Dial-up link (56 kb/s) with the ISP correctly established and browsing without problems when the connection suddenly breaks and kppp comes up with an error warning "... exit -16.."

Reproducible: Sometimes

Steps to Reproduce:
1. it happens randomly, no clue of how it may be reproduced
2.
3.



In one day I could experience such an interruption 5 times, after some 10, 20 and even 60 minutes that the connection was correctly operating. The day after, in a couple of hours of connection, I did not have any problem.
In all the cases, the ppp debug log indicated that the connection was terminated by a SIGHUP,
as in the example attached.
As far as I can investigate, it does not appear that there might be any evident "external" cause (in the hardware, line etc.).
Is the hangup request sent by the ISP, or by my terminal (pppd, kppp, ..) ? and why ? and in which circumstances can I expect it to occur?

==== start of log  ======
Feb  4 00:34:53 sar-dwz pppd[7251]: pppd 2.4.5 started by giuliano, uid 1000
Feb  4 00:34:53 sar-dwz pppd[7251]: using channel 8
Feb  4 00:34:53 sar-dwz pppd[7251]: Using interface ppp0
Feb  4 00:34:53 sar-dwz pppd[7251]: Connect: ppp0 <--> /dev/ttyS0
Feb  4 00:34:53 sar-dwz pppd[7251]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xc2715f8e> <pcomp> <accomp>]
Feb  4 00:34:53 sar-dwz pppd[7251]: rcvd [LCP ConfReq id=0x1 <mru 1524> <asyncmap 0xa0000> <auth chap MD5> <pcomp> <accomp> <mrru 1524> <endpoint [local:73.74.61.63.6b.31]>]
Feb  4 00:34:53 sar-dwz pppd[7251]: sent [LCP ConfRej id=0x1 <mrru 1524>]
Feb  4 00:34:53 sar-dwz pppd[7251]: rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0xc2715f8e> <pcomp> <accomp>]
Feb  4 00:34:53 sar-dwz pppd[7251]: rcvd [LCP ConfReq id=0x2 <mru 1524> <asyncmap 0xa0000> <auth chap MD5> <pcomp> <accomp> <endpoint [local:73.74.61.63.6b.31]>]
Feb  4 00:34:53 sar-dwz pppd[7251]: sent [LCP ConfAck id=0x2 <mru 1524> <asyncmap 0xa0000> <auth chap MD5> <pcomp> <accomp> <endpoint [local:73.74.61.63.6b.31]>]
Feb  4 00:34:53 sar-dwz pppd[7251]: sent [LCP EchoReq id=0x0 magic=0xc2715f8e]
Feb  4 00:34:53 sar-dwz pppd[7251]: rcvd [CHAP Challenge id=0x1 <c9b58ca6c581d90ee6aecde9458a9394>, name = "apx-rm3"]
Feb  4 00:34:53 sar-dwz pppd[7251]: sent [CHAP Response id=0x1 <2fceb52fccc0d0d7fc9aca381b62f346>, name = "gcabrel"]
Feb  4 00:34:53 sar-dwz pppd[7251]: rcvd [LCP EchoRep id=0x0 magic=0x0]
Feb  4 00:34:53 sar-dwz pppd[7251]: rcvd [CHAP Success id=0x1 "\000"]
Feb  4 00:34:53 sar-dwz pppd[7251]: CHAP authentication succeeded: 
Feb  4 00:34:53 sar-dwz pppd[7251]: CHAP authentication succeeded
Feb  4 00:34:53 sar-dwz pppd[7251]: sent [CCP ConfReq id=0x1 <deflate 15> <deflate(old#) 15> <bsd v1 15>]
Feb  4 00:34:53 sar-dwz pppd[7251]: sent [IPCP ConfReq id=0x1 <compress VJ 0f 01> <addr 192.168.1.7> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]
Feb  4 00:34:53 sar-dwz pppd[7251]: rcvd [IPCP ConfReq id=0x1 <compress VJ 0f 01> <addr 151.99.28.58>]
Feb  4 00:34:53 sar-dwz pppd[7251]: sent [IPCP ConfAck id=0x1 <compress VJ 0f 01> <addr 151.99.28.58>]
Feb  4 00:34:54 sar-dwz pppd[7251]: rcvd [LCP ProtRej id=0x3 80 fd 01 01 00 0f 1a 04 78 00 18 04 78 00 15 03 2f]
Feb  4 00:34:54 sar-dwz pppd[7251]: Protocol-Reject for 'Compression Control Protocol' (0x80fd) received
Feb  4 00:34:54 sar-dwz pppd[7251]: rcvd [IPCP ConfNak id=0x1 <addr 212.216.143.70> <ms-dns1 62.211.69.150> <ms-dns2 212.216.172.162>]
Feb  4 00:34:54 sar-dwz pppd[7251]: sent [IPCP ConfReq id=0x2 <compress VJ 0f 01> <addr 212.216.143.70> <ms-dns1 62.211.69.150> <ms-dns2 212.216.172.162>]
Feb  4 00:34:54 sar-dwz pppd[7251]: rcvd [IPCP ConfAck id=0x2 <compress VJ 0f 01> <addr 212.216.143.70> <ms-dns1 62.211.69.150> <ms-dns2 212.216.172.162>]
Feb  4 00:34:54 sar-dwz pppd[7251]: local  IP address 212.216.143.70
Feb  4 00:34:54 sar-dwz pppd[7251]: remote IP address 151.99.28.58
Feb  4 00:34:54 sar-dwz pppd[7251]: primary   DNS address 62.211.69.150
Feb  4 00:34:54 sar-dwz pppd[7251]: secondary DNS address 212.216.172.162
Feb  4 00:34:54 sar-dwz pppd[7251]: Script /etc/ppp/ip-up started (pid 7258)
Feb  4 00:34:54 sar-dwz pppd[7251]: Script /etc/ppp/ip-up finished (pid 7258), status = 0x0
Feb  4 01:00:56 sar-dwz pppd[7251]: Hangup (SIGHUP)
Feb  4 01:00:56 sar-dwz pppd[7251]: Modem hangup
Feb  4 01:00:56 sar-dwz pppd[7251]: Connect time 26.1 minutes.
Feb  4 01:00:56 sar-dwz pppd[7251]: Sent 328189 bytes, received 1132361 bytes.
Feb  4 01:00:56 sar-dwz pppd[7251]: Script /etc/ppp/ip-down started (pid 7460)
Feb  4 01:00:56 sar-dwz pppd[7251]: Connection terminated.
Feb  4 01:00:56 sar-dwz pppd[7251]: Waiting for 1 child processes...
Feb  4 01:00:56 sar-dwz pppd[7251]:   script /etc/ppp/ip-down, pid 7460
Feb  4 01:00:56 sar-dwz pppd[7251]: Script /etc/ppp/ip-down finished (pid 7460), status = 0x0
Feb  4 01:00:56 sar-dwz pppd[7251]: Exit.
======= end of log ===========