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Cisco ONS 15310-CL, ONS 15310-MA, and ONS 15310-MA SDH Ethernet Card Software Feature and Configuration Guide, R9.1 and R9.2
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Chapter 17 CE-Series Ethernet Cards
CE-MR-6 Ethernet Card
To prevent over-subscription, buffer memory is available for each port. When the buffer memory on the
Ethernet port nears capacity, the CE-MR-6 card uses IEEE 802.3x flow control to transmit a pause frame
to the attached Ethernet device. Flow control and a uto negotiation frames are local to the Ethernet (10
Mbps), Fast Ethernet (100 Mbps), Gigabit Ethernet (1000 Mbps) interfaces and attached Ether net
devices. These frames do not continue through the POS ports.
The CE-MR-6 card has asymmetric flow control and proposes asymmetric flow control when auto
negotiating flow control with attached Ethernet devices.
The pause frame instructs the source to stop sending packets for a specific period of time. The sending
station waits the requested amount of time before sending more data. Figure 17- 7 illustrates pause
frames being sent and received by CE-MR-6 cards and attached switches.
Figure 17-7 Flow Control
This flow-control mechanism matches the sending and receiving device throughput the bandwidth of the
STS circuit. For example, a router might transmit to the Ethernet port on the CE-MR-6 card. This
particular data rate might occasionally exceed 51.84 Mbps, but the SONET circuit assigned to the
CE-MR-6 port might be only STS-1 (51.84 Mbps). Under this condition, the CE-MR-6 sends out a pause
frame and requests that the router delay its transmission for a certain period of time. With flow control
and a substantial per-port buffering capability, a private line service provisioned at less than full line rate
capacity (STS-1) is efficient because frame loss is controlled to a large extent.
Ethernet Link Integrity Support
The CE-MR-6 supports end-to-end Ethernet link integrity (Figure 17-8). 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. Link integrity is implemented so that the Ethernet over SONET 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-MR-6 card when the remote Ethernet port does not
have a receive signal or when the SONET near end or 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. If any part of the end-to-end path
fails, the CE-MR-6 card soaks the defect for a fixed duration of 200 ms. The attached Ethernet devices
recognize the disabled transmit pair as a loss of carrier and consequently an inactive link or link failure.
The transport fail alarm is raised when the port transmitter is disabled. Link integrity supports a double
fault, that is, when both the Ethernet ports do not receive a signal.
Note
Only bidirectional link integrity is supported on the CE-MR-6 card.
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STS-N
SONET
Pause Frames
Ethernet ONS Node ONS Node
Pause Frames
Ethernet