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)

7/26/2012

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.

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

7/26/2012

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.

7/26/2012

125 μsec

9 Rows

Section Overhead

270 x N Columns

9xN Columns

STM-N VC capacity

STM-N frame

7/26/2012

Concatenated Frames

Fixed Stuff (9N-9 bytes)

9 Rows

STM POH

9 bytes

STM-Nc Payload Capacity (AU-4-Nc)

N x 261 Columns

125 μsec

STM-4c = 599.040 Mbit/s STM-16c = 2396.160 Mbit/s

N x 260 Columns

SDH terminology is using

X instead of N (X = N)

N-1 Columns

7/26/2012

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.

7/26/2012

Frame Structures for Each Common

Hierarchy Level 270 Columns

9 Rows

9 Rows

9 Rows

1,080 Columns

4,320 Columns

STM-1

155.52 Mbit/s

STM-4

STM-16

622.08 Mbit/s

2488.32 Mbit/s

STM-64 9 rows x 17280 columns, 9953.28 Mbit/s

7/26/2012

Mapping Hierarchy

C-4

C-3

C-2

C-12

C-11

VC-4

VC-3

VC-2

VC-12

VC-11

TU-3

TU-2

TU-12

TU-11

VC-3

STM-N AUG AU-4 139 Mbit/s ATM

AU-3

TUG-3

44 Mbit/s 34 Mbit/s

TUG-2 6.3 Mbit/s

2 Mbit/s

1.5 Mbit/s

xN

x3

x1

x7

x7

x4

x3

x1

x3

STM-0

x1

AUG

Aligning

Mapping

xN Multiplexing

x1

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)

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)

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

SKG/RTTC/BBS

Adoption of 2MBPS Signal over SDH.

IF C1C1C1-111 THEN S1 IS A JUSTIFICATION BIT

7/26/2012

7/26/2012

General Structure

9 columns 261 columns

270 columns

VC Capacity

(for AUG)

Section

overhead

(SOH)

1st

2nd

Order of transmission

7/26/2012

….. 9 1 261Byte

Information Payload

9 Rows

125 μs Transport overhead

270 bytes

RSOH

pointer

3 rows

5 rows MSOH

STM-1 frame

Synchronous Payload Envelope

7/26/2012

Pointer 4 Bytes

v5

VC-12

500 μsec

V1 & v2 points

V5

v1

v2

v3

TU12

S SKG/RTC/BBSR

Special OH octets:

A1, A2 Frame Synch

B1 Parity on Previous Frame

(BER monitoring)

J0 Section trace

(Connection Alive?)

H1, H2, H3 Pointer Action

K1, K2 Automatic Protection

Switching

810 Octets per frame @ 8000 frames/sec

9 rows

90 columns

1

2 Order of

transmission

A1 A2 J0 J1

B1 E1 F1 B3

D1 D2 D3 C2

H1 H2 H3 G1

B2 K1 K2 F2

D4 D5 D6 H4

D7 D8 D9 Z3

D10 D11 D12 Z4

S1 M0/1 E2 N1

3 Columns of

Transport OH

Section Overhead

Line Overhead

Synchronous Payload Envelope (SPE)

1 column of Path OH + 8 data columns

Path Overhead

Data

STS-1 Frame 810x64kbps=51.84 Mbps

7/26/2012

STM-0 Overheads

Data Com D8

Data Com D4

Data Com D7

Data Com D10

Data Com D5

Data Com D11

Data Com D6

Data Com D9

Data Com D12

APS K2

APS K1

Data Com D1

Data Com D3

Data Com

D2

Section Overhead

Path Trace J1

BIP-8 B3

Signal Label C2

Path Status G1

User Channel F2

Multiframe Indicator

H4

User Channel F3

APS K3

Tandem N1

Framing A1

BIP-8 B1

Pointer H1

BIP-8 B2

Sync S1

Orderwire E1

Pointer H2

RS Trace J0

User Channel F1

(REI) (M1)

Pointer H3

Orderwire E2

HO Path Overhead

R-Section Overhead

M-Section Overhead

Framing A2

AU pointer

7/26/2012

STM-1 Section Overhead

A1 A1 A1 A2 A2 A2 J0

B1 E1 F1

D1 D2 D3

H1 H1* H2 H2* H3 H3 H3

B2 K1 K2

S1 M1 E2

B2 B2

D4

D7

D10

D5

D8

D11

D6

D9

D12

H1* = 10010011 H2* = 11111111

H2* H1*

R-Section Overhead

M-Section Overhead

AU pointer

Δ

Δ

Δ

Δ

Δ

Δ

Δ - media dependent

national use

7/26/2012

MAPPING OF VC-4 IN TO STM1

9 rows

270 bytes

9 bytes

Transport

Overhead VC-4 Path Overhead

Trace

J1

BIP-8

B3

Label

C2

Status

G1

User

F2

Multiframe

H4

Growth

Z3

Growth

Z4

TCM

Z5 STM-1 Payload

Synchronous Payload

Envelope

Path Overhead • J1- Path Trace • BIP-8 - Parity • C2 - Payload Type Indicator • G1 - End Path Status • F2 - User • H4 - Use Depends On Payload • Z3-5 - Future Growth

AU-4 POINTER

RSOH

3ROWS

MSOH

5 ROWS

20 BLOCKS OF 13 BYTES

Asynchronous mapping of 139.264 MBPS Page-66

7/26/2012

Payload Pointer

Section Overhead

90 (VC-3) or 270 (VC-4) Columns

9 Rows

STM-1 Frame #1

9 Rows

STM-1 VC-3 or VC-4

125 μsec

250 μsec

STM-1 Frame #2

H1 H2 H3...

Payload Pointer marks

start of STM-1 VC-3 or

VC-4

STM-1 VC-3 or VC-4

POH column

9 rows

270 bytes

9 bytes

Transport

Overhead

Trace

J1

BIP-8

B3

Label

C2

Status

G1

User

F2

Multiframe

H4

Growth

Z3

Growth

Z4

TCM

Z5

STM-1 Payload

Synchronous Payload

Envelope

H1H1H1H2H2H2H3H3H3

RSOH

3ROWS

MSOH

5 ROWS

20 BLOCKS OF 13 BYTES

Asynchronous mapping of 139.264 MBPS Page-66

1 2 3 . . . . . . . . . 17 18 19 20

path

path

termination

path

termination

service (E1, E4..)

mapping

demapping service (E1, E4..)

mapping

demapping

TM TM

multiplex section multiplex section

multipl. section

termination

ADM

or

DCS

regenerator

section

regen. section

termination

regen. section

termination

REG REG

PTE = path terminating element

TM = terminal multiplexer

REG = regenerator

ADM = add/drop multiplexer

DCS = digital cross-connect system

DXC= digital cross connect

regen.

section

regen.

section regenerator

section

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

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

Optical port

Optical port

Electrical port

ADM(OEO)

•Ports have different

roles

•No switching between

the core ports

•Switching only

between the add-drop

and the core ports.

Uni- and Bi-directional

Routing

– Only working traffic is shown

– Subnetwork (path) or multiplex section switching for protection

A

C E

B F

D

Uni-directional Ring (1 fiber)

C-A

A-C A

C E

B F

D

Bi-directional Ring (2 fibers)

C-A

A-C

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).

USHR-L USHR/L

Incoming and

returning signal

routed

unidirectionally on

working ring.

On failure,

adjacent nodes

perform fold or

looping function.

Basic ADMs used

(TSI not needed).

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.

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

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

Multiplex Section Protection

Switching

– Conditions resulting in a protection switch:

• Loss of signal, loss of frame

• Line AIS (all 1’s)

• Signal degrade

– Excessive BIP-24 errors in MS overhead

LOS AIS

OCN REI upstream

down stream

Payload

R-Section Overhead

M-Section Overhead

information controlling protection switching

Path Protection Switching

– Conditions resulting in a protection switch:

• Loss of pointer, STM or VC AIS

• Excessive BIP errors for STM path, BIP errors for VC path

R-Section Overhead

M-Section Overhead

Info controlling protection switching

Payload

STM Path

Overhead

VC Path

Overhead

VC Payload

STM -N Mux

K1K2 Read/Sel

K1K2 Write

Working STM-N

Protect STM-N

STM-N Mux

K1K2 Write

K1K2 Read/Sel

Tributary Channels

Tributary Channels

MSTE

MSTE

Automatic Protection Switching - I.

– APS = Automatic

Protection Switching

• Allows network to

react to failed lines,

interfaces, or

poor signal quality

– Performed over the

entire STM-N payload

– Uses K1 and K2 bytes

of MS Overhead

Automatic Protection Switching - II.

– K1 byte:

• Type of request (bits 1-4)

• Channel requested (bits 5-8)

– K2 byte:

• Channel selected (bits 1-4)

• Architecture (bit 5)

• Mode of operation (bits 6-8)

– e.g. Alarm Indication Signal (AIS), Remote Defect Indicator (RDI)

STM -N Mux

K1K2 Read/Sel

K1K2 Write

Working STM-N

Protect STM-N

STM-N Mux

K1K2 Write

K1K2 Read/Sel

Tributary Channels

Tributary Channels

MSTE

MSTE

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

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