Third generation SDH bus: introduction of LVDS Technology

With the rapid development of related technology and China's communication market, the main network of the mainstream SDH equipment rate has risen to 10G, and 2.5G SDH transmission equipment by these more high-end equipment extrusion, network application level began to move down, gradually into the edge layer, replacing the original in the edge of the 622M equipment. On the other hand, with the rapid growth of the bandwidth demand of data and Internet service, more and more requirements are put forward to the SDH equipment which is carried by the edge layer, in order to adapt to this change, it is imperative to adopt the third generation SDH bus-LVDS technology.

Historical Review of SDH bus

The back board bus rate of early SDH equipment is 19.44mbit/s, which is a single terminal TTL bus technology, which is often said as the first generation bus technology. This kind of bus technology is low cost advantage in low speed situation, but it is not used in high speed SDH equipment. This is because: first, the single terminal TTL bus voltage swing amplitude is too large, which will lead to excessive power system. In SDH equipment, with the increase in speed, the equipment power also increases correspondingly, if the High speed single end TTL bus technology is used in the high speed SDH equipment, the power too assembly makes the system difficult to work normally; secondly, the voltage swing has brought obvious peak pulse current, overshoot and large AC noise, which seriously affected the signal quality, and caused the EMI problem; Thirdly, because the principle of TTL is to use the transistor electrode charge accumulation and dissipation process, this makes the bus signal rate must be limited by charge and discharge time, it is difficult to apply to high speed occasions; four, single terminal bus technology is difficult to effectively eliminate the noise on the bus, Limited this technology to a higher rate of development, its five, TTL on the high speed device Backplane application will greatly increase the complexity of the device design, such as on the 2.5G device with the 38.88mbit/s TTL bus, so where the need to process 2.5gbit/s signal to use 64 bus, This complexity is hard to imagine.

It is precisely because of the various drawbacks of TTL bus technology, the second generation of bus technology was born. Taking its representative gtl+ bus as an example, its basic characteristic is that the voltage swing amplitude is greatly reduced, and the signal quality is improved, and the power and EMI are reduced at the same time because of the control of the rising edge and the descending edge of the signal. At present, most of the sdh2.5g equipment used in the market is this technology. However, with the further improvement of SDH rate, when the gtl+ bus is used in higher speed equipment, it also shows the defects similar to the TTL bus. The engineer has made the corresponding improvement, this is the third generation bus--LVDS bus technology. (Computer science)

Why the LVDS?

We hope that the 3rd generation of bus technology can solve the above TTL bus technology of the five major drawbacks. Then, it should have the following characteristics: First, the pendulum amplitude is small, the power is small; second, to adapt to high speed, three, to reduce the bus noise mechanism. LVDS can fully meet the above 3 requirements (for LVDS standards, see IEEE P1596.3 and ansi/eia/eia-644). The average swing amplitude of the LVDS is about 350mV, the average DC bias voltage is about 1.25V, the average signal current is 3.5mA (in the case of the power supply voltage is 3.3V), the pendulum amplitude is small, the power is small; LVDS's technical principle determines that it can be applied to the occasion of the bus rate up to and has nothing to do with the physical media; the LVDS uses two close and close symmetrical differential signal lines, effectively eliminates common mode noise on the bus, and greatly improves the signal quality of the receiver. This shows that LVDS technology can be used in high-speed bus, which can greatly reduce the complexity of the system equipment, such as processing a 622mbit/s signal only a pair of 622MBIT/SLVDS bus.

OTS Super 2.5G 8501b/c Products

Shanghai Bell adopts LVDS third generation bus technology to launch the integrated multi-service SDH optical transmission products ots Super 2.5G 8501b/c. The system uses 622MBIT/S LVDS bus technology, processing a 622mbit/s signal only need a pair of 622mbit/s LVDS bus, greatly streamlining the equipment structure, so that products can achieve in small space or even exceed the "standard rack" system performance. It is small in size (box structure), low power consumption, is called "Notebook in transmission." Despite its streamlined structure, it is powerful and has the following key technical advantages:

1. Distributed Mesh Structure crossover system: the traditional centralized cross system, must be configured in accordance with the full configuration of the cross capacity, even for a very simple configuration is also the case, and the use of distributed crossover, the system can carry out on-demand configuration of the cross capacity. When the system configuration is simpler, the cross capacity of the configuration is correspondingly less, thus reducing the cost, on the other hand, it can be configured as 128 (128VC4 level crossover and 2016 at the 2016VC12 level). Such a powerful function can be fully up to the backbone of the network with 10G+DWDM, can also be down with a variety of interfaces connected to the access network.

2. The powerful function chip design: its low order cross chip may complete simultaneously 16 road VC4 Tupp processing and the 1008x1008vc-12 level cross, such formidable chip greatly enhances the system the integration, is also the system function is powerful but also the structure simplification basic guarantee.

3. Dual-clock bus structure, power supply hot backup centralized power supply, with electric plug and pull, two sets of completely independent clock bus, based on similar "double hair excellent" principle to choose the better quality of the clock, the clock can be seamless switching; using patented power technology (N:M protected shared power mode), any one Power module fault, will not affect the normal of the system, support with electric plug, greatly improve the reliability of the system.

4.CPU Centralized control: standard type transmission equipment, single board number, large back plate, control complex, if the use of centralized control, it is difficult to ensure the signal quality and control speed, so in each single board are configured CPU system; 8501 products of a small number of veneer, the back plate is relatively small, signal quality and control speed can be guaranteed, Control is relatively simple, can be centralized control of the way, only need a set of CPU system can realize the control of the system, do not need to configure the CPU system on each board, reduce the main CPU and single board CPU communication between the time and the unreliable communication, improve the speed and reduce the cost.

5. Strong business access, rich business interface: its maximum business access capacity 1008*2m (including a variety of intermediate rates), when the business access 504*2m, can achieve 1:1 complete protection; Business interface is rich, can provide 10M, 100M, GE Ethernet interface and 2M, 34/45m, 139M , 155M and other kinds of speed electrical interface.