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802.11 and IP

802.11 and IP. James Kempf Seamoby WG Co-chair DoCoMo Labs USA kempf@docomolabs-usa.com. Outline. Assumed 802.11 network deployment. Reactive Layer 3 handover drawbacks. Proactive Layer 3 handover. Context transfer and handover. IETF Seamoby Working Group work items.

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802.11 and IP

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  1. 802.11 and IP James Kempf Seamoby WG Co-chair DoCoMo Labs USA kempf@docomolabs-usa.com James Kempf, DoCoMo Labs

  2. Outline • Assumed 802.11 network deployment. • Reactive Layer 3 handover drawbacks. • Proactive Layer 3 handover. • Context transfer and handover. • IETF Seamoby Working Group work items. • Suggestions for 802.11/IETF further work. James Kempf, DoCoMo Labs

  3. 802.11 Deployment Assumption • 802.11 assumes a flat Layer 2 deployment. • Valid for small networks (SOHO market). James Kempf, DoCoMo Labs

  4. to the Internet... Neglected Deployment Scenario • Hierarchical network with routers between subnets • Valid for large networks (enterprise/telco market). James Kempf, DoCoMo Labs

  5. Layer 3 Handover • Triggered by a Reassociate between two 802.11 access points on two different IP subnets. • Requires changing routing reachability so packets are routed to the mobile host on the new subnet. • In Mobile IPv4, the Foreign Agent performs Layer 3 handover. • Typically implemented on the router. • Not implemented on access point. • In Mobile IPv6, the router performs handover. • No Foreign Agent. James Kempf, DoCoMo Labs

  6. Handover Loss Analysis • Handover between access points results in connectivity loss. • Total connectivity loss at handover has two components: • Layer 2 loss due to handover between access points (802.11 Reassociate). • Layer 3 loss due to IAPP + IP handover between access routers (IP handover). • Layer 3 handover requires Layer 2 handover. • Longer 802.11 Reassociate + IAPP means longer IP handover. • Not every handover will be a Layer 3 handover, but many will. 802.11 Reassociate start 802.11 Reassociate end IP handover complete Time IAPP + IP Handover Layer 2 Connectivity Lost Layer 3 Connectivity Lost James Kempf, DoCoMo Labs

  7. 3) IAPP 4) Get new subnet IP address 2) Drop Packets 1) Reassociate Reactive Layer 3 Handover Process Old Access Router New Access Router James Kempf, DoCoMo Labs

  8. Application Tolerance for Loss • For data applications, 100-300 ms or more is acceptable • Example: Web browsing • For voice applications, 40 ms or less for total (Layer 2 + Layer 3) loss is necessary. • If not, the user will perceive an artifact. • Current 802.11 product Layer 2 handover performance is in the range from 60 - 200 ms. • Informal measurements. For supporting VoIP, total 802.11 + IP handover times less than 40 ms are crucial! • This includes security and IAPP transaction (if any). • Reactive Layer 3 handover will not perform adequately for VoIP. James Kempf, DoCoMo Labs

  9. Proactive Layer 3 Handover • Need Layer 2 handover sequencing information at Layer 3. • At the old access router prior to Layer 2 handover. • At the new access router as soon as the mobile host shows up. • Integration of router and access point can achieve this. • Current products are bridges, not routers. • Separation of router and access point is still desirable. • Access points only cover a limited geographical area. • Network operator may not want to tie subnet topology to geographical coverage area of one access point. • Still need a protocol between the access point and access router and 802 is as good as any. • Bridging is still a viable option. James Kempf, DoCoMo Labs

  10. 5) Tunnel packets under old subnet address 1) Link Down 2) IAPP 6) Get new subnet IP address 4) Reassociate Proactive Layer 3 Handover Process Old Access Router New Access Router 3) Flush MAC address to IP address mapping James Kempf, DoCoMo Labs

  11. Context Transfer and Proactive Handover • Context transfer: sending context or state involving mobile host’s network access related services to new network point of attachment. • Example: QoS attributes. • To be effective, context transfer must complete before IP handover. • Otherwise, the mobile host must wait to gain network access at new point of attachment. • For that to happen, the router at the old point of attachment must know prior to Layer 2 handover where the host will be moving. • At the latest, the router must know when the old link is severed. • One context transfer transaction for Layer 2 and Layer 3 context is desirable, to avoid delay. James Kempf, DoCoMo Labs

  12. IETF Seamoby Working Group Charter • Context Transfer. • Problem statement and Requirements complete. • Next step: Designing a protocol. • Candidate access router discovery: Translation of reachable access point MAC address to router IP address. • Covers inter-domain as well as intra-domain. • Problem statement complete. • Next step: Complete requirements. • IP Paging • IP protocol for awakening a host out of low power mode when a message arrives • Includes ability to track host at IP level while in low power mode. • Layer 2 support important for efficient paging. • Cellular systems include Layer 2 support. • Problem statement and Requirements complete. • Next step: Architecture framework definition. James Kempf, DoCoMo Labs

  13. Suggested 802.11 Proactive Handover Support • Layer 2 signal between access point and router about progress of handover. • When a host leaves an access point – includes MAC address of host and new access point. • When a host arrives at an access point – includes MAC address of host and old access point • Router does all off-subnet communication. • Access point MAC address to IP address translation. • IAPP communication with old access point for resource deallocation. • Context transfer. • Authentication and authorization of host. • Router can background certain tasks, e.g. access point MAC address to IP address translation. • A simple version of IAPP if there is no router. • One access point could act as the “master” and take on the router’s role. James Kempf, DoCoMo Labs

  14. Specific Changes to IAPP and 802.11 • Extensible op codes for access point to router communication. • Extensible context blobs for IETF use. • Triggering IAPP on the old access point when the power level of the mobile host falls below a certain level and new access point is known. James Kempf, DoCoMo Labs

  15. Suggestions for Further Work • Collaboration between 802.11 Tgf and IETF Seamoby WG to co-ordinate protocols. • Support interaction between router and access point to increase performance and reliability of re-association. • Most common deployment scenario. • Ensure that a simple, easy to configure option is available for flat, SOHO style deployments. James Kempf, DoCoMo Labs

  16. Feedback? James Kempf, DoCoMo Labs

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