computer network basics an overview of computer networking which introduces many key concepts and...

Computer Network Basics

An overview of computer networking which introduces many key concepts and terminology

Päivä 1: luento 4Päivä 1: luento 4

Lappeenrannan teknillinen yliopistoTITEProf. Esa Kerttula20.3.2008

Operating systemsDeveloper or manufacturer Operating system

Apple Computers Inc. Mac OS 8/9/X

AT&T Bell Laboratories Unix

Be Inc. beOS

Berkeley University BSD, FreeBSD

Carnegie-Mellon University Mach 3.0

Cisco Systems Inc. IOS

HP HP-UX

IBM AIX and OS/2

Linus Thorvald Linux

Microsoft Windows Server 2008 and Vista

Novell NetWare

Santa Cruz Operation Inc. (SCO) SCO XENIX, SCO UNIX, SCO MPX

Siemens SINIX

Silicon Graphics IRIX

Sun Microsystems Solaris, SunOS, JavaOS

Operating Systems Developed for Portable Devices

Developer or manufacturer Operating system

Microsoft Windows CE

Microsoft Windows Mobile 6.1

Palm PalmOS

Symbian Symbian OS

RIM (Research In Motion Limited) RIM

A closer look at network structure:

network edge: applications and hosts

network core: routersnetwork of

networks

General Architecture of Computer Networks

Cloud

Externalnodes

Internal nodes

(or stations)

(swithing devices)

The Network Core

mesh of interconnected routers

the fundamental question: how is data transferred through net? circuit switching:

dedicated circuit per call: telephone net

packet-switching: data sent thru net in discrete “chunks”

Connection of Networks

networks or subnetworks

router orgateway

node(host,

station)

Network Topology

a) bus, b) star, c) ring, d) tree structure

a) b) c) d)

The Internet

MILnet

CompuServe

Academic Internet basedon TCP/IP Protocol(Full Access to all

Internet Resources)

Prodigy

Americaon-line

GEnie

Only E-mail

Networks

AT&T Mail

Sprint Mail

MCI mail

FidoNet

BIXeWorldDelphi

Value-AddedNetworks

Tymnet, GEISAdvantis, SprintLink

NSFnetARPAnetCSnet

EBone

PSInetAlternet

CERFnet

AsianNetworks

OnlineServiceProviders

The Internet = “Academic Internet” + “Business Internet”

“Business Internet”based on non-TCP/IP

protocols

Bandwidth Progression of the Internet

1969 - 9.6 Kbps1985 - 56 Kbps1987 - 1.544 Mbps (often called T1 Speed)1989 - 45 Mbps (often called T3)1995 155 Mbps 1997 622 Mbps1998 1024 Mbps2000 2048 Mbps2006 …

Types of ConnectionsGlobalInternet

ISPPSTNChannel

9.6-28.8 Kbps

Modem

DialupTerminal or SLIP/PPP(up to 56 kbps)

GlobalInternet

ISPISDNRouter

CustomerEnterpriseNetwork

ISDNChannel

64 Kbps

Integrated Services Digital Network (ISDN, up to 128 kbps)

GlobalInternet

ISP RouterCustomerEnterpriseNetwork

LeasedCircuit

56 Kpbs1.544 (T1)

Leased Lines: T1 or T3

NSFNET Backbone Structure

Houston

Los Angeles

San Francisco

Seattle

Denver St. Louis

Chicago

Cleveland

Atlanta

Greensboro

College Park

New York Hartford

Hawaii &Japan

Europe

Mexico &South America

Flow-control and Congestion Prevention

Flow-control: to protect the receiver against the overload, i.e.: the sender (source) sends more data than the receiver can process it is mainly necessary in link and

transport level Congestion prevention: to

prevent the intermediate nodes against the overload it is mainly necessary in network

level

Overload and Congestion

Overload: Too many packets occur in a subnetwork in the same time, which prevent each other and in such a way the throughput decreases

Congestion: the queues in the routers are too long, the buffers are full. As a consequence some packages are

dropped if the buffers of the routers are overloaded

In extreme case: grid-lock, lock-up

Deadlock

Deadlock: the most serious situation of the congestion, the routers wait for each other

Direct store and forward deadlock: the buffers of two neighbouring routers are full with the packets to be sent to the other router

Indirect store and forward deadlock: the deadlock occurred not between two neighbouring routers but in a subnetwork, where any of the routers has not free buffer space for accepting packets

Internet protocol stack application: supporting network

applications ftp, smtp, http

transport: host-host data transfer tcp, udp

network: routing of datagrams from source to destination ip, routing protocols

link: data transfer between neighboring network elements ppp, ethernet

physical: bits “on the wire”

application

transport

network

link

physical

Layering: logical communication

applicationtransportnetwork

linkphysical


linkphysical


linkphysical


linkphysical

networklink

physical

data

data

E.g.: transport take data from

app add addressing,

reliability check info to form “datagram”

send datagram to peer

wait for peer to ack receipt

analogy: post office

data

transport

transport

ack

Layering: physical communication


linkphysical


linkphysical


linkphysical


linkphysical

networklink

physical

data

data

Protocol layering and data

Each layer takes data from above adds header information to create new data unit passes new data unit to layer below


linkphysical


linkphysical

source destination

M

M

M

M

Ht

HtHn

HtHnHl

M

M

M

M

Ht

HtHn

HtHnHl

message

segment

datagram

frame

Operation of Protocols

(interlayer) protocol layerprotocol

Host Host

Physical connection

(n-1). layerprotocol entity

(n-1). layerprotocol entity

(n+1). layerprotocol entity

n. layerprotocol entity

(n+1). layerprotocol entity

n. layerprotocol entity

... ...

Communication among the layers

Connection oriented network service• Reliable transport service• Unreliable transport service

Connectionless network service• Reliable transport service• Unreliable transport service

Network Tools Repeater: connects network segments

logically to one network Hub: multiport repeater Bridge: datalink level connection of two

networks Switch: multiport bridge Router: connects networks that are

compatible in transport level subnetworks are connected to the interfaces

of the repeater Gateway (proxy server): router

between two individual network. The “Way Out”

Soft and Hard States State: the data collection, which are necessary for

keeping the connection between two protocol entities Hard state

If the connection is established once, it is never timed out, even if it is not in usage

Even there is not data exchange for a while, the client can trust in it that the state is existing

To cancel the connection one of the participants of the connection must explicitly close it

Soft state To keep the connection the participants must send

occasionally keep-alive messages, since without keep-alive message the state information is timed out after a certain period

The state is called as “soft” since in the ordinary operation the state can change easily

The clients are responsible for the maintenance of the state at the partner, therefore they have to refresh the state information at the communicating partner

Roots of the Recent Advantages Advantages of the computers (prices) Telecommunication network (fibre and

satellite telecommunication) Evolution of the network software

The Next Generation of the Computers The development rate is prognostised up to

2047 In the USA there is technological development

projects up to 2010 New physical phenomena and laws -

technological development Moore-law (duplication in 24 months) In 2047 the capacity of a storage chip is 100

human brains The power of one processor will be equals to

500 million Pentium

Some Internet Related organizations

Internet Society (ISOC) Internet Architecture Board (IAB) Internet Research Task Force (IRTF) Internet Engineering Steering Group (IESG) Internet Engineering Task Force (IETF) WWW Consortium (W3C)

Standardization

Types: patented standard (e.g.: IBM SNA) public standard (e.g.: ITU, ISO or IEEE

standards) non-official standard (e.g.: RFC)

Evaluation of RFC: proposed standard (6 month) draft (6 month maximum, but after 4

months it can became RFC) standard (RFC) (up to obsolescence)

Different Levels of Authority

Public Domain can copy without any restriction

Freeware can be used, but copyrighted, the copy or the

modification can be limited Shareware

for evaluation purposes (before buying), only Mixed:

individuals and non-profit organizations obtain freely

the profit oriented organizations must buy

computer network basics an overview of computer networking which introduces many key concepts and...

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