The capacity of Juniper Networks’ biggest broadband router may be causing some friction between it and one of its most valued customers, Verizon Communications.

Verizon, which contributes more than 10% of Juniper’s revenue, appears to be unsatisfied with the current capacity of Juniper’s E320 router, which the carrier uses for broadband subscriber management, Morgan Keegan analyst Simon Leopold wrote in a research note published today. As a result, he said, Verizon has turned to Juniper rivals Alcatel, Cisco Systems and Redback Networks, requesting updates on their offerings.

“We believe that Juniper has not delivered the promised switch fabric capacity [on the E320],” Leopold wrote. “Verizon has designed its network with the assumption of having a very high-capacity subscriber management solution, and a network redesign would not be trivial.”

When Juniper unveiled the E320 at the Supercomm trade show a year ago, it touted a maximum switching capacity of 100 Gb/s that would be upgradeable to 320 Gb/s when customers require it. The vendor has not yet set a timetable publicly for the availability of the 320 Gb/s switching fabric, which will come in the form of an insertable line card. But a Juniper spokesperson told Telephony today, “You’ll be hearing about that from us soon.”

“Our relationship [with Verizon] remains very strong,” the spokesperson added. “Things are on track with Verizon.”

A source familiar with Verizon’s broadband deployments said the company is currently seeking a secondary supplier for broadband subscriber management gear, following the typical dual-sourcing practices of major carriers.

“It does not seem that [Cisco, Alcatel or Redback] have products that could drop into [Verizon’s] network, replacing Juniper's role without redesigns and significant work,” Leopold wrote, predicting Juniper to deliver the 320 Gb/s capacity but lose some business to a secondary supplier, which he said was most likely to be Redback.

At the Globalcomm trade show last week, Juniper unveiled new Ethernet aggregation cards for its M- and T-Series routers, following several months of calls from analysts for more Ethernet functionality in its portfolio. Leopold called the Globalcomm news “anti-climactic,” adding, “We wish [Juniper] had addressed the Ethernet feature gap--real or perceived--on its E-Series routers.”

Juniper has promised more Ethernet-related announcements in coming months but has also expressed an aversion to introduce what it calls a “me too” Ethernet aggregation switch, one that merely duplicates the features of more established products.

Juniper is growing faster than both its chief rival, Cisco, and its overall sector. But with regard to its Ethernet-related offerings, Leopold wrote, “The company needs to do more, and do it faster, to improve investor confidence.”