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