Xylan Corp. signed an agreement with Northern Telecom, North America's No. 2 telephone equipment maker, to sell Xylan's computer switches to Northern's telecommunications customers. Northern began selling Xylan's OmniStack and OmniSwitch products, which are used to link computers in corporate networks, in the second quarter. More than 40% of Xylan's second-quarter revenue came through agreements with large equipment makers IBM Corp. and Alcatel Alsthom. Xylan expects sales to those customers to fall in the third quarter and is looking to other sources, including direct sales and sales made through other distributors, to maintain its revenue growth. Calabasas-based Xylan shares rose $1.31 to close at $26 on Nasdaq.