The document provides an overview of computer networks and the Internet by introducing key concepts and terminology. It describes the Internet as a network of networks that interconnects millions of computing devices and communication links. Protocols control the sending and receiving of messages and define how network entities communicate. The network is organized into layers with different protocols at each layer, known as the Internet protocol stack.

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

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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