Cisco Jabber “Share presentation” button is greyed out.

With the newest versions on CUCM and IM&Presence (10.5 and higher) greyed out “Share presentation” button in Cisco Jabber can be caused by a couple of things:
a) “Allow BFCP” checkbox isn’t checked in SIP profile of the CFS (TAB,BOT,TCT) device in CUCM
b) firewall is blocking a connection.
When investigating the latter I decided to discover what is this BFCP and how the presentation is shared.

1) When I make a call from Cisco Jabber to another video-capable endpoint (i.e SX20), a SIP invite is sent with following SDP attributes

Media Description, name and address (m): video 25990 RTP/AVP 126 97
Media Attribute (a): content:main

Media Description, name and address (m): video 26744 RTP/AVP 126 97
Media Attribute (a): content:slides

Media Description, name and address (m): application 5316 UDP/BFCP *
Media Attribute (a): floorctrl:c-s

Attribute with content:main describes our main video stream. The RTP stream will start right after called endpoint answers.
Attribute with content:slides is a presentation stream. This stream will be a usual RTP carrying payload with type of 126 (H264 coded video). It won’t start until we hit “Share presentation” button.
Attribute with application 5316 UDP/BFCP is a description of BFCP protocol. According to https://tools.ietf.org/html/rfc4582 it controls who is holding a shared resource (presentation in our case) and who’s transmitting (to avoid bidirectional presentation sharing).
Import thing here is who is going to be the server in this connection. In my case floorctrl:c-s shows that Jabber is willing to be a server as well as a client.

2) Let’s look at the SIP 200OK with SDP

Media Description, name and address (m): video 16880 RTP/AVP 126
Media Attribute (a): content:main

Media Description, name and address (m): video 16882 RTP/AVP 126
Media Attribute (a): content:slides

Media Description, name and address (m): application 28339 UDP/BFCP *
Media Attribute (a): floorctrl:c-only

First 2 media descriptions are obvious: they are usual answers to offers of the calling party. But in application 28339 UDP/BFCP there is an attribute of floorctrl:c-only.
This shows that called party is going to be a client in BFCP terms. Moreover it will initiate a BFCP connection. If there is a firewall which block UDP port 5316 in direction from endpoint to Jabber, BFCP server in Jabber won’t see an incoming connection and would grey-out the button. This BFCP connection will occur right after SIP 200 Ok and long before you can hit a “Share presentation” button in Cisco Jabber.

3) This only describes a case when you share the presentation during a call.
In addition you can share presentation without making a call from a chat window in Jabber. This is done without BFCP with a different protocol.