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

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

• Tom Henderson, Phil Spagnolo, Gary Pei
• thomas.r.henderson_at_boeing.com
• IETF-60 MANET WG meeting
• August 2004

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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

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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

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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

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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

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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

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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
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(reliable) Flooding optimizations

• Lins SI-CDS reduced overhead by 23 against
  benchmark
• Lins SI-CDS plus .
• Multicast ACKs reduced additional 32
• Ogiers 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

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Unreliable flooding advantage(draft-spagnolo-mane
t-ospf-wireless-interface)
best SI-CDS MPR w/out flag
MPR w/ flag (reliable)
(unreliable) (unreliable)
--------------------------------------------------
---- Total 110.0
17.70 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 0.78 0.78
0.78 Figure 17 Summary of overhead (kbps) for
comparison of reliable and unreliable flooding.
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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

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Next steps
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Fundamental design choices

• 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

Network LSA (desig. rtr.)
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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