Passive Optical LAN (POL) And Application Prospect

Preface: At present,most enterprise networks use traditional copper wire LAN, which are showing more and more drawbacks. With the rapid development of cloud computing, big data, and 4K video, more and more businesses are gradually migrating to cloud data centers. Followed by changes in traffic and architecture, the majority of traffic has shifted from a local switching architecture to a cloud switching architecture. On the other hand, with the explosive development of video, IoT, and the Internet, these applications have increasingly higher requirements for high bandwidth and low latency. In the age of digital transformation, enterprises urgently need a network that can carry all "things" access, and the POL network is the best choice.

I. POL Introduction

1.1 POL overview

POL is an enterprise LAN based on PON technology that provides users with integrated data, voice, video and other services through optical fibers. It is not a new technology, but applies the PON network technology that has been proven for a long time in the ISP network to the enterprise network. POL can bring great value to customers, at the same time, it will not change the existing business planning and customers network connection mode, and can provide all the functions provided by the traditional LAN network.

1.2 POL topology

POL provides a Layer 2 transmission network, adopts PON technology to provide gigabit access to user, and uses a single optical fiber to converge sevaral services such as video, data, wireless, and voice.

1.3 Comparison between POL and traditional LAN

In the POL network, the aggregation switch in the traditional LAN will be replaced by the OLT, the copper cable will be replaced by the optical fiber, and the access switch will be replaced by the passive optical splitter. The ONU provides Layer 2/Layer 3 functions and provide data, voice and video services by wired or wireless.

The downstream of PON network adopts the broadcast mode: the optical signal is sent by the OLT and divided into multiple optical signals to each ONU with the same information through the optical splitter. The ONU selectively receives its own packages according to the tags carried in the message and discard the packages that tags are not match.

The upstream of PON network: the OLT uniformly allocates a time slice to each ONU. The ONU strictly transmits signals according to this time slice window.ONU will shutdown the optical port when the time slice does not belong to its own time slice. The upstream time window scheduling mechanism is highly dependent on the PON distance measurement technology.

An understanding of PON technology principles will help us to apply this technology more proficiently in network design,In particular, the passive (no power supply required) characteristics of its optical distribution network, and the point distribution planning and design caused by the difference from traditional switches require special attention.To ensure the traffic packets in both directions are forwarded on a single-core fiber, PON uses wavelength division to process two-way signal transmission at the same time. Upstream and downstream signals use different wavelengths, but are transmitted on the same fiber. The direction from OLT to ONU/ONT is the downstream direction, and vice versa is the upstream direction. The downstream direction uses 1490nm and the upstream direction uses 1310nm.

Line structure comparison:

II. POL advantage analysis

Through the comparison between POL and traditional LAN in the previous section, we can find the challenges of traditional LAN and the unique advantages of POL.

Challenges of traditional LAN:

A large number of switches occupy the space of the computer room, high power consumption, and difficult heat dissipation.