指交换系统与交换系统间或交换系统与用户系统间.PPTVIP

Circuit SwitchesThe Telephone NetworkSignalingTraffic and Overload Control in Telephone Networks 學號：M9308383座號：9姓名：盧相平指導教授：陳明仕 教授 2005.04.27. Chapter 4 Circuit-Switching Networks Circuit Switches Circuit Switch －實體線路之連接。 －將主叫用戶之用戶迴路與被叫用戶之用戶迴路連接 在一起，成為一條完整的通信線路。 －這條通話線路在用戶傳送語音/數據之前須先建立， 其它用戶不能再佔用此通話線路。 －用戶語音在傳送過程中不被儲存，通話線路中間的 交換節點也不會更改語音內容，稱為透通性傳送。 Network: Links switches Circuit consists of dedicated resources in sequence of links switches across network Circuit switch connects input links to output links Circuit Switch Types Space-Division switches Provide separate physical connection between inputs and outputs Crossbar switches Multistage switches Time-Division switches Time-slot interchange technique Time-space-time switches Hybrids combine Time Space switching Crossbar Space Switch Multistage Space Switch Large switch built from multiple stages of small switches The n inputs to a first-stage switch share k paths through intermediate crossbar switches Larger k (more intermediate switches) means more paths to output Clos Non-Blocking Condition: k=2n-1 Time-Slot Interchange (TSI) Switching Write bytes from arriving TDM stream into memory Read bytes in permuted order into outgoing TDM stream Max # slots = 125 msec / (2 x memory cycle time) Time-Space-Time Hybrid Switch Use TSI in first third stage; Use crossbar in middle Flow of time slots between switches Only one space switch active in each time slot Time-Share the Crossbar Switch Interconnection pattern of space switch is reconfigured every time slot Very compact design: fewer lines because of TDM less space because of time-shared crossbar Example: T-S-T Switch Design For N = 960 Single stage space switch ~ 1 million crosspoints T-S-T Let n = 120 N/n = 8 TSIs k = 2n – 1 = 239 for non-blocking Pick k = 240 time slots Need 8x8 time-multiplexed space switch For N = 96,000 T-S-T Let n = 120 k = 239 N / n = 800 Need 800x800 space switch Pure Optical Switching