Transcript 5.1 Important of Standardization

Integrated Services Digital Network
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You do not need a modem but instead need a device called an ISDN terminal
adapter.
In this network sending voice, video and computer data and user can receive
telephone calls using the one line.
Conduct videoconferencing easily.
Designed to replace public telecom system
Wide variety of services
Entirely digital domain
First generation ( narrowband ISDN )
– 64 kbps channel is the basic unit
– Circuit-switching orientation
– Contributed to frame relay
Second generation ( broadband ISDN )
– 100s of mbps
– Packet-switching orientation
– Contributed to ATM ( cell relay )
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Disadvantages
• Your main telephone socket has to be changed
to an ISDN box by an engineer.
• Your computer has to be fitted with an ISDN
modem which is more expensive than a
standard modem.
• It is more expensive than Dial-up on a monthly
basis.
• Should you move house, you have to pay for
your telephone line to be converted back again
to a normal line.
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Asymmetric Digital Subscriber Line
• A technology that turns traditional copper
wires into fast data pipes.
• This offers internet connections up to 30
times faster than the fastest dial up
modem.
• The connections work by splitting your
phone line into two separate channels,
one for data (internet) and one for voice
(phone calls) which means you can talk on
the phone and be connected to the
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internet at [email protected]
same time.
Advantages
• Faster downloads compared to dial-up or ISDN
• No need for a second phone line - by allowing
voice and data transfer at the same time (you
can use the phone as normal while connected to
the internet).
• Because ADSL transfers data digitally it doesn't
need to convert the data from digital to analogue
and back again.
• ADSL connections are Always on, which makes
the usual long wait to connect a thing of the past
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Disadvantages
• ADSL connections are not available to everyone,
you need to be within 3 miles of an ADSL
enabled exchange.
• The hardware costs can be quite significant as
you will need a special ADSL modem and ADSL
filters to use the service, most ISPs allow you to
hire these items which can reduce the initial
cost.
• Because ADSL connections are Always on you
will need a firewall to protect your PC
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OSI( Open Systems
Interconnection Layers
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
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The Physical Layer
• Deals with transmitting raw bits over a
communication channel.
• How many volts for 1 or 0.
• How many microseconds a bit lasts.
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Data link Layer
• Break the input data up into data frames.
• Process the acknowledgement frames sent
back by the receiver.
• Solve the problems caused by damaged, lost
and duplicate frames.
• Full duplex transmission
• Physical details of interfacing with the cable.
• Handles data flow control.
• It can support Ethernet, Token Ring.
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Network Layer
• Routing packets from source to destination.
• Routes can be static or dynamic
• In broadcast networks, routing problem is
simple, so the network layer is thin.
• It contain IP address which is
connectionless Datagram protocol.
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Transport Layer
• Accept data from the session layer, split it up into
smaller units if needed, pass these to the network
layer and ensure that the all pieces arrive correctly
at the other end
• The transport layer is a true end-to-end layer, from
source to destination
• Establishing and deleting connections across the
network.
• what type of service to provide the session layer
with and ultimately, the users of the entire network
• TCP and UDP protocols
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Session Layer
• Allows users on different machines to establish
sessions between them
• A session might be used to allow a user to log into
a remote timesharing system or to transfer a file
between two machines
• Example: token management. Only the side
holding the token may perform the critical
operation.
• The Session Layer adds traffic flow and
control information, such as establishing and
terminating connections
between host
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computers
Presentation Layer
• Concerned with the syntax and semantics of the
information transmitted.
• The Presentation Layer adds formatting, display
and encryption information, such as helping to
maintain compatibility with different coding
methods and file types used on computer
systems.
• A typical example of a presentation service is
encoding data in a standard agreed upon way.
[Character strings, integers, floating-point
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Application Layer
• The application layer contains a variety of
protocols that are commonly needed.
• The application sends the continuous data
stream.
• Example: incompatible terminal type.
• Other application is file transfer (ftp) ,HTTP
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TCP/IP Protocol Stack
• The most standard protocol is the transmission
control protocol/Internet Protocol (TCP/IP).
• It has the similar protocols and functions.
• The TCP/IP protocol allows different computers
from many different suppliers which is running
different operating system.
• It is the protocol where internet is based.
• More correctly it is referred to as a protocol suite
because it is a collection of protocols
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TCP/IP and OSI Protocol Stack
Application Layer
• application: supporting
network applications
– ftp, smtp, http
Transport Layer
• transport: host-host
data transfer
– tcp, udp
Network Layer
• network: routing of
datagrams from
source to destination
– ip, routing protocols
Data link Layer
• link: data transfer
between neighboring
network elements
– ppp, ethernet, ATM
Physical
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• physical: bits “on the
wire”
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Sockets
• The combination of IP Address and port number.
• This is used in a similar way to a file, giving programs the
opportunity to exchange data across the network.
• Allows programmers to establish communication between process
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running on computers
There are two types pf sockets
Datagram: Allow a computer to send a single message
Stream: Supports ongoing data exchange between
participating processes. It has two components
IP Address
Port Number
Example:
196.102.89.124 :
80
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IP address
• Internet Protocol Address
– 4 groups of numbers ranging from 0-255,separated by
full stop.
– Every web site has a unique address known as IP
Address
– 32 bit (4-byte) binary number
Identify the network
– Like 216.183.103.150
IP address:
216.183.103.150
Identify the specific computer
Domain Name:[email protected]
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Hands-on: Find Your PC’s IP
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Click the “start” button on the taskbar
Click “Run”
Type in “cmd” to display a MS-DOS window
Type “ipconfig /all” at the prompt and press enter
key
• See who “owns” your IP address
– www.checkdomain.com
• Trace a route to your PC
– www.traceroute.org
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Ethernet
• Ethernet uses a system of sending signals called ‘Carrier
Sense Multiple Access / Collision Detect’ CSMA/CD.
• When a piece of data is to be sent, it is broken into smaller
packets, then data to be sent waits until the communication
line is clear, and then sends.
• If two different devices send at exactly the same time,
there will be a collision and the packet will become
corrupted.
• The system detects the collision and puts a stop to all
signals being sent until the communication line is clear,
devices are then able to send at random intervals, and the
destroyed packet can be resent.
• If the communication line is very busy some signals never
make it and have to be resent by the operator.
• Ethernet speeds are about 10 Mbps.
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Token Ring
• A ring network may use a Token to carry a
message from one device to another.
• The sender waits for the Token to arrive, sticks
the message on to it and the Token goes around
the ring visiting every device until the message
finds its destination.
• Occasionally the Token may get lost and if it
travels around the ring a second time it gets
destroyed and a new one created.
• The system avoids collisions as only one Token
is allowed on the network, it is also fair as busy
devices are serviced the same as less busy
ones.
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