Passive Optical LAN vs Traditional LAN


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Architecture Comparison

Scale and reach are the two distinct advantages to using POL over traditional switched copper LANs. Reach is accomplished through the use of single-mode fiber in the cabling plant as it provides a footprint of 12.4 miles as opposed to the 300-foot limitation of copper. Scale comes from the fact that POL is a point to multipoint technology. Single-mode fibers connect to Passive Optical Network (PON) ports on the Optical Line Terminal (OLT), reach into the enterprise, and then terminate into a passive optical splitter, turning the one single-mode fiber into 32 fibers. Each of these can terminate into a 4-port Optical Network Terminal (ONT), providing a total of 128 Ethernet ports. In contrast, a traditional LAN would require 128 home runs of copper to accomplish what POL provides with 33 total fibers. Keep in mind, there are different models of ONTs (2,8,16, and 24-port) that can provide more ethernet ports than a typical 4-port ONT.

A Cost Comparison

When drawing comparisons between Passive Optical LAN and a typical switched copper infrastructure solution, it is vitally important to ensure that all comparable aspects of each solution are taken into consideration. POL represents a true evolution of LAN connectivity by pushing the Ethernet edge out of the telco closets and to the end-user. Unlike a traditional infrastructure with the demarcation between the switches aggregated in the telco closets and the home runs to the end user, the POL solution is inclusive of the fiber connectivity. Therefore, a POL system is a turnkey approach to the traditional copper cabling and the distribution and workgroup switches. An accurate comparison must take into consideration each of the following components and activities:

Workgroup access switches

  • Switches
  • Transceivers
  • Patch cables
  • Maintenance
  • Professional services (rack/stack, configuration, documentation)

Structured Cabling

  • Copper Cabling
  • Fiber backbone
  • Racks
  • Patch Panels/Cable Management
  • Faceplates, jacks, etc. 

Based on an accurate comparison, taking all of the above factors into considerations, capital expenditure savings should be 25-55%. 

Operating expenses will also be drastically reduced. The most significant contributor to these savings is the reduction in power consumption that comes from the elimination of the workgroup access switches. The removal of the switches reduces or eliminates the impact on UPS and HVAC in the closets. Lastly, maintenance costs associated with the switches, UPS, and HVAC are reduced or eliminated.

Additional Considerations

Additional considerations in the evaluation of POL include security, reliability, green benefits, and future proofing. The security benefits provided by POL come from several sources. First, using an all fiber-cabling infrastructure, the physical security of the cabling is improved, as fiber is extremely difficult to tap and is immune to electro-magnetic interference. Secondly, the GPON standard calls for the use of AES 128-bit encryption on all downstream traffic. Lastly, the AXS1800 supports network access control (NAC, 802.1x) as an enable feature and not an overlay technology.

            The use of bend-insensitive single-mode fiber improves the overall quality and reliability of the cabling plant as it is stronger and more flexible than copper cabling and less sensitive to erosive element and vibration events in buildings. Additionally, the use of factory pre-terminated fiber assemblies drastically reduces install times and improves the quality of the overall assembly. The use of pre-terminated, plug-n-play assemblies means that future moves, adds, and changes can be handled by facilities personnel and does not required certified cabling installers.

            In addition to the space and power savings outlined above, POL’s use of a point to multipoint topology creates a drastic reduction in cabling mass including reductions in the use of non-renewable materials, fire load, and floor/ceiling space. The future proofing benefit comes from the fact that single-mode fiber has over 100tbps of potential throughput and the PON standards call for backwards compatibility. This means that migrations to 10gbps, 100gbps, or above would only require changes in the active components and that a rip and replace of the structure cabling infrastructure would not need to occur for 20-30 years.