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CMPE 257: Wireless and Mobile Networking

CMPE 257: Wireless and Mobile Networking. Spring 2005 Wireless Internetworking. Announcements. Homework on MAC up. Midterm moved to 05.10. Wireless Internet. Extension of Internet services to wireless/mobile users. Challenges? Wireless medium. Node mobility. TCP/IP stack. Challenges.

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CMPE 257: Wireless and Mobile Networking

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  1. CMPE 257: Wireless and Mobile Networking Spring 2005 Wireless Internetworking CMPE 257 Spring 2005

  2. Announcements • Homework on MAC up. • Midterm moved to 05.10. CMPE 257 Spring 2005

  3. Wireless Internet • Extension of Internet services to wireless/mobile users. • Challenges? • Wireless medium. • Node mobility. • TCP/IP stack. CMPE 257 Spring 2005

  4. Challenges • Network layer. • Transport layer. • Application. CMPE 257 Spring 2005

  5. Address mobility • IP assumes fixed nodes. • Hierarchical addresses. • IP address = network number+host number. • IP address uniquely identifies host’s PoA. • Host must attach to network specified by its IP address to send/receive datagrams. • But what if nodes move? • Change address? • How about packets destined to them? CMPE 257 Spring 2005

  6. Mobile IP • Address redirection. • Manages mobility at the IP layer. • Hides mobility from upper layers. CMPE 257 Spring 2005

  7. Mobile IP: Goals • Nodes can receive datagrams no matter where they attach to the Internet. • IMHP (Internet Mobile Host Protocol) as Mobile IP precursor. CMPE 257 Spring 2005

  8. “Last-hop” Mobility • Mobile IP is the Internet standard for “last-hop” mobility support in IP networks (RFC 2290). • How do we deliver IP packets when the endpoints move? • Mobile host must be able to communicate after changing its link-layer point-of-attachment. • Mobile host must be able to communicate using its permanent (home) IP address. CMPE 257 Spring 2005

  9. Mobile IP: Design Issues • Issues: • Impact on IP addressing. • Impact on routing. • Impact on higher layers. • Key design considerations: • Scale. • Compatibility. • Transparency. CMPE 257 Spring 2005

  10. Terminology Home Agent (HA) Foreign Agent (FA) HN CH Mobile Host (MH) CMPE 257 Spring 2005

  11. Terminology (Cont’d) • Similar to cellular. • Mobile Node (MN or MH): node changing its PoA. • Correspondent Host (CH). • Home Network (HN) and Foreign Network (FN). CMPE 257 Spring 2005

  12. Terminology (Cont’d) • Mobility Agents: • Home Agent (HA): router on MN’s HN that tunnels datagrams to MH when away and keeps MH’s current location info. • Foreign Agent (FA): router on foreign network; delivers datagrmas to MH while on FN. • Home Address (HoA) and Care-of Address (CoA): • HoA: MH’s permanent address on HN. • CoA: MH’s temporary address on FN. CMPE 257 Spring 2005

  13. Care of Address • FA-based. • MN’s address is its current FA’s address. • FN-based. • Locally-assigned address in FN. • E.g., DHCP address. • What’s the difference? CMPE 257 Spring 2005

  14. Mobile-IP: Basic Operation • MH normally uses its home address HoA. • When MH visits a foreign network, • Registration with FA. • Discover mobile agent and CoA. • Registration with HA. • Binding update (HoA -> CoA). • Communicating with MN: use HoA. • HA forwards packet from HoA to CoA. CMPE 257 Spring 2005

  15. Discovering Agents Agents periodically beacon advertisements CMPE 257 Spring 2005

  16. Agent Discovery • Agent advertisement (beaconing): • Mobile agent broadcast agent advertisement at regular intervals (“I am here”). • Agent solicitation: • MH can poll (“anyone here?”). • Mobile agent responds to poll. CMPE 257 Spring 2005

  17. Discovering Agents MH polls; agent responds. CMPE 257 Spring 2005

  18. Agent Advertisement • Follows ICMP router advertisement message. • List one or more available care-of addresses. • Inform the MN about special features provided by FA. • Example: Alternative encapsulation techniques, header compression. CMPE 257 Spring 2005

  19. Registration CMPE 257 Spring 2005

  20. Registering • When away, MH registers its CoA with HA (binding update). • Binding: (HoA->CoA) • Binding has a lifetime. CMPE 257 Spring 2005

  21. Registration Process • MH sends a registration request with CoA. • HA authenticates request. • HA approves or disapproves the request. • HA adds necessary information to its routing table. • HA sends registration reply back to MH. CMPE 257 Spring 2005

  22. Registration Process (cont’d…) • In the case of FA-based CoA: • FA is involved in registration. • FA is also involved in packet forwarding. • Encapsulation. • Tunneling. CMPE 257 Spring 2005

  23. Tunneling • HA tunnels datagrams destined to MN when MN is away. • Datagrams sent to MH directly. • Or sent to FA which forwards to MN’s CoA. • Tunnel terminates at MH’s CoA (either the MH or the FA). CMPE 257 Spring 2005

  24. Tunneling SRC Tunneled Data Packet HA keeps binding between MH and CoA CMPE 257 Spring 2005

  25. Encapsulation • Tunneling requires encapsulation. • Sending the original packet (CH->MH) in another packet (HA->CoA). • Default encapsulation mechanism: • IP-within-IP (tunnel). • Tunnel header: new IP header inserted by the tunnel source (home agent). • Destination IP: CoA CMPE 257 Spring 2005

  26. Tunneling in Mobile IP CMPE 257 Spring 2005

  27. The Triangle Routing Problem • Aka, “dogleg” routing. • MH->CH: direct. • CH->MH: CH->HA->MH • Inefficient • Solution: route optimization. • Deliver binding updates directly to CH. CMPE 257 Spring 2005

  28. Route Optimization • Binding caches: • Nodes can keep caches with CoA for MHs. • If node has entry for MH, sends data directly. • Otherwise, “triangulates” with HA. • Binding cache entries have TTL. • HA, FA, or MH can send binding cache updates to CH. CMPE 257 Spring 2005

  29. Simultaneous Bindings • MN can register multiple CoA’swith HA. • Why? • De-registration. • Explicit. • Implicit. CMPE 257 Spring 2005

  30. Handoffs • MH moving among FN. • New CoA registered with HA. • Previous FA not necessarily notified. • Old registration will expire. • New data delivered to new CoA. • In-flight data? • Dropped and retransmitted by upper layers, or • FA notified of new CoA; FA forwards data to new CoA. CMPE 257 Spring 2005

  31. Types of Handoffs • MN-initiated: • Handoff managed by MN. • MN measures signal strength to AP. • Decides target AP and switchs over. • Network-initiated: • APs decide when to hand over and to whom. CMPE 257 Spring 2005

  32. Hard versus Soft Handoff • Hard handoff: only a single active connection between MN and AP. • Soft handoff: two active connections during handoff. CMPE 257 Spring 2005

  33. Handoff Signaling • Forward handoff: • Target AP contacts current AP to initiate handoff. • Backward handoff: • Current AP contacts the target one. CMPE 257 Spring 2005

  34. Handoff Delay • 3 components: • Detect need of handoff. • Link establishment between MN and new AP. • Registration with HA. • Pre- and post-registration handoffs: • Pre-registration registers MN with HA before handoff. • Post-registration: HA registration happens after handoff. CMPE 257 Spring 2005

  35. Authentication • Malicious nodes can infiltrate FNs. • Mobile IP registration includes authentication info exchange. • MH-HA. • MH-FA. • HA-FA. • Protection against replay attacks. • Timestamp and nonces. CMPE 257 Spring 2005

  36. Mobility Support in IPv6 • Route optimization is default. • Fields for specifying both CoA and permanent IP address. • No need for encapsulation. CMPE 257 Spring 2005

  37. TCP Performance in Mobile-IP (Choong) • Source of overhead: triangle routing. • Additional processing at HA and FA. • Additional delay due to “triangulation”. • Additional delay due to fragmentation (extra IP header). • Handoffs. CMPE 257 Spring 2005

  38. Goal • Determine the impact on TCP performance of • Combined overhead sources. • Individual overhead sources. CMPE 257 Spring 2005

  39. Methodology • Several scenarios that compound or isolate overhead sources. • Compare performance of between scenario pairs. • FTP transfer btween MH and CH. • Metric: TCP throughput. CMPE 257 Spring 2005

  40. Summary of Results • Dogleg routing as main cause of TCP throughput degradation. • Solution: route optimization. • Handoff is second. • Mobile-IP’s inherent delay in re-establish connectivity with new FA. • Solutions: • Increase frequency of router advertisements. • Use link-layer information to trigger handoff. CMPE 257 Spring 2005

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