Specifications

9-4
Cisco ONS 15454 Installation and Operations Guide, R3.2
March 2002
Chapter 9 Ethernet Operation
G1000-4 Card
9.1.3 Ethernet Link Integrity Support
The G1000-4 supports end-to-end Ethernet link integrity. This capability is integral to providing an
Ethernet private line service and correct operation of layer 2 and layer 3 protocols on the attached
Ethernet devices at each end. End-to-end Ethernet link integrity essentially means that if any part of the
end-to-end path fails the entire path fails. Failure of the entire path is ensured by turning off the transmit
lasers at each end of the path. The attached Ethernet devices recognize the disabled transmit laser as a
loss of carrier and consequently an inactive link.
Figure 9-2 End-to-end Ethernet link integrity support
Note Some network devices can be configured to ignore a loss of carrier condition. If such a device attaches
to a G1000-4 card at one end then alternative techniques (such as use of layer 2 or layer 3 protocol 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.
Note Enabling or disabling port level flow control on the test set or other Ethernet device attached to the
G1000-4 port can affect the transmit (TX) laser. This can result in uni-directional traffic flow, if flow
control is not enabled on the attached test set or other Ethernet device.
As shown in Figure 9-2, a failure at any point of the path (A, B, C, D or E) causes the G1000-4 card at
each end to disable its TX transmit laser at their ends, which causes the devices at both ends to detect
link down. If one of the Ethernet ports is administratively disabled or set in loopback mode, the port is
considered a “failure” for the purposes of end-to-end link integrity because the end-to-end Ethernet path
is unavailable. The port “failure” also cause both ends of the path to be disabled.
9.1.4 Gigabit EtherChannel/802.3ad Link Aggregation
The end-to-end Ethernet link integrity feature of the G1000-4 can be used in combination with Gigabit
Ether Channel capability on attached devices. The combination provide an Ethernet traffic restoration
scheme that has a faster response time than alternate techniques such as spanning tree re-routing, yet is
more bandwidth efficient because spare bandwidth does not need to be reserved.
The G1000-4 supports all forms of Link Aggregation technologies including Gigabit EtherChannel
(GEC) which is a Cisco proprietary standard as well as the IEEE 802.3ad standard. The end-to- end link
integrity feature of the G1000-4 allows a circuit to emulate an Ethernet link. This allows all flavors of
layer 2 and layer 3 re-routing, as well as technologies such as link aggregation, to work correctly with
ONS Node
G-Series port
67952
Tx
Rx
ONS Node
G-Series port
Tx
Rx
STS-N/VC-N
SONET/SDH