CIS679: Anycast

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CIS679 Anycast

• Review of Last lecture
• Anycast

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Review of Last Lecture

• H.323

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Anycast

• Unicast, multicast and anycast

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Usage of Anycast

• Providing Service transparency
• DNS server, and mirrored Web site
• Improving network performance
• load balance at application and network layers

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An Example for Ancast Usage
R1
R2
R3
1 mbs
1 mbs
1 mbs
R4
R6
1 mbs
1 mbs
R5
3 mbs
R7
core
R9
R8
R13
R12
R11
R10
A traffic flow with SP-To-Core method
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Anycast at Different Layers

• Network-layer anycast
• Anycast address
• Anycast membership management
• Anycast routing
• Application-layer anycast

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Anycast Address

• Shares with unicast
• Advantage compatible to unicast
• Disadvantage too like unicast, some benefit of
  anycast lost
• Separate from unicast, just like multicast
• Advantage easy to make full use of anycast
  semantics
• Disadvantage difficult to deploy

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Anycast Membership Management

• Similar to multicast -- IGMP
• But, there is more freedom

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Anycast Routing

• Single-path Routing
• The path from the source to the destination
  is time
• invariant.
• Multi-path Routing
• The traffic from the source to the
  destination is
• split into different paths.

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Multi-Path Routing for Anycast Messages

• Two issues
• Loop free routing
• How to select multi-path?

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Loop in Anycast Routing
1
1
1
1
R1
R2
R3
R4
2
4
3
1
1
1
1
1
1
1
1
R7
R5
R6
R8
2
1
2
3
R9
R10
4
6
3
1
4
2
5
R14
R13
R12
R11
7
6
1
3
3
1
1
1
1
R15
R17
R18
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Loop-free Routing

• Ordered routing
• A router with a higher order can send anycast
  message to a lower order router.
• Methods to order the routers
• SSPF method
• MIN_D method
• SBT method
• CBT method

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The SSPF Method

• SSP order
• XgtSSPY if Y is the next hop of X on Pssp(X,
  G(A)).
• An anycast packet is routed to the nearest member
  of the anycast group.

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The SSPF Method
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The MIN-D Method

• Function min_d()
• MIN_D order
• X gtMIN_DY if min_d(X, A) gt min_d(Y, A).
• An anycast packet is routed to the nearer member
  of the anycast group.

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The MIN-D Method
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The SBT Method

• SBT order
• XgtSBTY if X is the father of Y on the
  source-based tree of Source S
• An anycast packet is routed along the
  source-based tree rooted at the source of the
  packet.

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The SBT Method
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The CBT Method

• CBT order
• XgtCBTY if X is the father of Y on the
  core-based tree.
• For an anycast packet
• at the on-CBT router, it is routed following CBT
  order.
• at the off-CBT router, it is routed following
  SSP order

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The CBT Method
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Summary of Router-ordering Methods

• The number of loop-free paths
• SSPF lt MIN_D lt SBT CBT
• Overhead in terms of the memory storage
• SSPF lt MIN_D lt CBT ltlt SBT

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Multiple Path Selection

• Weight Random Selection (WRS)
• A path with high weight has higher probability
  to be selected than the path with low weight.
• A rule of thumb
• the weight should be inversely proportionally to
  the distance of the route, i.e, W 1/D

• when r 0, Wi 1/K
• when r ?, Wi 1/Di if Di lt Dj for any j, o.w.
  0

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Weight Assignment

• Consider R12 with r1
• W15 0. 24, W16 0.42, W17 0.13, and
  W18 0.21

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Performance Evaluation

• Metrics the average end-to-end delay
• Evaluated systems lta, ß, ?gt
• a ?SSP, MIN_D, SBT, CBT
• ß ?fixed, adaptive
• ? ?independent, flow
• Network ARPANET, one group with 5 members
• Traffic Poisson

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Evaluation Results
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Conclusion

• Anycast motivation
• Anycast address
• Anycast membership management
• Anycast routing
• Multi-routing
• loop-free routing methods
• multiple path selection