SIP is easier to make redundant. If there is more than one physical cable to the provider, then SIP can be reserved in three ways at L2, it's the Portchannel, STP and the Fex link, the same as RTG from Juniper. CUBE routers can also be reserved for slightly modified HSRP technology (conventional HSRP technology does not work with SIP)
https://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-border-element/112095-cube-hsrp-config-00.html
And in the case of E1, very few E1 multiplexers support redundancy using two physically different links. and the router on which E1 is terminated can only be reserved by a second router in a cold standby. in the event of a failure, you must manually switch the patch cord.
