E1链路无损伤切换的研究与实现设计.doc

摘要
E1中继链路在我国民用通信系统和军事通信中都有着广泛的应用。在一些重要应用场合,需要确保通信不中断,对传输的可靠性和传输的质量有严格的要求。通过增加传输路径,提供主备链路切换,是提高可靠性的一种切实有效的手段。本文在研究E1链路无损伤切换机制的基础上,提出并实现了一种新的无损伤切换机制,通过使用某一用户时隙或者0时隙的Sa比特编码实现无损伤切换,并采用网管代理模块实现带内网管功能,对无帧2M实现有损伤切换。论文主要分三个部分:
第一、在研究E1相关建议和现有的E1切换设备基础上,提出总体设计方案,利用插入的信息完成延时的计算、校验和实现网管数据传送,无损伤切换功能由FPGA实现,中继芯片完成E1成帧解帧和线路接口的功能,ARM7模块实现网管代理功能。
第二、采用FPGA实现无损伤切换,主要完成数据缓存、切换控制、输出数据调整和中继芯片控制等功能。采用自顶向下的设计方法,划分了六个功能模块:接收模块、发送模块、时钟模块、中继芯片控制模块、外部接口模块和处理器接口模块。采用“顺序写入,控制读出”完成数据的缓存与读出,在每一帧的基础上实现自动切换,可以消除线路故障、误码、滑码和延时抖动的影响。经过测试和实际现场的运行证明,该系统较好的实现了设计要求。
第三、利用ARM7模块实现网管代理的功能。模块访问FPGA采用读写寄存器的方式实现,带内网管数据的收发利用一个外部中断实现,FPGA实现字节流传送服务,速率为8kbit/s。将从本地TCP Socket收到的网管消息和从带内网管通道接收的对端设备发送的网管消息使用消息队列机制统一处理,通过轮询相应链路告警寄存器的方法获得告警信息,并将每一条告警都存入模块的Flash中。经过与PC端网管软件的联调测试,工作稳定,告警记录正确,基本达到了设计要求。
关键词:E1链路,无损伤切换,FPGA,带内网管
Research and Implementation of Hitless Switching for E1 Trunk
Abstract
In Chinese civil and munication systems, the E1 trunk is widely used. When used to transmit important information, it should be insure that the link can’t be interrupted, and it has a high requirement for reliability and quality. It is an effective scheme, which provides a backup path to perform switching. In this dissertation, based on the present methods, a new hitless switching scheme for E1 trunk, that can provide hitless switching using coding on a user timeslot or timeslot 0 Sa bits, and support in-band management work management unit, and can also support the hitness switching for unframed 2M trunk, was proposed and implemented.
First, based on researching the mendations about E1 trunk and the present E1 hitless switching devices, an overall design was proposed. A coding scheme was used to calculate a delay difference between the first and second path, insert the check words and send the in-band management information. The switching function was implemented in FPGA. The transceiver chip was used plement the function of E1 framer and line interface. The management agent was implemented on the ARM7 microprocessor