What do people use for SIP redundancy? (Small office - 1-10 users, small budget) Scenario: 1. Analogue line used for fax machine. Also provides ADSL service. QoS configure on modem, works well. Issue: What if ADSL goes down for whatever reason, or the SIP provider has an outage? What would be the most cost effective backup to allow calls to be sent or received? The options I can think of are: 1. Additional analogue line with gateway - Will allow single concurrent call. Not a big help as it is only one concurrent call. 2. Have a second SIP provider on basic plan that is only used if SIP provider #1 of down and out. Would also need second internet connection to be fully redundant. Is 3G/4G/LTE suffcient/reliable as a backup for a fixed line ADSL connect? Will there be NAT/IP Address issues?