Data Centers

What you need to know about EPON: Enabling technology for NGNs

Learn what EPON is and how it can benefit access networks.

In my last post, I wrote briefly about some of the features of Next Generation Networks. One area that Next Generation Networks will rely on is high speed transmission and a robust layer 2 protocol. Ethernet Passive Optical Network (EPON) is one such technology.

PONs and AONs

The connection from the exchange to a customer premises is usually referred to as the "last mile." Another term used is "access network." This connection is usually done via copper cables, and is often a point-to-point connection. The use of copper creates a problem; the electrical resistance of the wire causes signal to drop over distance. Another problem is crosstalk, which is where an adjacent cable interferes with the signal. These problems can cause the signal to degrade, which in turn, affects the effective throughput.

One solution being deployed at present is optical cable, or fiber. In some countries, fiber networks are either largely in place (as in South Korea) or are being rolled out (as in Australia). In general, an optical network has a lower signal loss over the same distance when compared to a copper wire. Optical networks have other issues (such as chromatic dispersion), but in terms of the access network, they provide a reliable means to increase throughput.

A Passive Optical Network (PON) is a fiber-to-the-premises technology. Unlike an Active Optical Network (AON), it does not rely on routers or switches to split off signals to different users. A PON uses optical splitters; this means a single strand of fiber is able to service multiple users. This makes a PON simpler and more robust than an AON. Typically, one fiber will service up to 32 users (though up to 128 is possible). A PON can also be called a Point to Multipoint connection.

One of the main features of next generation networks is the use of IP in the network layer. Many applications (such as SIP, IPTV, etc) utilize IP. The obvious question then is what to use in the layer down (i.e., layer 2). Ideally, you want a mature layer 2 technology. This is where Ethernet comes in.

EPON basics

EPON stands for Ethernet Passive Optical Network. The original standard from the IEEE dates back to 2004 and was for 1GBits/sec. Since then, deployment of fiber networks and increasing demand for IP services have seen bandwidth requirements grow. A new standard for EPON that specifies 10GBits/sec was ratified by the IEEE in 2009.

EPON has two different types. There is symmetric, where the downstream data rate matches the upstream data rate, or there is asymmetric, where the downstream rate is higher than the upstream data rate. It is usually the case that asymmetric EPON is used with 10GBits/sec downstream and 1GBits/sec upstream.

EPON is an enabling technology for Next Generation Networks. What it also allows is the provisioning of higher bandwidth on 3G and 4G networks backhaul. LTE and WiMAX, with their emphasis on packet-switched technologies are expected to benefit from EPON. The specification for 4G defines peak downstream data rates of around 1GBits/sec. Whilst this is still being developed, the existing technologies (LTE and WiMAX) are being extended and are expected to be capable of reaching these rates. This means extra capacity is required on the backhaul (i.e., the part of the network that connects the base stations to the core network). EPON is one way to increase the backhaul capacity.

EPON is a way of using the ubiquitous Ethernet protocol in Next Generation Networks. It is an enabling technology that will not only benefit consumers, but will also benefit next generation wireless networks such as LTE and WiMAX.

About

Scott Reeves has worked for Hewlett Packard on HP-UX servers and SANs, and has worked in similar areas in the past at IBM. Currently he works as an independent IT consultant, specializing in Wi-Fi networks and SANs.

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