Browse Prior Art Database

Dynamic Automatic Optical Baud Rate Selection

IP.com Disclosure Number: IPCOM000104565D
Original Publication Date: 1993-May-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 122K

Publishing Venue

IBM

Related People

Carlson, BA: AUTHOR [+2]

Abstract

The ANSI Fiber Channel Physical Standard (FC-PH) defines multiple optical baud rates and many implementations are expected to support only one particular baud rate within this set. A method is described that permits an optical transceiver -- a transmitter and receiver pair which is itself capable of multiple baud rates to dynamically select an optical transmission baud rate matching that of another transceiver to which it is connected over a Fiber Channel Standard (FCS) link.

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This is the abbreviated version, containing approximately 43% of the total text.

Dynamic Automatic Optical Baud Rate Selection

      The ANSI Fiber Channel Physical Standard (FC-PH) defines
multiple optical baud rates and many implementations are expected to
support only one particular baud rate within this set.  A method is
described that permits an optical transceiver -- a transmitter and
receiver pair which is itself capable of multiple baud rates to
dynamically select an optical transmission baud rate matching that of
another transceiver to which it is connected over a Fiber Channel
Standard (FCS) link.

      A pair of Fiber Channel Standard (FCS) optical transceivers is
connected through a fiber optic medium directly, in a point-to-point
manner, to each other.  When an optical transceiver initially
powers-on, and during reset and recovery procedures, both
transceivers perform an interlocked protocol to establish an
operational state of the Fiber Channel Link.    This protocol
requires that the receiver elements of each transceiver first acquire
bit synchronization with the transmission signal of the other
transceiver's transmitter element.  This protocol further assumes
that both transceivers are operating at a common optical baud rate.
The link initialization protocol is composed of interlocked
"primitive sequences", which are repeated transmissions of an
"ordered set" within the FC-PH character transmission code.  These
primitive sequences are:

o   OLS
o   LR
o   LRR
o   IDLE

      The figure illustrates the synchronization states, and the
transitions between them, that comprise the transceiver
synchronization protocol.  The conditions within each of these
states, and the actions performed, at either of the two transceivers
is:

OLS XMIT       OLS Transmit State:

o   May be receiving an input bit stream, attempting to acquire bit
    and word sync
o   Transmitter sending OLS

OLS RCV        OLS Receive State:

o   Receiver in synchronization acquired state, decoding OLS
o   Transmit LR sequence

LR RCV         LR Recieve State:

o   Receiver in synchronization acquired state, decoding LR
o   Transmit LRR Sequence

LRR RCV        LRR Receive State:

o   Receiver in synchronization acquired state, decoding LRR
o   Transmit IDLE Sequence

ACTIVE         ACTIVE State:

o   Receiver in synchronization acquired state, decoding IDLE
o   Transmit IDLE Sequence (enabled for data transmission)

      When at least one of the transceivers in an interconnected pair
is capable of more than one of the FC-PH optical baud rates, two
methods are possible by which that transceiver may dynamically select
an optical transmission baud rate, from those within its
capabilities, to match the optical baud rate of its connected
transceiver.

      Method 1 requires that the optical receiver element within a
transceiver communicate its received baud rate in some manner that
the transmitter can apply to establish a transmission baud rate equal
to that of...