ITUITU › Telecommunication StandardizationPublic
ITU-T optical and transport network recommendationsITU-T recommendations define SDH, OTN, transport architecture, interfaces, protection, performance, timing, and operations.
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3 authoritative references · public telecom search
Telecom answer High confidence · 3 authoritative references
Telecom transport evolved from time-division circuits to optical transport and packet-based cores, with several generations still operating together.
TDM assigns fixed time slots, SONET and SDH organize synchronized optical hierarchies, OTN adds digital wrapping and switching for optical channels, and packet transport carries statistically multiplexed Ethernet and IP traffic.
ConceptWhat it isBest forWatch for
TDM
Fixed time slots combine multiple digital channels onto a shared transmission facility.
Legacy voice, private lines, control systems, and deterministic circuits
Capacity is reserved even when idle and legacy skills or spares may be scarce
SONET / SDH
Synchronous optical hierarchies with standardized rates, framing, protection, and operations.
Reliable metro and long-haul circuit transport
Rigid bandwidth increments and aging platforms limit flexibility
OTN
Digital wrappers, multiplexing, switching, monitoring, and forward error correction for optical channels.
High-capacity wavelength transport and multi-service optical cores
Layer mapping, reach, FEC, and vendor interoperability require engineering
Packet transport
Ethernet, MPLS, segment routing, and IP carry variable traffic over shared capacity.
Scalable data services, cloud, mobile backhaul, and converged networks
QoS, timing, congestion, convergence, and visibility must be designed
Practical guidance
Inventory the actual service mapping before migration. Preserve timing, protection, latency, OAM, circuit emulation, and regulatory requirements while simplifying legacy layers.
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