Computer Networks
Chapter 1:Introduction
Computer Networking:
A Top Down Approach ,
4th edition.
Jim Kurose, Keith Ross
Chapter 1: Introduction
Our goal:

 get “feel” and

terminology
 more depth, detail
later in course
 approach:
 use In...
What’s the Internet: “nuts and bolts” view
PC

 Interconnects millions Mobile network

of computing devices:
Global ISP
h...
What’s the Internet: “nuts and bolts” view


protocols control sending,
receiving of msgs




Global ISP

e.g., TCP, IP...
What’s the Internet: A Service View
infrastructure
that provides services to
applications:
 Involve multiple end system
t...
What’s a protocol?
Human Protocols:
 “what’s the time?”
 “I have a question”
 Interview
… specific msgs sent
… specific...
What’s a protocol?
a human protocol and a computer network protocol:
Hi

TCP connection
request

Hi

TCP connection
respon...
The Network Edge:
 end systems (hosts):




run application programs
e.g. Web, email
at “edge of network”

peer-peer

...
Network Access
Access Networks:
The physical link that connects an end
system to its “edge router”.

Q: How to connect end...
The Network Core
 Mesh of interconnected

routers
 the fundamental question: how
is data transferred through
net?
 circ...
Network Core: Circuit Switching
End-end resources reserved for the
duration of the call
 Three phases
 Establish, Transf...
Network Core: Packet Switching












Today’s internet is a packet switched network
Each end-end data strea...
Protocol Layers
Networks are complex!
• many “pieces”:
– hosts
– routers
– links of various
media
– applications
– protoco...
Organization of air travel
ticket (purchase)

ticket (complain)

baggage (check)

baggage (claim)

gates (load)

gates (un...
Layering of Airline Functionality
ticket (purchase)

ticket (complain)

ticket

baggage (check)

baggage (claim

baggage

...
Why layering?
Dealing with complex systems:
 Discuss a well defined, specific part of a
large and complex system
 Modula...
Internet Protocol Stack
 To provide structure to design of
network
protocols,
network
designers organize protocols in
lay...
Internet Protocol Stack
• Application Layer:
 Network applications and their application layer protocols
reside.
 Provid...
Internet Protocol Stack
• Transport Layer:
 Transports application-layer messages between application
end points.
 Trans...
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Week1 lec2-bscs1

  1. 1. Computer Networks Chapter 1:Introduction Computer Networking: A Top Down Approach , 4th edition. Jim Kurose, Keith Ross
  2. 2. Chapter 1: Introduction Our goal:  get “feel” and terminology  more depth, detail later in course  approach:  use Internet as example Overview:  what’s the Internet?  what’s a protocol?  network edge; hosts, access     net, physical media network core: packet/circuit switching, Internet structure performance: loss, delay, throughput Protocol layers, service models History of Internet
  3. 3. What’s the Internet: “nuts and bolts” view PC  Interconnects millions Mobile network of computing devices: Global ISP hosts = end systems wireless laptop  running network cellular Home network handheld apps Regional ISP  communication links  fiber, copper, radio, access points Institutional network satellite wired links  transmission rate = bandwidth (bits/sec)  routers: forward router packets (chunks of data) server
  4. 4. What’s the Internet: “nuts and bolts” view  protocols control sending, receiving of msgs   Global ISP e.g., TCP, IP, HTTP, Skype Internet: “network of networks”  Mobile network public Internet versus private intranet  Internet standards  IETF: Internet Engineering Task Force  RFC: Request For Comments  IETF standard Documents  More than 5000 RFCs Home network Regional ISP Institutional network
  5. 5. What’s the Internet: A Service View infrastructure that provides services to applications:  Involve multiple end system that exchange data with each other.  Web, VoIP, email, games, ecommerce, file sharing  Applications do not run on the routers  Communication services provided to applications:  reliable data delivery from source to destination (connection oriented)  “best effort” (unreliable) data  Communication
  6. 6. What’s a protocol? Human Protocols:  “what’s the time?”  “I have a question”  Interview … specific msgs sent … specific actions taken when msgs received, or other events Network Protocols:  machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt
  7. 7. What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? Get http://www.awl.com/kurose-ross 2:00 <file> time
  8. 8. The Network Edge:  end systems (hosts):    run application programs e.g. Web, email at “edge of network” peer-peer  client/server model   client host requests, receives service from always-on server client/server e.g. Web browser/server; email client/server  Peer-Peer model:   minimal (or no) use of dedicated servers e.g. Skype, BitTorrent, Kazaa  More in Chapter 2
  9. 9. Network Access Access Networks: The physical link that connects an end system to its “edge router”. Q: How to connect end systems to edge router? Access Networks can be loosely classified into three categories  Residential access networks  Dial up, DSL etc  Institutional access networks (school, company)  Ethernet  Mobile access networks  Wireless LAN (WiFi)  Wider-area wireless access (WiMAX)  Reading Assignment
  10. 10. The Network Core  Mesh of interconnected routers  the fundamental question: how is data transferred through net?  circuit switching: dedicated circuit per call: telephone networks  packet-switching: data sent through network in discrete “chunks” called packets  Hotel reservation analogy
  11. 11. Network Core: Circuit Switching End-end resources reserved for the duration of the call  Three phases  Establish, Transfer, Disconnect  dedicated resources: no sharing  Guaranteed performance  Very Reliable  Developed for Telephone networks  Inefficient  Channel capacity dedicated for duration of connection  If no data, capacity wasted  Set up (connection) takes time
  12. 12. Network Core: Packet Switching           Today’s internet is a packet switched network Each end-end data stream divided into packets Each packet contains a portion of user data plus some control info. Each packet has to find its own route to the destination No predetermined path Decision as to which node to hop to in the next step is taken only when a node is reached. Resources used as needed Congestion : packets queue, wait for link use Reliability Less reliable Store and forward switching Routers receives complete packet before forwarding Question: What is Cut through Switching?
  13. 13. Protocol Layers Networks are complex! • many “pieces”: – hosts – routers – links of various media – applications – protocols – hardware, software Question: Is there any way of organizing network architecture? Answer: Yes possible with a layered architecture
  14. 14. Organization of air travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing • A series of steps(actions)
  15. 15. Layering of Airline Functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim baggage gates (load) gates (unload) gate runway (takeoff) runway (land) takeoff/landing airplane routing airplane routing airplane routing departure airport airplane routing airplane routing intermediate air-traffic control centers arrival airport Airline functionality can be divided into layers, providing a frame work in which we can discuss air travel. • At the ticketing layer and below – Airline-counter-to-airline-counter transfer of a person. • At the gate layer – Departure-gate –to-arrival-gate transfer of a person is accomplished Layers: each layer implements a service – via its own internal-layer actions – Combined with the services directly below it •
  16. 16. Why layering? Dealing with complex systems:  Discuss a well defined, specific part of a large and complex system  Modularization eases maintenance, updating of system Change of implementation of layer’s service transparent to rest of system e.g. change in gate procedure doesn’t affect rest of system
  17. 17. Internet Protocol Stack  To provide structure to design of network protocols, network designers organize protocols in layers  Service – says what a layer does  Protocol – says how the service is implemented  Advantages  Drawbacks  When taken together the protocols of various layers are called the Protocol Stack.  Internet Protocol Stack consists of Five layers  Physical, Link, Network, Transport and Application layers .  Organization of Book
  18. 18. Internet Protocol Stack • Application Layer:  Network applications and their application layer protocols reside.  Provides user interfaces and support for services such as email, file transfer etc. Hyper Text Transfer Protocol (HTTP) File Transfer Protocol (FTP) Session Initiation Protocol (SIP)  An application layer protocol is distributed over multiple end systems  The packets of information at the application layer is called as a message.
  19. 19. Internet Protocol Stack • Transport Layer:  Transports application-layer messages between application end points.  Transport layer packet is called as a segment  Breaks long messages into shorter segments  There are two Transport Layer Protocols  Transmission Control Protocol (TCP)  Connection Oriented service  Guaranteed delivery of application layer messages  Flow control  Congestion Control  User Datagram Protocol (UDP)  Connectionless service  No reliability, flow control and congestion control

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