The Synchronous Digital Hierarchy (SDH) Part I

© Trend Communications

The Synchronous Digital Hierarchy (SDH)

- I part -

by JM Caballero

2/63© Trend Communications

PDH limitations

•• the multiplexing is bit ori-ented (second, third and fourth hierarchy)

•• it is not possible to exe-cute direct add&drop of low speed tributaries

•• poor monitoring capacity because computers are byte oriented

•• lack of management stan-dards and short space to implement them (S bits)

•• lack of standardization between Japan, USA and rest of the world

•• lack of optic standards just proprietary solutions

•• no mechanisms to man-age the quality, just for 2Mbit/s with CRC4


Causes to define SDH

•• The Antitrust law at US fol-lowed by Bell break into small companies.

•• Was necessary to intercon-nect new PTT´s: SONET definition

•• B-ISDN specification to in-tegrate any traffic: SDH and ATM standardization

•• Advanced management needs: computers and tele-com must work together

•• Requirement for having new infrastructures to fit any traffic: data, voice, multimedia


bytes vs. bits

Standardize since 1988 when appeared the G707, G708, G709 CCITT recommendations

•• SDH is byte oriented, it means that a byte is the unit for mapping and multiplexing

•• STM-N is the name for the transport frames. They have always a period of 125µs

•• An important consequence is that in SDH 1 byte represents a 64 Kbit/s channel

125 µs

0 n1 byte

rate =8 bits

125·10-6seg.= 64Kbit/s

0

125 µs

frame 1 frame 2


SDH objectives (i)

•• direct internetworkingbetween equipments

•• scalability in transmis-sion speeds until 0 Gbit/s

•• direct add&drop for low speed tributaries

•• capabilities for new con-trol channels supervi-sion, maintenance & service

•• support to fit any applica-tion: audio, video, voice

•• remote and centralized management

•• easy migration from PDH networks

•• fault tolerance


SDH is a flexible architecture

•• SDH has a reference model

•• It is an standard universally accepted

•• SDH is highly compatible with SONET

•• very efficient to manage circuits

•• fast circuit definition from a centralized point

•• advanced facilities for quality monitoring


Circuit provisioning

SDH provides an efficient, reliable and flexible transport for circuits

multiplexing, transport, routing, management, reliability

Internetservices Frame Relay ATM GSMRTB

transport network

SDH

transmission media cable/fiber/radio

Section

SDH architecture

client

server

SDH architecture 9/63© Trend Communications

The network is a function of the connectivity

The model considers the network as a connectivity function

•• it has a set of input/output interfaces

•• there are function to match requirement with capacities

The complexity of the functions moves to use simplified models which allow to define interfaces

and overheads

outputsinputsFunction of

connectivity


Topologic partitioning

The topology describes the potential connections and are expressed as relations between

points on the network

•• the network is an encapsulation that is able to be splitted repeatedly in subnetworks inter-connected through links

•• the subnetworks are decomposed until the desired level or when nodes and transmission media are visible (the last layer)

•• nodes are the network elements: switches, multiplexers, and regenerators


Functional partitioning

The model allow to define independent structures but connected. Each layer can be seen as a

network which can be divided in sublayers

In PDH the relationships are directs, in SDH are complex and the transport service has been

divided in two layers:

•• one to connect terminal points (paths)

•• one to connect routes (sections)

The model permits also a control of the network elements and a full connection compatibility

because all the vendor refer to the same abstract model.

Client layer

Server layer

network connection

Layer Adaptation: unifies the information format using

Layer Termination: adds/drops overheads in order to allow

path

digitalizationcodification

add/dropoverheads a service monitoring and supervision

techniques like mapping, justification, multiplexion, overheads


Reference points

•• AP - Access Point: it is the place where are executed the adaptation functions like framing, justification, multiplexing, and alignment. There are two by connection. They are the edge points which can interchange client information

•• CP - Connection Point: it is the place where are implemented the atomic connections. The CP association is known a Subnetwork. A link is the association of two subnetworks. Thesepoints are monitored in order to know the network status

•• TCP - Terminal Connection Point: it is the edge CP where it is checked the data integrity. A Network Connection is the association of two TCP

CP

Layer Adaptation

CP CP CP

TCPTCP

Layer Adaptation

AP

Network connection

link

Subnetwork

Layer Termination

AP

Layer Termination Network connection


Connectivity

•• A Network Connection is a concatenation of basic elements. The edge points (in/out) are TCP

•• Basis elements are subnetwork connections between CP and links between Subnetworks.

•• The connections can be half-duplex, full-duplex, point to point, point to multipoint, multipoint to multipoint

•• The connection monitors the client information integrity

CPCP CP

CP

TCP

AP AP

SubnetworkConnection

SubnetworkConnection

Link Connection

Network Connection

Client layer

Server layer

Client Path

Server Path

TCP


Transport stratification

There is a client/server relationship with headers and adaptation function similar to the OSI

layered model used to explain protocols

VC12 level path

VC12 level

2 Mbit/s level

VC4 level

STM level

VC4 level path

STM-1 section

2 Mbit/s circuit

DXC DXC

Subnetwork

connection

Subnetwork

connection

Layer Adaptation

Layer Termination

Layer Adaptation

Layer Termination

transmission media


Transference integrity: trails

•• The source delivers information which is adapted: digitalization, codification,...

•• The trail define the transport capabilities and it is able to monitor the integrity and quality of the information interchanged between AP

•• These functions allow to implement the OAM functions (Operation, Administration, and Maintenance)

•• The trails have associated the overhead between the interchange units

CP

trail

Layer Adaptation

CP CP CP TCPTCP

Layer Adaptation

AP

client connection

overheads management overheads management


Network Node Interface (NNI) location

NNI (Network Node Interface) are the connection between subnetworks:

•• NNI are internal network interfaces used to transmit the STM-N frames

•• NNI interface is defined at the access, the transport network; and the interconnection units

•• NNI, PDH, and ATM are SDH network interfaces. They are standards to guarantee the world network interconnections

M U X

sinc.

M U X

sinc.

M U X

sinc.

NNI

Media :

· fiber

· wireless

DIGITAL CONNETION

A C C E S S

Media :

· fiber

· wireless

NNI NNI NNI

M U X

sinc.

M U X

sinc.

M U X

sinc.

TributariesTributariesTributaries

TributariesTributaries

CXC

PDHATM

PDHATM


Reference model

physical interface

sección de regeneración

sección de multiplexión

low order VC-12

FrameRelayISDNRTB ATM

IP

SDH frame physical interface

regeneration section

multiplexing section

high order VC-4

low order VC-12

regeneration section

multiplexing section

optical/electrical/radio

paths

FrameRelay ISDN RTBATM

IP

sections

interchange unit

high order VC-4

MSOH

VC-4

RSOH

VC-12

STM-1

NNI

Section

Network elements and topologies


Regenerators (REG)

It maintains the physical the signal by means of strength, shape and delay

•• attenuation: reduction of strength of the signal per distance. Amplification

•• delay distortion: the velocity of propagation varies with frequency causing intersymbol inter-ference. Signal needs equalization

•• noise: different causes like thermal noise, intermodulation, crosstalk, impulse noise is al-ways present. The signal must be digitally filtered

STM-NSTM-NREG


Line Termination Multiplexors (LTMUX)

Mux/Demux of plesiochronous circuits to/from STM-N frames

•• The input and the output of the circuit from the SDH network define the paths

•• Are useful for line topologies providing easy migration form legacy PDH networks

•• Overhead management

S D H

M U X

2M

34M

140M

STM-1 STM-N

H O -P T EL O -P T E

45M

8M


Multiplexers (Mux/Demux)

Mux/Demux of STM-N signals in/from STM-M

•• Does not modify the contents of transported information

•• Multiplexion of four SDH signals:4 x STM-1 = STM44 x STM-4 = STM164 x STM-16 = STM64

SDH

MUX

STM-M

STM-N

STM-N

M >N


Add & Drop Multiplexer (ADM)

Put / get PDH circuits in/from STM-N frames

•• configures SDH rings topologies

•• can provide the network with fault tolerant capacities

STM-M STM-M

STM-N, PDH

West East


Digital Cross-Connect (DXC)

Switchs STM signals as well as add&drop funcionalities.

•• implements all the network element capacities

•• absolutly flexible for subnetwork interconnections

•• allows SDH networks interconnection

STM-N

STM-N

STM-N

STM-N


Point to point topology

•• Simples but scalable to complex topologies

•• Transport STM signal between two points

•• Allows an smooth migration from legacy PDH networks to SDH

LPTHPTSDH

MUX

SDHHPTLPT

2M

MUX34M

140M

STM-1 STM-N

45M

MUX

2M

34M

140M

STM-1STM-N

45M

MUX

MUXMUX

REG


Ring topology

•• flexible and scalable

•• provide a native way for reservation circuits

•• allow circuits add&drop at any nodeA

DM

ADM

AD

M

back up ring

active ring

ADM

tributary tributary


Star and hub configurations

•• Both configurations allow an smooth migration from PDH infrastructures

Star PDH network physical topology with star configurationand logical topology with ring configuration

SDH Network

A

B

C

D

E

A

B

C

D

E


Transport design

The networks are designed with topologies that try to drive a lot of traffic through the same ring

and a few inter rings or inter layer

National Backbone

Primary Network

Access Network

STM-16

STM-4

STM-1 or PDH


Low Order Paths & High Order Paths

The Virtual Container (VC) across the SDH defining a path and two edge points. One where

the VC is inserted and the other where it is dropped. There are two types of paths:

•• The High Order Path (HOP) links two points with a high rate transport capacity. The content can be a a circuit of 140 Mbit/s or combination of circuit of 1.5, 2, 6, or 8 Mbit/s

•• The Low Order Path (LOP) links two points with a high rate transport capacity. The content can be a a circuit of 1.5, 2, 6, or 8 Mbit/s

•• The circuits of 34 and 45 Mbit/s can be transported both, into High or Low Order Path

LOW ORDER PATH

HIGH ORDER PATH

LTMUXREG REGREGMUX DXC ADMHOLO

LTMUX

LOHO


Multiplexing Section (MS)

A section is the space limited by two network elements linked by a transmission media. There

are two types: the Multiplexing Section (MS) and the Regeneration Section (RS)

The MS is the space defined by two contigous multiplexers. Each MS manages an specifc

overhead to control the multiplexers by means of :

•• quality monitoring with alarms/errors detection between Multiplexers

•• provide voice and data channels to configure and operate the Multiplexers

•• facilities for synchonization and automatic protection (APS)

LOW ORDER PATH

HIGH ORDER PATH

MULTIPLEXING MULTIPLEXING

SECTION SECTIONSECTION

MULTIPLEXING


LTMUX

LOHO


Regeneration Section (RS)

The RS is the space betwen two regenerators united by the any media: fiber, wireless, coaxial.

(Pay attention that a Multiplexer works as a Regenerator too.)

Each RS manages an specifc overhead to control the Regenerators by means of:

•• quality monitoring with alarms/errors detection between Regenerators

•• provide voice and data channels to configure and operate the Regenerators

•• framing and contents information

LOW ORDER PATH

HIGH ORDER PATH

MULTIPLEXING

REG

MULTIPLEXING

SECTION SECTIONSECTION

SECT

MULTIPLEXING

REG

SECT

REG

SECT

REG

SECT

REG

SECT

REG

SECT


LTMUX

LOHO


Regeneration process

•• The optical signal must be amplified to compense the attenuation, distortion, and noise dur-ing the fiber, cable or wireless propagation.

•• the signal is converted to an electronic signal, then it is filtered and amplified and finally it is converted back to its original nature

•• onother technique to amplifly optical signals is to use Optical Fiber Amplifier (OPA). It con-sists of a fiber segment (about 70 mtr long) doped with erbiumis and pumped with a light that excites the erbium. And then when a signal passes through the fiber more photons out than photons in: the signal has been amplified

Original signal Regenerated signal

Regenerator

noiseattenuation distortion

Regeneration SectionRegeneration Section

Multiplexer

ADMREG REG

Regenerator


Transport Services

SDH provides circuit to public switched and routed networks

ADM

AD

M

AD

M

ADM

ADM

AD

M

AD

M

ADM

ADM

AD

M

AD

M

ADM

ADM

AD

M

AD

M

ADM

DXC

PSTN

ATM

STM-16 STM-4

ISDN

GSM

LTMUX

LTMUX

Circuit

34 Mbit/s

155 Mbit/s

2 Mbit/s STM-1 STM-1

2 Mbit/s

STM-1

140 Mbit/s

34 Mbit/s140 Mbit/s

STM-1,4

2 Mbit/sInternet

34 Mbit/s

2 Mbit/s

ATM

Section

Security

A B

A B


Security services

When a circuit goes down traffic can not stopped. Reliability is one of the strongest

characteristics of SDH networks. In order to assure that has been defined the following

strategies:

diversification

•• all the traffic between two sites are divided in several circuits. When one of them goes down the rest of the circuits continue working on

restoration

•• the routing is a task of the client network (IP, ATM)

•• when a circuit goes down an specialized multiplexer looks for an available circuit and switch-es the traffic to the alternate path

protection

•• the routing is a task of the transport network (SDH)

•• alternate circuits have been assigned previously, when a circuit goes down the multiplexer switched the traffic to the back up resource


Diversification

The circuits, between two points, are established using different physical routes. A fault in a

transmission route interrupts just a part of the traffic.

•• It has been used for PDH voice traffic

•• It is an acceptable strategy for no critical circuits

•• In order to provide the same service level it is required to duplicate the number of circuits

•• But most of the times it is no admissible, or possible, to reserve an unused route for each of the network circuits

A

B

C

D

C1 C2

route 1 (50% C1-C2)

route 2 (50% C1-C2)


Restoration

There is not a previous assignation of the circuits.

•• If an active circuit gets down then a protection protocol is executed in order to provide an alternative route

•• The protection circuits share the same network elements and transmission media that are used by the active circuits

•• Pay attention on that: the number of protection circuits is smaller than the active. Using a relation equals to 1/2 for protection circuits could be enough

•• Usually the relation goes from 40% to 80%

A

B

C

D

(5,2)

(active circuits, protection circuits)

(4,2)

(3,4)

(7,7)

(4,5)

A

B

C

D

(7,0)

(6,0)

(5,2)

(11,3)

(a,p) =


Protection (i)

The mechanism is similar to the restoration technic, but there is an previous assignation of

circuits before the fault appears

SDH path protection

•• multiplexing section protection for line topologies

•• multiplexing section protection for ring topologies

•• multiplexing section shared protection for line topologies

•• virtual container protection

SDH subnetwork protection

Is a specialized protection mechanism for all network topologies. It can be used for protecting

parts of the network or all the network

•• with internal supervision (witch uses information about the own network for switching)

•• with no intrusive supervision (witch uses associated information for switching)


Linear protection of multiplexing section

protection (P)service (S)

MUXSame traffic in S and P

1:1Different traffic in S and P

high priority

low priority

1:N

1+1MUX

MUXMUX

MUXMUX


Specialized protection: 1 fiber rings

•• one active ring and one protection ring

•• a new protection ring is established at the multiplexer edge of the fault

•• all the rings are unidirectional

Circuit in normal conditions Circuit under protection

protection ring

service ring

A circuit

A circuit in bakup

B circuit

B circuit

B circuit

A circuit B circuit

A circuit in bakup B circuit

AD

M

ADM

AD

M

ADM ADM

AD

M


Ring shared protection with 2 fiber

•• two active rings of one fiber

•• n/2 active circuits and n/2 protection circuits per section

•• to implement uses K1, K2 bytes

service and protection rings

service circuits


service circuitsservice circuits using

protection services

service circuits usingprotection services

two active rings in a single fibre

AD

M

AD

M

AD

M


Specialized protection in 2 fiber rings

•• 1 active ring of two fibers

•• 1 protection ring of two fibers

•• Note that rings are bidirectional

ADM ADM

A circuit

circuito A circuito Aen back up

circuito Aen back up

service&protection rings


AD

M

ADM

AD

M

ADM

Section

SDH transport services

M b i t / sM b i t / s

1 . 5 , 2 ,

6 , 8 ,

3 4 , 4 5

C - nV C - nTU-nT U G

C - nV C - nA U G

+ L O P O H + T U

( p o i n t e r )( p o i n t e r )

+ s t u f f i n g b i t s

+ j u s t i f i c a t i o n b i t s

+ o v e r h e a d b i t s

+ H O P O H + A U

( p o i n t e r )

S T M - 1

Mbit/s

1 4 0 ,

3 4 , 4 53 4 , 4 5


+ j u s t i f i c a t i o n b i t s


SDH transport services 43/63© Trend Communications

The SDH multiplexing map

AU-4AUG C-4

TU-3 VC-3

C-3

C-2VC-2TU-2

C-12VC-12TU-12

C-11VC-11TU-11

TUG-3

AU-3

STM-1

ATM 1600 kbit/s

T1: 1544kbit/s

ATM:2144kbit/s

E1:2048kbit/s

ATM:6874kbit/s

T2: 6312kbit/s

ATM:48384kbit/s

T3:44736kbit/s

E3: 34368 kbit/s

ATM:149760 kbit/s

E4: 139264kbit/s

x1

x3

x4

x7x7

x1

x1

TUG-2

x1

x3

STM-0

x3

POH addition

Multiplexing

Tributary mapping

Aliingning

Frame

Pointer processing

Container

Group

STM-64

STM-16

STM-4622 Mbit/s

10 Gbit/s

2,5 Gbit/s

155 Mbit/s

51 Mbit/s(ANSI)

(ANSI)

(AN

SI)

(AN

SI)

x1

VC-4

VC-3

AU44cAUG4 C-44cx1x1

VC44c

AU416cAUG16 C416cx1x1

VC416c

AUG16

x1

x1

x1

x4

x4

x4

x1


Transport of PDH circuits, ATM cells and IP datagrams

The mapping in standarized structures to provide circuits

•• PDH, and T-Carrier hierarchies are mapped in specific Containers (C-n)

•• ATM cells are mapped also in Containers C-n

•• IP datagrams are mapped in Containers C-n

M b i t / sM b i t / s

1 . 5 , 2 ,

6 , 8 ,

3 4 , 4 5

C -nV C -nT U -nT U G

C -nV C -nA U G

+L O P O H + T U

( p o i n t e r )( p o i n t e r )


+ just i f i cat i o n bits


+ H O P O H + A U

( p o i n t e r )

S T M -1

M b i t /s

1 4 0 ,

3 4 , 4 53 4 , 4 5


+ just i f i cat i o n bits



Containers

The mapping operation:

•• Multiplexers adjusts the capacity of containers with the provided info using byte stuffing

•• The containers have justification mechanism byte oriented also

•• The multiplexing function is a synchronous operation because all the network multiplexers must use the same clock.

•• With PDH it is not mandatory to synchronize the network equipments

8Mbit/s

PDH frames

2Mbit/s

MUX

mappingstuffing

MUX155Mbit/s

SDH container

2Mbit/s

MUXmappingstuffing

autonomous synchronized

synchronism

master clock master clock

justification

justificationbit oriented

byte oriented


The container C-4

During the mapping operation the multiplexer receives the tributary which is placed into the

container, justification bytes are used to accomodate the clock differencies, and the stuffing to

fill the extra space up.

•• The C-4 container provides big capacity services

•• It provides transport for E4 circuits (139264 kbit/s)

•• ATM cell can be mapped directly in C-4

1 1 1 1 112 12 12 12 12

S

S

S

S

S

S

S

S

S

S

S

S

S

X

X

X

X

Xco lumn 11

co lumn 270

Byte sequence in every row of a C-4 (260 by tes )27011

C-4

1

9

X

Z

: information byte(s) from a 139264 Kbit/s s ignal

= C S S S S S O O

= I I I I I IJ S

S : stuffing byte

1 C-4 row

Z

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

II

I: Information bitS: Stuffing bitC: Justification control bitJ: Justification opportunity bitO: Overhead bit


The VC-4 Virtual Container

•• C4+POH=VC4

•• The Path Overhead (POH) is added and will travel together until the termination point

•• Only the termination multiplexer is allowed to modify the POH contents

27010 11

1

9

VC-4 Path

Overhead

(POH) is added

C-4 into a VC-4

J1

B 3

C 2

G 1

H4

F3

K 3

N1

F2


AU pointer association

The ALIGNING process associates a pointer

•• The pointer allows to find the VC-4

•• The pointer occupies always a fixed position inside the STM-1 frame. The VC-4 does not occupies a fixed position in the frame to adapt clock impairments

POH

J1

B3

C2

G1

H4

F3

K3

N1

RSOH

MSOH

1 2709 10

27010 11VC-4

AUG

F2

STM-1


VC4 insertion to the STM-1 frame

perfect synchronization

V=150 km/h

155 km/h

Containers exactly allocated

VC-4 VC-4 VC-4 VC-4

STM-1 STM-1 STM-1


VC4 insertion to the STM-1 frame (ii)

common synchronization

V<150 km/h

155 km/h

Containers allocated

VC-4 VC-4 VC-4 VC-4

STM-1 STM-1 STM-1

between two frames


The STM-1 frame

•• STM-1 = AUG + RSOH + MSOH

•• In the carrier STM-1 frame are included the section overheads RSOH y MSOH to control and manage the network elements

•• The VC4 is floating inside the STM-1, it may change it position an integer number of bytes inside the space reserved in the STM-1 frame. In this way, clock fluctuations between the STM-1 and the VC-4 are absorved

•• The AU pointer always points to the position where the VC4 starts and follows possible fluc-tuations

P O H

J 1

B 3

C 2

G 1

H 4

F 3

K 3

N 1

R S O H

M S O H

1 2709 10

27010 11

VC-4

F 2

R e g e n e r a t o r

S e c t i o n

O v e r h e a d

Mul t ip lexer

S e c t i o n

O v e r h e a d

S T M -1

Admin i s t ra t i ve

U n i t G r o u p


How to fill up the payload:

Composition 2Mbit/s 34Mbit/s 140Mbit/s

1 VC4 0 0 1

3 VC3 0 3 0

21 VC12 + 2 VC3 21 2 0

42 VC12 + 1 VC3 42 1 0

63 VC12 63 0 0

P O H

J 1

B 3

C 2

G1

H4

Z 3

Z 4

Z 5

RSOH

MSOH

1 2709 10

27010 11VC-4

F 2

S T M - 1


The STM-N frames

4567

0123x4

0123

x4

4567

x4

89AB

x4

CDEF

x4

89AB

CDEF x16

direct multiplexing Frame Binary rate (kbit/s) Short Id.

STM-1 155.520 kbit/s 155 Mbit/s

STM-4 155.520 x 4 = 622.080 kbit/s 622 Mbit/s

STM-16 622.080 x 4 = 2.488.320 kbit/s 2,5 Gbit/s

STM-64 2.488.320 x 4 = 9.953.280 kbit/s 10 Gbit/s

0123456789ABCDEF

0123456789ABCDEF


The sequence transmission

Sequence is from top to down and letf to right

The top left corner is frame alignment word.

This word is the first transmitted in order to get

sinchronization

A1 A1 A1A2 A2 A2 J0

A1A1A1A2A2A2J0

125µs

125µs

Section

Example: transport of 45 Mbit/s

SDH 45 Mbit/s45Mbit/s


Transport of 45 Mbit/s as Low Order Path (i)

Complete sequence of mapping, framing, alignment and multiplexing of a circuit of 45 Mbit/s

in a STM-1 frame of 155 Mbit/s

34

C-3VC-3TU-3TUG-3

+ LO POH+ TU

pointer

VC-nA U GSTM-1

+ HO POH+ SOH

x 3

+ AU

pointer

+ stuffing bits

+ justification bits

+ overhead bits


Asynchronous mapping in a C-3 container (ii)

The public network can be a circuit for Interned, Frame Relay, ATM, leased....

•• mapping of a 45 Mbit/s signal in the C-3 container that is network synchronous

•• is also used for 34 Mbit/s transport with other mapping in the C-3

•• the frame period is 125 µs

•• There are pointer justifications for clock differences adjustment

45Mbit/s

C-3

VC-3

Public Network

863

C-3

1

9

11 1 11 1 11 125 25 25

YX Z

X = SSC I I I I I

Y = C C S S S S S S

Z = C C S S O O S J

: In fo rmat ion by tes f rom a 43 Mb i t / s t r i bu ta ry

I I III

I

I: Information bitS: Stuffing bitC: Justification control bitJ: Justification opportunity bitO: Overhead bit


Creation of the Virtual Container VC3 (iii)

Path overhead (POH) is added to the multiframe creating the VC3

2Mbit/s

C-3

VC-3

TU-3

862 3(85 columnas)

1

9

VC-3

C -3

G 1

H4

F 3

K 3

N1

F 2

J 1

B 3

C 2


Multiplexing and creation of the TU3 (iv)

•• a VC-3 plus a pointer is a TU-3

•• The pointer is always accessible and points to the frame start

TUG-3

VC-3

TU-3

x1H 1

H 3

H 2+

P o i n t e r b y t e s

862 3

1

9

G 1

H 4

F 3

K 3

N 1

F 2

J 1

B 3

C 2

V C -3

T U -3


Creation of the TUG3 (v)

•• Using only a TU-3 a TUG-3 is created adding the corresponding stuffing bits

•• The pointer is still located in accessible positions

x1

x3

TU-3

TUG-3

VC-4

T U G -3862 3

1

9

H 1

H 3

H 2

1

R

G 1

H 4

F 3

K 3

N 1

F 2

J 1

B 3

C 2


Creation of the Virtual Container VC-4 (vi)

•• A new structure is used for group all the three TUG-3 together

•• Then the POH overhead and the stuffing bits are added until the frame is completed

J 1

B 3

C 2

G 1

H4

F 3

K 3

N1

27011 12

F 2

1

9

13 14

R R

byte interleaving

3 TUG-3

stuff ing bytes

( 3 x 86 = 258 columns )

x3

TUG-3

VC-4

AU-4


Creation of the AU4 adding a pointer (vii)

•• A new pointer is added, the AU-4 pointer that points to the first byte of the VC-4

•• The AU4 is in a fixed position of the frame and thus it can be easily located

•• This operation is known as alignment

VC-4

AU-4

STM-1

POH

J1

B3

C2

G1

H4

F3

K3

N1

RSOH

MSOH

1 2709 10

27010 11VC-4

F2

STM-1


Creation of the STM-1 frame (viii)

•• Section overheads, RSOH and MSOH, are added

•• The AUG administrative unit is placed in the frame

VC-4

AU-4

STM-1

RSOH

MSOH

1 2709 10

A U G

RSOH: Regenerator Sect ion Overhead

MSOH: Mult iplexer Sect ion Overhead

STM-1

Documents

The Synchronous Digital Hierarchy (SDH) Part I