Spirent SmartBits System, Reference Manual

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Appendix B: Auto Negotiation
Gigabit Fiber Auto Negotiation
198 SmartBits System Reference
The default in all SmartBits applications is AutoNegotiation Disabled
Auto negotiation (AN) is an optional standard function defined in the 1998 IEEE 802.3
specification. AN is a process that takes control of the interface media when a connection
to another network interface is established. AN detects the operating capabilities of the
other interface (known as the Link Partner) and also advertises the capabilities of the local
interface. The highest common performance mode is then selected and configured.
There are two auto negotiation methods used with SmartBits Ethernet cards:
•
For gigabit fiber media, the PCS sub-layer state machine as defined in the IEEE
standard document 802.3z.
•
For copper media, the PHY transceivers and MII Registers.
Gigabit Fiber Auto Negotiation
The Gigabit Ethernet auto negotiation process is defined in the PCS sub-layer state
machine of the IEEE standard document 802.3z. The
PCS ( Physical Coding Sublayer )
contains the 8b/10b encoder/decoder, device synchronization process and the auto
negotiation process. Spirent Communications has implemented the PCS sub-layer in its
FPGA logic, as well as through the on-board microprocessor.
Fiber Gigabit Ethernet, in SmartBits systems, does not use MII registers. Instead, the port
sends a configuration register word to the connected interface. The configuration word is
composed of information similar to that contained in the MIIs and performs an equivalent
function. In addition, for fiber Gigabit Ethernet, the auto negotiation protocol sets other
parameters that are unique to fiber Gigabit operation.
The SmartBits port sends a configuration register word to the connected interface. The
configuration word is composed of information similar to that contained in the MIIs and
performs an equivalent function. In addition, for fiber Gigabit Ethernet, the auto
negotiation protocol sets other parameters that are unique to fiber Gigabit operation.
Smartbits detects the following conditions through its firmware/hardware to verify that the
auto negotiation process has completed successfully:
•
Device synchronization must be achieved.
— and—
•
The DUT completes the auto negotiation process per the PCS state machine.
Device synchronization is achieved by controlled emission of a “comma” pattern. The
comma pattern, as defined in the standard document, is
0011111XXXX , where the leading
zero corresponds to the first bit received. The comma pattern is not contained in any
normal 8b/10b encoded data or pair of adjacent characters. It occurs only within special
characters known as K28.1, K28.5 and K28.7. These characters have been defined
specifically for synchronization.