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PM36185: SIP RE-SENDS CANCEL WHEN RECEIVING 2ND PROVISIONAL RESPONSE

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You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • Product Version:  7.0.0.13
    Operating System and Additional Information:
    Linux, version 2.6.18-194.17.4.el5
    
    Example scenario:
    
    UAC          Proxy          UAS
    |             |             |
    1  |-- INVITE -->|             |
    2  |<-- 100 I ---|-- INVITE -->|
    3  |             |<-- 180 I ---|
    4  |<-- 180 I ---|             |
    |             |             |
    5  |-- CANCEL -->|             |
    6  |<-- 200 C ---|-- CANCEL -->|
    7  |             |<-- 100 I ---|
    8  |             |-- CANCEL -->|
    |             |             |
    9  |             |<-- 200 I ---|
    10  |<-- 200 I ---|             |
    11  |             |<-- 200 C ---|
    |             |             |
    12  |             |<-- 200 I ---|
    13  |<-- 200 I ---|             |
    
    Note the problem starts at message (7) where the UAS sends a
    provisional response after it received a CANCEL. This is not a
    bug, it is a race condition in the network, where the downstream
    CANCEL request (6) and the upstream Trying response (7) cross
    each other on the wire.
    However, this exposes a bug in the SIP container, which re-sends
    the CANCEL in (8). The container should not re-send the CANCEL
    just because it received another provisional response.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:  Session Initiation Protocol (SIP) users     *
    *                  of IBM WebSphere Application Server         *
    *                  Feature Pack for Communications Enabled     *
    *                  Applications (CEA).                         *
    ****************************************************************
    * PROBLEM DESCRIPTION: CANCEL is sent out twice                *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    The problem occurs in a call flow such as this.
    
       UAC          Proxy          UAS
        |             |             |
     1  |-- INVITE -->|             |
     2  |<-- 100 I ---|-- INVITE -->|
     3  |             |<-- 100 I ---|
     4  |-- CANCEL -->|             |
     5  |<-- 200 C ---|-- CANCEL -->|
     6  |             |<-- 180 I ---|
    
    There is a "race condition" between steps 5 and 6 - sending a
    CANCEL (5) and receiving a second provisional response (6).
    These two steps are executed in two different threads. Each
    thread first checks if a CANCEL was already sent, then sends
    out the CANCEL, and then updates the state machine about
    having sent the CANCEL. Because of a bug, this procedure is
    not "synchronized", that is, it is not guaranteed to execute
    as one atomic operation. As a result, specific thread timing
    conditions may cause both threads to send out the CANCEL,
    concurrently.
    

Problem conclusion

  • The bug is fixed in the SIP container. With this fix, the race
    condition is eliminated, and the CANCEL is sent out once only,
    irrespectively of thread or timing.
    
    The fix for this APAR is currently targeted for inclusion in
    fix pack 1.0.0.11 for the Feature Pack for Communications
    Enabled Applications. Please refer to the Recommended Updates
    page for delivery information:
    http://www-01.ibm.com/support/docview.wss?rs=180&uid=swg27017328
    

Temporary fix

Comments

APAR Information

  • APAR number

    PM36185

  • Reported component name

    CEA FEATUREPACK

  • Reported component ID

    5724J0855

  • Reported release

    700

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2011-04-03

  • Closed date

    2011-05-18

  • Last modified date

    2011-05-18

  • APAR is sysrouted FROM one or more of the following:

    PM36035

  • APAR is sysrouted TO one or more of the following:

Fix information

  • Fixed component name

    CEA FEATUREPACK

  • Fixed component ID

    5724J0855

Applicable component levels

  • R700 PSY

       UP



Document information

More support for: WebSphere Application Server V7 Feature Pack for Communications Enabled Applications
General

Software version: 700

Reference #: PM36185

Modified date: 18 May 2011