Signaling System No.7 Protocol Architecture And Sevices part 61

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MTP 2 Testing The MTP 2 test specification is found in ITU Q.781 [87]. The purpose of the tests is to ensure complete validation and compatibility of an SP's MTP 2 protocol according to ITU Q.703 [51].

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Nội dung Text: Signaling System No.7 Protocol Architecture And Sevices part 61

MTP 2 Testing The MTP 2 test specification is found in ITU Q.781 [87]. The purpose of the tests is to ensure complete validation and compatibility of an SP's MTP 2 protocol according to ITU Q.703 [51]. See Chapter 6, "Message Transfer Part 2 (MTP2)," for a description of the MTP2 protocol. The tests are split up by functional area into ten categories. Table 16-1 shows the test categories and the tests that they contain. Table 16-1. Test Categories and Numbers Found in Q.781 Category Test Total Number(s) Link state control—expected signal units/orders 1.1–1.35 35 Link state control—unexpected signal units/orders 2.1–2.8 8 Transmission failure 3.1–3.8 8 Processor outage control 4.1–4.3 3 SU delimitation, alignment, error detection, and 5.1–5.5 5 correction SUERM check 6.1–6.4 4 AERM check 7.1–7.4 4 Transmission and reception control (basic) 8.1–8.13 13 Transmission and reception control (PCR) 9.1–9.13 13 Congestion control 10.1–10.4 4 Totals 97 The remainder of this section explains fourteen of these tests, covering at least one from each category. The tests explained include: 1.1, 1.5, 1.22, 1.28, 2.7, 3.1, 3.2, 4.1, 5.1, 6.1, 7.1, 8.3, 9.3, and 10.1. These numbers refer to the test numbers that are allocated in Q.781. Many of the tests that are not used as examples are
variations of the example tests given; therefore, taking at least one test out of each category gives the reader a good understanding of the test methods. Test Configuration A single link is used for MTP2 tests. Figure 16-1 shows a single link between SP A and SP B. SP A is the device under test DUT, while SP B is the Tester. Figure 16-1. Test Configuration Used for MTP2 Testing Example 1: Initialization (Power-up), Test 1.1 This test ensures that the DUT enters the correct state upon power up and that it is used for both validation and compatibility testing purposes. It consists of two parts: part (a) and part (b). Part (b) is the same test repeated in the reverse direction. Part (a) Before beginning this test, switch the DUT off and the tester on. This results in status indication out of service (SIOS) periodically being sent in only one direction, from the tester to the DUT. The test begins when you power up the DUT. The DUT should periodically send LSSUs with the SIOS in the direction SP A to SP B. The FIB and the BIB should each be initialized to 1, and the FSN and BSN should both be set to 127. Figure 16- 2 shows the expected message sequence for this test. Figure 16-2. Expected Message Sequence for Test 1.1 (a) If the DUT sends an LSSU with the SIOS and the fields FIB, BIB, FSN, BSN are initialized correctly, then test 1.1(a) should be considered passed. Part (b)
Switch the DUT on and the tester off before beginning this test. This results in SIOS periodically being sent in only one direction, from the DUT to the Tester. The test begins when you power up the Tester. The Tester should periodically send LSSUs with the SIOS in the direction SP B to SP A. The FIB and the BIB should both be set to 1, and the FSN and BSN should both be set to 127. Figure 16-3 shows the expected message sequence for this test. Figure 16-3. Expected Message Sequence If the fields FIB, BIB, FSN, and BSN have been received correctly, then test 1.1(b) should be considered passed. Example 2: Normal Alignment—Correct Procedure (FISU), Test 1.5 This test ensures that the DUT can perform the normal alignment procedure, and that the "in-service" state can be maintained once it has been achieved. It consists of two parts, part (a) and part (b), which is the same test except that it uses two octet LSSUs. Part (a) is used for both validation and compatibility testing purposes, while part (b) is used for validation testing purposes only. Part (a) The link should be put in the "out-of-service" state before commencing this test. As shown in Figure 16-4, the test begins when you start the alignment procedure at the DUT. The normal alignment procedure should follow; DUT should cease to send SIOS and start sending SIO. Upon receiving SIO back from the Tester, it should request normal alignment by sending SIN. Upon receiving SIN back from the Tester, the "in-service" state should be entered. FISUs should flow in both directions, and the DUT should remain in the "in-service" state. Figure 16-4. Expected Message Sequence for Test 1.5
Consider the test passed if the DUT achieves link alignment, enters the "in-service" state, and remains in the "in-service" state after FISUs have been exchanged. Part (b) Part (b) is exactly the same as part (a), except that the Tester should send the LSSUs with a length of two octets rather than one. Example 3: Individual End Sets Emergency, Test 1.22 This test ensures that the DUT performs emergency alignment when requested by the other side even when it perceives a normal condition, but that the other side request emergency alignment. It is used for validation testing purposes only. You should put the link in the "out-of-service" state before commencing this test. The test begins when you start the alignment procedure at the Tester. The Tester should request emergency alignment by sending LSSUs with emergency alignment indication (SIEs). The DUT should be set to "perceive" normal alignment conditions, and should thus cease to send SIOS, send back SIO, and then start sending LSSUs with normal alignment indication (SINs). Even though the DUT "perceives" that normal alignment should be carried, it should carry out the alignment within the emergency proving period because it has received a request from the other side for emergency alignment. Figure 16-5 shows the expected message sequence for this test. Figure 16-5. Expected Message Sequence for Test 1.22 Pe is the emergency proving period, which can by measured by subtracting the time stamp of the SIN from the time stamp for the FISU. Consider the test passed if the alignment occurs within the emergency proving period. Example 4: SIO Received During Link In-Service, Test 1.28
This test ensures that the DUT can deactivate a link from the "in-service" state. It is only used for validation testing purposes. The link should be put in the in-service state before commencing this test. The test begins by sending an LSSU with the SIO from the Tester to the DUT. The DUT should then place the link in the out-of-service state returning an LSSU with SIOS. It should also indicate "out-of-service" to MTP3 with reason "Received SIO." Figure 16-6 shows the expected message sequence for this test. Figure 16-6. Expected Message Sequence for Test 1.28 Consider the test passed if the DUT responds to the SIO reception by returning SIOS. Example 5: Unexpected Signal Units/Orders in "In-Service" State, Test 2.7 This test ensures that the DUT ignores a corrupt LSSU receipt and unexpected requests from MTP3. The test is used for validation testing purposes only. The link should be put in the in-service state before commencing this test; if it is already in service, it should be put out of service, and then put back to the in- service state. The test begins by sending an LSSU with a corrupt status, or a status for which there is no meaning (such as 00000110) to the DUT. A sequence of unexpected MTP3 commands should be issued at the DUT. These commands are as follows: • –command "Set Emergency" • –command "Clear Emergency" • –command "Clear Local Processor Outage" (LPO) • –command "Start" Figure 16-7 shows the expected message sequence for this test. Figure 16-7. Expected Message Sequence for Test 2.7
Consider the test passed if the DUT ignores the corrupt LSSU status indication, and the unexpected MTP3 commands. Example 6: Link Aligned Ready (Break Tx Path), Test 3.1 This test ensures that the DUT responds correctly to a transmission failure that SUERM detects by placing the link out of service when in the Aligned Ready state. The test is used for validation testing purposes only. Put the link in the out-of-service state before commencing this test. The test begins when you initiate normal alignment at the DUT. The Tx path should be broken after alignment is achieved. Figure 16-8 shows the expected message sequence for this test. Figure 16-8. Expected Message Sequence for Test 3.1 Consider the test passed if the DUT places the link out of service by sending SIOS, sends "out-of-service" to the local MTP3 with reason "Excessive error rate SUERM," and remains in the "out-of-service" state. Example 7: Link Aligned Ready (Corrupt FIBs—Basic), Test 3.2 This test ensures that the DUT puts the link out of service after receiving two consecutive corrupt FIBs, while in the Aligned Ready state. It is used for validation testing purposes only. Put the link in the Aligned Ready state before commencing this test. The test begins by sending an FISU with an inverted FIB from the Tester to the DUT. Another consecutive FISU should be sent with the FIB still inverted.
According to the MTP2 specification, if any two out of three FIBs that were received consecutively (MSUs or FISUs only) indicate the start of a retransmission when no negative acknowledgment has been sent, then MTP3 should informed that the link is faulty with reason "Abnormal FIB Received." For more information, see Q.703 Clause 5.3.2. Figure 16-9 shows the expected message sequence for this test. Figure 16-9. Expected Message Sequence for Test 3.2 Consider the test passed if the DUT places the link out of service by sending SIOS, sends "out of service" to the local MTP3 with reason "Abnormal FIB Received," and remains in the "out-of-service" state. Example 8: Set and Clear LPO While Link In-Service, Test 4.1 This test ensures that the DUT performs correctly when a local processor outage (LPO) is set and then recovered from while the link is in service. It is used for validation testing purposes only. The link should be put in the "in-service" state before commencing this test. The test begins by sending two normal MSUs from the DUT to the Tester. An LPO condition should then be set at the DUT. While in an LPO state, the DUT should discard all received SUs. To verify that the DUT buffer is clearing properly, the Tester should send at least one MSU and one FISU to the DUT. Then the LPO state should be cleared at the DUT. The DUT should resume sending FSUs as normal and should be given at least one MSU to send after LPO clears. Clause 12 Q.703 [51] describes the LPO condition. Figure 16-10 shows the expected message sequence for this test. Figure 16-10. Expected Message Sequence for Test 4.1
Consider the test passed if the DUT sends SIPO, discards the received MSU and sends no further status messages after clear LPU is issued. Example 9: SU Delimitation, Alignment, Error Detection, and Correction, Test 5.1 This test ensures that the DUT detects seven or more consecutive "1's" as an error, realizes that SU alignment has been lost, regains SU alignment, and subsequently behaves as though unaffected. It is used for validation testing purposes only. The link should be put in the "in-service" state before commencing this test. The test begins by sending the DUT a corrupt MSU that contains seven or more consecutive "1's." The DUT should then go into "octet counting" by discarding all SUs until a correct SU is received, thereby ending the "octet counting" mode and remaining in the "In-Service" state. Q.703 clause 4.1.4 describes the "octet counting" mode. Figure 16-11 shows the expected message sequence for this test. Figure 16-11. Expected Message Sequence for Test 5.1 Consider the test passed if the BSN in the FISU that was sent immediately after the corrupt MSU was received remains unchanged (meaning that the corrupt MSU was discarded). opkiExample 10: Error Rate of 1 in 256—Link Remains In-Service, Test 6.1 This test ensures that the DUT has implemented the threshold to correctly increment the SUERM counter. It is used for validation testing purposes only. The link should be put in the "in-service" state before commencing this test. The test is performed by sending the DUT one corrupt FISU in every 256 FISUs, and sending enough blocks of 256 SUs to cause the SUERM to close the link if it
has been increased. As long as no more than one corrupt SU is detected in 256 SUs, the link should remain in-service because the SUERM counter should not be increased. Recall from Chapter 6 that the SUERM is an up/down counter that is weighted such that for every 256 SUs received correctly, it decreases by one; for each corrupt SU, it increases by one; and if it reaches the threshold value 64 (this value is for 64 Kbps links only), it should inform MTP3, which commands it to put the link out of service by sending SIOS. Q.703 clause 10.2 [51] describes the SUERM. Figure 16-12 shows this test's expected message sequence. Figure 16-12. Expected Message Sequence for Test 6.1 Consider the test passed if the link remains in the "in-service" state. Example 11, Test 7.1 This test ensures that the DUT has implemented the AERM threshold correctly. It is used for validation testing purposes only. The link should be put in the "out-of-service" state before commencing this test. The test is performed by sending the DUT up to three corrupt (bad CRC) LSSUs during the proving period. Three corrupt LSSUs should be sent. Recall from Chapter 6 that the AERM is a counter that is used during the proving of a link. It is zeroed at the start of proving, incremented for each corrupt LSSU received, and proving should be abandoned if it reaches the value 4 (for normal proving, or 1 for emergency proving). Q.703 clause 10.3 [51] describes the AERM. Figure 16-13 shows the expected message sequence for this test. Figure 16-13. Expected Message Sequence for Test 7.1
Consider the test passed if the proving period continues and the link aligns successfully. Example 12: Check RTB Full, Test 8.3 This test ensures that the DUT buffers MSUs when no acknowledgments are received. It is used for validation testing purposes only. The link should be put in the "in-service" state before commencing this test. The test is performed by sending the 100 DUT MSUs per second and, in order to fill the retransmission buffer (RTB), not providing any acknowledgments until T7 is on the threshold of timing out. The number of MSUs to send is not specified, but 128 is enough. The acknowledgment that is sent on the verge of T7's expiration should negatively acknowledge all messages received, thereby requesting the DUT to send all messages in its RTB. Timer T7 "excessive delay of acknowledgment" is used to detect when an unreasonably long period has elapsed while waiting for a positive or negative acknowledgment after sending an MSU. When T7 expires, link failure is assumed and it is reported to MTP3. This is the reason that MSUs should be generated at a rate of at least 100 per second to fill the RTB before T7 expires. Q.703 clause 5.3 [51] describes retransmission, including T7. Figure 16-14 shows the expected message sequence for this test. Figure 16-14. Expected Message Sequence for Test 8.3 Consider the test passed if the DUT retransmits the RTB's complete contents. Example 13: Forced Retransmission with the Value N1, Test 9.3 This test ensures that N1 detects the "RTB full" and that forced retransmission occurs as a result. It is used for validation testing purposes only.
Before beginning this test, the link should be put in the "in-service" state and set to use the preventive cyclic retransmission (PCR) method of error correction at both sides of the link. The test is performed by sending the DUT 128 MSUs at the rate of 100 per second. To fill the RTB, the Tester should not provide a positive acknowledgment until timer T7 is on the threshold of timing out. The acknowledgment that is sent on the verge of expiration of T7 should be a positive acknowledgment of message 0, thereby requesting that the DUT send all messages in its RTB. See Example 12 for more information about T7. Q.703 clause 6.4 [51] describes forced transmission. Recall from Chapter 6 that PCR does not use negative acknowledgments. Note that N1 is the maximum number of MSUs that are available for retransmission—usually 127. Q.703 clause 10.3 [51] describes N1. Figure 16-15 shows the expected message sequence for this test. Figure 16-15. Expected Message Sequence for Test 9.3 Consider the test passed if the DUT performs forced retransmission of all MSUs in the RTB and then ends forced retransmission after the last MSU in RTB has been sent. Example 14: Congestion Abatement, Test 10.1 This test ensures that the congestion abatement procedure has been implemented properly. It is used for validation testing purposes only. The link should be put in the "in-service" state before commencing this test. The test is performed by setting a MTP2 congested state at the DUT. The DUT should then send SIBs at intervals of Timer T5 "sending SIB" until congestion abates. Next, the congestion should be cleared, resulting in the DUT ceasing to send SIB and sending FISUs instead. Q.703 clause 9.3 [51] describes the sending of SIB. It is interesting to note that the mechanism for detecting congestion is implementation-dependent and is not
specified. Figure 16-16 shows the expected message sequence for this test. Figure 16-16. Expected Message Sequence for Test 10.1 Consider the test passed if the DUT sends SIBs when there is congestion at intervals of T5, and returns to a normal state when congestion is cleared.