JAMES F. KUROSE AND KEITH W. ROSS

What is the internet?

There is no one definition.

Two ways to try to describe it:

“Nuts and bolts” i.e. the basic hardware and

software components

A networking infrastructure that provides

services to distributed applications

The Nuts and Bolts Approach

The internet is a worldwide computer

network?

Also includes PDAs, TVs, cell phones, and

even toasters

These devices are known as “Hosts

or “End Systems”

End Systems

End systems are connected by

Communication Links

End systems do not directly connect but

are indirectly connected through devices

known as Packet Switches

Diagram showing

End Systems,

Packet Switches, and

Communication Links

ISPs and TCP/IP

End systems access the internet through Internet Service Providers (ISPs) AOL

T mobile

AT&T

End systems, packet switches, and other pieces of the internet run Protocols that control the sending and receiving of information. Transmission Control Protocol (TCP) and

Internet Protocol (IP) are the two most important Protocols on the public internet.

Service Description

The Internet allows Distributed Applications running on its end systems to exchange data with each other

Some distributed applications include: Web surfing

IM

Audio and video streaming

Two services: Connection-orientated Reliable Service

Connectionless Unreliable Service

"The Web is not

a separate

network but one

of many

distributed

applications that

use the

communication

services provided

by the internet.”

-Kurose and

Ross p.5

Protocol

A Protocol defines the format and order of

messages exchanged between two or

more communicating entities, as well as

the actions taken on the transmission

and/or receipt of a message or other event

Clients and Servers

End systems are also called Hosts

because they host application programs

Two categories: Clients and Servers

Client/server is the most prevalent

structure for internet applications,

including:

The Web

Email

Remote login

Online Toasters

Connection-Oriented Service

In Connection-Oriented Service, the client program and the server program send control packets to each other before sending data

This is called a “handshake procedure”

Reliable Data Transfer – an application can rely on the connec- tion to deliver all of its data without error and in the proper order

“A connection in the Internet

consists of nothing more than

allocated buffers and state variables

in the end systems; the intervening

packet switches do not maintain any

connection-state information.”

[emphasis added] p. 12

Connection-Oriented Cont.

Flow Control - makes sure neither side

overwhelms the other side by sending

too many packets

The Internet uses Congestion-Control to

prevent the internet from entering into a

state of gridlock

Transmission Control Protocol (TCP)

is the name of the Internet’s connection-

oriented service.

Connectionless Service

No handshake procedure

Faster but not as reliable

User Datagram Protocol (UDP) is the

name of the Internet’s connectionless

service.

Circuit Switching vs.

Packet Switching

Circuit switching

The resources needed along a path to

provide communication between end

systems are reserved for the duration of the

communication session

Used by telephones

Packet switching

The resources are not reserved

Used by internet

Circuit-Switching

Two kind of circuit switching:

Frequency division multiplexing

(FDM) – the frequency spectrum of a

link is shared among the connections

established across the link

Time-division multiplexing (TDM) –

time is divided into frames, which are

divided into slots. Each connection gets

its own reserved slot within each frame.

FDMs vs. TDMs

Packet Switching

Packets travel through communication

links and packet switches

Most packet switches use store-and-

forward transmission, which means

that the switch must receive the entire

packet before it can begin to transmit

the first bit of the packet onto the

outbound link

Packet Loss

Output buffer – stores packets that a router is about to send to a particular communication link

Queuing delays – arriving packet must wait in the output buffer when the link is busy transmitting another packet

Packet Loss – when the buffer is completely filled, either the arriving packet or one of the queuing packets will sometimes be dropped

Datagram Networks

Datagram Networks

Any network that forwards packets according to host destination

The internet is a datagram network

Example: Post office

Virtual Circuit Networks

A virtual connection between a source and a destination host

End systems are not needed; destination is identified through VC ID

Benefit to Libraries

Because the internet is so prevalent it is

important to understand how it works (in

general but especially for libraries!)

Knowledge of various end systems can

affect the way we make information

accessible

Could we print books on toast? (Many

possibilities!)