GE Multilin
Lentronics Multiplexers
SONET 101
Aman Mangat
Proprietary & Confidential to GE
Building the future together
What is SONET?
SONET = Synchronous Optical NETwork
Optical = This is a standard for optical
telecommunications. (Although some SONET
rates can be transported over microwave
radio.)
Synchronous = All terminals in a SONET
network are normally timed from the same
clock source.
Building the future together
2
What Preceded SONET?
Prior to SONET, digital transmission systems were generally
asynchronous, with each terminal running on its own clock.
North American Asynchronous Digital Transmission Hierarchy (PDH)
DS0
DS1
x 24
64 kb/s
DS2
DS3
x4
x7
x6
1,544 kb/s
6,312 kb/s
44,736 kb/s
24 DS0
channels
96 DS0
channels
672 DS0
channels
274,176 kb/s *
Asynchronous Multiplexing
The bit rates produced by devices running at nominally the same
rate could be slightly different (within specified range).
DS1: 1544 kb/s ± 50 ppm (±77 bits/sec)
DS3: 44,736 kb/s ± 20 ppm (± 895 bits/sec)
PDH = Plesiochronous Digital Hierarchy (Plesiochronous = Almost Synchronous)
* Not recognized by ITU-T
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Timing in Asynchronous System
f1A
T1A
R1B
R1A
T1B
fA
…
Site A
RB
RA
TB
…
fnA
TA
f1B
fB
TnA
RnB
RnA
TnB
Site B
fnB
Building the future together
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Timing in Synchronous System
T1
R1
R1
System
Clock
T1
fR
CLK
CLK
RB
RA
TB
…
…
TA
CLK
Tn
Rn
Rn
Tn
CLK
Site A
CLK
Site B
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Asynchronous vs. Synchronous
Asynchronous
Multiplexing
Synchronous
Multiplexing
Bit stuffing. During multiplexing,
extra bits are added to account
for bit rate variations.
No need for bit stuffing.
No “visibility” of lower order
signals in a higher-order
multiplex signal.
Full “visibility” of lower order
signals in a higher-order
multiplex signal.
Lower-order signals cannot be
Lower-order signals can be
accessed without demultiplexing. added/dropped without
demultiplexing of the higher
order signal.
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Asynchronous “Drop/Insert”
6,312 Mb/s
45 Mb/s
LTE
45
45
6
6
45 Mb/s
LTE
1,544 Mb/s
6
6
1.5
1.5
DS1 Terminal
Multi-stage multiplexing/demultiplexing
Multiplex equipment connected back-to-back
Building the future together
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Synchronous “Drop/Insert”
SONET
Optical
Aggregate
SONET Add & Drop
Multiplexer
SONET
Optical
Aggregate
DS1 Terminal
Single-stage multiplexing/demultiplexing
Complete add/drop functionality provided in
one box
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SONET Objectives
Eliminate need for multi-stage multiplexing
Provide optical interconnectivity in multi-vendor
environment (“mid-span meet”)
Enhance Operations, Administration, and Maintenance
(OAM)
Provide sufficient capacity for transmitting overhead
information
Create basis for efficient Network Management System
Come up with a universal multiplex signal structure
applicable to all (even future) SONET rates
Ensure scalability of bandwidth allocations to services
Position the network for transport of new services (ATM, IP,
Video…)
Ensure backward compatibility
Transparent for legacy PDH transport signals
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SONET Signal Hierarchy
STS Level
OC Level
Bit Rate
(Mbit/s)
# of DS1s
# of DS0s
STS-1
OC-1
51.84
28
672
STS-3
OC-3
155.52
84
2016
STS-12
OC-12
622.08
336
8064
STS-48
OC-48
2488.32
1344
32,256
STS-192
OC-192
9953.28
5376
129,024
STS = Synchronous Transport Signal
OC = Optical Carrier
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STS-1 Frame Format
810 bytes (125 µs)
STS-1 signal (51.84 Mbit/s)
3 columns
9 rows
Transport
Overhead
87 columns
STS-1 Envelope Capacity
125 µs
90 columns
Column width = 1 Byte (8 bits)
Building the future together
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STS-N Frame Format
Nx3 columns
N x 87 columns
9 rows
Transport
Overhead
STS-1 Envelope Capacity
125 µs
N x 90 columns
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SONET Multiplexing Hierarchy
10 Gb/s OC-192 STS-192
x4
2.5 Gb/s OC-48
x16
STS-48
x64
x4
622 Mb/s OC-12
STS-12
x4
155 Mb/s
OC-3
STS-3
x3
52 Mb/s
OC-1
STS-1
SPE
45 Mb/s
x7
VT-6
6 Mb/s
x3 VT-3
3 Mb/s
VT-2
2 Mb/s
VT Group
x2
x4
VT-1.5
1.5 Mb/s
Building the future together
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STS-1 Signal Structure
SONET
CLOCK
STS-1 or OC-1 (51.84 Mb/s)
TOH
}
3.3%
STS-1 Envelope Capacity
STS-1 SPE
(STS-1 Synchronous Payload Envelope)
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Sub-STS-1 Synchronous Signals
SONET
CLOCK
STS-1 SPE (≈
≈ 50 Mb/s)
STS-1 or OC-1 (51.84 Mb/s)
TOH
VT6 (1 x DS2)
VT3 (1 x DS1C)
STS-1 PAYLOAD
VT2 (1 xE1)
VT1.5 (1 x DS1)
1 x DS3 (or a broadband
tributary signal), or
1 x VT6, or
STS-1 SPE =
2 x VT3, or
VT-structured (7 x VT Groups)
VT Group
3 x VT2, or
4 x VT1.5
STS-1 SPE = 28 VT1.5 = 28 DS1s = 672 DS0 channels
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Sub-STS-1 Synchronous Signals
STS-1 SPE # 1
ATM
STS-1 SPE # 2
Ethernet
OC-12
STS-1 SPE # 3
DS3
VT1.5 # 1
STS-1 SPE # 12
VT1.5 # 2
VT1.5 # 28
Optical Level
STS-1 SPE Level
DS1
Ethernet
VT Level
DS0 # 1
DS0 # 2
DS0 # 24
RS-232
VF
Teleprotection
56/64k Data
DS0 Level
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SONET Layers
Terminal or ADM
Terminal or ADM
Regen.
VT
STS-1
SPE
Regen.
OC-N
OC-N
Section
Section
STS-1
SPE
VT
Section
Line
STS-1 Path
VT Path
VT … VT
VT VT VT
STS-1
SPE
VT … VT
VT VT VT
OC-3/STS-3
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STS-1 Frame Format
1
1
3
1
SECTION
OVERHEAD
3 rows
3
4
LINE
OVERHEAD
6 rows
87
P
A
T
H
O
V
E
R
H
E
A
D
90
STS-1 SPE
(Synchronous
Payload Envelope)
87 columns
PAYLOAD FORMATS
PAYLOAD FORMATS
9
125 µs
Transport
Overhead
3 columns
Payload
87 columns
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STS-1 Pointer
1
2
STS-1 Frame
3
90
0 µs
H1
H2
H3
J1
H1
H2
B3
C2
G1
F2
H4
Z3
Z4
N1
H3
STS-1 SPE
125 µs
STS-1 POH
250 µs
Transport Overhead
H1
STS Pointer:
N
N
N
N
H2
-
-
N = New Data Flag bit
Normal:
0
1
1
0
0
I
D
I
D
I
D
H3 byte
I
D
I
D
Negative Stuff Opportunity Byte
10-bit Pointer Value
0
Pointer Value (0-782 dec)
To indicate:
Positive Stuff
- Invert 5-I bits
Building the future together
Negative Stuff
- Invert 5-D bits
19
New pointer value - Invert NDF bits
Positive Justification
Pointer value = p
1
2
3
H1
H2
H3
STS-1 Frame
0 µs
Frame n
Positive Stuff Byte
Pointer value = “+”
90
H1
H2
H3
125 µs
Frame n+1
250 µs
Pointer value = p+1
H1
H2
H3
Frame n+2
375 µs
Building the future together
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Negative Justification
Pointer value = p
1
2
3
H1
H2
H3
STS-1 Frame
0 µs
Frame n
Negative Stuff Byte
Pointer value = “-”
90
H1
H2
H3
125 µs
Frame n+1
250 µs
Pointer value = p-1
H1
H2
H3
Frame n+2
375 µs
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Benefits of Pointer Use
Dynamic and flexible phase alignment of SPEs
Ease of dropping, inserting, and cross-connecting
payloads
Transparent transport of SPEs across network
boundaries with plesiochronous timing sources.
Accommodate transmission signal wander (low
frequency jitter).
Eliminate delays and loss of data associated with
use of large (125 µs frame) slip buffers for
synchronization.
Building the future together
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VT Superframe
VT1.5 Superframe
V1, V2
V3
V1
V4
Frame
1
125 µs
VT1.5 SPE (“VT Payload”)
- VT Payload Pointer bytes
- VT Pointer Action Byte
(Negative Stuff Byte)
- Undefined
VT Envelope Capacity
(excludes V1, V2, V3, V4 bytes)
V2
Frame
2
Asynchronous
Mapping of DS1
Byte-Synchronous
Mapping of DS1
V5
V5
R R R R R R I R
P1 P0 S1 S2 S3 S4 F R
24 Bytes
(192 I bits)
DS0 CHANNELS
1-24
J2
J2
C1 C2 0 0 0 0 I R
P1 P0 S1 S2 S3 S4 F R
24 Bytes
(192 I bits)
DS0 CHANNELS
1-24
Z6
Z6
VT SPE floats within
VT Envelope Capacity.
108
Bytes
250 µs
V3
C1 C2 0 0 0 0 I R
VT Payload Pointer (V1 and
V2 bytes) points to the start of
VT1.5 Payload).
Frame
3
375 µs
V4
Frame
4
500 µs
VT
POH
V5
J2
Z6, Z7
24 Bytes
(192 I bits)
DS0 CHANNELS
1-24
Z7
Z7
C1 C2 R R R S1 S2 R
P1 P0 S1 S2 S3 S4 F R
24 Bytes
(192 I bits)
DS0 CHANNELS
1-24
- VT Path Overhead byte 1
- Reserved for
VT Path Trace (future)
- Future use
VT Payload Capacity = VT SPE – VT POH
104
P1 P0 S1 S2 S3 S4 F R Bytes
500 µs
I
R
O
S
C
-
Information bit
Fixed stuff bit
Overhead bit
Stuff opportunity bit
Stuff control bit
P
S
F
R
-
Sig. Phase Indicator
Signaling bit
DS1 framing bit
Fixed stuff bit
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VT Pointer Bytes (V1 and V2)
V1
General:
N
N
N
N
V2
S
S
I
D
I
D
I
D
I
D
I
D
To indicate:
Positive Stuff - Invert 5-I bits
Negative Stuff - Invert 5-D bits
New Pointer Value - Invert NDF bits
10-bit Pointer Value
VT1.5:
0
1
1
0
1
1
0
0
0
Pointer Value (0-103 dec)
'6C'
S bits = VT Type (Size) Indication
SS
VT Type
VT Size
VT Pointer Range
00
VT6
428
0 - 427
01
VT3
212
0 - 211
10
VT2
140
0 - 139
11
VT1.5
108
0 - 103
V1, V2, V3, V4
VT SPE Size = VT Envelope Capacity = VT Superframe Size – 4
Building the future together
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VT Path Overhead Byte (V5)
V5
BIP-2
REI-V RFI-V
(FEBE)
Signal label coding:
ACRONYM
BIP-2
L1
L2
0
0
0
0
1
0
0
1
1
0
L3
0
1
0
1
0
RDI-V
(FERF)
Unequipped (unassigned)
Equipped – non-specific
Equipped – asynchronous mapping (DS1/E1/DS1C/DS2)
Bit-Synchronous Mapping of DS1/E1 (removed from standard)
Byte-Synchronous Mapping of DS1/E1
NAME
Bit Interleaved Parity
USAGE
Error Detection (used to calculate BER at receive end)
REI-V
VT Path Remote Error Indication
Info on errors detected in opposite signal direction (so far-end BER can be calculated)
RFI-V
RDI-V
VT Path Remote Failure Indication
VT Path Remote Defect Indication
Used in byte-synchronous DS1 mapping applications only
Status of signal received at transmit end (opposite signal direction)
(1 = ‘VT Yellow Alarm'; 0 = No ‘VT Yellow Alarm')
FEBE
FERF
Far End Block Error
Far End Receive Failure
Building the future together
25
0 µs
VT1.5 Superframe
Example with
Byte-Synchronously
mapped payload
capacity
Bit: 1
1
1
1
1
2
1
1
1
1
3
1
1
1
1
4
1
1
1
1
5
1
1
1
1
6
1
1
1
1
7
0
0
1
1
8
0
1
0
1
Next Frame
1
2
3
4
H4 = 1
V1
CH 24
Z6
PPSSSSFR
= ‘6C’ (hex)
CH1
...
CH23
125 µs
V2
H4 = 2
CH 24
Z7
PPSSSSFR
CH1
...
CH23
250 µs
104-Byte
VT Payload
(excludes V1…V4)
VT
Payload
Offset
(e.g. 27)
V3
CH 24
H4 = 3
V5
PPSSSSFR
CH1
...
CH23
H4 Byte* Coding Sequence
375 µs
H4 = 4
* H4 Byte is an STS-1 POH Overhead byte.
= Pointer
V4
CH 24
J2
PPSSSSFR
104-Byte
VT Payload
(excludes V1…V4)
CH1
...
CH23
500 µs
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VT1.5 Frame within STS-1 SPE Frame*
VT1.5
1
2
3
4
.
.
.
27
bytes
27
1
2
3
J1
B3
C2
VT
G1 1.5
F2 1 2
H4
Z3
Z4
N1
STS-1
POH
4 ...
3
125 µs
1
4
2
5
3
6
.
.
.
.
.
.
.
.
.
25
26
27
... 29 30 31 32 33 ...
... 58 59 60 61 62 ...
R
R
R
R
28 R 1 2 3
R
R
R
R
R
R
R
R
28 R 1 2 3
R
R
R
R
Fixed
Stuff
... 87
Columns
28
Fixed
Stuff
*Carrying only VT1.5s
Building the future together
27
VT1.5 Superframe within STS-1 signal
1
2
STS-1 Frame
3
VT#3 - Column 1
(STS-1 SPE Column#4)
VT#3 - Column 3
(STS-1 SPE Column#62)
VT#3 - Column 2
(STS-1 SPE Column#33)
90 0 µs
H1 H2 H3
H1 H2 H3
H1 H2 H3
H1 H2 H3
H1 H2 H3
J1
V1
78
79
B3
80
81
82
C2
83
84
85
G1
86
87
88
F2
89
90
91
H4
92
93
94
Z3
95
96
97
Z4
98
99
100
N1
101
102
103
J1
V2
0
1
B3
2
3
4
C2
4
6
7
G1
8
9
10
F2
11
12
13
H4
14
15
16
Z3
17
18
19
Z4
20
21
22
N1
23
24
25
J1
V3
26
27
B3
28
29
30
C2
31
32
33
G1
34
35
36
F2
37
38
39
H4
40
41
42
Z3
43
44
45
Z4
46
47
48
N1
49
50
51
J1
V4
52
53
B3
55
55
56
C2
57
58
59
G1
60
61
62
F2
63
64
65
H4
66
67
68
Z3
69
70
71
Z4
72
73
74
N1
75
76
125 µs
250 µs
375 µs
500 µs
77
Building the future together
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STS-1 POH
625 µs
Multiplexing of VTs into STS-1 SPE
VT1.5
1
1
3
9 rows
VT2
4
A
B
9 rows
C
A
X
x1
27
36
54
108
x7
C
D
O
VT Group 2
3 x VT2
X
B
B
M
X
Y
D
Y
12
x2
C
D
VT6
1
x3
A
B
6
x4
VT Group 1
4 x VT1.5
A
VT3
1
Y
Z
C
N
O
Z
D
M
O
X
X
VT Group 4
1 x VT6
VT Groups
5, 6, 7
X
Y
Z
Z
Y
O
M M M M M M
N N N N N N
x7
Y
A
N
VT Group 3
2 x VT3
x7
OOO OOO OOO OOO
x7
Z
B
M
O
Z
C
N
O
X
D
M
Y
O
A
N
Z
O
B
M
X
O
C
N
Y
O
D
M
O
Z
N
O
STS-1 SPE
9 rows
123
STS-1 POH
9
16
23
30 31
Fixed Stuff
38
45
52
59 60
67
74
81
87
Fixed Stuff
Building the future together
29
TOH and STS POH Structure
Section
Overhead
Line
Overhead
Framing
A1
BIP-8
B1
Data Com
D1
Pointer
H1
BIP-8
B2
Data Com
D4
Data Com
D7
Data Com
D10
Sync
S1
Framing
A2
Orderwire
E1
Data Com
D2
Pointer
H2
APS
K1
Data Com
D5
Data Com
D8
Data Com
D11
REI-L
M0
Trace
J0
User
F1
Data Com
D3
Ptr Action
H3
APS
K2
Data Com
D6
Data Com
D9
Data Com
D12
Orderwire
E2
Transport Overhead
STS
Path
Overhead
Trace
J1
BIP-8
B3
Signal Lab.
C2
Path Status
G1
User Chan.
F2
Multiframe
H4
Growth
Z3
Growth
Z4
Tand.Conn.
N1
STS-1 SPE
Building the future together
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SONET Network Elements
Terminal Multiplexer
Tributaries
TM
SONET
Aggregate
SONET Aggregate/Tributary
Async (PDH) Tributary
or Wide/Broadband
Service (Ethernet, ATM
etc.)
Add/Drop Multiplexer
ADM
SONET
Aggregate
Thru-Traffic
Tributaries
SONET
Aggregate
Building the future together
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SONET Network Elements
Wideband Digital Cross-Connect (W-DCS)
VT Switch
VT1.5
VT1.5
DS1
DS3
STS-N
VT1.5
VT1.5
DS1
DS3
DS1
Cross-Connects at
VT level
Broadband Digital Cross-Connect (B-DCS)
STS-1 Switch
STS-N/ STS-1/
STS-nC STS-nC
STS-1 STS-1
DS3
Broadband
Service (e.g. ATM)
Cross-Connects at
STS-1 level
DS1
Building the future together
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SONET Network Elements
Cross-Connect Functions
Traffic Consolidation
DCS
Traffic Segregation
DCS
DCS
Add/Drop
Flexible Routing
DCS
Building the future together
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SONET Network Elements
Regenerator
Needed when, due to
long fiber distance, the
optical signal level
becomes too low.
REG
Digital Loop Carrier (DLC)
(For telco’s & carriers only)
DS0
…
CO
Switch
Integrated
Digital
Terminal
OC-1
or
OC-3
A concentrator for narrowband services between
subscribers, remote digital
terminals and Central
Office switches.
Remote
Digital
Terminal
DS0 Subscribers
Building the future together
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SONET Network Topologies
Point-to-Point Topology
TM
TM
SONET Aggregate
Async (PDH) Tributary
TM
Terminal MUX
ADM Add/Drop MUX
Linear Add/Drop Topology
TM
ADM
ADM
TM
Building the future together
35
SONET Network Topologies
Hub Network
ADM
ADM
ADM
ADM
ADM
DCS
ADM
ADM
ADM
TM
DCS = Digital CrossConnect System
ADM
ADM
TM
Building the future together
36
SONET Network Topologies
Ring Network
ADM
ADM
ADM
ADM
Building the future together
37
SONET Network Topologies
Multiple Ring Network
ADM
ADM
ADM
ADM
ADM
ADM
ADM
ADM
ADM
Two tie points
(“Matched Nodes”)
Single tie point
ADM
ADM
ADM
ADM
ADM
ADM
ADM
ADM
ADM
Building the future together
38
SONET Network Topologies
“Combined” Network
ADM
TM
TM
ADM
ADM
ADM
ADM
ADM
DCS
ADM
ADM
ADM
ADM
ADM
TM
ADM
ADM
ADM
TM
ADM
ADM
TM
ADM
Building the future together
39
Automatic Protection Switching
Requires presence of alternate route
Criteria for making the switching decision
include:
AIS
Loss of pointer
Bit-error ratio
Path label set to “Unequipped”
– STS POH: C2 byte
– VT POH: Bits 5-7 of V5 byte
Remote Defect Indication (to prevent
asymmetric delays)
Building the future together
40
Automatic Protection Switching
Linear Protection mechanisms
1+1
W
No APS protocol
required
P
1:1
W
P
1:N
APS protocol
required. May
carry additional
traffic in “P”.
W
W
P
APS protocol
required. May
carry additional
traffic in “P”.
Building the future together
41
Automatic Protection Switching
Bidirectional Line Switched Ring (BLSR)
OC-48
OC-48
24 Working STS-1 Channels
24 Protection STS-1 Channels
Building the future together
42
Automatic Protection Switching
Unidirectional Path Switched Ring (UPSR)
OC-48
OC-48
Building the future together
43
RDI: Remote Defect Indication
A
VT#1
Standby Signal Path
Online Signal Path
OC-48
VT#1
C
B
Building the future together
44
C
RDI: Remote Defect Indication
A
VT#1
Symmetrical
Standby Signal Path
Symmetrical
Online Signal Path
OC-48
VT#1
LOS
C
B
Building the future together
45
C
RDI: Remote Defect Indication
A
VT#1
OC-48
VT#1
LOS
C
B
AIS
Building the future together
46
C
RDI: Remote Defect Indication
Asymmetrical
Signal Path
A
VT#1
OC-48
VT#1
LOS
C
B
AIS
Asymmetrical
Signal Path
Building the future together
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C
RDI: Remote Defect Indication
RDI Enabled
A
VT#1
OC-48
VT#1
LOS
C
B
AIS
RDI Enabled
Building the future together
48
C
RDI: Remote Defect Indication
RDI Enabled
A
VT#1
OC-48
VT#1
LOS
C
B
AIS
RDI Enabled
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C
RDI: Remote Defect Indication
Symmetrical
Signal Path
RDI Enabled
A
VT#1
OC-48
VT#1
LOS
C
B
AIS
RDI Enabled
Symmetrical
Signal Path
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Automatic Protection Switching
BLSR
UPSR
Main Characteristics
One half of each hop’s capacity is
used for working traffic; other half for
protection. Only working path for
each bidirect. circuit is provisioned.
Each tributary signal mapped is sent
both ways around the ring. At the
demapping point, the better of the
two receive paths is chosen.
Type of switching
Line layer (revertive or non-revertive).
Both directions are switched
simultaneously.
Path layer (revertive or non-revertive).
Each direction is switched
independently.
APS protocol
Yes (K1 & K2 bytes). Rather complex
protection switching mechanism
limits the number of nodes to 16.
No. (Simple implementation.)
Switch completion time (in addition to
problem detect time of max 10 ms)
Close to 50 ms.
Typically less than 10ms.
Cost
Generally less expensive than UPSR.
Generally more expensive than BLSR
(more hardware).
Maximum total amount of traffic in
ring
Depends on traffic matrix. Generally
higher than in UPSR rings.
Does not depend on traffic matrix.
Limited to “hop capacity”.
Potential for asymmetric delay
No
Yes, but can be addressed by use of
“Switch on RDI” function.
Able to carry additional* traffic?
Yes
No (Not/Applicable)
Typical use
Core networks
Access networks and some core
networks.
* Additional traffic is lost in case of any hop failure.
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SONET Benefits
Single-stage multiplexing
No need for back-to-back multiplexing
Simple add/drop functionality
Simple implementation of linear and ring configurations
Scalability of bandwidth allocation to various services.
Reduced end-to-end delays (thanks to pointers)
Traffic grooming (consolidation/segregation)
More efficient use of facilities
Ability to interconnect different vendors’ equipment
optically (“mid-span meet”)
Powerful Network Management System
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Are all SONET products acceptable
for utilities?
Can it operate in harsh environment?
Does it implement a fast enough protection switching mechanism?
(Important for mission critical applications.)
Can the protection switching mechanism ensure the same delay for
both directions of a bidirectional circuit regardless of the ring failure
type? (Some relays are sensitive to “asymmetric” delays.)
Does the overall solution provide acceptable end-to-end delays for
mission critical applications?
Is the implemented redundancy and related system availability
acceptable?
Does NMS cover all equipment in the system? (May be an issue if
multiple vendor equipment is used, if “access” and “transport” are
separated etc.)
Can it support switching to alternate traffic routing for backup
control center implementations (if required)?
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