Multitech MMH900 User manual

MMH900 Series Statistical
Multiplexer
User Guide

User Guide
S000315A Revision A
MultiMux (#MMH904Ca) (#MMH908Ca)
This publication may not be reproduced, in whole or in part, without prior
expressed written permission from Multi-Tech Systems, Inc. All rights
reserved.
Copyright © 2003, by Multi-Tech Systems, Inc.
Multi-Tech Systems, Inc. makes no representations or warranties with
respect to the contents hereof and specifically disclaims any implied
warranties of merchantability or fitness for any particular purpose.
Furthermore, Multi-Tech Systems, Inc. reserves the right to revise this
publication and to make changes from time to time in the content hereof
without obligation of Multi-Tech Systems, Inc. to notify any person or
organization of such revisions or changes.
Record of Revisions
Revision Date Description
A 11/01/03 Initial release of MultiMux MMH904/908C for
publication on CD.
TRADEMARK
Trademark of Multi-Tech Systems, Inc. are as follows: MultiMux,
MultiModem and the Multi-Tech logo.
Multi-Tech Systems, Inc.
2205 Woodale Drive
Mounds View, Minnesota 55112
[phone] or [phone]
Fax [phone]
Tech Support [phone]
Internet Address: http://www.multitech.com

Contents
Chapter 1 - Introduction & Description ................................ 8
1.1 Introduction.................................................................................... 9
1.2 About This Manual......................................................................... 9
1.3 Background ................................................................................... 11
1.3.1 Description of Statistical Multiplexing ................................... 12
1.3.1.1 StatisticalMultiplexing .......................................................... 12
1.4 Product Description ....................................................................... 14
1.5 System Features ........................................................................... 17
1.5.1 Response Time Control........................................................ 17
1.5.2 Dynamic Buffering ................................................................ 17
1.5.3 Flow Control ......................................................................... 18
1.5.4 Diagnostics .......................................................................... 18
1.5.5 Downline Parameter Loading ............................................... 18
1.5.6 Operational Statistics andAuto-Reporting............................ 19
1.5.7 Parameter Memory .............................................................. 19
1.5.8 Channel Flexibility ................................................................ 19
1.5.9 Command Modem................................................................ 19
1.5.10 Composite Link .................................................................... 20
1.6 FCC Regulations for Telephone Line Interconnection ................... 21
1.7 DOC Terminal Equipment .............................................................. 23
1.8 Specifications ................................................................................ 24
1.8.1 Channels .............................................................................. 24
1.8.2 System Control..................................................................... 24
1.8.3 Composite LInk .................................................................... 25
1.8.4 33,600 bps Link Modem ....................................................... 25
1.8.5 56,000 bps DSU.................................................................. 25
1.8.6 ISDN TerminalAdapter......................................................... 26
1.8.7 Command Modem................................................................ 26
1.8.8 Electrical/Physical ................................................................ 26
Chapter 2 - Configuration ..................................................... 27
2.1 Introduction.................................................................................... 28
2.2 Configuration 1 .............................................................................. 29
2.3 Configuration 2 .............................................................................. 31
2.4 Configuration 3 .............................................................................. 32

Chapter 3 - Front & Rear Panel Descriptions..................... 34
3.1 Introduction.................................................................................... 35
3.2 Front Panel .................................................................................... 35
3.3 LED Indicators .............................................................................. 36
3.4 Back Panel .................................................................................... 40
3.4.1 ON/OFF Switch .................................................................... 40
3.4.2 Power Connector ................................................................. 40
3.4.3 COMMAND MODEM DIAL-UP Connector .......................... 40
3.4.4 COMMAND PORT Connector .............................................. 40
3.4.5 COMPOSITE LINK INTERNAL MODEM DIAL-UP Connector40
3.4.6 COMPOSITE LINK INTERNAL MODEM LEASED Connector41
3.4.7 COMPOSITE LINK INTERNAL DIGITAL DSU Connector.... 41
3.4.8 COMPOSITE LINK EXTERNAL RS232C/V.35 Connector ... 41
3.4.9 CHANNEL 1 - CHANNEL 8 Connectors............................... 41
3.5 Switches/Jumper/Shunt................................................................. 42
3.5.1 8-Position DIP Switch........................................................... 42
3.5.2 4-Position DIP Switch........................................................... 43
3.5.3 144RKWL/OtherJumper ....................................................... 44
3.5.4 V.24/V.35 Shunt.................................................................... 44
3.5.5 V.29/V.33 Shunt and 2834 Shunt.......................................... 44
Chapter 4- Installation........................................................... 45
4.1 Introduction.................................................................................... 46
4.2 Safety Warnings ............................................................................ 46
4.3 Unpacking...................................................................................... 46
4.4 Installation ..................................................................................... 47
Chapter 5 - Commands ......................................................... 52
5.1 Introduction.................................................................................... 53
5.2 Command Description ................................................................... 58
5.2.1 General Commands ............................................................. 58
5.2.2 Channel Parameter Commands ........................................... 65
5.2.3 Composite Link Commands ................................................. 74
5.2.4 Composite Link Format Commands ..................................... 78
5.2.5 Internal 9600/14.4K Composite Link Modem Commands..... 81
5.2.6 Internal MMH2834 Modem Configuration Commands.......... 84

5.2.7 Internal Composite Link DSU Commands ............................ 86
5.2.8 Test Commands ................................................................... 87
5.2.9 Command Modem commands ............................................. 89
Chapter 6- Operating Procedures ....................................... 90
6.1 Introduction.................................................................................... 91
6.2 MultiMux Operating Procedures .................................................... 91
6.3 Command Modem Operating Procedures ..................................... 95
Chapter 7 - Troubleshooting ................................................ 97
7.1 Introduction.................................................................................... 98
7.2 Importance of Composite Statistics ............................................... 98
7.3 Test Cables.................................................................................... 99
7.4 Troubleshooting Guide .................................................................. 101
7.5 Channel Device Testing ................................................................. 107
7.6 Local Modem and Communications Line Testing .......................... 108
7.7 MultiMux Functional Testing Procedures ....................................... 110
Chapter 8- Service, Warranty, & Technical Support ......... 112
8.1 Introduction.................................................................................... 113
8.2 Warranty ........................................................................................ 113
8.3 Repair Procedures for U.S. and Canadian Customers.................. 114
8.4 Repair Procedures for International Customers (Outside U.S.A. and
Canada) ............................................................................................ 115
8.5 Repair Procedures for International Distributors............................ 116
8.6 Online Warranty Registration......................................................... 116
Appendices.......................................................................... 117
AppendixA .............................................................................................. 118
Ascii Character Code/Hex/Decimal Conversion Chart ...................... 118
Appendix B
RS232C Interface Specification ........................................................ 119

Appendix C.............................................................................................. 121
Cabling Diagrams.............................................................................. 121
Appendix D.............................................................................................. 125
Command Modem Commands ......................................................... 125
Appendix E Command Modem S-Register Function.............................. 138
Appendix F .............................................................................................. 143
Flow Control Background.................................................................. 143
Appendix G ............................................................................................. 146
MMH2834 S-Registers...................................................................... 146
Appendix H.............................................................................................. 149
Dial Back-up...................................................................................... 149
Appendix I ............................................................................................... 150
Testing Your MMH2834 ..................................................................... 150
I.1 Introduction ................................................................................ 150
I.2 LocalAnalog Loopback Test/V.54 Loop 3 .................................. 151
I.3 Digital Loopback Test/V.54 Loop 2 (Loc/Man)...................... 152
I.4 Digital Loopback Test/V.54 Loop (Rem/Auto) ............................ 154
I.5 Synchronous Mode Testing ................................................. 156
I.6 Local Analog Loopback Test (Sync Mode)........................... 157
I.7 Digital Loopback Test (Loc/Man) Sync Mode ...................... 158
I.8 Digital Loopback Test (Rem/Auto)(Sync Mode)................... 159
Appendix J - Internal MMH2834 Composite Link Modem Commands.... 160
J.1.1 DialingAction Commands ........................................................ 163
J.1.2 Dial Modifier Commands ...................................................... 165
J.1.3 Phone Number Memory Commands .................................... 168
J.1.4 Configuration and Default Storage Commands .................... 170
J.1.5 Command Response (Result Code) Commands..................... 172
J.1.6 Phone Line Conditioning Commands ...................................... 176
J.1.7 RS232C Interface Control Commands ..................................... 177
J.1.8 Error Correction Commands ................................................ 178
J.1.9 Compression and Maximum Block Size Commands ............ 180
J.1.10 Speed Conversion Commands............................................. 181
J.1.11 ImmediateAction Commands............................................... 183
Glossary............................................................................... 185
Index..................................................................................... 195

Chapter 1 - Introduction &
Description

8
Chapter 1 - Introduction & Description
1.1 Introduction
Congratulations! Your new MultiMux MMH900 series is one of the finest
statistical multiplexers on the market today. The MultiMux is completely
software driven and is controlled by you through its command port. This
gives you great flexibility and ease of operation. This Owner’s Manual
will help you to install and use your MultiMux, and also provide you with
a valuable information resource in the future.
DTR
OH
Statistical Multiplexer
R
E
T
R
A
N
S
M
IT 123
BUFFER
FULLNESS
LEVEL
F
L
O
C
T
R
L
R
C
V
L
I
N
K
A
L
A
R
M
R
E
M
O
T
E
D
W
N
T
E
S
T
M
O
D
E
MultiMux
Internal Composite Link
MMH2834 CD RCV XMT CTS 28.8 24.0 19.2 14.4 OH TR EC DBUP
DSU CD RCV XMT CTS 56 19.2 RTS NS OOS TM
V29/V33 CD RCV XMT CTS
External Composite Link
Channel Two Channel Three Channel Four
Command Modem
Channel Five
Channel Six Channel Seven Channel Eight
XMTRCV XMTRCV XMTRCV
A
S
Y
N
C
L
I
N
K
D
S
U
V
2
9
/
V
3
3
RCV
Channel one
RCV XMT
CD RCV XMT CTS V.35
XMTRCV
XMT RCV XMTXMTRCV
XMT
RCV
INTERNAL LINK DEVICE
(Modems)
Systems
MultiTech
M
M
H
2
8
3
4
CD
I
S
D
N
ISDN
Figure 1-1. MultiMux MMH900 Series
1.2 About This Manual
eThis manual is comprised of eight chapters. There are also several
appendices at the end of the manual, most of which is a condensed
version of the information contained in the chapters. These appendices
can be used as a quick reference. The information contained in each
chapter is as follows:
Chapter 1 - Introduction
This chapter is an introduction to the world of multiplexing. Since you
have already acquired the MultiMux, you may have an extensive
background in multiplexing. In which case, this introduction will provide a
good review.
Chapter 2 - Configuration
This chapter defines the configurations of the MMH900 series and
provides some typical examples of how the MultiMux is configured. The
MMH900 series is available in two models; the four and eight channel
units with an internal command modem, various composite link modems
supporting synchronous or asynchronous communications. The typical
examples explain how the MultiMux can be used in various
environments.

9
Chapter 1 - Introduction & Description
Chapter 3 - Front and Rear Panel Descriptions
Chapter 3 describes the front panel indicators, the switches and jumpers
within the cabinet and the rear panel connections. The front panel
indicators are described in the various groups depending on the
configuration of the MultiMux. Indicator groups are active depending on
how the MultiMux is used. The front panel is the same for all models
and contains some indicators for future enhancements. The back panel
provides all the cable connections for the early released models with the
addition of cable connections for future releases.
Chapter 4 - Installation
Chapter 4 provides the procedures for unpacking, installing and cabling
your MultiMux.After your MultiMux is cabled, an initial power on
procedure is provided for you to display and modify the channel and link
parameters to fit your configuration.
Chapter 5 - Commands
The MultiMux is software-driven and controlled through its command port
and the supervisory console. This chapter describes theAT commands
and the impact each has on your system’s operation.
Chapter 6 - Operating Procedures
Chapter 6 provides the operational information for your MultiMux. The
MultiMux operating procedures address the channel and composite link
parameters. The command modem operating procedures address the
command modem access, dialing, and remote access procedures.
Chapter 7 - Troubleshooting Procedures
This chapter is a guide to troubleshooting your MultiMux. It contains a
listing of error conditions, probable causes and suggested fixes or steps
designed to isolate the failing unit in your communications network.
Chapter 8- Service, Warranty and Tech Support
Chapter 8 provides instructions on getting service for the MultiMux at the
factory, a statement of the limited warranty, information about our user
bulletin board service, and space for recording information about your
multiplexer prior to calling Multi-Tech's Technical Support.

10
Chapter 1 - Introduction & Description
1.3 Background
Any data communications environment that has more than one
asynchronous line going between common locations can probably
benefit by installing a pair of statistical multiplexers (stat muxes). A stat
mux performs the function of combining several asynchronous data
communication channels into one composite signal that can be
transmitted between two locations more inexpensively than the cost of
the individual lines.
Figure 1-2 shows a simple communications network. Individual users
connect to asynchronous channels and the composite (or aggregate)
communications line between the two locations is the "link". Link
protocol is the communications discipline used between the two
multiplexers and typically operates at a speed higher than the individual
asynchronous units connected to each multiplexer.
Figure 1-2. Simple Communications Network
One reason that a stat mux works is that typically an asynchronous
terminal device is not used to its capacity. Studies show that as little as
10 to 15% utilization of such lines is a common occurrence. These
percentages indicate that the most efficient combination of lines in a
muxed asynchronous environment is between four and eight lines.
Although the primary reason for installing a mux is to save on
communications costs, two other benefits are also present. One is the
inherent error correction existing in muxed data and the other is data
security. Since a mux functions by taking individual asynchronous data
and transmitting it as data packets, there is an error detection and
retransmission scheme built in. Error correction is so vital in many
transmission types, such as graphic data and program transmission, that
many muxes are used mainly for their error correction capabilities.
The other benefit is data security which is achieved by the fact that the
individual data streams are encrypted into a single communication line

11
Chapter 1 - Introduction & Description
on one end of the link and then broken up into individual components on
the other end. Someone wishing to "tap" into a muxed signal must not
only have the link protocol which is typically a proprietary version of High
Level Data Link Control (HDLC), but must also know the individual
channel assignment schemes and data formats.
1.3.1 Description of Statistical Multiplexing
A statistical multiplexer (also known as a stat mux) is a device that
allows several other devices (usually computer terminals or PCs) to
communicate over a single transmission line. Sometimes called
concentrators, they take data from different devices and combine it into a
single stream that can be transmitted, via a modem, to an identical
multiplexer at another location, where the stream is then separated back
into its original form. Physically, a mux looks like a box with a bunch of
serial ports and some LEDs. The most typical task of the MultiMux is to
connect a group of PCs or terminals at one site to a mini or mainframe
computer at another site via a single set of modems rather than using
individual modems for each PC or terminal.
1.3.1.1 Statistical Multiplexing
Statistical multiplexing is sometimes referred to as statistical time-
division multiplexing (STDM). The use of the voice-grade phone line (or
any other communications link) is based not on peak data rates, but on
effective (or average) data rates.
During the peaks, when the sum of the data rates of the channels being
served exceeds the data rate of the composite link, a statistical
multiplexer saves the excess data in buffers (in effect, allowing individual
channel buffers to expand). The buffers are emptied as soon as the
activity falls off. The proper allocation of buffer space, plus the
implementation of “flow control” and “pacing” techniques to
accommodate unusually high peaks, allows the use of composite link
speeds that are less than the sum of the individual channel speeds.
In effect, a statistical multiplexer services only active channels. However,
the efficiency thus realized is not the only benefit of the technique.
Because composite link activity need not be synchronized with the
activity on the individual channels, there is considerable flexibility in the
choice of the composite channel protocol and speed. The use of a
synchronous protocol like HDLC provides for error detection and
retransmission over the composite link. Thus, asynchronous terminals,
which have no inherent error-recovery capability, can enjoy end-to-end
data integrity.

12
Chapter 1 - Introduction & Description
1.3.1.2 Communications
The basic functions of multiplexing are to make communications more
efficient, to provide a means of improving accuracy of asynchronous
communications by using synchronous techniques, and to improve data
security by encrypting several data streams into one coded link.
The channel devices can be any asynchronous RS232 compatible units,
from “dumb terminals” to personal computers running asynchronous
communications software. The connection between the channel devices
and the MultiMux is made through an RS232 interface cable.
Asynchronous modems (long haul or short haul), asynchronous modem
emulators and asynchronous line drivers (DCE devices) can be used in
this connection (up to 38.4K bps) to extend the distance between the
channel devices and the MultiMux.
The connection between the two MultiMuxes is the composite link, and
can be up to 128K bps. Using an internal modem, ISDN terminal
adapter, DSU, or external device, the MultiMux can be connected to
different types of communications links, such as a dial-up line, leased
line, Basic Rate Interface (BRI) ISDN service, or a DDS network. If an
external link device is used the MultiMux can communicate with it using
either the RS232 or V.35 standard.

13
Chapter 1 - Introduction & Description
1.4 Product Description
There are two basic models of MultiMux MMH900 series available: a
four channel and eight channel units with internal command modem,
optional composite link modems and a command port. The four channel
MultiMux MMH904 connects four async devices to asynchronous
channels that transfer data at a channel speed of up to 38.4K bits per
second (bps). The eight channel MultiMux MMH908 connects eight
async devices. The composite link of the MultiMux MMH900 series can
be configured for various dial-up and lease line modems, a Digital
Service Unit (DSU) for digital communications over a Digital Data
Service (DDS) or dedicated network, or an ISDN terminal adapter for
Basic Rate Interface Service. The command port allows you to
configure the MultiMux MMH900 series for your channel configuration,
internal hardware and composite link configuration.
A simplified block diagram of a MultiMux network is shown in Figure 1-3
to give you a pictorial view of a complete network. The MultiMux
represented in the figure is a MultiMux MMH904 connected to four async
devices on CHANNEL 1 through CHANNEL 4. The workstation
connected to the COMMAND PORT is the supervisory console in which
you can communicate with the command processor or command
modem. If a remote connection is needed to the command modem, a
separate DIAL-UP connection is provided. The composite link can be
configured for an internal 28.8K bps dial-up/leased line modem, internal
DSU for digital communications over a digital data service (DDS)
network or an ISDN terminal adapter for Basic Rate Interface Service. It
can also be configured for external synchronous link device with either
V.24 or V.35 interface.
Command
Port
Command
Modem
Dial-Up Modem
Lease Modem
DSU
Composite
Link Data Composite
Link
Workstation PC
Dial-Up Modem
Lease Modem
Digital
Data
Processor
Command
Processor
ATCommands
I/O
Channel
4
Channel
3
Channel
2
Channel
1
I/O
Dial-up
Workstation PC
AT Commands
AT Commands
AT Commands
Channel
Data
Channel
Data
MultiMux 900 Series
PDN
Composite
Link
Dial-up
Line
PDN
Dial-up
Line
C
o
m L
p i
o n
s k
i
t
e
Figure 1-3. MultiMux MMH900 Series Block Diagram
To setup a MultiMux MMH900 series, the async devices have to be
connected to the channels, the composite link connected to the public
data network (PDN) and the MultiMux has to be configured for the

14
Chapter 1 - Introduction & Description
channel devices and the composite link. The async devices are
connected to CHANNEL 1 through CHANNEL 4 connectors on the back
panel of the MultiMux MMH904 with an RS232 cable. The MultiMux
MMH908 has four additional channel connectors for connecting up to
eight devices.
A number of internal and external composite link devices can be used to
connect the MultiMux to the PDN. The MMH900 series has an internal
28,800 bps composite link modem or an internal 56,000 bps DSU. The
modem is connected to the PDN through the INTERNAL COMPOSITE
LINK LEASED MODEM connector on the back panel of the MultiMux.
The internal DSU is connected to a DDS or dedicated network through
the COMPOSITE LINK DIGITAL DSU connector on the back panel.
The supervisory console is connected to the MultiMux through the
COMMAND PORT connector on the back panel. The supervisory
console connection is also an RS232 connection. This completes a
typical hardware setup for a MultiMux. Now the MultiMux has to be
configured to talk to the channel devices and communicate over the
composite link.
Configuration of a MultiMux is accomplished through a combination of
setting DIP switches behind the front panel and software commands
entered through the supervisory console. The DIP switches determine
whether the MultiMux is a four or eight channel multiplexer, whether the
composite link device is an internal modem or DSU or an external
device, whether or not the command modem will accept remote access,
etc. The DIP switches control the hardware setup and the operating
setup is controlled through software commands. The software
commands are entered at a terminal connected to the COMMAND
PORT which are transferred to either the command processor or
command modem in the MultiMux. The software commands are AT
commands that configure the channel devices to communicate with the
MultiMux and configure the composite link device to communicate with
the PDN. To configure a channel device, the correct channel speed has
to be established, number of data and stop bits in a word determined,
the type of flow control and whether or not it is used and whether or not
pacing is active. These are just some of the AT commands that are used
to configure and display the status of the channel devices.
When the MultiMux MMH900 series is powered up, the command
processor transfers the stored configuration of the channel devices to
the data processor. The data processor takes the configuration
information and configures each channel for its particular conditions.

15
Chapter 1 - Introduction & Description
The composite link has to be configured for its parameters before data
can be transferred.
The composite link parameters are determined by more than justAT
commands transferred to the command processor. The composite link
parameters are determined by what type of device is used, whether it is
internal or external, speed, what type of remote multiplexer we are
communicating with and a number of line conditioning parameters. The
type of device used as the composite link device is determined by
whether the device is internal or external which is established by a DIP
switch setting and by the type of device installed in the MultiMux or
connected to the EXTERNAL COMPOSITE LINK RS232C/V.35
connector on the back panel. If an internal composite link MMH2834
modem is installed, the DIP switch would be set for an internal
composite link device. The type of MultiMux at the other end of the
composite link is determined by the setting of a four position DIP switch
within the MultiMux. The MultiMux MMH900 series is now ready to
transfer data from its async devices through an internal composite link
modem.

16
Chapter 1 - Introduction & Description
1.5 System Features
1.5.1 Response Time Control
Response time control is the technique used by a mux to make sure that
no user experiences undue delays in performance due to a specific
channel using too much link time. This can occur if one of the channels
is performing a high volume batch function, such as a print dump or
program transfer.
There are a variety of priority control (response time) schemes in use by
different mux vendors. Some vendors use a switch selection approach
where each channel can be given a high, medium or low setting with the
low used for those channels requiring higher volume batch transfers.
There are also software-sensing response time techniques where the
microprocessor actually monitors channel activity, and when a high
volume is sensed, that channel is given a lower priority so it will not
crowd out the others.
The MultiMux response time control method is one where data is
transferred from each channel on a timed basis while limiting the amount
sent with each transmission.
This insures that interactive users will not experience undue delays but,
on the other hand, batch activity can still be accommodated. This,
combined with a Response Time command and the ability to shut off
channels not being used, gives the MultiMux a very efficient priority
control system.
1.5.2 Dynamic Buffering
Abasic requirement of all muxes is some sort of buffering capability to
temporarily hold channel data while it is being assembled into a block. In
the early days, a mux was sometimes judged by the size of its buffers.
Large buffers are unnecessary in newer designs that include
sophisticated dynamic buffer allocation techniques where the amount of
buffer per channel is assigned on an as-needed basis.
In the MultiMux, each channel is assigned 1K of buffer, but in the case
where more buffer is needed, the MultiMux will start assigning additional
buffers from the channels not requiring it. In this way a single channel
can have up to 8K of buffer if required. When dynamic buffering is
combined with efficient flow control and the automatic transmission of
data from each channel at set intervals, as in the MultiMux, very smooth
operation for each user is the result.

17
Chapter 1 - Introduction & Description
1.5.3 Flow Control
Flow control regulates the volume of data entering the buffers. When a
particular channel buffer is almost full, a flow control command is issued
which stops further activity until the buffer is emptied. The most common
flow control methods currently used are Xon/Xoff, RS232C signal control
(using DTR or CTS) and ENQ/ACK. The MultiMux supports all three.
DATA DATA
CHANNEL DEVICE
INITIATED PACING
Channel
Device
Channel
Device Mux Mux
MUX INITIATED
FLOW CONTROL
Flow control stops the
input of data to the mux Pacing stops the output
of data from the mux
1.5.4 Diagnostics
Diagnostics in a multiplexer network are of considerable importance.
When a multiplexer fails there is not just one operator down, but many.
That is why the MultiMux is equipped with several diagnostic modes that
will test every aspect of the network. The diagnostics include easy-to-
execute tests for each channel, the composite link and for various
components of the MultiMux unit itself. There are nine different test
modes to ensure error free operation. They includeAnalog Loop, Digital
Loop, RemoteAnalog Loop, Switch and LED tests, Non-Volatile Memory
test, three other tests and a “Watchdog Timer” reset test.
1.5.5 Downline Parameter Loading
Operational parameters for both local and remote MultiMux units can be
set from one location. The MMH900 series can downline load
parameters to each other, but they cannot send parameters to the
MM16xx/MM32xx and MMH16/MMH32 units. When power is first applied
(or a Reset command is executed) to the local or remote MultiMux,
operational parameters are automatically sent over the composite link to
the remote MultiMux. For this function to work, the 8-position DIP switch
SW1 on the local (sending) MultiMux must be set to the OPEN position
and on the remote (receiving) MultiMux the 8-position DIP switch SW1
must be set to the CLOSED position.

18
Chapter 1 - Introduction & Description
1.5.6 Operational Statistics and Auto-
Reporting
Operational statistics provides the activity report for the MultiMux
network, andAuto-Reporting provides a means to report on these
statistics through the supervisory console on a set periodic time cycle.
Statistics such as receive-block errors pinpoint modem or line problems,
and flow control time totals indicate channel devices being set at
excessive speeds. Two simple commands are all that is necessary to
select statistical reporting and time cycle. If your command port is also
connected to a printer, the reports can provide an easy means of
generating data for better network management.
1.5.7 Parameter Memory
A nonvolatile memory for storing configurations and options means that
the MultiMux remains configured until you change it. Using this feature,
you can configure a MultiMux, turn it off, ship it and use it without having
to reconfigure it.
1.5.8 Channel Flexibility
The MultiMux permits a great deal of flexibility in configuring channel
parameters. You can mix up channel options, including speed, word
length, stop bits, parity, flow control, pacing methods, echoes and pass-
through characters. Channel control commands let you change single
channels, all channels or selected channels with a single command. By
using the downline loading capability or the command modem, channels
can be configured at the other end of the network.
1.5.9 Command Modem
The MultiMux can connect to a dial-up phone network through an
integral 2400/1200/300 bps V.22bis-compatible modem called the
“command modem”. The command modem is an asynchronous modem
used for remote configuration of the mux. The command modem is not to
be confused with the “link modem”, which is either an internal or external
synchronous or external asynchronous device handling the data
transfers over the composite link between two muxes.
By using the command modem, you get the equivalent of a remote
Command Port console. Your MultiMux can be dialed into from a remote
location for remote testing and configuration. The command modem will
automatically answer incoming calls.

19
Chapter 1 - Introduction & Description
1.5.10 Composite Link
The composite link of the MultiMux is capable of synchronous,
asynchronous and digital communications. The MultiMux can be
connected to several different types of communications links through
various modems and DSUs connected internally and externally.
Internally the MultiMux can be configured with synchronous lease line
modem at a link speed up to 28.8K bps or a Data Service Unit (DSU) at
link speeds up to 56K bps. Externally the MultiMux can be configured
with either a synchronous or asynchronous composite link modem or a
DSU for digital communications. The external modems must have error
correction and should have data compression for increased thru put and
only hardware flow control.

20
Chapter 1 - Introduction & Description
1.6 FCC Regulations for Telephone Line
Interconnection
1. This equipment complies with Part 68 of the FCC rules. On the
outside surface of this equipment is a label that contains, among
other information, the FCC registration number and ringer
equivalence number (REN). If requested, this information must be
provided to the telephone company.
2. As indicated below the suitable jack (USOC connecting
arrangement) for this equipment is shown. If applicable, the facility
interface codes (FIC) and service order codes (SOC) are shown.
3. The ringer equivalence number (REN) is used to determine the
quality of devices which may be connected to the telephone line.
Excessive REN’s on the telephone line may result in the devices not
ringing in response to an incoming call. In most, but not all areas, the
sum of the REN’s should not exceed five (5.0). To be certain of the
number of devices that may be connected to the line, as determined
by the total REN’s, contact the telephone company to determine the
maximum REN for the calling area.
4. If this equipment causes harm to the telephone network, the
telephone company will notify you in advance. But if advance notice
isn’t practical, the telephone company will notify the customer as
soon as possible.Also, you will be advised of your right to file a
complaint with the FCC if you believe it is necessary.
5. The telephone company may make changes in its facilities,
equipment, operations, or procedures that could affect the operation
of the equipment. If this happens, the telephone company will
provide advance notice in order for you to make necessary
modifications in order to maintain uninterrupted service.
6. If trouble is experienced with this equipment (the model of which is
indicated below) please contact Multi-Tech Systems, Inc. at the
address shown below for details of how to have repairs made. If the
trouble is causing harm to the telephone network, the telephone
company may request you remove the equipment from the network
until the problem is resolved.
7. No repairs are to be made by you. Repairs are to be made only by
Multi-Tech Systems or its licensees. Unauthorized repairs void
registration and warranty.