Networking and Internet

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Networking and Internet

National Chiao Tung University

Chun-Jen Tsai

3/30/2012

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A Networked World

The world is connected by heterogeneous networks:

TV station

Feeder link

mobile

base station mobile

base station

WAN (the Internet, or “cloud”)

MAN (wired or wireless)

mobile base station

MAN

LAN

Downlin

k broad cast

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Service Network Classifications

Broadcasting Networks (TV Networks)

Satellite Networks

Terrestrial Networks

Cable Networks

Communication Networks

Public Switched Telephone Networks (PSTN)

Mobile Networks (2G, 3G)

Computer Networks (using Internet Protocol)

Ethernet

Integrated Service Digital Network (ISDN)

Asymmetric Digital Subscriber Line (ADSL)

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Network Geographic Classifications

Local area network (LAN)

Small scale, usually within a diameter of a few kilometers (e.g., a company, lab, or school)

High speed (> 100 mega bits-per-second)

Complete ownership by a single organization

Metropolitan Area Network (MAN)

Medium scale, say, within a city

“Broadband” speed (around 1~10 mbps)

Examples: ADSL or Cable Modem

Wide area network (WAN)

Large scale, may cover entire country or across countries

Usually low speed (< 1 mbps)

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Network Topologies

Ring:

Bus:

computer

computer computer

computer

computer computer computer

computer computer

Star:

computer computer

The star configuration is popular today since wireless networks use this configuration; the central computer is called access point (AP) or base station (BS)

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Communication over a Network

The topology of a network determines its communication protocols

A network protocol is a set of rules for computers in a

network to perform data exchange

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Token Ring Protocol ^†

Developed by IBM in 1970

The computer that receives the “token” message can become the originating computer of a data message

Data messages are transmitted in one direction

Each computer on the ring topology forwards the message to the next one

Only the destination machine keeps a copy of the data message before it forward the message

The originating computer of the message will not forward it again when it received the message

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Ethernet Protocol for Bus Network

Ethernet protocol uses the rule called “Carrier Sense, Multiple Access with Collision Detection (CSMA/CD)”

Each computer on the network has an address ID

Any messages are broadcasted to all computers on the network

A computer only keeps the message addressed to it

If more than one computers try to send messages at the same time, they will all detect the “collision” and stop sending messages

They will try again later, after a random period of waiting

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Wireless Protocol

Wireless network uses Carrier Sense, Multiple

Access with Collision Avoidance (CSMA/CA) protocol

A “newcomer” must wait until it does not “hear” any messages before it can request to use the channel

To avoid the “hidden terminal problem,” the newcomer must wait for the AP to grant its request before it sends messages

AP

Invisible to other mobile terminals

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Combining Networks (1/2)

To connect two or more smaller networks to form a big network, we need some special devices

Repeater – a device that passes signals between two networks back-and-forth

Bridge – a device similar to a repeater, but it only performs

“meaningful” message-forwarding

Switch – a bridge with multiple connections

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Combining Networks (2/2)

A router is a device (maybe a computer) that

connects two (possibly heterogeneous) networks together

The two networks may be using different protocols and address IDs

computer computer

computer

computer computer

Router

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Interprocess Communication Model

Client-server model

One server, many clients

Server must execute continuously

Client initiates communication

Example: print server, file server

Peer-to-peer model

Two hosts communicating as equals

Peer hosts can be short-lived

Peer-to-peer network is a misuse of the terminology

requests services

server

client

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Client/Server Model vs. P2P Model

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Distributed Systems

A distributed system is a system with software units that run on different computers across the network

Each software unit is a process running on a host (i.e. a computer on the network)

Distributed processes usually have to perform data exchange, remote invocation, synchronization, etc.

Various distributed computing models

Cluster computing – tightly-coupled, supercomputer style

Grid computing – loosely-coupled, SETI@HOME style

Cloud computing – hyping-based, scammer style

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The Internet

The Internet: one internet spanning the world

Started by DARPA in 1970’s

Today involves millions of machines

The Internet is a packet-switched network. That is, all the data are transmitted on a packet-by-packet basis

Another type of network is called circuit-switched, which means a virtual connection will be established before the transmission of data

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Internet Architecture

The Internet is a collection of domains

Each domain is a network or a set of inter-connected networks controlled by a single organization

Domains must be registered through ICANN, Internet Corporation for Assigned Names & Numbers

A gateway is a router connecting a domain to the rest of the Internet

(referred to as the cloud)

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Strategies for Internet Connections

There are several ways to connect your computers to the Internet:

For a large organization, you can lease direct connections

Example: TANet run by Ministry of Education in Taiwan

For a small organization, you can link your domain to the domain of an Internet Service Provider (ISP)

There are three levels: Tier-1 ISPs, Tier-2 ISPs, Access ISPs

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Internet Addressing

Each machine on a network must have a unique address: for the Internet, this is called the Internet Protocol (IP) address

For IPv4, an IP address is a 32-bit identifier for a machine

For IPv6, an IP address is 128 bits

IP address is often written in dotted decimal notation

IPv4 example: 140.113.39.164

IPv6 example:

fe80::3153:525f:6964:8d84 or

fe80:0000:0000:0000:3153:525f:6964:8d84

identifies the domain

identifies the host

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Internet Textural Addressing

IP addresses are difficult for human to remember

Each IP may have an equivalent mnemonic address, which is composed of a domain name and a host

name (e.g. bsd1.cs.nctu.edu.tw)

Domain name is the part assigned by a registrar

Top level domain (TLD) is the classification of domain owner (for example, .com and .tw)

A domain name server (DNS) on the network translates the mnemonic addresses to binary IP addresses

Host name is assigned by domain administrator

Domain owner must run a name server in order for other computers to find your computer

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Internet Applications

Electronic mail (e-mail)

File Transfer Protocol (FTP)

Telnet and Secure Shell

Voice-over-IP (VoIP)

World Wide Web

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World Wide Web (WWW)

The WWW application model is a model of servers spreading hypertext (or hypermedia) documents over the Internet

A web site is a server hosting all hypertext documents controlled by one organization or individual

HTML is the most popular language of hypertext

documents

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World Wide Web Implementation

Web server:

provides access to documents on its machine as requested

Browser:

allows user to access web pages

Hypertext Transfer Protocol (HTTP):

communication protocol used by browsers and web servers

Uniform Resource Locator (URL):

unique address of a document on the web

http://ssenterprise.aw.com/authors/Shakespear/Julius_Caesar.html

Server name Server’s directory path document Server protocol

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Hypertext Document Format

Entire document is printable characters

Contains tags to control display, links to other

documents (or contents), and dynamic functions

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A Hyper-Linked Web Page

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Extensible Markup Language (XML)

Due to the success of HTML, some people decided to design a general presentation language similar to HTML, the result is the XML designed by W

³

C

XML: a language for constructing markup languages similar to HTML

XML has been extensively used for all kinds of presentation languages on the Internet (e.g. SMIL or SVG)

XML has been adopted as general configuration languages as well (e.g. for MS Visual Studio or Apple Quicktime server)

Microsoft uses XML, Open Office XML (OOXML), for all its MS Office file formats since Office 2007

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Dynamic Web Pages

To create multimedia-rich interactive web pages, you may require client-side activities and server-side

activities

Client-side activities can be created using Java applets, Javascript, Macromedia Flash, etc.

Server-side activities can be created using:

Common Gateway Interface (CGI)

Sun’s JavaServer Pages (JSP) or Microsoft’s Active Server Pages (ASP)

PHP Hypertext Processor

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ISO Network Models

Most networks are designed using layered approach (ISO 7-layer model

^†

):

Application Presentation

Session

Transport

Network

Data link

Physical

Application Presentation

Session

Transport

Network

Data link

Physical

Host A Host B

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Internet Protocols

The Internet, just like the ISO 7-layer model, is also using a layered protocol approach

The Internet only have four layers

Application layer:

Example: browser

Transport layer:

TCP – reliable transport

UDP – unreliable transport

Network layer:

Internet Protocol (IP)

Handles routing through the internet

Link layer: handles actual transmission of packets

Token ring or Ethernet

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Package-Shipping Example

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Send a Message through the Internet

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ISO Internetworking

To connect two networks together, one need a host that can handle translation of one protocol to another:

The translator can be called bridge, router, or gateway, based on their functions

Transport A

Network A

Data link A

Physical A

Transport A

Network A

Data link B

Physical B translator

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Port Number

A computer have a unique IP address; all

applications running in this computer shares the same IP address

When an Internet packet arrives at an IP addresses, which application on the computer will receive it?

Answer, port numbers are used to identify a particular application at an IP address

Each packet will be delivered to a IP:Port address that belongs to an application

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Choosing between TCP and UDP

UDP is a connectionless protocol: consecutive messages may be send to the destination

through different routes TCP is a connection-based protocol:

a two-way communication channel between the origin and destination must be established before any messages can be sent

Transport Layer

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Network Security

Integrity of machine exposed to internet can be attacked by

Viruses and worms

Trojan horses

Spywares (sniffing) and phishing

Denial of service attacks

Spamming

Defense techniques

Firewall

Virus and spam filters

Proxy server

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Privacy of Communication

In the old days, most data send over the Internet were unprotected

A network sniffer can be used to collect your private data

Today, encryptions are used to protect your privacy

Secure versions of network protocols such as FTPS, HTTPS, and SSL are used to transmit data with encryption

You can also encrypt data by yourself using public key encryption system such as the PGP system

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Public Key Encryption Concept

Before you do encryption, you must generate a pair of keys called the public key and the private key

^†

You broadcast your public key to everyone who

wants to send you a message so that your friend can encrypt the message using your public key

Certificate authorities may be needed to ensure the correctness of a public key

Networking and Internet