Application Series ATM Testing with the SunSet OCx or SunSet SDH
Contents
1. If the PULSES or rate LEDs are green but the FRAME LED is not verify that the interface you are connected to matches the Test Configuration You should also see the ATM CELL LED light green to indicate the presence of ATM cells If the ATM CELL LED is off the test set has not been configured for ATM testing If you are using a SunSet OCx 0C 12 you must first go to the ATM Functions menu for the ATM CELL LED to activate If you are testing a 45 Mbps or DS3 circuit verify that you have the proper ATM mapping If the LEDs are flashing red press the HISTORY or LED key to clear the history condition Once you are satisfied that the LEDs indicate no errors or alarms re start the measurement to clear away any errors that were detected during setup Go to the Measurement Results screen You should see NO ERRORS or NO ERR displayed on the summary screen ATM NETWORK MONITORING 4 On the SunSet OCx OC 48 or SDH the VCC Scan screen also shows the utilized or available band width as selected in the VCC Scan Configuration screen In addition the unit can filter on a specific VPI value allowing you to concentrate on a single VPC 5 If no traffic appears in the scan and the ATM CELL LED is green the circuit may be filled with idle or unassigned cells Go to VCC Scan Configuration and set the VPI Capture field to ALL to prevent the desired VPI from being filtered 6 If some traffic appears but important VPI VCI2. Individual APS 0001 provides protection against bit errors in the cell address field and provides a mechanism to delineate cells from the physical layer HEC provides no protection for the ATM cell payload A CRC algorithm generates the HEC value based on the preceding bytes in the header This algorithm can correct a single bit error within the 5 byte header thus these are called correctable HEC errors A non correct able HEC error consists of two or more bit errors in the address OAM Cells Operation Administration and Maintenance OAM cells provide alarms continuity checks performance reports protection switching and other messages for the ATM network OAM cells are typically only sent 5 octets 4 bits 4 bits 45 octets 6 bits 10 bits L Header Function J m Future Type Function Use Error De Type Specific Field tection Code 0 191 Test Cell ITU T specification 0 191 defines a special cell to test the QoS of an ATM connection The 0 191 test cell contains a sequence number timestamp and CRC field but no test pattern with which to make a BER measure ment For BER testing create a user cell with a pseudo random pattern such as 215 1 2e15 5 octets 4 bytes Header Timestamp Sequence Number 4 bytes 37 bytes I CRC 16 1 bytel 2 bytes Unused 2001 Sunrise Telecom Incorporated ATM Testing with the SunSet OCx or Sunset SDH COMMON TESTING
3. PITFALLS ATM Scrambling To prevent the ATM payload the SONET SDH framing bytes No A1 A2 the ATM payload can be scrambled Most switches have scrambling enabled by default Scrambling does not affect the cell header and will not impact the ability of a test set or switch to detect ATM cells However user data sent across an ATM connection with a scrambling mismatch will become incoherent and useless Basic network monitoring is not affected by scrambling but other ATM tests including QoS BER and IP testing will not function properly If you are able to receive ATM cells but unable to make a QoS or BER measurement double check the scrambling setting on both the ATM equipment and your SunSet The SunSet s scrambling setting is in the ATM Setup or Configuration Menu Bie FA from resembling 45 Mbps ATM Mapping Two methods of mapping ATM cells into a 45 Mbps DS3 signal are utilized by switches Physical Layer Convergence Protocol PLCP defined in IEEE 802 6 and ITU T G 804 maps the ATM cells into a SONET like frame inside the 45 Mbps signal HEC based mapping also defined in G 804 places the ATM cells directly into the 45 Mbps signal equivalent to the way ATM cells are mapped into SONET SDH If the mapping of the test set does not match the mapping used by the ATM switch the test set will not recognize any ATM cells from the switch and vice a versa To change your ATM mapping go to the ATM Setup or ATM Configur
4. pattern like 273 1 220 1 or 2 5 1 Be sure the transmitted and received VCCs are activated and both the transmitter and receiver are properly connected to the switch When you begin the test you should have a green ATM CELL LED If not see Physical Layer Testing above If problems occur during QoS and BER testing verify that both test sets are set to the same pattern both have proper scrambling setting and they have the same pattern truncate setting ATM Setup In BER testing the SunSet should show pattern synchronization with a green PAT SYNC LED 2001 Sunrise Telecom Incorporated ATM Testing with the SunSet OCx or Sunset SDH QoS Testing The key parameters for QoS testing are Errored Cells and Cell Error Ratio CER Lost Cells and Cell Loss Ratio CLR and Misinserted Cells and Cell Misinsertion Rate CMR Ideally all these values will be zero 1 2 If the CLR is above zero it may be due to cells being tagged for not complying with present bandwidth parameters Also check the CLR of cells with a CLP of 1 BER Testing 1 Verify that the test set receives the cells free of bit errors Inject a burst of one or more bit errors and verify the same number of bit errors is received Inject a specific BER such as 1x107 one errored bit error per million the test set should receive the same BER vvithout any added bit errors OAM Cells These tests are most appropriate during installati
5. 45M FRAME M13 RXLVL MONITOR TXLVL DSX TXSRC TESTPAT TXCLK INTERN SINGLE MUXTEST ATM Connect the test set 1 VVhen monitoring a live circuit be sure to use a monitor jack such as on a DSX panel Optical netvvorks should have a splitter such as 90 10 that passes 90 of the signal through to the network and allows a test set to access the 10 signal non intrusively When monitoring only do not connect the transmit jack of the test set 2 When connecting to a multimode system use multimode cables The receiver on your SunSet OCx OC 48 may not be multimode compatible depending on which configuration was ordered Verify with Sunrise Telecom customer service 3 If you see a Loss of Signal LOS or Loss of Framing LOF when connecting optical equipment a high powered transmitter that is saturating the receivers may be causing it This is especially true when connecting the SunSet s single mode lasers to a multimode system In these situations add an attenuator typically 10 dB is adequate 2001 Sunrise Telecom Incorporated ATM Testing with the SunSet OCx or Sunset SDH Physical Layer Testing 1 The first step to installing or monitoring any ATM network is verifying that the physical layer is free of problems Errors and defects on the physical layer are a major cause of problems that affect ATM traffic When you connect the SunSet you should get green LEDs for the selected interface and framing
6. SUNRISE TELECOM Fi a Step ahead Application Series ATM Testing with the SunSet OCx or SunSet SDH 302 Enzo Drive San Jose CA 95138 USA ph 1 408 363 8000 fax 1 408 363 8313 info sunrisetelecom com www sunrisetelecom com Publication Number APP OPT 002 Rev A INTRODUCTION Asynchronous Transfer Mode ATM is the most widely deployed backbone technology in the world ATM grew out of a need to provide a variety of broadband digital services over a wide area network WAN Today ATM carries voice data video and Internet Protocol IP traffic and is the predominant technology for DSL networks Unique among all technologies ATM guarantees a pre defined quality of service QoS With its emphasis on reliability and QoS ATM requires extensive testing when installing and turning up connections Once up ATM networks are typically very robust and stable especially those running on a SONET SDH backbone but periodic monitoring of ATM traffic and performance is required to ensure the network is running smoothly The test procedures described herein address physical layer testing QoS and BER testing IP layer testing and network monitoring QoS BER and IP testing are most appropriate for out of service testing such as when installing an ATM network or when troubleshooting a network that has failed Network monitoring is applicable for live or test traffic BACKGROUND ATM is a connection orientated techno
7. a single segment in the network or end to end F4 OAM cells are distributed to all VCls sharing the same VPI F5 OAM cells are only delivered to the specific VPI VCI indicated A VCI of 3 segment or 4 end to end indicates an F4 OAM cell A PTI of 100 segment or 101 end to end indicates an F5 OAM cell F5 OAM cells have a normal VCI value When generating OAM cells from your SunSet use the ATM Alarm generation function of the set Do not create a VCC and manually set the VCI or PTI value to in dicate an OAM cell OAM cells contain special informa tion fields that are not included in a user cell payload OAM Type Value z Function Type Usage Value set to 1 the cell has Alarm Indication Signal 0000 a higher probability to be dropped by a Fault ant Remote Defect Identification 0001 Management switch While useful for stress testing it Continuity Check Continuous monitoring of connections 0100 Cell Loopback Check connection continuity 1000 may not accurately reflect live traffic Management Backward Monitoring On line performance assessment 0001 therefore setting CLP Performance Monitoring Performance Monitoring 0000 to zero is recom 00 0 1000 5 Continuity Check Continuity Check 0001 mended ATM Protective Group Group APS 0000 Switching The HEC byte Individual Forward Monitoring On line performance assessment 0000 Performance 0010
8. a slight difference in their headers see figure to the right they are identical for testing purposes Network Network Interface NNI Header VC values from 0 to 31 are used for ATM layer alarms network messaging and other reserved uses Though the VCI can be as high as 65 535 not all ATM switches 2001 Sunrise Telecom Incorporated ATM Testing with the SunSet OCx or Sunset SDH support all VCI values When testing ATM Header Recommended Field Value s networks VCI values from 32 to 1023 are GFC 0000 binary best vPI 0 to 255 So long as the VCI va value is 32 or higher PTI 000 binary any VPI value can be used While NNI can CER 8 Set Automatically have a VPI up to 4094 UNI can only support VPI values up to 255 Therefore it is recom mended to use VPI of 255 or less The PTI is used to indicate alarms and traffic congestion PTI values of 000 or 001 are best for most testing applications Advanced users may wish to manually indicate congestion by setting the PTI to 010 or 011 and see if the cells are dropped When the CLP bit is once a second well below the typical bandwidth of user cells Alarm Indication Signal AIS and Remote Defect Indicator RDI cells are two types of Fault Management FM OAM cells ATM layer AIS and RDI defects have similar definitions to their SONET and SDH counterparts OAM cells are designated as F4 VPC or F5 VCC OAM cells can also apply to
9. address values this will not disrupt the network VCC Setup Your Sunset can generate up to 6 or 8 VCCs but in most cases you only need to test one VCC at a time The other 5 or 7 VCCs are used for background traffic filling up the bandwidth of the connection 1 Go to VCC Setup and select the first VCC Input the VPI VC values for the VCC under test You can set the received and transmitted header values indepen dently Again VCI values 32 and higher are best and leave the PTI and CLP values 0 unless you want to simulate congested or tagged cells In the traffic field select CBR for most applications For a new network start transmitting cells at a 100 bandwidth You can do this with a single VCC or a number of VCCs If adding a VCC to a live network the maximum bandwidth depends on the current utilization which you can see on the VCC Scan screen on page 5 You can then measure the QoS or BER at each bandwidth If you discover errors or poor QoS incrementally reduce the bandwidth until the QoS and BER are within acceptable parameters As your payload select Pattern for BER testing or Test Cell for QoS testing On the SunSet OC 12 3 or STM 1 black and white unit there is no option for Test Cell Instead select the ALL 0 pattern amp activate the timestamp and sequence number This is similar to an 0 191 test cell but lacks the CRC field For BER testing set your pattern to a pseudo random bit stream PRBS
10. ate If too many cells are congested or tagged cell loss may occur By moving to different switches you can identify network bottlenecks and increase bandwidth accordingly 4 Verify that the call control settings are correct and that the source of the ATM traffic is not exceeding this limit Cells rates below the minimum are very disruptive to the services like video and voice being carried over the ATM network In the case of Constant Bit Rate CBR traffic it is vital that the rate is a constant value and never drops or bursts 5 HEC errors in an ATM system indicate that bit errors are occurring on the physical layer Non correctable HEC errors result in dropped cells and an increased cell loss ratio CLR The customer s ATM service contract will specify maximum CLR and HEC error rate 6 You can also see any alarms such as AIS or RDI on the VCC An AIS is a very serious problem indicating a complete lack of service on the VPC F4 or VCC F5 An RDI is a far end response to an AIS when you see an RDI there is an AIS occurring in the channel s opposite direction Typically an AIS is due to an LOS LOF or Loss of Pointer LOP on the physical layer OUT OF SERVICE TESTING The goals of this step are to insert ATM cells verify that they are received with no errors and to test the bandwidth limitations of the network The test set will insert ATM cells into the network and analyze them upon return This type of test is typi
11. ation menu Payload Label Mismatch PLM SONET and SDH specifications indicate that ATM traffic should use a Payload Label C2 byte in the path over head of 13 hex However not all switches use this label and the SunSet OCx OC 12 3 will not send 13 until you enter ATM Functions When the C2 bytes do not match a PLM P alarm is declared The PLM does not interfere with physical layer measurements but may prevent an ATM switch from detecting ATM cells To prevent a switch from getting a PLM you can also change the C2 byte transmitted from your SunSet Go to the Send POH Bytes menu within SONET or SDH Features Your SunSet will transmit and receive ATM cells properly despite a PLM On your SunSet OCx you can disable the PLM measurement or you can change the expected C2 value by going to your Measurement Configuration menu SUNSET SETUP For a more detailed description of the functions options and measurements of your SunSet refer to the User s Manual Configure the test set 1 On the SunSet OCx OC 48 platform or the SunSet SDH set the Test Mode to ATM Then set the Interface and Payload rates to match the network being tested 2 On the SunSet OCx OC 12 3 platform set the Test Mode to PT PT and set the Interface and Payload rates to match the network being tested Then go to the ATM functions menu to begin transmitting and receiving ATM cells CONF IGURATION TEST MODE HATM TEST INTERFACE 45M TEST PAYLOAD
12. cal when installing ATM switches or turning up a network though it can also be used on an in service network The procedure below breaks down the test into several steps In practice these can be done simultaneously with the test set Creating an ATM circuit 1 Before testing the ATM network administrator must first establish a PVC through the network and specify which VPI VCI are to be used for the test When installing new ATM service the VPI VCI values will be the same as specified for the end customer Other wise the administrator will create a PVC specifically for the test If the network is also carrying live traffic the bandwidth available for testing will be restricted If the utilized bandwidth is already 80 or higher the test may affect the QoS on the network as the available bandwidth decreases even further 2 Most tests use two test sets one connected at each end of the PVC The test can be unidirectional or bidirectional but a PVC must be created for each direction under test When using a single test set some type of loopback is required A hard loopback uses a cable looped between the transmitter and receiver so that every transmitted cell comes back Hard loopbacks should not be used for in service testing and are most appropriate for testing a single ATM switch An alternative method is to specify a PVC that sends the cells back in the direction of the test set Because the PVC only applies to specific
13. e to ATM testing some knowledge of the routing tables is required to properly track specific cells at any part in the network ATM Cells ATM uses small fixed length cells to facilitate fast switching through a network Each cell consists of 5 bytes of header plus 48 bytes of payload Header 5 octets Payload 48 octets The ATM Cell header contains the VPI VCI Payload Type Indicator PTI Cell Loss Priority CLP and Header Error Control HEC byte UNI cells also include a field for Generic Flow Control GFC The GFC only has local significance and is not carried end to end In most testing applications the GFC can be ignored and simply set to zero User Network Interface UNI Header supports ATM testing from 1 5 Mbps T1 and 2 Mbps E1 up to 2 5 Gbps 0C 48 STM 16 The terminology and testing procedures for GFC ATM are independent of the physical layer I only the maximum cell rates differ ATM defines two types of interfaces User to Network Interface UNI and Network to Network Interface NNI NNI applies to traffic be tween ATM switches and UNI describes the traffic between an edge device and an ATM switch Aside from
14. ertion Rate Cyclic Redundancy Check Cell Transit Delay Digital Subscriber Loop Digital Signal Cross Connect Error Detection Code Fault Management Generic Flow Control Header Error Control Internet Protocol Loss of Cell Delineation Light Emitting Diode Loss of Cell Loss of Framing Loss of Pointer Loss of Signal User to Network Interface Network to Network Interface Operation Administration and Maintenance Payload Label Mismatch Pseudo Random Bit Stream Performance Management Payload Type Indicator Permanent Virtual Circuit Quality of Service Remote Defect Indication Synchronous Digital Hierarchy Synchronous Optical Network Switched Virtual Circuit Test Cell Payload Type Virtual Channel Connection Virtual Channel Indicator Virtual Path Connection Virtual Path Indicator Wide Area Network Refer to Publication GL 001 for a more extensive list of ATM terms 2001 Sunrise Telecom Incorporated ATM Testing with the SunSet OCx or Sunset SDH SUNRISE TELECOM a step ahead
15. l utilized bandwidth and can identify misconfigured switches Beware that the VPI VCI value of a VCC will change at each switch so knowledge of the proper VPI VCI values is vital to properly interpreting the results 2 After connecting to the circuit go to the ATM IP or ATM Functions menu amp select the VCC Scan feature 3 The header values are sorted by when they were detected The example also shows how a change in the GFC PTI or CLP bits for a single VCC will result in two or more entries Go to VCC Statistics and find the VPI VCI just saved Press Detail to see the detailed statistics Note the Cell Count and Cell Rate and verify they match the specified parameters PVCs and SVCs have pre defined maximum and minimum allowable cell rates Cells that exceed the limits will be given a CLP of 1 and may be dropped The test set shows the number of these tagged cells VPI ALL ST 13 32 03 ET 001 08 21 UTILIZATION 73 1 Z C VPI VCI PTI CLP 1 0000 000 00032 000 0 2 0000 000 00000 000 1 3 0000 008 00035 000 0 4 0000 008 00035 000 1 5 0000 000 00032 010 0 6 0001 015 00128 000 0 7 0000 015 00128 000 0 8 0000 000 00064 000 9 0000 000 00068 000 0 PAGE UP PAGE DNCONTINU more 2001 Sunrise Telecom Incorporated ATM Testing with the SunSet OCx or Sunset SDH 3 Congestion is indicative of bandwidth limitations and may result in cells dropping To assure good 005 monitor the congested cell r
16. logy The route through the network is defined before any user data is sent In this way the ATM network can be held to stringent quality of service and traffic parameters The goal of ATM testing is to quantify the quality of the connection at the physical layer ATM layer and higher layer applications such as IP whether installing a new connection or monitoring a live network ATM Connections ATM is defined across an array of physical carriers including SONET SDH and T Carrier PDH The SunSet OCx and SunSet SDH ATM provides two layers for addressing and switching based on a Virtual Path Indicator VPI and Virtual Channel Indicator VCI In a Virtual Path Connection VPC all ATM cells sharing the same VPI addresses share the same connection Within a VPC the user can choose between thousands of channels by designating the VCI of the ATM cell A Virtual Channel Connection VCC on the other hand is defined by a VPI VCI pair and only applies to that single channel In Permanent Virtual Circuits PVC connections are assigned with fixed VPI VCI values In a Switched Virtual Circuits SVC VPI VCI values are reassigned after every call The signaling and routing used for SVC circuits is not addressed in this application note VPI VCI values only have local significance the VPI VCI values are likely to change at each ATM switch Cells that start with VPI VCI of 0 32 may be changed to 8 45 for example This presents a challeng
17. on to verify proper handling of OAM cells and verify that the contents of the OAM cells are correct 1 On the SunSet OCx OC 48 or SDH send OAM cells from the Alarm Errors menu On the SunSet OC 12 3 or black and white SDH you must be in the detailed VCC statistics screen to inject OAM cells To view the contents of a cell go to Cell Capture To avoid capturing user cells set the cell type to OAM in the configuration screen The SunSet will decode the header and OAM fields as applicable of the captured cells simply select the Header or OAM F keys Warning Sending OAM cells may affect other traffic on the network 3 Insert an OAM cell such as a VP AIS or VC RDI and verify that the network element measures and reacts accordingly When an ATM switch receives a VP AIS it should send a VC AIS downstream and an VP RDI upstream Inject a VP or VC loopback cell and verify that the switch loops it back Instruct the switch to send a Performance Management PM OAM cell COMMON ACRONYMS AAL AIS ATM APS BER CER CLP CLR CDV CMR CRC CTD DSL DSX EDC FM GFC HEC IP LCD LED LOC LOF LOP LOS UNI NNI OAM PLM PRBS PM PTI PVC QoS RDI SDH SONET SVC TCPT Vci VPC VPI VVAN ATM Adaptation Layer Alarm Indication Signal Asynchronous Transfer Mode Automatic Protection Switching Bit Error Rate Cell Error Ratio Cell Loss Priority Cell Loss Ratio Cell Delay Variation Cell Misins
18. values are missing move the monitoring point closer to the source switch by switch until the cells appear Traffic can disappear because network bottlenecks force switches to drop cells or because a switch has been configured incorrectly and is sending cells down the wrong port The PTI and CLP fields in the header indicate when ATM connections are experi encing congestion or potential cell loss 7 If mystery VPI VCI values appear on the traffic scan a misconfigured switch may be sending cells with incorrect VPI VCI Detailed Traffic Analysis This process monitors a specific VCC for bandwidth problems errors and alarms 1 Select a specific VPI VC from the ATM traffic scan to be analyzed Do this by selecting SAVEVCC or SAVE RX while highlighting the desired VPI VCI When an ATM network is up and running use the test set to monitor the ATM cells on the network Review the procedure above for connecting the test set to the circuit The test set can monitor the network continu ously or be programmed to run a test during the peak usage times The latter frees a technician from having to personally monitor the test The test set can monitor for a specific length of time such as 15 minutes or 5 hours to get a snapshot of the network performance ATM Traffic Scan 1 Use the VCC Scan feature to observe all the channels currently used in that section of the network This process helps identify missing VCCs monitors tota
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