IEEE 802.3ae Standard - Physical Layer Requirements Define Stressed Receiver Sensitivity

Ethernet has a history of being a very robust plug and play architecture due the creation and adoption of the Ethernet standards. In similar fashion the 1 and 10GE standards have incorporated strict physical layer requirements to ensure an optical plug and play network. The standard defines the physical layer parameters of both the transmitter and receiver. The transmitter section of the standard allows for a fairly degraded transmitter plus when accounting for further degradations caused by the system, fiber, or other impairments. These degraded signals can dramatically decrease the receiver’s ability to correctly differentiate 1’s and 0’s. The result would be a degraded bit error rate in the system.

To avoid this the standard has included a physical layer stressed receiver sensitivity specification which is the measure of the receiver’s sensitivity when subjected to an impaired signal. The standard requires that the stressed eye is tuned, calibrated then applied to a receiver under test. The stressed eye is applied to the receiver while sweeping the power and measuring the bit error rate.

The standard specifies a particular impaired eye formation called the “stressed eye”. It is this “stressed eye” that needs to be tuned, calibrated and then applied to the receiver under test. The standard compliant stressed eye impairments are measured as VECP (Vertical Eye Closure Penalty) and must be created by adding four impairments to the optical signal as described in the section below.

Stressed Eye Configuration

The stressed eye impairments consist of the following 4 degradations that need to be configured and tuned.

1. Electrical Filtering to replicate ISI effects
   
2. Vertical Interference to replicate ISI effects
   
3. Swept Jitter per the standard Template to replicate system jitter
4. Lowered Extinction Ratio to 3-3.5dB to replicate a lower quality laser source such as a VCSEL and aging of the laser.

The stressed eye was designed to replicate the worst case conditions in the real world based on varying lengths of transmission. The standard defines the receiver sensitivities at a 1E-12 BER for three different impairments –S, -L, and –E.

10GEbase10-S
10GEbase10-L
10GEbase10-E

Stressed Eye Tuning

The standard recommends a test set up of nine instruments needed to generate a stressed eye. These nine instruments are calibrated then the eye is tuned using a scope as seen in the figure below.

Unfortunately a scope can only tune the eye to the 1E-4 or 1E-6 level but the receiver sees the eye quality down to the 1E-12 level or better. This is one of the major issues when tuning the stressed eye. Because of this ambiguity in the standard building more than one stressed eye generation system that will correlate with any other stressed eye generation system is near impossible. Circadiant has taken extreme measures to tune our stressed eye down to a 1E-12 level so that every system we ship will correlate to within 0.5 dB.

Circadiant Single System Solution

Circadiant has taken the guess work out of measuring Ethernet compliance at 1GE and 10GE. Circadiant’s OST is the only single complete system for testing 10GE physical layer compliance that will guarantee system to system correlation. The root of the system is a BERT with the added functionality to enable full control of the optical signal as well as the analyzing capability to produce BER vs Power curves automatically.

The Circadiant OST brings a new level of integration to the test industry. The OST integration is the key for system to system correlation which in the end enables the testing and definition of plug and play Ethernet networks.