While we can say this should just work, the reality is, it's not very reliably true and I would not build product or business on the assumption that it works well.
Yup. Understood. We can't get away from sending multi-packet messages. We try our best to keep SIP messages as small as possible though sometimes certain optional features required by customers push it beyond their MTU. We're also starting to see decreasing MTUs as customers deploy various SD-WAN solutions and it's tough to keep up with these when you're already teetering on the edge of what used to be considered a fairly common minimum MTU value. We can, of course, get away from using UDP. We can and do run SIP over TCP and indeed over TLS on TCP though the stateful nature of TCP often makes this undesirable. We see a lot of SIP phone implementations that do not handle TCP connection failures very well and result in a loss of calls for a period of minutes if this happens, as they take a while to notice the connection has dropped and should be re-established. Pros and cons of each. If anyone has any specific information about Spectrum CPE changes or indeed any contacts who may be able to interrogate this internally within Spectrum that would be appreciated.