[Network week5] Mobile IP, HoA, CoA, HA, FA, Routing, Intra-Domain Routing

Mobile IP

• Extension of IP protocol
  : That allows mobile computer to be connected to the Internet at any location

Stationary and Mobile Hosts

• Original IP addressing was based on the assumption that
  : A host is stationary, attached to one specific network
• The address is valid only when the host is attached to the network
  : If the network changes, the address is no longer valid
• Changing address
  : Let the mobile host change its address as it goes to the new network
• 2 major drawbacks
  : Rebooting
  : If the host roams from one network to another during a transmission, the exchange will be interrupted
  This is because the ports and IP address of the client and the server must remain constant for the duration of the connection

2 Addresses

• Home address (HoA) and care-of address(CoA)
  : Permanent address and a temporary address
  : Permanent address associates the host with its home network (HN)
  : When a host moves from one network to another, the CoA changes
  = It is associated with the foreign network (FN), the network to which the host moves
  

Agents

• To make the change of address transparent to the rest of the Internet requires a home agent and a foreign agent
• Shown the home and the foreign agents as routers
  : We need to emphasize that their specific function as an agent is perform in the application layer
  

HA and FA

• Home agent(HA)
  : A router attached to HN
  : Acts on behalf of the mobile host when a remote host sends a packet to mobile host
• Foreign agent(FA)
  : A router attached to FN
  : Foreign agent receives and delivers packets sent by the home agent to the mobile host
  

Data Transfer

• From a remote host (RH) to HA
  : RH sends a packet as though MH is at its home network
  : Uses RH address as source and home address of mobile host as destination

• From HA to FA
  : HA sends the packet to the foreign agent using the tunneling
  : HA encapsulates the whole IP packet inside another IP packet using its address as the source and the foreign agent's addres as the destination

• From FA to MH
  : When FA receives the packet, it removes the original packet
  : Since DST address is home address of MH, FA consults a registry table to find the care-of Address of MH

• From MH to RH
  : It sends as it does normally
  : MH prepares a packet with its home address as SRC, and the address of RH as DST

Transparency

• RH is unaware of any movement by MH
  : RH sends packet using home address of MH as DST
  : It receives packets that have home address of MH as SRC

Double crossing

• Occurs when RH communicates with an MH that has moved to the same network as RH
• When MH sends a packet to RH, there is no inefficiency
• When RH sends a packet to MH, the packet crosses the Internet twice
  

Triangle Routing

• Less severe
• Occurs when RH communicates with MH that is not attached to the same as MH
  

Intra-Domain Routing

Routing and Forwarding

• Main objective of network layer
  : Transport packets from source to destination
• Two mechanisms are used in network layer
  1) Forwarding
  : Algorithm use by each router to determine on which interface each packet should be sent to reach its destination or follow its virtual circuit
  : Relies on the routing table maintained by each router
  2) Routing
  : Distributed algorithm that distributes to all routers the information that allows them to build their routing tables

Principles

• How to build routing table of each router?
  : Include in the routing table of each router the path to allow it to reach each destination
• Selection of the shortest paths
  : How does "C" choose a next-hop one the path towards host "H"?
  : Based on metrics
  1) Minimum hop
  2) Cost
  3) Delay
  4) 1/Throughput

Metrics

• An internet is a combination of networks connected by routers
• A metric is a cost assigned for passing through a network
• Total metric of a route is equal to the sum of metrics of networks that comprise route
• Router chooses the route with the shortes (smallest) metric

Intra and Inter Domain Routing

• Because Internet can be so large, one routing protocol cannot handle the task of updating routing tables of all routers
• Internet is divided into autonomous systems(AS)
  : AS is a group of network and routers under authority of a single administration
• Intra-domain routing
  : Used for routing inside an AS
• Inter-domain
  : Used for routing between AS
  

Popular Routing Protocols

• A routing protocol is a combination of rules and procedures that lets routers in the Internet inform each other of changes

Intra-Domain Routing

Static Routing

• Network manager computes all routing tables and downloads them on all routers
  : Shortest path algorithms
• Advantages of static routing
  : Easy to use in small network
  : Routing tables can be optimized easily
• Drawbacks of static routing
  : Does not adapt dynamically to network load
  : How to deal with link and router failures?

Dynamic or Distributed Routing

• Routers exchange messages and use a distributed algorithm to build their routing tables
  : Used in almost all networks
• Advantages
  : Can easily adapt routing tables to events
• Drawbacks
  : More complex to implement than static routing
• Most common distributed routing methods
  1) Distance vector routing
  2) Link state routing

Shortest Path Algorithms

• Distance vector protocols
  -- Neighbors exchange list of distances to destinations
  -- Best next-hop determined for each destination
  -- Distributed Bellman-Ford algorithm
• Link State Protocol
  -- Link state information flooded to all routers
  -- Routers have complete topology information
  -- Dijkstra's shortest first algorithm