Category : Tutorials + Patches
Archive   : CLASS.ZIP
Filename : CHAPTER.09

 
Output of file : CHAPTER.09 contained in archive : CLASS.ZIP
==============================================================================
Date: 06-05-89 (10:30) Number: 881 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHAPT 9 - 1 Conf: (6) TeleComm
------------------------------------------------------------------------
This Chapter will be an introduction and an overview of Data
Communications and Alternatives.

The simplest form of Data Communication, is connecting up two
computers together when they are geographically in the same
proximity to each other (in the same room).

This usually involves connecting two computers together via their
Serial Comm Ports.

This is done through alternate operating systems, as in the case
of PC-MOS, a more 1 on 1 specific program such as Brooklyn Bridge
or by running a comm program like qmodem on each computer and
exchanging files via a transfer protocol.

In the business world, main frames can talk to mainframes or
to control units via direct cable with proper software.

Whether you are using special software or a simple comm program,
a comm port is still a comm port. It wants to receive and send
signals the traditional way.

In other words it ( a computer, DTE, Data Terminal Equipment) ;
wants to talk to a Modem ( DCE, Data Comm Equipment) OR at
least think it is talking to Data Comm Equipment.

When you connect 2 DTE's together ; as in 2 Computer Serial Comm
ports, you have to fake them out, and make them think they are in
fact talking from DTE to DCE.

We accomplish this via a NULL Cable or Crossover Cable.

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844
==============================================================================
Date: 06-05-89 (10:30) Number: 882 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHAP 9 - 2 Conf: (6) TeleComm
------------------------------------------------------------------------
We accomplish this via a NULL Cable or Crossover Cable.

The wiring of this cable is shown below.

Wiring Diagram of a Crossover Cable for ASYNC Communication


Pin # Pin #

GRD 1 -------------------------- 1 Ground

Tx Data 2 -------------------------- 3 Receive Data

Rec Data 3 -------------------------- 2 Transmit Data

RTS 4 ÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 8 Carrier Detect
³
CTS 5 ÄÄÄÙ

DTR 6 -------------------------- 20 Data Set Ready

GRD 7 -------------------------- 7 Ground

Carrier 8 ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄ 4 Request To Send
Detect ³
ÀÄÄÄÄ 5 Clear To Send

DTR 20 -------------------------- 6 Data Set Ready


It is important to note that aside from the common grounding
pins, that a crossover or fakeout takes place.

One computers DTR becomes the others DSR.

One's Send Data becomes the other Receive Data.

We tie RTS to CTS as they compliment each other. When RTS/CTS
goes high indicating that Data is about to be sent, it brings
Carrier Detect high at the other end simulating or indicating
what Carrier Detect means to the receiving computer.

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844
==============================================================================
Date: 06-05-89 (10:31) Number: 883 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHAPT 9 - 3 Conf: (6) TeleComm
------------------------------------------------------------------------
Wiring Diagram of the Crossover Cable for SYNC Communications

Pin # Pin #

GRD 1 ---------- GRD ----------- 1 GRD

GRD 7 -------------------------- 7 GRD

Tx Data 2 -------------------------- 3 Rec Data

Rec Data 3 -------------------------- 2 Tx Data

RTS 4 ÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 8 Carrier Detect
³
CTS 5 ÄÄÄÙ

DTR 6 -------------------------- 20 DSR

GRD 7 -------------------------- 7 GRD

Carrier 8 ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄ 4 RTS
Detect ³
ÀÄÄÄÄ 5 CTS

Receive 17 -------------------------- 25 Ext Transmit Clock
Clock

DTR 20 -------------------------- 6 DSR



The difference you will note is the addition of the CLOCK
lead. In Syncronous communication we need a clock. One of the
DTE's (computers) will have to be optioned to provide a clock
while the other is be optioned to slave or receive a clock.

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844
==============================================================================
Date: 06-05-89 (10:31) Number: 884 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHAPT 9 - 4 Conf: (6) TeleComm
------------------------------------------------------------------------
The next simplest form of Data Comm is via two dial up modems.
This we have been discussing in detail.


Computer Computer
³ ³
³ ÚÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿ ³
ÀÄÄ´ Modem ÃÄÄÄÄÄ Ø Dial Ø ÄÄÄÄÄ´ Modem ÃÄÄÙ
ÀÄÄÄÄÄÄÄÙ ³ Line ³ ÀÄÄÄÄÄÄÄÙ


It is possible, with the proper software, to connect up
to dialup modems together and tranmit data back and forth.

The next common way of Data Comm, and reserved usually for
computers in the same building or next door to each other,
is using a Local Area Modem or Modem Eliminator.

These Digital devices, pass the digital data from the comm ports
without modulating them into analog signals. They do amplify
the digital signals to give them the power to transmit over
distances of up to several miles.

They utilize twisted pairs (2 of them) of in house wiring or
you can order a Bell Metallic Line that runs those few miles
or around the block. Telco has a problem in installing these
lines. They like to add an interface device onto the line for
testing purposes (actually just to bill you more).

These testing devices are the same ones they use on Analog
circuits and that should tell you something. With those devices
on their, your digital data WILL NOT PASS.

You have to order them to take the darn things off. Once they do
that, your Local Area Modems will work just fine.

You can purchase these in 2 wire or 4 wire modes.



Computer
³
³ ÚÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿
ÀÄÄ´ Local ³ ³ Local ³
³ Area ÆÍÍÍÍ In House ÍÍÍ͵ Area ³______ Computer
³ Modem ³ Wiring ³ Modem ³
ÀÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÙ

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844
==============================================================================
Date: 06-05-89 (10:32) Number: 885 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHPATER 9 -5 Conf: (6) TeleComm
------------------------------------------------------------------------
The next alternative for more serious applications is the
DEDICATED LINE. It is a hard wired line running from
One location to another (city wide, country wide or even
world wide) not accessible by anyone else. The lines
are in continuous operation.

Sync Modem and Async modem may be used over a Dedicated Line


Computer Computer
³ ³
³ ÚÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿ ³
ÀÄÄ´ Modem ÆÍÍÍÍÍ Ø Dedicated Line Ø ÍÍÍÍ͵ Modem ÃÄÄÙ
ÀÄÄÄÄÄÄÄÙ ³ Point to Point ³ ÀÄÄÄÄÄÄÄÙ



One Mutant form of Data Communications is the MULTI-Modem

It uses one telephone line (one dedicated point to point line)
but is capable of acting like up to FOUR distinct modems.

A multimodem has up to four comm ports, Labelled ports 1, 2, 3
and four. At the other end is an exact duplicate Multi-Modem.

What you plug into port one at one end, will communicate with
whatever you plug into port one at the other end.

Likewise ports 2, 3 and 4.


ÚÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿
Computer 1 ÄÄÄ´ ³ ³ ÃÄÄÄ Main
³ ³ ³ ³ Frame
Computer 2 ÄÄÄ´ Multi ³ ³ Multi ÃÄÄÄ Computer
³ Modem ÆÍÍÍ Dedicated Line ÍÍÍ͵ Modem ³ Ports
Printer ÄÄÄ´ ³ Point to Point ³ ÃÄÄÄ
³ ³ ³ ³
ÚÄÄÄÄÄÄÄ´ ³ ³ ÃÄÄÄ
³ ³ ³ ³ ³
³ ÀÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÙ
ÚÄÄÄÁÄÄÄ¿
³ Modem ³
ÀÄÄÄÂÄÄÄÙ
³

Dial-up A typical application for this would be
Line a Company that has a remote sales location.
³ Ports 1 and 2 are computer terminals that
ÚÄÄÄÁÄÄÄ¿ access inventory and pricing information
³ Modem ³ On port 3, is connected a printer which
ÀÄÄÄÂÄÄÄÙ will print out invoices for the remote
³ office.
³
If your main frame is in Boston and your
Computer remote sales office is in Los Angeles,
Dumb Terminal you need not purchase 4 very expensive
Printer coast to coast dedicated Phone Lines.

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844
==============================================================================
Date: 06-05-89 (10:32) Number: 886 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHAPTER 9 - 6 Conf: (6) TeleComm
------------------------------------------------------------------------
Notice the dial up modem on port 4. Lets say you have another
remote sales office in a small town outside of L.A.. This office
can call the L.A. dial up modem and have their data transmitted
to Boston over port # 4. We call this REGENERATION.

MultiModems come in different speeds and their port configuration
is usually selectable.

If our 4 port MultiModem was a 9600 bps modem, this means that
the modulation on the line is 9600 bps throughput.

Our ports can thus be configured to any combination that does
not exceed that 9600 bps throughput.

We can select to have just 2 ports at 4800 bps each
OR 2 ports with one being 7200 and the other 2400.


We could selecte to have three ports. One at 4800 and Two
at 2400.

Or we could select to have 4 ports at 2400 bps on each port.

How we multiplex this Data will be discussed in our Multiplexing
Chapter.

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844
==============================================================================
Date: 06-05-89 (10:33) Number: 887 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHAPTER 9-7 Conf: (6) TeleComm
------------------------------------------------------------------------
Before we get into the last of the modem configuartion, there are
a few things we should review.

A dial up line is called a 2 wire line. Why, because it has two
wires. One telephone line pair for each phone line.

A dedicated line can be 2 wire, but more typically it is a four
wire line.

Four wires BUT two telephone line pairs.

In a point to point setup, one pair is used as the transmitter
of the 1st modem to the receiver of the second. On the other
side of the four wire , the first modem is receiving what the
second has transmitted. As shown below.

DEDCICATED POINT TO POINT TELEPHONE CIRCUIT


ÚÄÄÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄÄ¿
³ ³ ³ ³
³ M ³ ³ M ³
³ O TRANSMITÆÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ͵RECEIVE O ³
³ D ³ ³ D ³
³ E RECEIVE ÆÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ͵TRANSMIT E ³
³ M ³ ³ M ³
³ ³ ³ ³
³ ³ ³ ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÙ


Remember two separate distinct phone circuits make up a four wire
dedicted line. They can transmit and receive continuously in both
directions simultaneously.

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844
==============================================================================
Date: 06-05-89 (10:33) Number: 888 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHAPTER 9 -8 Conf: (6) TeleComm
------------------------------------------------------------------------
Let us look at another application. Your Mainframe is in Boston.
You have two remote distribution warehouses, one in the State
of Georgia and one in the state of Florida.

Two connect Boston to Georgia and Florida would take, 4 modems,
2 point to point lines and 2 computer ports on your mainframe.

Unless you use a MULTI DROP line. A Multidrop Line lets you
operate TWO remote modems off of the SAME central Modem.

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ Remote Modem ³
³ Georgia³
³ ³
³ Rec Trans³
ÀÄÄÄÒÄÄÄÄÄÄÄÄÒÄÄÙ
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ º º
³ Cental ³ º º
³ Modem ³ º º
³ in TransÆÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ͹ º
³ Boston ³ º º
³ Mass. ÆÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ º ÍÍÍÍÍÍ͹
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ º º
ÚÄÄÄÐÄÄÄÄÄÄÄÄÐÄÄ¿
³ Rec Trans ³
³ ³
³Remote Modem ³
³ Florida ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ


How can this be !!!!!!!

Very simple.

First lets look at the central site modems transmitter.
The mainframe transmits data to both locations simultaneously.
Each remote modem is receiving ONE carrier, that of the
Central Modem.

The remote modems alternate (take turns) turning carrier
on and off. This function is software controlled.

HOW ???

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844
==============================================================================
Date: 06-05-89 (10:34) Number: 889 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHAPTER 9-9 Conf: (6) TeleComm
------------------------------------------------------------------------
HOW ???

First lets look at the hardware. The Phone company uses something
called a BRIDGE which is used to DROP remote sites off of a
dedicated circuit. You can have many drops off of one line.
As many as your software will allow.

This bridge disperses the central site modem transmit carrier to
all remote modems. ALL remote modems receive the same thing.

This bridge also DIRECTS transmit carrier from any remote modem
on a ONE WAY trip back to the central modems receive side.
NO REMOTE MODEM can see another remote modems transmit signal.
The bridge acts as a traffic cop preventing a remote modems
transmitter from feeding back to another remote modems receive
side.

We must now look back at our control signals.

Remember RTS & CTS ??? Request to Send and Clear to Send ???

A modem DOES NOT turn its transmit carrier on until the Computer
turns Request to Send (RTS) ON. Carrier is then turned on BUT no
data is sent until the Modem turns on Clear To Send.

WHY ?? It takes the receiving modem a few milliseconds to sync
up on the incoming carrier.

Since all remote modems receive the Central Modems transmitter,
we can turn RTS (request to send) on permaneantly (if the
software allows) and transmit carrier continuously TO the remote
sites. This means there will be no delay with the remote modems
needing to sync up on the receiving carrier because it will always
be there and the remote modems will always be in sync with
the central modems transmitter.

This function is called CONTINUOUS CARRIER

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844
==============================================================================
Date: 06-05-89 (10:34) Number: 890 Comp-U-Ease
To: ALL Refer#: NONE
From: PHIL MARCELLO Read: YES
Subj: COMM COURSE CHAP 9 - 10 Conf: (6) TeleComm
------------------------------------------------------------------------
At the remote sites, we must control when these remote modems will
transmit. If more than one remote site were to transmit at the
same time, the central modem would not be able to sync on two
DIFFERENT carriers. They would clash and be garbled.

For this reason, we keep the RTS (request to send) low on the
remote modems. RTS must be switched on by the software to
turn carrier on. We call this SWITCHED CARRIER or CONTROLLED
carrier.

The software uses a polling method (refer to early chapter)
to talk to remote sites.

Each remote Computer has an address. The central computer
address ONE computer at a time. The remote computer than has been
addressed will respond by raising RTS and bringing carrier up.

When it is finished, it will bring RTS down dropping carrier and
opening up the line for the next remote site.




Request ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
TO SEND ³ ³
³ ³
ÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄ
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
Clear To Send ³ ³
³ ³
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄ

° ° ° ° ° °
°°° °°° °°° °°° °°° °°
°°°°° °°°°° °°°°° °°°°° °°°°° °°°
°°°°°°° °°°°°°° °°°°°° °°°°°° °°°°°° °°°
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°ÄÄÄÄÄÄÄÄÄ
°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°
Carrier as °°°°°° °°°°°° °°°°° °°°°° °°°°° °°°
would be seen °°°° °°°° °°° °°° °°° °°
using an °° °° ° ° ° °
oscilloscope

PCRelay:DATACOMM -> RelayNet (TM)
Data Comm - Rochester N.Y. 716-328-3844


  3 Responses to “Category : Tutorials + Patches
Archive   : CLASS.ZIP
Filename : CHAPTER.09

  1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

  2. This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

  3. But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/