White Paper 40Gbps and 100Gbps Services on Metro Networks D-5114 Introduction Long-haul 40Gbps and 100Gbps ITU / OTN transponders, based on active chassis-based and vendor proprietary systems are on the market since some time now. As those are targeted for the very challenging transport over hundreds if not thousands of kilometers solutions, all solutions are relying on complex technologies involving differing modulation formats such as DPSK (Differential Phase Shift Keying), DQPSK (Differential Quadrature PSK), DP-QPSK (Dual Polarization-QPSK) etc. Since this complexity does not come for free, the IEEE bodies have standardized pluggable 40Gbps and 100Gbps transceivers for "shorter reaches", and while limiting the requirements have reduced the associated cost tremendously. Although the majority of those transceivers covers very short distances (e.g. 10m, 100m) the 40GBase-LR4 and 100GBase-LR4 versions are capable for metro network applications and associated distances of up to 60km. Overlaying 10Gbps networks with additional 40Gbps or 100Gbps services In a typical scenario a metro network already exists, often relying on multiple 1Gbps or 10Gbps services which are multiplexed over the dark fiber network. The goal therefore, is not to take down the network and replace it by a new infrastructure but to add the new services without effecting the legacy installation, at lowest possible CAPEX and OPEX while still being simple to install and maintain. This can easily be achieved by adding the 40Gbps / 100Gbps service via a passive transport approach. In this scenario the according 40GBase-LR4 / 100GBase-LR4 (or future -ER4) transceiver (as e.g. CFP, QSFP, CFP2 etc MSA format) will be directly plugged into the terminal equipment, into the Ethernet switch, router etc. The new service can then be overlaid on the existing DWDM (or CWDM) network by adding it through a 1310nm band pass port on the (maybe existing) DWDM (or CWDM) passive multiplexer: If this 1310nm band port is integrated into a 40 channel 100GHz DWDM passive multiplexer, then this set-up allows the transport of up to 40 services at 10Gbps plus 100Gbps over 1 fiber pair, in total 500Gbps, implemented into 1HU/19" rack space without consuming any electric power. Overcoming reach limitations Although the IEEE bodies have standardized LR4 and ER4 versions for 10km and 40km reach, which are both operating in the 1310nm optical spectrum, the availability of the later ER4 (40km) versions is "limited". In practice this means ER4 transceivers are commercially not available and it is questionable if or when that might change. This effectively limits the use of metro applicable 40GBase and 100GBase to the LR4 versions. Those are nominally addressing distances of "up to 10km" - which are achieved for a perfect single mode fiber, without losses of splices, patch cords, ODFs or other reasons. Moreover the additional multiplexer will insert extra losses, hence the effective reach of such a LR4 transceiver will decrease to 6km or maybe even only 4km. This would then limit the use very drastically to some rare cases. Document: D-5114 Page 1/3
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