You need PPPoE connection type for your Cellular WAN ? This is something weird to me. May i know the service provider and country ? Private APN network ?
For cellular bridge connection you can consider IP Passthrough mode for the BR1 series.
Just to cut to the chase: Is the Balance 580 in place (and a given)? If not then you may be well served by an HD2 or HD4 (respectively two and four cellular radios, each with one or two SIM cards), which could also handle the routing (and a wired WAN).
yes we have been using Balance 580 for more than 3 years now. but existing ADSL connection PPOE is not enough
current connection
5 ports with 1mb speed ADSL with 2 fixed ip (for management and opendns control) total for our branch 5mb.
isp told us that they have no ports left to upgrade the speed
so we tested using personal 4G modem from other telco and the speedtest is quite good up to 20mb so we plan to use
2 ports with 4G LTE modem (ppoe with fixed public ip)
and maintain 1 port for ADSL fixed public ip if Peplink 580 could not support 4G LTE ppoe