Nortel Networks 3500, NTRN10AN manual GFP and Flow Control Enable Distance Extension

Operation, administration, and maintenance (OAM) features 2-97

To support storage extension over very long distances, the OPTera Metro 3500 platform is equipped with buffering and flow control functionality to ensure high throughput without requiring large buffer credits from the storage devices. The implementation is illustrated in Figure 2-39 on page 2-97. In this solution, BBC Flow control is implemented between a source storage device and the ingress OPTera Metro 3500 as well as between the egress OPTera Metro 3500 and the destination storage device. Flow control signals are used for flow control between the Nortel Networks network elements.

This solution is transparent to the source and destination storage devices. The OPTera Metro 3500 intercepts login and other messages from the source storage device and transmits them to the destination storage device. As far as they are concerned, the storage devices believe they are connected to each other. This is important for service providers to be able to offer a Storage Private Line service with an effective demarcation point.

Figure 2-39

GFP and Flow Control Enable Distance Extension

EX1496p

		Flow control signal
	R_RDY		Egress
			GFP card
	Memory
		SONET/SDH	Memory
Source	Ingress		R_RDY	Destination
				storage
storage	GFP card
				device
device

BBC flow	BBC flow
control domain	control domain

As the source storage device sends a Fibre Channel frame, the ingress OPTera Metro 3500 transmits it over the WAN connection and then returns an R_RDY to the source device. This mechanism ensures the source storage device never reaches its maximum allowed BBC count, and so enables it to maintain full throughput even at very long distances.

On egress, the OPTera Metro 3500 will send frames to the destination storage device only at the rate at which this device sends out R_RDY. This will ensure that the rate at which the data is sent by the egress OPTera Metro 3500 does not exceed that at which it can be received by the destination storage device.

Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004