Screen sharing not working when calling externally via expressways

[carl_townshend]

Hi All

We have VC devices, spark room kits, dx80's etc all on our CUCM, we have an expressway C and E for the VC's to make B2B calls.

We have an issue wherby we cannot do a screen share for external calls from our VC devices, i.e if we plug a laptop in and share the screen it says "sharing could not be initiated".

This works when doing internal to internal VC calls though.

Any ideas what this could be?

I have tried both settings below on the SIP trunk profile to the EXP-C, but still no joy

Early Offer support for voice and video calls - Mandatory and Best effort, and Allow Presentation Sharing using BFCP is also ticked.

Many thanks

[Jonathan Schulenberg]

Ensure BFCP is enabled on the Expressway Neighbor, Traversal, and DNS zones as well.

[carl_townshend]

Hi Jonathan

We have done a test call between 2 VC's, one on our network and another external one, this was a sip to sip call and the screen sharing worked fine, they called us though. so I would imagine from out end it's all OK? and the issue is with the Pexip interop service ? basically it allows MS Teams to join a Cisco VC call.

[Jonathan Schulenberg]

The Pexip status page is green; it seems unlikely to be an issue on their end. At the risk of stating the obvious: I'd try a call in the opposite direction with the external endpoint to verify BFCP content sharing is working in both directions. If not then your problem statement has narrowed to "BFCP content sharing fails on outbound B2B SIP calls." The most likely cause of that would either be a different call path (e.g. different Zones in Expressway) or CUCM invoking an MTP/transcoder - possibly because you set Early Offer = Mandatory or checked MTP Required. Looking at the SDP at each hop of the re-INVITE would help narrow down where BFCP is being stripped off. For example, if the re-INVITE from endpoint to CUCM includes BFCP but it's missing when CUCM sends a re-INVITE to Expressway then your issue is within CUCM.

[carl_townshend]

Hi jonathan

what should the settings be on the trunk for this to work?

should it be best effort for the early offer setting?

[Jonathan Schulenberg]

Best effort early offer is generally the recommended choice. CUCM will send EO if the calling endpoint/trunk supports it. If not, it'll fall back to DO instead of invoking an MTP.