Extension Mobility Login is Unavailable (23)

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Issue: Cisco 7821 SIP IP Phone intermittently login to Extension Mobility service. Error displayed on the phone was Login is Unavailable (23).

Cisco 7821 SIP IP Phone running on firmware version 10.1(1)SR1
Cisco Unified Communications Manager version

Time        Source                Destination           Protocol Length Info
0.000000       TCP      70     51493 > http-alt [SYN] Seq=0 Win=14480 Len=0 MSS=1460 TSval=195791 TSecr=619720525
0.000095        TCP      70     http-alt > 51493 [SYN, ACK] Seq=0 Ack=1 Win=14480 Len=0 MSS=1460 TSval=619767712 TSecr=195791
0.000686       TCP      66     51493 > http-alt [ACK] Seq=1 Ack=1 Win=14480 Len=0 TSval=195791 TSecr=619767712
0.006832       HTTP     510    GET /emapp/EMAppServlet?device=SEP00082F1B6653 HTTP/1.1 
0.006880        TCP      66     http-alt > 51493 [ACK] Seq=1 Ack=445 Win=15544 Len=0 TSval=619767719 TSecr=195792
0.062434        HTTP/XML 814    HTTP/1.1 200 OK 
0.063115       TCP      66     51493 > http-alt [ACK] Seq=445 Ack=749 Win=15708 Len=0 TSval=195797 TSecr=619767774
0.065465       TCP      66     51493 > http-alt [FIN, ACK] Seq=445 Ack=749 Win=15708 Len=0 TSval=195797 TSecr=619767774
0.065564        TCP      66     http-alt > 51493 [FIN, ACK] Seq=749 Ack=446 Win=15544 Len=0 TSval=619767777 TSecr=195797
0.065973       TCP      66     51493 > http-alt [ACK] Seq=446 Ack=750 Win=15708 Len=0 TSval=195798 TSecr=619767777
10.020709       TCP      70     51494 > http-alt [SYN] Seq=0 Win=14480 Len=0 MSS=1460 TSval=196793 TSecr=619767777
10.020821        TCP      70     http-alt > 51494 [SYN, ACK] Seq=0 Ack=1 Win=14480 Len=0 MSS=1460 TSval=619777733 TSecr=196793
10.021377       TCP      66     51494 > http-alt [ACK] Seq=1 Ack=1 Win=14480 Len=0 TSval=196793 TSecr=619777733
10.026852       HTTP     534    GET /emapp/EMAppServlet?device=SEP00082F1B6653&seq=35600&userid=35600 HTTP/1.1 
10.026900        TCP      66     http-alt > 51494 [ACK] Seq=1 Ack=469 Win=15544 Len=0 TSval=619777739 TSecr=196794
10.166359        HTTP/XML 576    HTTP/1.1 200 OK 
10.167019       TCP      66     51494 > http-alt [ACK] Seq=469 Ack=511 Win=15544 Len=0 TSval=196808 TSecr=619777878
10.176926       TCP      66     51494 > http-alt [FIN, ACK] Seq=469 Ack=511 Win=15544 Len=0 TSval=196809 TSecr=619777878
10.177023        TCP      66     http-alt > 51494 [FIN, ACK] Seq=511 Ack=470 Win=15544 Len=0 TSval=619777889 TSecr=196809
10.177447       TCP      66     51494 > http-alt [ACK] Seq=470 Ack=512 Win=15544 Len=0 TSval=196809 TSecr=619777889

Hypertext Transfer Protocol
    GET /emapp/EMAppServlet?device=SEP00082F1B6653&seq=35600&userid=switch HTTP/1.1\r\n
        [Expert Info (Chat/Sequence): GET /emapp/EMAppServlet?device=SEP00082F1B6653&seq=35600&userid=switch HTTP/1.1\r\n]
            [Message: GET /emapp/EMAppServlet?device=SEP00082F1B6653&seq=35600&userid=switch HTTP/1.1\r\n]
            [Severity level: Chat]
            [Group: Sequence]
        Request Method: GET
        Request URI: /emapp/EMAppServlet?device=SEP00082F1B6653&seq=35600&userid=35600
        Request Version: HTTP/1.1
    Accept: x-CiscoIPPhone/Menu, x-CiscoIPPhone/Text,  x-CiscoIPPhone/IconMenu, x-CiscoIPPhone/IconFileMenu, x-CiscoIPPhone/Directory, x-CiscoIPPhone/Input, x-CiscoIPPhone/Execute, text/*, */*\r\n
    Accept-Language: en_GB\r\n
    Accept-Charset: utf-8,iso-8859-1;q=0.8\r\n
    x-CiscoIPPhoneModelName: CP-7821\r\n
    x-CiscoIPPhoneSDKVersion: 8.5.1\r\n
    x-CiscoIPPhoneDisplay: 396,133,1,G\r\n
    [Full request URI:]
    [HTTP request 1/1]
    [Response in frame: 16]

Solution: Logging in to Cisco 7821 IP Phone via Extension Mobility was a hit and miss. Some phones worked okay after phone reboot and others didn’t. I took a packet capture on the Cisco Unified Communications Manager side, it showed the user ID and PIN passed were received correctly, user ID and PIN were 35600. Didn’t have a chance to get the Cisco Unified Communications Manager logs as I knew this kind of behaviour was a bug either on the phone or server side. I started to search over Cisco bug database and found this bug ID CSCuo99592 (problem description: 7841 Intermittently will not login to Extension Mobility). The bug ID I found was relevant to Cisco 7841 SIP IP phone but very close enough as they were in the same phone series. I went back to Cisco 7821 download page, guess what? A new firmware just released, version 10.2(1). I read the release notes but no mention of Extension Mobility bug fixed, however I still downloaded the firmware and installed it to three test phones. Tried to login and all login attempts were successful. Added more phones in my test setup, still I could login without any hiccups. Finally, I upgraded all the phones firmware to 10.2(1).