FAQs

These answers to frequently asked questions address both technical issues and questions about the services provided by the Network Services Interfaces Testlab.

General

What type of testing does your organization perform?
Our organization covers a wide range of digital equipment, services, and applications prior to their connection to the AT&T Network. Testing Services describes the types of testing we perform.
How far in advance should we schedule testing?
We recommend at least 3 months in advance.
Are our test results shared with anyone?
Test results are confidential and AT&T is bound by Nondisclosure Agreements. However, at a vendor's request and with their agreement, we may share the information that the CPE was successful in passing our tests. AT&T will not share detailed results and does not share any information when the CPE is not successful in any phase of testing.
Can we publicize our test results indicating that AT&T sanctions our product?
Yes, however, an agreement must be reached with AT&T.
What does testing cost?
The testing is free. The only costs your company may incur are related to shipping your equipment in and out of our test lab, sending engineers to participate in the testing and to fix any problems encountered during the tests. AT&T tests equipment for free to assure that our customers have equipment that works well with our services. Compatible equipment also reduces AT&T's maintenance costs.
What specifications are you using to test our equipment?
AT&T maintains Technical References on the interfaces to our services. Your equipment must meet the applicable AT&T Technical Reference(s).
What do we receive when we pass a compatibility test?
A letter is sent to the originator of the testing request indicating the equipment and the service which it was tested for compatibility. A test report is included.

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SS7

Why should we get our CRP product tested?
Our testing program reveals many protocol problems that could have disastrous effects if left undiscovered until the CRP is deployed at the customer's site. By discovering these problems early you can insure that your CRP performs flawlessly when connected to the AT&T Network and put into operation.
What type of testing is done?
Our ICP test program includes basic protocol testing at all levels of the ICP SS7 protocol stack, protocol error scenarios, and application level load testing with both continuous and bursty traffic at a variety of loads.
What preparations should we make before coming in for testing?
We suggest thoroughly reviewing AT&T Technical Reference TR54022 for ICP service to verify that your CRP product fully complies with the interface standard. You may also want to review the AT&T ICP test plan to insure that your product can pass the tests we conduct during the test session.
Where is the test session conducted?
Testing can be done on site at the AT&T compatibility test lab in Washington, D.C., or if appropriate circuits can be provided, testing can be done remotely to the vendor's location. Appropriate circuits are either 56kbps BRI dial up connections, or dedicated/switched 56 kbps data circuits.
How long does the test session last?
On site testing sessions typically last one week. For remote testing, the test session can be flexible to accommodate the needs of your development organization, and can be conducted either as one continuous block during a one week period, or spread out over several weeks.

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Transmission

  • Where is the test session conducted?
  • Can we obtain a copy of the test plan?
  • Can we just mail the equipment in to be tested?
  • How many engineers can we send to a test session?
  • How long does the testing take?
  • What happens if our equipment fails any of the tests?
  • What happens if the testing is not completed during the scheduled test date?
  • What if a problem cannot be fixed during the scheduled test time?
  • Do we get a preference for our retest scheduling over other vendors already on the schedule?
  • How do we get our equipment in and out of your lab?
  • If we have to come back for a retest, can we just leave our equipment in your lab?
  • Is there a dress code at the testlab?
  • On the T1.5 interface, what is the difference between AT&T's Extended Superframe Facility Data Link (ESF FDL) protocol and the ANSI version?
  • If the ESF FDL is used to transmit Yellow Alarm, what happens to the ESF FDL messages when Yellow Alarm is being sent?
  • What should my equipment do when it receives a Yellow Alarm from the other end of the T1.5 span?
  • What is the difference between Red CFA and AIS CFA?
  • What is jitter?
  • What is a slip?
  • What is jitter tolerance?
  • What is transfer jitter?
  • What is intrinsic jitter?
  • What is the loss of superframe synchronization?
  • Wouldn't that disrupt Robbed Bit Signaling?
  • When do I take timing from the network and when do I supply timing to the network?
  • Where is the test session conducted?
    Transmission testing is performed in the Holmdel, NJ, New York City and San Francisco test labs.
    Can we obtain a copy of the test plan?
    No.
    Can we just mail the equipment in to be tested?
    No. An engineer must accompany the equipment to option, configure and troubleshoot any problems that are discovered during testing. A development engineer on the product being tested is preferred.
    How many engineers can we send to a test session?
    Due to physical limitations, no more than three engineers can be accommodated in our testing facilities.
    How long does the testing take?
    It depends on what services are being tested and if any problems are encountered during testing. Vendors are scheduled the following number of days per service tested:

    E1 (2.048 Mb/s) - 2 days
    Fractional T45 - 1 day in addition to T1.5 or T45 testing.
    T45 - 2 days
    SONET - 20 days
    Primary Rate ISDN - 5 days remote, 5 days on site.
    SS7 - 5 days remote, 5 days on site.

    What happens if our equipment fails any of the tests?
    Vendors are encouraged to fix any problems causing a test failure during the scheduled test time. This is why it is beneficial to have development engineers accompany the equipment.
    What happens if the testing is not completed during the scheduled test date?
    A retest date will be scheduled.
    What if a problem cannot be fixed during the scheduled test time?
    A retest date will be scheduled.
    Do I get a preference for our retest scheduling over other vendors already on the schedule?
    No. You will be scheduled the next testing date the lab has available.
    How do we get our equipment in and out of your lab?
    The equipment vendor is responsible for shipping the equipment to the lab prior to the test. If practical it may be brought in by the engineers, but most vendors ship their equipment in via an overnight carrier 2 to 3 days prior to the test date. The equipment vendor is also responsible for having the equipment shipped out of the lab at the completion of the testing date.
    If we have to come back for a retest, can we just leave our equipment in your lab?
    No. Vendors are required to remove their equipment at the end of their scheduled testing date.
    Can we bring our camera / video camera?
    No.
    Is there a dress code at the testlab?
    Casual dress is appropriate.
    On the T1.5 interface, what is the difference between AT&T's Extended Superframe Facility Data Link (ESF FDL) protocol and the ANSI version?
    AT&T created and implemented the first ESF FDL protocol named after the defining Technical Reference, TR54016. The AT&T protocol uses a command/response arrangement with the Customer Installation (CI) such as an ESF CSU, Multiplexer or PBX. ANSI defines the ESF FDL protocol in their DS-1 specification, T1.403. The ANSI protocol requires the CI to generate Performance Report Messages (PRMs) at one-second intervals. The advantage of ANSI T1.403 over AT&T TR54016 is the monitoring equipment in the network can be non-intrusive, increasing circuit reliability. TR54016 and ANSI T1.403 conform to ITU Q.921 and can coexist on the same 4Kb/s ESF FDL. AT&T supports equipment conforming to both TR54016 and ANSI T1.403. It is recommended that new CI support both TR54016 and ANSI T1.403.
    If the ESF FDL is used to transmit a Yellow Alarm, what happens to the ESF FDL messages when a Yellow Alarm is being sent?
    The ESF FDL messages always have priority on the Facility Data Link. If any TR54016 or ANSI T1.403 messages need to be sent, such as the one-second PRM, then the Yellow Alarm (also called Remote Alarm Indication or RAI) pattern is interrupted, the PRM is sent and a Yellow Alarm is again transmitted.
    What should my equipment do when it receives a Yellow Alarm from the other end of the T1.5 span?
    The Yellow Alarm (or Remote Alarm Indication, RAI) is an indication that the remote end of the T1.5 has declared an alarm condition and wants to inform your end the T1.5 has failed (at least in one direction of transmission). Your equipment must enter a Yellow Carrier Facility Alarm (Yellow CFA) state. If your equipment is voice equipment, you must perform trunk processing (hang up all the existing calls and busy out the trunks so no new calls attempt to go over a failed T1.5). If your equipment is data equipment you should inform the DTE of the failure by dropping control leads on the data interface (such as DSR, CTS, CD).
    What is the difference between Red CFA and AIS CFA?
    The only difference is the conditions that caused the declaration of the alarm state. The Red Carrier Facility Alarm (Red CFA) state is entered after receiving 2.5 seconds of Out Of Frame (OOF) or Loss Of Signal (LOS). The Alarm Indication Signal CFA (AIS CFA) is entered after receiving 2.5 seconds of an unframed all ones signal (AIS). Whichever condition caused the initiation of the CFA, the device's actions are the same: transmit Yellow Alarm (Remote Alarm Indication, RAI) and perform trunk processing.
    What is jitter?
    Jitter is an imperfection of a digital signal, where bits are arriving early or late from their ideal time. The two components associated with jitter are amplitude and frequency. Jitter amplitude is measured in Unit Intervals (UI); each unit interval is equal to one bit time. This is a measure of how far the bits are sliding, usually measured peak to peak. The shifting of the bit arrival time is not random. Frequency components are measured in Hertz. Lower frequency jitter is easier to follow than higher frequency jitter.
    What is a slip?
    To reduce the effects of jitter every device has a receive frame buffer that gets filled up with bits coming off the line. The bits are read out of the buffer by the system clock. If the buffer fills faster than the bits are read out, then the buffer is flushed when it reaches capacity. This results in a loss of 193 bits to the data stream and is called a negative slip. If the buffer fills slower than the bits are read out of the buffer when the buffer runs dry, the last 193 bits in the frame buffer are repeated. This results in a repetition of 193 bits in the data stream and is called a positive slip.
    What is jitter tolerance?
    Jitter tolerance is the amount of jitter the device can receive before it experiences slips or bit errors.
    What is transfer jitter?
    Transfer jitter is a measure of the amount of jitter attenuation the device provides between its network receive and transmit signals while taking timing from the network.
    What is intrinsic jitter?
    Intrinsic jitter is the amount of jitter the device transmits using internal timing, this is thought of as quiet state jitter.
    What is the loss of superframe synchronization?
    This is when the data in the payload of the DS-1 is no longer in the same DS-1 frame number. For example a DS-1 signal passing through a Digital Cross Connect device is stripped of its framing bit, all 24 DS-0 (64 Kb/s) Channels are connected to another DS-1 port. When the DS-0's are reassembled, a framing bit is added to the DS-1. This framing bit is not synchronized to the original DS-1 entering the digital cross connect. So the 1536 Kb/s data may be "offset" from the original 8 Kb/s framing bit pattern.
    Wouldn't that disrupt Robbed Bit Signaling?
    Robbed Bit Signaling (RBS) assigns the bit 8 of the DS-0 byte every 6th frame as the signaling bits. A digital cross connect can not guarantee that frame 6 entering the digital cross connect will leave on frame 6. A special type of cross connect is made in the digital cross connect switch that buffers the signaling bits until the right transmit frame is sent. This results in overwriting the data that was contained in that 8th bit.
    When do I take timing from the network and when do I supply timing to the network?
    For any service that terminates the DS-1 in the network (ASDS, M24, BMS, ABM, ISDN or Special Access) you must take the stratum one traceable timing on the DS-1 from the network. For point to point T1.5 service, the service is transparent to timing. You must supply the timing at one end of the T1.5 and take that timing from the other end.

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    ISDN

    What implementation of ISDN PRI does AT&T support?
    AT&T uses a Custom ISDN PRI implementation, different from National ISDN. AT&T's ISDN PRI is described in AT&T Technical Reference (TR) 41459.
    What sort of testing does AT&T perform for ISDN?
    AT&T tests for conformance to the ISDN PRI protocol described in TR 41459. The conformance testing follows the AT&T ISDN PRI Test Plan.
    Where is the test conducted?
    ISDN testing is performed in San Francisco and Washington, DC.
    What AT&T Services are supported via ISDN PRI?
    AT&T Supports both Domestic and International Switched Services via ISDN PRI. The DOMESTIC switched services supported via AT&T Network ISDN PRI include the following:

    Software Defined Network (SDN)
    Software Defined Data Network (SDDN)
    Toll Free MEGACOM®
    MEGACOM®
    ACCUNET® Switched Digital Service
    AT&T MultiQuest®
    Toll Free Multimedia Services
    Termination Switched Access Arrangement (TSAA)

    The INTERNATIONAL switched services supported via AT&T Network ISDN PRI include the following:

    Switched Digital International Service (SDI)
    Global Software Defined Network (GSDN)
    International Toll Free Service
    International MEGACOM® Service

    How can I get more information about AT&T's ISDN services?
    The AT&T Business Communications Services Guide contains a description of AT&T's ISDN service offerings. You can order the AT&T Business Communications Services Guide by contacting the AT&T Customer Informaiton Center as follows (NOTE: When ordering, refer to document # 015-358-027):

    Call:
    AT&T Customer Information Center
    USA: 1-800-432-6600
    EUROPE: 010-1-317-322-6416
    FAR EAST: 010-1-317-322-6389
    AMERICAS/MID EAST/AFRICA: 010-1-317-322-6646

    Write:
    AT&T Customer Information Center
    2855 North Franklin Road
    P.O. Box 19901
    Indianapolis, IN 46219

    Descriptions of AT&T's services are also available on the AT&T Enterprise Web site.

    What is D-Channel Backup?
    D-Channel Backup allows a customer to designate at provisioning a pair of D-Channels in separate DS1 facilities as a mated pair. If one of the D-Channels were to fail, the D-Channel backup feature permits a customer continued access to the AT&T network by transferring most of the signaling information to the backup D-Channel. For detailed information about D-Channel Backup, see AT&T Technical Reference (TR) 41459.
    What is NFAS (Non-Facility Associated Signaling)?
    Non-facility associated signaling (NFAS) allows a D-Channel signaling entity to assign calls to channels on more than one interface (including the one containing the D-Channel). This is in contrast to facility associated signaling, in which the D-Channel signaling entity can only assign calls to channels on the interface containing the D-Channel.

    For detailed information about NFAS, see AT&T Technical Reference (TR) 41459.

    What is User-to-User Information (UUI) exchange?
    User-to User-Information exchange is a means by which two ISDN users can exchange packet-oriented data. The purpose and use of that data is left to the user's application. For example, a call center operator may redirect an incoming call to another party (such as a billing representative), using a B channel for the circuit-switched connection, and at the same time use the D channel to send information about that call (for example, the caller's account number). The types of UUI capabilities are:
    1. Message Associated User-to-User Information (MA UUI) - allows two users to exchange data in the call control messages exchanged during call setup and/or disconnect.
    2. Call Associated Temporary Signaling Connections - allows two users to exchange data in conjunction with a circuit-switched connection. The data exchange takes place during or after the call setup request.
    3. Non-Call Associated Temporary Signaling Connections - allows two users to exchange data without setting up a circuit-switched connection.

    For detailed information about User-to-User Information, see AT&T Technical Reference (TR) 41459.

    What are TSCs (Temporary Signaling Connections)?
    Temporary Signaling Connections (TSCs) are a means by which two ISDN users can exchange packet-oriented data. There are two kinds of TSCs:
    1. Call Associated Temporary Signaling Connections, which allow two users to exchange data in conjunction with a circuit-switched connection. The data exchange takes place during or after the call setup request.
    2. Non-Call Associated Temporary Signaling Connections, which allow two users to exchange data without setting up a circuit-switched connection.

    For detailed information about TSCs, see AT&T Technical Reference (TR) 41459.

    How should I code the Called Party Number Information Element for an International number?
    When coding for an International number, it is important to pay attention to the third octet of the Called Party Number Information Element. This structure of this octet is as follows:

    FIELD BIT VALUE MEANING
    Extension 8 1 last octet of the description
    Type of number 7-5 000 unknown
        001 international number
        010 national number
        100 subscriber number
    Numbering plan 4-1 0000 unknown
        0001 ISDN/telephony numbering plan (Recommendation E.164/E.163)
        1001 private numbering plan

    Use either of the following methods to indicate an International number:

    1. Code the Type of Number field as international number (001), and the Numbering plan field as ISDN/telephony numbering plan (0001). If you do this, DO NOT include the three digit prefix "011" in the Number digits.
    2. Code the Type of Number field as unknown (000), and the Numbering plan field as unknown (0000). If you do this, you MUST include the three digit prefix "011" in the Number digits.

    For complete information about coding the Called Party Number Information Element, refer to AT&T Technical Reference 41459, Part III, section 3.6.5.7.

    How should I initiate a call involving Access to Operator Services/Operator Express?
    To request the feature, "Access to Operator Services," users must send an appropriately coded Network-Specific Facilities (NSF) Information Element in a SETUP message. Complete information about coding the NSF is found in AT&T Technical Reference TR 41459, Part III, Section 3.6.5.19. TR 41459 also provides more detail about Access to Operator Services in Part III, Section 3.15.12.

    In summary, the NSF should be coded with 2 appearances of octet 4. The first serves to request the feature of "Access to Operator Services," and the second indicates the service used for access to the AT&T Network (i.e., MEGACOM®, Software Defined Network (SDN), or Long Distance Service (LDS)). The following table, taken from TR 41459, summarizes the rules for calls involving Operator Services:

    Call Type Information Element Coding Requirements
    0- calls for direct operator access Called Party Number = no digits
    Type of Number = National/Subscriber
    NSF (Feature, first Octet 4) = Operator or PCCO
    NSF (Service, second Octet 4) = LDS, MEGACOM or SDN
    0+ 7 digit or 10 digit calls Called Party Number = 7/10
    Type of Number = National/Subscriber
    NSF (Feature, first Octet 4) = Operator or PCCO
    NSF (Service, second Octet 4) = LDS, MEGACOM or SDN
    01+CC+NN international operator calls Called Party Number = CC+NN
    Type of Number = International
    NSF (Feature, first Octet 4) = Operator or PCCO
    NSF (Service, second Octet 4) = LDS, MEGACOM or SDN

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