Telecommunication Networks Group Technische Universität Berlin Synchronous Digital Hierarchy Synchronous Optical Network SDH/SONET Filip Idzikowski Hagen Woesner Berlin, 31.05.2007
Telecommunication Networks GroupTechnische Universität Berlin
Synchronous Digital HierarchySynchronous Optical NetworkSDH/SONET
Filip IdzikowskiHagen Woesner
Berlin, 31.05.2007
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
2
OverviewMotivationSDH/SONET LayeringGeneral Concept of SDH
Analogy to a railway trainSDH data streams and containersMultiplexingClockingAdaptation
Addressing + justificationExamples
SDH/SONET devicesMultiplexersRegeneratorsDigital Crossconnects
Ring structuresSummary
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
3
Literature
Mike Sexton, Andy Reid: "Transmission Networking: SONET and the Synchronous Digital Hierarchy", Artech House, Boston /London, 1992Sławomir Kula „Systemy Teletransmisyjne”, Wydawnictwa Komunikacji i Łączności, Warszawa, 2004
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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MotivationTo overcome drawbacks of PDH
Need for inbuilt management mechanismsLack of free bits in frames to send system informationLack of automatic protection systemsLack of fast, dynamic and automatic reconfiguration of the networkDifficulties while sending signals incompatible with PDH hierarchyHigh energy consumption and low reliability of cascade multiplexersLack of standards for optical interfacesMany different standards for plesiochronous hierarchy
Synchronous systemsTransmission speed of an output signal is assumed to match the overall data rates of multiplexed signalsMost popular nowadays despite the need for precise clocks
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Layering – SDH/SONET terminology
MUX MUX DEMUXMUXR R
WD
M
WD
M
RS RS RS RS RS
Multiplex Section (MS) Multiplex Section (MS) MS
Higher Order Path (HOP) HOP
Lower Order Path (LOP)
Digital Path
Optical Section (OS)
General goal of SDH/SONET:
Fast transmission of information on a digital path.
PathHigher/Lower Order Path
LineMultiplex section
SectionRegeneration section
SONETSDH
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The concept of SDH on an example
C-4
POH VC-4 = C-4 +
+ Path Overhead (POH)
VirtualContainer
VC-4PTR AU-4 = VC-4 + + Pointer (PTR)
AdministrativeUnit
C-4 Container C-4
Input signal e.g. ATM cells
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The concept of SDH (2)
Synchronous Transport Module (STM)STM-1 = AUG-4 + SOH, where SOH = RSOH + MSOH
VC-4PTRRSOH
MSOH
STM-1#n
AU-1 AUG-4 = 1 x AU-1
VC-4PTRRSOH
MSOH
STM-1#n-1
VC-4PTRRSOH
MSOH
STM-1#n-2
AdministrativeUnit Group
Overhead
Payload
time
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Synchronous Transport Module (STM-1)
9 columns 261 columns
5 rows
1 row
3 rows
Duration of a frame: 125 µs
STM-1 corresponds to the basic data rate in SDH:
9 · 270 · 8 bit / 125 µs = 155.52 Mbit/s
- Administrative Unit Group AUG-n
Multiplex Section Overhead (MSOH)
PayloadAdministrative Unit Pointer (AU-PTR)
Regenerator Section Overhead (RSOH)
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Synchronous Transport Module (STM-n)
9N columns 261N columns
5 rows
1 row
3 rows
Each byte in a frame creates a transmission channel with data rate:
P = 8 [bit]/125 [µs] = 64 kb/s (voice channel!!!))
- Administrative Unit Group AUG-n
Multiplex Section Overhead (MSOH)
PayloadAdministrative Unit Pointer (AU-PTR)
Regenerator Section Overhead (RSOH)
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Synchronous Transport Module STM-1
FunctionByte(s)
Engineering Orderwire Service (EOW)E1, E2
Transmission medium type∆
transmission error detection (Binary Interleaved Parity – BIP) BIP-8 for RSOH, and BIP-24 for MSOH
B1, B2
Access Point Identifier (APId) – identifies the receiverJ0
frame phasing formulaA1, A2
FunctionByte(s)
feedback information about block errorsM1
Quality of Synchronization ClockS1
Information about Automatic Protection Switching (APS)K1, K2
Data Communication Channel (DCC) – Management System (ISP dependant! Bytes in RSOH and MSOH!)
D1-D12
User’s channel – unspecified usage in International StandardsF1
XXE2M1S1
D12D11D10
D9D8D7
D6D5D4
K2K1B2B2B2
PayloadPTR-AU
D3∆D2∆∆D1
XXF1∆E1∆∆B1
XXJ0A2A2A2A1A1A1
- Regeneration Secion Overhead (RSOH) - Multiplex Secion Overhead (RSOH)
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SDH Containers
C-11, C-12, C-2, C-3Lower Order Containers
C-3, C-4, C-4-4-c, C-4-16c, C-4-64c, C-4-256cHigher Order Containers
Bas
ic
con
tain
ers
C-3 may be a Lower Order Container or a Higher Order ContainerRecall: a Virtual Container = a Container + Path Overhead
VC-n = C-n + POH
„c” stands for concatenated (not multiplexed) containers
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Higher Order Virtual Container (VC-4, VC-3)
N1
K3
F3
H4
F2
PayloadG1
C2
B3
J1
Information about Automatic Protection Switching (APS)K3
Engineering Orderwire Service (EOW)H4
Signal label (stores information about signal that was mapped into VC-n)
C2
FunctionByte(s)
Management of Tandem ConnectionsN1
User’s channel – mainly for managementF2, F3
Path Status (feedback information sent in reverse direction)
G1
transmission error detection (BIP-8)B3
Termination Element Identifier (coded)J1
9 ro
ws
261 columns (VC-4) / 85 columns (VC-3)
- Path Overhead (POH)
Tandem connections - connections that are established via networks belonging to different Internet Service Providers
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Lower Order Virtual Containers
Payload J2 Payload N2 Payload K4 PayloadV5
Management of Tandem ConnectionsN2
FunctionByte(s)
Information about Automatic Protection Switching (APS)K4
Termination Element IdentifierJ2
transmission error detection (BIP-2), signal label, Path Status
V5
1 ro
w25
34
106
- Path Overhead (POH)
VC-11
VC-12
VC-2
25
34
106
25
34
106
25
34
106Amou
nt
of b
ytes
Lower Order Virtual Containers are alligned to Tributary Units (and later to Tributary Unit Groups), what corresponds to Administrative Unit (AU) and Administrative Unit Group (AUG) fo Higher Virtual Order ContainersConcatenated containers are similar to presented Virtual Containers regarding system management
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SDH - multiplexingNo overhead bits needed for justificationHigher speed link is formed by byte-interleaving data from lower speed linksExact multiples of lower speed data rates (e.g. STM-4 contains exactly 4 byte-interleaved STM-1 frames)Just very small buffers needed due to byte-interleaving and synchronism
STM-1
STM-1
STM-1
STM-1
STM-4
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SDH - multiplexing
9510.9129621.5049953.28STM-64OC-19210
38043.64838486.01639813.12STM-256OC-76811
2377.7282405.3762488.32STM-16OC-489
1783.2961804.0321866.24STM-12OC-368
1188.8641202.6881244.16STM-8OC-246
891.648902.12933.12STM-6OC-185
594.824601.344622.08STM-4OC-124
445.824451.008466.56STM-3OC-93
148.608150.336155.52STM-1OC-32
49.53650.11251.84-OC-11
Data rate (user)
Data rate (AUG)
Data rate (gross)
Europe(SDH), Japan
US (SONET)Level
OC – Optical ChannelSTM – Synchronous Transport ModuleAUG – Administrative Unit GroupSPE – Synchronous Payload Envelope = AU in SDH
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SDH - clockingIn the ideal case, all network elements are totally synchronousExpensive clocks and synchronization networks are needed
A rubidium-clock with short-term (10 s) stability of 5·10-12÷ 5·10-11
costs < 10000 $ (year 2004)A ceasium-clock with short-term (10 s) stability of 5·10-11 and no linear frequency drift costs 25000 ÷ 50000$ (year 2004)
Still, there are differencies in the clock rates of different devicesDelay variance of 5·10-10 means that two tributaries differ in one frame length every 3 daysNeed of adaptation of signals to their nominal rates
Put the tributaries into containersLet the container start anywhere in the payload frame (Addressing)Keep and manage the movement of pointer to theses containers, when adding the excessive bytes, or when byte stuffing (Justification)
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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SDH Multiplexing Structure – ITU-TSw
ww
.iec.org
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Scenario – VC-4 in STM-1
FIFO
A B C
fBfA fC
STMA-1 STMB-1
………..….
Tl Tu
VC-4 VC-4
fIN fOUT
fIN may dynamically differ from fOUT
Three cases considered1. fIN = fNOMINAL – ideal synchronous case2. fIN < fNOMINAL – positive justification if threshold Tl exceeded3. fIN > fNOMINAL – negative justification if threshold Tu exceeded
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Addressing
Pointer structure in Administrative Unit-4
H1 Y Y H2 1 1 H3H3H3- used bytes
- unused bytes
Pointer of AU-4
Justification
N N N N S S I D I D I D I D I D
AddressingBytes H1 and H2 store the location of VC-4 in the STM-1 Payload (precisely byte J1)Every third byte out of 2439 is addressed (1024 addresses stored in 10 I and D bits)
JustificationBytes H3 used for data transmission by negative justificationThree bytes R are inserted into the payload just behind the pointer by positive justification
N – new data flagS S – bits with constant 1 0 valueI D – addressing and justification
control
Adap
tatio
n
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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VC-4 in STM-1 – addressing
H3H3H311H2YYH1
VC-4
VC-4
H3H3H311H2YYH1
VC-4PO
H
J1
Address
J1
STM-1
# i
STM-1
# i+1
See slide 12 for the structure of VC-4
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Creation of STM-1 – no justification
FIFO………..….
Tl Tu
fIN fOUT
VC-4RRR
RSOH, AU-PTR,MSOH
fOUT9 bytes 261 bytes
time
9 261 bytes
Payl
oad
(VC-
4)
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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VC-4 in STM-1 – no justification
H3H3H311H2YYH1
VC-4
VC-4
H3H3H311H2YYH1
VC-4PO
H
J1
Address
J1
STM-1
# i
STM-1
# i+1
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Creation of STM-1 – positive justification
FIFO………..….
Tl Tu
fIN fOUT
VC-4RRR
`
RSOH, AU-PTR,MSOH
fOUT9 bytes 261 bytes
time
9 261 bytes 12 258 bytes
3 bytes R
R R R
Payl
oad
(VC-
4)
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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VC-4 in STM-1 – positive justification
H3H3H311H2YYH1
VC-4
VC-4
H3H3H311H2YYH1
VC-4PO
H
J1
Address
RRR
address + 1
J1
Positive
justification
STM-1
# i
STM-1
# i+1
Sign
allin
g of
ju
stifi
catio
nJu
stifi
catio
n
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Creation of STM-1 – negative justification
FIFO………..….
Tl Tu
fIN fOUT
VC-4
RSOH, AU-PTR,MSOH
fOUT9 bytes 261 bytes
time
9 261 bytes 6 264 bytes
3 bytes from VC-4
Payl
oad
(VC-
4)
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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VC-4 in STM-1 – negative justification
H3H3H311H2YYH1
VC-4
VC-4
H3H3H311H2YYH1
VC-4PO
H
J1
Address
J1
address - 1
Negative
justification
STM-1
# i
STM-1
# i+1
Sign
allin
g of
ju
stifi
caio
nJu
stifi
caio
n
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Example of a multiplexing scenario in SDH
Scenario:Each STM-1 frame carries three VC-3 containers with ATM cellsVC-3 containers are multiplexed into STM-1 payload with the use of adaptation mechanismThe rates of incoming stream of VC-3 containers differ slightly
MUX
VC-3
VC-3
VC-3
STM-1
3 VC-3s in STM-1
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Steps in the multiplexing procedure
VC-3
Input data,
e.g. ATM cells
PTR AU-3
VC-3
Input data,
e.g. ATM cells
AU-3PTR
Input data,
e.g. ATM cells
VC-3
AU-3PTR
AUG-1PTR
3 Pointers showing the address of each VC-3, and signalling Pointer Justification Events (PJEs)!
MUX
STM-1
RSOH
MSOHSTM-1
VC-3
Two columnes of fixed stuff bytes
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Pointer structureH1H1H1H2 H2H2H3H3H3
N N N N S S I D I D I D I D I D
AddressingBytes H1 and H2 store the location of VC-3 in the STM-1 Payload (precisely position of byte J1)Every possible position of J1 byte in STM-1 payload can be addressed (1024 addresses stored in 10 I and D bits, and the VC-3s are byte interleaved)
JustificationBytes H3 used for data transmission by negative justificationStuff bytes R are inserted into the payload just behind the pointer by positive justification
N – new data flagS S – bits with constant 1 0 valueI D – addressing and justification
control
Adap
tatio
n
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3 x VC-3 in STM-1 – addressing
--------------------
--------------------
--------------------
H3H3H3H2H2H2H1H1H1
--------------------
--------------------
--------------------
--------------------
--------------------
H3H3H3H2H2H2H1H1H1
--------------------
Address 1
STM-1
# i
STM-1
# i+1
Address 3
Address 2
0 0 0 86 86 8629 29 29 58 58 58
3 x VC3 + 2x3x9 fixed stuff bytes (byte interleaved)
521521521
522522522
J1 J1 J1
782782782
875 µs
1000 µs
1125 µs
0 0 0 86 86 8629 29 30 58 58 58
521521521
523523523
783783783
Byte of the first VC-3 or corresponding fixed stuff
Byte of the second VC-3 or corresponding fixed stuff
Byte of the third VC-3 or corresponding fixed stuff
AU-3 PTR = a group consisting of a H1, H2 and H3 byte
STM-1 PTR = three groups consisting of a H1, H2 and H3 byte
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Streams perf. synchronous – no justification
HOSM
bytes (byte interleaved)3 x VC-3 + 2x3x9 fixed stuff RRRH2H2H2H1H1H1
HOSR
9 bytes 261 bytes
time
9 261 bytes
FIFO………..….
fIN fOUT
TL TU
VC-3+ fixed stuff
FIFO………..….
TL TU
fIN fOUT
VC-3+ fixedstuff
FIFO………..….
TL TU
fIN fOUT
VC-3+ fixedstuff
RSOH, AU-PTR,MSOH
fOUT
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3 x VC-3 in STM-1 – no justification
H3H3H3H2H2H2H1H1H1
H3H3H3H2H2H2H1H1H1
Address 1
STM-1
# i
STM-1
# i+1
Address 3
Address 2
3 x VC3 + 2x3x9 fixed stuff bytes (byte interleaved)
J1 J1 J1
J1 J1 J1
875 µs
1000 µs
1125 µs
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First stream too slow – positive justification
HOSM
bytes (byte interleaved)3 x VC-3 + 2x3x9 fixed stuff RRRH2H2H2H1H1H1
HOSR
fOUT
9 bytes 261 bytes
FIFO………..….
fIN fOUT
TL TU
VC-3+ fixed stuff
FIFO………..….
TL TU
fIN fOUT
VC-3+ fixedstuff
FIFO………..….
TL TU
fIN fOUT
VC-3+ fixedstuff
R
RSOH, AU-PTR,MSOH
time
9 261 bytes 10 260 bytes
1 byte R
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Positive justification for the first stream
H3H3H3H2H2H2H1H1H1
H3H3H3H2H2H2H1H1H1
Address 1
STM-1
# i
STM-1
# i+1
Address 3
Address 2
3 x VC3 + 2x3x9 fixed stuff bytes (byte interleaved)
J1 J1 J1
J1 J1
R
J1
(Address 1) + 1
875 µs
1000 µs
1125 µs
Sign
allin
g of
ju
stifi
caio
nJu
stifi
caio
n
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First stream too fast – negative justification
HOSM
bytes (byte interleaved)3 x VC-3 + 2x3x9 fixed stuff RRH2H2H2H1H1H1
HOSR
RSOH, AU-PTR,MSOH
fOUT
9 bytes 261 bytes
FIFO………..….
fIN fOUT
TL TU
VC-3+ fixed stuff
FIFO………..….
TL TU
fIN fOUT
VC-3+ fixedstuff
FIFO………..….
TL TU
fIN fOUT
VC-3+ fixedstuff
time1 byte
9 261 bytes 6 261 bytes2
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Negative justification for the first stream
H3H3H3H2H2H2H1H1H1
H3H3H2H2H2H1H1H1
Address 1
STM-1
# i
STM-1
# i+1
Address 3
Address 2
3 x VC3 + 2x3x9 fixed stuff bytes (byte interleaved)
J1 J1 J1
875 µs
1000 µs
1125 µs
J1 J1 J1
(Address 1) - 1
Sign
allin
g of
ju
stifi
caio
nJu
stifi
caio
n
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Demultiplexing
First 5 framesPosition of each input stream within the payload of STM-1 frame is identified with the address stored in the pointer. The receiver reads each address to find the position of each input stream in the output stream frame.
Subsequent framesThe receiver knows the addresses already, and updates (increments or decrements) it when an PJE happens.PJEs are signalled by negation of appropriate bits of the pointer
VC-3
VC-3
VC-3
STM-1 DEMUX
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SDH/SONET devices
MultiplexersTerminal MultiplexersLine MultiplexersAdd Drop Multiplexers (ADMs)Transmultiplexers
RegeneratorsDigital Crossconnects (DXCs) or Digital CrossconnectSystems (DCSs)
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Terminal and Line multiplexers
MultiplexersTerminal Multiplexers
Terminates connections on the Path layer – reads/writes Path Overhead (POH)Tributaries may be electrical or optical, e.g. map PDH streams into Virtual ContainersMay have switching capabilities
Line MultiplexersSimilar to terminal multiplexers, but operate just on the synchronous signals STM-N
MUX
2 Mb/s
34 Mb/s STM-N6 Mb/s
othersGbE
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ADMs and TransmultiplexersMultiplexers
Add Drop Multiplexers (ADM)Terminates connections of the Multiplex Section (Line layer in SONET) - writes MSOH in SDH or LOH in SONETMay receive and transmit synchronous signals in two different directionsSignals may come also from outside of an SDH networkE.g. Add and drop an STM-1 to/from an STM-4
TransmultiplexersAllows transition of a Virtual Container 3 from AU-3 to TU-3 and vice versa (recall that VC-3 may be treated as a Higher Order Container and Lower Order Container)
STM-N STM-NADM
STM-M or signals outside of SDH
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Regenerators
RegeneratorTerminates connections of the Regeneration Section (Section layer in SONET) – reads/writes just RSOH in SDH or SOH in SONETPerforms 3-R regeneration of signals (amplify, re-shape, re-clock) and opto/electro/optical conversionADMs and DXCs have the functionality of regenerators too.
Re.g. STM-4 STM-4
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Digital CrossconnectsDigital Crossconnect System (DXC or DCS)
cross connects signals of different ordersHigher order DXC
HDXC switches only STM-1 framesDXC 4|4 means ”receive AU-4 and switch AU-4 granularity”
Lower order DXCLDXC mostly receive AU-4, but switch Tributary Units (TU)DXC 4|3|1 receives STM-1, but may switch VC=12, VC-3 and VC-4.
......
......
......
......
STM-4
STM-1
Tributaries (VC-12, VC-3)
STM-4
Digital Crossconnect System (DXC or DCS)cross connects signals of different ordersHigher order DXC
HDXC switches only STM-1 framesDXC 4|4 means ”receive AU-4 and switch AU-4 granularity”
Lower order DXCLDXC mostly receive AU-4, but switch Tributary Units (TU)DXC 4|3|1 receives STM-1, but may switch VC=12, VC-3 and VC-4.
DXC switches connections according to day-time changesCan be used to change network topology
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Ring structures
Ring = bus with the interconnected terminating nodesGuarantees two alternative transmission paths => protection against link and node failuresMinimizes amount of links providing two alternative paths
SDH RingsReliability - reconfiguration of the ring within 50 ms (APS)
Maximum amount of nodes: 16Limited length (1200 km) ofa ring to lower propagationdelay and probability of failure
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Categorization of SDH ring structures
Amount of rings in the structure and relationships between themDivision according to amount of fibres used in a ringDirection of transmission in a ringProtection mechanisms
The most popular structures are presented in the next slides
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Unidirectional Self-Healing Ring (USHR)
One working ringOne protection ringStreams between nodes are sent just in one direction in a ring
ADMB
ADMA
ADMC
ADME
ADMD
Protection ring (2), STM-n
Working ring (1), STM-n
A-C
C-A
A-C
C-A
… …
…
ADMA
A-C
21
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USHR with path protection (USHR-PP)
Traffic sent in both rings in parallel – no need for signallingSignal from the protection ring may be received instead of the one from the working ring (1+1 protection)
ADMB
ADMA
ADMC
ADME
ADMD
Protection ring (2), STM-n
Working ring (1), STM-n
A-C
C-A
A-C
C-A
… …
…
ADMA
A-C
21
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USHR with line protection (USHR-LP)
Signalling of alarm states done with bytes K1 and K2 of MSOH (Automatic Protection Switching channel)A backup ring is created in case of a failurePossible to send Low priority traffic in protection ring
ADMB
ADMA
ADMC
ADME
ADMD
Protection ring (2), STM-n
Working ring (1), STM-n
A-C
C-A
A-C
C-A
… …
…
ADMA
A-C
21
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Bidirectional Self-Healing Ring (BSHR-2)
One reception ringOne transmission ringBandwidth of the rings divided into working part and protection part
ADMB
ADMA
ADMC
ADME
ADMD
Reception ring for A-C (2), STM-n
Transmission ring for A-C (1), STM-n
A-C
C-A
A-C
C-A
… …
…
ADMA
A-C
21
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BSHR-2 – line protection
Reconfiguration of nodes neighbouring the failureTime slot interchange neededPossible to send Low priority traffic in protection ring
ADMB
ADMA
ADMC
ADME
ADMD
A-C
C-A
A-C
C-A
… …
…
ADMA
A-C
21
Transmission ring for A-C (1), STM-n
Reception ring for A-C (2), STM-n
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Bidirectional Self-Healing Ring (BSHR-4)
Working BSHR-2Protection BSHR-2Two type of protections possible: link protection, and line (ring) protection
ADMB
ADMA
ADMC
ADME
ADMD
Protection ring STM-n
Working ring STM-n
A-C
C-A
A-C
C-A
… …
…
ADMA
A-C
W1 W2 R1 R2
Transmission fiber (A-C)
Reception fiber (A-C)
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BSHR-4 – span protection
Signalling with Automatic Protection Switching channelPotential low order traffic in Protection ring may be lost
ADMB
ADMA
ADMC
ADME
ADMD
Protection ring STM-n
Working ring STM-n
A-C
C-A
A-C
C-A
… …
…
ADMA
A-C
W1 W2 R1 R2
Transmission fiber (A-C)
Reception fiber (A-C)
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BSHR-4 – line (ring) protection
Signalling with Automatic Protection Switching channelPotential low order traffic in Protection ring may be lost
ADMB
ADMA
ADMC
ADME
ADMD
Protection ring STM-n
Working ring STM-n
A-C
C-A
A-C
C-A
… …
…
ADMA
A-C
W1 W2 R1 R2
Transmission fiber (A-C)
Reception fiber (A-C)
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Summary
YesYesYesNoPossibility to send low priority traffic
SeparateCommonSeparateSeparateWorking and protection fibers
YesYesNoNoReuse of bandwidth
4222Amount of transmitter-receiver pars in a node
N x STM-nN/2 x STM-nSTM-nSTM-nMax. usable throughput
STM-nSTM-nSTM-nSTM-nThroughput
NNNNAmount of nodes
Line protection
Line protection
Line protection
Path protection
Type of protection against fiber failure
2111Amount of fiber pairs
BSHR-4BSHR-2USHR-LPUSHR-PPType of the ring
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Multiring structures
Multiring structures allow an Internet Service Provider to build bigger and more robust topologiesConnection of separate ring structures by:
Sharing of two separate nodesHigher Layer rings
Protection schemes:Node protectionRing protection
Traffic between two neighbouring rings belonging to the same Layer may be:
carried by the neighbouring links themselvescarried by ring(s) belonging to higher layers
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Two USHR-PP ring structure
ADME
ADMH
ADMB
ADMF
ADMA
2xADMC
2xADMD
ADMG
A-C
G-A
A-G A-C
G-A
A-G
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Hierarchical structures
Node protection Ring protection
Traffic between Layer 1 rings carried by Layer 2
Layer 2Layer1
Layer 2
Layer1
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Hierarchical structures
Node protection Ring protection
Traffic between neighbouring Layer 1 rings carried by Layer 1
Layer 2
Layer1Layer 2
Layer1
TKN Telecommunication Networks GroupSDH/Sonet, Berlin, 31.05.2007
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Summary (1)
Why are SDH rings so reliable?Reconfiguration time in 50 msAdaptation mechanisms against loss of synchronizationMany signalling channels available in the Overheads of STM’sand VC’s (also the ones that are not standardized and are free to use)Many versions and combinations of ring structures available (extension of the network range)Possibility to send low priority traffic in the protection rings, and to increase the utilization of the network
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Summary (2)
SDH/SONET is the standard in the today’s backbone networksTransmission of data in streams with rates that are multiples of STM-1 (155.52 Mb/s) (51 Mb/s for SONET only)Physical layer was defined for copper and radio transmission media as well, but single mode fibre is mainly usedExtensive management and protection featuresHigh reliability due to high overprovisioningMappings of payload of different type into SDH/SONET frame has been defined – see the next lecture
IP over SONET, ATM over SONET etc.