Protection Dr. Jnos Tapolcai tapolcai@tmit.bme.hu - - PowerPoint PPT Presentation
Dedicated and Shared Protection Dr. Jnos Tapolcai tapolcai@tmit.bme.hu http://opti.tmit.bme.hu/~tapolcai/ 1 Design goals in Survivable Networks High connection availability Short recovery time Complex Scalability
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– Efficiency vs. complexity
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Simple Complex
1 working + 1 protection path is allocated The two path are disjoint
1 1 1 1 1 1 2 1 1
The reserved capacity along the common link is : A + B PRO: instantaneous recovery (no action is needed)
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capacity along their protection routes can be shared
– At most one of them is activated after a single failure
1 1 1 1 1 1 1 1 1
The spare capacity along the common link is : max{A,B} CONS: we need actions (signaling) after failure
architecture)
(isolation) (tl)
– Path selection (tp) – Device configuration (td)
Failure management
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Recovery time Recovery operation (switching) time Fault notification time Fault detection time time notification The service is
Failure detected by the nearast node The protection path is deployed Data flow arrives at the destination node
failure
Hold-Off time Sending fault notification The service is
On the example shared protection: tl = 10 ms, tn = 20-30 ms, tc = 20-30 ms, tp = 0-30 ms, td = 50 ms, tR= 100-150ms
Traffic Recovery time
Shared protection (pre-planned)
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Dedicated protection Dynamic restoration 150 ms 0 ms 0 % 100 % 150 ms 0 ms 0 % 100 % 150 ms 0 ms 0 % 100 %
Protection: the restoration process (e.g. protection paths) is planned at connection setup Dynamic restoration: the restoration process is computed on-the-fly after failure
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1 2 3 4 7 5 8 9 6 1 2 3 4 7 5 8 9 6 fault
Link protection: local, loop back
1 2 3 4 7 5 8 9 6
fault fault
1 2 3 4 7 5 8 9 6
Segment protection: A good compromise Working path Path protection: global, efficient
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100%, fast No guarantee, slower pre-planned (protection) after failure event occures (restoration) link path segment link path segment dedicated shared dedicated shared dedicated shared Failure dependent Faiure independent (the faied element is unknown) Failure dependent Faiure independent (the faied element is unknown)
Different protection approaches from down to top (e.g. Dedicated Path protection or Failure Dependent Shared Link Protection)
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and along the protection path
– The destination node switches to protection path
redundancy)
S D
swithcing
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– The source and destination node switches to protection path
used for best effort traffic
– It is called „preemption”
S D
switching switching
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and destination nodes
– Better capacity efficiency – CON: slightly smaller availability
– Aw, Ap
– Aw1, Aw2, Ap
A=1-(1-Aw)(1-Ap)=Aw+Ap-AwAp A=Aw1Aw2+(1-Aw1)Aw2Ap+Aw1(1-Aw2)Ap
S D
– For single failure – For n=2 it is the bitwise XOR of the two working path
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Path 1 Path 2 B A B Failure A
Switch
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Working ring A B A B Failure Protection ring
Switch Switch
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defined in advance in the spare capacity of the network
links
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– On-cycle link
– Straddling links
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– Protects unit working bandwidth if the working path is routed along the cycle – Protects two units of working bandwidth if the working path traverses on a straddling link
– No spare capacity reservation along straddling links – Could be a lot of straddling links – Efficient bandwidth usage – Only two switching needed at recovery
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– They are built up in the optical control plane, but the switches are not configured
1 1 1 1 1 1 1 1 1
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Free capacity Spare capacity Working capacity Non-shareable Free capacity Shareable Working capacity
with W sw
j
link j link j
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10 10 5 5 10 10
spare working free
Single link SRLGs are considered!
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– In which SRLGs are they involved
SRLGs
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sl
j = non-sharable spare capacity
along link j, if the working path is in SRLGl
SRLG (Working edge involved)
Protection edges (all edges in the network) l. 3 1 ……….2 …..………………... 2 2 ……… 3……………….……. 1 2 .………5.……………………. 2 1 .………2……………………. 2 2 .………4……………………. 3 1 ……….2 …..………………... 2 2 ……… 3……………….……. 1 2 .………5.……………………. 2 1 .………2……………………. 2 2 .………4……………………. column
=
S
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Link l
=
S
20 10 10 10 10
link j
keep track of the network state after each failure
failed at a moment.
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Link l
=
S
20 10 10
Link j 10 5 5
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capacity on link j?
shareable spare capacity along link j if the working path is known?
– finding the maximum demand
the SRLGs traversed by W
,
max
j j l l SRLG
v s
=
S
,
max
W j j l l W
s s
SRLG edge
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W j j
v s
W j j j
f v s b
W j j
v s b
spare vj free fj working
W j j
v s b
W j j j
f v s b
shareable Non-shareable
W j
s
W
W j
h
BLOCK ADMIT
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Input: – G=(V,E) network topology
– free – spare
– s,t – source and destination (target) node of the connection – b – bandwidth of the demand – SRLGs – Spare provision matrix (not in dedicated protection) – Cost funtion on the edges
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– a working path (containing edges W) for the connection with capacity requirement b existing so that – a protection path (containing edges P) for the connection with capacity requirement b existing so that – path W and P are SRLG disjoint.
W i i i
,
max
W j j l l W
s s
spare (vj = sj + hj) working free (fj)
b f W j
j
:
link j
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– First step:
– Second step
sharing of the protection capacity on links of the protection route
protection route
involved
reserved for the protection path
– Use this value as the edge cost in the auxiliary graph
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system
– Reserve the working path, collect the affected columns of the spare capacity matrix meanwhile – Calculate the protection path – Reserve the protection path
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– “trap topology” (we have seen at Suurballe’s algorithm)
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– Better capacity efficiency – One-step reservation:
protection path
protection path
– In a distributed environment the source need to know the spare provision matrix – More complex problem!
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restoration strategy
different links is shareable
1 2 3 4 7 5 8 9 6
failure
Link Cons
Pros
RHE RTE
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Protection domain 2 Protection domain 2 Protection domain 1 a b c d e f g h i j k l
Splitting node
Switching node
– Efficient capacity usage – Fast recovery time
– Complex
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After the failure
– Localize the failure – Along the disrupted connections free up the reserved capacity (stub release) – Build up new protection paths – Multiple protection path belongs to a single connection (working path)
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Pros
Cons
precise failure localization
control plane after the failure
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– Shortest path is routed as the working path – No trap topology
– For each SRLG the working path is involved in a protection path is calculated
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– The corresponding column of the spare provision matrix contains the non-shareable capacity
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spare vj free fj working shareable non- shareable
, j l
s
W
, j l
h
b - ( vj – sj,l )
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Dynamic re-routing Path pre-computation Signaling Path Selection yes Signaled with Resource Reservation Resource Selection Resource Allocation (cross-connection) yes yes yes Pre-planned re-routing without Extra-Traffic Pre-planned re-routing without Extra-Traffic Pre-planned re-routing Protection (switching) no no no no a.k.a. path re-provisioning a.k.a. soft provisioned Recovery LSP setup (including activating) Recovery LSP Activation e.g. shared M:N e.g. 1:1, 1+1 e.g. Faiure dep. e.g. re- route
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Capacity savings Recovery time Computati
complexity Dedicated minimal even P Shared path ~25% medium NP-hard Failure dependent ~37% slow “really” NP-hard Shared segment ~34% fast “really” NP-hard
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s1 s2 t2 t1 w1 w2
U=(1-Aw1)(1-Aw2) What is the availability of connection s1 – d1?
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– We should know the order of failures!!!
s1 t2 t1 w1 w2
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– What we know about the order of the failure of the two paths?
e f c d a b MTTF1=100 MTTR1=10 MTTF2=10 MTTR2=1
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UP1 UP2
m1 l1 m
DW2 UP1
DW1 UP2 DW1 DW2
DW2 DW1
m1 m1 m2
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Approach to Connection Unavailability Estimation in Shared Backup Path Protection’
reliability”
techniques in WDM networks”
Ethernet’
Fast Reroute”
Network”