1 - sdh basics

© Tejas Networks India Ltd., 2007, Proprietary Information Rev1.2 Last update 11 Dec 07 Reviewed by:

110-HTM000021-DSDH Basics


Objective

Standards

Frame Structure

Multiplexing

Regenerator Section Overhead

Multiplex Section Overhead

Path Overhead

Advantages


Plesiochronous Digital Hierarchy (PDH)

Notation Data Rate

E0 64 Kbps

E1 2048 Kbps

E2 8448 Kbps

E3 34368 Kbps

E4 139264 Kbps

Notation Data Rate

T0/DS0 64 Kbps

T1/DS1 1544 Kbps

T2/DS2 6312 Kbps

T3/DS3 44736 Kbps

T4/DS4 139264 Kbps

European Standard American Standard

• Used in South America, Europe, India etc

• Used in South America, Europe, India etc • Used in USA, Canada

Japan, Korea, Hong Kong etc

• Used in USA, Canada Japan, Korea, Hong Kong etc


SDH at glance:

1. SDH (Synchronous Digital Hierarchy) – Recommendation for Optical Telecomm. Networking formulated by ITU & can have line rate of 40Gbps.

2. SDH follows the Master-Slave clock technique with PLL to synchronize the nodes.

3. SDH provides mapping, MUXing (TDM) & framing to mainly carry PDH & Ethernet traffic to form STM frame.

4. Overhead bytes ensure the management of payload & Pointers allow dynamic allocation of payload in STM frame.

5. Automatic Protection Switching provide protection to traffic against the fiber cut & errors with the help of overhead bytes in SDH.

6. Performance Monitoring & Alarms strengthens SDH by giving sufficient indication using Overheads against errors like equipment, operator & comm.


The hierarchy is as follows:

Optical Signal Bit Rate Abbreviated as

STM-0 51.84 Mbps 51 Mbps

STM-1 155.52 Mbps 155 Mbps

STM- 4 622.080 Mbps 622 Mbps

STM-16 2488.320 Mbps 2.4 Gbps

STM-64 9953.280 Mbps 10 Gbps

STM-256 39813.12 Mbps 40 Gbps

Standards


TX END


RX END


STM-1 Frame Format

9 Rows

Administrative Unit

Capacity of theVirtual Container

+Pointers

1

2

3

4

5

6

7

8

9

RegeneratorSectionOverhead

MultiplexSection

Overhead

H3H1 H2Pointers

STM-1 = 270 Columns (2430 bytes)

H1H1 H1 H2 H2 H2 H3 H3H3

Frame =125µs Frame = 125µsFrame =125µs

Overhead width = 9 columns


STM-N Frame Format

Frame = 125µs


Frame Format

STM - Section overhead and Administrative unit

Section overhead – Regenerator section overhead and Multiplex section overhead

Administrative unit – Virtual container and pointers

Virtual container - Payload and Path overhead information

1 Byte=8bits * 8000 frames/sec=64 Kbps

Payload

STM-N

Administrative unit

Pointer Virtual Container

Path overhead

Section Overhead

Regenerator Overhead

Multiplex overhead


Mapping Elements

Container

Virtual Container

Tributary Unit

Tributary Unit Group

Administrative Unit

Administrative Unit Group

STM-N Frame


The Container (C)

– Basic packaging unit for tributary signals (PDH)

Mapping Elements


The Virtual Container (VC)

– Formation of the Container by adding of a POH (Path Overhead)

The Tributary Unit (TU)

– Is formed via adding a pointer to the VC

The Tributary Unit Group (TUG)

– Combines several TUs for a new VC

Mapping Elements


The Administrative Unit (AU)

– Is shaped if a pointer is allocated to the VC formed at last

The Syncronous Transport Module (STM-N)

– Formed by adding a Section Overhead (SOH) to AUs

Mapping Elements


SDH Multiplexing


SDH Multiplexing

9 X 261

743 6521 743 6521 743 6521

321

4321 9 rows

4 columns

TUG-2 9 X 12

TU – 12 9X4

TUG-3 9 X 84

POH

POH

POH

Stuffing and POH

TUG - 3TUG - 3TUG - 3

Section Over Head

(9 X 9)


A1 A1 A1 A2 A2 A2 J0

B1 E1 F1

D1 D2 D3

RegeneratorSection

Regenerator Section Overhead - RSOH


Regenerator Section Overhead - RSOH

A1 A2 J0

B1 E1 F1

D1 D2 D3

Framing (A1,A2)

Start of the STM-1 frame.Section Trace or Future

Growth (J0)J0 carries section trace

message.

Local Orderwire (E1)Channel for voice

communications between any two NEs.

Section User Channel (F1)

A 64kb/s user channel.

Section BIP-8 (B1)Byte interleaved Parity-8

(BIP-8) is used for regenerator section error

monitoring.

Data communication channel (DCC_R)

Provides a single 192 kb/s channel for Management


B2 B2 B2 K1 K2

D4 D5 D6

D7 D8 D9

D10 D11 D12

S1 M1 E2

MultiplexSection

Multiplex Section Overhead - MSOH


B2 K1 K2

D4 D5 D6

D7 D8 D9

D10 D11 D12

S1 M1 E2

Line BIP-24 (B2)Byte interleaved Parity-24

(BIP-24) is used for multiplex section error

monitoring.

Multiplex Section Overhead - MSOH

Data Communication Channel (DCC-M)

Provides a single 576 kb/s channel for

ManagementAutomatic Protection Switch (APS) (K1,K2)Used for APS signaling

Synchronization status or Future growth (S1)

5-8 bits of the byte defines Synchronous status message

Line Remote Error Indicator (M1)

Remote error indication. Conveys the BIP-24 error count back to the source

Orderwire (E2)Orderwire channel for voice communication between two

NEs


Pointers

SDH provides payload pointers to permit differences in the phase and frequency of the Virtual Containers (VC-N) with respect to the STM-N frame.

On a frame-by-frame basis, the payload pointer indicates the offset between the VC payload and the STM-N frame by identifying the location of the first byte of the VC in the payload.

The pointer value indicates the offset in bytes from the pointer to the first byte of the VC, which is the J1 byte.

Starting points are at 3-byte increments for a VC-4 payload, the possible range is: Total STM-1 bytes – Section Overhead bytes = Pointer value range

(2430 – 81)/3 = 783 valid pointer positions


For a VC-4 payload, this pointer is located in columns 1 and 4 of the fourth row of the Section Overhead

For a VC-3 payload, entire pointer bytes are used.

Pointers Continued


Pointers Continued

The pointer value, is carried in bits 7 through 16 of the H1-H2 pointer word.

The first four bits, the N-bits, are known as the New Data Flag.These bits contains the pattern 0110 by default to indicate “No Arbitrary Change”.In case of “Arbitrary Change” pattern is 1001.

1 2 3 4 S1 S2 I D I D I D I D I D

New Data Flag Size Bits

Pointer Values (0 – 782)

0110 No Arbitrary change

1001 Arbitrary change

H1+H2


Positive Pointer Justification (PPJ)

RSOH

MSOH

AU Pointer

Virtual Container (VC)

Data

When the data rate of the VC is too slow in relation to the rate of the STM-1 frame, then I bits are inverted & the pointer value is incremented by 1. This is known as PPJ.



PPJ Example

For block 256 in frame n

Tx END (H1 H2 bytes)

0110 10 0100000000 frame n+1 initialization

0110 10 1110101010 frame n+2 I bits inverted,same ptr value

1block stuffed after H3 byte.

0110 10 0100000001 frame n+3 pointer value increased by 1


PPJ Example continued

Rx END 256 in frame n


0110 10 1110101010 frame n+2 I bits inverted (5/5,4/5,3/5) to get

pointer value 256

0110 10 0100000001 frame n+3 ptr value changed to 257


RSOH

MSOH

AU Pointer

Virtual Container (VC)

Negative Pointer Justification (NPJ)Data

When the data rate of the VC is too fast in relation to the rate of the STM-1 frame, D bits are inverted and the pointer value is decremented by 1. This is known as NPJ.

Negative Pointer Justification (NPJ)


Negative Pointer Justification (NPJ)


NPJ Example

Tx END 642 block in frame n

(H1 H2 bytes)


0110 10 1111010111 frame n+2 D bits inverted,same ptr value,H3 bytes used.



NPJ Example continued

Rx END 642 block in frame n


0110 10 1111010111 frame n+2 D bits inverted (5/5,4/5,3/5)

to get ptr value 642



J1

B3

C2

G1

F2

H4

F3

K3

N1

Higher Order Path Overhead – HPOH(VC-4 / VC-3)Higher Order Path Overhead – HPOH(VC-4 / VC-3)

Path Overhead


J1

B3

C2

G1

F2

H4

F3

K3

N1

Path Signal Label (C2)

Indicates the type of payload in AU

Path Trace (J1)

J1 byte carries the trace information at path level

Path BIP-8 (B3)

Path error monitoring

Path Status (G1)

Provides status and performance information back to the remote end

Indicator byte (H4)

Carries multiframe information

Path User Channel (F2)

User data channel at path levelPath User Channel (F3)

User data channel at path levelBits 1-4 are allocated for

APS. Bits 5-8 are for future use.

Tandem Connection (N1)

IEC for tandem connection monitoring at

TCM source.

Higher Order Path Overhead – HPOH(VC-4 / VC-3)Higher Order Path Overhead – HPOH(VC-4 / VC-3)


Lower Order Path Overhead – POH(VC-11 / VC-12)

VC-12 VC-11


Lower Order Path Overhead - POH

V5

J2

N2

K4

Signal Label and parity check

Path Trace (J2)

J2 byte carries the trace information at lower order

path level

Tandem Connection (N2)

IEC for tandem connection monitoring at

TCM source.

Carries APS information at lower order path level


Advantages

High speed standards

Efficient Multiplexing / Demultiplexing

Enhanced Operation, administration, Provisioning, Maintenance

capabilities (OAM&P)

Tejas Supports Next Generation SDH

Supports data(Ethernet) as well as voice.

No need for separate data infrastructure.

Use of GFP, VCAT, LCAS, Auto Negotiation.


Thank You…

1 - sdh basics

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