Correct auth, but... потеря регистрации audiocodes

Приветствую. Есть шлюз MP-118 FXS. Периодически, раз в 1-2 недели, он теряет регистрацию на астере (1.8.7). В логи астериска сыпятся таки вещи:

<--- SIP read from UDP:192.168.1.236:5060 --->
REGISTER sip:192.168.1.7 SIP/2.0
Via: SIP/2.0/UDP 192.168.1.236;branch=z9hG4bKac953382862
Max-Forwards: 70
From: <sip:222@192.168.1.7>;tag=1c953377950
To: <sip:222@192.168.1.7>
Call-ID: 5896116181120104013@192.168.1.236
CSeq: 2113 REGISTER
Contact: <sip:222@192.168.1.236:5060>;expires=3600
Supported: path
Allow: REGISTER,OPTIONS,INVITE,ACK,CANCEL,BYE,NOTIFY,PRACK,REFER,INFO,SUBSCRIBE,UPDATE
Expires: 3600
User-Agent: Audiocodes-Sip-Gateway-MP-118 FXS/v.6.20A.012.005
Content-Length: 0

<------------->
[2012-04-12 15:43:34] VERBOSE[17745] chan_sip.c: --- (13 headers 0 lines) ---
[2012-04-12 15:43:34] VERBOSE[17745] chan_sip.c: Sending to 192.168.1.236:5060 (NAT)
[2012-04-12 15:43:34] VERBOSE[17745] chan_sip.c: 
<--- Transmitting (no NAT) to 192.168.1.236:5060 --->
SIP/2.0 100 Trying 
Via: SIP/2.0/UDP 192.168.1.236;branch=z9hG4bKac953382862;received=192.168.1.236 
From: <sip:222@192.168.1.7>;tag=1c953377950 
To: <sip:222@192.168.1.7> 
Call-ID: 5896116181120104013@192.168.1.236 
CSeq: 2113 REGISTER 
Server: prettyserver 
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH 
Supported: replaces, timer 
Content-Length: 0 


<------------>
[2012-04-12 15:43:34] VERBOSE[17745] chan_sip.c: 
<--- Transmitting (no NAT) to 192.168.1.236:5060 --->
SIP/2.0 401 Unauthorized 
Via: SIP/2.0/UDP 192.168.1.236;branch=z9hG4bKac953382862;received=192.168.1.236 
From: <sip:222@192.168.1.7>;tag=1c953377950 
To: <sip:222@192.168.1.7>;tag=as2aedde7e 
Call-ID: 5896116181120104013@192.168.1.236 
CSeq: 2113 REGISTER 
Server: prettyserver 
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH 
Supported: replaces, timer 
WWW-Authenticate: Digest algorithm=MD5, realm="asterisk", nonce="43f8a95b" 
Content-Length: 0 

<--- SIP read from UDP:192.168.1.236:5060 --->
REGISTER sip:192.168.1.7 SIP/2.0
Via: SIP/2.0/UDP 192.168.1.236;branch=z9hG4bKac953449374
Max-Forwards: 70
From: <sip:222@192.168.1.7>;tag=1c953377950
To: <sip:222@192.168.1.7>
Call-ID: 5896116181120104013@192.168.1.236
CSeq: 2114 REGISTER
Authorization: Digest username="222",realm="asterisk",nonce="43f8a95b",uri="sip:192.168.1.7",algorithm=MD5,response="5684dbbdad0d182c0787d02a04bb8ff0"
Contact: <sip:222@192.168.1.236:5060>;expires=3600
Supported: path
Allow: REGISTER,OPTIONS,INVITE,ACK,CANCEL,BYE,NOTIFY,PRACK,REFER,INFO,SUBSCRIBE,UPDATE
Expires: 3600
User-Agent: Audiocodes-Sip-Gateway-MP-118 FXS/v.6.20A.012.005
Content-Length: 0

<------------->
[2012-04-12 15:43:34] VERBOSE[17745] chan_sip.c: --- (14 headers 0 lines) ---
[2012-04-12 15:43:34] VERBOSE[17745] chan_sip.c: Sending to 192.168.1.236:5060 (no NAT)
[2012-04-12 15:43:34] VERBOSE[17745] chan_sip.c: 
<--- Transmitting (no NAT) to 192.168.1.236:5060 --->
SIP/2.0 100 Trying 
Via: SIP/2.0/UDP 192.168.1.236;branch=z9hG4bKac953449374;received=192.168.1.236 
From: <sip:222@192.168.1.7>;tag=1c953377950 
To: <sip:222@192.168.1.7> 
Call-ID: 5896116181120104013@192.168.1.236 
CSeq: 2114 REGISTER 
Server: prettyserver 
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH 
Supported: replaces, timer 
Content-Length: 0 


<------------>
[2012-04-12 15:43:34] NOTICE[17745] chan_sip.c: Correct auth, but based on stale nonce received from '<sip:222@192.168.1.7>;tag=1c953377950'
[2012-04-12 15:43:34] VERBOSE[17745] chan_sip.c: 
<--- Transmitting (no NAT) to 192.168.1.236:5060 --->
SIP/2.0 401 Unauthorized 
Via: SIP/2.0/UDP 192.168.1.236;branch=z9hG4bKac953449374;received=192.168.1.236 
From: <sip:222@192.168.1.7>;tag=1c953377950 
To: <sip:222@192.168.1.7>;tag=as1fefc1e5 
Call-ID: 5896116181120104013@192.168.1.236 
CSeq: 2114 REGISTER 
Server: prettyserver 
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH 
Supported: replaces, timer 
WWW-Authenticate: Digest algorithm=MD5, realm="asterisk", nonce="7943a183", stale=true 
Content-Length: 0

Все хорошо, но вот

[2012-04-12 15:43:34] NOTICE[17745] chan_sip.c: Correct auth, but based on stale nonce received from '<sip:222@192.168.1.7>;tag=1c953377950'

смущает. Что это и как с ним бороться? Пока помогает рестарт астера, но это фиговый вариант.