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I am receiving these messaged within the log of my VG-3631. What do they mean?
I am experiencing pronounced background noise on incoming PSTN phone calls (faint buzzing and static) while VOIP is crystal clear. I have changed filters, cables and nothing has corrected it...

1	2017-03-01 08:49:03	VOIP	Notice	PSTN status notify, status 0x1 pol 0
2	2017-03-01 08:49:03	VOIP	Notice	The PSTN line is unstable too long(>500ms)
3	2017-03-01 08:49:02	VOIP	Notice	PSTN status notify, status 0x0 pol 0
4	2017-02-27 14:12:27	VOIP	Notice	PSTN status notify, status 0x1 pol 0
5	2017-02-27 14:12:27	VOIP	Notice	The PSTN line is unstable too long(>500ms)
6	2017-02-27 14:12:26	VOIP	Notice	PSTN status notify, status 0x0 pol 0
7	2017-02-27 14:11:17	VOIP	Notice	PSTN status notify, status 0x1 pol 0
8	2017-02-27 14:11:17	VOIP	Notice	The PSTN line is unstable too long(>500ms)
9	2017-02-27 14:11:16	VOIP	Notice	PSTN status notify, status 0x0 pol 0
10	2017-02-27 14:09:35	VOIP	Notice	PSTN status notify, status 0x1 pol 0
11	2017-02-27 14:09:35	VOIP	Notice	The PSTN line is unstable too long(>500ms)
12	2017-02-27 14:09:34	VOIP	Notice	PSTN status notify, status 0x0 pol 0
13	2017-02-27 14:07:59	VOIP	Notice	PSTN status notify, status 0x1 pol 0
14	2017-02-27 14:07:58	VOIP	Notice	The PSTN line is unstable too long(>500ms)
15	2017-02-27 14:07:58	VOIP	Notice	PSTN status notify, status 0x0 pol 0
16	2017-02-27 14:07:19	VOIP	Notice	PSTN status notify, status 0x1 pol 0
17	2017-02-27 14:07:19	VOIP	Notice	The PSTN line is unstable too long(>500ms)
18	2017-02-27 14:07:18	VOIP	Notice	PSTN status notify, status 0x0 pol 0
19	2017-02-27 14:06:38	VOIP	Notice	PSTN status notify, status 0x1 pol 0
20	2017-02-27 14:06:38	VOIP	Notice	The PSTN line is unstable too long(>500ms)
21	2017-02-27 14:06:37	VOIP	Notice	PSTN status notify, status 0x0 pol 0
22	2017-02-27 14:04:43	VOIP	Notice	PSTN status notify, status 0x1 pol 0
23	2017-02-27 14:04:42	VOIP	Notice	The PSTN line is unstable too long(>500ms)