SDH Basics
Objective
Standards
Frame Structure
Multiplexing Section Hierarchy Regenerator Section Overhead Multiplex Section Overhead
Path Overhead
Advantages
Basic data rate
Common Characteristics a b c d e f Audible frequency range (fm) Sampling frequency (fs) Number of samples per signal Length of PCM frame Number of bits in each code word Telephone channel bit rate
E1 and T1 0 - 3.4kHz 4kHz 2 X fm = 8kHz 8000 per second 1/c = 125s 8 c X e = 8000/s X 8 bit = 64kbps
Plesiochronous Digital Hierarchy (PDH)
American Standard
European Standard Notation Data Rate
Notation
T0/DS0 T1/DS1 T2/DS2 T3/DS3 T4/DS4
Data Rate
64 Kbps 1544 Kbps 6312 Kbps 44736 Kbps 139264 Kbps
E0
E1 E2 E3 E4
64 Kbps
2048 Kbps 8448 Kbps 34368 Kbps 139264 Kbps
Used in South America, Europe, India etc
Used in USA, Canada Japan, Korea, Hong Kong etc
Limitations of PDH
Inability to identify individual channels in a higher-order bit stream. Multiplexing/Demultiplexing is cumbersome (Stage wise). Insufficient capacity for network management as limited OAMP operation. Theres no standardised definition of PDH bit rates greater than 140 Mbit/s. There are different hierarchies in use around the world. Specialized interface equipment is required to interwork the two hierarchies.
Standards
The hierarchy is as follows:
Optical Signal STM-0 Bit Rate 51.84 Mbps Abbreviated as 51 Mbps
STM-1
STM- 4 STM-16 STM-64 STM-256
155.52 Mbps
622.080 Mbps 2488.320 Mbps 9953.280 Mbps 39813.12 Mbps
155 Mbps
622 Mbps 2.4 Gbps 10 Gbps 40 Gbps
STM-1 Frame Format
Frame =125s
Frame =125s
Frame = 125s
STM-1 = 270 Columns (2430 bytes)
1 2 3 Regenerator Section Overhead H1 H2 H3
Administrative Unit
Capacity of the Virtual Container + Pointers
Pointers 4
5 6 7 8 9
H1 H1 H1 H2 H2 H2 H3 H3 H3
9 Rows
Multiplex Section Overhead
Overhead width = 9 columns
STM-1 Frame Format
STM-N Frame Format
Frame = 125s
Frame Format
STM-N
STM - Section overhead and
Administrative unit
Section overhead Regenerator
Section Overhead
Administrative unit
section overhead and Multiplex section overhead Regenerator
Administrative unit Virtual container
and pointers
Overhead
Multiplex overhead
Pointer
Virtual Container
Path overhead
Payload
Virtual container - Payload and Path
overhead information
Mapping Elements
Container Virtual Container Tributary Unit
Tributary Unit Group
Administrative Unit
Administrative Unit Group
STM-N Frame
SDH Multiplexing
Container
Input signals are placed into the containers
It adds stuffing bytes for PDH signals,which compensates for the permitted frequency deviation between the SDH system and the PDH signal
C12 (2 Mbps G.703) C11 (1.5 Mbps) C2 (6 Mbps) C3 (34 / 45 Mbps) C4 (140 Mbps)
Virtual Container
MAPPING : It is a process from Containers to Virtual containers.
POH
PAYLOAD
POH
PAYLOAD
ANALOGY: Packing C2 carton box with some more packing material and labeled as VC2 box
Virtual Container
It adds overheads to a container or groups of tributary units, that provides facilities for supervision and maintenance of the end to end paths VCs carry information end to end between two path access points through the SDH system
VCs are designed for transport and switching sub-SDH payloads
VC12 (C12 + POH) VC11 (C11 + POH) VC2 (C2 + POH) VC3 (C3 + POH) VC4 (C4 + POH)
Virtual Container
At each level, subdivisions of capacity can float individually between the payload areas of adjacent frames. Each subdivision can be readily located by its own pointer that is embedded in the overheads. The pointer is used to find the floating part of the AU or TU, which is called a virtual container (VC). The AU pointer locates a higher-order VC, and the TU pointer locates a lower-order VC. For example, an AU3 contains a VC3 plus a pointer, and a TU2 contains a VC2 plus a pointer.
A VC is the payload entity that travels across the network, being created and dismantled at or near the service termination point.
Tributary Unit
It adds pointers to the VCs
This pointer permits the SDH system to compensate for phase differences within the SDH network and also for the frequency deviations between the SDH networks
TUs acts as a bridge between the lower order path layer and higher order path layer
TU12 (VC12 + pointer) TU2 (VC2 + pointer) TU3 (VC3 + pointer)
Tributary Unit Group
It defines a group of tributary units that are multiplexed together As a result, a TU group could contain one of the following combinations
Three TU-12s (TUG 2) Seven TUG-2s (TUG 3)
Administrative Unit
It adds pointer to the HO Virtual containers(similar to the tributary unit)
AU - 3 (VC-3 + pointer) AU - 4 (VC-4 + pointer)
Administrative Unit Group
It defines a group of administrative units that are multiplexed together to form higher order STM signal
Synchronous Transport Module n
It adds section overhead (RSOH & MSOH) to a number of AUGs that adds facilities for supervision & maintenance of the multiplexer & regenerator sections This is the signal that is transmitted on the SDH line
The digit n defines the order of the STM signal
SDH Multiplexing
4 columns TU 12 9X4
1 2 3 4
9 rows
Stuffing and POH TUG-3 9 X 84
Section Over Head
P O H P O H P O H
1 2 3
TUG-2 9 X 12
1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7
TUG - 3 TUG - 3 TUG - 3
(9 X 9)
9 X 261
Mapping of 2Mbps into STM N
2.048 Mbps (E1) 1 23 32 Bytes 32
Stuffing Bytes C-12 1 23 34 Bytes 32
POH (Lower Order) VC-12
1 23 35 Bytes 32
Mapping of 2Mbps into STM N
Pointer TU-12 36 Bytes
TU 12 is arranged Into Matrix of 9 X 4
9 Rows
4 Columns
Mapping of 2Mbps into STM N
TU-12 TU-12 TU-12
9 Rows
4 Columns Multiplexing
4 Columns
4 Columns
TUG-2
9 Rows
12 Columns
Mapping of 2Mbps into STM N
7 TUG-2s
Stuffing Bytes
X 7 TUG-2
TUG-3(multiplexing)
TUG 3
84 Columns 86 Columns
Mapping of 2Mbps into STM N
TUG - 3
TUG - 3
TUG - 3
86 Columns
VC - 4
X 3 TUG3
HOPOH Stuffing Bytes
258 Columns 261 Columns
Mapping of 2Mbps into STM N
VC - 4
9 rows
Pay Load
261 Columns AU 4 (Adding Pointer)
AU Pointer
4 th Row
Pay Load
9 Columns
261 Columns
SDH System
TERMINAL EQUIPMENT REGENERATOR ADD / DROP MULTIPLEXER DIGITAL CROSS CONNECT
Regenerator (Reg.)
STM-N
Regenerator
STM-N
It mainly performs 3R function: 1R Reamplification 2R Retiming 3R Reshaping
It regenerates the clock and amplifies the incoming distorted and attenuated signal. It derive the clock signal from the incoming data stream.
Regenerator
Terminal Multiplexer (TM)
PDH SDH
Terminal Multiplexer
STM-N
It combines the Plesionchronous and synchronous input signals into higher bit rate STM-N Signal.
Terminal Multiplexer
Add/Drop Multiplexer (ADM)
STM-N
Add / Drop Multiplexer
PDH SDH
STM-N
Extraction from & insertion into high speed SDH bit streams of Plesiochronous and lower bit rate synchronous signal. Ring structure of network which provides the advantage of automatic back-up path switching in the event of fault.
Add/Drop Multiplexer
Regenerator Section Overhead - RSOH
Media dependent bytes
X Reserved for national use
Unscrambled Bytes
Regenerator Section Overhead - RSOH
Framing Bytes (A1,A2) Indicates start of the STM-1 frame. A1=F6 & A2=28 Section Trace (J0) J0 carries section trace message. Section BIP-8 (B1) Bit interleaved Parity-8 (BIP-8) is used for regenerator section error monitoring. Local Orderwire (E1) Channel for voice communications between any two NEs. Section User Channel (F1) A 64kb/s user data channel. Data communication channel (DCC_R) Provides a single 192 kb/s channel for Management & OAMP
Multiplex Section Overhead - MSOH
Multiplex Section Overhead - MSOH
MS BIP-24 (B2) Bit interleaved Parity-24 (BIP-24) is used for multiplex section error monitoring.
Automatic Protection Switch (APS) (K1,K2) Used for APS signaling
Data Communication Channel (DCCM) Provides a single 576 kb/s channel for Management Synchronization status (S1) 5-8 bits of the byte defines Synchronous status MS 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 NEs
K1 & K2 bit description
Condition
Selects the channel used by APS messages or Destination node ID
Selects bridged channel used or Source node ID
Selects APS architecture or Path code
111 => MS-AIS 110 => MS-RDI
S1 bit description
Future Use
0000 Quality unknown 0010 PRC (G.811) 0100 SSU-A (G.812 transit) 1000 SSU-B (G.812 local) 1011 SEC (G.813) 1111 DNU
Higher Order Path Overhead HPOH(VC-4 / VC-3)
Higher Order Path Overhead HPOH(VC-4 / VC-3)
Path Trace (J1) Path BIP-8 (B3)Label (C2) J1 byte carries thePathStatus (G1) at path level traceSignal Path information Path errorthe type of payload in AU Indicates monitoring Provides status and performance information back to the remote end
J1 B3 C2 G1 F2 H4 F3 K3 N1
Indicator byte (H4)
Carries multiframe (F2,F3) Path User data Channel information
User data channel at path level APS (K3) Bits 1-4 are allocated for APS. Bits 5-8 are for future use. Tandem Connection (N1) IEC for tandem connection monitoring at TCM source.
G1 bit description
Lower Order Path Overhead POH(VC-11 / VC-12)
VC-12
VC-11
Lower Order Path Overhead - POH
V5 J2 N2 K4
Tandem Connection (N2) Signal Label and parity check IEC for tandem connection monitoring at Path Trace (J2) TCM source. J2 byte carriesinformation Carries APS the trace informationorder path level at lower at lower order path level
V5 bit description
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.
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 & 1byte increment for VC-3 payload.
The possible range is: Total STM-1 bytes Section Overhead bytes = Pointer value range (2430 81) = 2349 pointer range
Pointers Continued
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
The pointer value, is carried in bits 7 through 16 of the H1-H2 pointer word. The first four bits indicates an arbitrary change in the value of the pointer. These four bits, the N-bits, are known as the New Data Flag.
H1+H2
S1
S2
Pointer Values (0 782) New Data Flag Size Bits
0110 No Arbitrary change 1001 Arbitrary change (Contiguous concatenation)
Positive Pointer Justification (PPJ)
Positive Pointer Justification (PPJ)
Data
RSOH AU Pointer
MSOH
Virtual Container (VC)
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.
Positive Pointer Justification (PPJ)
Negative Pointer Justification (NPJ)
Negative Pointer Justification (NPJ)
Data
RSOH AU Pointer
MSOH
Virtual Container (VC)
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)
Advantages
High speed standards Efficient Multiplexing / Demultiplexing Enhanced Operation, administration, Provisioning, Maintenance
capabilities (OAM&P)
Next Generation SDH:
Supports data(Ethernet) as well as voice.
Use of GFP, VCAT, LCAS, Auto Negotiation. Emulated LAN (ELAN)
