[asterisk-users] why is nonce="584760da" used in sip packets?

[Rizwan Hisham]

Hi all,
There is a parameter called "nonce" included in every register request that
a UA sends to asterisk. I have read sip debug a lot and only found out that
the "nonce" parameter value which is used in register request was generated
by asterisk server in a previous sip response.
As you can see in the sip debug (labled in red).

<--- Transmitting (NAT) to 208.120.167.146:80 --->
SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP 208.120.167.146:80;branch=z9hG4bK03891485;received=
208.120.167.146
From: <sip:bernart48 at magnum.axvoice.com>;tag=as65460c44
To: <sip:bernart48 at magnum.axvoice.com>;tag=as3a5cc850
Call-ID: 48f3a8b426c375a161dc1f4479bba956 at 127.0.0.1
CSeq: 19680 REGISTER
User-Agent: Asterisk PBX
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Supported: replaces
WWW-Authenticate: Digest algorithm=MD5, realm="asterisk", nonce="584760da"
Content-Length: 0


<------------>
Scheduling destruction of SIP dialog '
48f3a8b426c375a161dc1f4479bba956 at 127.0.0.1' in 32000 ms (Method: REGISTER)
magnum*CLI>
<--- SIP read from 208.120.167.146:80 --->
REGISTER sip:magnum.axvoice.com SIP/2.0
Via: SIP/2.0/UDP 208.120.167.146:80;branch=z9hG4bK0c6c6f53
From: <sip:bernart48 at magnum.axvoice.com>;tag=as65460c44
To: <sip:bernart48 at magnum.axvoice.com>;tag=as3a5cc850
Call-ID: 48f3a8b426c375a161dc1f4479bba956 at 127.0.0.1
CSeq: 19681 REGISTER
User-Agent: Asterisk PBX
Authorization: Digest username="bernart48", realm="asterisk", algorithm=MD5,
uri="sip:bernart48 at 64.182.161.2:9060", nonce="584760da",
response="948d3923bf2df47eca17c572713af2c7", opaque=""
Expires: 120
Contact: <sip:16474764942 at 208.120.167.146:80>
Event: registration
Content-Length: 0

What i dont know, and would very much like to know, is what is the purpose
of this parameter in sip packets?
-- 
Best Regards
Rizwan Hisham
Software Engineer
Axvoice Inc.
www.axvoice.com
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