From: WAYNE.HEINMILLER@x400gw.ameritech.com

To: WALTER.SUBORA@x400gw.ameritech.com



    Walt,

    The ICC LNP SCP Requirements Subcommittee is hoping that your 

    testing subcommittee can include some items in your plan for us.  I 

    haven't yet had time to view your current document, so some of the 

    following items may already be addressed in your current plan.  

    Perhaps you can share this request with the members of your test 

    plan committee.

    

    The SCP group has defined an "LNP GTT Function" in our document.  

    (GTT stands for Global Title Translation, and is the capability of 

    the SS7 network to use a DN or other value to route to a 

    destination.)  The LNP GTT Function capability provides an extension 

    to existing GTT capabilities of SS7 signaling networks to accommodate 

    services signaling (LIDB, CNAM, ISVM, CLASS, etc.) in an LNP 

    environment.

    

    We expect your plan will address testing of signaling for these 

    services, including measures of delay for various configurations.

    

    What your plan may not yet address is "GTT Looping".

    

    In an LNP network, routing of messages for services is performed by 

    a combination of 10 digit routing (for ported numbers) and six digit 

    routing (for non-ported numbers).  Data for the 10 digit routing is 

    downloaded from the NPAC.  Data for the six digit routing is built 

    within each network (as today).  In order to make GTT routing for 

    services work, the serving network must substitute internal data in 

    place of the 10 digit GTT data downloaded from the NPAC.

    

    If any of these tables/data are not properly configured and 

    populated, then messages for services may be routed in a circular 

    fashion, passing through the same systems repeatedly.  Messages 

    following a circular route may never arrive at their destination.  

    This has several impacts.  First, it adds unnecessary processing 

    loads to each system in the loop.  Second, it fills signaling links 

    with useless traffic, possibly blocking normal signaling traffic.  

    Finally, because the message does not arrive, the sending system 

    "times out", and may be forced to use default service logic, or the 

    service may fail.

    

    Circular routing can occur today on a six digit basis.  Since it is 

    a problem that can exist today, the LNP test does not need to 

    address this aspect of looping.  We would like the opportunity to 

    test the potential for looping because of problems with 10 digit 

    data, because of the new wrinkles added by LNP.

    

    We have identified three general categories when looping can occur.

    

    1) During NPAC Updates: When the NPAC downloads GTT data to all 

    networks, some networks will receive and incorporate the data in 

    their active routing tables faster than other networks.  During this 

    period, there will be mismatches among networks for the GTT routing 

    tables.  Messages (for services) processed through the SS7 network 

    for a DN in the process of porting may encounter circular routing.  

    This condition is normal and expected as a result of the LNP 

    architecture.  The condition is expected to resolve itself without 

    intervention once all networks complete their GTT updates.  During 

    this period, services may fail (systems will not be able to 

    communicate for services) until all updates are processed

    

    Testing Needed: Verify that if GTT looping occurs during porting, it 

    resolves without intervention.  Verify services behavior (failure or 

    default processing) during porting if messages encounter looping.

    

    2) 10 digit data "out of synch" between networks: If one or more 

    networks' GTT data is incorrect (10 digit data missing or wrong), 

    then looping may occur.  This condition does not resolve unless 

    intervention occurs.

    

    Testing Needed: Verify that GTT looping can be detected (perhaps 

    through end-user complaints).  Verify ability of troubleshooting 

    process to identify and correct network with incorrect data.

    

    3) All other reasons: Causes to be determined

   

    Testing Needed: To be determined.

    

    Anti-Looping Schemes

    

    We have identified a number of schemes which may be useful in 

    identifying, blocking, or correcting GTT looping conditions.  We 

    have endorsed two schemes for which technology is presently 

    available.  We have determined that the two endorsed schemes cannot 

    identify and/or block all looping situations.

    

    We hope to include some testing during the trial that would help 

    evaluate the following:

    

    1) What are the configurations when looping can occur despite the 

    use of the two endorsed schemes?

    2) How common are these conditions?

    3) Do any of the additional proposed schemes identify and/or block 

    looping that is not addressed by the two endorsed schemes?

    4) How accurate are any of the schemes that identify the occurrence 

    of message looping?

    

    At this point, we need to identify what anti-looping capabilities 

    may be deployed in the time frame of the trial.

    

    We would like to work with our group to include testing in support 

    of these objectives in your testing activities.  Please let me know 

   how our group should proceed.

    

    Thanks.

    Wayne