电路交换(Circuit Switching)优点 Dedicated communication path between two stationsCircuit capacity not reduced by othernetwork trafficTypically allows full duplex transmissionMultiple protection/restoration schemes Once connected, transfer is transparentLow loss, low latency, and minimal jitter缺点 Channel provides for transmission at constant rate. Thecapacity dedicated for duration of connection.must transmit and receive at same data rate. Limits versatility If no data, capacity wasted Set up (connection) takes time
电路交换（ Circuit Switching） ◼ 优点 ◼ Dedicated communication path between two stations ◼ Circuit capacity not reduced by other network traffic ◼ Typically allows full duplex transmission ◼ Multiple protection/restoration schemes ◼ Once connected, transfer is transparent ◼ Low loss, low latency, and minimal jitter ◼ 缺点 ◼ Channel provides for transmission at constant rate. The capacity dedicated for duration of connection. ◼ must transmit and receive at same data rate. Limits versatility ◼ If no data, capacity wasted ◼ Set up (connection) takes time
分组交换(Packet Switching)优点 Data transmitted in small packets, Packets are receivedbuffered and passed on to the next node Single node to node link can be shared by manypackets over timeEach station connects to the local node at its own speed缺点 May have concurrent transmissions over physicalchannelMay have delays and congestion
分组交换（Packet Switching） ◼ 优点 ◼ Data transmitted in small packets, Packets are received, buffered and passed on to the next node ◼ Single node to node link can be shared by many packets over time ◼ Each station connects to the local node at its own speed ◼ 缺点 ◼ May have concurrent transmissions over physical channel ◼ May have delays and congestion
电路交换VS分组交换分组交换电路交换在数据传输前，不必建立端到端的在数据传输前，必须建立端连接到端的连接数据的传输采用存储转发，延时不连接建立后，数据的传输没可估计有额外的延时共享带宽，可能会产生拥塞和丢包带宽独享，不会产生拥塞不能保证服务质量能保证服务质量信道利用率较高信道的利用率较低电路交换分组交换X带宽保证x保护/恢复xQoSX服务提供X可扩展性
电路交换 vs 分组交换 分组交换 ◼ 在数据传输前，不必建立端到端的 连接 ◼ 数据的传输采用存储转发，延时不 可估计 ◼ 共享带宽，可能会产生拥塞和丢包 ◼ 不能保证服务质量 ◼信道利用率较高 电路交换 ◼ 在数据传输前，必须建立端 到端的连接 ◼ 连接建立后，数据的传输没 有额外的延时 ◼ 带宽独享，不会产生拥塞 ◼能保证服务质量 ◼信道的利用率较低 - 电路交换 分组交换 带宽保证 × 保护/恢复 × QoS × 服务提供 × 可扩展性 ×
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数字复用体系
数字复用体系DS1DS2.复DSO::复用:DS1复DS3用:DS2STS-1适用DSO配输人：7DS2输人：24DS0输入：4DS1输入：DS3输出：DS3输出：DS1输出：DS2输出：STS-1传输单个数字语音及视频信号所需比特率远低于传输媒质的传输带宽STS-1OC-N光电复STS-N:复用是将多路信号同时在传输变换用STS-1媒介中进行传送的技术只有经过信道复用才可以充分速率=NX51.84Mbit/s利用传输媒介的传输带宽或NX155.52Mbit/s常用复用技术：时分复用（TDM）、频分复用（FDM）、码1数字复用体系（CDM）等分复用
北美数字复用体系 ◼ 传输单个数字语音及视频信号 所需比特率远低于传输媒质的 传输带宽 ◼ 复用是将多路信号同时在传输 媒介中进行传送的技术 ◼ 只有经过信道复用才可以充分 利用传输媒介的传输带宽 ◼ 常用复用技术：时分复用（ TDM）、频分复用（FDM）、码 分复用（CDM）等 数字复用体系