Understanding the Gigabit Ethernet Parameters

Ethernet Station Address

The Gigabit Ethernet cards come preprogrammed with an Ethernet Station Address in the read-only memory. This cannot be modified. However, the station address actually used by the card for sending and receiving network packets, also known as the MAC Address, can be set via lanadmin or SAM.

Maximum Transmission Unit (MTU)

The MTU can be either the regular Ethernet MTU (1500 bytes) or the Jumbo Frame MTU (9000 bytes). Both 1000Base-SX/T support use of Jumbo Frames; however, 1000Base-T supports Jumbo Frames only at 1000 Mbps.

Speed, Duplexity, and Autonegotiation

While 1000Base-SX operates only at 1000 Mbps in full-duplex mode, 1000Base-T operates at 10 or 100 Mbps in either half-duplex or full-duplex mode and also at 1000 Mbps in full-duplex mode.

The speed and duplexity of 1000Base-SX cannot be modified, but its ability to autonegotiate can be turned on and off for other link parameters. Thus, autonegotiation has no effect on the speed or duplexity of 1000Base-SX.

1000Base-T can be manually set to 10 or 100 Mbps but not 1000 Mbps. To achieve gigabit speed, it must be allowed to autonegotiate with its link partner, and provided the partner can autonegotiate, 1000Base-T will operate at the highest common speed and duplexity. The following table summarizes the valid settings for 1000Base-T:

*When autonegotiation is on, 1000Base-T will autonegotiate with its link partner; then, if its partner also autonegotiates and can attain a speed of 1000 Mbps, 1000Base-T will operate at 1000 Mpbs full-duplex (it is not designed to operate at 1000 Mbps half-duplex).

	NOTE: Partners on a link must be configured to have the same setting, that is, either both must autonegotiate or both must be set to the same manual setting. For example, if the card is set to 100 Mbps full-duplex, the link partner must also be set to 100 Mbps full-duplex. This will help ensure operation without degraded performance.

Receive flow control

Flow control allows use of flow control negotiation and sending and receiving of pause frames. When the flow control parameter is on, the card receives and manages pause frames sent by the link partner. When the flow control parameter is off, the card will silently discard these pause frames. The card cannot be configured to send pause frames.

Send Buffer Coalescing Threshold

Receive Buffer Coalescing Threshold

Send Interrupt Coalescing Ticks

Receive Interrupt Coalescing Ticks

the number of buffers sent by the card since the previous send interrupt equals send_max_bufs

or

the time that has elapsed since the previous send interrupt equals send_coal_ticks (a value of zero disables timer-based interrupt coalescing),

the number of frames received by the card since the previous receive interrupt equals recv_max_bufs

or

the time that has elapsed since the previous receive interrupt equals recv_coal_ticks (a value of zero disables timer-based interrupt coalescing),