Have not completely digested the below info, but it helped me to understand FTTX alternatives. Hope it proves of use. Borrowed from FC New TEchnology thred
ANALYSIS: Which FTTP technology will RBOCs use?
July 11, 2003 By: Joan Engebretson America's Network Weekly
CHICAGO - Although the RBOCs are planning the most wide scale deployments of fiber-to-the-premises to date, they won't be pioneers in this area. Rural telcos, municipalities and real estate firms already have deployed more than 700 operational FTTP systems, with many more in various phases of completion. What can RBOCs learn from them?
One industry executive who has a wide perspective on this is Bob Whitman, manager of broadband market optical development for Corning Optical Fiber. "We take an agnostic approach to the different technologies," says Whitman, whose goal is to sell the fiber strands that work with any of the technology alternatives-whether they be passive or active, or Ethernet or ATM-based.
Passive optical networks (PONs) have no active elements outside the central office or the customer premises. With PON, users in a neighborhood share the available bandwidth using a form of time division multiplexing to assign specific time slots, or bits, to specific customers. PON systems are easier to maintain than active systems, says Whitman, but tend to deliver less bandwidth to each user than with active systems.
[FAC: I'd have to differ with this, since the actual modality is a selection process (it could be either Ethernet or ATM, or something else, and the author is clearly discussing a TDM variant here), and the speed is an arbitrary call, assigned per the engineering of the system.]
Active systems use a point-to-point approach, rather than a shared medium. Although some bandwidth may be shared from the central office to a powered active element in the neighborhood, each customer has its own private connection to the neighborhood node.
To date, PON deployments have outpaced active system deployments by a ratio of about 60/40, Whitman estimates. But some types of network operators have tended to favor one option more than the other.
Real estate trusts have tended to choose active systems, while municipalities have used both PON and active systems. Those municipalities choosing active systems often have been driven by the desire to support open access video. "It's easier to support multiple carriers with an active solution," says Whitman.
Rural telcos, meanwhile, have primarily chosen PON-and although PON systems may be either ATM or Ethernet-based, rural telcos have favored ATM. "ATM's obvious advantage is that phone companies all have ATM-based networks so it's an easier fit," says Whitman. Active systems are all Ethernet based, adds Whitman, and carriers "are trying to get out of the dedicated lasers and equipment" that come along with active systems.
That same logic is likely to influence RBOC thinking on FTTP. Their request for proposal was given out under a non-disclosure agreement, so few industry players are willing to discuss details. But, says Whitman, "It appears they're choosing ATM-based PON."
To date, Optical Solutions has been the leading vendor of that type of equipment. But Alcatel also has an offering that some say is the lead candidate to win the RBOC bid.
In addition, "all the big telecom manufacturers are looking to get into the game," says Whitman, adding, " Some players abandoned their development efforts there so they will want to partner with someone to get back in."
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