Passive Optical LAN for Enterprise Networks – Advantages & Limitations

When you think of LAN (Local Area Network), you generally think of Cat 5/6 cables and network switches, don’t you? But certain developments in the carrier networking technologies has made optical fiber networking feasible, and maybe even beneficial, for the Enterprise LAN. Will all our copper cables be replaced by fiber cables sometime in the future? Not totally impossible.

What is Passive Optical LAN?

If you want to build a LAN, you’d have the following components: Core Switch, Distribution/Aggregation Switch, Edge/End-point Switch, Copper UTP Cables. Fiber Optic cables may also be used for interconnection of switches (backbone).

Passive Optical LAN proposes to change this fundamental LAN architecture by replacing copper UTP cables with single-mode optical fiber cables. Basically it’s an ALL Fiber network with small copper UTP patch-cords connecting only to computers/end-points, at the very end of the chain.

Architecture: Enterprise Access Switch (instead of Core Switch) -> Passive Optical Splitters (instead of aggregation, distribution switches) -> WGT (Work Group Terminal with Ethernet ports, instead of edge switches)* ::: {All the above components are inter-connected using optical fiber cables}.

Each Enterprise access switch supports up to 32/64 Passive Optical Splitters and each WGT supports up to 4 Ethernet ports (This configuration may differ based on the vendor).

* These components maybe called differently by different vendors.

Advantages of Passive Optical LAN (POL):

  1. Optical Fiber connections can travel much more distance (up to 20 KM) when compared to copper-based connections (up to 100 meters), without needing any form of re-transmission.
  2. The core (aggregation) fiber switch can accommodate more than 7000 IP connections. The distribution layer uses passive optical splitters which do not need power (the entire distribution layer can be done away with, in some cases).
  3. Since the distribution layer can be eliminated/doesn’t need to be powered, this architecture saves a lot of cables, space, wiring closets, power points, cooling costs, electrical costs, etc.
  4. POL can handle high-bandwidth connections with real-time traffic. Each end-point can be provided with more than 1 Gbps of bandwidth.
  5. The Work Group Terminals, which connects the optical network to the RJ-45 end-point copper ports come in POE versions, as well.
  6. Passive Optical LAN is a carrier-class solution – It is already being used to provide network connectivity to individual homes. Hence, the technology is tested and reliable.
  7. POL equipment manufacturers claim that both capital costs and maintenance costs are cheaper than copper networks. Read this report (pdf) to see a detailed cost calculation, comparing both.
  8. POL manufacturers claim that optical network is more secure than copper networks because information cannot be ‘tapped’ by capturing the electromagnetic radiation emitted (as in the case of copper cables). POL supports common security standards like AES, 802.1x, etc.
  9. POL vendors claim that it is relatively more green as the solution uses less electrical power.
  10. Passive Optical LAN for enterprises has been standardized.
  11. Optical Fiber cables need not be changed every now and then to support higher bandwidth, unlike copper cables that need to be changed. For fiber networks, only the active components may require upgradation to support higher bandwidth.
  12. Single vendor solution means single management interface and easier management/learning-curve (when compared to managing multiple switches manufactured by different vendors on a traditional LAN).
  13. POL can handle both IP voice and TDM phone connections using the same network.
  14. Good option for organizations that are based over a large area (educational institutions, hospitals, etc).
  15. Bend-resistive fiber cables are available for effective inside-building optical fiber cabling.

Limitations of Passive Optical LAN (POL):

  1. While this technology looks good for large greenfield deployments, existing networks  may not change to POL, at least immediately. All companies have invested heavily in the traditional LAN technologies.
  2. POL solutions maybe an overkill for smaller organizations. They may simply not use all the capacity offered by it and the solution might become very expensive, compared to copper-based networks.
  3. With POL (in its current form), possibilities of single-vendor lock-in is quite high.
  4. Optical fiber cables, adapters, patch cords, emitters (active components), etc. are more expensive than their copper counterparts.
  5. Installation, testing, adds, moves and changes in an optical network is generally more complicated than in an copper network.
  6. Upstream bandwidth is lesser than/different from downstream bandwidth.
  7. While power may not be required for the distribution layer, all end-point terminals (WTGs) needs to be powered.
  8. POL is largely based on Single-Mode Fiber cables. Many companies have existing investments in Multi-Mode Fiber cables.
  9. There will be a steep learning-curve involved in managing these networks for enterprise applications – Some applications may have to be redesigned.
  10. The options and range of equipment targeting the enterprise POL market is currently very limited.

Read more/References:

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