IP Phone Lagged / Unreachable

Selamat sore teman-teman asterisk.id
Saat ini saya menggunakan server voip untuk keperluan Call center (Schmooze 6.5 include Asterisk 11 & Freepbx 2.11)
saya ingin bertanya kenapa setiap Incoming Call yang masuk sangat banyak status IP Phone berubah seperti dibawah ini ya??

[2016-11-07 10:42:11] NOTICE[32600] chan_sip.c: Peer ‘818’ is now Lagged. (2334ms / 2000ms)
[2016-11-07 10:44:25] NOTICE[32600] chan_sip.c: Peer ‘808’ is now Lagged. (3206ms / 2000ms)
[2016-11-07 10:44:25] NOTICE[32600] chan_sip.c: Peer ‘861’ is now Lagged. (3206ms / 2000ms)
[2016-11-07 10:44:26] NOTICE[32600] chan_sip.c: Peer ‘806’ is now Lagged. (3458ms / 2000ms)
[2016-11-07 10:44:26] NOTICE[32600] chan_sip.c: Peer ‘855’ is now Lagged. (3458ms / 2000ms)
[2016-11-07 10:44:27] NOTICE[32600] chan_sip.c: Peer ‘871’ is now Lagged. (3971ms / 2000ms)
[2016-11-07 10:46:58] NOTICE[32600] chan_sip.c: Peer ‘809’ is now Lagged. (2660ms / 2000ms)

Kemudian setelah status nya Lagged berubah jadi UNREACHABLE (seperti dibawah ini)
[2016-11-07 10:47:03] NOTICE[32600] chan_sip.c: Peer ‘812’ is now UNREACHABLE! Last qualify: 3725
[2016-11-07 10:47:14] NOTICE[11174] chan_sip.c: Peer ‘862’ is now UNREACHABLE! Last qualify: 0
[2016-11-07 10:48:58] NOTICE[11174] chan_sip.c: Peer ‘864’ is now UNREACHABLE! Last qualify: 2861
[2016-11-07 10:49:05] NOTICE[11174] chan_sip.c: Peer ‘862’ is now UNREACHABLE! Last qualify: 40
[2016-11-07 10:49:16] NOTICE[11174] chan_sip.c: Peer ‘849’ is now UNREACHABLE! Last qualify: 7
[2016-11-07 10:49:16] NOTICE[11174] chan_sip.c: Peer ‘859’ is now UNREACHABLE! Last qualify: 36

apakah ada teman-teman yang pernah mengalami kejadian seperti diatas??, mohon bantuannya…

Terima kasih

Itu servernya pake IP Public kang?

Kalau pake IP Public apakah di dialplan ada context [default] yang terisi?
Apa sip from externalnya dinyalakan mas?

Pake IP Local kang, topologi nya mikrotik—switch/hub—server elastix. kasus ini hanya muncul apabila incoming call lagi banyak…, apa ada settingan yang harus dirubah ya kang??

Bisa di screenshot engga kang hasil top , dan spek server yang digunakan ?

Ini kang hasil top nya :

  • Intel® Xeon® CPU E3-1230 v3 @ 3.30GHz
  • DDR3 8 GB
  • Hdd 2 Tb