Analysts seem to agree that Juniper Networks Inc. (NYSE: JNPR) is the big loser in the pending Cisco Systems Inc. (Nasdaq: CSCO) acquisition of Starent Networks Corp. (Nasdaq: STAR). There might even be an AT&T Inc. (NYSE: T) deal at stake that's been swiped from Juniper's grasp.

The $2.9 billion acquisition, announced this morning, "basically locks Juniper out of the next-generation Packet Core market," writes analyst Michael Genovese of Soleil Securities Group Inc. , in a research note published today. (See Cisco to Buy Starent for $2.9B.)

The problem is that Juniper is left without a complete packet-core offering to match what Alcatel-Lucent (NYSE: ALU), Ericsson AB (Nasdaq: ERIC), and Huawei Technologies Co. Ltd. have.

And Cisco would have it, too, with Starent in tow. The router vendor has been trying to sell its 7600 into the packet core, without much success, writes analyst Catharine Trebnick of Avian Securities LLC , in another note published today.

"Cisco is intent on remaining relevant within the core networking equipment segment and snatching Starent out from under Juniper is an indication of how far Cisco will go to maintain its market share within core networking products," Trebnick writes.

But there's more. In making its offer for Starent, Cisco might have stolen an AT&T deal from Juniper.

According to Genovese, AT&T had already picked Starent for a packet core upgrade. And because of the carrier's domain supplier program -- which limits the number of suppliers AT&T uses in certain categories -- Juniper would have been the company to sell the Starent gear into the network. (See AT&T Unveils Domain Supplier Strategy.)

Cisco, which happens to be the incumbent router vendor at AT&T, couldn't have been happy about that. "This win by Starent/Juniper apparently added to Cisco's motivation to step up and buy Starent," Genovese writes.

Juniper's options for a response seem limited. Genovese doesn't think the company has the appetite to try to outdo Cisco's offer, but he notes that an acquisition of a startup could be possible.

— Craig Matsumoto, West Coast Editor, Light Reading