[Osip] Strange Frame when unsuccessfull registration

[Alain Ronce]

Hi,
When I send a registration with error (for example not implementated on the 
server), I can see strange frame form my UA to the server, it is a UDP frame 
Src Port 5060 and Dst Port 5060, size is 60. The timing is :
-> SIP Request : REGISTER
<- SIP Status : 501 Not implemented (Ok !)
(+35 sec) UDP 60 bytes (5060->5060) ???
(+45 sec) UDP 60 bytes (5060->5060) ???
(+40 sec) -> SIP Request : REGISTER retry
Does someone explain what is this frame ?
Best Regards
AR

Frame Details:
Frame 14 (60 bytes on wire, 60 bytes captured)
Ethernet II, Src: Private_00:07:4c (00:0e:17:00:07:4c), Dst: 
Grandstr_1a:a0:ee (00:0b:82:1a:a0:ee)
Internet Protocol, Src: 192.168.20.23 (192.168.20.23), Dst: 192.168.20.32 
(192.168.20.32)
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 5060 (5060)
    Source port: 5060 (5060)
    Destination port: 5060 (5060)
    Length: 12
    Checksum: 0x7964 [correct]
        [Good Checksum: True]
        [Bad Checksum: False]
Data (4 bytes)
0000  6a 61 4b 00   jaK.