Computer Networks ワラ ハッサン 岡山大学大学院自然科学研究科
Chapter 1: Introduction outlines: • Definition of Computer networks • Uses of Computer Networks • Network Hardware - Local Area Networks - Metropolitan Area Network - Wide Area Network -Wireless Network -Home Networks -Internetworks Computer Networks, Chapter 1 2
1 -Def. Computer networks A System that contains a large number of separate but interconnected computers do a job is said to computer networks (interconnected by a single technology). Two computers are said to be interconnected if they are able to exchange information. Computer Networks, Chapter 1 3
The Difference between a computer network and a distributed system A distributed system is a collection of independent computers appears to its users as a single coherent system. A well known example of a distributed system is the WWW. In a computer network users are exposed to the actual machines, without any attempt by the system to make the machines look and act in coherent way. Computer Networks, Chapter 1 4
Uses of Computer Networks Business Applications Client-Server Model Computer Networks, Chapter 1 5
Home Applications Access to remote information. Person-to-person communication. Interactive entertainments. Electronic commerce. Some of these applications used the client-server model while others used peer-to-peer communication. Or combination between them. Computer Networks, Chapter 1 6
Mobile Users Wireless networks and mobile computing are often related , but they are not identical. A whole different application area for wireless network such as cell phones and PADs that could display stripped down Web pages on their tinier screen. WAP 1. 0 (Wireless Application Protocol), WAP 2. 0 Social issues(? ? ? ) Computer Networks, Chapter 1 7
2 -Network Hardware There is no generally accepted classifications in which all computer networks are fit. , But two dimensions stand out as important: transmission technology and scale There are two widespread types of transmission technology 1 -Broadcast links. 2 -point-to-point links. Computer Networks, Chapter 1 8
1 - Broadcast networks -A single communication channel that is shared by all the machines on the network. -Packets in a certain contexts, sent by any machine are received by all the other. ignore Packet A ignore B ignore Address Broadcasting Multicasting (question) Computer Networks, Chapter 1 9 received
2 -Point-to-point or unicasting Point-to-point networks consisting of many connections between individual pairs of machine. ☆As a general rule, smaller, geographically localized networks tend to use broadcasting, whereas larger networks usually are unicasting. Computer Networks, Chapter 1 10
Scale, physical size Computer Networks, Chapter 1 11
Local Area Networks 1. 2. 3. LANs are privately-owned networks within a single building or campus of up to few kilometers in size. LANs are distinguish from other kind of networks by three characteristics: Their sizes. Their transmission technology. Their topology . Computer Networks, Chapter 1 12
Topology: the shape of the LAN Two broadcast networks (a) Bus (b) Ring Broadcast networks can be divided into static and dynamic. Computer Networks, Chapter 1 13
Static allocation A typical static allocation would be to divide time into discrete intervals and use a round-robin algorithm(Question), allowing each machine to broadcast only when its time slot comes up. Dynamic allocation method for a common channel either centralized or decentralized. -In the centralized channel allocation method, there is a single entity. For example, bus arbitration unite -In the decentralization channel allocation, there is no certain entity. Each machine must decide for itself whether to transmit. Computer Networks, Chapter 1 14
Metropolitan Area Network “MAN” be back in chapter 2 Computer Networks, Chapter 1 15
Wide Area Network “WAN” It contains a collection of hosts connected by a subnet The relation between hosts in LANs and the subnet The subnet consists of two distinct components, The transmission lines and switching elements. Computer Networks, Chapter 1 16
Continue…. WAN (2) Message sent, store-and-forward Computer Networks, Chapter 1 17
Continue…Networks hardware Wireless Networks Wireless networks can be divided into three main categories: 1 - System interconnection 2 - Wireless LANs 3 - Wireless WANs Computer Networks, Chapter 1 18
Continue…. Wireless Networks(2) 1 - System interconnection is all about interconnecting the components of a computer using short-range radio waves or Bluetooth 2 - Wireless LANs, the wireless LANs are systems in which every computer has a radio modem and antenna with which can communicate with other systems IEEE 802. 11 details will be discussed in chap. 4 Computer Networks, Chapter 1 19
Continue…. Wireless Networks(3) 3 - Wireless WANs, the third kind of wireless networks is used in wide area systems (a) Individual mobile computers (b) A flying LAN Computer Networks, Chapter 1 20
Home Networks, 1. 2. 3. 4. 5. 6. Home networking has some fundamentally different properties than the other network types, The network and devices have to be easy to install The network and devices have to foolproof in operation. Low price is essential for success The main applications is likely to involve multimedia, so the network needs sufficient capacity. It must be possible to start out with one or two devices and expand the reach of the network gradually Security and reliability will be very important. Computer Networks, Chapter 1 21
Continue ……Home Networks (2) An interesting question is weather home networks will be wired or wireless. Wireless is cost favors network Wired is security favors network Most of the home networks are related to the need to be easy to manage, dependable, and secure, especially in the hands of non-technical users, while at the same time delivering high performance with low cost, Computer Networks, Chapter 1 22
Internetworks An internetwork or internet, is a collection of interconnected networks. (How? ? ) Different and frequently incompatible networks can be connected , sometimes, by means of a machines is called gateways to make the necessary translation both in terms of hardware and software. Subnet, networks, and internetnetwork !!!! Computer Networks, Chapter 1 23
3 -Network software The following outlines describes the network software structuring technique in some details - Protocol Hierarchies - Design Issues for Layers - Connection oriented and connectionless services -Service Primitives -The relationship of services to protocols Computer Networks, Chapter 1 24
Protocol Hierarchies Most networks are organized as a stack of layers or levels. Each layer is a kind of virtual machine, offering certain services to the layer above it. A protocol is an agreement between the communication parties on how the communication is to proceed Computer Networks, Chapter 1 Layers, protocols, and interfaces 25
Continue……. . Protocol Hierarchies (2) The interface defines which primitive operations and services the lower layer makes available to the upper one. An important consideration in designing network is defining clean interface between layers, Why? ? -minimizing the information -replace implementation Network architecture, is a set of layers and protocols Computer Networks, Chapter 1 26
Continue……. . Protocol Hierarchies (3) A list of protocols used by a certain system, one protocol per layer, is called a protocol stack. Q 1 Q 2: protocol and interface Example information flow supporting virtual communication in layer 5. Computer Networks, Chapter 1 27
Design Issues for the Layers Addressing Rules for data transfer Error control Message order Flow control Long messages and small massages Multiplexing and demultiplexing Routing Computer Networks, Chapter 1 28
Connection-Oriented and Connectionless Services Layers can offer two different types of services to the layer above: Connection. Oriented and Connectionless. Connection-Oriented, it is the service that the layer establish a connection, uses the connection, and then releases the connection. In contrast, Connectionless in this service each message carries the full destination address, and each one is routed through the system independent of all the others. Computer Networks, Chapter 1 29
Continue……Connection-Oriented and Connectionless Services (2) A quality of the service, Some services are reliable in the sense that they never loss data. By using Ack. Reliable connection-oriented service has two minor variations: message sequence and byte stream. The acknowledged datagram service Request-replay-service Computer Networks, Chapter 1 30
Continue……Connection-Oriented and Connectionless Services (3) Six different types of service. Why would anyone actually prefer unreliable communication to reliable one? Computer Networks, Chapter 1 31
Service Primitives A service is specified by a set of primitives (operations) available to a user process to access the service. Five service primitives for implementing a simple connection-oriented service. Computer Networks, Chapter 1 32
Continue……Service Primitives(2) Packets sent in a simple client-server interaction on a connection-oriented network. Computer Networks, Chapter 1 33
The Relationship of Services to Protocols The relationship between a service and a protocol. Computer Networks, Chapter 1 34
Continue…. Computer Networks Chapter 1: Introduction, Section 1. 4: Reference Models -OSI -TCP/IP - OSI vs. TCP/IP - OSI critiques - TCP/IP critiques Computer Networks, Chapter 1 35
4 -Reference Models -OSI -TCP/IP The OSI -Open System Interconnection- Reference Model -A layer should be created where a different abstraction is needed -Each layer should perform a well-defined functions -The function of each layer should be chosen toward defining ISO protocols -The layer boundaries should be chosen to minimize the information across the interface. -The no. of layers should be large enough that distinct functions. Computer Networks, Chapter 1 36
The OSI reference model 6 -syntax and semantics of the information transmitted 5 -establish session between different users 4 -accept the data from above split it pass it to network layer ensure arrived correctly ? 3 -Controls the operation of the subnet 2 -Transform a row transmission facility 1 -Transmitting row bits Computer Networks, Chapter 1 37
The TCP/IP Reference Model The TCP/IP model was used in the grandparent of all computer networks. The major design goals of TCP/IP are: The ability to connect multiple networks together in a seamless way. The ability to survive loss of subnet hardware, with conversations not being broken off. A flexible architecture for supporting applications with divergent requirements, ranging from transferring files to real-time speech transmission Computer Networks, Chapter 1 38
The TCP/IP Reference Model …. . Continue(2) TCP (Transmission Control Protocol): a reliable connection-oriented protocol. UDP (User Datagram Protocol): an unreliable connectionless protocol Its job is to inject IP packets into any network and have them travel independently to the destination The TCP/IP model just points out that the host has to connect to the network using some protocol so it can send IP packets over it. This protocol is not defined and varies from host and network to network Computer Networks, 39 Chapter 1
The TCP/IP Reference Model …. . Continue(3) Protocols and networks in the TCP/IP model initially. Computer Networks, Chapter 1 40
A comparison of the OSI and TCP/IP reference models Fundamental similarities: The same concept of a stack of independent protocols. Similar functionality of the layers. The three central concepts to the OSI model: Services: which tell what the layer does, not how entities above it access it or how the layer works. Interfaces: which tell the processes above it how to access it (i. e. , what the parameters and results are), not how the layer works inside. Protocols: which are used between peer entities to implement the offered services. Computer Networks, Chapter 1 41
A comparison of the OSI and TCP/IP reference models. …. Continue (2) major differences OSI makes the distinction between services, interfaces, and protocol clearly, however the TCP/IP model did not clearly distinguish them. The OSI model was devised before the protocols were invented, but the reserve was true with the TCP/IP model. The OSI model has seven layers, but the TCP/IP model has only four layers. The OSI model supports both connection-oriented and connectionless communication in the network layer, but only connection-oriented communication in the transport layer. Computer Networks, Chapter 1 42
A comparison of the OSI and TCP/IP reference models. …. Continue (3) Computer Networks, Chapter 1 43
A critique of the OSI model and protocols Bad timing. Bad technology. Bad implementation. Bad politics. Bad Timing Computer Networks, Chapter 1 44
A critique of the TCP/IP reference model Service, interface, and protocol not distinguished Not a general model Host-to-network ‘layer’ not really a layer No mention of physical and data link layers Protocols other than the IP and TCP were ad hoc. Computer Networks, Chapter 1 45
A critique of the TCP/IP reference model ……. Continue (2) As a summary The OSI model minus the session and presentation layers) is exceptionally useful for discussing computer networks, but the OSI protocols have not become popular. The TCP/IP model is practically nonexistent, but the protocols are widely used. Computer Networks, Chapter 1 46
Continue…. Computer Networks Chapter 1: Introduction, Section 1. 5 Example Network - Internet -ARPANET -NSFNET Computer Networks, Chapter 1 47
5 -Example Network The ARPANET “Review” It is the creation of ARPA (later DARPA, now ARPA), the (periodically Defense) Advanced Research Projects Agency of the US Dept. of Defense. ARPANET (Datagram subnet ) technologies : -IMP (Interface Message Processor) minicomputers connected by 56 kbps transmission lines. -Protocols (subnet and host protocols) The TCP/IP model and protocols were specifically designed to handle the interconnection of the vast number of WANs and LANs comprising the ARPA internet. Computer Networks, Chapter 1 48
Example Network: The ARPANET …. . continue(2) The original ARPANET design. Computer Networks, Chapter 1 49
Example Network: NSFNET By the late 1970 s, the NSF (National Science Foundation, USA) set up CSNET to provide networking facilities to the computer science community in USA as a whole (particularly those without access to ARPANET). By 1984, NSF began designing a high-speed network, called NSFNET, that would be open to all university research groups. NSFNET consists of a backbone network connecting six supercomputer centers, and about 20 regional networks. Computer Networks, Chapter 1 50
Example Network: NSFNET …. . continue(2) The NSFNET backbone in 1988 Backbone speeds: 56 kbps 448 kbps 1. 5 Mbps 45 Mbps (ANSNET-Advanced Network services) In Dec. 1991, the US Congress passed a bill authorizing NREN (National Research and Educational Network). The goal was a national network running at 3 Gbps before the millennium -- a prototype for the much discussed information supper highway. Computer Networks, Chapter 1 51
Example Network: The Internet After the interconnection of ARPANET and NSFNET (using TCP/IP as the only official protocol), many regional networks in the world joined up. Sometime in the mid-1980 s, people began viewing the collection of networks as an internet, and later as the Internet. By 1990, the Internet consisted of 3000 networks and 200, 000 computers. By 1995, the Internet contained multiple backbones, hundreds of regional networks, tens of thousands of LANs, millions of hosts, and tens of millions of users. The size doubles approximately every year. The glue that holds the Internet together is the TCP/IP model and TCP/IP protocol stack. Computer Networks, Chapter 1 52
Example Network: The Internet. . continue(2) What does it actually mean for a machine to be on the Internet ? It runs the TCP/IP protocol stack, has an IP address, and has the ability to send IP packets to all other machines on the Internet. In Jan. 1992, the Internet Society was set up to promote the use of the Internet. Computer Networks, Chapter 1 53
Example Network: The Internet. . continue(3) Internet Usage Four major traditional Internet applications: Email. News. Remote login. File transfer. By the early 1990, one new application, the WWW (World Wide Web) changed the picture and brought millions of new, non-academic users to the Internet Computer Networks, Chapter 1 54
Architecture of the Internet Overview of the internet Computer Networks, Chapter 1 55
Connection Oriented Networks: X. 25, Frame Relay, and ATM The connection-less (datagram) and connection-oriented idea. Why do the telephone companies like connection-oriented? There are two reasons 1. Quality. 2. Billing Computer Networks, Chapter 1 56
Connection Oriented Networks: X. 25, Frame Relay, and ATM …. . Continue (2) X. 25 networks public network is a subnet owned by the network operator (government or private companies), providing communication service for the customers' hosts and terminals. X. 25 provides a reliable and connectionoriented packet (up to 128 bytes) delivery service, running at speeds up to 64 kbps Computer Networks, Chapter 1 57
X. 25, Frame Relay, and ATM …. Continue (3) Frame relay provides a unreliable connectionoriented (permanent virtual circuit) frame (i. e. , packet of up to 1600 bytes) delivery service, running at a speed 1. 5 Mbps. Computer Networks, Chapter 1 58
Continue…. Computer Networks Chapter 1: Introduction, Section 1. 5 - Connection Oriented Networks ATM -Ethernet -Wireless Network Computer Networks, Chapter 1 59
Connection Oriented Networks: ATM Broadband ISDN and ATM ISDN (Integrated Services Digital Network) is an international undertaking to replace the entire worldwide telephone system and all the specialized networks with a single integrated digital network for all kinds of information transfer services. The new B-ISDN service will offer: video on demand, live TV from many sources, full motion multimedia electronic mail, CD-quality music, LAN interconnection, high-speed data transport, and many other services, all over the telephone line. Computer Networks, Chapter 1 60
Connection Oriented Networks: ATM …. . Continue (2) The underlying technology that makes B-ISDN possible is called ATM (Asynchronous Transfer Mode) because it is not synchronous (tied to a master clock), as most long distance telephone lines are. The basic idea behind ATM is to transmit all information in small, fixed-size packets called cells, Computer Networks, Chapter 1 61
Connection Oriented Networks: ATM …. . Continue (3) ATM Virtual circuits Computer Networks, Chapter 1 62
Connection Oriented Networks: ATM …. . Continue (4) Main reasons for choosing cell switching: It is highly flexible and can handle both constant rate traffic (audio, video) and variable rate traffic (data) easily. At the very high speeds envisioned (gigabits), digital switching of cells is easier than using traditional multiplexing techniques. It can provide broadcasting which is essential for TV distribution and many other applications. ATM networks are connection-oriented. Cell delivery is not guaranteed, but their order is. Computer Networks, Chapter 1 63
Connection Oriented Networks: ATM …. . Continue (5) Intended speeds for ATM networks: 155 Mbps (used by AT&T's SONET for high definition TV), 622 Mbps (for carrying four 155 -Mbps channels), and gigabits speed later. ATM Reference Model Computer Networks, Chapter 1 64
Connection Oriented Networks: ATM …. . Continue (6) The physical layer deals with the physical medium : voltage, bit time, and other various. ATM has been designed to be independent of the transmission medium. The ATM layer deals with cells and cells transport. The ATM adaptation layer (AAL) provides an interface to allow users to send packets larger than cell and then segment these packets, transmits the cells individually, and reassemble them at the other end Computer Networks, Chapter 1 65
Connection Oriented Networks: ATM …. . Continue (7) The ATM layers and sub layers, and their functions Computer Networks, 66 Chapter 1
Example Network: Ethernet Architecture of the original Ethernet Computer Networks, Chapter 1 67
Example Network: Wireless LANs: 802. 11 The range of a single radio may not cover the entire system A multicell 802. 11 network Computer Networks, Chapter 1 68
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