Network and the Internet

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Network and the Internet
CS1356 ??????

• ????????????

2015/6/12
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Network

• An intricately connected system of things or
  people
• Webster dictionary
• Computer network
• A linked computer system

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Outline

• Layered approach for network
• Link layer
• Network layer/Transport layer
• Application layer

Application
Transport
Network
Link
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Layered Approach

• What and why?

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A Story

• ??,????????????????????????????????,???????????12?
  ,???????,???4?,????2??????,????4?,??4?????????????
  ?GPS,??????????????????????????????????????,????
  ?????????

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Layered Approach

• ????????
• Decide where to go and what to do
• 4???, 4???, 4????
• Decide the transportation methods
• GPS,????,????
• Decide the routes from the source to the
  destination
• ??,???,??,??,??,???,??
• Make the real transportation happen

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Network layers

• Application Constructs message with dest address
• Transport Provides reliable data transfer
  services
• Network Handles routing through the network
• Link Handles actual transmission of packets

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Layered Approach Why?

• Each task in different layer can be handled more
  easily without considering the details of the
  tasks in other layers.
• For example, they can decide a best restaurant
  without considering how to go there
• Methods in different layers can be changed
  easily.
• For example, different applications can use the
  same transport protocol.

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Protocols

• A set of rules used to communicate with each
  other across a network.
• Example 1????????,??????
• Example 2 bus route and schedule
• Example 3 traffic regulations
• Protocol is a special algorithm that enables and
  controls the data communications.

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(Fig. 4.14)
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Message Encapsulation

• To transmit the data, each layer appends some
  information to the original message.
• The corresponding layer in the receiver side
  needs to decapsulate the message.

address 2 name 2
address 3 name 3
address 4 name 4
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Link Layer
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LAN, MAN, WAN

• Network can be classified by the scope
• Local area network (LAN)
• Metropolitan area (MAN)
• Wide area network (WAN)
• Network for different scopesuses different media
  and has different protocols.

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Network Topology

• Popular network topologies used in LAN
• Bus (Ethernet)
• Star (Wireless network with central Access Point,
  AP)
• Different topology uses different protocols.

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Ethernet and CSMA/CD

• CSMA/CD protocol for Ethernet
• Carrier Sense, Multiple Access with Collision
  Detection
• Broadcast messages to all machines on the bus
• Resend message if detecting more than one
  messages sent at the same time (collision)

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WiFi and CSMA/CA

• CSMA/CA protocol for WiFi
• Carrier Sense, Multiple Access with Collision
  Avoidance
• Similar to CSMA/CD
• Sensing carriers before sending
• WiFi cannot detect collisions
• Self signal drowns out others
• Hidden terminal problem

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Collision Avoidance

• Before sending data, a node listens to the
  channel for a period.
• If the channel is silent, it sends data.
• If the channel is busy, it waits another random
  period. After waiting, if the channel is silent,
  it sends data immediately.
• Cannot avoid collisions totally.
• Before sending data, it sends a request to AP.
  AP sends an acknowledgement to all machines after
  receive the data.

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Network Equipments for LAN

• Hub relays signals it received
• Repeater connects two buses
• Bridge similar to repeater,but only forwards
  necessarymessages
• Switch a bridge that connects multiple buses
• All those do not change the protocol

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Network layer/Transport layer

• IP, TCP, UDP, and the Internet

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Terminology

• An internet
• a network of networks
• It is different from the Internet.
• The Internet a global internet that uses TCP/IP
  protocol suite.
• TCP/IP protocol suite IPTCPUDP
• TCP and UDP Transport layer protocols
• IP Network layer protocol

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Internet Service Provider (ISP)

• A company/organization that offers its customers
  access to the Internet.
• The ISP hierarchy

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How ISPs Work

• Connection method to ISPs
• Direct connection
• Dial-up, DSL
• Cable modem
• Wireless

TANet ??????
SeedNet ?????
Hinet ????
Cable modem ??????
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Internet Protocol (IP)

• A protocol used for communicating data across an
  internet.
• It is a connectionless protocol.
• Telephone network is connection-oriented. 
• For the same source and destination, different
  message may be routed differently.

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IP address

• How to design a global address
• ?? ??? ????? 101?
• 886-3-571-5131
• IP address the global identification for each
  computer connected to an internet
• Pattern of 32 or 128 bits, usually represented in
  the dotted decimal notation.
• For example 140.114.87.5 is for ????

nation-city-road-number
nation-area-phone number
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Gateway and Router

• Gateway the point linked to an internet
• Router forwards and routes messages
• Forwarding relay messages on an internet
• Routing update and maintain the forwarding table

Destination Next hop Cost
140.114.87.5 103.121.1.2
140.114.79.3
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Domain Name

• The mnemonic address for human
• For example, bbs.cs.nthu.edu.tw is the domain
  name for ????
• Top level domains (TLD) suffixes in the domain
  name .gov, .edu, .com, .net, .org,
• Country-code TLD .tw, .ca, .jp, .au,
• Subdomains prefixes of an domain name, bbs.,
  www.,

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Domain Name System (DNS)
Machines like binary addresses
Humans prefer domain names

• Provides translation between IP addresses and
  domain names.
• Name server
• DNS lookup

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Transport Layer

• Two protocols
• TCP (Transmission Control Protocol)
• UDP (User Datagram Protocol)

TCP UDP
Handshaking ? ?
Retransmission ? ?
Flow control ? ?
Congestion control ? ?
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Transmission Control

• Handshaking
• Make reservation before go to a restaurant
• Retransmission
• Ask someone to repeat what he/she said
• Flow control
• Ask someone to talk slower
• Congestion control
• Lineup of a crowd of people

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Port Number

• TCP/UDP need to know which application should a
  received message be sent to
• This is identified by port numbers
• IP address is for the address of computer
• Examples

Port number Application
53/TCP,UDP Domain Name System (DNS)
80/TCP,UDP Hypertext Transfer Protocol (HTTP)
513/TCP Login
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Application Layer

• Client/server, peer to peer, distributed system
• The Internet applications and WWW

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Client/server Model

• Server provides service to clients
• One server, many clients
• Server must execute continuously
• Client initiates communication

• Examples
• Printer server,
• File server,
• Web server,
• Email server,
• BBS server,

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Peer-to-peer (P2P) Model

• Two processes communicating as equals

• Examples
• Peer-to-peer file sharing
• FastTrack, BitTorrent,
• VoIP Skype,
• Streaming media TVant,
• Instant message, online chat MSN, google talk,

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Distributed System

• Consists of software units that execute as
  processes on different computer.
• Examples
• Multitier architecture
• Computer cluster
• Cloud computing
• Grid computing
• BOINC system

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The Internet Applications

• Telnet, ssh
• Email
• WWW
• File transfer
• Peer2peer
• Internet phone (VoIP), instant message
• Streaming media

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Electronic Mail (email)

• Email address
• Email server
• Email client
• Outlook
• Thunderbird
• Pine
• Webmail
• Yahoo mail, gmail, hotmail,

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World Wide Web (WWW)

• A system, invented by Tim Berners-Lee (1989), of
  interlinked hypertexts via Internet.

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Web Browser

• A software application for retrieving,
  presenting, and traversing information resources
  on the World Wide Web.
• Internet Explore
• Mozilla Firefox
• Apple Safari
• Google Chrome
• Bookmark, RSS, download management

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HTTP and URL

• Hypertext Transfer Protocol (HTTP) is an
  application-level protocol for distributed,
  collaborative, hypermedia information
• Uniform Resource Locator (URL) web address

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HTML

• Hypertext Markup Language (HTML) encoded as
  text file
• Uses tags to communicate with browsers
• XML eXtensible Markup Language
• A language for constructing markup languages
  (meta-language)

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Related Courses

• Computer network
• ????????????????????????????
• Textbook chap 4 sec1,2,3,4
• The Internet

References