Use Wireless Bridge access technology to achieve E1 access

The Wireless Bridge access technology is used to achieve E1 Wireless Bridge access. A large number of wireless bridge devices adopting the IEEE 802.11a standard have emerged. To meet the Wireless Bridge access needs of users' business, provides inexpensive and effective means of transmission. For example, a 5.8g wireless bridge can implement wireless communication between two points within several kilometers to dozens of kilometers, and non-line-of-sight communication can also be achieved within a short distance.

This type of equipment is low in price and fast and convenient to install, and because it is in the ISM band, The National no commission has not uniformly allocated it, so it is easier to obtain approval for use, it is conducive to large-scale application in the Construction of Wireless Bridge access networks. However, for customers who want to achieve wireless E1 Wireless Bridge access, the cheap Wireless Bridge does not seem to be appropriate because such bridges are based on IP technology and generally do not have E1 interfaces, but only Ethernet interfaces.

To this end, we have to use a much more expensive Microwave Device Based on circuit or ATM. Wireless Bridges are widely used in simple data transmission scenarios that do not require E1 services. Can I use a wireless bridge to provide the E1 service? The answer is yes. Through the E1 over Ethernet Interface Converter device, you can simulate the E1 channel on the Ethernet link established by the Wireless Bridge. However, can such a simulation channel meet the needs of E1 devices?

The time-division multiplexing technology of E1 signal source self-PCM encoding transmits information at a constant rate of 2048kbps, commonly known as "2 Mbps port ". Ethernet adopts the statistical multiplexing technology, and its transmission and exchange are based on data packets. The time-division multiplexing technology has the characteristics of fixed bandwidth, low transmission latency and stability, high signal transparency, jitter, and low drift. It is suitable for applications with high requirements on real-time transmission and timing stability for voice and images.

The data packet-based statistics multiplexing technology has a higher reusability efficiency and is suitable for data transmission scenarios where the latency is not strict and the regular information is usually not needed to be restored accurately. Due to the technical differences between E1 and IP, it is not easy to use Ethernet to provide the simulation E1 channel. The difficulty lies in the effective reconstruction of E1 code stream timing information at the network outlet.

It is necessary to overcome the disadvantages such as random packet delay, no effective timing transmission mechanism, transmission error code, and collision which may cause packet loss. The E1 over Ethernet Interface Converter must be able to solve the above problems in order to truly replace traditional circuit-based microwave devices. The judgment mainly relies on the stability of the E1 code stream clock recovery and the additional processing latency. Practice has proved that the superior performance of the Interface Converter and the wireless bridge can be well used in most E1-based applications.

Clock stability includes clock jitter, drift, and Frequency Holding. Jitter may cause error codes on the E1 terminal device, and drift may cause slide frames and other types of service damage. A hop on the clock frequency may cause Frame loss and re-capturing, serious error codes.

At present, the E1 over Ethernet Interface Converter is better on the market. The jitter value is usually below 0.1UI, and the recovery clock drift can be controlled within 5ppm (if there is an independent clock network in the Application Scenario, this indicator is not very important ). When packets containing E1 data are occasionally lost (especially in wireless conditions), is it possible to maintain the clock frequency stability without a hop, it is also an important indicator for such devices.

When used for real-time bidirectional communication, processing latency is also an important indicator of the E1 channel. For example, the total latency of one-way speech for PCM speech services without an echo canceller should be within 50 milliseconds. If it is close to 100 milliseconds, you can hear an echo that affects the quality of the call.

This latency not only includes the processing latency of the Interface Converter, it also includes the transmission latency of wireless bridges, the latency introduced by the buffer required for data packet transmission jitter, the latency of voice codec processing, and other latencies introduced by telephone transmission and switching systems, therefore, it is required that E1 over Ethernet devices introduce as little processing latency as possible. The processing latency of devices with good algorithms can be within 6 milliseconds.

Some E1 over IP devices provide frame sharding for the E1 channel. This means that you do not need to transmit a complete E1 channel between two points, but only need to transmit several 64 Kbps time slots, it makes sense. Generally, such devices can encapsulate each time slot stream into an IP packet. Therefore, the transmission unit in an IP network is in the unit of time slot, which is highly flexible, for example, an E1 signal is split and sent to multiple remote sites.

You can save bandwidth because you do not need to transmit the entire E1 signal. The main difficulty of frame separation encapsulation lies in the contradiction between efficiency and latency. To achieve high efficiency, each data packet must have a certain length. For 64 Kbps code streams, the encapsulation latency is 32 times longer than the E1 code stream under the same encapsulation length, which often causes serious echo to the Real-Time Speech service.

Encapsulation of E1 data into data packets affects the network performance of data packets. Some E1 over Ethernet interface converters allow you to select various encapsulation modes to match the transmission network characteristics for optimal results. Encapsulation methods include: encapsulation length, whether to add IP address headers, and whether to add VLAN headers.

For a wireless bridge, it is usually used for point-to-point connections without routing addressing. Generally, it does not need to be added with an IP header or VLAN header. This can save bandwidth, while the bandwidth of a wireless bridge is usually not sufficient. In addition, the bandwidth of some wireless bridges depends on the package length. Therefore, selecting the appropriate E1 Data encapsulation length is sometimes crucial.

For applications that require the use of a wireless bridge to provide both E1 and Ethernet Wireless Bridge access, such as network and session integration, another function of the converter should also be investigated, that is, whether strict traffic control can be performed on data services transmitted together. Because the valid transmission bandwidth of the Wireless Bridge is usually not large, and it usually cannot provide adequate QoS for E1 packets.

Therefore, when sending data bursts, it is natural to have an impact on E1 data packets, resulting in packet loss, seriously interfering with the transmission of E1 signals, generating error codes or even interruptions. Therefore, for such applications, you should select a product that has a downstream Ethernet interface and can effectively limit the priority of the upstream and downstream interface data packets, and pay attention to the connection mode ,.

The E1 over Ethernet interface adapter provides various alarm indication and loop back control functions. It is of practical significance for E1 wireless transmission devices. In the project installation and troubleshooting phase, understand the Signal status of the local and peer E1 interfaces, control the loop back of the E1 interface so that the channel performance can be tested with the E1 Incorrect code meter, and observe the packet loss phenomenon, it helps engineers understand the situation and determine the fault location.

In short, the launch of low-cost wireless bridge devices not only enables Wireless Bridge access for data services, but also provides a good solution for Wireless Bridge access for traditional E1 signals. In most cases, wireless systems built by wireless bridges and E1 over Ethernet interface adapters can replace traditional transmission methods such as optical fiber and microwave, and offer better performance and price ratios.