Mobility Management in Mobile Hotspots with Heterogeneous Multihop Wireless Links

1. IEEE Communication Magazine Sep. 2007 Mobility Management in Mobile Hotspots with Heterogeneous Multihop Wireless Links Sangheon Pack, Xuemin (Sherman) Shen,Jon W. Mark, Jianping Pan

2. Outline • Introduction • Mobility Management in Mobile Hotspots • Evaluation • Handoff Latency Analysis • Open Research Issues • Conclusion

3. Introduction • 3G, 4G • WiMAX, Wibro • Mobile Hotspot • the extension of WiFi hotspots to moving vehicles • such as subways, trains, and buses • a novel approach to realize always best connected (ABC) services • WWAN provides extended service coverage to the vehicle • WLAN accommodates more users without excessive usage of the WWAN resources.

4. Introduction (cont.) • Mobility management • Seamless mobility management is a key aspect for the success of mobile Internet services. • MIPv4, MIPv6, HMIPv6 • NEMO basic support protocol, SIP-NEMO • Quality of Service support [6] • Link layer transmission technique [2] • Gateway architecture [7] [6] A. Lera et al., “End-to-End QoS Provisioning in 4G with Mobile Hotspots,” IEEE Network, vol. 19, no. 5, Sept./Oct. 2005, pp. 26–34. [2] D. Ho and S. Valaee, “Information Raining and Optimal Link-Layer Design for Mobile Hotspots,” IEEE Trans. Mobile Comp., vol. 4, no. 3, May/June 2005, pp. 271–84. [7] P. Rodriguez et al., “MAR: A Commuter Router Infrastructure for the Mobile Internet,” Proc. ACM MOBISYS 2004, June 2004.

5. Mobility Management in Mobile Hotspots • Network Mobility Basic Support Protocol

6. Mobility Management in Mobile Hotspots • Network Mobility Basic Support Protocol (cont.)

7. Mobility Management in Mobile Hotspots • SIP-Based Network Mobility Support protocol Modify the “Contact” field

8. Mobility Management in Mobile Hotspots • SIP-Based Network Mobility Support Protocol (cont.)

9. Evaluation • Deployment/implementation • NEMO-bs • Requires the installation of an MR • the HA should be upgraded to support MNP-based tunneling • SIP-NEMO • only needs an NMS at the vehicle, which is an application server • Typically, an application server is easier to deploy and modify than a network device. • System bottleneck • NEMO-bs • the HA and MR can be bottlenecks • SIP-NEMO • SIP servers are not bottlenecks for packet delivery • session establishment and packet delivery are separated • Only the NMS can be a single bottleneck point

10. Evaluation (cont.) • Usability • NEMO-bs • network layer mobility solution can be applied to any kind of application • SIP-NEMO • can be useful only when SIP is employed as a signaling protocol • more attractive solution for multimedia applications • High mobility support • NEMO-bs • an MN performs binding update procedure only when it first attaches • SIP-NEMO • high signaling traffic due to an invitation procedure for every MR handoff • Much longer message length, larger handoff latency

11. Evaluation (cont.) • Overhead • NEMO-bs • high tunneling overhead • SIP-NEMO • message translation overhead at the NMS • affects the session establishment time • explicit session establishment leads to increased packet delivery latency • Nested mobile hotspot support • NEMO-bs • all packets have to traverse all HAs involved • SIP-NEMO • Supports route optimization

12. Handover Latency Analysis • Handoff latency • the time until a location update procedure is completed when a vehicle moves to the coverage of a new subnet. • consider the location update procedure by the MR or NMS • consider only location update to the HA (or home SIP server) • focus on the latency over a wireless channel

13. Handover Latency Analysis (cont.) • consider a Rayleigh fading channel, and a two-state Markov channel model is used to approximate the error process at the frame level over the fading channel [10] • a good (g) state and a bad (b) state: • frame error probability is 1 in the bad state and 0 in the good state. • given the velocity and carrier frequency • average transmission error probability and state transition probabilities can be obtained from [10] • assume that a truncated ARQ scheme • Retry limit L(-1) • pXY: the state transition probability from state X ∈ {b, g} to state Y ∈ {b, g} • πX: the stationary probability in state X ∈ {b, g} [10] M. Zorzi, R. Rao, and L. Milstein, “ARQ Error Control for Fading Mobile Radio Channels,” IEEE Trans. Vehic. Tech., vol. 46, no. 2, May 1997, pp. 445–55

14. πb Handover Latency Analysis (cont.) • the transmission latency of Y ∈ {RAdv, BACK} • only link layer retransmission by ARQ is supported • D: the time slot duration (i.e., 5 ms) • k frames per message

15. Handover Latency Analysis (cont.) • the average transmission latency of X ∈ {RSol, BU, INVITE, 200OK} • an end-to-end retransmission mechanism using a backoff timer is specified • qk: the probability a message consisting of k frames is lost over a wireless link • qk = 1–成功傳輸每個frame = 1–(一個frame成功)k = 1–(1–一個frame失敗)k= 1 – (1 – πbpbbL–1)k • N: the end-to-end retransmission limit for X • θ(j): the retransmission timer at the jth retransmission, and it is given by 2j–1TInit 直到第 i 次傳輸成功所需時間

16. link bandwidth increasesframe size increasesthe number of frames for an IP/SIP message decreaseshandoff latency can be reduced • V increaseDoppler frequency increases (i.e., the wireless link’s coherence time decreases), which in turn reduces the burstiness of the transmission errors in the wireless linkframe loss rate decreases

17. Open Research Issues • Fast and smooth handoff • At the link layer, an information raining scheme is introduced in [2], • where multiple link layer frames are disseminated to a group of BSs to minimize packet losses • A network layer solution: fast handover for MIPv6 • with the assistance of the link layer for reducing handoff latency and packet loss • To minimize packet loss during handoff and achieve seamless handoff, a cross-layer approach may be a solution. • TCP and UDP performance analysis due to handoff is also an interesting research issue. • System availability and fault tolerance • For successful deployment of mobile hotspots • In the IETF NEMO working group, a multihoming issue is being actively discussed. • By installing multiple interfaces on the vehicle, • how to optimally distribute packets to multiple interfaces(for downlink/uplink traffic), and • how to quickly detect and recover a failure are open issues.

18. Open Research Issues (cont.) • Security • key distribution mechanism • how to authenticate an MN within a vehicle in heterogeneous wireless networks where different wireless access technologies are integrated is an important issue. • Multimedia support • a promising application • efficient resource management • since the WWAN-WLAN integrated link in mobile hotspots has different characteristics than traditional wireless systems, a new transport protocol for multimedia transmission should be developed.

19. Conclusion • We studied two mobility management schemes in mobile hotspots with heterogeneous multihop wireless links: • the NEMO basic support protocol and • SIP-based network mobility support protocol. • easy deployment, no tunneling overhead, and nested mobile hotspot support. • SIP message length is much larger  longer handoff latency over a wireless fading channel • open research issues are identified • for the successful deployment of mobile hotspots