Download Networking and the Internet

Networking and the Internet
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Che-Rung Lee
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CS135601 Introduction to Information Engineering
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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?
Application
Transport
Network
Link
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A story
某日，某資工系某家族決定要去竹北某餐廳
家聚。他們決定先在某資電館前集合，再出
發到餐廳。家族共有12人，某學長有一輛車，
可以坐4人，另外還有2個人有摩托車，共可
以載4人，另外4個人決定坐公車。某學長車
上有GPS，可以找出路要怎麼走；有摩托車
的同學上網查出地圖路線；要坐公車的同學
查出要轉一次車，再走一小段路就可以到餐
廳了…
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Layered approach
• 去竹北某餐廳家聚
Application layer
– Decide where to go and what to do
• 4人坐車， 4人騎車， 4人搭公車
– Decide the transportation methods
• GPS,地圖路線,公車班次
Transport
layer
Network layer
– Decide the routes from the source to the
destination
Link layer
• 汽車,摩托車,公車,司機,馬路,紅綠燈,路標…
– 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:先在資電館前集合，再出發到餐廳
– 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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Figure 4.14 Following a message through the Internet
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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 1
address32
address
name 1
name
address
name 342
name 4
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Link Layer
Application
Transport
Network
Link
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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 scopes
uses 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 perfectly
– 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.
– Handshaking: Before sending data, a node sends
a request to AP. AP sends an acknowledgement
to all nodes after receiving the request.
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Network equipments for LAN
• Hub: relays signals it received
• Repeater: connects two buses
• Bridge: similar to repeater,
but only forwards necessary
messages
• Switch: a bridge that
connects multiple buses
– All those do not change the protocol
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Network layer/Transport layer
Application
IP, TCP, UDP, and
the Internet
Transport
Network
Link
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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: IP+TCP+UDP
– TCP and UDP: Transport layer protocols
– IP : Network layer protocol
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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
– 台灣 新竹市 光復路二段 101號 nation-city-roadnumber
– 886-3-571-5131 nation-area-phone number
• 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 楓橋驛站
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Domain name
• The mnemonic address for human
– For example, bbs.cs.nthu.edu.tw is the
domain name for 楓橋驛站
– 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
DNS
Humans prefer
domain names
• Provides translation between IP addresses
and domain names.
– Name server
– DNS lookup
楓橋驛站
Bookmark
Domain name bbs.cs.nthu.edu.tw
IP address
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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: select a route to reach destination
• Update and maintain the forwarding table
Destination
Next hop
140.114.87.5
103.121.1.2 …
140.114.79.3
…
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Cost
…
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Examples in windows
The IP address
of your computer
The mask for
gateway
The IP address
of gateway
The IP addresses
of domain name
servers
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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 examples
• Handshaking:
– Make reservation before go to a restaurant
• Retransmission:
– Ask someone to repeat what he/she said
when you did not hear it clearly
• Flow control:
– Ask someone to talk slower
• Congestion control:
– 匝道管制 or line up 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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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
台灣學術網路
SeedNet
新世紀資通
Hinet
中華電信
Cable modem
東森有線電視
http://rms.twnic.net.tw/twnic/User/Member/Search/main7.jsp?Order=ORG.ID
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Exercises
1. Use nslookup to checkout the IPs of
google.com
2. Use ipconfig (or ifconfig on Linux)
to check out (1) The IP address of the
computer (2) The gateway of the LAN (3)
DNS server (use /all options) (4)
Physical (MAC) address of the computer
3. Use netstat –a to scan port numbers
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Application
Transport
Application layer
Network
Link
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 • Examples:
– Server must execute
continuously
– Client initiates
communication
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– 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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Hypertext Transfer Protocol (HTTP)
& Uniform Resource Locator (URL)
• HTTP is an application-level protocol for
distributed, collaborative, hypermedia
information systems
• URL (web address)
Figure 4.8 A typical URL
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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
– 計算機網路概論, 密碼與網路安全概論,
訊號與系統,作業系統
References
• Textbook chap 4 sec1,2,3,4
• The Internet
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