Wireless and Mobile Networks

Elements of a wireless ntework

• wireless hosts
  
  laptop,smartphone
  run application
  may be staionary(non-mobile) or mobile(wireless does not always mean mobility)

• base station
  
  typically connexted to wired network
  relay-responsible for sending packets between wired host(s) in its “area”(e.g.,cell towers,80.11 access points)

• wireless link
  
  typically used to connect mobile(s) to base station
  also used as bcakbone link
  multiple access protocol coordinate link access
  various data rates,transmission distance

• infrastructure mode
  
  base station connects mobile into wired network
  handoff:mobile changes base station providing connection into wired network

• ad hoc mode
  
  ad hoc mode
  no base stations
  nodes can only transmit to other nodes withink link coverage
  nodes organize themselves into a network:route among themselves

Wireless network taxonomy

single hop	multiple hops
infrastructure(e.g.,APs)	host connexts to base station(WiFi,WiMAX,cellular)which connects to larger Internet	host may have to relay through several wireless nodes to connects to larger Internet:mesh net
no infrastructure	no base station,no connection to larger Internet(Bluetooth,ad hoc nets)	no base station,no connection to larger Internet.May have to relay to reach other relay to reach other a given wireless node MANET,VANET

Mobility
spectrum of mobility,from the network
perspective:

• vocabulary
  
  home network:permanent “home” of mobile
  permanent address:address in home network,can always be used to reach mobile
  home agent:entity that will perform mobility functions on behalf of mobile,when mobile is remote
  
  permanent address:remains constant
  care-of- address:address in visited network
  visited network:network in which moobile currently
  correspondent:wants to communicate with mobile
  foreign agent:entity in visited network that performs mobility functions on behalf of mobile

Mobility:approaches

• let routing handle it:
  routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange.
  routing tables indicate where each mobile located
  no changes to end-systems

• let end-systems handle it:
  indirect routing:communication from correspondent to mobile goes through home agent,then forwared to remote
  direct routing:correspondent gets foreign address of mobile,sends directly to mobile
  ⚡️Mobility:registration
  
  ⚡️Mobility via indirect routing
  

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• mobile uses two addresses:
  permanent address:used by correspondent(hence mobile location is transparent to correspondent)
  care-of -address:used by home agent to forward datagrams to mobile

• foreign agent functions may be done by mobile itself

• traingle routing:
  correspondent-home-network-mobile
  
  inefficient when correspondent,mobile are in same network.

Indirect routing:mobving between networks
suppose mobile user moves to another network

• registers with new foreign agent
• new foreign agent registers with home agent
• home agent update care-of -address for mobile
• packets continue to be forwarded to mobile(but with new care-of-address)
  mobility,changing foreign networks networks transparent:on going connections can be maintained!

⚡️Mobility via direct routing

overcome traingle routing problem
non-transparent to correspondent:correspondent must get care-of-address from home agent

Accomodating mobility with direct routing
anchor foreign agent:FA in first visited network
data always routed first to anchor FA
when mobile moves:new FA arranges to have data forwarded from old FA(chaining)

Mobile IP

• RFC 3344

• has many features we’ve seen:
  home agents,foreign agents,foreign-agent regitration,care-of-address,encapsulation(packet-within-a-packet)

• three components to standard:
  indirect routing of datagrams
  agent discovery
  registration with home agent

Mobile IP:indicate routing

Mobile IP:agent discovery
agent advertisement:foreign/home agents advertise service by broadcasting ICMP messages(typefield=8)

Mobile IP:registration example

Wireless,mobility:impact on higher layer protocols

• logically,impact should be minimal…
  best effort service model remains unchanged
  TCP and UDP can (and do) run over wireless,mobile

• …but performance-wise
  packet loss/delay due to bit-error(discarded packets,delays for link-layer retransmissions),and handoff
  TCP interprets loss as congestion,will decrese congestion window un-necessarily
  delay impairments for real-time traffic
  limited bandwidth of wireless links