计算机网络课件5-桂林电子科技大学

Public Circuit Switched Network
Telecomms Components
Subscriber (用户)
– Devices attached to network
Subscriber line(本地环路)
– – – – Local Loop Subscriber loop Connection to network Few km up to few tens of km
Nodes Nodes may connect to other nodes only, or to stations and other nodes Node to node links usually multiplexed Network is usually partially (部分的) connected – Some redundant (冗余的) connections are desirable for reliability
• Short duration calls
Non-blocking (无阻塞网络) – Permits all stations to connect (in pairs) at once – Used for some data connections
Space Division (空分) Switching
– Establish connections
• • • • Generally on demand Handle and acknowledge requests Determine if destination is free construct path
– Maintain connection – Disconnect
Multistage Switch
Reduced number of crosspoints More than one path through network – Increased reliability More complex control May be blocking
Three Stage Space Division Switch
Total
12
12
12
54H
Chapter 10 Circuit Switching and Packet Switching
10.1 Switching Networks 10.2 Circuit-Switching Networks 10.3 Circuit-Switching Concept 10.4 Control Siganling 10.5 Softswitch Architecture 10.6 Packet-Switching Principles 10.7 X.25 10.8 Frame Relay
Wavelan)
– Problem: coordinate the access of all nodes to the shared communication medium (Multiple Access Problem)
• Switched communication networks
– information is transmitted to a sub-set of designated nodes.
Exchange(交换)
– Switching centers(交换中心) – End office (端局) - supports subscribers
Trunks
– Branches between exchanges (交换局之间的干线) – Multiplexed
CircuiБайду номын сангаас Establishment
Switched Communication Network
Broadcast Communication Network
Circuit-Switched Communication Network
Packet-Switched Communication Network
Datagram Network
examples: WANs (Telephony Network, Internet)
– Problem: how to forward information to intended node(s).
this is done by special nodes (e.g., routers, switches) running routing protocols
Circuit Switching - Applications
Inefficient – Channel capacity dedicated for duration of connection – If no data, capacity wasted Set up (connection) takes time Once connected, transfer is transparent (透明的) Developed for voice traffic (phone)
0. A Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information:
Communication Network
Developed for analog environment Separate physical paths (通路之间物理上是隔开的) Crossbar (纵横) switch – Number of crosspoints grows as square of number of stations – Loss of crosspoint prevents connection – Inefficient use of crosspoints
III. WIDE AREA NETWORKS . 10. Circuit Switching and Packet Switching. 11. Asynchronous Transfer Mode. 12. Routing in Switched Networks. 13. Congestion Control in Switched Data Networks. 14. Cellular Wireless Networks. IV. LOCAL AREA NETWORKS. 15. Local Area Network Overview. 16. High-Speed LANs. 17. Wireless LANs. V. COMMUNICATIONS ARCHITECTURE AND PROTOCOLS. 18. Internetwork Protocols. 19. Internetwork Operation. 20. Transport Protocols. 21. Network Security. 22. Distributed Applications.
Two different switching technologies
– Circuit switching – Packet switching
Simple Switched Network
10.2 Circuit Switching
Dedicated communication path between two stations Three phases – Establish (建立) – Transfer (传输数据) – Disconnect(拆除电路) Must have switching capacity (容量) and channel capacity to establish connection Must have intelligence to work out routing
Virtual Circuit Network
Broadcast vs. Switched Communication Networks
• Broadcast communication networks
– information transmitted by any node is received by every other node in the network. examples: usually in LANs (Ethernet,
Blocking or Non-blocking
Blocking(阻塞网络) – A network is unable to connect stations because all paths are in use – A blocking network allows this – Used on voice systems
Data and Computer Communications
（数据与计算机通信）
Dr. Y. XU， 2009
Contents
I. OVERVIEW. 6 0. Introduction. 1. Data Communications and Networking Overview. 2. Protocol Architecture. II. DATA COMMUNICATIONS. 12 3. Data Transmission. 4. Guided and Wireless Transmission. 5. Signal Encoding Techniques. 6. Digital Data Communication Techniques. 7. Data Link Control. 8. Multiplexing. 9. Spread Spectrum.
10.1 Switching Networks
Long distance transmission is typically done over a network of switched nodes Nodes not concerned with content of data End devices are stations – Computer, terminal, phone, etc. A collection of nodes and connections is a communications network Data routed by being switched from node to node
Time Division Switching
Modern digital systems rely on intelligent control of space and time division elements Use digital time division techniques to set up and maintain virtual circuits Partition low speed bit stream into pieces that share higher speed stream(把低速的比特流分割成许多小块,然后与其他比特 流一起共享速率较高的容量) e.g. TDM bus switching(总线交换)
• All stations connected, only a few crosspoints in use
– Non-blocking
Crossbar Matrix的缺点：交叉点的数量已相连站点数量的平方 数上升；一个交叉点损坏，使该交叉点上相交线路所属设 备间无法连接；交叉点的利用率很低
Space Division Switch
Circuit Switch Elements
10.3 Circuit Switching Concepts
Digital Switch (数字交换的功能)
– Provide transparent signal path between devices
Network Interface(数字设备连接到网络上所需要的功能和 硬件) Control Unit