Browse Prior Art Database

Access Scheme for Slotted Unidirectional Bus Configurations

IP.com Disclosure Number: IPCOM000120425D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 3 page(s) / 121K

Publishing Venue

IBM

Related People

Birk, Y: AUTHOR [+2]

Abstract

Disclosed is a slotted-and-tagged unidirectional-bus (Stub), a novel access scheme for slotted unidirectional-bus configurations. Its most salient feature is light-load bus-access time of few packet transmission times while providing the capability of transmitting an entire packet in consecutive slots. Due to this slot-contiguity feature, there is no need for segment labeling or concurrent packet reassembly.

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This is the abbreviated version, containing approximately 52% of the total text.

Access Scheme for Slotted Unidirectional Bus Configurations

      Disclosed is a slotted-and-tagged unidirectional-bus
(Stub), a novel access scheme for slotted unidirectional-bus
configurations. Its most salient feature is light-load bus-access
time of few packet transmission times while providing the capability
of transmitting an entire packet in consecutive slots. Due to this
slot-contiguity feature, there is no need for segment labeling or
concurrent packet reassembly.

      One unidirectional-bus configuration for N nodes is the folded
bus shown in Fig. 1 Packets are transmitted on the outbound portion
and received on the inbound portion.

      The Stub access scheme operates in conjunction with slotted
transmission and fixed-sixe slots. The most upstream node ("head"
node) sends out an infinite sequence of blocks, each containing a
number of slots whose combined space for data equals or exceeds the
maximum permissible packet size. Each slot, as shown in Fig. 2,
begins with a "busy/empty" bit, which is followed by a "tag" bit and
then by a fixed- size tag/segment sield. A slot is "busy" if it
contains part of a packet, and "empty" otherwise.

      All slots are generated "empty", with the tag/segment field in
each slot containing the number of remaining slots in its block. The
first slot of each block has its "tag" bit set to one, while the
others have it set to zero. When a node has a packet for
transmission, 0D063, it does the following:
(1) Waits until it encounters an empty slot.
(2) If the tag bit of this slot is one and its tag value is
equal to or greater than the number of slots required for the packet,
transmission commences:
         Every slot is marked "busy".
         Unless the end of block is reached, the "tag" bit of the
first slot following the packet is set to one. (This slot is always
empty.)
     Else go to (1).

      Requiring that a transmission begin in a slot whose tag bit is
set to one is absolutely necessary for Stub to guarantee that a
transmission never needs to be repeated due to a packet's being
overwritten or aborted. A side benefit of the tagged-slot requirement
is that all the transmission in a block are packed together,
eliminating intra-block fragmentation.

      Note that the protocol is designed such that only empty slots
contain slot-count numbers (tag values). Moreover, so long as the
maximum number of segments (slots) per packet does not exceed 2**
(number of bits per slot), the slot size, as determined by the
desired segment size, always suffices to contain the count. Thus, the
only intra-slot overhead of Stub is one "busy" bit per slot and one
"tag"...