NTNU Protection switching TTM1: Optical transport and access networks By Steinar Bjørnstad 2014

NTNU 21. aug. 2015Telenor2 IP restoration v.s. WDM protection..... Fumagalli et.al. l Components in a network may fail –Equipment ports and connections between client equipment and optical equipment –Optical layer hardware, transponders etc. –Fibre connections is known as the least reliable component. –Operator faults (Fingertrøbbel) at nodes, power failures with long duration

NTNU 21. aug. 2015Telenor3 Protection/Restoration l Several definitions may be found in the literature l Definition in this paper: l Restoration –Dynamically looks for backup paths of spare capacity in the network –Efficient from a capacity viewpoint l Protection –Reserves in advance dedicated backup-paths and wavelengths in the network –Faster than restoration

NTNU 21. aug. 2015Telenor4 Proposals for protection service classes l Lightpaths with guaranteed protection within a specific restoration time. l Lightpaths being protected at a best effort basis. l Lightpath not being protected. l Low priority lightpaths employing spare paths when these paths are not applied.

NTNU 21. aug. 2015Telenor5 Detection methods l IP layer (MPLS) Restoration –Periodic Internet Control Message Protocol (ICMP) messages Pinging Echo –Timers and Keepalive/Hello messages l SDH (protection) –Loss of sync. l Optical layer (WDM) –Loss of optical power (typical detection method) –Abnormal polarization variation (pre-detection) (curiosity).

NTNU Optical protection switching questions l Is protection at the optical layer sufficient? l How about failures in an Ethernet switch or interface? l Do we need protection at the optical layer? l What benefits does protection at the optical layer have?

NTNU 21. aug. 2015Telenor7 Protection schemes I l Individual lightpath – path –Protection of a single wavelength –Path layer, Optical Channel protection (OCh) –Require demultiplexing/multiplexing at every node for individual processing of wavelengths l Aggregated WDM signal - line –Line layer, Optical Multiplex Section (OMS) –Recover all lightpaths (wavelengths) on the failed line

NTNU 21. aug. 2015Telenor8 Protection schemes II l Dedicating resources –Dedicated protection (e.g. separate dedicated wavelength) –1+1 duplicating data, or 1:1, pre-empting low-pri. data –In context of rings these are called DPRings –Optical unidirectional path switched rings (OUPSRs), path (wavelength) –Optical unidirectional line-switched rings (OULSRs), line (a multiplex) l Shared protection –Protection resources shared between several lightpaths –1:N, requires signalling –In context of rings these are called SPRrings –Optical bidirectional path switched rings (OBPSRs), path (wavelength) –Optical bidirectional line-switched rings (OBLSRs), line (a multiplex)

NTNU 21. aug. 2015Telenor9 Dedicated versus shared protection l Dedicated Path Protection (DPP) –Reserved wavelength between end nodes for each path: Fast, simple, low resource utilization. l Dedicated Line Protection (DLP) –A spare line is standing-by Fast, simple, low resource utilization. l Shared path protection (SPP) –Protection wavelengths are shared, slower, more complex, efficient l Shared line protection (SLP) –1:N Protection, local line protection of faulty line –Better resource utilization than DLP –Faster than SPP because of local signaling

NTNU 21. aug. 2015Telenor10 Dedicated protection approaches in ring networks l Optical Unidirectional Path switched ring, OUPSR (DP- WSHR) –Two counter propagating paths (wavelengths) in a ring, one for working and one dedicated for protection l Optical Unidirectional Line-switched ring, OULSR –Two counter propagating lines (fibres) in a ring, one for working and one dedicated for protection, joint switching of wavelengths

NTNU 21. aug. 2015Telenor11 Ring protection approaches, shared l Shared-path WSHR Optical Bidirectional path-switched ring (OBPSR) or OCh shared protection ring (OCh/SPRing) –Non loop-back –Each working lightpath switched to protection lightpath at its source node l Bidirectional shared line-switched WSHR (SL-WSHR) OMS/SPRing –Two or four fibres. Working and protection in both directions, simple & fast –Employs loopback switching: Working lightpaths switched to counterpropagating protection lightpaths at failure end. Loopback at the other failure end

NTNU 21. aug. 2015Telenor12 Protection in mesh network (Also used in other networks) l 1+1 protection –Continuous signal on two alternative paths, choose the best. –Hitless protection switching possible (switching without loss) l 1:N protection –Several parties share a single common protection path. –Enables the path to be employed by low priority traffic when not in use. –Implies information loss because of switching. Data in the fibre is lost. Not hitless.

NTNU 21. aug. 2015Telenor13 Classification of resilience schemes WDM l Restoration –Dynamic lookup for backup paths, spare capacity in the network. Typical IP-layer. l Protection –Reserving dedicated backup paths in advance. Typical WDM layer.

NTNU 21. aug. 2015Telenor14 Fast protection l SONET/SDH –60/50 milliseconds for establishing a connection. –May avoid interruptions in a phone call. l Optical layer –2 micro – 60 milli seconds. –SONET detects errors within 2.3 – 100 micro seconds. Protection at higher layers may be initiated. l IP-layer –Slow detection, calculation and signalling, typically seconds. l MPLS –Relatively fast detection possible with HELLO messages, BUT the higher frequency of the messages, the higher the overhead. –Fast switching if pre-planned path, LSP.

NTNU 21. aug. 2015Telenor15 Overview protection times l Protection at different layers must be coordinated –Else, protection at multiple layers may result. l Power detection at optical layer may be applied by e.g. MPLS –Lower layer interface issues an alarm

NTNU 21. aug. 2015Telenor16 Protection tables l Precomputed –Several alternatives pr. lightpath is calculated and stored in advance. l Recomputed –Centralized unit calculates and distributes new protection path for every lightpath after each failure. l Working path Restoration (In IP context) –Heals failed path by using dynamic switching in OXCs l Single fault per protection domain –Decompose mesh network into smaller logical networks (ring- structures) –Allows multiple error handling, even if the mechanism do not handle multiple errors. –OXCs necessary only at borders between logical rings, OADMs sufficient elsewhere.