1

SONET/SDH

2

T1/E1

Time division multiplexing Allows a link to be utilized simultaneously by many users

3

Trunks and channels The transmission is organized into frames

Each frame contains a fixed number of time slots

Each time slot Is pre-assigned to a specific input link

The duration of a time slot is either a bit or a byte

Each time slot dedicated to a user repeats Continuously frame after frame, thus forming

A channel or a trunk

4

TDM in telephony

TDM is used in telephony

Voice analog signals are digitized at the end office Using Pulse Code Modulation

Voice signal is sampled 8000 times/sec Or every 125 microseconds

A 7-bit or 8-bit number is created over 125 microseconds

5

The digital signal (DS) and ITU-T standard

DS A north American standard that specifies

How to multiplex several voice calls onto a single link

The DS standard is a North American standard And it is not the same as

The international hierarchy standardized by ITU-T

6

T carrier/ E carrier The DS signal is carried over a carrier system

Known as the T carrier T1 carries the DS1 signal (24 voice calls)

T2 carries the DS2 signal

The ITU-T signal is carried over a carrier system known as the E carrier

The DS and ITU-T hierarchy Is known as the plesiochronous digital hierarchy PDH

Plesion means “nearly the same”, and

“Chronous” means “time” in Greek

7

T/E hierarchy

8

Transmission rate

T1 Total transmission rate

24 time slots plus one bit for synchronization

=> 24 x 8 + 1 = 193 bits per 125 microseconds = 1.544 Mbps

E1 30 voice time slots plus 2 time slots for synchronization

=> Total transmission rate

32 x 8 = 256 bits per 125 microseconds = 2.048 Mbps

9

Fractional T1/E1

Fractional T1 or E1 allows The use of only a fraction of the T1 or E1 capacity

For example If N =2

Then only 2 time slots are used by the user per frame

Which correspond to channel with total bandwidth of 128 Kbps

10

The synchronous optical network (SONET)

Proposed by Bellcore (Telecordia) It was designed to multiplex DS-n signals

And transmit them optically

ITU-T adopted Synchronous digital hierarchy (SDH) As the international standard

It enables the multiplexing of level 3 signals (34.368 Mbps)

11

STS, STM, OC

The electrical side of the SONET signal is Known as the synchronous transport signal (STS)

The electrical side of the SDH is known as The synchronous transport module (STM)

The optical side of a SONET/SDH signal is Known as the optical carrier (OC)

12

SONET/SDH multiplex rates

13

The STS-1 frame structure

87 columns carry The actual data being transported

is called synchronous payload envelope (SPE)

14

Two back-to-back SONET frames