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Browse Prior Art Database

ATM Switch with Cut-Through Shared Buffers

IP.com Disclosure Number: IPCOM000112423D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 153K

Publishing Venue

IBM

Related People

Sheu, TL: AUTHOR

Abstract

Described is an ATM switch with cut-through shared buffers. An ATM cell is waiting in the input port. It will be passed through the switch using a cut-through link, if the destination output port is available. On the other hand, it will be stored into the switch's shared buffers, if the destination output port is busy and the buffers are not full.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 35% of the total text.

ATM Switch with Cut-Through Shared Buffers

      Described is an ATM switch with cut-through shared buffers.  An
ATM cell is waiting in the input port.  It will be passed through the
switch using a cut-through link, if the destination output port is
available.  On the other hand, it will be stored into the switch's
shared buffers, if the destination output port is busy and the
buffers are not full.

      This disclosure presents an ATM switch with point-to-point link
connections for multiple simultaneous data transfers.  The ATM switch
receives and stores fixed-size cells into its shared buffers only
when the destination output ports are not available.  Existing
switches for ATM can be divided into two categories: i) No buffering
within the switch; and ii) Buffering within the switch.  An ATM
switch with internal buffers will consume significant
store-and-forward delay, since every incoming cell has to be buffered
in switch's memory regardless of the availability of destination
output ports.  Two major drawbacks of using a buffered switch.
First, it requires more memory on switch for buffering every incoming
cell.  Second, the cell delay is proportional to the number of stages
in a large-scale, multi-staged switch configuration.

      Also introduced is an ATM switch with cut-through shared
buffers.  The incoming cells are not stored into shared buffers as
long as the destination output ports are available.  To determine
whether an output port is available, the switch needs to decode a
Self-Routing Tag (SRT), used to direct the cell to its destination
port, within a time constraint.  From the decoding of SRT and the
monitoring of output port status, the switch can notify the input
port either passing through or storing into the cell.  In other
words, the whole ATM cell, not including the SRT, is waiting in the
input port.  It will be passed through the switch using a cut-through
link, if the destination output port is available.  On the other
hand, it will be stored into the switch's shared buffers, if the
destination output port is busy and the buffers are not full.  The
purposes of building cut-through links on switch are to significantly
reduce i) the mean packet latency time, ii) the mean cell delay, and
iii) the mean buffer size.

      Fig. 1 shows a functional diagram of a single-stage N * N
nonblocking ATM switch.  Note that, for simplicity, the control
signals and their flows, although not shown in the figure, will be
illustrated later.  The switch can transfer N cells at a time when
there is no output port contention.  In addition, full duplex
transfer is provided through two completely disjoint paths.  As shown
in Fig. 1, the switch consists of N input routers, N output
selectors, N shared buffers, and N * N cut-through links.  Their
major functions are described one by one as follows.

o   Input Router (IR): IR receives the first byte (SRT) of a switch
    cell, decodes it, and sends a si...