Browse Prior Art Database

Seamless Inter-LAN Isochronous Communications

IP.com Disclosure Number: IPCOM000105508D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 8 page(s) / 228K

Publishing Venue

IBM

Related People

Herzberg, LP: AUTHOR

Abstract

Present day LAN isochronous transmission technology is based on a timed protocol {1}. It provides the required guaranteed bandwidth at a fixed latency within a common LAN. However, this does not allow true isochronous transmissions from one LAN to another LAN. Inter-LAN transmission of real-time isochronous traffic is essential to the developing multimedia applications. A means is necessary to provide the requirements of true isochronous communication between one LAN and another. This invention provides such a means in a seamless and contentionless manner capable of meeting all specifications of the applicable LAN standards.

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This is the abbreviated version, containing approximately 29% of the total text.

Seamless Inter-LAN Isochronous Communications

      Present day LAN isochronous transmission technology is based on
a timed protocol {1}.  It provides the required guaranteed bandwidth
at a fixed latency within a common LAN.  However, this does not allow
true isochronous transmissions from one LAN to another LAN.
Inter-LAN transmission of real-time isochronous traffic is essential
to the developing multimedia applications.  A means is necessary to
provide the requirements of true isochronous communication between
one LAN and another.  This invention provides such a means in a
seamless and contentionless manner capable of meeting all
specifications of the applicable LAN standards.

      What is claimed is an apparatus consisting of the elements
listed in Section 2.3 and described herein which together provide a
means to obtain true isochronous communication between two stations
each resident on separate otherwise independent LANs as delineated
herein.  Together the elements are a means for time-slot-cell
succession from one isochronous capable LAN to another isochronous
capable LAN.

      This invention consists of an Isochronous Succession
Controller, ISC.  The ISC provides the means for across LAN
transmission succession of the time-slot-cells assigned to carryout
specific isochronous communications between stations resident on two
different LANs, LAN/A and LAN/B.  It only requires that both LAN/A
and LAN/B be capable of supporting normal timed intra-LAN isochronous
communications.  The ISC is placed between any two arbitrary stations
of each LAN so as to interconnect LAN/A and LAN/B as shown in Fig. 1.
The ISC performs the function of automatically forwarding the
isochronous time-slot-cell transmissions it receives from either LAN
onto the assigned time-slot-cells of the proper successor destination
LAN.  Section 3.1 describes the broadcast transmission capability.

      Ordinary isochronous transmission is based on the assignment of
particular time-slot-cells to each station-to-station isochronous
communication.  The time-slot-cells are addressed and located as to
their time position relative to a periodic header.  Each station
inserts its transmission information during its assigned time.
Correspondingly, the destination station receives and uses the
information embedded in those particular time-slot-cells.  In this
way, communicating stations know when to transmit information to, and
receive information from, each other.

      Since all isochronous capable LANs must operate so as to
provide fixed latency and guaranteed bandwidth, the rotation time
around each LAN is maintained at a fixed duration.  For reasons known
to those familiar with the art, the duration is maintained as a fixed
multiple of 1.25 usec.  The time-slot-cell assignments are made
within each 1.25usec cycle such as to provide the required
station-to-station isochronous bandwidth.  The position of a
time-slot-cell is in reference to...