Good information provided by Amit. I would add, in laymens terms, the following description of VCS and VCS-E:
If you are familiar at all with CUCM - then think of VCS, which sits on the internal network, as the Call Control platform for video endpoints. By video endpoints - think room based physical video servers often called "codecs" or software clients like Cisco Jabber Video for TelePresence.
Do not confuse the use of "codec" here with the concept of a codec like G.711. The VCS acts as a SIP proxy and an H.323 GK - meaning your video endpoints can talk SIP or H323 to register to the VCS.
The VCS-E, which typically sits in a firewall DMZ, support external video endpoints. By that, I mean it enables the ability of someone sitting "outside" of your company, to establish a video call to a video endpoint physcally inside of your companies firewall.
Once you install the VCS software - a VCS-E software key can be installed which then "makes" this VCS a VCS-E. So basically they use the same underlying software installation and a simple key is what makes that platform a VCS-E.
Good luck!
Amir
