Application of PCM devices in DDN Network in Dalian Telecom networking

Chapter 1: DDN Network: main solutions for large user access
With the rapid development of China's economy in recent years and the increasing requirements of enterprises for communications, especially data communication, the communication traffic is larger and the business types are richer, at the same time, the flexibility and manageability of the provided services are greatly increased. All these require that telecom operators be able to provide as flexible and diverse access services as possible to group users, including traditional voice services, it also provides a wide range of data and image services, such as Ethernet, environmental monitoring, Image Monitoring, and video conferencing. This is called Integrated Service Access. At the same time, this access service is measurable for users and provides relevant traffic and other statistical data so that users can "manage" their own business channels, in addition, such services must have quality assurance. In addition, the requirements for access services by group users of different scales, industries, and regions vary greatly, which constitutes the complexity of access network services. While vigorously constructing the transmission network, the telecom operation department is constantly looking for solutions to access networks to meet the different needs of different users for business access.
Currently, there are many ways to solve business access problems. For historical reasons, access to different services is often completed by different networks, such as DDN, PSTN, FR, ATM, X.25, and Ethernet. DDN network is the main means to access data services. DDN is combined with the traditional voice network PSTN to provide integrated service access including voice and data for large users. At present, the DDN network has formed a certain scale after a long period of development. According to the network level, it can be divided into the backbone networks of the first-level networks across provinces) and municipal networks of the second-level networks within the Province), three-level network at the city or county level) and four-level network at the township level ). Taking Dalian as an example, the three-level DDN network has been built, and a four-level DDN network is being considered. An end-to-end connection is formed through the configuration of DDN online nodes to provide data interfaces at different rates. Because the DDN network has the advantages of high transmission rate, low latency, and quality assurance, it has become the main means for operators to solve the access problems for large users.
However, using DDN Network as a means of access for large users also encountered some practical problems in application: First, due to the requirements of DDN Network for business reliability and the complexity of circuit processing, DDN connection machines are generally foreign products, and their high prices limit the popularity of DDN nodes, so that DDN network coverage can only be concentrated in economically developed towns or major cities with relatively developed areas, and the vast majority of markets such as rural areas cannot take into account. That is to say, the traditional DDN network has a good profit advantage in level 3, but its input-output ratio is relatively low in Level 4. For bank users, there are usually few daily transactions in rural savings offices, and the required bandwidth is 1 to 2 64 K. Therefore, it is difficult to recover the investment by covering the DDN network in rural areas.
Second, due to the geographical distribution of large users in cities, nearby access is very important for operators to save investment. For the DDN network that has been built, it is difficult for the Operation Department to add DDN devices to meet the new user needs of growing locations due to factors such as network planning and cost. It is important for operators to consider how to connect to more users while minimizing device investment.
Third, because DDN is designed for data services, it often needs to be integrated with PSTN when both data and voice are required. The networking is complex and cannot be managed in a unified manner. In addition, the maintenance of DDN devices and networks is also complicated.
The various types analyzed above indicate that DDN has its own characteristics as a comprehensive access platform. It is suitable for users with a single business type that require high service quality and stability. At the same time, these users are also in relatively developed areas, close to the DDN nodes already laid. So how can we effectively extend and expand the DDN Network range to meet the requirements of more users? PCM devices are a good solution.
Chapter 2: PCM device is an effective solution for DDN Network Extension
As a traditional concept, PCM refers to re-connecting multiple voice services to E1. Today, the concept of PCM has been greatly expanded. It is not only limited to the reconnect of voice, but can be integrated into E1 for businesses including voice, data, and images. This makes it possible for PCM devices to complete most of the functions completed by traditional DDN devices. Such PCM devices provide a variety of interfaces for businesses that can access different rates and different electrical standards. See table 1). The above interfaces are standard E1, facilitating interconnection with transmission equipment. In addition, with the decreasing cost of optical transmission media, the coverage of optical transmission links based on SDH or PDH is wider and wider, and has reached the village level in some areas. A large number of underground optical cables provide a large number of E1 links, which are cheap and available everywhere.
 
All of these make the DDN Network Based on PCM devices a good choice, providing a solution for access to large users in both the township level 4 network and the urban level 3 network. In this solution, there is no need for an expensive DDN node host, just a cheap PDH or SDH optical terminal and a PCM device that reused 64 K services to E1, it can provide users with a speed channel from 64 K to M, so that users can easily access various services. The advantages are obvious:
The cost and operation cost of the entire network are low, which makes the network cost-effective. Generally, the cost of PCM equipment is 1/4 to 1/5 of the cost of DDN equipment. In addition, because of the popularity of Halo roads in cities and rural areas, large users who need to access services can generally access the nearest node by adding PCM devices instead of DDN devices, which further saves costs.
The rental bandwidth is flexible, from one to several 64 K to one complete E1, allowing users to have a lot of options, but also convenient for users to calculate their own expenses. For example, the current monthly rental fee for a 64 K circuit is ￥200, and the monthly rental fee for a complete E1 circuit is about ￥2000, users with low bandwidth requirements only need to rent a few 64 K to meet their needs, without the need to pay for extra bandwidth. In addition, this bandwidth can be appended, that is, users can increase the bandwidth to meet their needs when they think that the bandwidth cannot meet business needs.
PCM devices can provide various interfaces: voice, data, images ...... All these services are connected through an E1 channel, which saves Bandwidth Resources and can provide different bandwidth support based on different business needs. This facilitates the unified management of services and users by operators. Taking bank users as an example, the Internet of bank outlets generally involves a variety of services, such as voice services, real-time image services used to monitor counters, ATMs, entrances and exits, and environment monitoring for data centers. In addition, there will be more requirements such as video conferences. All these services can be reconnected to E1 through a PCM device.
Since the PCM equipment has been developed for many years, it is relatively simple, making the Operation and Maintenance more difficult, so that O & M personnel can master it well.
In terms of bandwidth utilization, because the E1 circuit is used for network management in a small number of bytes, and at present, common PCM devices do not occupy 64 K channels, only a small number of bytes are transmitted in the encoding format for monitoring. Due to performance management and circuit scheduling requirements, the DDN device has a large amount of code streams for network management and low bandwidth utilization. Low bandwidth utilization directly reduces the profits of operators.
From the above analysis, we can see that the PCM device is an effective means of extending the DDN network. PCM can provide service access capabilities in the original DDN network architecture, both in towns and cities. It is more suitable for relatively scattered users or users with less bandwidth needs, and provides users with access solutions with higher performance and price ratios.
Chapter 3: Data Network Solution for Dalian edge region
Dalian Agricultural Bank is a major customer in Dalian. In the early days, it used a 56 K audio circuit MODEM to connect to the Internet. As the business continues to grow, ABC has put forward the need to expand its online business. In response to the demands of ABC for system networking, Dalian Telecom provides the 64 K circuit Leasing Service Based on PCM equipment to ABC for networking. ABC's main services include voice and real-time image services for monitoring. Among them, the image monitoring service is mainly for the counter, ATM, entrance and other locations monitoring using MPEG-1 format encoding, the bandwidth is generally about K ). In addition, the Environment Monitoring for unattended data centers includes access control, smoke, temperature, humidity, fire alarms, etc. The data interface is RS232 ). The scope of Internet connection is agricultural bank branches, business offices, and township savings offices in various cities and cities. The networking equipment mainly includes PDH or HSDL providing E1 transmission channel), PCM equipment providing various service interfaces), video equipment including camera, video audio codec decoder, hard disk video equipment, etc, supports encoding, storage, and control of videos and audios ). The specific networking is as follows:
 
After more than a month of actual operation, the network runs stably and reliably, and the real-time image continuity and resolution can both meet the requirements. Data, images, and voice services can be transmitted in a hybrid manner on the same network, in addition, you can flexibly allocate different bandwidths for different services at different times ). According to reports, the cost of the network is much lower than that of using DDN.
In the above scheme, in order to be able to provide access to multiple services at the same time in an E1 channel, PCM equipment is required to provide multiple interfaces to meet different electrical and Protocol requirements, at the same time, PCM equipment is required to provide different flexibly adjustable and manageable bandwidths for each service interface, so that operators can conveniently provide circuit rental services for external use and complete access for large users. In addition, due to network management and other requirements, it is often necessary to manage E1 transmission links and PCM devices in a unified manner, so it is best for a manufacturer to complete the entire network. In the Dalian solution, Beijing Greenwell provides equipment configuration and solutions for the entire network, including transmission and PCM devices and most equipment including image monitoring devices, it also provides a unified network management platform for these devices. The current system operation and customer feedback are in good condition.
The above analysis and actual cases show that the PCM device can be effectively supplemented by the DDN Network, extending the DDN Network in villages and towns, and expanding the DDN network coverage in cities. Using PCM equipment to extend the DDN network can effectively reduce the network cost, provide good network management and network structure, simple operation, and have a high cost-effectiveness, is a good choice.