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Over the last year, PON (passive optical networking) has come back into vogue as service providers recognize the enormous market potential for optical access services. Specifically, PON enables providers to roll out a wide range of flexible broadband services without having to invest heavily in outside plant infrastructure.
Decisions on PON deployment must take into account the provider's overall access strategy and the characteristics of its optical access architecture. Therefore, providers must often decide which protocol-ATM or Ethernet/IP-- is best suited for their optical access network. PON deployment is still a nascent strategy, and the jury is out on which flavor will ultimately win. A number of characteristics and provider requirements need to be solidly in place for either-or both-protocols to be used successfully.
ATM: Dial Tone Comes From God
ATM is very important in many networks, especially those of incumbents, which are responsible for roughly 85 percent of all telecom capital expenditures in North America. The main reason for ATM's staying power is its inherent QoS capabilities and its rich set of OAM&P
(operation, administration, maintenance and provisioning) features. In the words of one provider, "Dial tone comes from God." Providers focused on offering both voice and data services will not deviate from the proven to dabble in the experimental. While data represents the largest volume of per-bit traffic, voice represents the highest revenue. In applications such as straight data services, QoS and operations support are not needed and could burden the system. However, many providers need them to deliver the full gamut of demanded services. This will change as Ethernet evolves, but for now demand is driving the deployment of APON (ATM PON) systems.
Ethernet: Cost Is King
While most established providers agree that IP over Ethernet is the transport protocol of the future, greenfield carriers are bullish on Ethernet-based networks today. The classic argument in favor of Ethernet as a Layer 2 protocol is one of simplicity, low-cost and efficiency. However, as Ethernet evolves into a carrier-class access network protocol, all three advantages may be affected. Complexity is introduced as more features (e.g., flow control, QoS, VLAN) are added. Requirements such as OAM&P are threatening the cost advantage. Efficiency which stems from the lack of an ATM-like cell tax, is in...