happens not respond to ppp lcp config request

[winman]

xl2ftpd version : 1.3.15
lns:192.170.6.206
lac:10.60.0.61

Logs as below:

root@IKD-RL05:~# tcpdump -i modem -w 1.pcap &
root@IKD-RL05:~# tcpdump: listening on modem, link-type EN10MB (Ethernet), capture size 262144 bytes

root@IKD-RL05:~# tail -f /var/log/messages
Feb  6 15:20:07 router daemon.info l2tpc[19578]: pid is [19616]{l2tpc.c->338}
Feb  6 15:20:07 router daemon.debug l2tpc[19616]: /usr/sbin/xl2tpd /usr/sbin/xl2tpd -c /tmp/l2tp/l2tpc.conf -C /tmp/l2tpc.control -D{l2tpc.c->268}
Feb  6 15:20:07 router daemon.info xl2tpd[19616]: Not looking for kernel SAref support.
Feb  6 15:20:07 router daemon.info xl2tpd[19616]: This binary does not support kernel L2TP.
Feb  6 15:20:07 router daemon.info xl2tpd[19616]: xl2tpd version xl2tpd-1.3.15 started on IKD-RL05 PID:19616
Feb  6 15:20:07 router daemon.info xl2tpd[19616]: Written by Mark Spencer, Copyright (C) 1998, Adtran, Inc.
Feb  6 15:20:07 router daemon.info xl2tpd[19616]: Forked by Scott Balmos and David Stipp, (C) 2001
Feb  6 15:20:07 router daemon.info xl2tpd[19616]: Inherited by Jeff McAdams, (C) 2002
Feb  6 15:20:07 router daemon.info xl2tpd[19616]: Forked again by Xelerance (www.xelerance.com) (C) 2006-2016
Feb  6 15:20:07 router daemon.info xl2tpd[19616]: Listening on IP address 0.0.0.0, port 1701
Feb  6 15:20:07 router daemon.notice xl2tpd[19616]: Connecting to host 192.170.6.206, port 1701
Feb  6 15:20:07 router daemon.notice xl2tpd[19616]: Connection established to 192.170.6.206, 1701.  Local: 3102, Remote: 250 (ref=0/0).
Feb  6 15:20:07 router daemon.notice xl2tpd[19616]: Calling on tunnel 3102
Feb  6 15:20:07 router daemon.notice xl2tpd[19616]: Call established with 192.170.6.206, Local: 15182, Remote: 22, Serial: 1 (ref=0/0)
Feb  6 15:20:07 router daemon.debug xl2tpd[19616]: start_pppd: I'm running: 
Feb  6 15:20:07 router daemon.debug xl2tpd[19616]: "/usr/sbin/pppd" 
Feb  6 15:20:07 router daemon.debug xl2tpd[19616]: "/dev/pts/1" 
Feb  6 15:20:07 router daemon.debug xl2tpd[19616]: "passive" 
Feb  6 15:20:07 router daemon.debug xl2tpd[19616]: "nodetach" 
Feb  6 15:20:07 router daemon.debug xl2tpd[19616]: ":" 
Feb  6 15:20:07 router daemon.debug xl2tpd[19616]: "file" 
Feb  6 15:20:07 router daemon.debug xl2tpd[19616]: "/tmp/l2tp/a321.options" 
Feb  6 15:20:22 router daemon.info xl2tpd[19616]: control_finish: Connection closed to 192.170.6.206, serial 1 ()
Feb  6 15:20:22 router daemon.debug xl2tpd[19616]: Terminating pppd: sending TERM signal to pid 19617
^C
root@IKD-RL05:~# 

any comment is welcomed, thanks in advance.