Functions and performance indicators of access-type ATM Switches

There are many areas worth learning about the access-type ATM switch. Here we mainly introduce the functions and performance indicators of the access-type ATM switch. The access-type ATM switch contains a variety of service interfaces and is directly oriented to users, it can be used for private networks (such as campus networks and enterprise networks) and public networks (such as long-distance intercommunication between Ethernet networks and interconnection between access ATM switches). It has broad application prospects, this thesis is based on the completion of the device.

The service interfaces of the device include: Ethernet interface, E1 circuit simulation interface, and 155.520 Mbit/s cell interface. The 155.520 Mbit/s interface can be connected to high-speed services, it can also interconnect access-type ATM switches. In addition, the device also has the maintenance and management functions.

Functions and performance indicators

The access-type ATM Switch provides the following functions: Ethernet simulation interface and E1 circuit simulation interface to the ATM layer adaptation, non-exchange between different ports, and cell multiplexing to the ATM line terminal. Supports PVC point-to-point and point-to-point/broadcast connections and maintenance functions.

Performance indicators

The following issues should be taken into account when formulating a scheme: first, the applicability of the scheme. The solution must first meet the user's usage requirements and make it easy to use. The second is reliability and advancement. For practical equipment, mature standards and technical systems should be adopted as much as possible in the formulation of the scheme to avoid development failures due to technical system defects, at the same time, mature devices should be used to ensure the reliability of the equipment. Advanced technologies and special devices should be used to prolong the use cycle of the equipment. The third is universality. In the formulation of the Scheme, as far as possible to use general standards, such as International or ITU-T standards, as far as possible to use general devices, which can not only shorten the device development cycle, but also facilitate the interconnection with other communication networks, reduce the complexity of interconnection; the fourth is economic. During the design process, devices should adopt general standards and general-purpose devices as much as possible. The more basic technologies they research and develop, the higher the cost. At the same time, large-scale integrated circuits should be used in the hardware to make the device small in size, light in weight, and easy to use.

Basic Structure of an access-type ATM Switch

An access-type ATM switch consists of a variety of business adaptation interfaces, line Terminals (LT), switching, and maintenance. Service interfaces include: Ethernet ports (supporting Ethernet simulation) and E1 circuit simulation interfaces. In addition, there is a 155.520 Mbit/s line interface. 2.2 hardware implementation (1) the overall hardware implementation focuses on the processor system and switching system when considering the overall hardware implementation scheme.

The processor system adopts a two-level processing structure. Each business adapter or cell interface board has its own local CPU to complete local initialization, hardware driver, management, statistics, and other functions, the tasks of the CPU in the main control board are managed, controlled, maintained, and other functions in public, and the working status of each module is coordinated. The advantages of this system are: ① CPU processing is modular, and the burden is small. Each module (including the main control board) can select an appropriate CPU processor as needed; ② It can be modularized from design to debugging, to minimize inter-module involvement, this helps accelerate development progress and reduce development costs, and also facilitates independent development and maintenance of software for each module. To speed up the development of devices, the Main Control Board adopts the ready-made industrial computer board, with the CPU of MC68040 and other parts developed independently. The CPU of each business adapter or cell interface board is MC68302. The communication bus between the main longitude plate is VME bus. Because the device is an access device, its switching capacity is not large, so the type of the switching matrix adopts the bus type. At present, the common exchange systems at home and abroad mainly include bus-type exchange and shared cache exchange. Their advantages and disadvantages are as follows:

Advantages: ① the access-type ATM switching mechanism is simple and easy to implement. It is suitable for small-capacity switching systems; ② It is easy to design hardware and software. Only one shared bus is required for the backboard, and no switching matrix board is required, each module is connected to the bus through the bus transceiver and exchange controller, so each module has a strong versatility. ③ the technology is mature and reliable. Currently, the bus exchange product has been commercialized and the cost is low.
Disadvantage: it is not easy to implement a large-capacity switching system.

(1) Dedicated switching matrix circuit units are required. Master-slave redundancy switching must be achieved for reliability. ② the connection between various business modules and switching matrices is a point-to-point relationship, and the Backplane Design is complex, poor versatility.

(2) E1 circuit simulation interface unit

The EI circuit simulation interface unit consists of the interface circuit, SAR segmentation and assembly, SAR overhead addition and processing, header assembly and removal, and SRTS generation and recovery, this circuit does not separate and package different channels, but treats the entire information stream of the interface as a whole. It is packaged in segments and adapted with a non-structured AAL1, the interface between the Unit and the switch part is UTOPLA Level1. The interface circuit completes the code type conversion and line clock extraction between HDB3 and NRZ code. It consists of DHB codec, clock extraction dedicated chip and transformer. The AAL1 adaptation function is implemented by a dedicated chip.

(3) Implementation of Ethernet interface units

The Ethernet simulation service consists of two components: one is the Ethernet simulation client and the other is the Ethernet simulation server. The Ethernet simulation interface unit provides the simulation client function in the Ethernet simulation, including Ethernet protocol processing, ATM Adaptation and control.

The input Ethernet information received from the AUI interface is sent to the Manchester decoder. After decoding, a MAC frame is formed and sent to the MAC receiver for processing. The MAC receiver identifies the destination and source addresses, executes ARP Based on the destination address of the frame to obtain the corresponding ATM address, and stores user data in the receiving FIFO, the CPU system sends the location information of the data in the FIFO through the Controller to inform the SRA-S, The SRA-S uses AAL5 to pack the user data into a 48-byte SAR-PDU, and adds the header to form a cell, which is sent to the swap part after the UPC. The output part obtains information from the exchange part and sends the SRA-R, The SRA-R removes the header and executes the AAL5 receiving protocol, stores it in the FIFO, the CPU system notifies the MAC sender, it extracts the frame from the FIFO and executes the Protocol to form a MAC frame, which is sent to the line after being encoded by Manchester. In addition, it also provides functions such as diagnosis loop and OAM. The interface between this interface unit and the switch part is UTOPIA Level1. The AUI interface is isolated from external transformers, and Manchester codec and MAC codec adopt dedicated chips. The dual-port RAM is used for receiving FIFO messages and sending FIFO messages. SRA-S and SRA-R complete AAL5 transmission and receiving functions, respectively, by two dedicated chips. The following describes the specific configurations of the Ethernet simulation server in the ATM network and the implementation of the Ethernet simulation server software.

① Ethernet simulation server configuration position in the access-type ATM Switch: the Ethernet simulation server is implemented on the Main Control Board 2.

② The Protocol is implemented based on the "atm lan simulation (version 1.0)" of the ATM Forum. The LAN simulation layer software consists of two parts: LEC (Local Network Simulation customer) and LEServer (LAN simulation service). LEServer includes LES (LAN simulation server), CS (configuration server), and BUS (Broadcast Server ). The LEC software maps MAC addresses to ATM addresses, dynamically registers with LES the MAC addresses of the Ethernet terminals it "acts as proxies", and other functions; as the management and control center of the simulation LAN, LES mainly performs functions such as dynamic address logon, dynamic conversion of MAC addresses and ATM addresses, and BUS is responsible for transmitting all broadcast/Point-to-multi-point data; CS is responsible for providing the configuration information of the ATM network, for example, providing the les atm address to LEC.