Is uPnP a requirement?

Hi all,
We're encountering problems discovering a Sonos bridge connected to a Cisco router from iPad, Macs & iPhones. The issue is somewhat non-uniform, with some devices finding it, but others not discovering at all. We have about 9 devices for testing at our disposal, including iPhone 5, iPad mini, mac air, IBM Windows 7 notebook, iPad 1, etc. All equipment has the latest respective OS versions and Sonos software, standard DHCP IP settings, with trouble free access to the internet, network shares, etc from within the network. There are plenty of free DHCP addresses in the pool.

We then put the Sonos bridge on to a switch as a test and was able to find the bridge from devices previously unable.

We are using an enterprise grade router (Cisco 897VA) which does not support UPnP and suspect this is the issue. We simply need to know whether UPnP is a requirement of Sonos, as this doesn't seem to be well documented. If it is, then we can install a workaround and won't keep trying to make this router work.

Is UPnP a requirement of Sonos for devices to discover bridges, etc.?

Thanks in advance.