Special Report: Next Generation Internet Applications
ATM passive optical networks are the most promising candidates for access networks. Groups including the Full Services Access Network (FSAN), ATM-Forum, and ITU-T are creating standards for ATM-PONs. Most notable of the standards is the ITU-T SG15 standardization designated G.983.1 adopted during October 1998. ITU-T standard G.983.1 specifies the ATM-PON physical layer. G.983.1 ATM-PONs support fiber-to-the-home (FTTH), fiber-to-the-cabinet (FTTCab), and fiber-to-the-curb (FTTC). ITU-T G.983.1 supports a 1310 nm burst mode uplink to a service provider office operating at OC-3 and an OC-3 or OC-12 downlink to a customer premise operating in 1550 nm continuous mode. [9] ITU-T G.983.2 and G.983.3, when published, will add management, control, and new service features to ATM PONs.
ITU-T Recommendations G.971 through G.977 spell out many aspects of all-optical submarine cables. G.975 harmonizes forward error correction methods for submarine cable and G.977 defines the standard requirements for submarine optical amplifiers. Three groups are focusing on IP-over-DWDM standards. The IETF is working on MPLS and other standards designed to realize the peer-to-peer architectural model. The Optical Internetworking Forum (OIF) is proposing schemes based on both the client-server and the peer-to-peer models. OIF standards rely on MPLS for use in both models. The Optical Domain Service Interconnect (ODSI) proposes user network interfaces for rapid service provisioning based upon modifications to the transport control protocol/internet protocol (TCP/IP) stack.[29]
Fifty vendors including Williams Communications, Siemens, and Sycamore Networks formed the ODSI consortium.[48][49] ODSI seeks a standardized signaling interface between service networks and optical transport networks for the automatic provisioning of optical paths. ODSI-proposed standards assume that services networks consist primarily of electronic IP routers and ATM switches. Optical transport networks consist of DWDM with provisioning capacities of OC-48 or OC-192. The proposed ODSI protocol adds extensions to the IP and MPLS protocols. If adopted, it would allow customers to provision additional bandwidth within seconds. It would support short-term provisioning of high-definition TV, router, and switched connections to meet immediate demand. The standard is nearing finalization. Sycamore Networks hopes to market equipment based upon the protocol by the end of 2001.
The OIF is working on direct interfaces between IP and DWDM devices. Direct IP-over-DWDM interfaces would bypass ATM and SONET conversions that currently exist in the commercial networks. The standard setting bodies will create many more standards before all-optical networks become a mature technology. There is a general lack of standards for all-optical management, protection, and restoration. Standards exist for optical cables and are rapidly developing for DWDM. Standards do not exist for optical add/drop multiplexers and optical cross-connect system signaling or management. Optical cell and packet switches are primarily laboratory prototypes and first generation products. Consequently, standardization of optical switching has not begun in earnest.
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