1. CMPE 257 - Wireless and Mobile Networking 1 CMPE 257 Spring 2006 Wireless Internetworking Wireless and Mobile Networks

2. CMPE 257 - Wireless and Mobile Networking 2 Wireless Internet Extension of Internet services to wireless/mobile users. Issues: –Wireless medium unreliability. –Node mobility.

3. CMPE 257 - Wireless and Mobile Networking 3 Challenges Network-, Transport-, and Application layer.

4. CMPE 257 - Wireless and Mobile Networking 4 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?

5. CMPE 257 - Wireless and Mobile Networking 5 Solution Mobile IP. –Manages mobility at the IP layer. –Hides mobility from upper layers.

6. CMPE 257 - Wireless and Mobile Networking 6 Mobile IP Maintains IP addressing scheme with additional support for mobility. –Address redirection.

7. CMPE 257 - Wireless and Mobile Networking 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.

8. CMPE 257 - Wireless and Mobile Networking 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.

9. CMPE 257 - Wireless and Mobile Networking 9 Mobile IP: Design Issues Issues: –Impact on IP addressing. –Impact on routing. –Impact on higher layers. Key design considerations: –Scale. –Compatibility. –Transparency.

10. CMPE 257 - Wireless and Mobile Networking 10 Terminology Home Agent (HA) Mobile Host (MH) Foreign Agent (FA) HN FN CH

11. CMPE 257 - Wireless and Mobile Networking 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).

12. CMPE 257 - Wireless and Mobile Networking 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.

13. CMPE 257 - Wireless and Mobile Networking 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?

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

15. CMPE 257 - Wireless and Mobile Networking 15 Discovering Agents Agents periodically beacon advertisements

16. CMPE 257 - Wireless and Mobile Networking 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.

17. CMPE 257 - Wireless and Mobile Networking 17 Discovering Agents MH polls; agent responds.

18. CMPE 257 - Wireless and Mobile Networking 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: Alternate encapsulation techniques, header compression.

19. CMPE 257 - Wireless and Mobile Networking 19 Registration

20. CMPE 257 - Wireless and Mobile Networking 20 Registering When away, MH registers its CoA with HA (binding update). Binding: (HoA->CoA) –Binding has a lifetime.

21. CMPE 257 - Wireless and Mobile Networking 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.

22. CMPE 257 - Wireless and Mobile Networking 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.

23. CMPE 257 - Wireless and Mobile Networking 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).

24. CMPE 257 - Wireless and Mobile Networking 24 Tunneling Tunneled Data Packet HA keeps binding between MH and CoA SRC

25. CMPE 257 - Wireless and Mobile Networking 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

26. CMPE 257 - Wireless and Mobile Networking 26 Tunneling in Mobile IP

27. CMPE 257 - Wireless and Mobile Networking 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.

28. CMPE 257 - Wireless and Mobile Networking 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.

29. CMPE 257 - Wireless and Mobile Networking 29 Simultaneous Bindings MN can register multiple CoA’swith HA. –Why? De-registration. –Explicit. –Implicit.

30. CMPE 257 - Wireless and Mobile Networking 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.

31. CMPE 257 - Wireless and Mobile Networking 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.

32. CMPE 257 - Wireless and Mobile Networking 32 Hard versus Soft Handoff Hard handoff: only a single active connection between MN and AP. Soft handoff: two active connections during handoff.

33. CMPE 257 - Wireless and Mobile Networking 33 Handoff Signaling Forward handoff: –Target AP contacts current AP to initiate handoff. Backward handoff: –Current AP contacts the target one.

34. CMPE 257 - Wireless and Mobile Networking 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.

35. CMPE 257 - Wireless and Mobile Networking 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.

36. CMPE 257 - Wireless and Mobile Networking 36 Mobility Support in IPv6 Route optimization is default. Fields for specifying both CoA and permanent IP address. –No need for encapsulation.

37. CMPE 257 - Wireless and Mobile Networking 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.

38. CMPE 257 - Wireless and Mobile Networking 38 Goal Determine the impact on TCP performance of –Combined overhead sources. –Individual overhead sources.

39. CMPE 257 - Wireless and Mobile Networking 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.

40. CMPE 257 - Wireless and Mobile Networking 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.