Chassis
Each Ixia chassis can operate as a complete standalone system when connected to a local monitor, keyboard, and mouse. The interior of an Ixia XGS12-SD chassis is shown in the following figure.
Figure: Ixia XGS12-SD Interior View (Top View)
The PC embedded in the chassis system is an Intel-compatible computer system which includes the following components:
- A Pentium processor
- Main memory
- Keyboard interface
- Mouse interface
- Internal connection to the Ixia Backplane
- Video interface capable of 1024 x 768 or greater resolution
- Management Port
The Ixia Backplane is connected to the PC Motherboard, through an Ixia custom PCI interface card, and to the card slots where the Ixia load modules are installed.
Chassis Synchronization
Measurement of unidirectional latency and jitter in the transmission of data from a transmit port to a receive port requires that the relationship between time signatures at each of the ports is known. This can be accomplished by providing the following signals between chassis:
- Clock (frequency standard): This allows chassis to phase-lock their frequency standards so that a cycle counter on any chassis counts the same number of cycles during the same time interval. Each Ixia port maintains such a counter from a common chassis-wide frequency standard.
- Reset: A means must exist to either discover the fixed offset between their counters, or to simultaneously set the counters to a known value. You may think of this as the zero reset.
The use of both Reset and Phase Lock allow the establishment and maintenance of a fixed time reference between two or more chassis and the ports supported by the chassis.
In test setups where chassis and ports are physically close together, a sync cable is used to connect chassis in a `chassis chain' for synchronization operation.
In widely distributed applications, such as monitoring traffic characteristics over a WAN, clock reference and/or reset signals cannot be transmitted between chassis over a physical connection because of unknown delay characteristics. An alternative means is required to satisfy these requirements.
Ixia has facilities that allow for the synchronization of independent Ixia chassis located anywhere in the world by replacing the existing inter-chassis sync cables with a widely available frequency and time standard supplied from an external source. This source provides a reference time used to obtain accurate latency and other measurements in a live global network. When geographically dispersed chassis are connected in this way, the combination is called a virtual chassis chain.
Physical Chaining
Independent Ixia 400T, Optixia XM12, or Optixia XM2, chassis may synchronize themselves with other chassis as shown in the following figure. The timing choices are explained in the following table.
Figure: Physical Chaining
Choice | Usage |
---|---|
Internal Sync (Synchronous) |
If a chassis is used in a standalone manner or the primary of a chassis chain, it may generate its own start signal. In general, there is insufficient timing accuracy between timing of primary chassis for measurements over any distance. This is also known as the Synchronous Timing mode. |
Sync-In (SI) |
If a chassis is a secondary one, either directly connected to the primary chassis or further down the chain, it derives its timing from the previous chassis' Sync-Out (SO) signal. |
Virtual Chaining
If two chassis are separated by any significant distance, a sync-out/sync-in cable cannot be used to connect them. In this case, an Ixia Auxiliary Function Device (AFD1) is used, one attached to each chassis through sync-out/sync-in cables, as shown in the following figure. The Ixia 100 maintains an accuracy of less than 150 nanoseconds when attached to a GPS antenna, or 100 microseconds when attached to a CDMA receiver, and provides chassis to chassis synchronization.
Figure: Virtual Chaining
To generate traffic for system latency testing, the Ixia 100 can be used alone or in conjunction with another Ixia chassis, or the Ixia AFD1 (GPS receiver) can be used with any other Ixia chassis. The timing features available with these chassis are shown in the following table. A GPS antenna requires external mounting. Refer to Appendix C, GPS Antenna Installation Requirements for more information.
Choice | Usage |
---|---|
GPS |
The Ixia 100 or ixia AFD1 requires connection to an external antenna to `capture' multiple GPS satellites. It maintains an accuracy of less than 150 nano-seconds. |
CDMA |
The CDMA cellular network transmits an accurate time signal. CDMA (Code Division Multiple Access) cellular base-stations effectively act as GPS repeaters. The Ixia 100-CDMA receives the CDMA signals passively from an external antenna (you do not need to subscribe to any service) and decodes the embedded GMT time signal. Using this approach, the CDMA chassis can be time-synched to GMT. A CDMA antenna does not require external mounting. |
The Sync-Out from a GPS or CDMA chassis is used as primary timing source for a chassis chain at a specific geographic location. Since the Ixia 100 chassis has all other functions provided by the other Ixia chassis, it may also use independent timing when not used to synchronize with other chassis at other locations.
Note: CDMA reception depends on signal availability and may be impacted by cell location and chassis installation within the selected site. Consult your Ixia representative to determine the best solution for your installation.
For more information, including a formula for Calculating Latency Accuracy for AFD1 (GPS), see Ixia GPS Auxiliary Function Device (AFD1).
Ixia Chassis Connections
A number of LEDs are available on the front panel of the Ixia 100, as described in the following table.
LED | Usage |
---|---|
Set Lock |
Three LEDs indicate three separate status events:
|
Time Stamp |
Three LEDs indicate the Stratum connection level. The Stratum indicates the accuracy the time stamp. The following list explains the significance of the number of LEDs lit:
|
Shutdown |
The chassis is in the process of being shut down. |
Power |
Power is applied to the chassis. |
Similar information is available for the AFD1 GPS receiver in the Time Source tab of the Chassis Properties form (viewable through IxExplorer user interface).