Computer Networks ワラハッサン岡山大学大学院自然科学研究科. Computer Networks, Chapter 1 2 Chapter 1: Introduction outlines: Definition of Computer networks Uses

Computer Networks

　ワラハッサン岡山大学大学院自然科学研究科

Computer Networks, Chapter 1

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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


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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.


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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.


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Uses of Computer Networks

Business Applications Client-Server Model


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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.


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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.

WAP1.0 (Wireless Application Protocol), WAP2.0 Social issues(???)


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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.


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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.

PacketA B

ignore

ignore ignore

ignore

ignore

ignore

received

Address

Broadcasting

Multicasting (question)


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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.


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Scale, physical size


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Local Area Networks

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:

1. Their sizes.

2. Their transmission technology.

3. Their topology .


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Topology: the shape of the LAN

Two broadcast networks (a) Bus (b) Ring Broadcast networks can be divided into static and

dynamic.


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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

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.


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Metropolitan Area Network “MAN”be back in chapter2


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Wide Area Network “WAN”It contains a collection of hosts connected by a subnet

The subnet consists of two distinct components, The transmission lines and switching elements.

The relation between hosts in LANs and the subnet


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Continue…. WAN (2) Message sent, store-and-forward


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Continue…Networks hardware

Wireless Networks Wireless networks can be divided into

three main categories:

1- System interconnection

2- Wireless LANs

3- Wireless WANs


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Continue….Wireless Networks(2)1- System interconnection 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 IEEE802.11

details will be discussed in chap. 4


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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


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Home Networks, Home networking has some fundamentally

different properties than the other network types,1. The network and devices have to be easy to install2. The network and devices have to foolproof in

operation.3. Low price is essential for success4. The main applications is likely to involve

multimedia, so the network needs sufficient capacity.

5. It must be possible to start out with one or two devices and expand the reach of the network gradually

6. Security and reliability will be very important.


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Continue ……Home Networks (2) An interesting question is weather home networks

will be wired or wireless.

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,

Wireless is cost favors network

Wired is security favors network


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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 !!!!


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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


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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 Layers, protocols, and interfaces


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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


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Continue……..Protocol Hierarchies (3) A list of protocols used by a certain system, one

protocol per layer, is called a protocol stack.

Example information flow supporting virtual communication in layer 5.

Q1

Q2: protocol and interface


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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


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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.


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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


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Continue……Connection-Oriented and Connectionless Services (3)

Six different types of service.

Why would anyone actually prefer unreliable communication to reliable one?


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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.


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Continue……Service Primitives(2)

Packets sent in a simple client-server interaction on a connection-oriented network.


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The Relationship of Services to Protocols

The relationship between a service and a protocol.


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Continue…. Computer Networks Chapter 1: Introduction, Section 1.4: Reference Models -OSI -TCP/IP - OSI vs. TCP/IP - OSI critiques - TCP/IP critiques


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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.


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The OSI reference model

1-Transmitting row bits

2-Transform a row transmission facility

3-Controls the operation of the subnet

4-accept the data from above split it pass it to network layer ensure arrived correctly

?

5-establish session between different users

6-syntax and semantics of the information transmitted


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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


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The TCP/IP Reference Model …..Continue(2)

Its job is to inject IP packets into any network and have them travel independently to the destination

TCP (Transmission Control Protocol): a reliable connection-oriented protocol.

UDP (User Datagram Protocol): an unreliable connectionless protocol

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


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The TCP/IP Reference Model …..Continue(3)

Protocols and networks in the TCP/IP model initially.


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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.


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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.


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A comparison of the OSI and TCP/IP reference models . ….Continue (3)


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A critique of the OSI model and protocols Bad timing. Bad technology. Bad implementation. Bad politics.

Bad Timing


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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.


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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.


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Chapter 1: Introduction,

Section 1.5

Example Network

- Internet

-ARPANET

-NSFNET

Continue…. Computer Networks


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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 56kbps 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.


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Example Network: The ARPANET ….. continue(2)

The original ARPANET design.


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Example Network: NSFNET

By the late 1970s, 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.


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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.


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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-1980s, 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.


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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.


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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


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Architecture of the Internet

Overview of the internet


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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


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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 connection-oriented packet (up to 128 bytes) delivery service, running at speeds up to 64 kbps


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X.25, Frame Relay, and ATM …. Continue (3) Frame relay

Frame relay provides a unreliable connection-oriented (permanent virtual circuit) frame (i.e., packet of up to 1600 bytes) delivery service, running at a speed 1.5 Mbps.


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Continue…. Computer Networks Chapter 1: Introduction,

Section 1.5

- Connection Oriented Networks

ATM

-Ethernet

-Wireless Network


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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.


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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,


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ATM Virtual circuits


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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.


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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


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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


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The ATM layers and sub layers, and their functions


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Example Network: Ethernet

Architecture of the original Ethernet


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Example Network: Wireless LANs: 802.11

The range of a single radio may not cover the entire system

A multicell 802.11 network

Documents

Computer Networks ワラ ハッサン 岡山大学大学院自然科学研究科. Computer Networks, Chapter 1 2 Chapter 1: Introduction outlines: Definition of Computer networks Uses

Computer Networks ワラハッサン岡山大学大学院自然科学研究科. Computer Networks, Chapter 1 2 Chapter 1: Introduction outlines: Definition of Computer networks Uses