communication network: definition

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  • 1. TTM4100: Communication Services and Networks Kommunikasjon Tjenester og Nett (KTN) Overview: Evolution of Communication Networks Yuming Jiang 2007 1 Communication Network: Definition A communication network is a set of devices (often referred to as nodes) connected by communication links. It provides a service: the transfer of information between users located at various geographical points. 2
  • 2. Evolution of Communication Networks Telegraph Networks and Message Switching Telephone Networks and Circuit Switching Computer Networks, the Internet and Packet Switching 3 Driving Forces Services (or user expectations / demands) Technological innovations 4
  • 3. Switching 5 Model We focus on how the information to be sent between the Hosts or users is handled by the network of Nodes. 6
  • 4. Switching is the way the link transmission capacity and Node resources (e.g. CPU, buffers, internal switching resources*) are allocated for the transfer of information. (* A Node can internally have a complicated switching network structure.) 7 Telegraph Networks Starting time: 1850s Driving service: Telegram service The transmission of text messages over long distances. Techniques Digital transmission, in which system transmission takes place in binary signals: Morse code; short and long pulses of electrical current over a copper wire, e.g. A: . Message switching 8
  • 5. Message Switching When a message or telegram arrives at a telegraph station, the operator makes a routing decision based on the destination address of the message. The operator stores the message until the desired communication line becomes available. Then, the operator will forward the message to the next appropriate station through the available communication link. 9 Message Switching (cont) Timing of events Store-and-forward Each message has its destination address information. Time A B C D 10 Tanenbaum Fig. 2-39(b)
  • 6. Telephone Networks Starting time: 1870s Driving service: Telephone service The transmission of voice signals over long distances. Techniques Analog transmission (originally): The transmitted electrical signal is analogous to the original voice signal. Circuit switching 11 Structure of the Telephone System Tanenbaum Fig. 2-21 A typical circuit route for a medium-distance call. Major components Local loops: Analog twisted pairs going to houses and businesses Trunks: Digital fiber optics connecting the switching offices Switching offices: Where calls are moved from one trunk to another 12
  • 7. Circuit Switching Tanenbaum Fig. 2-38(a) 13 Circuit Switching (cont) Timing of events Circuit switching: when a phone call is made, the telephone system seeks out a physical path between the callers phone and receivers phone. Exclusively reserved transmission link/channel capacity. A B C D 14 Tanenbaum Fig. 2-39(a)
  • 8. Computer Networks Starting time: 1950s Driving service: Datagram service The transmission of data information between computers, across possibly multiple dissimilar networks. Techniques Digital transmission Packet switching (store-and-forward) 15 Packet Switching based on Datagram Tanenbaum Fig. 1-10 16
  • 9. Packet Switching (cont) Tanenbaum Fig. 2-38(b) 17 Packet Switching (cont) Timing of events Store-and-forward Each packet has a header providing an address to identify the destination. Packets are of different sizes. Similar to Message Switching if each packet were treated as a message. A B C D 18 Tanenbaum Fig. 2-39(c)
  • 10. Packet Switching v.s. Circuit Switching Tanenbaum Fig. 2-40 A comparison of circuit-switched and (datagram-based) packet-switched 19 networks. ATM Networks and Cell Switching Starting time: 1990s Driving service: Virtual circuit service The transmission of data information between network hosts/notes through virtual circuits. Techniques Digital transmission Cell switching (store-and-forward) Virtual circuit 20
  • 11. ATM Virtual Circuits ATM = Asynchronous Transmission Mode Asynchronous here means that there is no other periodic time structure for the use of the transmission channels except for the repetition of the time slots for the individual cells. A virtual circuit is established btw the sender & receiver. 21 Tanenbaum Fig. 1-30 Cell Switching Cell 1 Timing of events Cell 2 Store-and-forward Cell 1 Cell 3 Each cell has a header Cell 2 providing information to Cell 1 Cell 3 identify the Virtual Circuit. Cell 2 Similar to Message and Cell 3 Packet Switching. Cells have fixed size. A B C D 22
  • 12. Comparison of Switching Techniques Tanenbaum Fig. 2-40 ++ 23 The Internet An internetwork of computer networks Starting time: 1950s Popular: 1990s Driving service: WWW (World Wide Web) Techniques: same as computer networks 24
  • 13. Future (Multimedia) Networks Time: research already started (1990s) Driving service: Multimedia service Real-time transfer of multimedia information between users with high quality of service. Techniques: Integrated Services [IETF RFC1633] Differentiated Services [IETF RFC2475] 25 Evolution of Networks and Services Networks /