Introduction to Data Communications
Computer communication has n "town always been interesting f" r fooling around, but it was not f "rr" np †
1980s that it really b "rjade take off. D †, there was usually no f "ofthe finished
communications programs that k 'on, but it got sj' lv supplement or "Change in the software. IN
mid-80s b "rjade you connect personal computers into" t, f "r to be able to share printers p †
and common storage media. Large f "companies such as IBM and Novell b" rjade develop f "ofthe finished
Products f "r communication. Today, users' data nds "ten infront" of all for f "r information dissemination.
Gen. "n communication
Communication inneb "r to move meaningful information from † n an End" users to a receiver.
The receiver m † ste then be able to interpret information accurately p † s "tt. Problems p † v "gene" rm † nga
- T "nk you a person to talk about n † got f" r another person. We will now look p † which problems
that d † r † Scab.
If the TV † persons are in the same room, they can talk directly to each other and to
users' commits ice † where the air as a medium f "r that" Verf "ra information. But if the people are
in various television † l "commits ste m † to resort to other methods. One can, for example, users' NDA phone or perhaps
radio. The only requirement "is to be v" are following the same medium. A medium usually n "in mns
communication contexts "r Indians 'r' ksignaler, p † d" rf "RG" r I it also †. Suppose we
are in the wild v "stern and Indians should send a message to the colonizer" tors. It will be
not particularly successful if the colonizer "tors f" rv "NTAR to a telegraph message and sends Indians
If there are multiple people in the same room m † ste man best "tting whom to talk to.
This can g "race by f" rst crying person's name and then b "rjar discuss. If
users' commits phone has phone f "r the best" tting whom they want to communicate with and
letter, we have addresses.
Another problem "r at which time they will send a specific message.
One can, for example, the "going to
every day at 16:03 p † b "rjar we" Verf "ring of current share prices over the phone. Another s "tt" r to
f "rst l † take a ringtone g † presented as g" r that the receiver knows that now "is the time to receive today's
Which spr † k users 'nds' † is also important.
B † m † da ste users' NDA same spr † kf "r to be
f "rst † each other. When to Use It "commits Telegraph p † m † ste to Use It" NDA same spr † k, e.g.
this morning. If the "recommended that each user has their own Morse code and the receiver is not called" nd it. How it works
d †? Well, no information will be g † up!
We ste m † also † be "verens about what we're talking about.
If the "recommended that each user eg sending 10 5 13 3 2 11 9 can
it is interpreted as b † the r "tt lotto and winning h" Starna in V75. The "rd" rf "is important to f" rst talk
about what information is all about.
We see h "is that the problems can be grouped into different groups and treated each f" r itself.
This is called
layering. F "rst and fr" mst ste m † we agree on the medium to be users' NDAS and who we want
n †. D "refter at which time we will send, or if maybe we should give some signal n 'r we want" Verf "ra
information. Since that spr † k to g "ll. Last ste m † † we also know what we should talk about. F "r
everything to work m † ste agreeing in each layer of how to communicate.
Of course there are more obstacles p † v "gene" n those n 'mns h "r.
A major problem to which may
n "MNase" r st "rningar. L † ts "ga that you are sitting in the break room, talking to a colleague. Pl "tsligt
s "tter n † anyone else in g † ng an impact drill. You can not h "ra what your colleague has to s' ga.
N "r drill then falls silent, ask your colleague to ask" eight whole thing a g † ng to. This example
shows a p "tt r" eight to needle "rningar.
Communication between computers "r sl † only like communication between m" nniskor.
Male m ''s
same concerns as above with the different layers. The two parties † m † ste be unanimous.
But a big difference "is that the computer can not drag n † gra own conclusions.
Man m † ste exactly, down to the last
detail, describing how communication will take place. If n †'ve got to errs s † absent communication or s †
missf "rst † r computers together.
F "is that there will be n † gra missf" rst † nd between computers s † create descriptions that p † a
exactly p "tt describes how each part of the communication should g † to. These descriptions are called protocol
and are often written by international organizations "are independent of f" corporations and capital gains.
The idea "is that s † m † many as m" jligt then f "are following these protocols. A protocol that g "cells" all over the
v "WORLD called standard. For example, the Internet had not been a reality if we had not agreed on what
protocols to users' NDAS. All computers "are linked to the Internet ste m † f" LJA same protocol.
F "r to describe a s † h" r complicated process that it "is to communicate between different
computers beh "ver divide the problem into smaller sub-problems. A p † same sub-problems can be
best "tting how to tell which computers on a n 't to communicate with. Grouping
problems in groups and arrange them in a certain order. Each group is called f "r layers and described
then with one, possibly several minutes.
F "control section with layering communication" rm † nga.
One may fairly l "tt replace a protocol in a
layer if it turned out that the protocol was written d † p † n † got s "tt. P † s † wise man does not
technological developments. Another f "rdel" is a "layer is independent of other layers. (In practice,
m † nga exception to independence. The coupling between the layers' r a.) This medf "is that you can change
medium without f "r it would" change the spr † k or n † got in the other layers. One can additionally mix
more different media at the same "Verf" ring. N "r calling n † gon 'Is it likely that you are using" commit
b † the ordinary koppartr † d and fiber optics. In addition, users' connects you air between your head and
handset as a medium f "r sound. Spr † Ket you are using "commit" is hardly dependent on whether you are using "commit
koppartr † d or fiber optics.
The OSI model
Anyone involved with data communication n "mner always OSI model.
The OSI model describes a
s † dan h "r layering as I have described above. Various protocols assigned to the various layers of
OSI model and we f † is an "open communications architecture that medf" is that we can "Verf" raw data
between different types of computers and various computer environment "s p † different media. The opposite of "open system" is a
system d "r communication can only occur between like computer environment" s and the given media. OSI st † r f "
"Ther f" r Open Systems Interconnection.
OSI model best † r of seven different layers that the picture above shows. I will not f "Explain what each layer
describes f "r problem, but a parallel with my examples above can be fun. Which medium
users "nds, and the management, are placed in the two lowermost † layers of the OSI model. The addressing and
how n † r receiver is placed in the third layer. Handlings of st "rningar occurs p † layer four
and spr † that we feel users' commits in layers five and six. What we want to s "ga described in the" versta layer. Addition
there are a lot of other features in the different layers.
N "town every protocol that asks" r data communication "is created utifr † n a s † dan h" r model.
The difference "is that some want to sl † together some layers and want to move parts from † n one layer to another,
but the principle of layering "is all" verens about.