of LM in Ad Hoc Networks

• Proactive LM periodically exchange location
  information
• Some-for-some
• Some-for-all
• All-for-some
• Home region based
• Quorum node based
• All-for-all
• Location dissemination
• Reactive LM discover location on demand

45
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 update
• Send update to nodes in home region
• Via a geographical forwarding protocol

Problems?
46
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 management
• Update 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.
47
Uniform Quorum System (UQS)

• Quorum construction
• A 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 update
• Sends new location information to the nearest VB
  node
• The VB node forward the update to a quorum of
  nodes
• Location query
• Similar to update

48
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 nodes row
• Similar to column, but in west and east direction
• Update
• To the column nodes
• Query
• To the row nodes

49
Column/Row Quorum

• The void region problem special mechanism to
  address it.

50
Grid Location Service (GLS)

• The set of location servers is determined by a
  predefined geographic grid and the ordering of
  node id.
• Key issues
• Location server selection,
• Location query request, and
• Location server update

51
Location Server Selection in GLS

• Hierarchical grids

Order-1
Order-2
Order-3
52
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.

53
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

54
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?
55
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.

56
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 network
• With list of locations collected
• To collect location info.
• To disseminate location info.

57
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.

58
9.4 Mobile IP

• IP assumes end hosts are in fixed physical
  locations
• What 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 part
• This keeps host specific information out of
  routers
• DHCP is used to get packets to end hosts in
  networks
• This still assumes a fixed end host
• What if a user wants to roam between networks?

59
IP Routing Breaks Under Mobility
.50 .52 .53
router
137.30.2.
.200
router
139.20.3.

• Why this hierarchical approach? Answer
  Scalability!
• Millions of network addresses, billions of hosts!

60
Mobile IP Basics

• To allow a mobile host to move about without
  changing its permanent IP address
• Standards
• Mobile IPv4 IETF RFC 5944, IETF RFC 4721
• Mobile IPv6 RFC 6275

61
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
  MNs location
• Since this IP doesnt change it can be used by
  long-lived applications as MNs location changes
• Home Agent (HA)
• This is router with additional functionality
• Located on home network of MN
• Does mobility binding of MNs IP with its COA
• Forwards packets to appropriate network when MN
  is away
• Does this through encapsulation

62
Mobile IP Entities

• Foreign Agent (FA)
• Another router with enhanced functionality
• If MN is away from HA the it uses an FA to
  send/receive data to/from HA
• Advertises itself periodically
• Forwards MNs registration request
• Decapsulates messages for delivery to MN
• Care-of-address (COA)
• Address which identifies MNs current location
• Sent by FA to HA when MN attaches
• Usually the IP address of the FA
• Correspondent Node (CN)
• End host to which MN is corresponding (eg. a web
  server)

63
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 MN
5. MN answers the CN

64
Mobile IP Support Services

• Agent Discovery
• To determine where a MN is
• Registration
• To registers MNs COA with its HA
• Tunneling
• To tunnel the data between CN and MN

65
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
• MN
• Listens for agent advertisement messages.
• ?Compares the network portion of the router's IP
  address with the network portion of the home
  address.

66
Agent Advertisement
67
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
Lifetime The maximum number of seconds that the router addresses may be considered valid.
Router Addressi The sending router's IP address (es) on the i 1..Num Addrs interface from which this message is sent.
Preference Leveli The preferability of each Router Addressi
Mobility Adv. Ext.
Type 16 (Mobility Advertisement Extension)
Length 64COAs (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 Lifetime The longest lifetime in seconds that the Registration Request will be accepted by this agent. 0xffff infinity.
68
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.

69
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 address
• IP 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

70
Move Detection

• How can a MN detect it has moved away?
• Algorithms to detect move
• Use of lifetime field
• a mobile node uses the lifetime field as a timer
  for agent advertisements.
• ?Use of network prefix
• a mobile node checks if any newly received agent
  advertisement messages are on the same network as
  the node's current care-of address.

71
Registration

• Via UDP, port 434

72
Registration Messages
73
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 nodes 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

74
Registration Procedure Security
A random number (64 bits) for avoid replay attacks
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
Authenticator A code used to authenticate the message. (variable length) Default is 128-byte keyed MD5
75
Tables Maintained on Routers

• Mobility Binding Table
• Maintained on HA of MN
• Visitor List
• Maintained on FA

76
IP Tunneling

• HA intercepts all packets destined for MN
• This 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 address
• MN can perform FA functions if co-CoA is used
• Bidirectional communications require tunneling in
  each direction

77
IP Tunneling
78
IP-in-IP Tunneling
Not support IP fragmentation Path MTU discovery
must be enabled
79
Generic Routing Encapsulation (GRE)
80
Routing Inefficiency
Mobile host and correspondent host might even be
on the same network!!
correspondent host
home agent
81
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

82
Possible Route Optimization
83
Other Mobile IP Problems

• Single HA model is fragile
• Possible solution have multiple HA
• Frequent reports to HA if MN is moving
• Possible solution support of FA clustering
• Security
• Connection hijacking, snooping
• Many open research questions

84
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 IPv6
• MNs can function in any location without the
  services of any special router in that location
• Security
• Nodes are expected to employ strong
  authentication and encryption
• Other details

85
A Summary

• Concept of location management
• Key issues in LM
• LM in cellular networks
• LM in ad hoc networks
• LM via MIP