[컴퓨터 통신] L3 : Mobile IP

meow

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Proviously...

• IP addresses are designed to work with stationary hosts because part of the address defines the network to which the host is attached.

• However...
  이제.. 단말이 가만히 있지 않음..ㅠ
  

• In end-to-end connection, if one end moves, the network session breaks. So does all the networking services layered on top of IP
  

• Solution?

  • Option 1: Completely redesign each layer of the protocol suite. 🙄→🤮
  • Option 2: Provide additional services at the network layer in a backward compatible manner - Mobile internetworking!
  
  

Mobile IP

• Mobile IP has two addresses for a mobile host: home address and care-of-address
• The home address is permanent.
• The care-of address changes as the mobile host moves from one network to another.
  

Mobile ip introduces Agents: Home agent & foreign agent

• To make the change of address transparent to the rest of the Internet.
  

Three phases

• Agent discovery

  • ICMP

    • Router advertisement
      

    • Router solicitation

• Registration

  • After a mobile host has moved to a foreign network and discovered the foreign agent -> it must register!
  • Request and Reply
    

• Data transfer

  • The movement of the mobile host is transparent to the rest of the Internet..
    
  1. From Remote Host to Home Agent
     The remote host sends a packet as though the mobile host is at its home network.
     This is done using the proxy ARP.
  2. From Home Agent to Foreign Agent
     After receiving the packet, the home agent sends the packet to the foreign agent using the tunneling concept.
  3. From Fereign Agent to Mobile Host
  4. From Mobile Host to Remote Host
     When a mobile host wants to send a packet to a remote host, it sends as it does normally.
  • Mobile host
    • Source - home address
    • Destination - address of remote host
      The packet comes from th foreign network, it has the home address of the mobile host.

  -> Remote host is unaware of any movement by the mobile host.

There are inefficiencies.. 😥

Inefficiency in Mobile IP

• Double crossing
  • Double Crossing occurs when a remote host communicates with a mobile host that has moved th the same network(or site) as the remote host.
    
  • When the mobile host sends to the remote host → No inefficiency!
  • When the remote host sends a packet to the mobile host → the packet crosses the Internet twice

• Triangle routing
  • Triangle routing occurs when the remote host communicates with a mobile host that is not attached to the same network(or site) as the mobile host
    
  • When the mobile host sends to the remote host → No inefficiency!
  • When the remote host sends to the mobile host, the packet goes from the remote host to the home agent and then to the mobile host
• The reson of this inefficiency?
  • Home Agent manages the location/address information.

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Mobile IPv4 RFC 문서입니다아.

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