Ciena Corp. reported a surprise loss in the October quarter, as revenue growth in its biggest network segment was unable to offset expected hits from a supplier agreement with AT&T Inc. The telecom-equipment maker had earlier warned that uncertainty tied to the timing of potential orders, as well as concessions related to its recent supplier agreement with AT&T would dent its revenue in for the fourth quarter. Early-stage network deployment and other related costs could put pressure on margins, while certain upfront incentives and concessions as part of its agreement to be a Domain 2.0 supplier for AT&T will have a disproportionate impact on the quarter's revenue and margins.