RS8234 Mindspeed Technologies, RS8234 Datasheet - Page 196

• Manufacturer Part Number: RS8234
• Description: Atm Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

6.0 Traffic Management
6.4 GFC Flow Control Manager
6.4.1 A Brief Overview of GFC
6.4.2 The RS8234’s Implementation of GFC
6-36
6.4 GFC Flow Control Manager
Generic Flow Control (GFC) is a one-way control mechanism which allows the
network equipment to control the input from an end station, for the class(es) of
traffic defined as controlled. This mechanism does not allow the end station to
exert any control on traffic from the network.
input side of the network switch buffers. This allows a much higher degree of
multiplexing than is otherwise possible, and allows the network-side costs of
connections to be significantly reduced. By overbooking the input bandwidth, a
high degree of sharing is possible and the buffer system can be used by more end
nodes than full bandwidth input would allow. GFC is used to coordinate access to
that bandwidth when temporary conflicts occur.
mechanism that only works on the link from the end station to the first piece of
network equipment. The GFC protocols are defined and described in ITU
Recommendation I.361.
The RS8234 implements the GFC one-queue mode. The reassembly coprocessor
provides Auto Configure and Command Detection. The segmentation
coprocessor provides Halt Processing and Per-transmit Queue SET_A control. It
does not implement the optional Queue B.
sub-section below), a received HALT indication will cause the segmentation
coprocessor to halt processing of all channels, both controlled and uncontrolled.
This halt condition will continue until a cell is received without the HALT
indication.
GFC controlled cell can be sent only when the GFC credit counter is equal to one.
Transmission of a GFC controlled cell decrements the credit counter by one. Each
of the eight transmit priority queues can be configured for GFC control by setting
the appropriate GFCn bit(s) in the Scheduling Priority (SCH_PRI) register. In this
way the SAR can segment both GFC controlled and GFC uncontrolled traffic
simultaneously. GFC controlled queues will be active only when the GFC credit
counter is equal to one.
a transmit priority queue. In addition, the segmentation coprocessor implements a
credit borrow algorithm that provides better utilization of the line when receive
and transmit cell streams are not synchronized. Up to one credit can be borrowed.
GFC_DATA fields in the buffer descriptor entries. For GFC controlled channels,
GFC_DATA = 0101; and for non-GFC controlled channels, GFC_DATA = 0001.
The usefulness of GFC is that it allows overbooking of the bandwidth on the
GFC provides a link-level, short-term, XON/XOFF-type flow control
Once the link has been configured for GFC operation (as described in the
A received SET_A indication will increment the GFC credit counter by one. A
CBR traffic is not affected by the SET_A command since it is not mapped into
The user must control the transmitted GFC field via the HEADER_MOD and
Mindspeed Technologies
ATM ServiceSAR Plus with xBR Traffic Management
™
28234-DSH-001-B
RS8234