MOBILITY

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MOBILITY

• Beyond Third Generation Cellular
• Feb 5 1998

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Overview

• Mobile IP
• IMHP
• Mobility in GSM

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Mobility IP The Problem

• Hierarchical IP addressing based on physical
  location
• The same address is used for identification as
  well as location
• For identification, an unchanging address is
  required
• For mobility, a dynamic address is required

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Solution

• A level of indirection
• Use two addresses
• Home address (identification)
• Foreign address (location)
• How to obtain a foreign (care-of) address?
• How to manage the binding between the two
  addresses?
• How to forward packets?

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Why handle mobility at the Network Layer?

• Higher layers should not be concerned with
  mobility
• Mobility management independent of physical layer
• can move from one physical network to another
• The problem of mobility is transformed to one of
  routing

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Goals

• Mobility
• Communicate with nodes that run old IP
• Messages about the location of a mobile should be
  authenticated
• No constraints on assignment of IP addresses

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Previous Approaches

• Sony MHP, Columbia MHP, IBMs MHP
• Use IP options
• Use a mobility router backbone or home gateways
• Use of multicast in the backbone
• Propagation of bindings for route optimization

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Mobile IP Architecture
Mobile Host
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Specifications

• Agent Discovery
• Registration
• Tunneling

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Agent Discovery

• Agents advertise their presence
• Mobile can send solicitation messages
• Mobile-IP modifies the ICMP router discovery
  procedure

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Registration

• Mobile registers its care-of address with its HA
• This could be strongly authenticated
• shared secret between mobile HA
• Registration request reply messages
• UDP port 434 is used

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Tunneling (forwarding)

• HA should intercept messages coming for the
  mobile (may use proxy ARP)
• HA tunnels the IP packet to the care-of address

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Care-of Address

• Could be FAs address
• the FA de-tunnels the packet and sends it to the
  mobile
• Mobile could have its own foreign address
  (obtained through DHCP)
• the mobile de-tunnels the packets itself

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New Concerns

• Inefficiency triangle routing

HA
FA
Mobile
Host talking to mobile

• Security concerns Any node on the internet can
  do remote redirection

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Internet Mobile Host Protocol

• Aims to provide
• routing efficiency
• authentication
• Route optimization Security is difficult
• Security Current Internet security
• Ideal solution would require key distribution

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Route Optimization

• Cache Agents (CA)
• cache bindings
• cache entries are authenticated
• entries are timed out
• A node that wishes to optimize its communication
  should function as CA

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Binding Management

• Lazy notification
• Mobile host always notifies its HA when it moves
  (registration)
• Node N (CA/HA/LA) receives a packet to be
  tunneled to the mobile gt N sends binding
  notification to source node S
• Binding notifications are re-sent with back-off

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Authentication

• Mobile to HA
• strong authentication based on shared secret
• secret exchanged while mobile is at home
• Authenticating a binding at CA
• send request to mobile/HA with random number
• get reply and check random number

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Authentication (Continued)

• Visitor-List entries at FA
• need not be authenticated (since binding is
  authenticated)
• Visitor-List entry deletion
• mobile exchanges a secret with the LA when entry
  is created
• this shared secret is used to authenticate
  visitor-entry deletion

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Other features

• Binding advertisement may be suppressed
  optionally
• Intermediate CAs may provide partial
  optimization
• snoop to detect location update messages

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Mobility in GSM

• Designed for mobility integrated approach
• Identification is not tied with location
  information
• Cryptographic keys for authentication
• Other differences
• scale
• connection oriented nature

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Architecture
HLR
MSC
MSC
VLR
EIR
MSC
BSC
BSC
BTS
BTS
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Location Update
Mobile
Base-Station
channel request

• When a mobile
• moves from one cell
• to another
• or when it powers up
• it initiates a location update procedure

immediate assignment
location update request
authentication request
authentication response
location updating accept
TMSI allocation complete
channel release
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Hand-over

• Hand-over may involve
• Only one BSC
• Only one MSC
• More than one MSC
• When more than one MSC is involved, the old MSC
  is still in control of call-management

Mobile
Base-Station
conversation
measurement report
conversation
hand-over command
hand-over access
physical information
hand-over complete
conversation
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Authentication

• Authentication request, response, reject messages
• Ki Secret Authentication key in SIM
• Identification request, response messages
• IMSI, IMEI, TMSI
• Ki is used to compute Kc - to encrypt data
  control messages