I have a strange problem that I was hoping somebody out there may have a creative solution for. The vast majority of our installations are done in remote locations where hardline DSL or Cable are unavailable. Therefore, we use both Satellite and Cellular to provide data connectivity. Satellite is the most reliable and we are able to control this connection on a granular level as well as provide our clients with an SLA on service. Cellular is anybody's guess, but sometimes it works great and other times it does not.
Most of our clients want the ability to load balance between satellite and cellular and we have employed the SA520 for this purpose, but I'm running into a problem with the SIP trunk registration. Again, due to the nature of our client's work, these systems are usually dormant (and shut down) until needed. At that time, everything gets powered up including satellite and cellular, but it takes a mere number of minutes for the cellular to come up and online whereas the satellite takes closer to 10 minutes to complete the connection. On a typical startup, the SA520 will look at both WAN ports and perform a DNS lookup on the DNS servers supplied by each connection. Satellite appears to be down, even though it is still coming online, whereas Cellular responds much more quickly. The SA520 routes all traffic through the Cellular connection, and the UC540 registers with the SIP trunk provider via the cellular connection. In the next few minutes, the satellite connection comes up and the SA520 begins routing traffic through this port via the RTP and SIP protocol bindings that I have set in the SA520 for this traffic.
Now this is where I'm scratching my head. The SIP trunk provider has a static IP for incoming calls (the SA520 WAN interface for the satellite modem). But because the UC540 has already registered SIP via the cellular WAN port on the SA520, incoming calls are getting denied. If I manually unregister the UC540 and tell it to register (once the satellite connection is up), incoming calls work again. I thought that I found a solution by setting the reregistration time very low (60 second), but the SIP provider complains (understandably) that they are being bombarded by register requests. Their recommendation is to remove the registrar server completely, but this also seems to break my incoming calls.
Has anybody run into anything like this or have a creative solution? Anything to check or try?
Outbound calls are available through any Internet Connection. Inbound calls do not seem to work properly through the cellular connection. This is likely because the SP configuration is set to forward all calls to a specific IP. I could change the SP configuration to all for dynamic registration which would theoretically allow the PBX to function over cellular or Satellite. I'm pretty sure that the cellular connection does not have a static IP, so this could be a little troubling. In addition, some of our clients are using ATT as their cellular Internet carrier. ATT does not allow RTP over their cellular data network which effectively means that the IP PBX can register, and calls can be completed, but no audio traffic will flow. I'm open to any suggestions.
Doesn't the SP offer a failover number? If they do, you can get an analog line into the UC500 and then use that for inbound calls if the satellite becomes unavailable. In that case, you would only allow the registration to take place over the satellite connection and not the cellular. This would only be used for data.
Failover is available, but it costs the client extra per month and would require a cellular voice terminal. Each of these sites is mobile, so we're relying on wireless (satellite and cellular) to provide IP for dialtone.
As for the option of forcing the registration through the Satellite link, this is preferrable, but I was told by the SBSC guys that this was not possible with the SA520. Even when I configure protocol binding, SIP and RTP traffic will still failover to the cellular WAN if the Satellite WAN is not detected in an operational state. There does not appear to be the capability within the SA520 to force specific info over one WAN port and reject that traffic type if that port is unavailable until it is available. If there is another way to do this, please let me know as we have several customers with this network design.
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