Flow Control Threshold Provisioning; Ethernet Link Integrity Support; Figure 25-3 End-To-End Ethernet Link Integrity Support - Cisco ONS 15454 SDH Configuration Manual

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 supports 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 user 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 the buffer size of Flow Ctrl Lo and Flow Ctrl Hi thresholds.
The range is 1 to 511 units, where 1 unit is equal to 192 bytes. Make sure that the value of Flow Ctrl Lo
is lesser than Flow Ctrl Hi with a difference of at least 160 units between the two values to ensure
packets are not dropped.

Ethernet Link Integrity Support

The CE-1000-4 card supports end-to-end Ethernet link integrity
to providing an Ethernet private line service and correct operation of Layer 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 remote 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
Ethernet port
Rx
Tx
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 techniques (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.
Cisco ONS 15454 and Cisco ONS 15454 SDH Ethernet Card Software Feature and Configuration Guide, R8.0
25-4
End-to-End Ethernet Link Integrity Support
ONS Node
STS-N
SONET
Chapter 25 CE-1000-4 Ethernet Operation
(Figure 25-3). This capability is integral
Ethernet port
ONS Node
Rx
Tx