Packet network equipment, circuit emulation application-TDMoP, backhaul design,
TDMoP is based on TDM and IP technologies developed a new technology that can be existing TDM circuits run at various businesses in the direct fit to the IP network, without changing any device, has broad application prospects.
1 Introduction With the rapid development of Internet, IP network with its ubiquitous nature and cost advantages, such as real-time voice and video delivery business showed a huge potential advantage.
TDMoP (TDM over PacketNetwork), also known as circuit emulation packet network equipment is based on TMD and IP technology developed a new technology that may be present in various types of TDM circuits run business direct fit to the IP network, data network in the play, while low-cost advantage, with existing TDM Terminal devices be totally seamless connection to organically combine the two. TDMoP equipment allows operators to sell, while voice services to maximize the use of their income-generation packet-switched infrastructure, which has broad application prospects. This paper describes the technical characteristics of TDMoP principle and based on the circuit emulation packet networks focus on a variety of communications equipment in a typical application environment.
2 TDMoP principle and technical characteristics
TDMoP is to make voice and leased circuit services (such as video, data, etc.) in the IP online cheap transmission technology, it also can keep the public telephone network (PSTN) the reliability and quality of service.
TDMoP a "tunnel" principle to achieve TDM circuit in IP transparent transmission: E1 synchronous bit stream at the source side after being packaged with IP head, packaged IP data packets through the network to the data IP packet transmission to the destination, the destination re-generate synchronous clock signal, and then remove the IP header, the other data into a synchronous bit stream E1 sent. For packet-switched network transmission E1 operations, jitter smoothing and clock synchronization is necessary to solve the problem.
IP network packet to a random delay to reach the destination, the delay is called jitter. E1 jitter mainly depends on the package store and forward switch caused by the delay. TDMoP package by way of setting hair. E1 Ethernet packet length of the data set N × 32Bytes, exactly N E1 frames. N values to the appropriate selection, because the package is delayed too long and too short then the proportion of spending too much. Jitter buffer can be overcome by using the. As the TDM circuit is constant bit rate, it is necessary to reach the packet buffer before the output, so that you can compensate with other differential delay between the slow group. Cache is set to absorb packet jitter, and capacity can accommodate the larger the greater the jitter. However, the increase of the cache will be linearly increased voice delay, it should be able to accommodate the case of packet jitter to minimize cache.
In the buffer process, the original clock reference information is not extracted, therefore, TDMoP technology to take the necessary clock synchronization. Clock recovery algorithm is directly related to the product stability. Industry group statistics generally used to restore the clock, the algorithm because the clock generated by the packet loss impact of vibration problems; other statistics take time, so there is convergence of the clock. Wood Green technology TDMoP equipment using remote measurement of proximal restoration algorithm to achieve synchronization, the algorithm does not need statistics, remote sampling the local clock detection, to extract accurate TDM clock signal, coupled with the clock signal with the package marking and TDM into packets at the receiving end as long as the received packet can be immediately read the tag information to the clock to restore the clock for network synchronization. Remote measurement is the use of differential clock recovery methods to achieve, so that the destination node to ensure synchronized TDM circuit, does not slip any buffer. Practice has proved that the algorithm performance is superior to similar algorithms. The following focuses on a variety of communications environments TDMoP typical application.
3 TDMoP Typical Application 3.1 TDMoP in mobile communication system
In mobile communication systems, base stations (BTS) and base station controller (BSC) and mobile switching center (MSC) as a return communications link between the (Backhaul). In the future planning of 3G networks, it was suggested that cellular backhaul network design relates to the effectiveness of the overall reduction in 3G network construction costs.
Mobile network backhaul is a major part of the operating costs, the industry was generally agreed that a point is: the total cost of the transmission part of 40% to 75% of the cost may be the return. Of particular note is that mobile network operators have to choose the cost of the access platform, applicability and availability to make trade-offs, to meet the expected increase in bandwidth capacity requirements, and reduce network voice and data integration complexity.
BTS and the BSC and the BSC and the MSC between the communication between the general there are three ways:
First is the traditional cable transmission, or E1 leased telecommunications lines, or self-laying;
Second optical transmission is required to lay a special cable transmission of data from the BTS to BSC, and the need to configure the Optical;
Third is the wireless transmission, using microwave technology or this article will introduce the "TDMoP + Wireless Bridge" approach to achieve.
First two methods are wire transfers, on the first approach, the cost of leased lines in the long run will be relatively high, while laying their own lines there are also problems of high costs; on the second ways, the geographical environment on the network construction have been affected, particularly where certain conditions are poor, such as base stations in the top or a river barrier and so on, wired up and there will be some difficulties in the realization or economic waste. The wireless transmission is concerned, in practice, most microwave equipment to transmit, but because of its transmission, transmission services, network models and prices is difficult because large area.
This article to discuss "TDMoP + Wireless Bridge" approach allows the cost effective wireless control, but also make the cellular backhaul network design more flexible and efficient. From the transmission perspective, the wireless bridge using IP packet transmission, packet loss in wireless interference retransmission when the microwave will result in error; from the transmission business perspective, "TDMoP + Wireless Bridge" mode can either send E1, you can also send IP services, while most of the current device can transmit E1 microwave business; view from the network model,
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