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

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