Design and Implementation of the control unit in the ATM switch Center

1 Overview
The central control unit of an ATM switch is the control and command center of the entire switch. The Network Management proxy and maintenance terminal manages and maintains the ATM switch through this unit, each Service Board collects and reports data through this Unit. In addition, the core part of the ATM switching software-the signaling software includes user-to-network signaling and network-to-network signaling, I .e., UNI/NNI signaling) will run on the hardware of the central control unit. This article mainly discusses the hardware design and implementation of the central control unit.
The central control unit provides the 10 BASE-T Ethernet interface conforming to the IEEE 802.3 protocol for the network management proxy, provides a serial interface conforming to the RS232C standard for the maintenance terminal, and uses the HDLC interface with each business unit, exchange matrix interfaces are used with switching units. Because the signaling software and operating system must be loaded to the hardware of the central control unit, and the signaling information must be adapted to AAL5, therefore, hardware is required to provide sufficient program storage space and data storage space, and the CPU processing capability is high enough. To this end, we chose the MPC860SAR chip produced by Motorola.
The MPC860SAR chip is a powerful communication processing chip that can not only process Ethernet, HDLC, UART, and other protocols, but also implement SAR functions. The ATM cells produced by the MPC860SAR arrive at the routing and business management modules first, and the routing and business management modules determine the switching routes and queue the caches before they arrive at the Switching Matrix for switching. The Interface Conversion Circuit must be designed because the interfaces between the MPC860SAR and the routing and business management modules do not match.
2. Functions completed by the central control unit
* Receives information from the network management agent, sends it to the business unit, and reports the data of the business unit to the network management agent;
* Receives information from the maintenance terminal, sends it to each business unit, and summarizes and reports the status and other information of each business unit to the maintenance terminal;
* Completes the CP public part of the SAALSingling ATM adapt layer and signaling ATM Adaptation layer), that is, the AAL5 adaptation to the signaling information generated at the upper layer, the UTOPIA interface sends the ATM cells to the routing and business management modules, and then to the switching units.
3. Design and Implementation of central control unit
3.1 working principle and Function Description between modules
The central control unit consists of the CPU module, communication processing module, and routing and business management module. In normal operation, the CPU module only controls whether to allow receiving and sending of a communication protocol, and does not directly participate in the processing of a specific communication protocol. The communication processing module independently processes specific communication protocols and receives and sends protocol data.
The CPU module controls the communication processing module through a command register, and data exchange between them is performed through dual-port RAM.
The ATM service module in the communication processing module refers to the information of the SAR module, which is sent to the switching matrix after the routing and business management modules. The communication processing module provides an 8-bit Utopia interface for receiving and receiving at the ATM side, while the routing and business management module provides a 16-bit Utopia interface at the ATM side. The two cannot be directly connected, utopia Interface Conversion is required between two modules, and the conversion circuit is implemented by CPLD.
As an external CPU device, the routing and business management module is connected to the CPU module through the CPU's external data bus, address bus, and control bus. Because the CPU module of the routing and business management module provides separate external data bus and address bus, bus interface conversion is required between the two modules. The conversion circuit is implemented using EPLD.
3.2 Function Description in the module
1) CPU module
The CPU module includes the CPU core, 32-bit wide data memory SDRAM), 32-bit wide program memory FLASH), and the hardware reset configuration circuit of the CPU. The CPU core adopts a 32-bit PowerPC structure, which contains the command unit and Command Execution Unit, which are the execution of user programs. The SDRAM is used to store the data generated or required during program execution; FLASH is used to store the program compiled by the user. Compared with the EPROM device, FLASH has the outstanding advantage of enabling the system to have online programming capability and flexible block lock storage, which plays a protective role; the hardware reset configuration circuit is used to set certain CPU parameters and reuse pins during hardware reset.
2) communication processing module
The communication processing module includes asynchronous serial communication UART) processing module, Ethernet processing module, HDLC communication processing module, and AAL5 SARATM cell segmentation and restructuring function module. The UART processing module is used to process the information of the maintenance terminal. The Ethernet processing module is used to process the information of the network management proxy meeting the 802.3 protocol. The HDLC communication processing module has two types: one is used for communication between the central control unit and each business board, and the other is used for communication between the master and slave control units; the SAR function module is used to implement the SAR function and some ATM layer functions that support the AAL5 protocol. Each function module is briefly described as follows:
The working principle of each function module in the communication processing module is roughly the same, but the SAR module is slightly different. The working principle is as follows: Some registers are set through the CPU module, initialized to a specific communication protocol, and then the parameter RAM in the dual-port RAM is set to the parameter for the communication protocol. Of course, the interface control signals of different communication protocols are different.
The SAR function module is used to implement the SAR function and some ATM layer functions that support the AAL5 protocol, that is, to adapt AAL5 to the information generated by the upper layer, divide it into a 48-byte CS-PDU plus a 5-byte ATM cell header to form a 53-byte ATM Cell and send it to the routing and business management module; on the contrary, reorganize the ATM cells received from the routing and business management modules and send them to the senior management.
3) routing and Business Management Module
* Function Overview
As an advanced communication device, the ATM Routing and business management module supports very powerful and high-performance ATM switching systems. The rich performance of RTM can provide flexible network services for system design. It is a combination of exchange matrix applications consisting of an ATM Switching Matrix unit SE. It can build a 622 Mbps to Gbps switching capacity. This module can provide Mbps UTOPIA access. This module can also build a 622Mbps exchange separately.
RTM uses each VC receiving queue and 64 receiving service classes. 31 virtual outputs can be used for flexible multi-priority sorting. This sorter can be used as the calculation of QoS for virtual channel connections of CBR, VBR, and UBR. RTM also provides five independent blocking thresholds, each with a lagging and selective control over AAL5 early packet discard EPD) and UBR discard cells based on the cell loss priority, RTM also supports full VPI/VCI header translation, 64 K input/output cell buffering, and VP/VC switching. 16 k vcs are supported on the receiving and sending sides.
* Cell flow Overview
1) on the receiving side, find the channel number from the cells received by the UTOPIA interface. The received cells are either discarded or sent to the receiving cell buffer DRAM, Which is queued Based on Six blocking management check mechanisms, including the maximum threshold, blocking threshold service group, service class, and connection.
2) When an available cell time occurs, the receiving-side sequencer selects four units and caches DRAM read cells from the receiving cells and sends them to the switching matrix.
3) on the sending side, once a cell is received from the switching matrix, or the buffer DRAM is discarded or sent and queued in the sending queue. This relies on ten blocking management check mechanisms, including the maximum threshold, blocking threshold, VO, SC, SCG, SCQ, and connection );
4) When a cell is selected as a sender, it is removed from the cell buffer DRAM and processed by the corresponding header translation and the allocated multi-point or header matching, the cell is sent to the UTOPIA interface and leaves the module on the sending side.
* Business Management Module
Application RTM business management is used to monitor and control RTM resources. This module uses CAC to allow and deny calls based on the allocation and queue depth.
1) receives connections and rejects connections: receives connections or rejects connections based on the current blocking situation;
2) allocates service-class queue connections. For each connection, the corresponding queue depth of the connection is set in the receiving and sending directions based on the QoS of different services;
3) Adjust the SCQs round-robin service order weight to ensure that high-priority cells are sent first;
4) Update the depth of the connection and service queue: flexibly change the parameter settings online as needed.
* Advantages
1) Meet QoS requirements;
2) Minimize CDV;
3) MCR guarantee: the application of the time slot table ensures that all service class SCS are equally able to obtain the minimum cell rate;
4) obtain the maximum value fairly: allow different SCs to support different bandwidths;
5) Independent output: Channel cells to different virtual outputs are stored in an independent data structure, so that blocking of one virtual output will not cause blocking of another virtual output, thus play a very good role in isolation.
4 Conclusion
The central control unit is the core of the normal operation of the ATM switch. The central control unit enables the network management agent to configure the parameters of the ATM network and manage the network through the unit, so that the maintenance terminal can maintain the ATM switch through the unit, the Service Board reports the status and summarizes the data through this unit, thus completing the command and control functions for the ATM switch.