Post on 30-Dec-2015
SONET
What is SONET?
• Synchronous Optical Network standard
• Defines a digital hierarchy of synchronous signals
• Maps asynchronous signals (DS1, DS3) to synchronous format
• Defines electrical and optical connections between equipment
• Allows for interconnection of different vendors’ equipment
• Provides overhead channels for interoffice OAM&P
SONETNetworkElement
SONETNetworkElement
DigitalTributaries
DigitalTributaries
Asynchronous Vs Synchronous
• Assume Maximum Clock Rate• Bit-Stuff As Required
• Assume Maximum Clock Rate• Bit-Stuff As Required
DS-M
DS-(M+1)
Asynchronous (aka Plesiochronous)
ooo
• Use Network Clock Rate• Use Pointers To Find Payload
• Use Network Clock Rate• Use Pointers To Find Payload
SONETVT1.5 OrSTS-M
STS-N(M < N)
ooo
Digital Signal HierarchiesMost Common Rates
Asynchronous
SONETVT1.5(1.7 Mb/s)
STS-3(156 Mb/s)
STS-12(622 Mb/s)
STS-48(2500 Mb/s)
28 84 336 1344Capacity
(DS-1 Equiv)
DS-1(1.544 Mb/s)
STS-1(52 Mb/s)
[Non-Standardized]
STM-1 STM-4 STM-16 SDH
DS-0(64 Kb/s)
VC-11 VC-3
DS: Digital SignalSONET: Synchronous Optical NETwork (US)SDH: Synchronous Digital Hierarchy (ITU)STS: Synchronous Transport SignalSTM: Synchronous Transfer ModeVC: Virtual ContainerVT: Virtual Tributary
DS-3(45 Mb/s)
SONET Rates
STS-1 OC-1 51.840
STS-3 OC-3 155.520
STS-12 OC-12 622.080
STS-48 OC-48 2,488.320
STS-192 OC-192 9,953.280
Level OpticalDesignation
Bit Rate(Mb/s)
STS = SYNCHRONOUS TRANSPORT SIGNALOC = OPTICAL CARRIER (“..result of a direct optical conversions of the STS after synchronous scrambling” - ANSI)
SONET Network Layers
DS3etc
DS3etc
Path • Map Services & POH Into SPE• Path Protection/Restoration • Other Path OA&M Functions
Line • Combine SPE & LOH• Sync & Mux For Path Layer• Line Protection/Restoration• Other Line OA&M Functions
Section • Add SOH & Create STS Signal• Framing, Scrambling• Section OA&M Functions
Physical(Photonic)
• E/O Conversion• Line Code• Physical Signal[No additional overhead]
MUX LTE Regen MUXLTELTERegen
ServicesDS3, DS1, etc
SONET ADM
Path
Line Line
SectionSection Section Section
Case Study: Two Path Layer Processors are Exchanging DS3s
SONETTerminal
STS-1OC-1
SONETTerminal
STS-1OC-1
RegenMux Mux
SectionSection
Line
Path
PTE PTE
LTE LTE
Map services & Path Over-Head into SPE
Map SPE & Line Over-Head into STS-N
Map STS-N & SectionOverhead into “Pulses”
Optical Conversion
Terminal TerminalRegen
Path
Line
Section
Photonic
Functional Description of SONET Layers
OH: Overhead
Path Layer
Line Layer
SectionLayer
PhotonicLayer
Information Payload
PathOH
LineOH
SectionOH
E/O Conversion
Transmission over OC-N
Function
Payload MappingError Monitoring
SynchronizationMultiplexingError MonitoringLine MaintenanceProtection SwitchOrder Wire
FramingScramblingError MonitoringSection MaintenanceOrderwire
E/O ConversionPulse ShapingPower LevelWavelenght
SONET STS-1 Frame Structure
SynchronousPayloadEnvelope
(SPE)
TOH
Ptr
87Bytes
3Bytes
SPE
87 Columns
POH
9Rows
87Bytes
3Bytes
t
t
FIxed
Stuff
FIxed
Stuff
Efficiencies
Mb/sec % STS1STS1 51.84 100%SPE (87 col) 50.11 96.67%SPE (84 col) 48.38 93.33%DS3 43.23 86.30%672 DS0’s 43.00 82.96%
POH
STS-1 Payloads1
VT1.5(1.7 Mb/sec)
DS-1(1.544 Mb/sec)
27
3 Columns
4 columns
VT Group(12 Columns)
x 4
VT2(2.3 Mb/sec)
6 columnsVT3(3.5 Mb/sec)
12 columnsVT4(6.9 Mb/sec)
VT Group(12 Columns)
VT Group(12 Columns)
VT Group(12 Columns)
x 3
x 2
SPE(84 Usable Columns)
SubSTS-1
Mappings
90 Total Columns
POH
Ctl&
StuffInformation
Stuff
Ctl&
StuffInformation
Stuff
Ctl&
StuffInformation
3 2528 Columns
3 2528 Columns
3 2528 Columns
DS-3
STS-1 Overhead Structure
SectionOH
A1 A2 J0
B1 E1 F1
D1 D2 D3
H1 H2 H3
D4 D5 D6
D7 D8 D9
D10 D11 D12
Z1 Z2 E2
B2 K1 K2
Framing STS1 ID
BIP-8(previous frame)
Orderwire(64 kb/sec) User Channel
DataComm ( 192 kb/sec)
Pointer Action
BIP-8(previous LOH+SPE)
ProtSwitching
DataCom(576 kb/sec)
NESync
FEBE Orderwire(64 kb/sec)
LineOH
Transport Overhead(3 Columns)
J1
B3
C2
G1
F2
H4
Z3
Z4
Z5
Path Overhead(1 Column)
Path Trace(multi-frame)
BIP-8
Signal Label
Path Status
User Channel
Indicator(multi-frame)
Growth
Growth
0 - 2 BytesFor Sync
IdentifiesSource of Sync
Eg, CLLI Code
BIP-8: Bit Interleaved Parity-8 (each bit set to give even parity over same-positioned bits)
SPE Type:• DS3• ATM• VT-Structured• Unequipped• Etc
• Path FEBE (4 bits)• RDI-P (4 bits) showing
• AIS-P• LOP-P
SPE Type-Dependent
Growth
FEBE: Far End Block Error (Count of BIP-8 Errors On Reverse Channel)
AIS-L
STS-N And STS-Nc(N = 3, 12, 48)
• STS-N• Formed By Byte-Interleaving N STS-N Signals• 3N Columns of Transport Overhead
• Frame Aligned• Redundant Fields Not Used - eg APS, Datacomm
• N Distinct Payloads (87N Bytes)• NOT Frame Aligned• N Columns Of Path Overhead - All Used• 2N Columns Of Fixed Stuff Bytes• 84N Columns Of Information
• STS-Nc• 3N Columns of Transport Overhead
• Frame Aligned• Redundant Fields Not Used - eg APS, Datacomm
• Single Payload• 1 Column Of Path Overhead• 3/N - 1 Columns Of Fixed Stuff Bytes• 87N - 3/N Columns Of Information
STS-1, STS-3, & STS-3c
TOH
POH
125 sec
TOH
POH
125 sec
TOH
POH
125 sec
POH
POH
POH
TOH
125 sec
POH
TOH
125 sec
STS-1
STS-3c
STS-3
Layering Application Bellcore Approach
A
B
C D
E
Trunks(DS1 = 24 Trunks)4E 4E
4E 4E
A
B
CD
DS3 or OC3
A
D
E
OC-48
A
B
C D
E
Switched
Cross-Connect
Multiplex
Photonic
LAYER
B
C
DCSDCS
DCS
DCS
DCS
ADMADM
ADM
ADM
ADM
ADM ADM
DS1
DS3/OC3
OC48
CustomerService Requests
Pt-Pt Traffic(Erlangs)
DS1 Private Line
DS3/OC3/OC12Private Line
[OC48Private Line]
Generic SONET Network Elements
ooo
ooo
STS-NPorts
STS-NPorts
STS-MFabric(M<N)
o o o
STS-MPorts
M:NDigital Cross-Connect System
(DCS)
STS-MFabric(M<N)
o o o
STS-MPorts
M:NAdd/Drop
Multiplexer(ADM)
STS-N
o o o
STS-MPorts
W E
STS-N
STS-N
M:NMultiplexer
(aka “End Terminal”)
SONET Configurations
Key SONET Configurations
48 S
48 P
PointTo
Point
• Compatible With OLS• 2 Nodes Per System• All T3’s Use DACS III• 1x1 Protection Switching
• Compatible With OLS• 2 To 16 Nodes• Add/Drop Multiplexing (“Tributary Add/Drop”) - Only DS3’s Changing Routes Or Terminating Use DACS III• 1x1 Protection Switching
48 S
48 P
DACSIII
DCSIII
ADM
ADM ADM ADM
ADM ADM
48 S
48 P
All DS3’s All DS3’s
48 S
48 P
ET: End TerminalADM: Add/Drop Multiplexer
ET
ET ET
ET
ET ET
ET ET
Key SONET ConfigurationsLinear Office Sequences
ET IIIPoint
ToPoint
LinearAdd/Drop
(“Open Ring”)
o o o IIIET ET IIIET ETIII ET IIIET ETETIII
N Offices• 2 End Offices• N-2 Interior Offices
ET
IIIIII ETADM ADMET ADM ADM o o o
Key SONET Configurations
III III III
IIIIII
PointTo
Point
ClosedRing
S
P
• Compatible With OLS• 2 Nodes Per System• 1x1 Protection Switching, • DACS III - Based Restoration
• Compatible With OLS• 2 To 16 Nodes - End Terminals At Ends, ADM’s Elsewhere• Add/Drop Multiplexing (“Tributary Add/Drop”)• 1x1 Protection Switching,• DACS III-Based Restoration At Ends & Add/Drop Points Only
• Compatible With OLS• 2 To 16 Nodes• Add/Drop Multiplexing (“Tributary Add/Drop”)• 1x1 Protection Switching• Ring Loopback Protection Switching• Must Be Of Uniform Size Around Entire Loop
DACSIII
ET ET ET ET
“MESH”“RING”
LinearAdd/Drop
(“Open Ring”)
DACSIII ADMET ET DACS
III
ADM ADM
ADM ADMADM
ET: End TerminalADM: Add/Drop Multiplexer
III
S
P
S
P
S P SP
S
P
S
P
S
P
S
P
SONET Network Management
SONET Ring APS (Automatic Protection Switching)
• Uni-directional Vs. Bi-directional Rings
• Two-Fiber Vs. Four Fiber Rings
• Ring Switching Vs. Span Switching
Applications of:• Bi-directional Line Switched Ring (BLSR)• Uni-directional Path Switched Ring (UPSR)
Definition of a RingA Ring is a collection of nodes (NE1, NE2, ….)
forming a closed loop. Each node is connected to two adjacent nodes
via a duplex communications facility.
A SONET Ring will provide:• Redundant Bandwidth
• Redundant Network Equipment• or both.
Ring Classification
• A Unidirectional Line Switched Ring (ULSR)• A Bidirectional Line Switched Ring (BLSR)• A Unidirectional Path Switched Ring (UPSR)• A Bidirectional Path Switched Ring (BPSR)
Any of the above type can be a two-fiber or a four fiber ring. Therefore, for all practical applications, SONET/SDH standards provide eight types of ring for network node interconnections.
Unidirectional Vs. Bidirectional Rings
C
BA
D
A B : 1
B A : 2 3 4
1
2
3
4
5
6
7
8
A - Unidirectional Ring
C
BA
D
A B : 1
B A : 5
1
2
3
4
5
6
7
8
B - Bidirectional Ring
Two-Fiber Vs. Four-Fiber Rings
C
BA
D
A
BWorking 1
Protection 2
Working 2
Protection 1
A - Two-Fiber Ring/Span
C
BA
D
A
BWorking 1
Protection 1
Working 2
Protection 2
B - Four-Fiber Ring/Span
Ring Switching 2-Fiber Ring
C
BA
D
Failure
Route before PS (Protection Switching)
A: Ring Switching: Two-fiber ring
50%
50%
50% - original+
50% - additional
50% - original+
50% - additional
Ring Switching 4-Fiber Ring
B: Ring Switching: Four-fiber ring
C
BA
D
Route before PS
Span Switching - 4-fiber Rings only
C
BA
D
Route before PS
B: Ring Switching: Four-fiber ring
A B
Route before PS
Route after PS
Bi-directional Line Switched RingNo Failures
CB
A
F
S
S
S
S
S
P
P
P
P
P
D
E
S
P
Original Circuit
A
B
C C
B
A
BidirectionalTraffic
UnidirectionalTraffic
SONET Add-Drop Multiplexer (ADM)Lucent FT-2000 LCT Example
)
OC-48 OC-48
OC-48 OC-48
STS-3Fabric
STS-3 Terminations (<= 4x16 = 64)
STS-3 STS-3STS-1/DS3
OC-48TerminatingEquipment
OC-48TerminatingEquipment
OC-48TerminatingEquipment
OC-48TerminatingEquipment
SERVICEWEST
PROTECTIONWEST
SERVICEEAST
PROTECTIONEAST
Bi-directional Line Switched RingSpan Switch
S
F
CB
S
S
S
S
P
P
P
P
P
D
E
S
P
X
A
Original Circuit
Protection Switch
SONET ADM Automatic Protection Switching
Lucent FT-2000 LCT Example
)
OC-48 OC-48
OC-48 OC-48
STS-3Fabric(60 msswitchtime)
STS-3 Terminations (<= 4x16 = 64)
STS-3 STS-3STS-1/DS3
OC-48TerminatingEquipment
OC-48TerminatingEquipment
OC-48TerminatingEquipment
OC-48TerminatingEquipment
SERVICEWEST
PROTECTIONWEST
SERVICEEAST
PROTECTIONEAST
Bi-directional Line Switched RingRing Switch
S
E
CB
A
F
S
S
S
S
P
P
P
P
P
D
S
P
Original CircuitRing Switch
X
SONET ADM Ring Protection SwitchingLucent FT-2000 LCT Example
)
OC-48 OC-48
OC-48 OC-48
STS-3Fabric(60 msswitchtime)
STS-3 Terminations (<= 4x16 = 64)
STS-3 STS-3STS-1/DS3
OC-48TerminatingEquipment
OC-48TerminatingEquipment
OC-48TerminatingEquipment
OC-48TerminatingEquipment
SERVICEWEST
PROTECTIONWEST
SERVICEEAST
PROTECTIONEAST
Ring Restoration Protocol
Reference: GR-1230-COREIssue 1, 12/93
1-4 5-8
Bridge Request Priority Destination Node ID
K1 K2
Sourcing Node ID
1-4 5S / L Completed Action
1111 LP-S Protection Lockout (span) or Signal Fail Of Protection(span)1110 FS-S Forced Switch (Span)1101 FS-R FS (Ring)1100 SF-S Signal Failure (Span)1011 SF-R Signal Failure (Ring)1010 SD-P Signal Degrade (Protection)1001 SD-S Signal Degrade (Span)1000 SD-R Signal Degrade (Ring)0111 MS-S Manual Switch (Span)0110 MS-R Manual Switch (Ring)0101 WTR Wait To Restore0100 EX-S Exerciser (Span)0011 EX-R Exerciser (Ring)0010 RR-S Reverse Request (Span)0001 RR-R Reverse Request (Ring)0000 NR No Request
0 Short Path1 Long Path
111 Line AIS110 Line RDI :010 Bridged and Switched)001 Bridged000 Idle
AIS = Alarm Indication SignalFS = Forced SwitchRDI = Remote Defect Indication
SF = Signal FailureSD = Signal DegradeFS = Forced Switch
4 bits 4 bits
Route Failure In Ring
F AD EP
RingBridge& Switch
XX
XS
P
X
RingBridge& Switch
SF-R/EF/L/Br&Sw
XSF-R/FE/L/Br&Sw
Detect Failureon Working & Protection
Detect Failureon Working & Protection
SF-R/EF/L/Idle
SF-R/FE/L/Idle
SF-R/EF/L/Idle SF-R/F
E/L/Idle
1
1
2
2
Bi-directional Line Switched RingRing Switch - Node Failure
F
CB
A
S
S
S
S
S
P
P
P
P
P
D
S
P
E xOriginal Circuit
Ring Switch
Bi-directional Line Switched RingNo Failures
CB
A
F
S
S
S
S
S
P
P
P
P
P
D
E
S
P
Original Circuits (Both Slot 2)
Bi-directional Line Switched RingNeed For Squelching
CB
A
F
S
S S
S
P
P
P
P
P
D
E
S
P
Original Circuits (Both Slot 2)x
• Requires Sharing of State Information• Significant Software Complexity
Bi-directional Line Switched RingDouble Ring Failure (No Recovery)
Original Circuit
Ring Switch
CB
A
F
S
S
S
S
S
P
P
P
P
P
D
E
S
P
X
X
SONET Rings will fail -- The question is “When?”
• Initial estimates of DWDM hardware show that it is 8 times more reliable than WDM equipment. – POEs not included
• Ring reliability is dependent upon ring mileage.– Ring sizes vary from 200 miles to 2800 miles.
• Ring Failures:– Given 100, 1000-mile perimeter rings:
• Current optimistic estimation is 1 network ring failure every 5 yrs.
• PCIs not included
– Most probable cause of a complete ring failure is an equipment failure and a fiber cut.
• Physical diversity violations in some rings (single-pt-of-failure).
Restoration Alternatives
Target Failure ModesRoute(Ring)
1 Fiber(Ring or
Pt-Pt)
Span Protection Switch
Ring Protection Switch
NominalResponse
Time
Yes
No
No
Yes
50 ms
100 ms
No
No
No
No
No
No
Total Ring
Ring Interconnect
Node
Access/EgressNode or ADM
MultipleRings
No
No
RingNode
No
Yes
Route(Pt-Pt)
No
No
Ring InterworkingInterconnect Problem (No Recovery)
A
C
BD
Z
E
D
S
S
S
S
S
P
P
P
P
P
Office X
S
S
S
S
S
P
P
P
P
PRing1
Ring2
X
Original Circuit
Failure
Dual Ring Interworking(Unidirectional A => Z Circuit)
No Failure
A
C
B
Z
E
D
S
S
S
S
S
P
P
P
P
P
Office X
Office Y
S
S
S
S
S
P
P
P
P
P
SS
Ring1
Ring2
v
v
v
v
v
v
v
Original CircuitSecondary (Inactive)
v
v
Dual Ring Interworking(Unidirectional A => Z Circuit)
ADM Failure
A
C
B
Z
E
D
S
S
S
S
S
P
P
P
P
P
Office X
Office Y
S
S
S
S
S
P
P
P
P
P
SS
Ring1
Ring2
v
v
v
v
XOriginal CircuitSecondary CircuitRing Switch
Dual Ring Interworking(Unidirectional A => Z Circuit)Office Or Double ADM Failure
E
v
A
C
B
Z
D
S
S
S
S
S
P
P
P
P
P
Office X
Office Y
S
S
S
S
S
P
P
P
P
PRing1
Ring2
SSXXOriginal CircuitSecondary CircuitRing Switch
DRI Capacity ImpactAll Transit Traffic Example
X
Y24
DS-3s Z
X
Y Z
48DS3s
48DS3s
48DS3s
(a) No DRI (b) With DRI (Secondary Channel On Service Capacity)
24DS3s
24DS3s
Restoration Alternatives
* If restoration capacity is available** Can help in a limited number of specific failure situations
Target Failure ModesRoute(Ring)
1 Fiber(Ring or
Pt-Pt)
Span Protection Switch
Ring Protection Switch
DRI
NominalResponse
Time
Yes
No
No
No
Yes
No
50 ms
100 ms
100 ms
No
No
Yes**
No
No
No
No
No
Yes
Total Ring
Ring Interconnect
Node
Access/EgressNode or ADM
MultipleRings
No
No
No
RingNode
No
Yes
No
Route(Pt-Pt)
No
No
No
Ring/Mesh Example - 1
40 T3
40 T3
40T3
40T3
BalancedDemands
1 OC48 (1x1)
1 OC48 (1x1)
1OC48(1x1)
1OC48(1x1)
1 OC48 (1x1)
1 OC48 (1x1)
1OC48(1x1)
1OC48(1x1)
ADM/DWDM $2.0M $2.0M $2.0MProtection Access 0 0.8 0.4
TOTAL $2.0 $2.8 $2.4
Ring/Mesh Ratio 0.72 0.83
RING Restn Restn 100% PMO
MESH
Ring Mesh
ADM
DACS III
ADM
DACS III
Svce Svce Prot
Note: DWDM Costs Prorated Per OC-48. No OA’s.
Ring/Mesh Example - 1
40 T3
40 T3
40T3
40T3
60 T3
40 T3
40T3
40T3
BalancedDemands
UnbalancedDemands
1 OC48 (1x1)
2 OC48 (1x1)
1OC48(1x1)
1OC48(1x1)
1 OC48 (1x1)
1 OC48 (1x1)
1OC48(1x1)
1OC48(1x1)
2 OC48 (1x1)
2 OC48 (1x1)
2OC48(1x1)
2OC48(1x1)
1 OC48 (1x1)
1 OC48 (1x1)
1OC48(1x1)
1OC48(1x1)
ADM/DWDM $2.0M $2.0M $2.0MProtection Access 0 0.8 0.4
TOTAL $2.0 $2.8 $2.4
Ring/Mesh Ratio 0.72 0.83
ADM/DWDM $4.0M $2.9M $2.9MProtection Access 0 0.9 0.6
TOTAL $4.0 $3.8 $3.5
Ring/Mesh Ratio 1.06 1.15
RING Restn Restn 100% PMO
MESH
RING Restn Restn 100% PMO
MESH
Ring Mesh
Note: DWDM Costs Prorated Per OC-48. No OA’s.
Ring/Mesh Example - 2
40 T3
40 T3
40 T3
40 T3
40 T3
40 T3
40 T3
Ring Mesh
OneExtra
1x1 OC-48
40T3
40T3
40T3
40T3
40T3
40T3
40T3
40T3
40T3
40T3
40 T3
40 T3
40 T3
Ring/Mesh Example - 3
Ring MeshNewRoute
Hybrid Network Concept
• Both Ring & Mesh Restoration Architectures Would Be Used
• Each OC-48 Would Be Either Ring Or Mesh Protected, But Not Both
• DWDMU Network Would Be Shared
• An Office Would Have A Mix Of Ring & Mesh OC-48’s, Depending On
Service Mix & Economics
Sample SONET Architecture
P
Circuit
DCS
DCS
48 S
48 S
48 P
48 P
48 P48 P
48 S
48 S
ADMADM
DCS
P
S
Circuit
DCS
DCS
SP
S
ADM ADM
DCS
Light Terminatingequipment
Restoration of DS-3 Services DS-3s services can be routed on all rings, all mesh, or
hybrid ring/mesh. Ring portion of DS-3:
– Restored by self-healing ring for multiple electrical or single optical/fiber failures, including fiber cuts.
– Backed up using DCS for multiple failure scenarios. Restoral is semi-manual and expected to take at least 20 min.
Mesh portion of DS-3:
– Restored via some “restoration platform”.
– Future restoration via the SONET DCS.
Sample T3 Architecture
T3
ADM
DCS
LGX
48 S
48 P
48 P48 P
48 S
48 S
48 S
48 P
ADM
ADMADM
DCS
DCS
ADM
P
S
LGX
DCS
P
S
P
S
T3Normal Service PathRing Restoration PathRestoration
DCS: Digital Cross Connect System
Sample SONET Architecture
P
Circuit
DCS
DCS
48 S
48 S
48 P
48 P
48 P48 P
48 S
48 S
ADMADM
DCS
P
S
Circuit
DCS
DCS
SP
S
Light Terminating Equipment
ADM ADM
DCS
P
Circuit
DCS
DCS
48 S
48 S
48 P
48 P
48 P48 P
48 S
48 S
ADMADM
DCS
P
S
Circuit
DCS
DCS
SP
S
Light Terminating
ADM ADM
DCS
P
Circuit
DCS
DCS
48 S
48 S
48 P
48 P
48 P48 P
48 S
48 S
ADMADM
DCS
P
S
Circuit
DCS
DCS
SP
S
ADM ADM
DCS
Other Types Of SONET Self-Healing Rings(2-Fiber Unidirectional Line-Switched Ring)
ADMA
ADMA
ADMADM ADMZ
ADMZ
ADMADM
Notes: Each Link Is Just 1 (1-Way) Fiber Transmission Directions Routed Differently
Ser
vice
Service
Ser
vice
Service
Pro
tect
ion
Pro
tect
ion
Protection
Protection
A=>Z
Z=>A
Z=>A
A=>Z
A=>Z
Z=>A
Other Types Of SONET Self-Healing Rings(2-Fiber Unidirectional Line-Switched Ring)
ADMA
ADMA
ADMADM ADMZ
ADMZ
ADMADM
Ser
vice
Service
Ser
vice
Service
Pro
tect
ion
Pro
tect
ion
Protection
ProtectionZ=>A
A=>Z
Z=>A
A=>Z
Z=>A
A=>Z
Other Types Of SONET Self-Healing Rings(2-Fiber Bi-directional Line-Switched Ring)
ADMA
ADMA
ADMADM ADMZ
ADMZ
ADMADM
Note: Each Link Uses 1 (1-way) Fiber Capacity On Each Fiber Divided Equally Between Service & Protection (2 “Logical Fibers”)
Serv
ice/
Pro
tect
ion
Service/Protection
Serv
ice/
Pro
tect
ion
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Service/Protection