1. CIS679: Anycast
Review of Last lecture
Anycast

2. Review of Last Lecture
H.323

3. Anycast
Unicast, multicast and anycast

4. Usage of Anycast Providing Service transparency
DNS server, and mirrored Web site
Improving network performance
load balance at application and network layers

5. An Example for Ancast Usage
1 mbs
1 mbs
1 mbs R4 R6
1 mbs R5
1 mbs
3 mbs R7
core R8 R9
R10
R11
R12
R13
A traffic flow with SP-To-Core method

6. Anycast at Different Layers
Network-layer anycast
Anycast address
Anycast membership management
Anycast routing
Application-layer anycast

7. 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

8. Anycast Membership Management
Similar to multicast -- IGMP
But, there is more freedom

9. 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.

10. Multi-Path Routing for Anycast Messages
Two issues
Loop free routing
How to select multi-path?

11. Loop in Anycast Routing1 1 1 1 H1 R1 H2 R2 R3 H4 R4 H3
Dest
Dist
hop
A, H15
A, H16
A, H17
A, H18 10 R7 9
R12 8
R13 3
R14
Routing table at R10 R9
R10 5
Routing table at R7
R11 6 13
Routing table at R9 7 4
R16
Routing table at R12 4 1 1 3 2 1 1 1 1 1 1 H5 R5 H6 R6 H7 R7 H8 R8 1 2 3 2 4 R9
R10 6 3 1 2 4 5
R11
R12
R13
R14 7 6 1 3 3 1 1
H16 1
R16 1 1
H15
R15
H17
R17
H18
R18
H1~H8 Anycast packet sources G(A) = {H15, H16, H17, H18} Hi
Router
Host Ri
Link with distance 1
Link in a loop 2

12. Loop-free Routing Ordered routing Methods to order the routers
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

13. The SSPF Method SSP order:
X>SSPY 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.

14. The SSPF Method Dest Dist hop Routing table at R11 Routing table at R1*
Dest
Dist
hop
A, H15
A, H16
A, H17
A, H18 2
R11 9 R9 16 11 R2
Routing table at R11 7 R5 12 20 15
Routing table at R1 6 19
R12 14
Routing table at R5 1
H15 10 17
Routing table at R15 H1 H2 H6 H7 H8 H4
H17
H18 H5 4 3 R1 R3 R4 R6 R7 R8
R10
R14
R13
R15
H16
R16
R17
R18 5 H3
H1~H8 Anycast packet sources G(A) = {H15, H16, H17, H18} Hi Ri
Router
Host
Link with distance
Link on DBTs
Congested link

15. The MIN-D Method Function min_d() MIN_D order
X >MIN_DY if min_d(X, A) > min_d(Y, A).
An anycast packet is routed to the nearer member of the anycast group.

16. The MIN-D Method Dest Dist hop Routing table at R10
A, H15
A, H16
A, H17
A, H18 10 R7 9
R12 8
R13 3
R14
Routing table at R10 6 R9 7 14
R10
Routing table at R6 5
R11 13
Routing table at R9 4
R16
Routing table at R12 * 1 H1 H2 H6 H7 H8
H15 H4
H17
H18 H5 2 R1 R2 R3 R4 R5 R6 R8
R15
H16
R17
R18 H3
Link with distance
Link on a general graph
Congested link
H1~H8 Anycast packet sources G(A) = {H15, H16, H17, H18} Hi Ri
Router with MIN-D
Host

17. The SBT Method SBT order:
X>SBTY 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.

18. The SBT Method R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R14 R13 R12 R11 R15 R16
Link with distance
Link on a SBT tree rooted at R3 Ri
Router
H1~H8 Anycast packet sources G(A) = {H15, H16, H17, H18} Hi
Host
Dest
Dist
hop
A, H15
A, H16
A, H17
A, H18 14 9
Routing table at R6 * 13 8
Routing table at R9 10
Routing table at R7 11
Routing table at R3

19. The CBT Method CBT order:
X>CBTY 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

20. The CBT Method R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R14 R13 R12 R11 R15 R16Ri
Router
H1~H8 Anycast packet sources G(A) = {H15, H16, H17, H18} Hi
Host
Dest
Dist
hop
A, H15
A, H16
A, H17
A, H18 10 9 8
Routing table at R10
Routing table at R7 13
Routing table at R9
Routing table at R12 *
Link with distance
Link on a CBT tree rooted at R7
Link on the truncated DBTs

21. Summary of Router-ordering Methods
The number of loop-free paths
SSPF < MIN_D < SBT = CBT
Overhead in terms of the memory storage
SSPF < MIN_D < CBT << SBT

22. 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 < Dj for any j, o.w. 0

23. Weight Assignment Consider R12 with r=1
Dest
Dist
hop
A, H15
A, H16
A, H17
A, H18 10 R7 9
R12 8
R13 3
R14
Routing table at R10 6 R9 7 14
R10
Routing table at R6 5
R11 13
Routing table at R9 4
R16
Routing table at R12 * 1 H1 H2 H6 H7 H8
H15 H4
H17
H18 H5 2 R1 R2 R3 R4 R5 R6 R8
R15
H16
R17
R18 H3
Link with distance
Link on a general graph
H1~H8 Anycast packet sources G(A) = {H15, H16, H17, H18} Hi Ri
Router with MIN-D
Host
Consider R12 with r=1
W15 = 0. 24, W16 = 0.42, W17 = 0.13, and W18 = 0.21

24. Performance Evaluation
Metrics: the average end-to-end delay
Evaluated systems: <α, β, γ>
α {SSP, MIN_D, SBT, CBT}
β {fixed, adaptive}
γ {independent, flow}
Network: ARPANET, one group with 5 members
Traffic: Poisson

25. Evaluation Results (b) <*, Fixed, Flow>
(a) <*, Fixed, Non-Flow>
0.00
0.50
1.00
1.50
2.00
Throughput
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
SSP GO
CBT
SBT
DOR
MIN-D
(b) <*, Fixed, Flow>
(c) <*, Adaptive, Non-Flow>
(d) <*, Adaptive, Flow>

26. Conclusion Anycast motivation Anycast address
Anycast membership management
Anycast routing
Multi-routing
loop-free routing methods
multiple path selection