Cisco Systems Cisco ONS 15310-MA, ONS 15310-CL manual Ethernet Link Integrity Support, 17-3

Chapter 17 CE-Series Ethernet Cards

CE-100T-8 Ethernet Card

The CE-100T-8 card supports selective auto negotiation on the Ethernet ports. If selective auto negotiation is enabled, the port attempts to auto negotiate only to a specific speed and duplex. The link will come up if both the speed and duplex of the attached auto negotiating device matches that of the port. You cannot enable selective auto negotiation if either the speed or duplex of the port is set to auto.

The CE-100T-8 card supports IEEE 802.3x flow control and frame buffering to reduce data traffic congestion. Flow control is on by default.

To prevent over-subscription, buffer memory is available for each port. When the buffer memory on the Ethernet port nears capacity, the CE-100T-8 card uses IEEE 802.3x flow control to transmit a pause frame to the attached Ethernet device. Flow control and auto negotiation frames are local to the Fast Ethernet interfaces and the attached Ethernet devices. These frames do not continue through the POS ports.

The CE-100T-8 card has symmetric flow control and proposes symmetric flow control when auto negotiating flow control with attached Ethernet devices. Symmetric flow control allows the CE-100T-8 cards to respond to pause frames sent from external devices and to send pause frames to external 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 17-2illustrates pause frames being sent and received by CE-100T-8 cards and attached switches.

Figure 17-2	Flow Control
	ONS 15310-CL		ONS 15310-CL
	Ethernet	STS-N	Ethernet
		SONET
	Pause Frames		Pause Frames

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This flow-control mechanism matches the sending and receiving device throughput to that of the bandwidth of the STS circuit. For example, a router might transmit to the Ethernet port on the CE-100T-8 card. This particular data rate might occasionally exceed 51.84 Mbps, but the SONET circuit assigned to the CE-100T-8 port might be only STS-1 (51.84 Mbps). In this example, the CE-100T-8 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 can be controlled to a large extent.

Ethernet Link Integrity Support

The CE-100T-8 supports end-to-end Ethernet link integrity (Figure 17-3). 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.

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 on the CE-100T-8 card if the remote Ethernet port is unable to transmit over the SONET network or if the remote Ethernet port is disabled.

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.

Cisco ONS 15310-CL, ONS 15310-MA, and ONS 15310-MA SDH Ethernet Card Software Feature and Configuration Guide, R9.1 and R9.2

78-19415-01 17-3