Complete SDH access manual

SDH access is also one of the most popular access technologies. Many people may not understand the basic concepts and application scope of SDH access technology. After reading this article, you must have gained a lot, I hope this article will teach you more things.

I,SDH access generation

In the integrated business digital network, we need to set different transmission rates such as 64 KB/s phones, 2 Mbit/s conference TVs, 4 ~ 34 Mb/s TV programs) all kinds of information are integrated and transmitted on a single line. The original quasi-synchronous Digital series PDHPseudo-synchronous Digital Hierarchy ), the H12 transmission rate of the base group signal is 2.048 Mb/s, And the H31 transmission rate of the three groups is 8.448 Mb/s), the four group H4 transmission rate is 139.264 Mb/s) and so on.

What does this mean !? For example, if you want to separate a specific base group signal 1 from the four groups that Beijing has uploaded to Shanghai in Tianjin, then, we should first divide the four groups into three groups, then the three groups into two groups, and then the two groups into the base group. After obtaining the base group signal 1, add a base group signal 1' to Tianjin, connect the base group to the Secondary Group repeatedly, and then group the secondary group to the third group ......), In this way, we can continue to transfer data to Shanghai. It can be seen that for a group signal, many sub-and re-connect devices need to be set up in Tianjin, which not only increases the cost, but also damages the signal. In addition, PDH does not have uniform standards and norms around the world, making it difficult for countries to communicate with each other. To address the disadvantages of PDH, the bell Institute of Communications proposed a transmission technology system for the synchronous Optical fiber NETwork SONETSynchronous Optical NETwork, which gradually became the u. S. National standard. In 1988, CCITT of The International Telegraph Telephone Advisory Committee reached an agreement with the American National Standardization Association to change SONET to an international technology system and rename it Synchronous Digital Hierarchy, which can be applied to optical fibers, microwave and satellite transmission networks.

Ii. SDH access features

SDH access is a synchronous digital transmission network. The so-called synchronous means that the method of its re-connection adopts synchronous re-connection, and the low signals of each branch are synchronized with each other. Its transmission rate classification is called synchronous transmission Module synchronous Transport Module), where the STM-1 transmission rate is 155.520 Mb/s, The STM-4 transmission rate is 622.080 Mb/s, The STM-16 transmission rate is 2488.320 Mb/s, the transmission rate of the STM-64 is 9953.280 Mb/s. Compared with PSH, SDH access has many outstanding advantages.

1. in SDH access, digital signals with different transmission rates are easily reconnected and switched over. You only need to use software to receive low-speed signals from high-speed signals at a time, it simplifies the operation steps and facilitates the expansion and upgrade of the communication system, especially suitable for high-speed and large-capacity optical fiber transmission systems.

2. The basic transmission module of SDH access can accommodate several major transmission series in the world, so as to facilitate communication between countries and be compatible with the existing PDH.

3. SDH provides Unified Specifications for network interface contacts. devices of different manufacturers can be used on the same network, which has good horizontal compatibility.

4. SDH devices are smart devices, and a wide range of overhead bits for management are arranged in the frame structure, which accounts for about 5% of the signal ), the capability of running, managing, and maintaining OAM is greatly enhanced, the flexibility of networking is increased, and the network efficiency and reliability are improved.

5. Although the cost of SDH Equipment is about 5% higher than that of PDH, its operation cost is only 1/6 of that of PDH. The cost of SDH is less than 70% of that of PDH, which has good economic benefits.

6. SDH supports asynchronous transmission of ATM) to facilitate the transfer to the Broadband Integrated Information Network.

Of course, SDH also has some disadvantages, such as low band utilization. In PDH, A 139.264 Mbit/s group of four groups can accommodate 64 base group signals of 2.048 Mb/s), and the bandwidth utilization is 64X2.048)/139.264 = 94%. In SDH access, a 155.520 Mbit/s STM-1 can only accommodate 63 base group signals with a bandwidth utilization of 63X2.048)/155.520 = 83%. Similarly, a 139.264 Mbit/s four group in PDH can tolerate four three group signals, in SDH access, a 155.520 Mbit/s STM-1 can only tolerate three group signals. In addition, there are complex technologies, as well as network faults that are easily caused by human factors and computer viruses due to large-scale adoption of software control.

III. Basic concepts of SDH access

A. Main devices connected by SDH

1. Terminal multiplexing TM)
The terminal multiplexing is a device that combines multiple low-speed signals into one high-speed signal, or, in turn, splits one high-speed signal into multiple low-speed signals.

2. Shunt ADM)
Plug-in multiplexing is a device that connects or inserts low-speed signals in high-speed signals.

3. Digital crossover device (DXC)
A digital crossover device is a device with one or more signal ports that can be connected to any port for control, including regeneration, it has multiple functions, including multiplexing, wiring, protection/recovery, monitoring, and network management.

4. RG)
The reactor is located in the middle of the network transmission link. It is a device that can receive STM-N signals and make the signals continue to be transmitted forward according to the specified amplitude, waveform and timing characteristics.

B. Channel multiplexing and regeneration segments

In an SDH access network, the link between the terminal and the terminal is called a channel, and the link between the multier and the multier is called a multiplexing segment; the network between the regeneration device and other network elements is called a regeneration segment.

C. SDH access layered model

Similar to a common computer network, SDH access also uses a layered model to facilitate design and management. The SDH access network can be divided into circuit layer, channel layer and transmission media layer. The channel layer is divided into low-level channel layer and high-level channel layer, and the transmission media layer is divided into physical media layer and segment layer, the Section layer consists of the reusable section layer and the regeneration section layer.

1. Circuit layer: The network directly provides communication services for users, such as circuit switching, group switching, and broadband integrated digital network. Its main device is a switch or cross-connection device. On the basis of the call, it takes a short time to establish and release the circuit.

2. Channel layer: The network supports one or more circuit Layer Networks, which are shared by various types of circuit layer networks to provide transmission services for the circuit layer. Channels at the channel layer are transparent to network nodes at the circuit layer. The channel layer can be divided into a low-level channel layer that provides virtual container VC-1/2/3 and a high-level channel layer that provides virtual container VC-3/4.

3. transmission media layer: The network supports one or more channel layer networks. It depends on whether the transmission media is an optical fiber or a radio signal. The physical media layer network transmits bits in the form of photoelectric pulses. The multiplexing layer network provides synchronization and multiplexing functions for the channel layer to process and transmit the overhead of multiplexing segments; the CIDR Block network completes frame setting, scrambling code, error monitoring of the CIDR block, and transmission of overhead of the CIDR block between the CIDR block or between the CIDR Block and the CIDR Block of the CIDR block.

1. Optical fiber access technology leads the communication storm
2. Smart wireless access technology will become a Development Trend
3. Future development of optical access networks
4. Advantages and disadvantages of two access layer technologies for instance analysis
5. Next-generation wireless access technology