Network

• Defined as interconnected systems– Nodes & interconnect systems that connect nodes

• Examples:-– Power grid, water supply, Telephone system, Postal

system

• Computer network– System of nodes, hosts & routers, connected by

communication links

• Node– host or router

Computer network

• Components– Communication links - the physical medium

through which information flows– Hardware - the computers, network interface

cards, switches– Software - the operating system, drivers,

protocols– Applications/services - mail, file transfer,

terminal access

Goals of computer network

• End tyranny of geography

• To provide high reliability

• Distributing computing power• Communication network

• Cluster computing

Applications of network

• Sharing of high cost software

• Education

• Health care in remote areas• Communication

• Business

What is the Internet?What is the Internet?

• The largest network of networks in the world.The largest network of networks in the world.• Uses TCP/IP protocols and packet switching Uses TCP/IP protocols and packet switching • Runs on any communications substrate.Runs on any communications substrate.

Dr. Vinton Cerf,

Co-Creator of TCP/IP

Birth of InternetBirth of Internet

• Around end of 1969, four-node network Around end of 1969, four-node network was formed betweenwas formed between– University of California Los-Angeles University of California Los-Angeles

– Stanford Research Institute Stanford Research Institute – University of California Santa BarbaraUniversity of California Santa Barbara– University of Utah in Salt Lake CityUniversity of Utah in Salt Lake City

Stanford Research InstituteStanford Research Institute

Baby InternetBaby Internet

University C

alifornia Santa B

arbaraU

niversity California S

anta Barbara

University of U

tah in S

alt Lake C

ityU

niversity of Utah

in Sa

lt Lake City

University California Los AngelesUniversity California Los Angeles

Baby’s first cryBaby’s first cry

Kleinrock, a pioneering computer science professor at UCLA, and his Kleinrock, a pioneering computer science professor at UCLA, and his small group of graduate students hoped to log onto the Stanford small group of graduate students hoped to log onto the Stanford computer and try to send it some data.They would start by typing computer and try to send it some data.They would start by typing "login," and seeing if the letters appeared on the far-off monitor."login," and seeing if the letters appeared on the far-off monitor.

"We set up a telephone connection between us and the guys at SRI...," "We set up a telephone connection between us and the guys at SRI...," Kleinrock ... said in an interview: "We typed the L and we asked on Kleinrock ... said in an interview: "We typed the L and we asked on the phone, the phone,

"Do you see the L?" "Do you see the L?" "Yes, we see the L," came the response. "Yes, we see the L," came the response. "We typed the O, and we asked, "Do you see the O." "We typed the O, and we asked, "Do you see the O." "Yes, we see the O." "Yes, we see the O." "Then we typed the G, and the system crashed"..."Then we typed the G, and the system crashed"...

Yet a revolution had begun"...Yet a revolution had begun"...

Brief History of the InternetBrief History of the Internet

• 1968 - DARPA 1968 - DARPA (Defense Advanced Research Projects Agency) (Defense Advanced Research Projects Agency)

contracts with BBNcontracts with BBN (Bolt, Beranek & Newman) (Bolt, Beranek & Newman) to create to create ARPAnetARPAnet

• 1970 - First five nodes: 1970 - First five nodes: – UCLAUCLA– StanfordStanford– UC Santa BarbaraUC Santa Barbara– U of Utah, and U of Utah, and – BBNBBN

• 1974 – TCP/IP specification by Vinton Cerf1974 – TCP/IP specification by Vinton Cerf• 1984 – On January 1, the Internet with its 1000 hosts 1984 – On January 1, the Internet with its 1000 hosts

converts en masse to using TCP/IP for its messagingconverts en masse to using TCP/IP for its messaging

Internet Protocol ver 4Internet Protocol ver 4• Current version 4 : IPv4 Current version 4 : IPv4

– Substantially unchanged since 1981:RFC 791Substantially unchanged since 1981:RFC 791– Proven to be robust, easily implemented and Proven to be robust, easily implemented and

interoperableinteroperable– Stood the test of time for over two decadesStood the test of time for over two decades– A tribute to its initial designA tribute to its initial design

• Basic functions of IPBasic functions of IP– AddressingAddressing– RoutingRouting

Internet: Pictorial view

Hop by Hop Routing

Internet

Routing net12 to net13

12.0.0.1(src)

13.0.0.2 (dst)

12N1 --> R212N2

12N312.0.0.1

12N113.0.0.2

13N2

Routing net12 to net13

12.0.0.1(src)

13.0.0.2 (dst)

R2 --> R3

12.0.0.1

12N113.0.0.2

13N2

Routing net12 to net13

12.0.0.1(src)

13.0.0.2 (dst)

R3 -->13N2

13.0.0.2

13N2

12.0.0.1

12N1

Routing net12 to net14

12.0.0.1(src)

14.0.0.4 (dst)

12N1 --> R212N2

12N312.0.0.1

12N113.0.0.2

13N2

14.0.0.4

14N4

Routing net12 to net14

12.0.0.1(src)

14.0.0.4 (dst)

R2 --> R1

12.0.0.1

12N113.0.0.2

13N1

14.0.0.4

14N4

Routing net12 to net14

12.0.0.1(src)

14.0.0.4 (dst)

R1 -->R4

13.0.0.2

13N1

14.0.0.4

14N4

Routing net12 to net14

12.0.0.1(src)

14.0.0.4 (dst)

R4 -->14N4

13.0.0.2

13N1

14.0.0.4

14N4

Network structure

• Hosts – PCs, routers

• Subnet– Switching elements, transmission lines.

• Subnet Topologies– Point to point– Star– Tree– Ring– Bus

Message,circuit,packet switching

• Circuit switching– Classic telephone system– Call set up before transfer– Dedicated, fast, congestion free– Inefficient usage of resources

• Message switching– No prior set up– Store and forward by IMP, hop by hop– No limit on block size– Storage at IMP is a limitation– Not suitable for interactive due to delays

Packet switching

• Limit on block size

• Suitable for interactive communication

• Higher throughput• Computer networks

– Packet switched

• Better bandwidth management

• Congestion possible