Browse Prior Art Database

Architecture and Apparatus for Implementing Flow Control in an Ethernet Adapter

IP.com Disclosure Number: IPCOM000123333D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Allison, SS: AUTHOR [+2]

Abstract

Described is a technique for implementing IEEE 802.3x Flow Control in the Receive direction. Flow Control is accomplished using Media Access Control frames the format of which is defined in the IEEE 802.3x standard. The standard separates the Flow Control process into receive and transmit sub-processes. This disclosure describes a method of implementing the receive sub-process defined in this standard. For end-nodes (for which this disclosure applies) the transmit sub-process is optional.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Architecture and Apparatus for Implementing Flow Control in an Ethernet
Adapter

   Described is a technique for implementing IEEE 802.3x
Flow Control in the Receive direction.  Flow Control is accomplished
using Media Access Control frames the format of which is defined in
the IEEE 802.3x standard.  The standard separates the Flow Control
process into receive and transmit sub-processes.  This disclosure
describes a method of implementing the receive sub-process defined in
this standard.  For end-nodes (for which this disclosure applies) the
transmit sub-process is optional.

   In other words, this disclosure describes a method of
detecting MAC frames, decoding the Flow Control OpCode, locating the
Pause value within the frame, and halting transmission of frames
until the Pause expires.

   If the frame received from the media contains a
Destination Address, Type field, and Opcode that matches those shown
in the Figure 1 the frame is assumed to be a MAC Pause frame.  The
Destination Address can also be the adapter's Individual Address.
Once the frame is determined to be a MAC Pause frame the "Time" value
is used to stop the transmission of frames until the "Time" limit has
expired.  The units of the Time field are Ethernet Slot Times.  One
Slot Time is the amount of time required to transmit 512 bits.  This
disclosure does not generate MAC frames in the transmit direction.
However the device driver or higher level code can generate MAC Pause
Frames and have them transmitted.  These frames are not blocked when
a Pause is in effect.  MAC Pause frames transmitted by the host
software are transmitted via a High Priority Transmit Queue, and all
other frames are directed to a Low Priority Queue by the host
software.  Only transmits via the Low Priority Transmit Queue are
stopped by the MAC Pause frame.

   The unique feature of this design is the fact that the
MAC Pause Frame detection logic uses the same registers and state
ma...