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Ethernet Card Software Feature and Configuration Guide, R7.2
January 2009
Chapter 23 E-Series and G-Series Ethernet Operation
Ethernet Link Integrity Support
Although the G-Series cards do not actively run GEC, they support the end-to-end GE C functionality of
attached Ethernet devices. If two Ethernet devices running GEC co nnect through G-Series cards to an
ONS network, the ONS SONET/SDH side network is transparent to the EtherChannel devices. The
EtherChannel devices operate as if they are directly conn ected to each other. Any combination of
G-Series parallel circuit sizes can be used to support GEC th roughput.
GEC provides line-level active redundancy and protection (1:1) for attached Ethernet equipment. It can
also bundle parallel G-Series data links together to provide more aggregated bandwidth. Spanning Tree
Protocol (STP) operates as if the bundled links are one link and permits GEC to utilize these multiple
parallel paths. Without GEC, STP permits only a single nonblocked path. GEC can also provide G-Series
card-level protection or redundancy because it can support a group o f ports on different cards (or
different nodes) so that if one port or card has a failure , traffic is rerouted over the other port or card.
The end-to-end Ethernet link integrity feature can be used in combination with Gigabit EtherChannel
(GEC) capability on attached devices. The combination provides an Ethernet traffic restoration scheme
that has a faster response time than alternate techniques such as spanning tree rerouting, yet is more
bandwidth efficient because spare bandwidth does not need to be reserved.
Ethernet Link Integrity Support
The G-Series supports end-to-end Ethernet link integrity (Figure 23-3). This capability is integral to
providing an Ethernet private line service and correct operation of Layer 2 and L ayer 3 protocols on the
attached Ethernet devices. 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 23-3 End-to-End Ethernet Link Integrity Support
Note Some network devices can be configured to ignore a loss of carrier condition. If a device configure d to
ignore a loss of carrier condition attaches to a G-Series 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. T he response
time of such alternate techniques is typically much l onger than techniques that use link state as
indications of an error condition.
As shown in Figure 23-3, a failure at any point of the path causes the G-Series card at each end to disable
its Tx transmit laser, which causes the devices at both ends to detect a 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 disables both ends of the path.
ONS Node
G-Series port
67952
Tx
Rx
ONS Node
G-Series port
Tx
Rx
STS-N/VC-N
SONET/SDH