Network Applications Fax, Voice, and Information Services Person to Person Communications Group Communications Exchanging Files
Fax
A facsimile machine is a telephone copy machine
FAX FAXPrintout to printout
Computer ComputerDigital to digital
FAX ComputerPrintout to digital
Computer FAXDigital to printout
Fax-back services You dial their number, answer a few
questions by pressing numbers on your phone, and hang up. The company’s fax machine then automatically send you a fax of the information you requested.
Your phone
Your fax Fax-back Service
Voice mail Automates phone answering and
messaging Sophisticated systems have an
automated attendant that routes you to the right person when you press the keys of a touch-tone phone
Now, it’s even possible to leave video voice mail
On-line services Networks were introduced at home through
the large commercial information services such as CompuServe, AOL, and Microsoft Network.
You can locate important information or exchange e-mail with other subscribers
You can post messages on forums Type messages back and forth in chat mode
Person to Person Communications
Electronic mail E-mail makes it possible to have
almost instantaneous communication Cost is low More convenient
User name Domain name
Electronic mail When you send a message, it is stored
on a computer somewhere until the addressee reads it. This process is called store and forward
Message sent and stored
Message retrieved
09:00 A.M. 10:00 A.M.
Electronic mail E-mail software is used to write, read,
and file messages
E-mail software courtesy of Microsoft
E-mail etiquette Don’t ever write and send nasty notes
impulsively Don’t ever refer to third parties in an
unflattering way Be careful of inflections, nuances, and sarcasm Don’t ever use your company’s name in
personal postings outside the company Try to act as civilized as possible – and do unto
others as you would have them do unto you
Emoticons:-) means “I’m smiling”<s> or <g> indicates a smile or grin:-( means “I’m sad or unhappy”;-) means “I’m saying this in jest”:*) means clowning:-& means tongue tied;-/ means skeptical:-\ means undecided:-| means ambivalent|-o means boredUse all uppercase letters WHEN YOU WANT TO SHOUT
OUT
Group Communications Newsgroup Mailing lists Internet relay chat (IRC) Network games Video conferencing
Newsgroup Usenet (Users Network) is a collection of
thousands of ongoing topical discussions called newsgroup
Also known as bulletin boards or discussion groups, newsgroups are used by people to share common interests
Usenet is not a part of the Internet, or even a network of any kind
It ’s a system for carrying on discussions that can be delivered in a number of ways, the Internet being just one of them
Mailing lists Mailing lists use e-mail to keep groups
informed on topics or events they wish to know about such as when a particular Web site has been updated
As you get more involved with the Internet, you may find yourself the recipient of a mass-mailing called a spam
Internet relay chat (IRC) IRC allows you to chat with other
users in real-time Any user with IRC software can go to
an IRC computer called an IRC server, create a channel on some topic, and invite others to join in
Network games The first popular games were text-
based The most popular are MUDs (multiuser
dialogue) and their variants such as MOOs – object-oriented MOOs
Graphical games are becoming more popular
Network games hongkong.gameeast.com hk.games.yahoo.com www.microsoft.com/games/empires Igz2.microsoft.com
Exchanging Files Uploading and downloading ASCII and binary files Shared disks FTP on the Internet Binary files as e-mail attachments
Uploading and downloading
Uploading means you are sending the file to another system
Downloading means you are transferring a file from another computer to yours
Your computer Any other computer
Upload
Download
ASCII files ASCII files contain only a limited set of
characters and have almost no formatting
They are easy to transfer because of their simplicity
Binary files Binary files have lots of formatting and
much of it is specific to the program that created the file
A picture, a video, a word processing document, a spreadsheet, a database, an animation, or an executable program don’t transfer easily between the networks that use different protocols before being converted with a messy process
Shared disks It’s as easy as moving or copying a file
to a public folder. Friends or coworkers can then move it
from there to one of their own folders
Shared disk
FTP on the Internet FTP (File Transfer Protocol) is the
Internet tool used to transfer files form one machine to another
ftp://ftp.loc.gov/pub/american.memory/
FTP on the Internet Normally you would need a password
to log onto the system However, using anonymous ftp, you
can browse through computers that allow you to do so by using the name anonymous to log on
Binary files as e-mail attachments
One of the most convenient ways to transfer files is as attachments to e-mail messages
If you are sending it across the Internet to a different network, the message will pass through other computes called gateway that may not be compatible
Binary files as e-mail attachments
Binary attachments may be corrupted Needed to use a program to convert
the them to an ASCII text file. This is called encoding
The recipient muse use a similar program to convert it from ASCII back to binary, decoding
2 dominant encoding schemes in use
UUcoding (binary to ASCII) and Uudecoding (ASCII to binary)– They were originally developed for UNIX-to-
UNIX e-mailing MIME (multipurpose Internet Mail
Extension)– Uses a form of encoding called “Base64”
which has been better designed to allow messages to pass through a network’s various e-mail gateways
Local Area Networks (LAN)
Networks of computers within a small area are called LANs
Network resources– The whole is greater than the sum of its parts– E-mail– Sharing peripherals– Sharing files– Groupware– Network applications
Network resources E-mail
– The sending of messages to others on the network
Sharing peripherals– Share expensive peripherals such as plotters,
laser printers, and hard disk drives Sharing files
– Share or exchange files with other users on the network
Network resources Groupware
– Groupware have been developed to make team or group activity easier
– A typical groupware application is a common calendar on which anyone can make entries that others can see
– Another is a document anyone can add to or change while others can see who is making the changes
Network resources Network applications
– The application rests on a computer somewhere on the network, not on your own machine
– You transfer it to your system when you want to see it
– A company has to fix or upgrade only one copy on the network
– Often written in languages such as Java or ActiveX for Internet
Network users To use a network, you first log on with an ID and
a password The ID is assigned by the network administrator The password is selected by you and can (and
should) be changed frequently to improve security
Normally you’ll find printers, hard disks, and other shared assets listed on your system’s dialog boxes even though they are located elsewhere on the network
Network administrators Systems organized into a network are
supervised by a network administrator/manager
The network manager/administrator is responsible for:– Setting up or enforcing network procedures– Adding and removing users– Assigning Ids and levels of access– Troubleshooting problems should users arise and
assisting both new and experienced users with problems
Network administrators One user may be authorized access to
correspondence files but denied access to financial analysis files
Some users can be given just read-only access, whereas others can be allowed to enter and update the files
Passwords Don’t share your password with anyone Hard to guess. E.g. mix letters with numbers Don’t use a password that is your address, pet’s name,
nickname, spouse’s name, telephone no., or one that is obvious such as sequential numbers or letters
Longer password, more secure. Six to eight characters is realistic
Password is not visible on the computer screen when you enter it
Password does not appear on printouts Don’t tape passwords to desks, walls, or terminals.
Commit yours to memory
Network’s Topologies Computers and other devices can be
connected to form a LAN in several ways These connections are the network’s
architecture or topology A network’s architecture is the way the
data flows within the network, not to the way its parts are physically arranged in an office
Basic network architecture/topology
Node– A node is any piece of hardware on the system
that can be addressed by a message from another node, that is, a computer, printer, fax, modem, or CD-ROM drive
Hub– Nodes are connected to a hub / concentrator,
whose purpose is to simplify the wiring of the nodes to each other and to route signals between the nodes
Basic network architecture/topology
Backbone– A backbone is a high-capacity link to which
many nodes or hubs can be connected. It’s designed to carry lots of traffic
Node 1
Node 2
Node 3
Hub HubBackbone
Node 4 Node 5
Servers A server on a LAN is any computer
that can be shared by other computers working on the LAN
In many cases, the server has to be the most powerful computer on the network
It is shared among so many users, or clients
Clients Computers depend on the server for
programs and data, or connections to other computers and devices
File server Stores data files and some
applications programs Large amounts of secondary storage
in the form of hard disks, CD-ROM drives, tape drives, and other storage devices
Communication server Can be a fax or modem over which
from any other node can be sent It can also be used as a gateway to
the InternetClient
Client
ClientServer
Server
Star topology Star topology has the nodes connected to
a central, or host, computer or a central hub
When one of the computers on the network sends signal, the host routes it to the node it’s addressed to
There are no direct connections between the nodes on the network except through the host computer
Star topology Advantages:
– Star topology are relatively easy to install and manage– it's easy to add and remove nodes– one malfunctioning node doesn't affect the rest of the
network Disadvantages:
– they require more cabling than other topologies– bottlenecks can occur because all data must pass
through the central hub– if the central computer fails, the entire network
becomes unusable
Bus topology Bus, or linear, topology connects all
nodes to a single bus / backbone, much as the components are organized within the computer
A signal addressed to another node is sent to the bus
All other nodes on the network examine the signal to see if it is addressed to one of them
Bus topology Typically, wires connect each node to the
network’s backbone, which is a fixed length of cable with terminators at both ends to stop reflections when signals hit the end
Bus topology Advantages:
– are relatively inexpensive and easy to install for small networks
– one malfunctioning node doesn't affect the rest of the network
Disadvantages:– are relatively slow– Terminators are required to connect at
the both ends
Ring topology Ring topology arranges the nodes on the
network in a circle When one of the computers on the networks
sends a signal, it passes it to the next node on the network
If it is not addressed to that node, it is retransmitted to the next node and so on around the circle until it reaches the node it is addressed to
Ring topology The connections between computers
are not direct; instead, each computer attaches to a hub and the ring itself resides inside the hub
Ring topology Advantage:
– they can span larger distances than other types of networks, such as bus networks, because each node regenerates messages as they pass through it
– offer high bandwidth and can span large distances
Disadvantage:– are relatively expensive and difficult to install
Peer-to-peer networks Relatively easier and less expensive to set
up and administer the networks Set up and run by users All computers are equals Data do not pass through a server You could be working on a spreadsheet on
your computer while it was also routing print jobs from all of the other computers to your laser printer
Client/server vs. peer-to-peer networks
server
client client
Client/server network Peer-to-peer network
Wireless LANs Connected by signals through the air instead of by
wires The base station connected to the network broadcasts
to individual computers They eliminate the need to run cabling through an old
building The benefits of using wireless LANs:
www.nokia.com/corporate/wlan/benefits.html(for business reference only)
Other references:www.nokia.com/corporate/wlan/index.html
The System Network interface card (NIC) Physical links between devices
– Twisted-pair wires (STP and UTP)– Coaxial cables– Fiber-optic cables
Media access control (MAC) Ethernet Token ring
Network interface cards (NIC)
A network interface card (NIC), or LAN adapter, plugs into a slot in the computer to connect it to the LAN
On laptops, credit-card-sized NICs slip into bus slots on the machines
Wireless LAN PC card
Laptop LAN card PCI LAN cardNIC courtesy of 3Com
Network interface cardsAn NIC serves a number of purposes: It makes the physical connection or bridge
between the computer and the network It converts the parallel data on the
computer’s bus into serial data for the network
It boots or amplifies the signal’s strength so it can flow through the cables
Physical links between devices
Twisted-pair wires– STP (shielded twisted-pair)
STP is used in noisy environments where the shield protects against excessive electromagnetic interference
– UTP (unshielded twisted-pair) Coaxial cable Fiber-optic cable / Optical fiber
Twisted-pair wires the ordinary copper wire that connects
home and many business computers to the telephone company.
two insulated copper wires are twisted around each other to reduce crosstalk or electromagnetic induction between pairs of wires
Twisted-pair wires Advantages:
– Cheap– Easy to install
Disadvantages:– Relatively slow– Tendency to pick up noise that can cause
high error rates
Coaxial cables Like those in your cable TV system are
layered with an inner wire surrounded by an insulating material that is, in turn, surrounded by a braided wire
This braided wire shields the inner wire from any noise in the environment that can affect the quality of the transmission
Coaxial cables
Coax is a two-wire cable. The inner wire is the primary conductor, and the metal sheath is used for ground
Coaxial cables Reliable Have a wider bandwidth than twisted-
pair wires Much faster than twisted-pair wires
Fiber-optic cable Are made of plastic or glass fibers the
thickness of a human hair and covered with an opaque sheath that keeps light from entering or escaping
The digital signals from a computer are used to code pulses of a light beam that carry information read at the receiving end
A single hair-thin fiber is theoretically capable of supporting 100 trillion bits per second
Fiber-optic cable Fast Reliable Light allow longer distances to be spanned
without repeaters more secure, because taps in the line
can be detected But more difficult to install
Media access control (MAC)
A LAN needs an MAC scheme to prevent any overlapping signals
The NIC determines the access method used by the network
The two most popular access methods are Ethernet and token-ring
Ethernet The first network access system was
developed by Xerox in the 1970s to link computers to laser printers
Employs Carrier Sense Multiple Access/Collision Detection (CSMA/CD)
All nodes listen to the traffic on the network and try to send data only when it’s quiet
Ethernet If two nodes transmit at the same time,
they detect the collision, and all nodes go quiet for a short, random period before attempting to resend the data
Since the periods are random, one node will send first and gain control of the network
Ethernet The three most popular
implementations of Ethernet are:– 10Base-5– 10Base-2– 10Base-T
10Base-5
10 MHz
Based on Ethernet
0.5-inch thick coax
Twisted pair
Ethernet Ethernet can use any of the network
topologies, star, bus, or ring 10Bae-5 and 10Base-2 use a bus
topology 10Base-T uses a star topology
Ethernet Gigabit Ethernet delivers data at
gigabit speeds making it possible to deliver multimedia applications over the network
Fast Ethernet operating at 100 megahertz is being widely installed
Token ring Token ring networks are more orderly Nodes cannot address the network
without first obtaining permission in the form of an electronic token that circulates around the network
Token-ring networks use a ring topology
STP or UTP wiring are used
Token ring Advantages:
– The sending node always gets confirmation that its data was received
– It always guarantees that the next node on the network gets access when a transmission is complete
Token ring model1. A free token circulates through the
network
2. A node wanting to send data grabs the token when it arrives, changes it to a message with an address to another node and resends it out onto the network
3. Each node in the network looks at the circulating message and if it’s not addressed to it, puts it back into circulation
Token ring model4. When the token reaches the node to which
it was addressed, that node takes the message, attaches an acknowledgement of receipt and readdresses it to the sending node
5. When the sending node receives the token in acknowledgement, it puts the token back into circulation as a free token and the cycle repeats itself
Wide Area Networks (WANs)
Metropolitan area networks (MANs)– MANs are scattered around a
metropolitan area– Cellular phone networks are an
example Wide area networks (WANs)
– WANs are scattered over a larger geographic region
WAN Parts of the network may be connected by
cables and other parts by microwave or satellite transmissions
Typical WANs are those operated by the telephone companies
The Internet is probably the widest of all networks in that it links not only LANs but also other WANs
Intranets Corporations are building company wide
intranets accessible only to their employees and other invited users
Used for posting documents within an organization
Used for linking software, databases, and hardware into a universal network
Speak the same language Are fenced off from others on the Internet by
firewalls
Why are Intranets popular?
The resources on the intranet are accessible to anyone, anywhere as long as they have a computer, a modem, and a password
Complex data and applications can be used over the intranets with ease
Learning to use an intranet is simple Costs are lower because so much software
and so many connections are available from so many sources
Firewalls Prevent unauthorized users on the
Internet from reaching the files and programs on the LAN
When a computer connected to the outside Internet is also connected to an inside LAN, a firewall is installed between the Internet and the local network