Hello, everyone!
This sticker will share the development of the Optical Transmission Network.
1. PDH - Plesiochronous Digital Hierarchy
Although the PDH equipment is optical transmission equipment, it mainly processes electrical signals. The transmission rate is less than 150 Mbit/s.
Advantage: Time-division multiplexing is supported.
Disadvantages:
There is no worldwide standard (the rate standards are different in Europe, North America, and Japan).
There is no worldwide standard optical interface specification.
The structure is complex, the quantity of hardware is large, the cost of adding/dropping circuits is high, and the flexibility is lacking.
Poor network operation, maintenance, and management capabilities.
After the emergence of SDH, it replaces PDH equipment. Currently, the PDH equipment is used only for the communication between two points that require less than 34 Mbit/s bandwidth.
2. SDH - Synchronous Digital Hierarchy
SDH is an early optical transmission technology (but developed after PDH). It is an integrated information transmission network that integrates multiplexing, line transmission, and switching functions and is operated by a unified network management system.
Transmission rates include 155 Mbit/s, 622 Mbit/s, 2.5 Gbit/s, 10 Gbit/s, and 40 Gbit/s.
Advantages:
The rate is the same as that of the optical interface.
Strong management capability (OAM management information).
The bifurcation multiplexing circuit is convenient.
Standardized frame structure, multiplexing mode, transmission rate level, and interface code type of digital signals.
Supports protection switching of multiple services.
Disadvantages: rigid pipes, exclusive resources, and fixed rate.
3. WDM - Wavelength Division Multiplex
WDM multiplexes optical signals of different wavelengths into one fiber for transmission. There are two modes: DWDM and CWDM. Currently, DWDM is the mainstream. Currently, the mainstream WDM systems are 40-wavelength and 80-wavelength systems (which are being converted to more than 96-wavelength and 120-wavelength systems) that carry more wavelengths. This is one of the future WDM evolution directions. The transmission rates of a single optical wave signal are 10 Gbps, 40 Gbps, 100 Gbps, and 200 Gbps.
Advantages:
One line has multiple channels, improving the capacity. 800 Gbit/s (80 wavelengths x 10 Gbit/s)
long distance
The problem of insufficient fiber resources is solved.
Disadvantages:
Lack of OAM, inflexible scheduling, and inadequate protection, leading to the emergence of OTN.
High latency and high cost.
Strong tributary-line binding, low bandwidth efficiency
4. MSTP - Multi-Service Transport Platform
Extended SDH, supporting multiple services such as PDH, SDH, Ethernet, ATM, and PCM.
MSTP = SDH + Ethernet (Layer 2 switching) + ATM (signaling transmission)
Based on SDH containers.
The features are basically the same as those of SDH. The bandwidth is exclusive and cannot be multiplexed statistically. Therefore, the bandwidth multiplexing efficiency is low.
5. PTN - Packet Transport Network
Definition: PTN = MPLS + OAM + Protection - IP
Packets are transmitted based on IP packets and the packet size is variable.
Compatible with SDH services and transmitted as IP packets through PWE3.
Features:
MPLS: Multi-Protocol Label Switching (MPLS) establishes a label forwarding channel (LSP) for packets based on pre-allocated labels. Each device that the LSP passes through only needs to perform fast label switching (one-time search).
The technology comes from ATM networks.
TMPLS: simplifies the Layer 3 technology that is not related to transport in MPLS, enhances the OAM and protection mechanism, and makes up for the disadvantage of not being able to support transport networks.
OAM: Similar to traditional SDH overheads, OAM provides carrier-class protection.
Remove IP: Remove the IP handshake protocol.
6. MSTP+/Hybird MSTP
Hybrid MSTP = MSTP + PTN, supporting the hybrid transmission capability of TDM and PKT.
Similar to MS-OTN.
7. OTN - Optical Transmission Network
Based on WDM, OTN integrates some advantages of SDH, such as abundant OAM overheads, flexible service grooming, and perfect protection modes.
OTN service grooming is classified into optical-layer grooming and electrical-layer grooming.
Optical-layer grooming can be considered as WDM.
Electrical-layer grooming can be understood as SDH.
Features:
OTN = SDH + WDM, compatible with Ethernet: EoO technology is used to transmit Ethernet packets to ODUk.
Disadvantage: The ODUk granularity is too large, which cannot meet the requirements of a large number of low-speed services.
8. MS-OTN - Multi-Service Optical Transport Network
Definition: MS-OTN = OTN + MSTP
Advantages of Integrated MSTP/MSTP+ for Small-granularity Service Bearer
MPLS-TP Technology Improves Management Capability
Features:
Multi-service access: Any service at any rate (SDH, SONET, PDH, ETH, FC, SDI, PON, SAN, CPRI...) can be accessed.
Unified cross-connection: Integrates the L0+L1+L2 technology to provide unified cross-connection grooming based on λ, PKT, ODU, and VC.
Unified transmission: Various services can be mapped to the most matched pipes and converged to large-capacity wavelengths for unified transmission.
Unified maintenance: The unified network management system implements unified visualized O&M for L0, L1, and L2.
9. Liquid OTN
Liquid OTN: It is as flexible as liquid OTN. The core idea is to abstract smaller OSUs and provides flexible containers.
In essence, it provides variable container sizes to meet service requirements of different rates.
The variable rate of IP packets is used, but the adjustment granularity is limited.
Advantages:
The OSU supports flexible timeslot multiplexing.
Intermediate nodes do not need to cache data based on the maximum latency of the switching fabric to obtain the absolute latency advantage.
Thank you!
