ISL (inter-switch link)
A method of encapsulating tagged LAN frames and transporting them over a full-duplex, point-to-point Ethernet link. The encapsulated frames may be token-ring or Fast Ethernet, and are carried unchanged from transmitter to receiver.
Because ISL carries data hop-by-hop over point-to-point links, neither the Fast Ethernet nor Gigabit Ethernet constraints of 1,500-byte data frame size are applicable. Therefore, ISL can be used to transport the far-larger 18K-byte token-ring frames (or alternatively, 100-byte packets). And because ISL is based on Ethernet technology, Fast Ethernet Category 5 copper cabling or fiber-optic cabling can be used as a transport medium, allowing speeds of 100M bit/sec or even gigabit speeds between switches and to servers.
From How to's of mixing token ring, Ethernet, Network World Tech Update, 08/09/98.
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