This chapter provides information on looping back Ethernet, IP, TCP/UDP, and multiple streams of traffic.
Topics discussed in this chapter include the following:
– “About Loop back testing” on page 168 – “Specifying a unit identifier” on page 172
– “Using LLB to loop received traffic back to the local unit” on page 172 – “Using Loop Up to initiate a loop back from the local unit” on page 174
Chapter 7 Loop back Testing About Loop back testing
About Loop back testing
If your instruments are configured and optioned to do so, you can use two Transport Modules (or other JDSU compliant Ethernet test instruments) to transmit Ethernet, IP, or TCP/UDP traffic from one instrument, and then loop the traffic through a second instrument back to the sending instrument. By transmitting and then looping traffic back, you are essentially emulating a longer circuit on the network.
Before looping back traffic, it is important to understand the terminology and concepts in the following sections.
Loop back terminology
The following terms are used to explain loop back testing in this chapter.Local unit Used in this chapter to refer to the traffic-originating unit (which is always placed in Terminate mode).
Loop back unit Used in this chapter to refer to the unit that loops received traffic back to the traffic-originating (local) unit. If the loop back unit is capable of generating traffic, place it in terminate mode when you want to loop traffic through to the transmitter. If the loop back unit is not capable of generating traffic (it is a loop back-only unit), place it into loop back mode.
Terminate mode Mode used for loop back applications when both the local unit and the loop back unit are capable of generating traffic. Also used by local unit to generate traffic that will be looped back by a unit that is only capable of looping received traffic back. In this scenario, the loop back unit is placed in loop back mode.
All T-BERD ⁄ MTS 5800s are shipped with the ability to generate and transmit traffic; therefore, when running loop back applications using two
T-BERD ⁄ MTS 5800s, both instruments should be placed in terminate mode.
Loop back mode Previously, loop back tests were always performed with both the local traffic transmitting unit and the loop back unit in Terminate mode. Assuming both units can transmit traffic, this is still the case.
When you purchase an Multiple Services Application Module, you can order a unit that is capable of generating, transmitting, and analyzing Ethernet traffic, or you can order a unit that simply loops back traffic received from another transmitting unit. The loop back unit is not capable of generating its own traffic;
it functions simply as a loop back device.
If you are using a loop back-only unit at the far end, you must place the local unit in Terminate mode; the loop back unit must be placed in Loop back mode.
Configure and transmit traffic from the local unit just as you would for an end-to-end test; and verify that the filter settings on the loop back unit will allow traffic to pass from its receiver through to its transmitter.
You can still initiate the loop back from your local unit using the Loop Up action button, or you can actively loop traffic back from the loop back unit using the LLB action button.
Chapter 7 Loop back Testing About Loop back testing
Key loop back concepts
The following concepts apply when configuring loop back applications.ARP settings If you are looping back layer 3 or layer 4 traffic, and you want to use ARP to obtain the units MAC addresses, be certain to enable ARP on both units.
If ARP is disabled on all units on the circuit, you can issue a broadcast request to loop up the first device that responds (rather than a specific unit).
Address swapping On the loop back unit, received frames and packets are looped through to the transmitter after the destination and source MAC addresses (layer 2, 3, and 4 loop backs), IP addresses (layer 3 and 4 loop backs), and if applicable, port numbers (layer 4 loop backs) are swapped.
Filter criteria on the loop back unit Only Unicast frames that pass the filter criteria specified on the loop back unit are looped back to the local unit.
If the Ethernet filter settings are all Don’t Care, and/or the IP and TCP/UDP filters are both disabled, traffic carrying any payload will pass through the filter for analysis.
Loop types When configuring the local traffic-generating unit, you can specify that you want to issue a Unicast loop-up command, or a Broadcast loop-up command.
If you are running an Ethernet application, Unicast commands are used to loop up a specific test instrument on the far end; Broadcast commands are used to loop up the first instrument on the circuit that responds.
LBM Traffic Used for loop back Message/loop back Reply (LBM/LBR) frame analysis where the far-end unit (any equipment that responds to LBM messages) loops back any packet containing the LBM message.
VLAN and Q-in-Q traffic The loop back unit uses the same IDs and priorities assigned to the received traffic, and loops the traffic back on the same virtual LAN using the same priority.
VPLS labels The labels for traffic received by the loop back unit are replaced with the labels specified for transmitted traffic on the Ethernet tab before the traffic is passed through to the loop back unit’s transmitter.
If you are looping back multiple streams of VPLS traffic, you can specify a unique tunnel label and VC label for each individual stream, or you can specify the labels for one stream, and then copy them to the other streams.
VPLS service provider and customer destination addresses
When looping back VPLS traffic, the loop back unit swaps the service provider destination address (SP DA) and service provider source address (SP SA) carried in received traffic before looping the traffic through to the transmitter.
When configuring traffic on the local unit, you must specify the service provider source address of the loop back unit as the service provider destination address for all traffic transmitted from the local unit. This is because when looping back VPLS traffic, the local unit will not issue a broadcast request to loopup the next JDSU Ethernet test instrument on the circuit. Essentially, you must tell it to loop up a specific test instrument by specifying the correct service provider DA.
Chapter 7 Loop back Testing About Loop back testing
Where are the VPLS addresses specified?
The SP destination address is specified on the Ethernet tab by selecting the DA field for the service provider frame; the customer destination address is specified by selecting the Data field for the SP frame, and then selecting the DA field for the customer frame (displayed graphically underneath the SP frame).
Looping back multiple streams of VPLS traffic.
If you are looping back multiple streams of VPLS traffic, you must specify a destination SP address for all enabled streams (on the All Streams tab), but you can specify a unique customer destination address for each individual stream on it’s corresponding setup tab. You can also copy the customer desti-nation address for one stream to all enabled streams.
MPLS labels Before received traffic is passed through to the loop back unit’s transmitter, the labels for the traffic are automatically replaced with the labels specified for traffic transmitted from the loop back unit; therefore:
– If your local unit is configured to transmit traffic with a second MPLS label, but the loop back unit is configured to transmit traffic with a single label, the out of sequence and lost frames counts reported by the local unit may increment if the incoming frame rate is too high.
– If your local unit is configured to transmit traffic with a single MPLS label, but the loop back unit is configured to transmit traffic with a second label, the local unit’s receive bandwidth utilization will exceed its transmitted bandwidth utilization.
If you are looping back multiple streams of MPLS traffic, you can specify unique labels for each individual stream, or you can specify the labels for one stream, and then copy them to the other streams.
MPLS destination addresses If you initiate a loop back from a local unit using the Loop Up button, and ARP is enabled on both units, you must specify the destination IP address and subnet mask for the next hop on the circuit.
If you use the LLB button on the loop back unit to loop traffic back to the local unit, and ARP is enabled on both units, you must manually specify the desti-nation IP addresses for the traffic transmitted from the local unit and for the traffic looped back by the loop back unit.
If ARP is disabled, you must also specify the destination MAC address for traffic transmitted by the local unit.
If you are looping back multiple streams of MPLS traffic, and ARP is disabled, you can specify a unique destination MAC address (on the Ethernet tab), and a unique destination IP address (on the IP tab) for each individual stream, or you can specify the addresses for one stream, and then copy them to the other streams.
TCP/UDP ATP Listen IP Address and Listen Port
The Transport Module and Multiple Services Application Module use an ATP Listen IP Address and ATP Listen Port to determine whether received layer 4 traffic carries an ATP payload.
If you issue a Loop Up command from a local unit, after the local unit receives a response from the loop back unit indicating that the loopup was successful, the local unit’s ATP Listen IP Address and ATP Listen Port are automatically set to the destination IP address and destination port number carried in the
Chapter 7 Loop back Testing About Loop back testing
looped back traffic. The loop back unit’s ATP Listen IP Address and
ATP Listen Port will also automatically be set to the destination IP address and destination port carried in the traffic it receives from the local unit.
If you use the LLB action button on the loop back unit, it is essential that you specify the destination IP address and port carried in received traffic as the ATP Listen IP Address and ATP Listen Port when you configure tests that require an ATP payload (such as delay measurements, out of sequence counts, lost frames counts, and packet jitter measurements).
Understanding the graphical user interface
When running loop back tests, the user interface looks much like it does for standard end-to-end or multiple streams tests.
Loop back action buttons Three action buttons are used for the purpose of initiating or ending loop back tests, and placing a unit into loop back mode.
Loop Up
Press Loop Up when you want to initiate the loopup of another unit on the circuit from your unit. In this scenario, you are initiating the loopup from the local unit.
Loop Down
Press Loop Down when you want to end the loopup of another unit on the circuit. In this scenario, you are ending the loopup from the local unit.
LLB
Press LLB to loop received traffic back through to a units transmitter, or to stop looping traffic back through to the transmitter. In this scenario, you are initiating or ending the loopup from the loop back unit itself.
Loop back messages During loop back testing, if you initiate or end the loop back from the local unit using the Loop Up and Loop Down actions, messages are sent to each loop back partner indicating the status of the loop back. These messages appear in the Message Bar provided on the Main screen of the user interface.
When you configure your unit for a loop back test, you can specify a “Unit Iden-tifier” which will be provided in each loop up or loop down frame sent from the unit.
Loop back tests
If your instrument is configured and optioned to do so, you can run a loop back test using each of the applications listed in Table 19.Table 19 Applications used for loop back testing
Application1 10/100/
Chapter 7 Loop back Testing Specifying a unit identifier
Specifying a unit identifier
You can specify an identifier to be carried in all loop up and loop down frames originating from your unit. This allows a technician on the far end to determine where the loop commands came from.
The default identifier for the T-BERD ⁄ MTS 5800 is “JDSU 5800”.
To specify a unit identifier
1 If you haven’t already done so, use the Test Menu to select the application for the interface you are testing.
2 Select the Setup soft key, and then select the Interface tab.
3 Select the Unit Identifier setting, and then type the identifier using up to 25 characters.
The identifier is specified.
Using LLB to loop received traffic back to the local unit
You can loop received traffic through to a unit’s transmitter and back to the local (traffic-originating) unit by selecting the LLB action button provided on the loop back unit.
To loop received traffic back using LLB
1 If you haven’t already done so, on both units, launch the layer 2, layer 3, layer 4, triple play, or multiple streams application for the circuit you are testing (see “Step 1: Selecting a test application” on page 2).
If you are looping back traffic on an Ethernet circuit, and both units are capable of transmitting traffic, place each in Terminate mode; otherwise, if the loop back unit is not capable of generating traffic, place it in Loop back mode.
Layer 4 Traffic N/A
Layer 4
Multi-ple Streams N/A
1. If both units are capable of generating traffic, select a Terminate mode application for each unit. If the loop back unit cannot generate traffic, place it in Loop back mode.
Table 19 Applications used for loop back testing (Continued)
Application1 10/100/
If you are observing loop up or loop down messages on another
T-BERD ⁄ MTS 5800, the full unit identifier appears in the messages. If you are observing the messages on other JDSU Ethernet testers, such as the FST-2802 or the HST (with an Ethernet SIM), the identifier will be truncated, and will display only the first ten characters.
Chapter 7 Loop back Testing Using LLB to loop received traffic back to the local unit
Refer to the sections below for a list of available applications:
– “Ethernet and IP applications” on page 25 – “MiM applications” on page 25
– “TCP and UDP applications” on page 129 – “Multiple Streams testing” on page 147
2 On the local unit, specify the link initialization settings.
– If you are looping back traffic on an Ethernet circuit, see “Specifying interface settings” on page 41.
3 On the local unit, specify the settings for transmitted traffic.
If you are looping back a single stream of layer 2 traffic, refer to one of the following:
– “Layer 2 testing” on page 40
– “Configuring layer 2 MAC-in-MAC tests” on page 115
If you are looping back a single stream of layer 3 traffic, refer to the following:
– “Layer 2 testing” on page 40 – “Layer 3 testing” on page 73
If you are looping back a single stream of layer 4 traffic, refer to the following:
– “Layer 2 testing” on page 40 – “Layer 3 testing” on page 73
– “Specifying layer 4 settings” on page 131
If you are looping back multiple streams of traffic, refer to the following as appropriate for your application:
– “Enabling multiple streams” on page 152
– “Specifying layer 2 stream settings” on page 156 – “Specifying layer 3 stream settings” on page 157 – “Specifying layer 4 stream settings” on page 158
– “Specifying layer 2 and layer 3 settings for Triple Play services” on page 164
4 On the loop back unit, do the following:
a If you are running a single-stream application, verify that the applicable filter settings are either disabled, set to Don’t Care, or that they match the settings for the traffic transmitted from the local unit.
b On the Main screen, select the Actions tab, and then select LLB.
5 On the local unit, select the Actions tab, and then select one of the following:
– Start Traffic (if you configured a constant or bursty load).
– Start Ramp (if you configured a ramped traffic load).
Chapter 7 Loop back Testing
Using Loop Up to initiate a loop back from the local unit
When the loop back unit receives the traffic, it does the following:
– Determines which frames or packets satisfy its filter criteria. Only traffic that satisfies the criteria will be looped back to the near end unit.
– Swaps the destination and source addresses or port IDs, and if appli-cable, port number for every frame or packet it receives.
– Transmits the traffic back to the local unit.
Traffic is looped back to the local unit.
Using Loop Up to initiate a loop back from the local unit
You can select the Loop Up button on the local (traffic generating) unit to loop up another unit on the circuit. After sending the Loop Up frame, a confirmation message from the loop back unit appears in the message bar of the Main screen of your local unit informing you that the loop back is successful.
Before sending the Loop Up frame, your unit must be configured as follows:
– If you are looping back layer 2 non-VPLS Ethernet traffic, the near end unit automatically detects the MAC address for the next unit on the circuit;
therefore, you do not need to configure the destination MAC address. It will be populated automatically for you.
If you want to loop up a specific device, you can specify that you are using a Unicast loop type, and then specify the destination MAC address for the device you are looping up.
– If you are looping back layer 3 traffic, you must specify the source IP address for the unit on the far end of the circuit as the destination IP address for traffic transmitted by the local unit.
Be certain to specify the same destination address for the filter on the receiving loop back unit.
– If you are looping back layer 3 or layer 4 traffic, and you want to use ARP to populate the units MAC addresses; be certain to enable ARP on both units.
– If you are looping back layer 4 traffic, after you issue the Loop Up
command (from the local unit), and the unit receives a response from the far end unit indicating that the loopup was successful, the local unit’s ATP Listen IP Address and ATP Listen Port are automatically set to the destina-tion IP address and destinadestina-tion port number carried in the looped back traffic. The far end unit’s ATP Listen IP Address and ATP Listen Port will also automatically be set to the destination IP address and destination port carried in the traffic it receives from the local unit.
– You can optionally specify unit identifiers for each unit (for example,
“SamsUnit” and “JoesUnit”). When the units send confirmation messages to each other indicating the status of the loop back, the messages will identify each unit using the identifier. For details, see “Specifying a unit
“SamsUnit” and “JoesUnit”). When the units send confirmation messages to each other indicating the status of the loop back, the messages will identify each unit using the identifier. For details, see “Specifying a unit