Cisco\u00a0is remaining tightlipped as speculation swirls around the challenges its next-generation core router will face in the market.After years of anticipation, Cisco's so-called HFR -- which stands for Huge (Expletive) Router -- will be unveiled May 25 along with a new, modular operating system for the product.Though Cisco won't provide additional details beyond an executive's confirmation that it will be\u00a0shown at Supercomm in June, HFR is expected to support at least 640G bit\/sec of switching capacity in a full telco rack.HFR, however, comes two years after rival Juniper Networks began shipping a 640G-bit\/sec half-rack system. And Juniper is expected to soon raise the stakes by announcing trial customers for its TX router interconnect, which clusters multiple 640G bit\/sec T640 routers together into a multiterabit system.In addition to ostensibly being late, the rack requirements of HFR are also an issue. Sources say it will require a non-standard 23-inch wide equipment rack as opposed to the standard 19-inch width.With central office real estate and square footage at a premium, HFR may require a bit more expense and installation disruption than other Cisco and non-Cisco routers."It's not NEBS-compliant," says Frank Dzubeck, president of consultancy Communications Network Architects, referring to the spatial and environmental requirements for central office equipment. "Everybody I talk to says [NEBS-compliance] is mandatory, you can't get away from it. You can't go into a [central office]" without it.HFR's new software may also raise red flags. Speculation has it that HFR and its new modular operating system are undergoing tests at Sprint, and at some visible Juniper accounts like Deutsche Telekom, MCI, and a large Asian carrier -- perhaps NTT.\u00a0New operating system software requires a year, perhaps even two, in production use to prove itself reliable, according to a bulletin on HFR issued by Erik Suppiger, an analyst at Pacific Growth Equities, as well as other sources. This may extend HFR's sales cycle as carriers wait until HFR's operating system stabilizes, the Suppiger bulletin states.Some analysts view the stabilization process as standard operating procedure and not unique to Cisco."Taking a year or two to break in the software is not unreasonable," says Joe McGarvey of Current Analysis. "Avici went through the same thing with AT&T, and Juniper went through the same deal" with its customers.But Cisco may turn out to be its own worst enemy here. The company is expected to market the HFR operating system as "purpose-built" -- optimized -- for the carrier environment even though it has a sizable installed base of previous generation IOS operating system implementations in carrier networks."What have carriers been deploying for the last couple of years then?" asks Kevin Mitchell, an analyst at Infonetics Research. "There's a dangerous line for Cisco to tread there. It could end up knocking [its] own previous products."If carrier demand for IOS wanes while they wait for the "purpose-built" software to stabilize, Cisco could take a sales hit on two fronts. It\u2019s a double whammy that Cisco can ill afford.Sales of Cisco's high-end, carrier-class routers were down 10% sequentially in the company's third fiscal quarter ended May 1. And even though Cisco owns two-thirds of the core router market, the company's market share slipped in the fourth quarter of 2003, from 66% to 62%, while rival Juniper's rose 3% to 31%, according to Dell'Oro Group.Some feel that Cisco customers have been holding out for HFR despite the software and rack space issues."We believe this downturn [in Cisco's Q3] is mostly due to Cisco customers withholding orders until the delivery of the HFR core router, rather than direct share loss to Juniper," stated Paul Sagawa, an analyst at Sanford C. Bernstein, in a bulletin on Cisco's third quarter results. "Once the HFR begins to ship, likely in [Q4 2004], we expect Cisco to recover its lost market share quickly."Demand for core routers is picking up as well. Dell'Oro expects the market to grow 31% this year, up from 22% in 2003.And Cisco, as always, will feed and feed off of that demand regardless of the challenges -- real or perceived -- facing its next-generation core router."There's a window of opportunity open for other vendors to win accounts because of this generational shift taking place," says Infonetics' Mitchell. "Cisco is very good at managing its customers and making sure that they're satisfied. I think Cisco's going to be very careful about how they navigate this."