25-4
Ethernet Card Software Feature and Configuration Guide, R7.2
January 2009
Chapter 25 CE-1000-4 Ethernet Operation
Flow Control Threshold Provisioning
In pass-through mode, transmit flow control frames are not generated by the Ethernet port interfaces,
and received flow control frames pass through transparently. Pass-through mode support s end-to-end
flow control between clients using Ethernet over SONET/SDH transport.
Flow Control Threshold Provisioning
The CE-1000-4 card has flow control threshold provisioning, which allows a use r to select one of three
watermark (buffer size) settings: default, low latency, or custom. Default is the best setting for general
use. Low latency is good for sub-rate applications, such as voice-over-IP (VoIP) over an STS-1. For
attached devices with insufficient buffering, best effort traffic, or long access line lengths, set a higher
latency.
The flow control high setting is the watermark for sending the Pause On frame to the attached Ethernet
device; this frame signals the device to temporarily stop transmitting. The flow control low setting is the
watermark for sending the Pause Off frame, which signals the device to resume transmitting. The default
watermark setting values are 485 for the high threshold and 25 for the low threshold. Low latency
watermark setting values are10 for the high threshold and 5 for the low threshold.
The custom setting allows you to specify an exact buffer size threshold for Flow Ctrl Lo and Flow Ctrl Hi
with a range of 1 to 511 for both thresholds, although the low threshold must be set to a smaller value
than the high threshold.
Ethernet Link Integrity Support
The CE-1000-4 card supports end-to-end Ethernet link integrity (Figure 25-3). This capability is integral
to providing an Ethernet private line service and correct operation of La yer 2 and Layer 3 protocols on
the attached Ethernet devices. Link Integrity is implemented so that the Ethernet over SONET/SDH
connection behaves more like an Ethernet cable from the viewpoint of the attached Ethernet devices.
End-to-end Ethernet link integrity means that if any part of the end-to-end path fails, the entire path fails.
It disables the Ethernet port transmitter on the CE-1000-4 card when the remo te Ethernet port does not
have a receive signal or when the SONET/SDH near end of a far-end failure is detected. The failure of
the entire path is ensured by turning off the transmit pair at each end of the path. The attached Ethernet
devices recognize the disabled transmit pair as a loss of carrier and consequently an inactive link or link
fail. The transport fail alarm is also raised when the port transmitter is disabled. Link integrity will
support a double fault, which is when both Ethernet ports do not receive a signal.
Figure 25-3 End-to-End Ethernet Link Integrity Support
Some network devices can be configured to ignore a loss of carrier condition. If a device configured to
ignore a loss of carrier condition attaches to a CE-1000-4 card at one end, alternative technique s (such
as use of Layer 2 or Layer 3 keep-alive messages) are required to route traffic around failures. The
response time of such alternate techniques is typically much longer than techniques that use link state as
indications of an error condition.
ONS Node
Ethernet port
115780
Tx
Rx
ONS Node
Ethernet port
Tx
Rx
STS-N
SONET