Feature |
Product |
Release introduced |
---|---|---|
IEEE 802.3X Pause frame transmit |
5320 Series |
Fabric Engine 8.6 |
5420 Series |
VOSS 8.4 |
|
5520 Series |
VOSS 8.2.5 |
|
5720 Series |
Fabric Engine 8.7 |
|
7520 Series |
Fabric Engine 8.10 |
|
7720 Series |
Fabric Engine 8.10 |
|
VSP 4900 Series |
VOSS 8.1 |
|
VSP 7400 Series |
VOSS 8.0 |
The switch uses MAC pause frames to provide congestion relief on full-duplex interfaces.
When congestion occurs on a port, the system can send or receive pause frames, also known as flow control, to temporarily pause the packet flow. The system uses flow control if the rate at which one or more ports receives or sends packets is greater than the rate the switch can process or accept the packets.
The switch can generate pause frames to tell the sending device to stop sending additional packets for a specified time period. After the time period expires, the sending device can resume sending packets. During the specified time period, if the switch determines the congestion is reduced, it can send pause frames to the sending device to instruct it to begin sending packets immediately.
If you enable flow control mode, the switch drops packets on ingress when congestion occurs. If the switch is not in flow control mode, it drops packets at egress when congestion occurs.
Configure an interface to send pause frames when congestion occurs to alleviate packet drops due to flow control mode.
Interfaces that support auto-negotiation advertise and exchange their flow control capability to agree on a pause frame configuration. IEEE 802.3 annex 28b defines the auto-negotiation ability fields and the pause resolution. The switch advertises only two capabilities. The following table shows the software bit settings based on the flow control configuration.
Note
Not all interfaces support Auto-Negotiation. For more information, see your hardware documentation.
Interface configuration |
Pause |
ASM |
Capability advertised |
---|---|---|---|
Flow control enabled |
1 |
0 |
Symmetric pause |
Flow control disabled |
1 |
1 |
Both Symmetric pause and asymmetric pause |
The following tables identifies the pause resolution.
Local device pause |
Local device ASM |
Peer device pause |
Peer device ASM |
Local device resolution |
Peer device resolution |
---|---|---|---|---|---|
0 |
0 |
Do not care |
Do not care |
Disable pause transmit and receive. |
Disable pause transmit and receive. |
0 |
1 |
0 |
Do not care |
Disable pause transmit and receive. |
Disable pause transmit and receive. |
0 |
1 |
1 |
0 |
Disable pause transmit and receive. |
Disable pause transmit and receive. |
0 |
1 |
1 |
1 |
Enable pause transmit. Disable pause receive. |
Disable pause transmit. Enable pause receive. |
1 |
0 |
0 |
Do not care |
Disable pause transmit and receive. |
Disable pause transmit and receive. |
1 |
Do not care |
1 |
Do not care |
Enable pause transmit and receive. |
Enable pause transmit and receive. |
1 |
1 |
0 |
0 |
Disable pause transmit and receive. |
Disable pause transmit and receive. |
1 |
1 |
0 |
1 |
Disable pause transmit. Enable pause receive. |
Enable pause transmit. Disable pause receive. |
The following list identifies the type of interfaces that support auto-negotiated flow control:
10 Mbps/100 Mbps/1 Gbps copper
100 Mbps/1 Gbps/10 Gbps copper
1 Gbps fiber (in both SFP and SFP+ ports)