CSC 290e Mobile Computing

Mobile IP

12 November 2001

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Mobile IP -- rfc 2002
       
IETF: since 1986
      Applications (usenet, instant messaging)
      Internet (IP, multicast)
      Operations and Management Area (DNS, MBONE)
      Routing (manet, source routing)
      Security (ssh, ipsec)
      Sub-IP (IP over optical)
      transport (ip telephony, header compression)
      User services (responsible use of the network)
      
      make recommendations for standards

  notation: rfc, ID
  
Components
  Mobile node MN 
  correspondent node CN 
  Home network 
  Foreign network 
  Foreign agent FA 
  Care-of-address COA 
                  two options:  foreign agent coa
                                  + MNs can share the same address
                                  + MN does not have to deal with tunneling
                                colocated coa
                                  + each MN is more independent
                                  - need more addresses on the network

  Home agent HA - "node" on the home network
                     1. router - all packets need to go through router anyway
                     2. arbitrary node - all packets double cross the route
                  source for the tunnel  
                  maintains a location registry with current COA


How to find the foreign agent?  Advertisement!
  periodic agent advertisements which MN listens for
           beacon broadcast to the subnet
  agent solicitation message from MN to agent
        take care that there are not so many of these that network is flooded

Registration
  exchange current binding info among MN, HA, FA
  MN->FA->HA->FA->MN
  registrations have a lifetime - must update periodically
  Registration requests sent with UDP
    do not need all the complexity of TCP, just do own retransmissions
    tcp performs poorly for wireless comm
  what to do when hear your own home agent's advertisement?
       deregister -- "turn off" forwarding
 
Tunnelling and encapsulation
  IP-in-IP

Broadcast Datagrams?
  should they be forwarded?
  If MN requests, some should be forwarded
     do not forward ARP
  Just b-cast packet with with IP destination COA
  what if MA is using a FA?  
    FA needs to know which FN to give the broadcast to
    use double encapsulation
  
multicast datagram routing?
  join group
    1. via local mcast router on visited subnet
       ?? what address to use: coa or home
    2. via tunnel to home agent -- if no local mcast router
  sending
    1. send directly  -- MUST use COA, why?
    2. send via tunnel to home -- MUST use home address, why?

Route Optimization
  eliminate triangle routing, minimize delay
  concerns:
    1. supply "binding update" to CN
    2. authentication so that CN believes update
    3. enabling smooth handovers to new FA
  

Why might mobile ip not catch on?
  no one really needs persistent connections
  firewalls cause problems - filter packets not from "here"
  wireless connections are more lossy, but no buffering in mobile IP
  

Why might mobile ip catch on?
  recent work on providing mobile ip support for GSM telephones