An Agile Vertical Handoff Scheme for Heterogeneous Networks Hsung-Pin Chang Department of Computer Science National Chung Hsing University Taichung, Taiwan, R.O.C.

Outline  Motivation  Related work How to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

Outline  Motivation  Related work How to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

Hierarchical Overlay Network  Many different communications systems coexist around us Ethernet, Wireless LAN, GPRS, 3G …  Each owns different characteristics Bandwidth, delay, cost ……  Hierarchical overlay network The combination of these heterogeneous networks

Example: An Overlay Networks Campus-wide (3G, GPRS) Building-wide (WLAN) Room-wide (Ethernet)

Horizontal versus Vertical Handoff  Problem: handoffs Horizontal handoff  The same kind of network technology  Ex: BSS to BSS Vertical handoff  Different kinds of network technologies  Ex: Wireless LAN to 3G <= what we are addressed

Horizontal Handoff AP BSS Internet

Vertical Handoff WCDMA WLAN AP BS Internet

Outline  Motivation  Related work: how to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

Previous Approaches to Vertical Handoff 1/2  Mobile IP/Infrastructure Based Approaches  Mobile IP with multicast Care-of-address is changed to a multicast address  Integration of WLAN and GPRS  Integration of WLAN and 3G Problem  Require modification of network infrastructure Hindrance to deployment  Need to be keep up to data New technologies are always introduced

Previous Approaches to Vertical Handoff 2/2  End-to-end based Application layer  SIP (Session Initiation Protocol) Transport layer: enable TCP connection alive even the underlying IP address is changed  TCP-R  TCP Migrate Between transport layer and network layer  C. Guo, et. al., “ A Seamless and Proactive End-to-End Mobility Solution for Roaming Across Heterogeneous Wireless Networks, ” IEEE JSAC, 22(5), pp Jun. 2004

Network Applications BSD Sockets TCPUDP User Kernel Socket Interface Transport Layer IP PPPSLIPEthernet Network Devices Network Layer LCT Table Translation A Seamless and Proactive End-to-End Solutions for Roaming Across Heterogeneous Wireless Networks (1/4)

Original address Original port Mapped address Mapped port Ap1A WLANWLAN LANLAN LANLAN Nego A B Tell B that A support vertical handoff Nego+Ack B A B Tell A ok. Notify C B A Ack B C A B C Original address Original port Mapped address Mapped port Ap1A Mobile Client Fixed Host … Original address Original port Mapped address Mapped port Ap1Cp2 Original address Original port Mapped address Mapped port Ap1Cp2 A Seamless and Proactive End-to-End Solutions for Roaming Across Heterogeneous Wireless Networks (2/4)

Handoff Layer Application Handoff Layer Kernel Application Kernel ABAB CB Table Lookup 圖 3 封包表頭替換過程 A Seamless and Proactive End-to-End Solutions for Roaming Across Heterogeneous Wireless Networks (3/4)

A Seamless and Proactive End-to-End Solutions for Roaming Across Heterogeneous Wireless Networks (4/4)  Problems NAT issue  Require an S/N (Subscription/Notification) Server  Modify the infrastructure TCP performance  Do not consider

Outline  Motivation  Related work: how to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

How to pass NAT gateway ?  Problem Communication must always be initiated by the private network  Solution Use the previous IP address as the source IP address

WLAN Fixed Host Ethernet NAT AP Switch Update New IP address Problem

WLAN Fixed Host Ethernet NAT AP Switch Update Old IP address Solution

Outline  Motivation  Related work: how to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ? => CWND-Restore  Experiments  Conclusion

How to adapt TCP behavior ?  Problem TCP consider packet loss as network congestion Slow down …  But … now packet lose is because “ handoff ”  Solution CWND-Restore

WLAN Fixed Host Ethernet NAT AP Switch CWND-Restore CWND 20 CWND 2CWND 50

Outline  Motivation  Related work: how to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

System Implementation- Linux Kernel Ethernet Driver Ethernet Driver WLAN Driver WLAN Driver 3G Applications Connection Manager TCP User Mode Kernel Mode UDP IP Handoff Detection CWND-restore

Experimental Platform Fixed HostMobile Host CPU AMD XP 2600+Intel Pentium M 1.4GHz RAM 512 MB256 MB NIC #1 100Mbps Ethernet 100Mbps Fast Ethernet Ethernet NIC #2 Philips g WLAN miniPCI Adapter NIC #3 Novatel UMTS/WCDMA USB Adapter

Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

TCP Handoff Verification 1/7 Internet Ethernet WCDMA Fixed Host Mobile Host WLAN NAT BS BA C AP Switch Experiment environment

TCP Handoff Verification 2/7  LAN to WLAN Handoff

TCP Handoff Verification 3/7  WLAN to LAN Handoff

TCP Handoff Verification 4/7  LAN to WCDMA Handoff

TCP Handoff Verification 5/7  WCDMA to LAN Handoff

TCP Handoff Verification 6/7  WLAN to WCDMA Handoff

TCP Handoff Verification 7/7  WCDMA to WLAN Handoff

Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

Handoff Latency 1/2 WCDMA Internet WLAN Fixed Host Mobile Host Ethernet NAT AP Switch BS B A C Experiment environment

Handoff Latency 2/2 Handoff Latency (ms) LAN to WLAN3 LAN to WCDMA438 WLAN to LAN1 WLAN to WCDMA503 WCDMA to LAN1 WCDMA to WLAN3

Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

TCP Handoff Performance 1/8 WCDMA Internet WLAN Fixed Host Mobile Host Ethernet NAT AP Switch BS B A C Experiment environment

TCP Handoff Performance 2/8 Original (KB/s)CWND Freeze (KB/s) WLAN to LAN LAN to WLAN WCDMA to LAN WCDMA to WLAN LAN to WCDMA WLAN to WCDMA

TCP handoff performance 3/8  LAN to WLAN Handoff

TCP handoff performance 4/8  WLAN to LAN Handoff

TCP handoff performance 5/8  LAN to WCDMA Handoff

TCP handoff performance 6/8  WCDMA to LAN Handoff

TCP handoff performance 7/8  WCDMA to WLAN Handoff

TCP handoff performance 8/8  WLAN to WCDMA Handoff

Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

UDP Handoff Verification 1/3  Experiment environment Switch AP Internet 1. WLAN 2. LAN FH MH

UDP Handoff Verification 1/3 Internet WLAN Fixed Host Mobile Host Ethernet AP Switch WLAN A B

UDP Handoff Verification 2/3  LAN to WLAN Handoff

UDP Handoff Verification 3/3  WLAN to LAN Handoff

Outline  Introduction Hierarchy Overlay Network Horizontal v.s. Vertical Handoff  Challenge How to achieve seamless vertical handoff ? How to pass NAT gateway ? How to adapt TCP behavior ? How to adapt application behavior ?  Experiments  Conclusion

Conclusion  A Vertical Handoff framework Support NAT while follows the end-to-end discipline  Without an modification to infrastructure Improve TCP performance  CWND Freeze  At most 2.3 times the original TCP