In case of DSL Modem , normally service providers employ PPPoE connection between Modem and BRAS (BNG). We all know that when Modem dials , it goes through PPPoE stages namely 1 ) PADI 2) PADO 3) PADR and 4) PADS.
After PPPoE session is established , PPP session starts establishing whereby it went through PPP stages namely 1) LCP 2) PAP or CHAP and 3) NCP.
After PPP session is established , Modem gets dynamic IP from BRAS and user starts browsing. However for session maintenance / house keeping , PPP keepalives are exchanged between Modem and BRAS after pre defined interval.
Please note that this is vendor independent query and is related to standard implementation which usually all vendors follow.
The question is Who initiates the PPP keepalives packets?
Below are the three possibilities
Is it like that the modem initiates and BRAS answers or BRAS initiates and modem answers?
Is it like both modem and BRAS send PPP keepalives packets independently to each other? BRAS sends PPP keepalives packets to modem and wait for answer. Likewise Modem sends PPP keepalive packets to BRAS and wait for answer.
If possible , please share documented proof (standards) which supports argument.