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. Mobile IP: Architecture Home Network Foreign Network

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 Security concerns: Any node on the internet can do “remote redirection” FA HA Mobile Host talking to mobile

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

22. Architecture HLR VLR EIR

23. Location Update MobileBase-Station channel request location update request immediate assignment authentication request authentication response location updating accept TMSI allocation complete channel release When a mobile moves from one cell to another or when it powers up it initiates a location update procedure

24. Hand-over MobileBase-Station conversation measurement report hand-over command hand-over access physical information hand-over complete conversation 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

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