Network classification and Protocols

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Network Classification

Definition of a communication Network:

– An interconnected system of computers, terminals, and other hardware established for the purpose of exchanging information or services.

– Node: a point of connection into a network

Networks can be classified by their geography, topology,etc…

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Networks by Geography

Local Area Networks (LANs)

LAN are limited to a premises of organization,generally used for data sharing in that organization.

Metropolitan Networks (MANs)

– Typically connect several LANs in locations scattered around a city.

– Term: dark fiber

Wide Area Networks (WANs)

– May be made up of a combination of switched and leased, terrestrial and satellite, and private microwave circuit

• Almost any circuit speed can be found in WANs

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Networks Topology

Network topology: the configuration of a communication

network

– Star

– Hierarchical

– Mesh

– Bus

– Ring

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Star Networks

Computers connected by cable segments to a central node.

Pros & Cons:

– The central node contacts every other location easy to manage and control the network

– Easy to expand a star network

– Single point for failure

Star topology is very common before.

– Is not used in computer network nowadays.

– still common in another type of network.

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Mesh Networks

The most fault tolerant and the most expensive topology.

n (n -1) / 2 cable segments for a mesh topology with n computers.

Mesh topology is usually used in WANs

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Bus Networks

A bus is a communication medium to which multiple nodes are attached.

Bus networks are usually implemented in situation where the distance between all nodes is limited.

Why?

– Signal loss on tap connection

– There is another reason …

All nodes are independent of one another

– Bus networks are reliable unless the bus is fail

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Signal Propagation

In any network, computers communicate by sending information across the media as a series of signals

– In a bus network, the signals travel along the length of the bus in both directions

– The signals continue to travel until …

• they weaken enough so as no to be detectable

• OR until they encounter a device that absorbs them

This traveling across the medium is called signal propagation

– At the end of a cable, the signal bounces back

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Signal Bounce

Is there any problem with signal bouncing?

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Cable Termination

A terminator attached to each end of a cable prevents signals from bouncing. Clearing the network for new communications.

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Ring Networks

Each computer connects directly to the next computer in a line;

– A circle of cable forms a ring;

– Every computer in a ring is responsible for regenerating the signal

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How do ring networks work

Data in a ring network travels from one computer

to the next computer until the data reaches its destination

Token passing is one method for sending data around a ring

Token is a small packet, passes around the ring to each computer in turn.

– If a computer (sender) has packets to send, it modifies the token, adds address and data, and sends it around the ring.

– The receiver returns an acknowledge packet to the sender.

– Upon receiving the acknowledge packet, the sender releases the tokens and sends it around the ring.

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Hybrid networks

Networks are generally hybrid networks

– Almost all networks are combination of the geographies, topologies, and technologies.

– E.g., hybrid topology, carry both voice and data traffic

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OSI Model Overview

The Open Systems Interconnection (OSI) reference model is an industry standard framework that is used to divide the functions of networking into seven distinct layers.

Each layer provides specific services to the layers above and below it in order for the network to work effectively.

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OSI Model Overview

A message begins at the top application layer and moves down the OSI layers to the bottom physical layer.

As the message descends, each successive OSI model layer adds a header to it.

A header is layer-specific information that basically explains what functions the layer carried out.

Conversely, at the receiving end, headers are striped from the message as it travels up the corresponding layers.

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What is a Protocol?Protocol – in general ……

- an acceptable way of behaving.

- driving on the left hand side of the roadProtocols are critical and there must be agreement on them.

A network protocol Is the set of very detailed rules, sequences, message formats, and procedures that computer systems use and understand when exchanging data with each other

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Transmission Control Protocol/Internet Protocol

The Transmission Control Protocol/Internet Protocol (TCP/IP) suite of protocols has become the dominant standard for inter-networking.

TCP/IP represents a set of public standards that specify how packets of information are exchanged between computers over one or more networks. 

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Transmission Control Protocol/Internet Protocol

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Transmission Control Protocol/Internet Protocol (TCP/IP)

It is a group of protocols that allows networked computers to communicate with each other

It doesn't matter whether:

• they are part of the same network or are attached to separate networks.

• one computer is a mainframe and the other a Macintosh.

TCP/IP is a platform-independent standard that bridges the gap between dissimilar computers, operating systems, and networks

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So TCP/IP allows two computers to exchange data. This is achieved as follows:

– When two or more networks are involved they are physically connected by devices called IP routers. A router is a computer that transfers packets of data from one network to another.

– TCP/IP software makes everything seem like one big network. That is, TCP/IP has the affect of allowing two separate networks to communicate as though they were part of the same physical network.

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What is the family of TCP/IP protocols?

Some of the common TCP/IP application protocols include :

File Transfer Protocol (FTP),

Telnet,

Domain Name System (DNS),

Simple Mail Transfer Protocol (SMTP),

Multipurpose Internet Mail Extensions (MIME),

X Window System,

Dynamic Host Configuration Protocol (DHCP).

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SO HOW DOES TCP/IP WORK?

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Firstly the Internet Protocol (IP)

Allows for data to be sent over the Internet occurs in packets contains from 1 - 1500 bytes of data

each packet is given a destination IP address:

• An IP address is an unique identifier for a particular computer on the Internet

• The addresses include four eight-bit octets, which are often written in decimal format for simplicity. To illustrate this, it is easy to see that the following address 10000111.10100101.00100011.11110000 is more easily written and understood as 135.165.35.240

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More on IP

It is a connectionless protocol meaning that all packets are sent on a "best effort" basis.

There is no guarantee that the packets will get to the destination in the order they that were sent, or even at all.

Therefore the problems are ……

packets may get lost

packets may arrive out of sequence

the message may be longer than 1500 bytes

Answer ……….

Another protocol ….

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The second protocol: Transmission Control Protocol (TCP)

ensures a sent message is sent without any loss of data or any mix up of the order of the data

will request re-transmission of lost or damaged packets.

How does it do this?

a long message is broken up into many IP packets

each packet have a number allocated to it

there is error checking

damaged or missed packets may be asked for again

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What is File Transfer Protocol (FTP)???

protocol that allows for the transfer of files across the Internet.

both computers need to run FTP - one acts as a server (remote), the other as a client (local).

mainly shareware type of files.

usually stored in ZIP format or self-extracting EXE

disadvantage must know the name of the file you are after

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Steps to FTP:

1. log on to machine e.g. to csusap

2. Connect to a another remote machine by either:

a. anonymous FTP - very common - but can only access files in the pub directory.

login name anonymouspassword <your email address>e.g

maddy9293@yahoo.in

Anonymous FTP allows users to enter public data archives and download file

b. log in as yourself - this requires you to have an account on that machine i.e. username and password.

This is what you do on CSUSAPTypically these machines are UNIX boxes

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Pictorial explanation of FTP

ComputerA

file1.txt

Computer B

file2.txt

Both Computer A and Computer B have FTP running

Computer B hasestablished an FTPsession with Computer A and issues the get and put statement

get file1.txt

put file2.txt

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Other Web based protocols - HTTP

'HyperText Transfer Protocol' is the primary protocol of the World Wide Web (WWW).

When a Web browser connects to a Web server, it uses HTTP to request Web pagesA Web browser is an Internet client application, and the Web server is an Internet server application.

HTTP has the ability to transfer Web pages, graphics, and any other type of media that is used on the Web.It is a means to format of Web pages

It consists of a set of tags and internal commands that are embedded inside Web pages to control the appearance and layout of Web pages, as well as links to other Web pages

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۩Infrastructure servicesDomain Name Services (DNS)

۩Multimedia applications

some of the popular applications in the Internet

۩Electronic mail, World Wide Web

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Traditional Applications

Two of the most popular—

– The World Wide Web and

– Email.

Broadly speaking, both of these applications use the request/reply paradigm

—users send requests to servers, which then respond accordingly.

It is important to distinguish between application programs and application protocols.

For example, the HyperText Transport Protocol (HTTP) is an application protocol that is used to retrieve Web pages from remote servers.

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There can be many different Web clients that provide users with a different look and feel, but all of them use the same HTTP protocol to communicate with Web servers over the Internet

TWO VERY WIDELY-USED, STANDARDIZED APPLICATION PROTOCOLS:

SMTP: Simple Mail Transfer Protocol is used to exchange electronic mail.HTTP: HyperText Transport Protocol is used to communicate between Web browsers and Web servers.

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Electronic Mail

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World Wide Web

– Request Messages

HTTP request operations

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World Wide Web

– Response Messages

Five types of HTTP result codes

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– Uniform Resource Identifiers

• The URLs that HTTP uses as addresses are one type of Uniform Resource Identifier (URI).

• A URI is a character string that identifies a resource, where a resource can be anything that has identity, such as a document, an image, or a service.

• The first part of a URI is a scheme that names a particular way of identifying a certain kind of resource, such as mailto for email addresses or file for file names.

•

• The second part of a URI, separated from the first part by a colon, is the scheme-specific part.

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World Wide Web

– TCP Connections

HTTP 1.0 behavior

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World Wide Web

– TCP Connections

HTTP 1.1 behavior with persistent connections

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World Wide Web

– Caching

• Caching has many benefits. From the client’s perspective, a page that can be retrieved from a nearby cache can be displayed much more quickly than if it has to be fetched from across the world.

• From the server’s perspective, having a cache intercept and satisfy a request reduces the load on the server.

• Caching can be implemented in many different places..

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• For example, a user’s browser can cache recently accessed pages, and simply display the cached copy if the user visits the same page again

• As another example, a site can support a single site-wide cache.This allows users to take advantage of pages previously downloaded by other users.

• Closer to the middle of the Internet, ISPs can cache pages.

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• Note that in the second case, the users within the site most likely know what machine is caching pages on behalf of the site, and they configure their browsers to connect directly to the caching host. This node is sometimes called a proxy

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Infrastructure Services

Domain Hierarchy

Example of a domain hierarchy

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Name Resolution

Name resolution in practice, where the numbers 1–10 show the sequence of steps in the process.

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Web Services

– The SOAP architecture’s approach to the problem is to make it feasible, at least in theory, to generate protocols that are customized to each network application.

– The key elements of the approach are a framework for protocol specification, software toolkits for automatically generating protocol implementations from the specifications, and modular partial specifications that can be reused across protocols.

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Custom Application Protocols (WSDL, SOAP)

The architecture informally referred to as SOAP is based on Web Services Description Language (WSDL) and SOAP.4

Both of these standards are issued by the World Wide Web Consortium (W3C). This is the architecture that people usually mean when they use the term Web Services without any preceding qualifier.

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