PDH, SDH, OTN & ASON for Telecom Transmission

Identify transmission media as the physical path for signals, distinguishing guided media (twisted pair, coaxial, optical fiber) from unguided wireless media, with radio waves traveling through free space between antennas.

Choose the physical transmission medium by distance, data rate, and cost; twisted pair (E1), coaxial (E3), microwave (E4), and optical fiber (up to 80 km, five 65 mbps) with repeaters.

Microwave communication enables reliable point-to-point links in remote areas using parabolic antennas at each end, with line-of-sight transmission of radio waves from 300 megahertz to 30 gigahertz.

Optical fiber communication sends information as light pulses from a transmitter to a receiver via optical fiber. It offers high bandwidth, long-distance transmission with minimal losses, and security against tapping.

Explain total internal reflection as the basis of optical fiber communication, where light remains in a high-index core by reflecting at the core-cladding boundary, with impurities and dispersion causing degradation.

Identify the three optical fiber types—multi mode step index, multimode graded index, and single mode—by core diameter, refractive index profiles, and cladding relationships, and compare their transmission implications.

The lecture demonstrates multimode step index fiber modal dispersion by showing how rays with incidence angles follow varied paths, causing pulse distortion and limiting data rate due to bit errors.

Explore how multimode graded index fiber reduces modal dispersion through a center-high refractive index that gradually decreases toward the cladding, versus step-index fibers.

Explain how a single mode fiber uses a very small core to support a single propagation mode, minimizing modal dispersion for high data rate communication.

Observe that impurities and fiber absorption attenuate the light pulse, with plastic fibers for short distances and glass fibers for long, using low-attenuation windows at 850, 1300, and 1550 nanometers.

PDH relies on bit-by-bit multiplexing of four e-1 inputs to yield an 8 mbps output, complicating channel identification and demanding costly demultiplexing infrastructure up to 565 mbps.

Introduce SDH as an improvement over PDH, enabling add/drop of low-rate signals from a high-rate stream, using byte-by-byte multiplexing with overhead, backward compatible with PDH, and enabling automatic path switching.

Explore the SDH bit-rate hierarchy based on STM-n framework, with STM one at 55.5 mbps, STM four four times the rate, STM sixteen 2.5 gbps, and STM sixty-four 10 gbps.

SDH accommodates existing PDH signals as input by multiplexing E1–E4 into STM-1. STM-1’s higher bit rate enables fitting PDH signals, such as E1s, E3s, or E4.

Demonstrate basic SDH operations—mapping, aligning, and multiplexing—to convert E1, E3, and E4 signals into STM-1, and show STM-1 can be multiplexed into higher-order STMs.

Understand STM-1 frame format, defined in ITU-T G.707, transmitted every 125 microseconds as a 9×270 byte matrix with a VC-4 payload, including the Asuu pointer and regenerator/multiplex section overhead.

Convert e4 to a c4 container with nine rows and 260 columns, then add high order path overhead, asuu pointer, and regenerator and multiplex section overhead to yield STM one.

Explain E3 to STM-1 conversion by rate justification, forming C3 and VC-3 with tissue pointers and path overhead, and multiplexing tributary unit group three to VC-4, like E4 to STM-1.

Convert a 2.048 mbps E1 to STM-1 by applying justification to 2.304 mbps, forming the C12 container and VC12, then multiplex tributary unit groups into VC4 with pointers and overhead.

Explain the regenerator as a network element in SDH networks, used on long haul optical fiber links to remove noise and regenerate the signal between multiplexers, preserving quality.

Learn how SDH multiplexers convert low-order signals into high-order streams using terminal and add-drop multiplexers, enabling selective add/drop of low-rate signals in ring, point-to-point, and point-to-multipoint networks.

Discover how the digital cross-connect (DXC) enables flexible routing and switching of diverse rate signals at VC-12, VC-3, and VC-4 levels, enabling traffic grooming and rerouting in mesh networks.

Explore the point to point SDH network topology, with two terminal multiplexers and regenerators along optical fiber to boost signals, enabling demultiplexing of low-rate tributaries.

Illustrate how point-to-multipoint topology uses two terminal multiplexers and add/drop multiplexers to drop and add low-rate E1 signals within a high-rate SDH stream.

Explore the mesh network topology of digital cross connects with add drop multiplexers, connecting low-rate tributaries through scalable, flexible links that optimize network capacity and routing.

Explore the ring network topology where add/drop multiplexers form a closed loop carrying traffic in clockwise and anti-clockwise directions via optical fibers, enabling self-healing for backbone and metro networks.

Explore how SDH overheads are classified and why they are used within STM-1 frame, including path overhead and section overhead, with the latter subdivided into regenerator and multiplex section overhead.

Examine the SDH path architecture, focusing on the regenerator and multiplex sections, their overheads for signal quality and maintenance, and the path overhead guiding end-to-end monitoring and switching.

Explore the regenerator section overhead, including A1/A2 for frame alignment, C1 for section trace, B1 for even parity, and D1–D3 data channels at 192 kbps for maintenance signaling.

Describe how the AU pointer uses H1, H2, and H3 bytes to mark the VC-4 start and buffer the boundary byte during pointer updates between network elements.

Explore the multiplex section overhead, including B2 parity and M1 remote error reporting, plus D4–D12 maintenance data, S1 clock status, k1/k2 protection switching, and the E2 order wire channel.

Understand automatic protection switching in telecom networks, focusing on the linear protection mechanism for point-to-point links and the one plus one and one to n architectures with protection paths.

Explore unidirectional ring protection in SDH networks, using line switching to reroute traffic from a working line to a protection line when a cable cut occurs, with coordinated switching.

Demonstrate unidirectional ring protection with path switching, where traffic runs on both working and protection lines. Station A monitors both paths for fast, receiver-only switching during a cable cut.

Reroute traffic after an A–B fault using bidirectional ring protection's line switching, with B sending k1 and k2 to A to switch to the protection path A, D, B, C.

Learn how wavelength division multiplexing increases capacity by multiplexing multiple wavelengths on a single fiber, using multiplexers, amplifiers, demultiplexers, and transponders to convert STM 16 signals to wavelengths and back.

Wavelength-division multiplexing technology increases data capacity on a single fiber by multiplexing multiple wavelengths, enabling 16 stm 16 channels at 2.5 gbps to reach 40 gbps.

Compare CWDM and DWDM systems. CWDM uses 20 nm spacing, no amplifiers, and shorter range. DWDM uses 0.8 nm spacing, cooled lasers, and optical amplifiers for higher capacity and cost.

The optical supervisory channel enables centralized management of dwdm nodes by carrying a dedicated wavelength for monitoring performance, detecting faults, and reconfiguring networks from a central network management station.

Explore how the optical add drop multiplexer enables adding or dropping specific wavelengths at intermediate sites in a multiplexed optical fiber, while other wavelengths pass through.

Transition from SDH to OTN enables statistical multiplexing and flexible bandwidth for bursty IP and Ethernet traffic, transparently transporting client signals and delivering data rates beyond 100 Gbps per wavelength.

An optical transport network defined by ITU-T G.872 consists of network elements connected by fiber links that transport, multiplex, route, manage, and protect client signals across metro and core subnetworks.

Migration to packet transport networking moves IP and Ethernet traffic over OTN. OTN acts as a wrapper with header and error correction, transparently carrying protocols and managing WDM wavelengths.

Explore why modern IP traffic cannot be transported directly over DWDM and how OTN provides clocking, framing, error detection, protection, and path management for reliable IP over optical networks.

Explore OTN network interfaces, especially the inter domain interface at operator boundaries or between vendor-subnetworks, where the three R functions—re amplification, reshaping, and retiming—restore signal integrity.

Explain how a client signal maps to an optical channel by adding payload, data, and transport overhead with forward error correction, then converting to light on a dwdm wavelength.

Add the optical payload unit overhead and optical transport unit overhead to enable OTN transmission with three R capable nodes, forward error correction, and frame alignment on a single wavelength.

Clarifies the OTN layered architecture, tracing a client signal through audio and O2 frames to an optical channel, then through a DWDM multiplexer, amplifier, and demultiplexer.

Explore the ITU-T G.709 standard and the initial OTN data rates across three levels, from OPU1 to OPU3, and their use with STM-16, STM-64, and 10/40 gigabit Ethernet.

Explore the OTN multiplexing structure, detailing how low-rate signals are multiplexed into higher-rate frames (ODU into ODU, ODU into OTU), with headers and forward error correction.

The optical transport module, or otn protocol stack, defines protocol at each layer, from client signals to channels multiplexed by wavelength division multiplexing on a fiber, with three types.

Explore the full function otm, converting electrical client signals to optical channels and multiplexing wavelengths on a single fiber, using n.m to denote wavelength count and per-wavelength rate.

Learn the reduced function OTM-nr.m with no optical supervisory channel or overhead, where each optical channel uses its own wavelength and external WDM handles multiplexing for point-to-point links.

Explore the OTM zero, a single wavelength OTM carrying a single client signal with reduced functionality, no overhead, no multiplexing, and no optical supervisory channel, OPS zero.

Understand how ODU0 efficiently carries 1 gigabit ethernet using a 1.238 gbps payload, via the generic mapping procedure into Apu zero and multiplex into higher ODU levels.

ODUflex enables dynamic allocation of bit rate in 1.25 Gbit/s time slots to support variable-rate clients like 1, 10, and 25 gigabit Ethernet, matching ODU containers to demand.

Identify the commonly used ODU containers for gigabit Ethernet and STM signals, from ODU zero to ODU three, with the audio flex option for scalable bit rates.

Explore the OTN overhead bytes, including the OPU overhead, path and section monitoring, payload structure identifier, and justification control bytes for positive and negative rate adaptation.

Describe the ODU overhead bytes for path monitoring, error detection, and protection switching, detailing three bytes: DTI, bit interleaved parity, and status bits.

Use six tandem connection monitoring fields in the ODU overhead to track a client signal through multiple operators, with each three-byte TCM word carrying trail trace identifier and status bits.

Describe the ODU overhead bytes, including general communication channels for network management and supervision, the TCM activation/deactivation byte, protection switching channels, experimental bytes, fault type and location, and reserved bytes.

Explore o2 overhead bytes for section monitoring and frame alignment, frame alignment signal bytes with a fixed hex value, a 256-frame counter, t, bip, incoming alignment fields, and gcw zero.