Transcript Relationship between bandwidth and the transmission

Telecommunications and the
Internet
Chapter 4
The Role of Telecommunications
and Networks in Organizations
• Definitions
– Telecommunications – the transmission of all forms of
information, including digital data, voice, fax, sound,
and video, from one location to another over some type
of network
– Network – a group of computers and associated
peripheral devices connected by a communication
channel capable of sharing information and other
resources (e.g., like a printer) between users
– Bandwidth – the carrying capacity of
telecommunications networks
Types of Networks
• Computer networks are commonly classified by
size, distance covered, and structure.
• The most commonly used classifications are:
– PBX (Private Branch Exchange)
– LAN ( Local Area Network)
– WAN ( Wide Area Network)
– MAN ( Metropolitan Area Network)
– PAN ( Personal Area Network)
Private Branch Exchanges
• A private branch exchange (PBX) supports local phone
and data communications, as well as links to outside
phone and data networks.
• PBX is a special-purpose computer designed for
handling and switching office telephone calls at
company site.
• PBX can store, transfer, hold, and redial telephone
calls.
• Since they use ordinary telephone lines, PBX systems
have limited bandwidth.
• The advantage of digital PBX over local networking is
that PBX does not need special wiring.
Local Area Network
Server
Network
Operating
System
Computer1
Other
Network
Network
Gateway
Computer2
Printer
Computer3
Local Area Network
• LAN is used to connect PCs or resources (e.g. printers) in one
building or several buildings in close proximity.
• LAN has higher transmission capacity than PBX (Private Branch
Exchange).
• LAN can transmit video and graphics.
• LAN is more expensive to install than PBX and less flexible. It
requires new wiring each time a LAN is moved.
• The server acts as a librarian. It stores programs and data files for
network users. The server determines who will get access to what
and in what sequence.
• Sever can be powerful PCs with large hard-disk capacity,
workstations, minicomputers, or mainframes.
• The network gateway connects the LAN to public networks, such
as the telephone network, or to other corporate networks.
Local Area Network
• A gateway is a communications processor that can
connect dissimilar networks by translating from
one set of protocols to another.
• LAN can use twisted wire, coaxial , or fiber-optic
cable.
• LAN also can use wireless technology.
• The network operating system (NOS) can reside
on every computer in the network, or it can reside
on a single server.
• The NOS routes and manages communications on
the network and sharing of network resources.
Wide Area Network
• It spans a broad geographical distance, ranging from
several miles to the span of entire continent.
• WAN may consist of a combination of switched and
dedicated lines, microwave, and satellite
communications.
• Switched lines are telephone lines that a person can
access from his or her terminal to transmit data to the
designated destination.
• Dedicated lines are continuously available for
transmission. This lines can be leased or purchased
from a common carriers or private communications
media vendors.
• Most WANS are switched.
Metropolitan Area Networks (MAN)
• Computer network of limited geographic
scope, within a city.
• MAN is a better option for organizations
that need high-speed data transmission
within a limited geographic area.
Personal Area Networks (PAN)
• It uses wireless communication to exchange
data between computing devices using
short-range radio communication (10 m).
• It uses Bluetooth technology, a new
technology.
• Uses for networking of desktop computers,
pagers, portable devices, mobile phones,
and other handheld devices.
Network services: Value-Added
Networks (VANS)
• Networks can be classified by types of service they provide.
• Value-added networks are private, multipath, data-only, thirdparty-managed network that is used by multiple organizations on
a subscription basis.
• The VAN is set up by a firm that is in charge of managing the
network.
• The subscribers pay only for the amount of data they transmit
plus a subscription fee.
• Customers do not have to invest in network equipment and
software or perform their own error checking, editing, routing,
and protocol conversion.
• The network can use twisted-pair lines, satellite links, and other
communication channels leased by the value-added carrier.
Switching Techniques
In large networks there might be multiple paths
linking sender and receiver. Information may be
switched as it travels through various communication
channels. There are three typical switching techniques
available for digital traffic.
• Circuit Switching
• Message Switching
• Packet Switching
Circuit Switching
• Circuit switching is a technique that directly
connects the sender and the receiver in an unbroken
path.
• Telephone switching equipment, for example,
establishes a path that connects the caller's telephone
to the receiver's telephone by making a physical
connection.
• With this type of switching technique, once a
connection is established, a dedicated path exists
between both ends until the connection is terminated.
• Routing decisions must be made when the circuit is
first established, but no decisions are made after that
time.
Circuit Switching
• Circuit switching in a network operates almost the
same way as the telephone system works.
• A complete end-to-end path must exist before
communication can take place.
• The computer initiating the data transfer must ask for
a connection to the destination.
• Once the connection has been initiated and completed
to the destination device, the destination device must
acknowledge that it is ready and willing to carry on a
transfer.
Circuit switching
Advantages:
• The communication channel (once established) is dedicated.
Disadvantages:
• Possible long wait to establish a connection, (10 seconds,
more on long- distance or international calls.) during which
no data can be transmitted.
• More expensive than any other switching techniques,
because a dedicated path is required for each connection.
• Inefficient use of the communication channel, because the
channel is not used when the connected systems are not
using it.
Message Switching
• With message switching there is no need to establish a
dedicated path between two stations.
• When a station sends a message, the destination address is
appended to the message.
• The message is then transmitted through the network, in its
entirety, from node to node.
• Each node receives the entire message, stores it in its entirety
on disk, and then transmits the message to the next node.
• This type of network is called a store-and-forward network.
Message Switching
A message-switching node is typically a general-purpose
computer. The device needs sufficient secondary-storage
capacity to store the incoming messages, which could be long.
A time delay is introduced using this type of scheme due to
store- and-forward time, plus the time required to find the next
node in the transmission path.
Message Switching
Advantages:
• Channel efficiency can be greater compared to circuitswitched systems, because more devices are sharing the
channel.
• Traffic congestion can be reduced, because messages may be
temporarily stored in route.
• Message priorities can be established due to store-and-forward
technique.
• Message broadcasting can be achieved with the use of
broadcast address appended in the message.
Message Switching
Disadvantages
• Message switching is not compatible with interactive
applications.
• Store-and-forward devices are expensive, because they
must have large disks to hold potentially long messages.
Packet Switching
• Packet switching can be seen as a solution that tries to combine the
advantages of message and circuit switching and to minimize the
disadvantages of both.
• There are two methods of packet switching: Datagram
and virtual circuit.
Packet Switching
• In both packet switching methods, a message is broken into
small parts, called packets.
• Each packet is tagged with appropriate source and destination
addresses.
• Since packets have a strictly defined maximum length, they
can be stored in main memory instead of disk, therefore access
delay and cost are minimized => store-and-forward networks.
• Also the transmission speeds, between nodes, are optimized.
• With current technology, packets are generally accepted onto
the network on a first-come, first-served basis. If the network
becomes overloaded, packets are delayed or discarded
(``dropped'').
Packet Switching
(16 bits)
Start
Framing (64 bits)
(16 bits)
Header Text
(24 bits)
End
Error
Framing Control
Check
Bits
Message Destination
No.
Source Link
No.
Packet No.
Data are grouped into small packets, framed by identifying information,
which are transmitted independently via various communication
channels to maximize the potential of the paths in a network.
Frame relay
• A shared network service.
• It is faster and less expensive than packet switching.
It can achieve transmission speed upto 1.544
megabits per second.
• Frame relay packages data into frames that are similar
to packets.
• But it does not perform error correction.
• It works well on reliable lines that do not require
frequent retransmission because of error.
Asynchronous Transfer Mode (ATM)
• ATM is a method of transmitting voice, video, and data
over high-speed LAN. It is well accepted in LAN &
WAN
• ATM technology parcels information into uniform
cells, each with 53 groups of eight bytes, eliminating
the need for protocol conversion.
• It can seamlessly and dynamically switch voice, data,
images, and video between users.
• It can pass data between computers from different
vendors.
• It permits data to be transmitted at any speed the
network handles. ATM can transmit up to 2.2 GBPS.
• It can connect LAN and WAN together more easily.
The Internet
• How Fast Is Your Connection?
– Plain Old Telephone Service (POTS/PSTN): 52 kbps
– Integrated Services Digital Network (ISDN): operates
on existing copper telephone line. Replaces analog sys
– Digital Subscriber Line (DSL): operates on existing
copper telephone line. 32 Mbps (down link), 32 kbps
to 1 Mbps (uplink)
– Cable Modems: operates on cable TV lines. 2 Mbps
– Satellite Connections
– T1 Lines: Can carry up to 1.544 Mbps, T3 lines: 45
Mbps
– Asynchronous Transfer Mode (ATM): 2.2 Gbps
Internetworking, Connectivity & Open System
• Internetworking => The linking of separate networks,
each of which retains its own identity, into an
interconnected network.
• Connectivity => The ability of computers and
computer-based devices to communicate with one
another and share information in a meaningful way
without human intervention.
• Open Systems => Open systems promote connectivity
because they can operate on different hardware
platforms. They are built on public non-proprietary
operating systems, user interfaces, application
standards, and networking protocols.
Models of Connectivity for Networks: TCP/IP
Host A
Host B
Application
Application
Identical
message
Transport (TCP)
Internet Protocol
(IP)
Network
Interface
Transport (TCP)
Identical
message
Identical
datagram
Identical
frame
Physical net
Internet Protocol
(IP)
Network
Interface
Open System Interconnect (OSI)
• This model is an alternative model developed by the
International Standards Organization for linking
different types of computers and networks.
• It is designed to support global networks with large
volume of transaction processing.
• Like TCP/IP , OSI enables a computer connected to a
network, regardless of the manufacturer, by establishing
communication rules that permit the exchange of
information between dissimilar systems.
• OSI divides the telecommunications process into seven
layers.
Electronics Commerce & its applications
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•
•
•
•
Electronic mail
Voice mail
Facsimile Machine (fax)
Digital Information Services
Teleconferencing, Dataconferencing, and
Videoconferencing
• Groupware: The leading commercial groupware
product has been Lotus Notes from Lotus
Development Corporation.
– Group writing and commenting, e-mail distribution,
scheduling meeting and appointments, shared files and
databases, shares timelines and plans, electronic meeting