Nortel Networks OPTera Metro 3500 - Manual (Page 135)

Operation, administration, and maintenance (OAM) features 2-97
Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
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
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.
Flow control signal
R_RDY
Source
storage
device
BBC flow
control domain
Ingress
GFP card
Egress
GFP card
Destination
storage
device
R_RDY
Memor
y
Memor
y
SONET/SDH
BBC flow
control domain