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Sdh concept
2. Advantages
of SDH over PDH.
• High transmission rates up to 40 Gbit/s
• Simplified add & drop function
• High availability and capacity matching
• Reliability
• Future-proof platform for new services.
• Interconnection (SONET,SDH,PDH)
3. What is SDH?
• The basis of Synchronous Digital Hierarchy
(SDH) is synchronous multiplexing - data
from multiple tributary sources is byte
interleaved.
• In SDH the multiplexed channels are in fixed
locations relative to the framing byte.
• De-multiplexing is achieved by gating out the
required bytes from the digital stream.
• This allows a single channel to be ‘dropped’
from the data stream without de-multiplexing
intermediate rates as is required in PDH.
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4. Multiplexing Processes
– Multiplexing is composed of various processes:
• Mapping
–Tributaries adapted into Virtual Containers
(VC) by adding stuffing and POH
• Aligning
–Pointer is added to locate the VC inside an AU
or TU
• Multiplexing
–Interleaving the bytes of multiple paths
• Stuffing
–Adding up the fixed stuff bits to compensate
for frequency variances
5. TRANSPORT OF PDH
PAYLOAD
SDH is essentially a transport mechanism for carrying a
large number of PDH payloads.
• A mechanism is required to map PDH rates into the
STM frame. This function is performed by the
container (C).
• A PDH channel must be synchronized before it can
be mapped into a container.
• The synchronizer adapts the rate of an incoming PDH
signal to SDH rate.
SDH and non synchronous signal
• At the PDH/SDH boundary Bit stuffing is
performed when the PDH signal is mapped into
its container.
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6. STM-N frame
270 x N Columns
9xN
Columns
STM-N VC capacity
9
Rows
125 μsec
Section
Overhead
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7. Concatenated Frames
N-1 Columns SDH terminology is using
X instead of N (X = N)
N x 260 Columns
STM
POH
9 bytes
9 Rows STM-Nc Payload Capacity
(AU-4-Nc)
Fixed
Stuff
(9N-9 STM-4c = 599.040 Mbit/s
bytes) STM-16c = 2396.160 Mbit/s
125 μsec
N x 261 Columns
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8. SDH Rates
• SDH is a transport hierarchy based on
multiples of 155.52 Mbit/s.
The basic unit of SDH is STM-1:
STM-1 = 155.52 Mbit/s
STM-4 = 622.08 Mbit/s
STM-16 = 2588.32 Mbit/s
STM-64 = 9953.28 Mbit/s
• Each rate is an exact multiple of the lower rate therefore
the hierarchy is synchronous.
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9. Frame Structures for Each Common
Hierarchy Level
270 Columns
STM-1
9 Rows 155.52 Mbit/s
1,080 Columns
STM-4
9 Rows 622.08 Mbit/s
4,320 Columns
STM-16
9 Rows
2488.32 Mbit/s
STM-64 9 rows x 17280 columns, 9953.28 Mbit/s
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11. Containers - I.
– In SDH terminology, the original PDH payload
with special framing is called a container (C-x)
– Various container sizes with some space for
stuffing are defined
• C-11 for DS1 (25 bytes = 1.600 Mbit/s)
• C-12 for E1 (34 bytes = 2.176 Mbit/s)
• C-2 for DS2 (106 bytes = 6.784 Mbit/s)
• C-3 for DS3 or E3 (84 columns = 48.384
Mbit/s)
• C-4 for E4 (260 columns = 149.760 Mbit/s)
12. Virtual Containers - II.
– Various VC sizes defined:
• With 1 byte allocated for POH
– VC-11 for DS1 (26 bytes = 1.664 Mbit/s)
– VC-12 for E1 (35 bytes = 2.240 Mbit/s)
– VC-2 for DS2 (107 bytes = 6.848 Mbit/s)
• With 1 column allocated for POH
– VC-3 for DS3 or E3 (85 columns = 48.960 Mbit/s)
– VC-4 for E4 (261 columns = 150.336 Mbit/s)
13. Tributary Unit Structure
– TUs are defined to fit into a number of columns
• This requirement determines the size of virtual
containers and containers
• TU-3 adds up 3-byte pointer plus stuffing to VC-3
• Lower TUs add up 1 byte for pointer storage
–Organized into 4 frames (500 μs multi-frame)
–This provides V1, V2, V3, V4 TU pointer bytes
– Lower TUs also organize POH along the multi-
frame
• This provides V5, J2, Z6, Z7 POH bytes
• Lower TUs use V1, V2, V3, V4 bytes in 500 μs
multi-frame
14. Adoption of 2MBPS Signal over SDH.
IF C1C1C1-111 THEN S1 IS A JUSTIFICATION BIT
SKG/RTTC/BBS
19. STS-1 Frame 810x64kbps=51.84Mbps
810 Octets per frame @ 8000 frames/sec
90 columns
A1 A2 J0 J1
B1 E1 F1 B3
1
D1 D2 D3 C2
Order of
2 transmission H1 H2 H3 G1
9 rows B2 K1 K2 F2
Special OH octets: D4 D5 D6 H4
D7 D8 D9 Z3
A1, A2 Frame Synch
D10 D11 D12 Z4
B1 Parity on Previous Frame
(BER monitoring) S1 M0/1 E2 N1
J0 Section trace
(Connection Alive?) 3 Columns of Synchronous Payload Envelope (SPE)
H1, H2, H3 Pointer Action Transport OH 1 column of Path OH + 8 data columns
K1, K2 Automatic Protection
Switching Section Overhead Path Overhead
SKG/RTC/BBSR
S Line Overhead Data
20. STM-0 Overheads
HO Path
Section Overhead Overhead
Framing Framing RS Trace Path Trace
A1 A2 J0 J1
R-Section BIP-8 Orderwire User Channel BIP-8
Overhead B1 E1 F1 B3
Data Com Data Com Data Com Signal Label
D1 D2 D3 C2
Pointer Path Status
AU pointer Pointer Pointer
G1
H1 H2 H3
BIP-8 APS APS User Channel
B2 K1 K2 F2
Multiframe
Data Com Data Com Data Com Indicator
M-Section D4 D5 D6 H4
Overhead Data Com Data Com Data Com User Channel
D7 D8 D9 F3
Data Com Data Com Data Com APS
D10 D11 D12 K3
Sync (REI) Orderwire Tandem
S1 (M1) E2 N1
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25. path
multiplex section multiplex section
regenerator regen. regen. regenerator
section section section section
ADM
TM REG or REG TM
DCS
path regen. section multipl. section regen. section path
termination termination termination termination termination
PTE = path terminating element
service (E1, E4..) TM = terminal multiplexer
mapping service (E1, E4..)
demapping REG = regenerator mapping
ADM = add/drop multiplexer demapping
DCS = digital cross-connect system
DXC= digital cross connect
26. Regenerator
– A regenerator simply extends the possible
distance and quality of a line by decomposing
it into multiple sections
• Replaces regenerator section overhead
• Multiplex section and path overhead is not altered
27. Add-drop Multiplexer - I.
– Add/drop multiplexer (ADM)
• Main element for configuring paths on top of line
topologies (point-to-point or ring)
• Multiplexed channels may be dropped and added
• Special drop and repeat mode for broadcast and
survivability
• An ADM has at least 3 logical ports: 2 core and 1 or
more add-drop
•Ports have different Optical port
roles Optical port ADM(OEO)
•No switching between
the core ports
•Switching only Electrical port
between the add-drop
and the core ports.
29. Uni- and Bi-directional
Routing
A A
A-C A-C
F B F B
C-A
C-A
E C E C
D D
Uni-directional Ring Bi-directional Ring
(1 fiber) (2 fibers)
– Only working traffic is shown
– Subnetwork (path) or multiplex section switching for
protection
30. USHR
• Working traffic is carried around the ring in
one direction only.
• Ring capacity is sum of demands between
nodes.
• Also called “Counter–Rotating–Ring”;
traffic in prot. rotates opposite.
• 1:1 (USHR/L); extended to 1:N, then not
entirely self–healing.
• 1+1 (USHR/P).
32. USHR Concepts
– USHR/P = Unidirectional Self-Healing Ring / Path Switched
– 2-fiber ring topology
• Head-end bridge, tail-end switch logical topology
– 1+1 protection with uni-directional routing on each fiber
– Traffic is sent in both directions on the ring on separate
fibers
– The better signal is selected by the receiver.
33. BSHR Concepts - I.
– BSHR/MS = Bi-directional Self-Healing Ring /
Multiplex Section Switched
– 1:1, or 1:N redundancy options
– 2 fibers with shared protection configuration
• Half the bandwidth in each direction in a link
is reserved for the shared protection of all
traffic in that reverse direction of the link
–An even number of
STM-1s are required
– 4 fibers for dedicated protection configuration
• Bi-directional routing on 2 fibers (working
line)
• Each direction has a working and a protect
fiber
34. BSHR Concepts - II.
– Multiple fail-over options for 4-fiber BSHR/MS
• In normal operation traffic is sent only in the required direction
• During fiber interruption, the traffic is routed around the break in
opposite direction (long path)
– Ring switching
• Optionally if the other 2 fibers are still available, then traffic might
be routed onto the parallel 2 fibers (short path)
– Span switching
35. Multiplex Section Protection
Switching
R-Section
Overhead
information
controlling
protection Payload
switching
M-Section
Overhead
– Conditions resulting in a protection switch:
• Loss of signal, loss of frame
LOS AIS
• Line AIS (all 1’s)
down
• Signal degrade REI
upstream
OCN
stream
– Excessive BIP-24 errors in MS overhead
36. Path Protection Switching
R-Section Payload
Overhead
VC
Path
Overhead
STM Info
Path controlling
Overhead protection
M-Section switching
Overhead VC
Payload
– Conditions resulting in a protection switch:
• Loss of pointer, STM or VC AIS
• Excessive BIP errors for STM path, BIP errors for VC
path
37. Automatic Protection Switching - I.
– APS = Automatic Tributary
Channels
Protection Switching STM-N Mux
• Allows network to MSTE K1K2
Read/Sel
K1K2
Write
react to failed lines,
interfaces, or
poor signal quality
– Performed over the Working
STM-N
Protect
STM-N
entire STM-N payload
– Uses K1 and K2 bytes
of MS Overhead
MSTE K1K2
Write
K1K2
Read/Sel
STM -N Mux
Tributary
Channels
39. Uni- and Bi-directional APS
– Uni-directional APS
• Only traffic on the affected fiber is switched to the
protect line
– Bi-directional APS
• TX and RX are both switched when channel is
affected
40. Revertive and Non-revertive
APS
– Revertive switching
• Will restore to the working channel when WTR
timer expires
– Non-revertive switching
• Will not move to working channel after failure
unless requested