Compare TDM, SONET, OTN, and packet transport.
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.
The key concepts
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
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
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
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.
Trusted telecom references
Use these original standards and public resources to verify details. References are related by topic, not claim-level citations.
- ITU-T optical and transport network recommendationsITU · ITU-T recommendations define SDH, OTN, transport architecture, interfaces, protection, performance, timing, and operations.
- IEEE Ethernet interface standardsIEEE · IEEE 802.3 defines Ethernet physical and link technologies used throughout modern access, metro, data-center, and core networks.
- MEF carrier Ethernet service standardsMplify (formerly MEF) · MEF standards define carrier Ethernet services, service attributes, operations, and performance objectives.
General telecom guidance · Reviewed August 28, 2026 · Verify current commercial, regulatory, and safety-sensitive details with the applicable primary authority.