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><H1
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><A
NAME="USING"
>4. Using the Software</A
></H1
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="DIRECTCONNECT"
>4.1. Direct Connection</A
></H2
><P
> You can use OpenH323's <B
CLASS="COMMAND"
>ohphone</B
>
program to connect directly to a
NetMeeting client. Specify the <TT
CLASS="OPTION"
>-n</TT
>
option to indicate that you're
not using a gatekeeper, and either the DNS name or IP address of
the NetMeeting client:
</P
><TABLE
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><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
>bash$ <TT
CLASS="USERINPUT"
><B
>ohphone -n 208.130.48.22</B
></TT
>
</PRE
></FONT
></TD
></TR
></TABLE
><P
> You can also start <B
CLASS="COMMAND"
>ohphone</B
> to receive incoming
calls from NetMeeting clients:
</P
><TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
>bash$ <TT
CLASS="USERINPUT"
><B
>ohphone -n</B
></TT
>
</PRE
></FONT
></TD
></TR
></TABLE
><P
> See the <B
CLASS="COMMAND"
>ohphone</B
> documentation for more information
on its additional features, including video conferencing, codec
selection, and auto-answer.
</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="DIROPT"
>4.2. Directory Operation</A
></H2
><P
> Make sure you have an LDAP server running the NetMeeting directory kit,
as described above.
</P
><P
> On the NetMeeting client, select the
<SPAN
CLASS="GUIMENU"
> Tools
</SPAN
>-><SPAN
CLASS="GUIMENUITEM"
> Options
</SPAN
>
menu item to display a configuration dialog. Under the
"General" (NetMeeting 3) or "Calling" (NetMeeting 2) tab,
there will be a section for "Directory Settings".
Here you can enter the IP address or DNS name of the server.
The client will then attach to the server and register itself
either automatically, if the "Log on to directory server when
NetMeeting starts" checkbox is selected.
You can also log on to the directory server manually, by selecting
<SPAN
CLASS="GUIMENU"
> Call
</SPAN
>-><SPAN
CLASS="GUIMENUITEM"
> Log on
</SPAN
>
.
</P
><P
> If the user selects
<SPAN
CLASS="GUIMENU"
> Call
</SPAN
>-><SPAN
CLASS="GUIMENUITEM"
> Directory
</SPAN
>,
a directory window will be displayed showing all users
registered on the LDAP server.
Double-clicking on one of the names will initiate a connection
to that user.
</P
><P
> Querying the NetMeeting LDAP server from Linux can be done, but
is tricky because the client's IP address is stored in decimal,
and I don't mean dotted decimal. For example, the IP address
63.216.69.197 is stored as 3309688895. Here's some
Perl code to convert back and forth from the NetMeeting
IP address format:
</P
><TABLE
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><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
># Convert $addr (IP address or DNS name) to a NetMeeting decimal IP address
use Socket;
$bytestring = inet_aton($addr);
if (defined $bytestring) {
($sipaddress) = unpack('V', $bytestring);
} else {
die "Can't resolve $addr\n";
}
# Convert $sipaddress (from a NetMeeting LDAP server) into dotted decimal form
$packedipaddr = pack 'V', $sipaddress;
$ipaddress = join '.', unpack('C4',$packedipaddr);</PRE
></FONT
></TD
></TR
></TABLE
><P
> Included with the NetMeeting directory kit is
<B
CLASS="COMMAND"
>nmdirectory</B
>, a simple Perl/Tk script to query
a NetMeeting LDAP server and display the clients registered with it.
It's very primitive, and doesn't work well with large databases,
but provides a rudimentary example of how to interpret search
results from a NetMeeting LDAP server.
</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="LNKFRMWEBPAGE"
>4.3. Linking From A Web Page</A
></H2
><P
> Microsoft Internet Explorer understands URLs with a "callto:" scheme
that specify NetMeeting destinations in one of two forms. When a
link with a "callto:" URL is selected, Internet Explorer runs
NetMeeting and directs it to connect to the specified destination.
</P
><P
> The first URL form, "callto:destination", where 'destination' is
either an IP address or a DNS name, causes NetMeeting to open an
H.323 connection to port 1720 on 'destination'. Use this form
to connect directly to another NetMeeting or OpenH323 client.
</P
><P
> The second URL form, "callto:server/alias", causes a directory lookup
on LDAP server 'server', searching for a CN attribute of 'alias'.
Assuming a match is found, a connection is made to the IP address
specified in the entry's sipAddress attribute. NetMeeting clients,
by default, register their user's E-mail addresses in the CN
attribute. Use this form to perform a directory lookup based
on E-mail address.
</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="PERMDIRENT"
>4.4. Permanent Directory Entries</A
></H2
><P
> NetMeeting clients aren't the only source of LDAP directory entries.
In particular, permanent directory entries can be manually inserted
into the LDAP server using the OpenLDAP client tools. Assuming the
attributes are specified properly, these entries will then appear in
NetMeeting directory listings and can be used as targets in "callto:"
URLs. This is useful when working with OpenH323 clients that don't
register themselves by default with the LDAP server.
</P
><P
> To simply creating directory entries, the <B
CLASS="COMMAND"
>nmaddentry</B
>
script is included in the NetMeeting directory kit. Run it
without arguments for a usage message. For example, if you've
started <B
CLASS="COMMAND"
>ohphone</B
> on "y2k.freesoft.org", you
can register it with the LDAP server on "ils.freesoft.org" using
alias "baccala@freesoft.org" like this:
</P
><TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
>bash$ <TT
CLASS="USERINPUT"
><B
>nmaddentry -h ils.freesoft.org baccala@freesoft.org y2k.freesoft.org</B
></TT
>
Successfully added cn=baccala@freesoft.org, objectclass=rtperson
bash$
</PRE
></FONT
></TD
></TR
></TABLE
><P
> This entry will now appear in NetMeeting directory listings and
can be addressed as "ils.freesoft.org/baccala@freesoft.org".
The entry will automatically timeout after 30 minutes.
The <TT
CLASS="OPTION"
>-p</TT
> switch creates a permanent directory
listing that won't time out, but this only works on
OpenLDAP servers using the NetMeeting directory kit.
To remove a permanent entry,
use the <B
CLASS="COMMAND"
>ldapdelete</B
> program
included with the OpenLDAP distribution, specifying the LDAP
Distinguished Name returned by <B
CLASS="COMMAND"
>nmaddentry</B
>:
</P
><TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
>bash$ <TT
CLASS="USERINPUT"
><B
>ldapdelete -h ils.freesoft.org 'cn=baccala@freesoft.org,objectclass=rtperson'</B
></TT
>
bash$
</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="SERVMULTALIAS"
>4.5. Serving Multiple Aliases</A
></H2
><P
> The attributes registered by a NetMeeting client include 'sport',
the TCP port number it listens on for incoming H.323 requests, but
since this attribute is never retrieved in search requests, it
isn't as useful as it first appears. In fact, NetMeeting always
opens H.323 connections to the default port (1720), which raises
the question of how to serve multiple aliases from a single IP
address.
</P
><P
> The key to doing this is the <B
CLASS="COMMAND"
>forwarder</B
>
program, included in the OpenH323 CVS archive.
<B
CLASS="COMMAND"
>forwarder</B
> listens for connections
on port 1720, and can be configured to redirect them based on the
alias being called. This allows calls for each alias to be sent to
a unique port number, where a program like <B
CLASS="COMMAND"
>ohphone</B
>
or <B
CLASS="COMMAND"
>openam</B
> is listening.
</P
><P
> To use aliases, an LDAP directory is required, with an entry for each
alias. Each alias entry should specify a 'cn' attribute with the
alias name, and a 'sipAddress' attribute with the IP address of the
host where <B
CLASS="COMMAND"
>forwarder</B
> is listening.
</P
><P
> I've successfully configured a single host to act as a combination
LDAP server (on port 389), <B
CLASS="COMMAND"
>forwarder</B
>
(on port 1720), and
<B
CLASS="COMMAND"
>ohphone</B
> and <B
CLASS="COMMAND"
>openam</B
>
clients on various private port numbers and remote systems.
</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="ANSWERINGMACHINE"
>4.6. Using the Answering Machine</A
></H2
><P
> The OpenH323 answering machine, <B
CLASS="COMMAND"
>openam</B
>, will
listen for incoming H.323 connections, play a pre-recorded
message, and then record any audio sent to it into a file.
It can optionally be configured to run another program at the
end of the call, to email the recorded audio, perhaps.
</P
><P
> It's usefulness is currently (December 2000)
limited by the lack of a gatekeeper
program clever enough to redirect calls to it if there's no
answer at the main address. Thus, it will only act as an
answering machine if the <B
CLASS="COMMAND"
>ohphone</B
> program
is running at the main address, and has been configured to
redirect calls to another address, using
the <TT
CLASS="OPTION"
>--forward-no-answer</TT
>
and <TT
CLASS="OPTION"
>--forward-busy</TT
> options.
</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="CONFERENCECALLS"
>4.7. Conference Calls</A
></H2
><P
> The <B
CLASS="COMMAND"
>openmcu</B
> program, in the OpenH323 CVS
archive, implements an H.323 Multipoint Control Unit (MCU).
Multiple NetMeeting or <B
CLASS="COMMAND"
>ohphone</B
> clients
can connect to the MCU and form a conference call. As of
December 2000, the quality and reliability of the connection
is problematic, but hopefully this will improve.
</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="NATROUTING"
>4.8. Routing Calls Through NAT</A
></H2
><P
> Special support is required on a NAT (IP Masquerade)
router to allow H.323 traffic to pass through.
If the NAT router is running Linux, two masquerading modules
are available:
</P
><P
></P
><UL
><LI
><P
><A
HREF="http://www.coritel.it/coritel/ip/sofia/nat/nat2/nat2.htm"
TARGET="_top"
>http://www.coritel.it/coritel/ip/sofia/nat/nat2/nat2.htm</A
></P
></LI
><LI
><P
><A
HREF="http://netmeetingmasq.sourceforge.net/"
TARGET="_top"
>http://netmeetingmasq.sourceforge.net/</A
></P
></LI
></UL
><DIV
CLASS="NOTE"
><P
></P
><TABLE
CLASS="NOTE"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/note.gif"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
> I have not tested either of these modules.
</P
></TD
></TR
></TABLE
></DIV
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="CUSTOMCONFIGURATION"
>4.9. Custom Configurations</A
></H2
><P
> The server capabilities can be customized by modifying the
'netmeeting.perl' script. For example,
calls for stale entries could be redirected to an
"forwarder" configured to hand off to "openam" answering
machines. Thus, calls to a unavailable user would be answered
and recorded for later playback.
</P
><P
> As OpenH323's development continues, it's expected that
these techniques will become more sophisticated, for example
by ringing the user first and only forwarding to an answering
machine if there's no answer after a given time.
Such functionality would most likely be placed in a gatekeeper.
</P
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