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 SHADOWNET DATACOMMUNICATION TUTORIAL
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         ~V                                                            ~N
         ~V THE FOLLOWING IS WHAT I HOPE WILL BE A CATALYST TO ENHANCE ~N
         ~V        ONE'S UNDERSTANDING OF PACKET SWITCHING.            ~N
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~r~I~Gial ~N
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~r~I~Grial ~N
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~r~I~Gtorial ~N
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~r~I~Gutorial ~N
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~r~I~GTutoriaL
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~r~I~G Tutorial
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~r~I~G5 Tutorial
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~r~I~G25 Tutorial
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~r~I~Gx25 Tutorial
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SHADOWNET X.25 LESSON1 

We'll start with an ~Iexplanation~N of the ~b~"TECHNICAL"~N details of x.25.

We'll delve into the ~I~c"ARCHITECTURE"~N of the ~Ix.25~N protocal.

We will present an overview of what a ~I~mPACKET_SWITCHING NETWORK~N is
and its function.

Introduced ~ITERMS~N and ~IDEFINITIONS~N essential in understanding ~IPACKET~N
~ISWITCHING~N.

What ~I~rX.25 protocol~N is.
~I~yWhat its three level do and how it functions~N.
The general format for the ~I~cFRAME and PACKET~N.

The ~ICONTENTS~N of this lesson will ~Iprovide the foundation necessary~N
to ~Iunderstand~N and ~Iassimilate~N the lessons to follow.
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Shadownet X.25_TUTORIAL

Lesson ~I3~N ~I~bFRAME LEVEL~N

This lesson will cover the ~b~IX.25 FRAME LEVEL~N

You will learn the ~I~wnomenclature or terminology and function~N

off the ~I~rframe level,frames types and frame coding~N.

as well as ~I~wnormal frame flow control~N commands and responses.

In addition you will learn :

~IFrame level error detection and recovery~N procedures.    

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Shadownet X25_TUTORIAL


Lesson ~I4~N ~I~bPACKET LEVEL~N

Here you will learn the packet level ~I~yterminology~N

~Ifunctions,normal flow control~N;

and the ~Istructure and coding~N of individuals packets.



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Shadownet X25_TUTORIAL


Lesson ~I5~N ~I~bX75 Internetwork Protocol~N

The final lesson of this course will discuss ~IINTERNETWORK PROTOCOL~N

You will be introduce to the ~I~rX.75 protocol~N,

~I~cpacket level procedures,and the coding of the X.75 packets~N.

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Shadownet X.25 Tutorial
~b What is a~I protocol?~N
  
   What ~bdoes it entail~N and ~Iwhy~N?
  
 ~IHow~N does ~Iit work~N and ~Iwhy~N?
 
  What is ~IX.25~N protocol?

At the outset we must state that the ~IX.25~N protocol,is simply
~ra set of rules~N.
~VIt does not specify the procedures to follow to implement those~N
~Vrules.                                                         ~N

For example,let us make the rule that says:

~I"The number represented by ~CA~N ~I must equal~N ~C30"~N.

In saying this we have not said anything about how to come up

with the ~b~I "number represented by~N ~CA"~N.
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Shadownet X.25 Tutorial 
~VWould you say the following statement or expresion is a valid~N 
  implementation of the rule? ~I~b(yes or no)~N.
.Q
~b A = 5 + 25(yes or no)~N
yes
Definetly , ~I~yA =30~N ,and that satisfies the rule.
Now try this one...
.Q
~b A = 6 x 5 (yes or no)~N
yes
correct , ~I~yA = 30~N ,and that satisfies the rule.
Let's try one more.
.Q
~b A = 120 / 4 (yes or no)~N
yes
of course , ~I~y A =30~N , and this too satisfies the rule.
Try this one 
.Q
~CPimentel~N is currenntly at the ~I~F~mP N A CENTER?~N(yes or no)
yes
~I~gSTUPENDOUS~N you are ~I~rrocket scientist~N material!
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Shadownet X.25 Tutorial
We have seen,that we can ~b~I"implement"~N our rule any number of ways.

And the same is ~Itrue~N of ~r~I X.25~N and its related protocols.

~I~yThey define rules,not the procedures by which the rules are implemented.~N

Another point to ~F~Ithink~N about,though it may be a subtle one.

Must of us tend to ~I~cimply human traits to inaminate objects~N.

You may find that at times I would say ~I~b"The protocol does this,or knows~N
~I~bthe other"~N.

In reality,the ~Iprotocol doesn't do anything,execpt define the rules that~N
~Iour implementation procedures must meet to conform to the standard.~N

Alright, so where did these ~I~cX.25 "RULES"~N come from?

~IWho set these standards?~N
  
  Let us ~Ifind~N out.
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Shadownet X25_tutorial

~IToday~N we have a number of ~b~I"STANDARD ORGANIZATIONS"~N.
Each off them operate according,to its own charter (and timetable).

~IThey~N ~r~Ihave~N a very ~I~ydifficult TASK~N.

~VThey somehow develop sets of rules, protocols, standards, ~N

~Vthat will meet future needs in a world of rapidly changing~N ~I"technology"~N.

~I~cYet, these standards must be implemtable now,with today's TECHNOLOGY~N.

~VAnd it must take into consideration (as much as possible)   ~N

~Vmultiplicity of equiptment that are in place in place today.~N
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Shadownet X25_tutorial

Do you know who these ~I~bSTANDARD MAKERS~N are?
~VLet's see if you can name them.?~N
By trying to ~Vsupply the missing letters~N of the ~Iacronym~N. 
.Q
~I~bCC_ _ T~N
I T
~IConsultative Communication International Telephone & Telegraph~N

.Q
~I~bI_O~N
S
~IInternational Standard Organization~N

.Q
~IE_ _~N
I A
~IElectronic Interface A~N

.Q
~IA _ _ I~N
N S
~IAmerican national standard institute~N 
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Shadownet X25_TUTORIAL

~I~rX.25~N was adopted by the ~ICCITT in 1976~N in an attempt to
provide a standard interface between user's ~IDTE~N equiptment
and ~IDCE~N entry point of the growing number of 
~IPACKET SWITCHED NETWORKS~N worldwide today.

For example ~F~I~bPULSELINK~N,~IDATAAMERICA,TYMENET,COMPUSERVE~N.
So it can be stated that ~IX.25~N focuses on the ~IDTE_DCE connection~N.

The related Protocols were adopted in ~I1980~N to allow the huge
embeded base of no_x25 equiptment to take advantage of the 
standard interface.

Each 4 year CCITT ~I"study period"~N points out ~Iadded enhancement~N to 
the X25 family standards.
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Shadownet X.25_TUTORIAL


  ~I~b7.application~N                  ~I~b7.application  ~N 
  ~I~c6.presentaion~N                  ~I~c6.presentation ~N
  ~I~y5.session    ~N                  ~I~y5.session      ~N
  ~I~g4.transport  ~N                  ~I~g4.transport    ~N
  ~I~m3.packet     ~N                  ~I~m3.network      ~N
  ~I~r2.frame      ~N                  ~I~r2.datalink     ~N
  ~I~V~W1.physical   ~N                  ~I~V~W1.physical     ~N
                     
 ~I~bCCITT x25 model~N                 ~I~b   OSI model   ~N  

 By ~I~ydividing~N the ~Iresponsibility~N of the model in this 

~Vfashion~N a ~Ilayered architecture protocol~N ~Vcan be developed~N

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  X.25
                      








~I~rThis is the end of this module~N please press ~I~FQ~N

~I~bcontact your local CAI sys.admin.~N


                                                    01/03/89  ~I~cEd Pimentel~N
.WNQ