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 = 193 bits per 125 microseconds = Mbps E1 30 voice time slots plus 2 time slots for synchronization => Total transmission rate 32 x 8 = 256 bits per 125 microseconds = 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 ( 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