Transcript ECT 250: Survey Of e-commerce Technology

ECT 250: Survey of e-commerce technology
Networking
Networking
In a network, communications equipment is used
to connect two or more computers allowing the
sharing of various hardware, software, and data
resources.
The basic components of a data communications
systems used to transmit information are:
• A sending device
• A communications link, consisting of both
communications hardware and software.
• A receiving device
2
Data transmission
Binary information is represented by the presence
or absence of an electronic pulse. This is referred
to as digital signaling.
Some communications devices in place today were
designed for voice data which uses analog signals.
Data communications systems may use these
existing lines.
3
Piggybacking technology
If the wires in place for communication use analog
signals, digital data must be converted to an analog
signal in order to be transmitted.
•The digital signal is transformed into an analog
wave in a process called modulation.
•The analog wave is transmitted.
•The analog signal is converted back into a digital
signal during a process called demodulation.
4
Modems
A modem is the hardware device that does these
conversions. (Short for modulate/demodulate).
Modem speeds are referred to by the number of
bits per second (bps) at which they can transmit
and receive data.
• The earliest modems has speeds around 300 bps.
• Later modems had speeds ranging from 9600
to 33,600 bps.
• Today modems have speeds of 56,000 bps (or
56 Kbps).
5
Communication links
A communications link is the physical medium
used for transmission of data.
There are several kinds:
• Wire pairs/twisted pairs
• Coaxial cables
• Fiber optics
• Microwave transmission
• Satellite transmission
6
Wire pairs
Sometimes called twisted pair, this media uses
wire pairs twisted together to form a cable. The
cable is then insulated.
Wire pairs are popular since this form of cabling
is already installed and available in most places
(telephone cabling).
It is, however, susceptible to electrical interference,
called noise.
7
Coaxial cables
A coaxial cable is a single conductor wire that is
thickly shielded.
• It sends a very powerful signal.
• It is used for cable television.
• These cables can transmit data at a very fast
rate.
Bundles of these cables can be laid underground
or under the sea.
8
Fiber optic cables
Fiber optic cables use light instead of electricity
to transmit data.
• The cables are made of ultra thin glass wires.
Light beams can be transmitted for miles with
little attenuation (reduction in signal strength).
• This media can handle many different types
of information including voice and data at the
same time.
9
Microwave transmission
In microwave transmission the signals are wireless
and can travel through the atmosphere.
Signals can, however, be blocked by the curvature
of the earth. (Line of sight transmission)
To prevent this, relay stations are located in high
areas and are used to retransmit data to other relay
stations.
10
Satellite transmission
The basic components of satellite transmission:
• Earth stations: Send and receive signals.
• Transponder: Receives a transmission from
an earth station, amplifies the signal, changes
the frequency, and retransmits the data to the
receiving earth station.
The entire process takes only a few seconds.
Communications satellites are positioned in a
geosynchronous orbit.
11
Internet service providers
• Internet access providers or Internet service
providers offer individuals and companies
access to the Internet.
• There are typically several connection options.
• The primary difference between various ISPs
is the connection bandwidth (the amount of
data that can travel through a communication
line in a given unit of time) available.
12
Connection terminology
• The traffic on the Internet and the ISP can affect
the net bandwidth (the actual speed at which
information travels taking traffic into account).
• Upstream, also called upload, occurs when
information is sent from you to the ISP.
• Downstream, called download or downlink, occurs
when information flows to your computer from
the ISP. Example: Web page download.
• Upstream bandwidth differs from downstream
bandwidth for satellite and cable connections.
13
Telephone service
• POTS uses existing telephone lines and an analog
modem to provide a bandwidth of about 56Kbps.
• Higher grades of service use the Digital Subscriber
Loop (DSL) protocol.
These include:
– Integrated Services Digital Network (ISDN),
available since 1984.
– Asymmetric Digital Subscriber Line (ADSL)
– Symmetric Digital Subscriber Line (SDSL)
Upstream: 16 to 640 Kbps
Downstream: 1.5 to 9 Mbps (million bps)
14
Cable connections
• Cable modems connect to the same coaxial cable
that serves television.
• It is connected via twisted pair wire to a PC and
provides a cost-effective and high bandwidth
connection to an ISP.
• Upstream: 768 Kbps
• Downstream: 10 Mbps
• Cable bandwidths vary with the number of users.
15
Higher bandwidth options
• Large firms with high traffic connect to an ISP
using higher bandwidth telephone connections.
– T1: Operates at 1.544 Mbps
– T3: Operates at 44.7 Mbps
These connections are more expensive than the
previous options.
• Network access providers use T1 and T3 lines as
well as Asynchronous Transfer Mode (ATM)
connections with bandwidths up to 622 Gbps.
16
Price and speed comparisons
• When making decisions about Internet connections
you must consider:
– Bandwidth needed
– Cost of startup
– Monthly fees
– Traffic issues
• There is a chart comparing features between various
options on page 72 of the text.
• Depending on where you live, you may have other
options, such as satellite connections.
See the e-commerce links and sites.
17
Types of networks
Networks can be classified according to their
geographical reach.
• Local area network
• Metropolitan area network
• Wide area network
18
Wide-area network
A wide area network (WAN) is a network of
computers, terminals, and peripheral devices
that is located over a very large area.
• It can span a state, country, or the world.
• The central hubs or servers are usually
powerful minicomputers or mainframes.
(The server is usually referred to as the
host computer).
• A single WAN may use a variety of
transmission methods.
19
Local-area network
A local area network is a collection of computers
that share hardware, software, and data over a
shorter geographical area than a WAN.
(Usually limited to a single building or compound).
A LAN can also be very small.
Example: LAN in my apartment contains one PC,
one printer, and two laptops.
20
Purposes for networks
Networks can also be classified according to
their purpose:
1. Internet
2. Intranet
3. Extranet
21
Intranets
• Only selected individuals can use an intranet.
Example: CTI Intranet
• Intranets are a popular and inexpensive way to
distribute information.
• Intranets typically use existing infrastructure.
• Benefits include timely and current information
delivery, cheaper internal communication, low
maintenance costs, and easy on-line training.
22
Extranets
• Extranets provide the private infrastructure for
companies to coordinate their purchases,
exchange business documents, and communicate
with each other.
• Some start out as intranets and become available to
people outside the institution in an effort to reduce
the workload for employees. Example: FedEx
• There are three types of extranets:
– A public network
– A secure (private) network
– A virtual private network (VPN)
23
Public network
• A public network extranet is one which can be
accessed by the public or one in which two or
more companies agree to link their intranets
using a public network.
• Security is an issue in this configuration.
• This type of extranet is uncommon because of
the risk.
24
Private network
• Uses a private, leased-line connection to connect
two companies.
• A leased line is a permanent, dedicated telephone
connection between two points. The line is
always active.
• This arrangement is significantly more secure.
• The big drawback is the cost.
• This type of arrangement does not scale well since
each new company requires another leased line.
25
Virtual private network
• A VPN uses public networks but through a system
called tunneling or encapsulation.
• Tunnels are private passageways through the public
Internet that provide secure transmission from one
partner to another.
• Separate security shells are used with the most
sensitive data under the tightest controls.
• VPNs establish short-term connections in real time
that are broken once the session ends.
• This arrangement is inexpensive and scales well.
26
Protocols
A protocol is a set of rules for the exchange of
data across communication lines.
Because telecommunications systems use a wide
variety of hardware and software, protocols are
needed to coordinate communication.
What kinds of issues do protocols need to handle?
27
Tasks for protocols
Protocols need to handle the following tasks:
• Identify the different devices in the communications path.
• Establish the speed and method for transmission of data.
• Alert the receiving device to the incoming data.
• Define the method for the receiving device to confirm the
receipt of the data.
• Determine the methods of error checking and correction.
Common Internet protocols include TCP/IP, SMTP,
POP, IMAP, FTP, and HTTP. We will discuss each
of these in more detail later.
28