Browse Prior Art Database

Loop network performance enhancement by automatic bypassing of unaddressed ports

IP.com Disclosure Number: IPCOM000015471D
Original Publication Date: 2002-Feb-15
Included in the Prior Art Database: 2003-Jun-20
Document File: 4 page(s) / 37K

Publishing Venue

IBM

Abstract

Described is a system by which a loop network such as Fibre Channel Arbitrated Loop (FC-AL) can be improved such that the performance of the system in large configurations is increased by reducing the loop tenancy required for basic data transfer. Also disclosed is a system whereby a loop network system could be defined such that it will further improve the performance in large configurations and also allow multiple data transfers concurrently. In a loop network, such as FC-AL, in order for a port to be able to send any data at all, it must 'take control' of the loop network and then it is allowed to 'open' a connection with a port and then the data transfer can occur. Using FC-AL as an example, there is a well defined procedure for the 'take control' phase. This occurs as follows. In FC-AL a loop network is a collection of ports, where each port contains a receiver and a transmitter. Each port's transmitter is connected to the next port's receiver and so on, forming a loop network. A port wanting to send data will attempt to win arbitration to the hole of the loop. This is the 'take control' bit. The port sends a special FC-AL defined primitive command word, ARB (AL_PA), which is this port's attempt to arbitrate for the whole FC-AL. The port has an AL_PA which is a temporarily assigned unique address within the FC-AL loop network. If there are no other ports wanting to arbitrate at this time then the port wins arbitration and will have taken control. If there is another port wanting to 'take control' at this time, then a 'tie-break' rule is applied where the port with the numerically lowest AL_PA wins arbitration. The port can now 'open' a connection with any other port in the loop network and send data to that port. Once the data transfer process completes the port can either 'open' another connection or 'release control' of the loop network, which is done by allowing other arbitration attempts from other ports to continue. To be able to send data at very high data rates, FC-AL operates at 1 or 2 Gb/s currently and plans are for even faster rates. To be able to achieve data integrity as words are transmitted around the loop network, special re-generation buffers are used. These buffers will consume FC-AL words in order to re-synchronise signals. To put all this into a proper picture more detail is required. The basic data rate of a 2Gb/s FC-AL loop network is 2 x 10^9 bits per second. FC-AL uses a well known and understood standard called 8b/10b endoing which for the purposes of this invention, mean that each 8 bit byte will allows use 10 bits of actual data. Also, a basic FC-AL loop network word is 4 bytes or 40 bits. When a port receives a 1

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  Loop network performance enhancement by automatic bypassing of unaddressed ports

Described is a system by which a loop network such as Fibre
Channel Arbitrated Loop (FC-AL) can be improved such that the
performance of the system in large configurations is increased by
reducing the loop tenancy required for basic data transfer. Also
disclosed is a system whereby a loop network system could be
defined such that it will further improve the performance in
large configurations and also allow multiple data transfers
concurrently. In a loop network, such as FC-AL, in order for a
port to be able to send any data at all, it must 'take control'
of the loop network and then it is allowed to 'open' a connection
with a port and then the data transfer can occur.

     Using FC-AL as an example, there is a well defined procedure
for the 'take control' phase. This occurs as follows. In FC-AL
a loop network is a collection of ports, where each port contains
a receiver and a transmitter. Each port's transmitter is
connected to the next port's receiver and so on, forming a loop
network. A port wanting to send data will attempt to win
arbitration to the hole of the loop. This is the 'take control'
bit. The port sends a special FC-AL defined primitive command
word, ARB (AL_PA), which is this port's attempt to arbitrate for
the whole FC-AL. The port has an AL_PA which is a temporarily
assigned unique address within the FC-AL loop network. If there
are no other ports wanting to arbitrate at this time then the
port wins arbitration and will have taken control. If there is
another port wanting to 'take control' at this time, then a
'tie-break' rule is applied where the port with the numerically
lowest AL_PA wins arbitration. The port can now 'open' a
connection with any other port in the loop network and send data
to that port. Once the data transfer process completes the port
can either 'open' another connection or 'release control' of the
loop network, which is done by allowing other arbitration
attempts from other ports to continue.

     To be able to send data at very high data rates, FC-AL
operates at 1 or 2 Gb/s currently and plans are for even faster
rates. To be able to achieve data integrity as words are
transmitted around the loop network, special re-generation
buffers are used. These buffers will consume FC-AL words in
order to re-synchronise signals. To put all this into a proper
picture more detail is required. The basic data rate of a 2Gb/s
FC-AL loop network is 2 x 10^9 bits per second. FC-AL uses a
well known and understood standard called 8b/10b endoing which
for the purposes of this invention, mean that each 8 bit byte
will allows use 10 bits of actual data. Also, a basic FC-AL loop
network word is 4 bytes or 40 bits. When a port receives a

1

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request for arbitration it receives a FC-AL word which is ARB
(FC_AL). Each port needs to determine whether or not it wants to
arbitrate and possibly do the 'tie-break' test and whilst doing
so it must continue to send valid alternate FC-AL...