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Design Considerations for a Wireless OSPF Interface draft-spagnolo-manet-ospf-design

This draft examines the fundamental performance problems of OSPF in a wireless environment and studies the performance trends of different OSPF MANET proposals.

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Design Considerations for a Wireless OSPF Interface draft-spagnolo-manet-ospf-design

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  1. Design Considerations for a Wireless OSPF Interface draft-spagnolo-manet-ospf-design Tom Henderson, Phil Spagnolo, Gary Pei {thomas.r.henderson@boeing.com} IETF-60 MANET WG meeting August 2004

  2. Problem statement(draft-baker-manet-ospf-problem-statement-00) • OSPF does not have suitable interface type for MANET (wireless, multi-access subnet) operation • Leads to scalability problems with respect to overhead (primarily flooding overhead) • OSPF seems extensible to cover this case • proposals have centered on a new interface type • could be for IPv4 or v6, or both

  3. Purpose Design Considerations for a Wireless OSPF Interface draft-spagnolo-manet-ospf-design • examine fundamental performance problems of OSPF in this environment • study the performance trends of different OSPF MANET proposals

  4. OSPF analysis (Sec. 3) • Multicast-capable Point-to-Multipoint interface type is the benchmark • Finding: LSU flooding and acknowledgment is by far the dominant contributor to overhead • backed up by simulations as well

  5. Methodology • Simulation-based study using QualNet 3.7 • 802.11-based and Rockwell Collins USAP TDMA • Ricean fading model, no power control • OSPFv2 implementation (validated against Moy ospfd implementation) • random waypoint mobility on square grid • Performance metrics • OSPFv2 overhead measured at IP layer • User data delivery ratio

  6. Network size Network density Network churn Scenario-independent parameters • Number of nodes • Number of neighbors per node • averaged over all nodes • Number of neighbor state changes per unit time • averaged over all nodes • (Number of external LSAs) • not included in this study

  7. OSPFv2 benchmark simulations Mobility | Low Medium High ------------------------------------ Hello | 2.20 2.00 1.71 LSU-flood| 43.55 66.33 67.59 LSU-rxmt | 35.62 72.04 87.28 LSAck | 3.70 7.28 9.16 LSR | 0.04 0.10 0.20 DDESC | 2.67 4.91 6.80 Total | 87.80 152.70 172.70 Figure 8: Summary of overhead (kbps) at the three mobility levels. Dominant overhead factor

  8. (reliable) Flooding optimizations • Lin’s SI-CDS reduced overhead by 23% against benchmark • Lin’s SI-CDS plus …. • Multicast ACKs reduced additional 32% • Ogier’s receiver-based ACK suppression reduced overhead by 8% (created more overhead) • Originator-based LSA suppression reduced overhead by 28% • Retransmit-timer backoff reduced overhead by 24%

  9. Unreliable flooding advantage(draft-spagnolo-manet-ospf-wireless-interface) | best SI-CDS MPR w/out flag MPR w/ flag | (reliable) (unreliable) (unreliable) ------------------------------------------------------ Total | 110.017.70 28.40 Hello | 1.65 1.79 1.79 LSA Flood | 34.94 15.97 26.63 LSA Rxmt | 57.13 - - LSAck | 8.07 - - LSR | 0.39 - - DDESC | 7.81 - - Deliv ratio | 0.780.78 0.78 Figure 17: Summary of overhead (kbps) for comparison of reliable and unreliable flooding.

  10. Summary • LSU flooding is by far the dominant contributor to overhead • can reliable flooding optimizations do better than 50% reduction? • unreliable flooding can provide up to 10x reduction without sacrificing performance • large numbers of external LSAs are a concern • Database exchange optimization also may be important in a frequently partitioning network

  11. Next steps

  12. Fundamental design choices Network LSA (desig. rtr.) • Broadcast-based interface • provides abstraction • may be most scalable for large networks • Point-to-multipoint-based interface • provides visibility into structure of MANET • important for picking good entry points into network, over bandwidth-constrained links

  13. Layer-2 triggers • Should we specify how implementations might make use of layer-2 information? • neighbor discovery suppression • link quality issues • How does this affect interoperability? • Examples: • A Triggered Interface: draft-corson-triggered-00.txt (expired) • PPPoE interface for link metrics: draft-bberry-pppoe-credit-01.txt

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