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Understanding SONET/SDH and T1/E1 for Telecommunications<br>

Explore the fundamentals of Time Division Multiplexing (TDM) in SONET/SDH and T1/E1 systems, voice signal digitization, frame structures, and hierarchical standards in telephony. Learn about synchronization, multiplexing rates, and more.<br>

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Understanding SONET/SDH and T1/E1 for Telecommunications<br>

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  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

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