Dedicated and Shared Protection Dr. János 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 • Maintainability Simple • Efficient usage of network resources • We search for the best trade off – Efficiency vs. complexity 2
Dedicated Protection • For single connection 1 working + 1 protection path is allocated The two path are disjoint 1 1 1 1 2 1 1 The reserved capacity along the 1 1 common link is : A + B PRO: instantaneous recovery (no action is needed)
Shared Protection • If two working path is (SRLG) disjoint, the 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 The spare capacity along the 1 1 common link is : max{A,B} CONS: we need actions (signaling) after failure 4
Recover Time – The Tasks After Failure • 1st phase: Failure detection (depends only on the network architecture) • 2nd phase: Failure localization Failure management (isolation) ( t l ) • 3rd phase: Failure notification ( t n ) • 4th phase: Failure correlation ( t c ) • 5th phase: Fault restoration – Path selection ( t p ) – Device configuration ( t d )
Recovery Cycle Sending fault Data flow arrives at the notification destination node Hold-Off time Traffic Recovery time Recovery time Recovery operation (switching) time Fault detection Fault notification time time time notification failure The service is Failure detected by the The protection path is The service is operational nearast node deployed operational On the example shared protection: t l = 10 ms, t n = 20-30 ms, t c = 20-30 ms, t p = 0-30 ms, t d = 50 ms, t R = 100-150ms 6
Network resource usage vs. recover time Dedicated protection Shared protection Dynamic restoration (pre-planned) 150 ms 100 % 150 ms 100 % 100 % 150 ms R T R T T ? 0 % 0 % 0 ms 0 ms 0 ms 0 % 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 3
Link, Segment or Path Protection 1 2 3 1 2 3 6 fault 4 5 6 4 5 7 8 9 7 8 9 Working path Link protection: local, loop back 2 1 3 1 2 3 fault fault 4 5 6 4 5 6 8 7 9 8 7 9 Segment protection: Path protection: A good compromise global, efficient 8
Protection and restoration 100%, fast No guarantee, slower Different protection approaches from down to after failure event occures pre-planned top (e.g. Dedicated Path (restoration) (protection) protection or Failure Dependent Shared Link Protection) path path link link segment segment dedicated dedicated shared shared dedicated Failure dependent shared Faiure independent (the faied element is unknown) Failure dependent Faiure independent (the faied element is unknown) 9
Dedicated 1+1 Path Protection • Two signal is sent parallel along the working path and along the protection path • If the working path is interrupted by a fault – The destination node switches to protection path • Simple, high network resource usage (100% redundancy) R T swithcing D S 10
Dedicated 1:1 protection • We reserve two disjoint path for the connection • If the working path is interrupted by a fault – The source and destination node switches to protection path • In no failure state the protection route can be used for best effort traffic – It is called „preemption” R T switching switching D S 11
Dedicated 1:n Path Protection • There is n disjoint working path between the same source and destination nodes – Better capacity efficiency – CON: slightly smaller availability • What is the avalabiltiy of 1:1 protection? – A w , A p A=1-(1-A w )(1-A p )=A w +A p -A w A p • What about 1:2? S D – A w1 , A w2 , A p A=A w1 A w2 +(1-A w1 )A w2 A p +A w1 (1-A w2 )A p 12
Diversity Coding (DC) • Split the traffic into n sub data flows • Use coding techniques along the protection route – For single failure – For n=2 it is the bitwise XOR of the two working path • There are not many (short) disjoint paths in the network R T 13
Self healing rings – 1+1 dedicated path protection • Used in ring acces networks Switch Failure Path 1 B B Path 2 A A 14
Self healing rings – 1:1 dedicated link protection • Used inside a building/office Switch Failure Switch Working ring B B Protection ring A A 15
P-cycles • Shared Protection • Protection cycles are defined in advance in Amsterdam Hamburg London the spare capacity of Berlin Brussels Frankfurt the network Prague Munich Strasbourg • On-cycle and straddling Paris Zurich links Vienna Lyon • Only two switching Zagreb Milan R T Rome 16
P-cycles • Similar to Self-healing rings • Working path is routed along the shortest path • Failure occurs along – On-cycle link • Route the connection into the other direction – Straddling links • Decompose the working data into two parts 17
P-cycles • Unit bandwidth along the p-cycle – 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 • Pros: – No spare capacity reservation along straddling links – Could be a lot of straddling links – Efficient bandwidth usage – Only two switching needed at recovery • Two nodes along the cycle 18
Shared protection • Working path is reserved • Protection path are only calculated – They are built up in the optical control plane, but the switches are not configured • Soft-switching 1 1 • Shared protection • Backup multiplexing 1 1 1 1 1 1 1 19
Capacity on the edges link j link j Free capacity Free capacity with W Shareable Spare capacity s w Non-shareable j Working capacity Working capacity 20
Example Single link SRLGs are considered! 5 10 5 free 10 10 spare working 21 10
Calculation of the shareable spare capacity • Depends from the working paths SRLGs – In which SRLGs are they involved 22
Spare provision matrix SRLG (Working edge involved) column l . 3 1 ……….2 …..………………... 3 1 ……….2 …..………………... (all edges in the network) 2 2 ……… 3……………….……. 2 2 ……… 3……………….……. Protection edges j . row 1 2 .………5.……………………. 1 2 .………5.……………………. 2 1 .………2……………………. 2 1 .………2……………………. S = 2 2 .………4……………………. 2 2 .………4……………………. s l j = non-sharable spare capacity along link j , if the working path is in SRLG l 23
Spare Provision Matrix l. column j . row S = 10 10 • To obtain the matrix we need to 20 10 keep track of the network state after each failure link j 10 • With the single failure scenario, only one SRLG could possibly be failed at a moment. Link l 24
Spare Provision Matrix l. column j . row 0 10 5 20 10 10 0 5 0 S = Link j Link l 25
Spare provision matrix • How much is the spare capacity on link j ? v max s j j l , l SRLG SRLG • How much is the non- l. column shareable spare capacity along link j if the working path is known? j . row – finding the maximum demand of spare capacity among all S = the SRLGs traversed by W edge W s max s j j l , l W 26
Shared protection When a new demand arrives: • The whole capacity of working path need to be reserved • In the case of the protection path: W h shareable j W v s 0 W v s b W v s b j j j j j j free f j spare v j W W W f v s b f v s b Non-shareable j j j j j j working W s ADMIT BLOCK j 27
Routing in the case of shared protection Input: – G=(V,E) network topology • Capacity along links – 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 28
Routing in the case of shared protection • The following conditions have to hold for a solution in a network: – a working path (containing edges W ) for the connection with capacity requirement b existing so that j j W : f b – a protection path (containing edges P ) for link j the connection with capacity requirement b existing so that free (f j ) W s max s W f v s b j j l , i i i spare l W – path W and P are SRLG disjoint. (vj = s j + h j ) working 29
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