The nature of analog modems and a phone line limits
any single modem to connecting to one phone number
at a time, and if one application is using the modem
to connect to a certain phone number, it would not
be possible for another application to dial out to
another phone number on that modem at same time.
However, Windows has a feature called "Internet
Connection Sharing" which can allow a PC to share
one internet connection with other PCs on their local
network. It does not matter if the source of the internet
connection is thru a Dial-Up Networking (DUN) modem
connection, or a full time connection such as DSL,
cable, etc. NetModem can be used to make a DUN connection,
and this DUN connection could be shared just as if
it had been done on a local modem.
For dialup applications other then DUN, you would
need either multiple modems or a multi-modem PCI card,
and you would also need multiple phone lines. NetModem
Server is designed to "pool" multiple modems, so
each time another user needs to dial out, the next
modem in the pool is automatically assigned to them.
If RAS / RRAS is installed
on the NetModem Server PC, NetModem Server will allow
modems to be pooled both by RAS (for Dial-In) and
by NetModem Server (for Dial-Out). Each time a client
requests a modem, NetModem Server will ask RAS if
a modem is currently in use, and if RAS says its available,
NetModem Server will borrow that modem from RAS, returning
it to RAS's use after the client is finished with
Is Active Directory required to support User Authentication?
Active Directory is not required for user authentication,
and you can locally authenticate on a network without
a domain controller by simply defining users and groups
on the NetModem Server PC. NetModem Server also supports
multiple Active Directory controllers and NT4 domain
NetModem Server allows each pool of modems be individually
configured for user authentication. If user authentication
is enabled for a pool, only the users and groups defined
in that pool properties access list will be given
Does NetModem support multiple modem pools?
NetModem Server allows multiple pools to be defined. Each modem pool can contain one or
multiple modems, and all the modems in the pool share
the same properties and security settings.
Yes, this can be done in the NetModem Client Configuration
window by setting the "Remote COM port to connect"
pulldown ment to "Automatic Pooling".
Yes, but we reccomend that you use fax modems which support
Class 2 or Class 2.0 fax and the PC faxing software
you are using must also be configured to use Class
2 or Class 2.0. Class 1 is timing sensitve and therefore
it may not always be reliable when used over a networked modem. For more
information please refer to the faxing
NetModem allows using a modem for inbound modem data/fax
calls by a client PC, but this would cause the modem
to be constantly in-use by the client that is holding the Modem port open while listening
for an incoming RING, thereby preventing other clients from using this modem during that this time.
For receiving inbound DUN (Dial Up Networking) calls
on the modems, you can enable Microsoft RAS (Remote
Access Service) on the NetModem Server PC, allowing
NetModem Server to share the modem resources with
RAS. Then when a client requests a modem, NetModem
Server will ask RAS if the modem is currently available,
and if it is, NetModem Server will borrow the modem
and return it to RAS after the client releases it.
If the Network Administrator does not want to allow
the NetModem Client PC's to be able allow modem applications
such as pcAnywhere to accept incoming modem calls,
a pool of modems can be configured to block Dial-In.
This option is found under Pool Properties in NetModem
When a client application attempts access a modem,
but all the shared modems on the server are currently
in-use by other clients (or local applications on
the Server PC), the client will receive a pop-up message
on their screen indicating that NetModem Server does
not have any available modems. This pop-up message
can be disabled in a client under the "Advanced"
settings button. The client application will be told
that the Modems COM port could not be opened, due
to being in use by another application.
When attempting to add a modem driver to the client's
virtual COM port, the COM port is not listed. Why?
Some Plug-and-Play modem drivers (Including US Robotics
and Multitech external modems) will fail to see a
modem attached to a virtual COM port by default. This
is also true for most Software based modems (commonly
called SoftModems), which look for PCI or USB hardware
to be present before allowing a COM port to be selected.
Another possible reason for this is if the virtual
COM port has not been configured with the correct
IP address, or the "Save" button has not
been clicked after setting the IP Address, thus preventing
it from reaching the physical modem on the NetModem
Server PC. You should verify that your NetModem Client
COM port is configured properly, by going to the "NetModem
Client Configuration", selecting that COM port,
and run the "Test Server Connection" to
verify that the modem on the server is detected.
If the test is successful, then please contact a
PC Micro support engineer and provide your modem driver
.INF file, and we can modify it to allow installing
it on a virtual COM port. You can email the file to
email@example.com. If you don't have the .INF file,
then please provide the exact model number of the
Modem. Note: Some mail servers do not allow sending/receiveing .INF file extentions, so before sending it to us, please rename the extention to something else such as .TXT or .IN_.
By default NetModem Server does not check to see
if there is a modem connected to one of the shared
COM ports before passing that COM port to a client.
In order to enable this behavior, click on "Properties"
from the NetModem Server Configuration tab, and enable
the checkbox named "Reset Modem when opening port".
Then click "Ok" followed by "Save Changes".
This will cause NetModem Server to send an "ATZ"
initialization command to the next available modem
in the pool, and it then waits for the modem to respond
with an "OK" before passing that COM port to the client.
If an "OK" response is not received within 1 second,
it will try the next available shared COM port.
NetModem Client may need to update the IPv4 routing table
to ensure that it allows the NetModem Server to remain
reachable. This is nessesary because a Dial-Up Networking
(PPP) connection will change the IPv4 routing table to
reach the DUN destination. Each time a NetModem Virtual
COM port is opened, the default action is to update
the routing table as needed to allow the NetModem
Server to always remain reachable. If there are multiple
default routes in the table, NetModem Client will
use the first default route to determine a new route
which might need to be added.
Problems can appear if the route table has default
route(s) which are bad, for example, if the IP address
listed as the gateway doesn't exist or is unreachable.
If the only default route is bad, or the first one
of multiple default routes are bad, it is likley you
will experience a problem when creating a Dial-Up
Networking conection. If NetModem Client needs to
create a specific route for a NetModem Server which
is on a different subnet, it will use that unreachable/non-existant
gateway, which then renders the NetModem Server PC
NetModem Client will implement incorrect specific
routes only if the routing table is misconfigured
and/or reports invalid information.
For information on how to solve multiple route issues see https://pcmicro.com/netmodem/support_routing.html
Depending on its configuration on your network,
the keep-alive feature of the TCP/IP protocol takes
a long time (10 to 15 minutes) to differentiate between
a merely idle connection and a broken one. The TCP
protocol opts to err on the side of keeping a possibly
idle connection open.
To improve on this, NetModem Client and NetModem
Server use a separate mechanism to detect lost connection
in approximately one minute.
A small time delay (known as latency) is added when
communicating over a network, compared to using a
local serial port and modem. There is a small number
of applications that are sensitive to latency, The
most common is Class 1 fax applications. Therefore
we do not reccomend using NetModem with class 1 fax
applications. Most hardware-based modems support Fax Class 2 or 2.0 protocols which are not effected by latency.
Dial-Up Networking will always add a new "default
route" to the TCP/IP IPv4 routing table once a DUN
session is started. If the local area network uses IPv4 and contains
multiple subnets, and the PC connects to those subnets
using a default route in the routing table, the new
default route added by Dial-Up Networking will be
used instead of the original one.
This results in the PC now having access only to the
local subnet, because any TCP packets destined for
the other subnets will be routed to the modem rather
than to the network interface card.
This issue is not unique to NetModem Client, as it
will also also occur on a PC using a local modem.
For more information, see the following Microsoft
Knowledge Base articals:
While these KB Articles only refer to Windows NT, they
also apply to all later versions of Windows.
The solution is to modify the routing table by adding
a static route to the other subnets, as described in
KB Article 140859.
NetModem Client has an option to update the routing
table automaticly when the NetModem Server is on another
subnet. This can be found under the Advanced section
of the NetModem Client Configuration, and is enabled
Client and NetModem Server run as a Windows Service.
Either Service can be stopped or even disabled by
going to the Windows Control Panel under Services,
and configuring the "NetModem Client" or
"NetModem Server" service. It is also possible
to run NetModem Server as a non-service executable.
This indicates that when the client sent an AT
command to the modem on the server, the modem failed
to send back an OK response.
This could be caused by a number of reasons, such
as a defective modem, or selecting a COM port in NetModem
Server which does not have a modem attached to it.
If you encounter this issue, verify that your modem
is working by going to the NetModem Server PC and under the Windows Control panel open "Phone and Modem", then select your modem under the "Modems" tab, and click Properties > Diagnostics > Query Modem. If the query fails to communicate with the modem, or of none of the Responses show "Success", then the modem is not functioning, or is already in use by another application or service. Contact a PC Micro support engineer for further
The 2 most common reasons are a bad phone number
or a modem driver issue.
Phone Number issues:
Verify that the telephone number is entered correctly
(1+area code for long distance, any access codes you
may need for an outside line such as 9 before the
number.) You may also try plugging in a standard analog
phone and try to dial the number to verify that the
phone line supports outbound or long distance calls.
Modem driver Issues:
On the server side check that there is not more then
one modem driver assigned to the COM port, byt going
to Control Panel > Phone and Modem Options >
Modems. If more then one modem driver is assigned
to the same COM port, NetModem Server will not be
able to open the port correctly.
On the client side check the installed modem drivers
to make sure they match the modem which is installed
on the server side. if these drivers are for a generic "Standard 56k modem"
rather then being for the specific brand and model of modem(s) installed on the NetModem Server, it can cause connections to fail due to mismatched
"AT" commands. Therefore it is never reccomended to use the "Standard 56k modem" driver (or a driver for a different model of modem), on the NetModem Client PC.
Some modem drivers (most commonly PCI and USB) will
not install on a Client's virtual com port, because
they expect to see the PCI or USB hardware present.
Our support department can modify these modem drivers
for you to allow you to install them.
There are known issues with older versions of the
Digi Acceleport Xp firmware, which can cause advanced
modem applications to fail, hang, or crash. This has
been solved in the current Digi firmware, which is
a free downloadable update available from Digi's web
site here: https://www.digi.com/support/productdetl.jsp?pid=1374&osvid=0&tp=2
No. They are independent from each other.
Assuming NetModem Server is installed
on the ISA Server PC, and the NetModem clients are
on the internal network, You will need to define the
following two rules in ISA Server, one for inbound
traffic and one for outbound traffic:
NetModem Server version 3.33 installer was the first
version to use InstallShield 2008 which can result
in an install error 1721 in some rare cases. This
installer error appears when trying to uninstall or
upgrade to a newer version. This can be resolved by
performing a manual uninstall as shown on the
Solving Error 1721 page.
How can I remotly deploy NetModem Client with pre-configured
This can be done by passing the installer a registry
configuration file for the Virtual COM port settings
on the command line. Please review the NetModem
Unattended Installation tips
NetModem uses the latest release branch of the OpenSSL Library, version 1.1.1. OpenSSL is an Encryption
Library that allows a secure connection between the
server and the client connections.. Over the years,
security exploits and vulnerabilities have been discovered
in OpenSSL from time to time, and when this happens
the OpenSSL team releases an updated version to fix
such issues. Due to the importance of such issues,
we will generally release a new version of NetModem within a
few days of a new version of OpenSSL being released.
is not avalible in all countries the evaluation version
may have the encryption feature disabled by default. Contact
your account manager if you require encryption.
The sample SSL certificate included with NetModem
server is not signed by a Certificate Authority, so
when testing with this certificate the client should
be configured to *not* require a signed certificate
(found under advanced options in the client configuration).
The sample certificate should only be used for testing
purposes, as it uses a known password and is therefore
not truly secure.
If you need assistance with encryption please go
to the support section of our web site and a fill
out a support
NetModem Server and Client v4.x are developed using Microsoft Visual C++ 2008 SP1, with all Microsoft security patches applied.
The only Visual C++ libraries used are MFC and CRT, and we specifically avoid using the ATL (Active Template Library) and .NET
code due to both having a history of vulnerabilities. For the kernel mode drivers, only C# is used without any libraries.
The NetModem client and server installers only provide the Microsoft Merge Modules for MFC and CRT, rather then the full VC++ Redistribution Package.
For SSL/TLS Encription, the OpenSSL toolkit libraries are used.