Transcript Synchronous Optical NETwork

SONET
What is SONET?
•
Synchronous Optical Network standard
SONET
Network
Element
Digital
Tributaries
•
•
•
•
•
SONET
Network
Element
Digital
Tributaries
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
Asynchronous Vs
Synchronous
DS-M
o
o
o
VT1.5 Or
STS-M
o
o
o
Asynchronous
(aka Plesiochronous)
• Assume Maximum Clock Rate
• Bit-Stuff As Required
DS-(M+1)
SONET
• Use Network Clock Rate
• Use Pointers To Find Payload
STS-N
(M < N)
Digital Signal Hierarchies
Most Common Rates
DS-0
DS-1
DS-3
(64 Kb/s)
(1.544 Mb/s)
(45 Mb/s)
28
[Non-Standardized]
84
336
Asynchronous
1344
Capacity
(DS-1 Equiv)
VT1.5
STS-1
STS-3
STS-12
STS-48
(1.7 Mb/s)
(52 Mb/s)
(156 Mb/s)
(622 Mb/s)
(2500 Mb/s)
SONET
VC-11
VC-3
STM-1
STM-4
STM-16
SDH
DS:
Digital Signal
SONET: Synchronous Optical NETwork (US)
SDH:
Synchronous Digital Hierarchy (ITU)
STS:
Synchronous Transport Signal
STM: Synchronous Transfer Mode
VC:
Virtual Container
VT:
Virtual Tributary
SONET Rates
Level
Optical
Designation
Bit Rate
(Mb/s)
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
STS
OC
= SYNCHRONOUS TRANSPORT SIGNAL
= OPTICAL CARRIER
(“..result of a direct optical conversions of the STS after
synchronous scrambling” - ANSI)
SONET Network Layers
Services
DS3, DS1, etc
Path
Line
Section
• Map Services & POH Into SPE
• Path Protection/Restoration
• Other Path OA&M Functions
Path
• 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 • E/O Conversion
(Photonic) • Line Code
• Physical Signal
[No additional overhead]
Line
Line
DS3
etc
MUX
LTE
Section
Regen
Section
Regen
SONET ADM
Section
LTE
LTE
MUX
DS3
etc
Case Study: Two Path Layer Processors are
Exchanging DS3s
Path
Line
SONET
Terminal
STS-1
OC-1
Section
Section
SONET
Terminal
Regen
Mux
Mux
PTE
STS-1
OC-1
PTE
LTE
LTE
Map services & Path OverHead into SPE
Path
Map SPE & Line OverHead into STS-N
Line
Map STS-N & Section
Overhead into “Pulses”
Section
Optical Conversion
Terminal
Photonic
Regen
Terminal
Functional Description of SONET Layers
Function
Path Layer
Line Layer
Section
Layer
Photonic
Layer
Information
Payload
Path
OH
Line
OH
Section
OH
E/O Conversion
Transmission over OC-N
Payload Mapping
Error Monitoring
Synchronization
Multiplexing
Error Monitoring
Line Maintenance
Protection Switch
Order Wire
Framing
Scrambling
Error Monitoring
Section Maintenance
Orderwire
E/O Conversion
Pulse Shaping
Power Level
Wavelenght
OH: Overhead
3
Bytes
SONET STS-1 Frame
Structure
87
Bytes
t
87 Columns
Ptr
t
T
O
H
P
O
H
Synchronous
Payload
Envelope
(SPE)
9
Rows
P
O
H
F
I
x
e
d
SPE
S
t
u
f
f
F
I
x
e
d
S
t
u
f
f
Efficiencies
Mb/sec
3
Bytes
87
Bytes
STS1
SPE (87 col)
SPE (84 col)
DS3
672 DS0’s
51.84
50.11
48.38
43.23
43.00
% STS1
100%
96.67%
93.33%
86.30%
82.96%
STS-1 Payloads
VT1.5
3 Columns
(1.7 Mb/sec)
1
x4
DS-1
VT Group
(12 Columns)
(1.544 Mb/sec)
4 columns
27
Sub
STS-1
Mappings
x3
VT2
(2.3 Mb/sec)
x2
VT3
(3.5 Mb/sec)
VT4
(6.9 Mb/sec)
SPE
(84 Usable
Columns)
VT Group
(12 Columns)
6 columns
VT Group
(12 Columns)
12 columns
VT Group
(12 Columns)
90 Total Columns
DS-3
P Ctl
O &
H Stuff
3
Information
25
28 Columns
S
t
u
f
f
S
Ctl
t Ctl
u
& Information
& Information
f Stuff
Stuff
f
3
25
28 Columns
3
25
28 Columns
STS-1 Overhead Structure
Transport Overhead
Path Overhead
(3 Columns)
(1 Column)
A2
A1
J0
Framing
Section
OH
B1
E1
BIP-8
STS1 ID
Orderwire
(previous frame)
D1
J1
(64 kb/sec)
D2
(multi-frame)
F1
B3
BIP-8
User Channel
D3
C2
Signal Label
DataComm ( 192 kb/sec)
H1
B2
Line
OH
BIP-8
K1
(previous LOH+SPE)
D5
D4
G1
H3
H2
Pointer
Path Status
Action
ProtK2
Switching
Path Trace
AIS-L
D6
F2
0 - 2 Bytes
For Sync
User Channel
H4
D7
DataCom
D9
Z3
D12
Z4
(576 kb/sec)
D11
D10
Z1
NE
Sync
Z2
E2
FEBE
Orderwire
(64 kb/sec)
Z5
Growth
Growth
Growth
Identifies
Source of Sync
BIP-8: Bit Interleaved Parity-8 (each bit set to give even parity over same-positioned bits)
FEBE: Far End Block Error
(Count of BIP-8 Errors On Reverse Channel)
SPE Type:
• DS3
• ATM
• VT-Structured
• Unequipped
• Etc
• Path FEBE (4 bits)
• RDI-P (4 bits) showing
• AIS-P
• LOP-P
Indicator
(multi-frame)
D8
Eg, CLLI Code
SPE Type-Dependent
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
P
O
H
P
O
H
125 m sec
TOH
125 m sec
TOH
STS-1
P
O
H
125 m sec
TOH
P P P
O O O
H H H
STS-3
125 m sec
TOH
P
O
H
STS-3c
125 m sec
TOH
Layering Application Bellcore Approach
LAYER
Switched
Customer
Service Requests
Pt-Pt Traffic
(Erlangs)
4E
Trunks
(DS1 = 24 Trunks)
4E
DCS DS3 or OC3 DCS E
DS1
Private Line
DCS
E
ADM OC-48
DS3/OC3/OC12
Private Line
ADM ADM
E
[OC48
Private Line]
DS1
B
DCS
DCS
D
DS3/OC3
B
ADM ADM
A
CADM
Photonic
4E D
A
C
Multiplex
4E
A
C
CrossConnect
B
ADM D
B
A
C
D
OC48
Generic SONET Network
Elements
STS-N
o
STS-N
o
Ports
o
W
STS-N
STS-M
Fabric
(M<N)
STS-N
E
o
o
o
STS-M
Fabric
(M<N)
o
o
o
o
o
o
o
o
o
STS-N
Ports
STS-M
Ports
STS-M
Ports
STS-M
Ports
M:N
Digital Cross-Connect System
(DCS)
M:N
Add/Drop
Multiplexer
(ADM)
M:N
Multiplexer
(aka “End Terminal”)
SONET Configurations
Key SONET Configurations
All DS3’s All DS3’s
48 S
Point
To
Point
48 S
ET
ET
DCS
III
48 P
ET
ET
48 P
ET
ET
ADM
ADM
48 P
48 P
DACS
III
ADM
•
•
•
•
Compatible With OLS
2 Nodes Per System
All T3’s Use DACS III
1x1 Protection Switching
48 S
48 S
ADM
ET
ET
ADM
• Compatible With OLS
• 2 To 16 Nodes
• Add/Drop Multiplexing
(“Tributary Add/Drop”) Only DS3’s Changing Routes Or
Terminating Use DACS III
ADM
• 1x1 Protection Switching
ET: End Terminal
ADM: Add/Drop Multiplexer
Key SONET Configurations
Linear Office Sequences
Point
To
Point
III
ET
ET
III
ET
ET
III
ET
ooo
ET
III
ET
ET
III
ET
ET
III
N Offices
• 2 End Offices
• N-2 Interior Offices
Linear
Add/Drop
(“Open Ring”)
III
ET
ADM
ADM
ooo
ADM
ADM
ET
III
Key SONET Configurations
S
Point
To
Point
S
ET
ET
DACS
III
ET
ET
P
Linear
Add/Drop
(“Open Ring”)
S
ET
DACS
III
ET
ADM
P
P
III
“MESH”
“RING”
S
ADM
ADM
III
P
III
III
P
ADM
III
III
S
P
ADM
ADM
S
ET: End Terminal
ADM: Add/Drop Multiplexer
• 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
S
P
Closed
Ring
Compatible With OLS
2 Nodes Per System
1x1 Protection Switching,
DACS III - Based Restoration
P
S
DACS
III
•
•
•
•
P
S
• 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
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 Ring
A 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
1
1
A
A
B
B
5
5
8
4
A B : 1
6
B  A : 2 3 4
2
8
4
A B : 1
7
C
3
A - Unidirectional Ring
2
B A: 5
7
D
6
D
C
3
B - Bidirectional Ring
Two-Fiber Vs. Four-Fiber Rings
A
B
A
B
D
C
D
C
Working 1
A
B
Working 1
Protection 2
Protection 1
Working 2
Working 2
Protection 1
A - Two-Fiber Ring/Span
A
B
Protection 2
B - Four-Fiber Ring/Span
Ring Switching 2-Fiber Ring
Route before PS (Protection Switching)
50%
Failure
A
50%
B
50% - original
+
50% - additional
D
A: Ring Switching: Two-fiber ring
50% - original
+
50% - additional
C
Ring Switching 4-Fiber Ring
Route before PS
A
B
D
C
B: Ring Switching: Four-fiber ring
Span Switching - 4-fiber Rings only
Route before PS
Route before PS
A
B
A
D
B: Ring Switching: Four-fiber ring
C
Route after PS
B
Bi-directional Line Switched Ring
No Failures
S
B
S
C
P
A
A
B
B
C
C
Bidirectional
Traffic
Unidirectional
Traffic
S
P
P
A
D
P
P
S
S
P
F
E
S
Original Circuit
SONET Add-Drop Multiplexer (ADM)
Lucent FT-2000 LCT Example
SERVICE
WEST
OC-48
OC-48
Terminating
Equipment
OC-48
Terminating
Equipment
STS-3
Fabric
OC-48
OC-48
Terminating
Equipment
SERVICE
EAST
OC-48
)
OC-48
Terminating
Equipment
OC-48
PROTECTION
EAST
PROTECTION
WEST
STS-3 Terminations (<= 4x16 = 64)
STS-3
STS-1/DS3
STS-3
Bi-directional Line Switched Ring
Span Switch
S
B
S
C
P
S
P
P
A
D
P
P
S
S
P
F
X
S
E
Original Circuit
Protection Switch
SONET ADM Automatic Protection
Switching
Lucent FT-2000 LCT Example
SERVICE
WEST
OC-48
OC-48
Terminating
Equipment
OC-48
Terminating
Equipment
SERVICE
EAST
OC-48
STS-3
Fabric
OC-48
OC-48
Terminating
Equipment
(60 ms
switch
time)
)
OC-48
Terminating
Equipment
OC-48
PROTECTION
EAST
PROTECTION
WEST
STS-3 Terminations (<= 4x16 = 64)
STS-3
STS-1/DS3
STS-3
Bi-directional Line Switched Ring
Ring Switch
S
B
S
C
P
S
P
P
A
D
P
P
S
S
P
F
X
S
E
Original
Circuit
Ring Switch
SONET ADM Ring Protection Switching
Lucent FT-2000 LCT Example
SERVICE
WEST
OC-48
OC-48
Terminating
Equipment
OC-48
Terminating
Equipment
SERVICE
EAST
OC-48
STS-3
Fabric
OC-48
OC-48
Terminating
Equipment
(60 ms
switch
time)
)
OC-48
Terminating
Equipment
OC-48
PROTECTION
EAST
PROTECTION
WEST
STS-3 Terminations (<= 4x16 = 64)
STS-3
STS-1/DS3
STS-3
Ring Restoration Protocol
K1
1-4
5-8
Bridge Request Priority
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 Restore
0100 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
AIS = Alarm Indication Signal
FS = Forced Switch
RDI = Remote Defect Indication
Reference: GR-1230-CORE
Issue 1, 12/93
K2
SF = Signal Failure
SD = Signal Degrade
FS = Forced Switch
Destination Node ID
4 bits
1-4
Sourcing Node ID
4 bits
5
S
/
L
Completed Action
0 Short Path
1 Long Path
111
110
:
010
001
000
Line AIS
Line RDI
Bridged and Switched)
Bridged
Idle
Route Failure In Ring
D
E
P
X
S
P
Detect Failure
on Working & Protection
X
F
A
X
Detect Failure
on Working & Protection
SF-R/F
E/L/Idle
X
SF-R/E
F/L/Idle
1
2
2
1
SF-R/E
F/L/Idle
SF-R/F
E/L/Idle
Ring
Bridge
& Switch
Ring
Bridge
& Switch
SF-R/F
E/L/Br&Sw
X
SF-R/E
F/L/Br&Sw
Bi-directional Line Switched Ring
Ring Switch - Node Failure
S
B
S
C
P
S
P
P
A
D
P
P
P
F
S
x
S
E
S
Original Circuit
Ring Switch
Bi-directional Line Switched Ring
No Failures
S
B
S
C
P
S
P
P
A
D
P
P
S
S
P
F
E
S
Original Circuits (Both Slot 2)
Bi-directional Line Switched Ring
Need For Squelching
B
S
C
P
S
P
• Requires Sharing
of State Information
• Significant Software
Complexity
P
A
D
P
P
P
F
S
x
S
E
S
Original Circuits (Both Slot 2)
Bi-directional Line Switched Ring
Double Ring Failure (No Recovery)
S
B
S
XP
C
S
P
P
A
D
P
P
S
S
P
F
X
S
E
Original Circuit
Ring Switch
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
Nominal
Response
Time
Target Failure Modes
1 Fiber
(Ring or
Pt-Pt)
Route
(Ring)
Route
(Pt-Pt)
Ring
Node
Total
Ring
Multiple
Rings
Ring
Access/Egress
Interconnect Node or ADM
Node
Span Protection Switch
50 ms
Yes
No
No
No
No
No
No
No
Ring Protection Switch
100 ms
No
Yes
No
Yes
No
No
No
No
Ring Interworking
Interconnect Problem (No Recovery)
S
S
B
D
D
S
P
S
P
P
P
Ring
1
A
P
S
S
Ring
2
P
Z
P
P
P
P
S
S
X
C
S
Office X
E
S
Original Circuit
Failure
Dual Ring Interworking
(Unidirectional A => Z Circuit)
No Failure
S
S
B
v
S
D
P
P
S
P
S
Ring
2
P
Z
v
Ring
1
P
P
P
v
v
P
SS
C
v
S
E
S
Office X
S
v
S
v
v
S
P
Office Y
P
A
v
Original Circuit
Secondary (Inactive)
Dual Ring Interworking
(Unidirectional A => Z Circuit)
ADM Failure
S
S
B
S
D
v
P
P
P
S
S
Ring
2
P
Z
v
v
P
Office Y
Ring
1
A
S
P
P
P
S
C
S
X
P
S
SS
Office X
E
S
v
P
Original Circuit
Secondary Circuit
Ring Switch
Dual Ring Interworking
(Unidirectional A => Z Circuit)
Office Or Double ADM Failure
S
S
B
S
D
P
Office Y
P
Ring
1
P
S
P
S
Ring
2
P
Z
P
P
P
S
XX
P
S
SS
C
S
Office X
E
S
v
A
S
P
Original Circuit
Secondary Circuit
Ring Switch
DRI Capacity Impact
All Transit Traffic Example
X
X
48
DS3s
48
DS3s
Y
48
DS3s
(a) No DRI
24
DS3s
Z
Y
24
DS3s
24
DS-3s
Z
(b) With DRI (Secondary Channel On Service Capacity)
Restoration Alternatives
Nominal
Response
Time
Target Failure Modes
1 Fiber
(Ring or
Pt-Pt)
Route
(Ring)
Route
(Pt-Pt)
Ring
Node
Total
Ring
Multiple
Rings
Ring
Access/Egress
Interconnect Node or ADM
Node
Span Protection Switch
50 ms
Yes
No
No
No
No
No
No
No
Ring Protection Switch
100 ms
No
Yes
No
Yes
No
No
No
No
DRI
100 ms
No
No
No
No
Yes**
No
Yes
No
* If restoration capacity is available
** Can help in a limited number of specific failure situations
Ring/Mesh Example - 1
Ring
40 T3
Balanced
Demands
40
T3
Mesh
1 OC48 (1x1)
1
OC48
(1x1)
40
T3
40 T3
1
OC48
(1x1)
1 OC48 (1x1)
1
OC48
(1x1)
1
OC48
(1x1)
TOTAL
$2.0
$2.8
0.72
$2.4
0.83
ADM
Svce
DACS III
ADM/DWDM
$2.0M $2.0M $2.0M
Protection Access
0
0.8
0.4
Ring/Mesh Ratio
1 OC48 (1x1)
ADM
Svce
MESH
RING Restn Restn
100% PMO
1 OC48 (1x1)
Prot
DACS III
Note: DWDM Costs Prorated Per OC-48.
No OA’s.
Ring/Mesh Example - 1
Ring
40 T3
Balanced
Demands
40
T3
1 OC48 (1x1)
40
T3
1
OC48
(1x1)
40 T3
40
T3
40
T3
60 T3
MESH
RING Restn Restn
100% PMO
1 OC48 (1x1)
1
OC48
(1x1)
1
OC48
(1x1)
1
OC48
(1x1)
1 OC48 (1x1)
1 OC48 (1x1)
2 OC48 (1x1)
1 OC48 (1x1)
ADM/DWDM
$2.0M $2.0M $2.0M
Protection Access
0
0.8
0.4
TOTAL
$2.0
Ring/Mesh Ratio
$2.8
0.72
$2.4
0.83
MESH
40 T3
Unbalanced
Demands
Mesh
2
OC48
(1x1)
2
OC48
(1x1)
2 OC48 (1x1)
1
OC48
(1x1)
RING Restn Restn
100% PMO
1
OC48
(1x1)
2 OC48 (1x1)
ADM/DWDM
$4.0M $2.9M $2.9M
Protection Access
0
0.9
0.6
TOTAL
Ring/Mesh Ratio
$4.0
$3.8
1.06
$3.5
1.15
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
40
T3
40 T3
40
T3
40
T3
40
T3
40 T3
Ring
40 T3
40
T3
40 T3
40
T3
40
T3
40
T3
40 T3
One
Extra
1x1 OC-48
Mesh
Ring/Mesh Example - 3
New
Route
Ring
Mesh
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
Circuit
DCS
DCS
48 S
ADM
ADM
48 P
48 P
48 S
S
48 S
P
48 P
48 P
ADM
ADM
48 S
DCS
Circuit
DCS
S
DCS
DCS
P
Light
Terminating
equipment
S
P
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
Normal Service Path
Ring Restoration Path
Restoration
DCS
LGX
48 S
ADM
ADM
48 P
48 P
48 S
P
48 S
48 P
S
48 P
ADM
ADM
48 S
DCS
T3
LGX
S
DCS
DCS
P
P
ADM
S
DCS: Digital Cross Connect System
Sample SONET Architecture
Circuit
DCS
DCS
48 S
ADM
ADM
48 P
48 P
48 S
S
48 S
P
48 P
48 P
ADM
ADM
48 S
DCS
Circuit
DCS
S
DCS
DCS
P
Light
Terminating
Equipment
S
P
Other Types Of SONET Self-Healing Rings
(2-Fiber Unidirectional Line-Switched Ring)
Service
A=>Z
A=>Z
ADM
A
ADM
Protection
Service
Service
Protection
Protection
Z=>A
A=>Z
Protection
ADM
Z=>A
Z=>A
Service
Notes: Each Link Is Just 1 (1-Way) Fiber
Transmission Directions Routed Differently
ADM
Z
Other Types Of SONET Self-Healing Rings
(2-Fiber Unidirectional Line-Switched Ring)
Service
A=>Z
A=>Z
ADM
A
ADM
Protection
Z=>A
Protection
ADM
Service
Service
Protection
Protection
Z=>A
A=>Z
ADM
Z
Z=>A
Service
Other Types Of SONET Self-Healing Rings
(2-Fiber Bi-directional Line-Switched Ring)
Service/Protection
ADM
A
ADM
Service/Protection
ADM
Service/Protection
Note: Each Link Uses 1 (1-way) Fiber
Capacity On Each Fiber Divided Equally Between Service & Protection
(2 “Logical Fibers”)
ADM
Z
Service/Protection
Service/Protection
Service/Protection
Service/Protection
Service/Protection