Transcript Week 1 - cda college

COM211 Communications and Networks
CDA College
Pelekanou Olga
Email: [email protected]
www.cdacollege.ac.cy/site/info-com-technology-ll/
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Lecture 1: Introduction to Computer Networks, OSI Model
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Lecture 2: Hardware building blocks and encoding
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Lecture 3: Physical Media and Cabling
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Lecture 4: Protocols
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Lecture 5: LAN and WAN Technologies
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Lecture 6: Data Link Layer and Ethernet
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Lecture 7: Midterm
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Lecture 8: Network Layer of OSI
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Lecture 9: Transport Layer of OSI
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Lecture 10: Application Services
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Lecture 11: Security in Computer Networks
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Lecture 12: Wireless Networks
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Lecture 13: Revision for the Final examinations
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Andrew S. Tanenbaum, Computer Network,
Prentice-Hall
Doughlas E. Comer, Computer Networks and
Internet
Larry L. Peterson and Bruce S. Davie,
Computer Networks: A Systems Approach
A collection of autonomous computers
interconnected by a single technology.
Two computers are said to be interconnected
if they are able to exchange information.
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Interconnect machines.
Maintain data confidentiality, data integrity,
and system accessibility.
Support growth by allowing more and more
computers, or nodes, to join in (scalability).
Support increases in geographical coverage.
Is not a single network but a network of
networks
Each node needs one interface for each link.
(a)
point-to-point
(b)
multiple-access
Geographical coverage and scalability are limited.
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Transmission technology
◦ Broadcast links
◦ Point – to – point links
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A single communication channel that is
shared by all the machines on the
networks
Packets (short messages) sent by any
machine are received by all the others
The machines ignored or processes the
packet from the address field
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Broadcasting: addressing a packet to all
destinations
Multicasting: transmission to a subset of
the machines
Unicasting: one sender and one receiver
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Consist of many connections between
individual pairs of machines
To go from the source to the destination,
a packet may have first visit one or more
intermediate machines
Often multiple routes, of different lengths,
are possible
◦ Find the good ones
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As a general rule
◦ Smaller geographically localized networks tend
to use broadcasting
◦ Large networks usually are point – to -point
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Defines the way in
which computers,
printers, and other
devices are connected
Describes the layout
of the wire and
devices as well as the
paths used by data
transmissions.
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This topology connects
all devices to each other
for redundancy and
fault tolerance
It is used in WANs to
interconnect LANs and
for mission critical
networks (banks,
financial institutions,
etc.)
Implementing the mesh
topology is expensive
and difficult
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All the devices on a bus topology are
connected by one single cable.
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The star topology is
the most commonly
used architecture in
Ethernet LANs.
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Larger networks use the
extended star topology
also called tree topology.
When used with network
devices that filter frames
or packets, like bridges,
switches, and routers,
this topology
significantly reduces the
traffic on the wires by
sending packets only to
the wires of the
destination host.
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A frame travels around the ring, stopping at
each node. If a node wants to transmit data,
it adds the data as well as the destination
address to the frame.
The frame then continues around the ring
until it finds the destination node, which
takes the data out of the frame.
Types:
 Single ring – All the devices share a single cable
 Dual ring – Allows data to be sent in both directions
and provides redundancy
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Physical Media
Network Devices
Computers
Protocols
Services
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Twisted Pair
Coaxial
Fiber Optics
Wireless Transmissions
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Hub
Switches ( Level 2 and 3 )
Routers
Wireless Access Points
Modems
NIC’s
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End Devices: Acts as a source/destination.
For message transmitting or receiving.
Server: In a client/server network
environment, network services are located
in a dedicated computer whose only
function is to respond to the requests of
clients. The server contains file sharing,
http and other services that are
continuously available to respond to client
requests.
Client: Our computers. We request a service
from a server (ex. We log into gmail to
check our email )
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A protocol, in contrast, is a set of rules
governing the format and meaning of the
packets, or messages that are exchanged
by the peer entities within a layer. Entities
use protocols to implement their service
definitions. They are free to change their
protocols at will, provided they do not
change the service visible to their users.
TCP, UDP, IP, X.25, ICMP, IPSec
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DHCP - Dynamic Host Configuration
Protocol
DNS – Domain Name System
HTTP - Hypertext Transfer Protocol
SSH – Secure Shell
Telnet
SNMP - Simple Network Management
Protocol
SMTP - Simple Mail Transfer Protocol
FTP – File Transfer Protocol
IRC – Internet Relay Chat
POP – Post Office Protocol
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To interconnect two or
more networks, one needs a
gateway or router. Host-tohost connectivity is only
possible if there’s a uniform
addressing scheme and a
routing mechanism.
Messages can be sent to a
single destination (unicast),
to multiple destinations
(multicast), or to all
possible destinations
(broadcast).
Divide time into equal-sized quanta and
assign each them to flows on the physical link
in round-robin fashion.
Flows are transmitted simultaneously on the
link, but each one uses a different frequency.
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Flows are transmitted simultaneously on the
link, but each one uses a different coding
scheme.
For a chosen group of nodes, a unique
coding scheme can be used. Each bit is
encoded in multiple pulses. Multiple
senders may use the same time slots with
different coding.
Flow is broken into packets and sent
to a switch, which can deal with the
arriving packets according to the
switch policy (FIFO, round-robin, etc).
Computer A
Computer B
queue
switch
Computer C
Computer networks can be classified according to their geographical
coverage:
In Interconnecting multiple networks (internetworking), we are
interested in the seamless integration of all these levels. Have in mind
that different levels use different technologies!
• LAN: local area network
• WLAN: wireless local area network
• MAN: metropolitan area network
• WAN: wide area network
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Privately-owned networks
Within a single building or campus of up
to a few kilometers in size
Covers a city
A large antenna send the signal to the
host
Large geographical area
Often a country or continent
Application
The protocol stack:
The idea behind the model: Break up the
design to make implementation simpler.
Each layer has a well-defined function.
Layers pass to one another only the
information that is relevant at each level.
Communication happens only between
adjacent layers.
Presentation
Session
Transport
Network
Data link
Physical
• Physical: Transmit raw bits over the medium.
• Data Link: Implements the abstraction of an error free medium (handle
losses, duplication, errors, flow control).
• Network: Routing and Addressing. IP
• Transport: Break up data into chunks, send them down the protocol
stack, receive chunks, put them in the right order, pass them up.
• Session: Establish connections between different users and different
hosts.
• Presentation: Handle syntax and semantics of the info, such as
encoding, encrypting.
• Application: Protocols commonly needed by applications (cddb, http,
ftp, telnet, etc).
sender
receiver
data
data
AH
Application
PH
Presentation
data
Application
data
Presentation
Session
SH
data
Session
Transport
TH
data
Transport
Network
NH
data
Network
Data link
Physical
DH
data
BITS
DT
Data link
Physical
Application
Presentation
FTP
HTTP
DNS
NFS
…
Session
Transport
ICMP
Network
TCP
UDP
IGMP
IP
ARP
Data link
Physical
RARP
Questions??