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MOBILITY. Beyond Third Generation Cellular Feb 5 1998. Overview. Mobile IP IMHP Mobility in GSM. Mobility & IP: The Problem. Hierarchical IP addressing based on physical location The same address is used for identification as well as location

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  1. MOBILITY Beyond Third Generation Cellular Feb 5 1998

  2. Overview • Mobile IP • IMHP • Mobility in GSM

  3. 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

  4. 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?

  5. 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

  6. 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

  7. Previous Approaches • Sony MHP, Columbia MHP, IBM’s MHP • Use IP options • Use a mobility router backbone or home gateways • Use of multicast in the backbone • Propagation of bindings for route optimization

  8. HA Home Network Internet Foreign Network FA Mobile IP: Architecture Mobile Host

  9. Specifications • Agent Discovery • Registration • Tunneling

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

  11. 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

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

  13. Care-of Address • Could be FA’s 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

  14. New Concerns • Inefficiency: triangle routing HA FA Mobile Host talking to mobile • Security concerns: Any node on the internet can do “remote redirection”

  15. 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

  16. 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

  17. 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 ==> N sends binding notification to source node S • Binding notifications are re-sent with back-off

  18. 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

  19. 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

  20. Other features • Binding advertisement may be suppressed optionally • Intermediate CA’s may provide partial optimization • snoop to detect location update messages

  21. 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


  23. 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

  24. 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

  25. 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

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