Digital Carrier Systems

(1)

Applied Network Research Group Department of Computer Engineering, Kasetsart University

Digital Carrier Systems

Surasak Sanguanpong nguan@ku.ac.th http://www.cpe.ku.ac.th/~nguan

Last updated: 11 July 2000

2/28

Digital carrier standard

z T-carrier

z North America, Japan

z E-carrier

z Europe, South America

z SONET/SDH

z world-wide new standard

(2)

Comparison of the layer

Physical Data link Network Transport

Session Presentation

Application

Physical Physical

OSI T-1 SONET/SDH

4/28

Organization of telephone services

The telephone message are routed through :

• a switch at the central office (CO) for a local calls

• a switching center for out-of-area calls

• toll exchanges for long distance calls

CO CO

switch switch to local

call

local loop

Toll exchange

Area toll change

Inter-office trunk (IOT)

z

The original IOT connections were made over an analog system called N-carrier.

z

The T-carrier system was the first widely deployed digital transmission system

z

The original IOT connections were made over an analog system called N-carrier.

z

The T-carrier system

was the first widely

deployed digital

transmission system

(3)

T-1 carrier system

CH1 CH2

CH24

PCM CH1 CH2 CH3 CH23 CH24

CH23

x x x x x x x x

MSB

(sign bit)

LSB

z

24 voice channels are sampled, quantized and encoded into a TDM PCM signal

z

T-1 carrier has a transmission rate of 1.544 Mbps

z

Bipolar encoding

z B8ZS for T-1

z B3ZS for T-3

z

Full duplex

z

Channel-based digital transmission

z

Bipolar encoding

z

B8ZS for T-1

z

B3ZS for T-3

z

Full duplex

z

Channel-based digital transmission

6/28

T-1 frame

CH 1 (8 bit) CH 1

(8 bit) CH 2 (8 bit) CH 2

(8 bit) . . . . . . . . CH 24 (8 bit) CH 24 (8 bit)

1 frame bit

192 bits

T-1 bit rate : (24x8 +1 bit)/125 µµµµs = 1.544 Mbps 125 µµµµs

z

The early frame standard called D1, D2 and D3 were used.

z

There are two framing standard for the T-1, called D4 (superframe) and extended superframe (ESF)

z

The T-3 used the M13 framing

z

The early frame standard called D1, D2 and D3 were used.

z

There are two framing standard for the T-1, called D4 (superframe) and extended superframe (ESF)

z

The T-3 used the M13 framing

(4)

Frame and Superframe

z

T-1 carrier frames are transmitted in groups of 12 called superframes

z

F-bit in even-numbered frame has a pattern of 101010 for synchronization

z

Signaling information is accomplished by robbing the LSB position of each channel. This is performed only in the 6

^th

and 12

^th

frame to keep distortion minimum

F

_combine

1 0 0 0 1 1 0 1 1 1 0 0

F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12

F

even

0 0 1 1 1 0

F

_odd

1 0 1 0 1 0

1 superframe = 12 frames (2316 bits in 1.5 ms)

Frame # F data (192 bits) 1 1 dddd dddd -- dddd dddd 2 0 dddd dddd -- dddd dddd 3 0 dddd dddd -- dddd dddd 4 0 dddd dddd -- dddd dddd 5 1 dddd dddd -- dddd dddd 6 1 dddd dddX -- dddd dddX 7 0 dddd dddd -- dddd dddd 8 1 dddd dddd -- dddd dddd 9 1 dddd dddd -- dddd dddd 10 1 dddd dddd -- dddd dddd 11 0 dddd dddd -- dddd dddd 12 0 dddd dddX -- dddd dddX

8/28

Extended Superframe

z

ESF framing groups 24 frames into an ESF superframe

z

every 193rd bit are used for the above purposes

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Remote configuration and monitoring (4Kbps) CRC

Frame synchronization

(5)

Multiplexing

z

CSU (Channel Service Unit)

z

performs several protective and diagnostic functions

z

DSU (Data Service Unit)

z

convert the digital data from a (for example) router to T1 voltages and encoding.

CSU/DSU MUX

router phone

T-carrier

10/28

T-carrier Digital Multiplexing Hierarchy

DS1

DS1C

DS2

DS3

DS4

DS1C

DS2

DS2 DS2 DS2 DS2

DS2

DS3 DS3 DS3 DS3

DS3

DS1 Two 1.544 Mbps DS1 channels are multiplexed into a single 3.152 Mbps DS1C channel

Two DS1C channels are multiplexed into a single 6.312 Mbps DS2 channel

Seven DS2 channels are multiplexed into a single 44.736 Mbps DS3 channel

Six DS3 channels are multiplexed into a single 274.176 Mbps DS4 channel

T1

T2

T3

T4

T1-C

(6)

E1-frame

CH 0 CH

0 CH

1 CH

2 CH

16 CH

31 CH 31

125 µs

frame synchronization

signaling channel

30 voice channels+2 control channels

E1 bit rate : (32x8 bit)/125 µµµµs = 2.048 Mbps

12/28

E-carrier

E1 E1 E1 E1

E2

E2 E2 E2

E3

E3 E3 E3

E4 E4 E4 E4

E5

Thirty 64 Kbps channels are multiplexed to create one 2.048 Mbps E1 channel

Four E1 channels are multiplexed into a single 8.448 Mbps E2 channel

Four E2 channels are multiplexed into a single 34.368 Mbps E3

channel Four E3 channels

are multiplexed into a single 139.264 Mbps E4 channel

Four E4 channels are multiplexed into a single 565.148 Mbps E5 channel

(7)

Digital carrier comparison

2.048 2.048 8.448 8.448 34.368 34.368 139.264 139.264 564.992 564.992

1.544 1.544 6.312 6.312 44.736 44.736 274.176 274.176

1.544 1.544 6.312 6.312 32.064 32.064 97.728 97.728 397.200 397.200 64 64

J1 E1

T1

J2 E2

T2

J3 E3

T3

J4 E4

T4

J5 E5 x31

x24

x 4

x 2

x 4

x 7

x 5

x 4

x 6

x 3

x 4

Europe

USA

Japan 3.152

3.152 x 2 T1C

14/28

PDH

z

PDH = Plesiochronous Digital Hierarchy

z

Digital transmission systems (T-carrier, E carrier) combine lower order multiplex stream to get higher bit rate

z

Each device runs its own free-running clock

z

Different streams have small differences in clock signals.

z

Solve by adding justification bit

almost synchronous

(8)

PDH deficiencies (I)

140 M LTE

140

34

34 8

8 2

140 34

34 8

8 2

140 M LTE

34 Mbps

8 Mbps

2 Mbps

Customer site

z Lack of flexibility

z

impossible to identify a lower bit rate channel from the higher-order bit stream.

demux the high bit

rate down to the lower level remux back into higher

level for onward transmission

Extraction of 2 Mbps channel from 140 Mbps channel

16/28

PDH deficiencies (II)

z Lack of performance

z

No standard for monitoring the performance of traffic channel

z

No management channel z Lack of ‘Mid-Fibre meet’

z

undefined interface specification on the line side of a line transmission

LTE

G.703 interface

non standard line code and optical levels

standard Network Node Interface (NNI) functional integration

of MUX and LTE

PDH SDH

(9)

SDH & SONET

z

What is SDH/SONET ?

z

Standard interface developed for using in the public network

z

multiplexing standard for optical fiber transmission

z

SONET = Synchronous Optical Network

z

refers to the system used within the U.S. and Canada

z

SDH = Synchronous Digital Hierarchy

z

international community term (ITU-T recommendations)

18/28

SDH/SONET goals

z

Goals

z

make it possible for different carrier to interwork

z

unify the U.S., European and Japanese digital system

z

Provide a way to multiplex multiple digital signal together

z

provide support for operations, administration, and maintenance

z

Characteristics

z

use single master clock to synchronize

z

Bit stream can be a added or extracted directly

z

Basic transmission rate = 155.52 Mbps

(10)

SDH/SONET topology

z

Typical SDH/SONET topology is a dual ring (fiber optics)

z

One ring is the working facility, and the other ring is the protection facility (standby)

z

End-user devices operating on LANs or other transport systems are attached through terminal adapter ADM

DCC ADM

DS1 DS3

Other SONET/SDH

networks

TA TA

20/28

SDH/SONET System

z

consists of switches, mux and repeaters

section

section section section

line line

path

mux repeaters mux repeaters mux

(11)

Multiplexing level

SONET SDH Bit rate (Mbps)

STS-1/OC-1 51.84

STS-3/OC-3 STM-1 155.52

STS-9/OC-9 STM-3 466.56

STS-12/OC-12 STM-4 622.08

STS-18/OC-18 STM-6 933.12

STS-24/OC-24 STM-8 1244.16

STS-36/OC-36 STM-12 1866.24

STS-48/OC-48 STM-16 2488.32

STS = Synchronous Transport Signal OC = Optical Carrier

STM = Synchronous Transport Module (Not defined)

22/28

SDH Basic Frame structure

1 frame = 2430 bytes in 125 µs

1 2 3 4 5 6 7 8 9

STM-1

Overhead

: for system management information (OAM)

SOH = Section Overhead LOH = Line Overhead TOH = Transport Overhead

Payload

: user data row/column mapping

261 bytes

3 bytes

6 bytes 9 bytes

9 bytes

SOH

LOH

Payload

(12)

Applied Network Research Group Department of Computer Engineering, Kasetsart University 87 bytes

3 bytes

SONET Basic Frame structure

1 frame = 810 bytes in 125 µs

1 2 3 4 5 6 7 8 9

STS-1/OC1

3 bytes

SOH

LOH

Payload

TOH

Overhead

^:

for system management information

SOH = Section Overhead LOH = Line Overhead TOH = Transport Overhead

Payload

: user data row/column mapping

24/28

STM-1 Frame

SOH

LOH pointer

SOH

LOH pointer frame #1

frame #2

Payload #1

Payload #1 Payload #1

Payload #1

Payload #2 Payload #2

PO H #1 PO H #2

(13)

SDH mux scheme

AUG AU-4 VC-4

TUG-3 TU-3 VC-3

C-4

AU-3 VC-3

TUG-2 TU-2 VC-2 C-2

TU-12 VC-12 C-12

TU-11 VC-11 C-11 C-3

x1

x3

x7

x7 x1

x3 x4

140 Mbps

45 Mbps 34 Mbps

6 Mbps

2 Mbps

1.5 Mbps STM-1

SONET-specific Europe-specific Universal

PDH Tributaries

26/28

Administrative Unit Tributary Unit Group

SDH Elements

Containers

Virtual Containers

Tributary Unit Administrative Unit Administrative Unit Group path overhead

pointer

Tributary Unit Group Tributary Unit Tributary Unit

section overhead

STM-1

(14)