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Communication Network: Definition


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Communication Network: Definition

  1. 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. 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. 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. 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. 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. 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. 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 caller’s phone and receiver’s phone. • Exclusively reserved transmission link/channel capacity. A B C D 14 Tanenbaum Fig. 2-39(a)
  8. 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. 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. 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. 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. 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. 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 / services Multimedia Internet multimedia Internet ATM Computer Net WWW virtual circuit E-mail datagram Telecom Net Telegraph Net telephone telegram 1830 1850 1900 1950 2000 time 26
  14. 14. Information Transfer Time • Transfer Time = Flying (or Propagation) Time + Transmission Time • T = L/C + D/V – T (sec): Total transfer time that is the tme the first bit leaves A to the last bit arrives at B. – L (bits): Length of information; C (bits/sec): Transmission capacity btw A and B – D (m): Distance btw A and B; V (m/sec): Wave velocity in the transmission medium 27 Evolution of Transmission Rates Transmission rate (bps) 1.0E+14 1.0E+12 DWDM 1.0E+10 SONET OC-48 1.0E+08 T4: 274.176 Mbps 1.0E+06 T1: 1.544 Mbps 1.0E+04 1.0E+02 telephone telegraph 1.0E+00 1830 1850 1900 1950 2000 time 28
  15. 15. Reading • Andrew S. Tanenbaum, Computer Networks (4th ed.), Pearson Education, 2003. Ch.1.1, Ch.1.5, Ch. 2.5. • Alberto Leon-Garcia and Indra Widjaja, Communication Networks – Fundamental Concepts and Key Architectures (2nd ed.), McGraw-Hill, 2004. Ch.1.1-1.2. 29
  16. 16. TTM4100: Communication – Services and Networks Kommunikasjon – Tjenester og Nett (KTN) Overview: Network Use, Hardware & Software Yuming Jiang & Finn Arve Aagesen 2007 1 Uses of Communication Networks • Communication networks have a lot of applications and uses. • In general, communication networks are used for information sharing and retrieval. 2
  17. 17. Retrieval and Sharing: Client-Server • Server is the information provider who shares the information. • Client is the information user who retrieves the information. • In this figure, Client and Server is related to the physical hardware arrangement. • Any kind of service can be used between the users. 3 Tanenbaum Fig 1-1 Client-Server (cont’) • In this figure Client and Server is related to both the physical hardware arrangement and the software structure and operation. Retrieval involves requests and replies. • Any kind of service can still be used. But the realization must be implemented within this client server architecture. Tanenbaum Fig 1-2 4
  18. 18. Retrieval and Sharing: Peer-to-Peer • Retrieval is not necessarily associated with the client-server structure. • In a peer-to-peer system there are no fixed clients and servers. Each peer shares information to and retrieves information from other peers. • Conceptually, peer-to-peer can be related to the software structure. In this case, the peers may not be related to the hardware structure. 5 Tanenbaum Fig 1-3. Direction of Information Flow • Communication between two devices can be: – Simplex: The communication is unidirectional. – Half Duplex: Either device can both transmit and receive, but not the same time. When one is sending, the other can only receive. – Full Duplex: Both devices can transmit and receive simultaneously. Simplex Half Duplex Full Duplex 6
  19. 19. Network Hardware • Network classification • Physical network topologies • Internetworks and the Internet 7 Network Classification • Networks can be classified along many dimensions based on different classification criteria: – Owners, e.g. Home Networks; Enterprise Networks – Switching techniques – Transmission media – Mobility support – Transmission technology types – Scales 8
  20. 20. Network Classification (cont’) • Based on switching techniques: – Circuit-Switched Networks – Packet-Switched Networks, etc. • Based on transmission media – Wired Networks – Wireless Networks • Based on mobility support – Fixed Networks – Mobile Networks 9 Example: Wireless Networks • (a) Bluetooth configuration • (b) Wireless local area network (LAN) 10 Tanenbaum Fig. 1-11
  21. 21. Note: Wireless and Mobile are Different Concepts! Wireless Mobile access terminal Tanenbaum Fig 1-5. Notice the difference between wireless access, terminal mobility and personal mobility. Personal mobility is person 11 mobility independent of terminal. Network Classification (cont’) • Based on transmission technology types • Link classification – Point-to-point link: A dedicated link between two Link devices. – Broadcast (also called multipoint) link: A link shared by more than two devices. Link • Network classification – Broadcast network: one to all – Multicast network: one to many – Point-to-point (also called unicast) network: one to one 12
  22. 22. Example • Cable TV is a fixed broadcast network. 13 Tanenbaum Fig. 1-8 Network Classification (cont’) • Based on scale – PAN: Personal Area Network – LAN: Local Area Network – MAN: Metropolitan Area Network – WAN: Wide Area Network – The Internet 14
  23. 23. PAN, LAN, MAN,WAN and Internet 15 Tanenbaum Fig. 1-6 Example: A MAN based on Cable TV Tanenbaum Fig. 1-8 16
  24. 24. (Physical) Network Topologies • Mesh Topologies – Full mesh topology: Every device has a dedicated point-to-point link to every other device. – Partial mesh topology: Some devices are connected to all the others, while some are connected to only part of the other devices. • Star Topology – Each device has a dedicated point-to-point link only to a central device, usually called hub. • Bus Topology – Devices are connected through a broadcast link called bus. • Ring Topology – Each device has a dedicated point-to-point connection only with the two devices on either side of it. • Hybrid 17 (Physical) Network Topologies: Illustration Full Mesh Star Ring Bus 18
  25. 25. Physical vs. Logical Topology • Physical topology: The actual layout of a network and its transmission media. • Logical topology: The way in which the data access the network medium and pass through the network from one device to the next. • A network’s logical topology is not necessarily the same as its physical topology. Twisted Pair Ethernet Physical topology: Star (/Mesh?) Logical topology: Bus 19 Example: Cable TV Based MAN • Physical: Hybrid (star + bus) • Logical: Bus (typically) 20 Tanenbaum Fig. 1-8
  26. 26. Internetworks • An internetwork or internet is a collection of interconnected networks. • A gateway is a device to make the connection and provide the necessary translation, both in hardware and software, between different types of (and often incompatible) networks. Gateway 21 Internetworks (cont’) • A communication subnet is the part of network excluding hosts. • The subnet consists of transmission links and switching elements (commonly called routers). 22 Tanenbaum Fig. 1-9
  27. 27. Communication Subnet and Routing • In a packet-switched subnet, each router uses a routing algorithm to decide to which link a packet should be forwarded. 23 Tanenbaum Fig. 1-10 The Internet The Internet is an internetwork (internet). It is the worldwide internet. 24
  28. 28. Network Software Operating Hardware System and Screen Structure Procedure Operating- Applications Operating- system- Library Model system- 5 Process Operating- Operating-Process 4 system- Operating- system- Process 3 Layer 7 system- Process 2 Process 1 Layer 6 Board Memory Layer 5 Layer 4 Layer 3 -Driver Driver 1 Driver i Layer 2 Board Board CPU Layer 1 Modem Modem Software Layered Structure Functional Communication Channels Model 25 Structure Model Network Software • Protocol Hierarchies • Design Issues for the Layers • The Relationship of Services to Protocols • Connection-Oriented and Connectionless Services • Service Primitives 26
  29. 29. Protocol Hierarchies • The philosopher-translator-secretary architecture. Location A Location B I like J'aime Message Philosopher rabbits bien les lapins 3 3 Information L:Norsk L: Dutch for the remote Translator L:L:Norsk Dutch Ik vind translator Ik vind Jeg konijnen Jeg konijnen 2 2 liker leuk leukliker kaniner kaniner Fax:# Information Fax #--- Fax:# Fax #--- for the remote L: Dutch L:Norsk secretary L: Dutch Secretary L:Norsk Ik vind Ik vind 1 1 Jeg konijnen Jeg konijnen liker leuk leukliker kaniner kaniner 27 Protocol Hierarchies Tanenbaum Fig. 1-13: Layers, Protocols and Interfaces 28
  30. 30. Important Concepts • Protocol architecture: A set of layers and protocols. – Note: The Tanenbaum book uses the concept of network architecture instead of protocol architecture. • Layer: A subsystem of a certain rank offering certain services to the layer above it. • Interface: It is between each pair of adjacent layers and defines services the lower layer provides to the upper layer. • Protocol: Set of rules and formats (syntax and semantics) that determine the behavior between peer entities. – Entity: An active unit within a layer. It handles a protocol type within a specific device (Host or Node). – Peer entities: Entities of same layer with a common protocol in different devices. 29 Example: Entities in Various Layers 30
  31. 31. Layer N offers Services to Layer N+1 (N+1)-SAP The (N+1)-service transfers (N+1)-SDUs The (N+1) Protocol transfers (N+1)-PDUs (N+1)- (N+1)-entity layer: (N)-SAP The (N)-service transfers (N)-SDUs (N)-layer: (N)-entity The (N) Protocol transfers (N)-PDUs (N)-header (N)-SDU” SAP=Service Access Point, PDU=Protocol Data Unit, 31 SDU=Service Data Unit, SDU’’ = The whole, split or concatenated SDU Relationship between Protocol & Service • The protocol comprises both syntax and semantics for PDUs that are exchanged between peer-entities. • The service defines what a layer offers externally to the layer above. • The entity behavior implements the service by using the protocol of this layer and the service from the lower layer. 32 Tanenbaum Fig. 1-19
  32. 32. Message, Headers and Trailers • Example information flow supporting virtual communication in layer 5 33 Tanenbaum Fig. 1-15 Design Issues for the Layers • Addressing • Error Control • Data Unit Length Control • Control of Data Exchanging (simplex, half duplex, full duplex) • Flow Control • Multiplexing • Routing 34
  33. 33. Connection-Oriented (CO) Service & Protocol • CO:. (N+1)-layer has a connection establishment session with the (N)-layer before the data transfer. – Analogous to the classical telephone system • Circuit switched networks, and virtual circuit based packet-switched and cell-switched networks are of CO nature. 35 Tanenbaum Fig. 1-30 Connectionless (CL) Service & Protocol • CL: (N+1)-layer delivers the data to be transferred as one unit with an address. – Analogous to the postal system • Message-switched networks and datagram based packet- switched networks are of CL nature. 36 Tanenbaum Fig. 1-10
  34. 34. Connection-Oriented and Connectionless Services and Protocols Within an applied protocol architecture, some layers can be connection-oriented and some others can be connectionless. 37 Analogy between the connectionless Internet IP protocol and the postal system • The Internet consists of different network types. • A common protocol is needed that makes it easy “to convert between” the protocols of the various networks types. Internet Protocol (IP) is such a common protocol. Network of Host Gateway Type P Network of Type Q Network of Host Gateway Type R 38
  35. 35. The information Message is sent in an IP envelope understood by Hosts as and Gateways. This envelope is put in an additional new envelope every time there is a new network to cross. Q addr. Network of IP addr. Host Type P Gateway Mess age P addr. P addr. IP addr. IP addr. Network of Mess Mess Type Q age age R addr. Q addr. R addr. IP addr. IP addr. IP addr. Mess Mess Mess age age age Network of Gateway Host 39 Type R The transport service is an end-to-end service and is found only in the Hosts. The transport protocol is only end-to-end. 40 TLE = Transport Protocol Entity
  36. 36. Examples: Connection-Oriented and Connectionless End-to-End Services Tanenbaum Fig. 1-16. 41 Service Primitives (/Operations) • There is a need to define a service. • The service is described by the use of service primitives (also called operations). • Both the (N+1)-service and the (N)-service are used to describe the (N+1)-layer behavior. Ch.1.3.4 presents a simplified version of the TCP service primitives to be more detaily handled in Ch.6. A more general handling of ISO OSI/RM Service and Protocol 42 Conventions will also be given later.
  37. 37. The description of the (N+1)-layer behavior comprises the (N+1)-service, the (N)-service and the (N+1)-protocol. (N+1)-SAP The (N+1)-service transfers (N+1)-SDUs The (N+1) Protocol (N+1)-Layer: transfers (N+1)-PDUs (N+1)-entity (N)-SAP The (N)-service transfers (N)-SDUs (N)-Layer: The (N) Protocol (N)-entity transfers (N)-PDUs 43 (N)-header (N)-SDU” Example: Service Primitives for Implementing a CO Service • Five service primitives for implementing a simple connection- oriented service. • This is simplified version for TCP and will be introduced in more detail in Ch. 6. 44 Tanenbaum Fig. 1-17
  38. 38. TCP Socket Service Based on Procedure Calls I will wait I will wait Connection-number = LISTEN( ) Connection-number = CONNECT( ) status = SEND( ) status = RECEIVE( ) status = DISCONNECT( ) 45 The TCP Protocol Operation Signals *) The Transport Illustration of the The Transport Layer Service the Transport Layer Layer Service Primitives Protocol Behavior Primitives Tanenbaum Fig. 1-17 + *) A Signal (message) does not lock the sender as a Procedure Call 46 does.
  39. 39. Service Primitives in Client & Server The TCP Client TCP PDUs The TCP Server Service Primitives: Service Primitives: Connect, Send, Listen, Receive, Receive, Disconnect Send The TCP Service is based on a procedure call interface while the TCP 47 Protocol is based on a message exchange interface. Reading • Andrew S. Tanenbaum, Computer Networks (4th ed.), Pearson Education, 2003. Ch.1.1 - Ch.1.3. • Behrouz A. Forouzan, Data Communications and Networking (3rd ed.), McGraw-Hill, 2003. Ch.1.1, Ch.1.2. 48
  40. 40. TTM4100: Communication – Services and Networks Kommunikasjon – Tjenester og Nett (KTN) Some Practical Information - Reminder Yuming Jiang 2007 1 Course Times • Lectures – Tuesday 14:15 - 15:00 (R1) – Wednesday 10:15 - 12:00 (F1) • Tuition – Tuesday 15:15 – 17:00 (R1) – Friday 14:15 - 16:00 (R1) • Projects – Week 9 (Monday) – Week 10 (Friday) – Week 15 (Wednesday) – Week 18 (Wednesday) • Exam: – Friday, 18 May 2006. Clock: 0900-1300 – For the exam, both English and Norwegian (bokmål) versions will be provided. If one prefers Ny Norsk for the exam, he or she must let me know BEFORE 1st April 2007. • For detail, see Lecture Schedule at the course home page. 2
  41. 41. Syllabus • Mainly based on textbook: – Andrew S. Tanenbaum, “Computer Networks”, 4th edition, Pearson Education, 2003. – Chapter 1 – Chapter 7 • Details are available from the course home page. • Note: Some subsections included in the syllabus may not be introduced in the lectures. They are for self-reading and also are part of the syllabus. 3 Deadlines & Languages for Submitting Assignments Project Reports • Handing in assignments or project reports will be through NTNU It’s Learning system. Both Norwegian and English are acceptable. • Deadlines are HARD. 4
  42. 42. Course Home Page • • Check the home page regularly • Questions/feedbacks: send email to – 5 Reference Group • Need 2 students from each study fields (Data, IndØk, KomTek, Kyb, etc.). • 2 to 3 meetings during the semester with course staff • A forum for providing feedbacks about the course • If you are interested, report to me or send email to: 6