in reply to CGI Parameters

When your manager says that "Comms-Branch" is a "HTTP header variable", he means that it is in the HTTP header. The HTTP header is a big chunk of text in the request and the reply. For example, an HTTP request might look something like this: 
GET /dir/page.pl HTTP/1.1
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, */*
Referer: http://www.foo.bar/otherdir/otherpage.pl
Accept-Language: en-us
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 5.0; Windows 98; DigExt)
Host: www.foo.bar
Cookie: monster=blue;
My-Other-Header: yippy yahoo!

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All of those lines except for the first one are "headers"... they basically act (sorta) like a perl hash, in that they are name-value pairs. Some of those headers have particular meaning to the web browser and web server (most of them, in fact). However, the user agent (the application making the web-service request in this case) can really put any arbitrary header in there, as long as it doesn't conflict with a name used by a real header.

Anyway, if I wanted to find the value used by, for example, the "My-Other-Header" header... I could find it in the environment by looking at (yes, it does get driven all into uppercase): $ENV{HTTP_MY_OTHER_HEADER}. So, in your example, you could find "Comms-Branch" http header in $ENV{HTTP_COMMS_BRANCH}. For more information, you can examine the environment by putting: 

use Data::Dumper;
warn Dumper \%ENV;

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in your code, and then looking at the error-log. All of the (non-special) HTTP headers get written into the subprocess's environment with the prefix HTTP, all uppercase, and with non-word characters turned to underscore.

Anyway, hope that helps. Oh, and this should be the same whether you are using old-school CGI (not CGI.pm, mind you... but the common-gateway-interface, which CGI.pm is a wonderful tool to help you use) or under mod_perl (again... with or without CGI.pm). 

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:Wq
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In Section Seekers of Perl Wisdom