Exploration on the standardization of access networks for major customers

There are many areas worth learning about access networks for major customers. Here we will mainly introduce the exploration of the standardization of access networks for major customers. The following provides a reference model for access networks of major customers. Access networks of major customers are composed of several relatively independent subnets composed of several access entities. They are connected to the transmission network through UNI, NNI, and DCI interfaces. Each access subnet has its own subnet manager, which implements interfaces through standard management interfaces Qa and TMN. Major customer access networks are also responsible for transmitting the network synchronization clock, which is especially important for SDH networks.

The reference model is in line with the layered model of ITU-T telecom network, and its guiding significance is: to establish the status of access networks of major customers. Some people in the industry think that the access network of major customers is a natural extension of the transmission network and the access network of major customers is a subsidiary of the transmission network. By specifying the access network interface, you can achieve hierarchical construction and management of access networks and man for major customers.

1) UNI interface Discussion

UNI interface is an interface between access networks of major customers and user devices. Common electrical interfaces include E1, FE1, V35, and Ethernet interfaces. The optical interface has a channelized cSTM-1 interface. For some users who want to provide RS-232 and telephone interfaces, it is not recommended to define these interfaces as UNI interfaces, because doing so makes it difficult to determine the service quality of these interfaces and clarify responsibility when there is a problem. These functions can be completed by purchasing other access devices, such as a multiplead, and maintained by the user.

2) NNI interface Discussion

NNI directly affects network interconnection and interconnectivity, it is recommended to adopt open interface protocol, that is, the protocol recommended by the ITU-T. Including the physical layer and link layer. The physical layer adopts STM-1 optical interface, E1 electrical interface and Ethernet interface. The Ethernet encapsulation protocol can be in two forms: If NNI is E1 interface, EOPDH encapsulation protocol should be adopted, according to The ITU-T standard G.7043; If NNI is STM-1 optical interface, the EOPDH encapsulation protocol can be used either by VCAT + green + LCAS encapsulation protocol defined by ITU-T 7041/7042) or by EOPDH encapsulation protocol. This depends on the protocol used by the peer device.

3) DCI interface Discussion

DCI interface is a data communication interface provided by the transmission network. It establishes a communication channel between the access subnet manager and the access entity. DCI has multiple possible interfaces: the physical layer is Ethernet, and the network layer is TCP/IP. This interface is fast and easy to use and should be provided as much as possible. A transparent E1/FE1 channel is provided through the NNI optical interface. This DCI is embedded in NNI, which can reduce additional electrical interfaces and facilitate the use. The physical layer provides transparent E1/FE1 electrical interfaces, and the physical layer provides RS-232 channels. It can be point-to-point or bus type. In the second and third cases, if the transmission network can provide the E1 channel of chrysanthemum chain, multiple type C devices can share one E1 circuit, which can save network resources and is a better choice.

4) Qa interface Discussion

Qa is the interface of the major account subnet manager and TMN. This interface should be simple and effective, and should not be too complex. Since many software technologies have been designed, we will not discuss them here.

5) Access entity Discussion

The access entity consists of the Network Element and Network Element Manager. There are two basic types of access entities: C and U. They can form a variety of network topologies, either star or chain or ring. C-type devices are responsible for NNI interfaces, while U-type devices are responsible for UNI interfaces. Under certain conditions, the functions of these two devices can be exchanged. The C-type device has the hub function and can reuse multiple user lines. It is usually called an uplink port through NNI) and connects to the transmission network. There are two scenarios for Type C devices: if the point is a branch user, there are usually only a few user interfaces, which can be relatively simple. This kind of device is referred to as a light cat device. If it is a headquarters user, the device is complicated and needs to restore a large number of user services, such as Ethernet circuits. Generally, centralized plug-in card devices are used.

There are two types of U-type devices. One type is simple without 64 K time slot multiplexing, And the other type is flexible with 64 K time slot multiplexing. Flexible reuse has a benefit, is to provide FE1 Extended Interface for some voice, RS-232 data or conference television equipment to provide extended interface, can enhance the scalability of equipment. The M function is responsible for managing network elements. Manages both C-type and multiple related U-type devices. Provides configuration, alarm, performance, resources, and security management functions. Can be embedded into U-type and C-type devices. It can also be an independent device dedicated for management or communication. Equipment reliability and various protection capabilities should be standardized. Such as power supply protection, line protection, board protection, and business interface protection. Cross-connection capability of normal equipment. Major customer access devices should be able to enable services. Some circuits can be activated and closed through the software interface. It also provides the bandwidth management function to adjust the bandwidth of the circuit as needed. It can be adjusted based on 64 K granularity or 2 M bandwidth.

6) subnet manager Discussion

The subnet manager collects configuration information and alarm information of multiple subnets for information processing, stores SLA record data, and reports data to TMN.

7) Several details

Recommendation 1: major customer access networks should focus on Star and point-to-point topologies to reduce the use of the ring and chain networks. This simplifies the configuration process and reduces costs. Unless special protection is required.

Recommendation 2: when the network element of the access network uses the SDH line interface, the timing function should adopt the device timing mode or the cycle-back Timing mode, and the Free oscillation mode is not recommended. The free-oscillating mode can reduce the cost, but this will not allow reliable transmission of network synchronization timing information. For mobile base stations, such as terminal devices with high timing quality requirements, this will cause some usage problems.

Recommendation 3: Provides business-based management functions. Service-based management is different from the device management functions provided by most devices. The device management function is used to manage devices. It is difficult to see the status of the entire circuit because a circuit may pass through multiple devices of different manufacturers ). Business Management is the management of each circuit. When the end-to-end transmission of the VC-12 channel or the frame transmission of the E1 channel is available, the performance and alarm of the complete circuit can be obtained by recording and analyzing the V5 byte or E1 frame overhead, to manage the business. Major customers generally need to access networks through devices of different manufacturers. Once an error code or fault occurs in the circuit, problems can be quickly discovered through business management, so as to win time for troubleshooting.

Recommendation 4: Major account access networks should enhance the use of J2 overhead. J2 is the Access Point identifier of SDH VC-12 channel, which consists of 15 strings. Using J2 can simplify network activation. Because major customers need to access networks through the transmission network, there may be multiple digital cross-connections in the middle, sometimes the circuit configuration error may occur, and it is not easy to find the error, causing trouble to activate the service. With J2, you can easily identify the number of the received circuit, which is very helpful for troubleshooting.

Suggestion 5: implement the built-in probe function. Probe is a new concept that monitors, controls, and counts the running status of a circuit. It must be used with business-based management software. This technology enables end-to-end management of lease circuits and generates SLA reports. Perform remote loop back, insert test sequence, and so on. At present, although some manufacturers claim to support the probe function, they use a private protocol and cannot communicate with other manufacturers. Therefore, we recommend that you standardize probe overhead usage as soon as possible. Control by preparing probe command words, such as remote loop back, reading remote virtual registers, and writing to remote virtual registers. The probe command word can be placed in the overhead of E1 TS0, or the 8bit of K4. The specific frame format needs to be further defined. The probe should be placed in the U device and in the C device. This can not only monitor the end-to-end status, but also the status of the intermediate node for fault locating. The following are some concepts about probes.