中文
English
中文
English
A long time ago, the early products of the development of optical communications: PDH and SDH, PDH existed before SDH.
The common PDH is 4E1 and 8E1 optical transceivers, which basically do not include branch circuit boards and main control boards. PDH optical transceivers can also use AC power.
The SDH outgoing line is basically determined by the branch circuit model, generally 8E1, 16E1, 32E1, etc. It is composed of branch circuit boards, main control boards, etc. AC power is rarely used.
Most of the data that does not need to be delivered when connected to the power supply and the optical fiber is PDH, and most of the data that is required by the network management is SDH.
To be simple is that 2M, 34M, and 45M services are all PDH, and STM levels are all SDH.
In terms of transmission rate, PDH has a maximum of 154Mbps and 64 2M; SDH can reach more than 10Gbps.
Product performance characteristics:
(1) Multiplexing mode: SDH's multiplexing mode is synchronous multiplexing, PDH's multiplexing mode is asynchronous multiplexing, PDH's multiplexing mode is equivalent to cigarette packaging, 20 boxes per box, 10 boxes per box, 60 boxes per box Box, you need to take out any cigarettes after loading, you need to unpack them step by step; SDH multiplexing method can directly get any specified cigarettes, as if all the cigarettes are placed on a numbered shelf
(2) Networking mode: PDH is basically point-to-point open, used in pairs, SDH is a variety of networking
(3) Rate: the highest rate of PDH is 155M, the highest rate of SDH is tens of G
(4) Interfaces: There are three types of PDH ethernet interfaces (ethernet signal rate standards). Europe, Japan, and North America. Optical interfaces are manufacturers' own optical interface standards. It is difficult to be compatible between them.
(5) Poor PDH network management function, strong SDH network management function
(6) SDH can be compatible with PDH
知识点：
Knowledge points:
(1) The network transmits control information, called the control plane (Control Plane); the other is used to transmit data information, called the user plane (User Plane).
(2) TDM time division multiplexing is to divide a standard duration (1 second) into a number of small time periods (8000), and transmit a signal every hour (1/8000 = 125us).
(3) SDH synchronous digital transmission system. The circuit scheduling of the SDH system is based on TDM, so many people see that SDH service is TDM service, which is the traditional circuit scheduling.
(4) The English abbreviation of Ethernet is ETH, which is a computer local area network technology. Several computers are networked to form an Ethernet.
short story:
In a society mainly dominated by telephone communications at that time, SDH showed its strength and became the number one hit. Then Ethernet emerged and became another big hit after SDH. The two joined forces and SDH + Ethernet gave birth to MSTP.
MSTP(Multi-service Transport Platform)
MSTP (Multi-service Transport Platform) is a multi-service transport platform. It is a metro transmission network technology. It integrates SDH transmission technology, Ethernet, ATM, POS and other technologies. Based on SDH technology, A variety of services are aggregated and effectively adapted to achieve comprehensive access and transmission of multiple services, and to achieve SDH from a pure transport network to a multi-service platform that integrates transport and service networks. Since then, the STP-based MSTP technology has played a very important role in the field of metropolitan area network applications.
The distribution of shares in MSTP is not even: SDH accounts for 70% of shares, Ethernet accounts for 20% of shares, and other includes ATM accounts for 10% of shares. The power is still SDH, and the core is still TDM.
As the business continues to develop, with more and more services and insufficient bandwidth, the new partner WDM has entered the stage of history.
WDM WDM is to place vehicles (signals) in multiple lanes (channels) on the same road (optical fiber) for transmission. There are two types of lanes according to the lane interval:
Lane spacing of 20nm is sparse WDM, also known as coarse wavelength division (CWDM);
Lane separation less than or equal to 0.8nm is Dense Wavelength Division (DWDM);
This doubles the bandwidth, which temporarily solves the problem of insufficient bandwidth! Fibre Channel WDM WDM products are shown below:
The original intention of WDM is to solve the problem of insufficient bandwidth. It does not take into account that after the bandwidth is increased, management has not kept up (lack of OAM); scheduling is not flexible enough; it is easy to block (incomplete protection).
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Due to the serious development of the situation, the next separation and reorganization: SDH + WDM gave birth to OTN!
OTN is based on WDM and combines some advantages of SDH, such as rich OAM overhead, flexible service scheduling, and perfect protection methods.
OTN's service scheduling is divided into: optical layer scheduling and electrical layer scheduling. Optical layer scheduling can be understood as the category of WDM; ethernet layer scheduling can be understood as the category of SDH, so briefly: OTN = WDM + SDH, which is mainly used in backbone transmission networking. Fibre Channel OTN transmission solution is shown in the following figure:
For the construction of MAN Ethernet, it is divided into two directions: IP-RAN and PTN.
SDH customers (TDM business) get on the bus. If they must come in, they must change their face-camouflage (simulation). At the same time, we have no time guarantee (no time synchronization). We serve our Ethernet purely. -RAN;
Absorbed some SDH customers, SDH has been operating for so many years, and it still has a lot of customers (and many TDM business needs). After entering the same, you still have to make a face-up-camouflage (simulation), then work in our gang, Remove the camouflage and restore it to its original appearance. The company named it PTN.
