Dial on Demand Routing

[kirandeep.singh]

Why do we need Dialer interface/DDR routing for cisco wireless lte routers (c819, c1121) when the cellular interface can be assigned static IP address or automatic IPCP negotiated address? This cellular interface is up all the time and can be configured to use default route exit interface so what's the point of using dialer interface to wake this interface up? Please correct me if I am wrong anywhere?

[balaji.bandi]

Not sure what is context you have here.

Dial on demand in the old days, people have one Standard Leased line and one ISDN connection.

if the leased Line go down, then the Router does dials on demand to connect using ISDN - that is the most use case.

nowadays many things are changed and links cost very so people can have more than 1 link in a cost-effective way.

[kirandeep.singh]

At my work place, we are using cisco c819 router as a back up for primary (fiber ) wan connection and I see that dialer interface is getting used in configuration in addition to the cellular interface of the c819 wireless router. 

What  confuses me is that if the cellular interface doesn't use the dialer routing for dialing(or call) why does it need a "dialer interface"?

[balaji.bandi]

Depends on use case as i mentioned, if required or not depends on the requirement,

if you need more assistance you need to provide a show run here.

[Joseph W. Doherty]

"What  confuses me is that if the cellular interface doesn't use the dialer routing for dialing(or call) why does it need a "dialer interface"?"

Possibly for similar reasons as Peter explains here.

[MHM Cisco World]

friend
the Cellular interface is  L1/L2/L3 interface 
the dialler interface is L3 only which can use L1/L2 of Cellular 

why we used dialer interface 
1- some command is found in dialer interface only 
2- you can use two cellular L1/L2 and one dialer interface, i.e. for backup