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[color=Blue]1.1.1 Internet Protocol (IP) Technology
The radio system employs an advanced IP (Internet Protocol) based infrastructure that offers significant advantages compared with circuit switched solutions. The IP infrastructure is inherently expandable because its distributed architecture overcomes the bottlenecks caused by the physical limitations of circuit switches.
IP infrastructure is also ideal for integrating voice and data services across the whole network, offering greater bandwidth and less propagation delay. By employing the very widely employed IP standard, Taiwan High Speed Rail can benefit from the enormous advances that have been made through Internet technology: providing highly reliable, fast and robust solutions.
The technologies used are Unicast IP and Multicast IP. Point to point traffic (Individual calls) employs Unicast IP and Group calls use Multicast IP, which is ideal because it simultaneously delivers data from a single source to multiple destinations without requiring multiple copies of the message to be transmitted.
The radio system employs a method that refines distribution still further by ensuring that traffic is only sent to routers that have an interest in receiving it. Messages are therefore only replicated where the distribution tree branches to reach different members of the receiving multicast group. Group memberships are arbitrated using a protocol that allows local hosts on the WAN to join and leave these groups.
The radio system makes very efficient use of router resources in the system by creating Multicast IP groups only for the duration of a group call.
1.1.2 Switching Components
The wide area switching components comprise:
a) Wide Area Network (WAN) switch, which is in a fully redundant chassis. The link between the WAN switch and the Base Stations employs the Frame Relay packet protocol, over an X.21 link.
b) Zone Controller, which are the central processors of the system. High availability is ensured by using a redundant configuration, with two controller units, one of which is active and the other is stand-by. The radio system supports automatic switchover to the stand-by controller if the active one goes off-line.
c) Other Network equipment such as network switches and routers. Routers are network nodes that link together different LAN or WAN segments, and carry out routing decisions for individual packets. Pairs of core routers are used to channel traffic to the base sites, both for load sharing and so the site link cannot be lost by the failure of a single router.
1.1.3 Base Station
The trainer should only brief the trainees on this topic as details of the EBTS will be provided in “EBTS Maintenance and Troubleshooting Workshop”. The detail description provided here is for the trainer reference.
The EBTS is a stand-alone rack mounted unit providing the RF air interface from the switching main infrastructure to the radio units.
The EBTS consists of four sub-system elements:
Base Radio (BR) Transceiver
The base radio transceiver is a high-powered station delivering up to 25 Watts at the antenna port. Each BR utilizes TDMA technology to provide 4 logical channels in a 25 kHz carrier channel. Various configurations are available to meet capacity requirements ranging from 4 to 32 logical channels.
TETRA Site Controller
The TETRA Site Controller provides the E1 remote interface to the TETRA network and controls BR operation over an Ethernet link. The TETRA Site Controller also contains the Site Reference ISA (SRI) time and frequency reference module. The module includes a high stability oscillator to provide the frequency reference and a GPS receiver to provide the timing reference for its own equipment operation.
The TETRA Site Controller basic operating system software includes Local Site Trunking (LST). In addition, the TETRA Site Controller basic operating system software also supports Short Data Transport Service (SDTS). To enhance reliability, two TETRA Site Controllers are configured in hot standby mode to provide redundancy.
Environmental Alarm System (EAS)
Each EBTS incorporates an EAS to provide fault reporting and remote control functions at the EBTS site. The EAS can provide 48 local inputs for monitoring EBTS functions and radio site environmental conditions. Up to eight outputs are provided to enable remote control functions.
RF Distribution System (RFDS)
The RFDS is consists of duplexers, receiver multicouplers, cavity combiners and isolators. The duplexers enable a single antenna to provide both transmit and receive functions. The receiver multicouplers provide multiple receive signal ports. The cavity combiners combine the transmit output of the BRs. The isolator protects the Base Radio power amplifier form unwanted reflections.
译稿：
[color=Teal][color=Navy][color=Maroon][color=LimeGreen][color=Maroon][color=Navy][color=Maroon][color=LimeGreen][color=Maroon][color=Navy][color=Teal][color=Navy][color=Maroon][color=LimeGreen][color=Maroon][color=Navy]1.1.1 IP技术
无线系统使用先进的网络协议，这比电路控制有着更好的优势。IP 基础设施具固有的可扩展性，它的分布型架构可以克服因为线路转接的物理局限而造成的瓶颈。
IP 基础设施对于越过整个网络将声音与资料服务融为一体来说也很理想，提供了更大的带宽并减少了传播延迟。IP网络基础结构对于集成整个网络中的声音和资料服务也很理想，可实现更大的带宽和更少的传输延迟。通过采用应用广泛的IP标准，台湾高铁从网络技术的巨大进展中获益：取得可信度高，迅捷和强有力的解决方案。
所使用的技术是单点传播与多点传播IP。点对点的传播（个体电话）使用单点传播而群组电话则使用多点传播，这是非常理想的，因为可从单个的信号源同时把资料传送出去而无需多个拷贝要传输的信息。
这种无线系统所采用的方式通过优化分发以确保信息能传输到有权收到的路由器。因此信息只有在其分流处才会被复制以传到可获取信息的不同组员。组员通过充许当地WAN的主人参与或离开的协议来得以仲裁。
无线系统通过为群组创建多个网络协议而高效地利用了系统中的路由器资源。
1.1.2 转换组成
广域转换器的组成
a.广域转换安插在底盘上,广域开关与基地的链接使用桢继小包协议，在X.21 链接之外。
b.区域控制器是系统的中央处理器，高可及性由备用配置得到保证,其有两个控制器单位,一个在使用中，另一个备用。万一正在使用的控制器离线，无线电系统则可自动启用备用控制器。
c.其它网络设备譬如网络开关和路由器。路由器是连接不同的LAN 或WAN 段的网络节点, 并为个体信息包执行路由决定。成对的核心路由器则将资料导向基地站。两者都是用来装载信息的，因此站点链接不会因为某一路由器的失常而丢失。
1.1.3 基地
培训员只须简要向学员解释相关内容，因为更多详情会在"EBTS 维护和和故障排除部分" 得以陈述,此处提供的细节描述仅作参考。
The EBTS是一个独立单位，它提供了从主要基础设施向无线电单位转换的RF空中接口。EBTS 包括四个子系统元素:
基地无线电收发器
基地无线电收发器是一个大功率的基地，可提供25 瓦特的天线口岸。每个BR 运用TDMA 技术以25 千赫载体渠道提供4 条逻辑信道。多样的配置可满足从4 至32 条逻辑信道的不同范围要求。
四站点控制器
四站点控制器向四站点网络提供提供E1 远程接口并通过以太网链接控制BR 操作。四站点控制器包含站点参考ISA (SRI) 时间和频率参考模块。模块包括一台高的稳定摆动器以提供频率参考和GPS 接收器为它自己的设备操作提供时间参考。和控制BR 操作在以太网链接。四站点控制器包含站点参考ISA (SRI) 时间和频率参考模块。模块包括一台高稳定摆动器，可提供频率参考和一台GPS 接收器提供自身操作的时间。
四站点控制器基本操作系统软件包括地方站点中继(LST) 。另外, 四站点控制器基本操作系统软件支持短数据传输业务(SDTS) 。为提高稳定性,配置两个四站点控制系统以备用。
环境警报系统(EAS)
每个EBTS 都有一个EAS 提供错误报告和EBTS 站点的远程操作功能。EAS 可为监控EBTS 功能和无线电站点环境状况提供48单位的 地方输入。提供多达8个单位的输出以实现遥控。
分发系统(RFDS) RFDS 是包括天线共享器、多路耦合器、洞合成仪和绝缘物。天线共享器使单一天线具有传送和接受作用。多路耦合器提供多倍的信号接收口岸。洞合成仪将传送给BRs产品的输出结合起来。绝缘物可防止基地无线电功率放大器形成不必要的反射[/color]
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