Computer Networks I Introduction to Computer Networks

Version Feb 21, 2011
Computer Networks I
application
transport
network
link
physical
Introduction to
Computer Networks
David.Villa@uclm.es
Outline
Internet history
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Internet history
Other Internet stories
What is a network
Network classification
Inter-networks
Networking issues
Packet switching modes
Network architectures
Reference models
● OSI model
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TCP/IP model
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1950-1960 – Project RAND. Networking was limited to some
terminals connected to a mainframe by means of leased lines.
1962 – J.C.R. Licklider published “On-Line Man Computer
Communication”.
1962 – Licklider was hired by DARPA to “interconnect the DoD
main computers at Cheyenne Mountain, Pentagon and SAC”
(ARPAnet).
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Three network terminals were installed: Santa Monica,
Berkeley and MIT.
1962 – Leonard Kleinrock proposes packet switching.
● References
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Internet history
Internet history
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1968 – Douglas Engelbart and ARC presents the NLS. That
event was known later as “The mother of all demos”.
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1969 – RFC 1 “Host software”
1969 – First ARPANET: 4 nodes
● 1971 – 15 nodes
The Internet Archive
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The NLS (oNLine System) was the first operating system
including graphic interface, desktop, icons, mouse, windows,
hyperlinks and video-conference!!
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life.com – Click! A Brief History of Computing
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● 1981 – ARPANET has 213 nodes
The TCP/IP network testbed (February 1982)
Internet history
Internet history
Sigma 7 mainframe at UCLA
PDP-10
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1971 – Ray Tomlinson sent the first
email.
1971 – FTP (File Transfer Protocol).
1973 – Robert E. Kahn and Vinton
Cerf work in a common
internetwork protocol.
1974 – RFC 675 “Specification of
Internet Transmission Control
Program”, by Vinton Cerf.
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Internet history
Internet history
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1981 – RFCs 791-793 define the basics of TCP/IP.
1983 (January 1th) – the flag day, TCP/IP replaced all earlier
protocols in ARPANET.
1983 – Paul Mockapetris proposes DNS (Domain Name
System).
1983 – Berkeley Unix 4.2BSD includes the socket API.
1984 – 4 Berkeley students write BIND (Berkeley Internet
Name Domain). The DNS Unix first implementation.
1985 – IETF (Internet Engineering Task Force) is created.
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1991 – Tim Berners-Lee (CERN)
develop the first network based
hypertext implementation and the HTTP
protocol in the "WorldWideWeb" project.
1993 – University of Illinois
creates the Mosaic graphical web
browser.
1994 – Classless Inter-Domain
Routing.
1998 – IPv6.
2008 – 1500 M-users.
NeXT computer. It ran the first
web server at CERN
● 1989 – First ISP “The World” in USA.
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Other Internet stories
Other Internet stories
1994 – Jerry Yang and David Filo, graduate students at
Standford, create Yahoo!
● 2008 → Microsoft offers 44.6 G$
1994 – Jeffrey Bezos founded Amazon.
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2010 – 74.4 G$, 31.200 employees
● 2009 → 14.100 employees, Assets: 14.9 G$
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Other Internet stories
Other Internet stories
1996 – Stanford PhD students Larry Page and Sergey Brin
create Google.
● 2009 → 192 G$
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2010 → 24.400 employees
1999 – 18-year-old Shawn Fanning creates Napster.
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2001 (Feb) → 25 M-users, 80 M-mp3
2001 (July) → It closes
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Other Internet stories
Other Internet stories
2001 – Larry Sanger and Jimmy Wales found Wikipedia.
2004 – The Harvard student Mark Zuckerberg creates
Facebook.
● 2010 → 41 G$
● 2011 → 17 M-articles, 278 languages
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2011 → 1700 employees and 600 M-users.
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Other Internet stories
Other Internet stories
How is it possible that a bunch of
students may create some of the most
successful world companies
How is it possible that a bunch of
students may create some of the most
successful world companies
The reason is
TCP/IP
(one of them at least)
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The nature of the Internet
What is a network
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Communication is the base of the human society, and
Internet has definitely changed the way that we
communicate ourselves.
Internet core protocols were designed to be open,
scalable and interoperable.
Most of the Internet standards and protocols are on
public domain (RFC).
Nowadays, nobody can control Internet, but this might
change soon...
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Is a set of interconnected autonomous computers so
they may interchange information.
The network users are aware that there are different
computers with associated resources.
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The network is usually represented
by a cloud, to emphasize that we do
not know its internal structure.
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Network classification
Networks
by link type
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By link type
By scale
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A point-to-point connection provides a link that
only can be used by the two peers.
Usually they are wires, but microwaves or satellite
links are also feasible.
● By topology
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Networks
by link type
Networks
by scale
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In a multipoint connection several nodes (more
that two) share a the link.
Usually, it allows different addressing methods:
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Unicast. The address identifies a single destination host.
Broadcast. A special address identifies all hosts in the net.
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IPN: InterPlanetary and Delay Tolerant Networks (DTN).
Global (Internet).
WAN: Wide Area Network – a country or intercontinental links.
MAN: Metropolitan Area Network – A city or part of it.
LAN: Local Area Network – A department or building.
PAN: Personal Area Network – Computer and desktop.
SAN: System Area Network – Clusters and embedded
systems.
NoC: Network On Chip – Network concepts inside a chip.
● Multicast. The address identifies a host subset.
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Networks
by scale: LAN
Networks
by scale: WAN
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The LAN is privately administered.
High speed (100Mbps – 1Gbps), focused on resource
sharing and the needs of a set of people.
It uses a single transmission technology and topology.
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It involves hosts and sub-networks (that use p-t-p links).
A subnet is composed by:
router
● Link lines
● Routers
LAN
subnet
LAN
bus
ring
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The router must store messages and forward them to the
appropriate destination. That “store and forward”
mechanism (or “packet switching”) is the opposite to
“circuit switching”.
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Networks
by topology
inter-networks
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An inter-network is a set of interconnected (heterogeneous)
networks.
Networks with different software and hardware technology
may share information due to a logical network protocol
and gateways.
gateway
web server
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Networking main issues
Packet switching modes
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Addressing
Data flow: Simplex, half-duplex and full-duplex
Error detection and correction
Message ordering
Flow control
Fragmentation
Multiplexing
Routing
Connectionless
Each message is sent as a unrelated individual unit.
The message includes destination (and probably
source) address and other information for its delivery.
Connection-oriented
It requires a connection set-up phase, then the
communication works as a continuous byte stream,
usually supporting duplex transmission.
● ...
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Network architecture
Reference models
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It is a framework that describe a communication
network, its components and protocols.
The network design is organized as a layer stack.
Each layer provides a set of services to the upper
layer and requires services to the lower layer.
The layer 'n' of a node maintains a virtual
conversation with the same layer the destination
node. That conversation must meet a specific
protocol.
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OSI model
TCP/IP model
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The reference model and the protocol
suite implementation are very different
things. They must not be confused.
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OSI model
OSI layering
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The Open System Interconnection (OSI) is an ISO
(International Organization for Standardization)
It is an initiative is a general conceptual model to
describe and study any protocol stack.
The model defines three basic concepts:
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service: the function that a layer may provide.
interface: the way to get the layer services.
● protocol: the set of rules between homologous peers.
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application
presentation
session
transport
network
link
physical
segments
packages
frames
bits
physical media
application
presentation
session
transport
network
link
physical
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1. Physical layer
OSI model
media layers
It defines the electrical, mechanical and temporal
characteristics for devices required in a particular data
communication technology.
2. Data link layer
It supports data transfers between directly reachable nodes
(neighbors). It provides physical addressing.
3. Network layer
It supports end-to-end communication with variable length
individual messages. It provides the logical addressing.
4. Transport layer
OSI model
host layers
It provides a reliable error-free communication channel between end
users. It also support process multiplexing.
5. Session layer
It allows to create sessions among hosts and it manages
synchronization.
6. Presentation layer
It define on-the-wire data representation and its semantic.
7. Application layer
Application specific protocols like mail, news, remote shell, etc.
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TCP/IP model
TCP/IP model
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The TCP/IP model arrives years
later of first implementations. The
aim is to formalize and
standardize its use and
development.
It is closely related with TCP/IP
protocols stack, and it can not be
used to describe other protocols
or networks.
application
transport
inter-net
host to net
host to net
Application layer
High level protocols like: DNS, SMTP, HTTP, FTP and many others.
Transport layer
It defines transport protocols: TCP (Transport Control Protocol) and UDP
(User Datagram Protocol).
Inter-network layer
It provides mechanisms to network interconnection and package routing.
It defines the IP protocol, that provides a connectionless delivery service.
Host-to-net layer
It provides (does not provides) required mechanisms to make possible
that “a IP packet reaches other host in the network”.
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OSI, TCP/IP and hybrid models
Encapsulation
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6
5
4
3
2
1
OSI
application
presentation
session
transport
network
data link data link
physical
TCP/IP
application
transport
inter-net
host to net
host to net
hybrid
application
transport
network
data link data link
physical
The user information can not go directly “on the wire”.
Data transmission requires group bytes in PDUs (Protocol Data Units). The PDU adds
control information as header and tails.
application
transport
network
network
header
transport
header
user data
segment
package
i
When we talk about a “x layer thing”
we always refer to the OSI model.
i
Although... we will
use the hybrid.
data link data link
link
header
tail
frame
physical
bits
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Encapsulation
The recipe
1. Data build (from an application).
2. Segment the data for end-to-end transportation.
3. Add network addresses and build one (or several)
datagrams.
4. Add physical link address and build frames for
each datagram.
5. Code frame bits in signals that can be sent by the
physical medium.
References
B.F. Transmisión de datos y redes de comunicaciones, 3th edition 2007.
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Chapter 1
A.S. Redes de computadores. Pearson, 4th edition, 2003.
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Chapter 1: Sections 1.1 a 1.4 y 1.6
CISCO Systems. Inc. Guía del primer año. CCNA 1 y 2. Cisco Press, 2003.
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Chapter 1
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Chapter 2: Pages 39 – 69
CISCO Networking Academy e-learning.
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Modules 1 y 2.
All unlabeled figures are taken from the Wikipedia.
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CISCO Icons
Bridge hub switch
multilayer
switch
router
PC dumb terminal laptop
file server
FDDI
FDDI ring
serial line
network cloud
circuit switched
serial line
Ethernet
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