Thursday, June 26, 2008

Aggressive Passive Optical Networking

PON or Passive Optical Networking is proving to be a cost effective technology for establishing fiber to the premises for residential and business users. So fast is this technology developing that PON is blowing through standards almost as soon as they are released. The latest increment is 10 Gbps GPON being demonstrated by Ericsson. Do I hear 100 Gbps? How about Tbps?

Well, not so fast (so to speak). Bandwidth demands are certainly rising in home applications and business WAN networks. But the transition from wireline to fiber has really just gotten underway. Not that you'd know it by watching the development of PONs.

The big appeal of passive optical networks versus the active variety is capital expense. In a SONET or Ethernet fiber optic network the cable is passive but transmission, reception and control is done with active electronic circuits at every node. This results in fine increments of multiplexed bandwidths and support for a wide variety of protocols and upgrades. That's the beauty of optical fibers. Once the considerable cost of construction has been paid off, the possibilities for pressing bandwidth into service is almost limitless. It gives carriers a lot of flexibility but at a price.

The thing about residential broadband is that cost really matters. In fact, the daunting bill for replacing the sunk costs of the century old copper wire infrastructure with higher capacity fiber has held back the telcos, cable operators and competitive carriers alike, until just recently. PON changes the equation. PON doesn't make high bandwidth packet transmission cheap, but it does make it much cheaper.

It's the P in PON that does the trick. The passive designation means not just the cable, but the distribution system as well. There is an active Optical Line Termination or OLT at the central office. Each premises gets an ONU or Optical Network Unit, which is also an active electronics box. In between everything else is practical. Passive optical splitters divide the fiber beam from the main line to multiple drops. There are typically 32 drops from a single trunk line, although that can vary from more to fewer depending on the length of the lines.

Then there are the PON standards. The first was APON or ATM based Passive Optical Networking. ATM or Asynchronous Transfer Mode is a technology based on small cells instead of large packets. It was primarily for business applications.

Next is BPON or Broadband Passive Optical Networking. This ITU-T G.983 standard offers downstream and upstream speeds of 155 (OC3 bandwidth) or 622 Mbps (OC12 bandwidth).

Speeding this up further is GPON or Gigabit Passive Optical Networking, standardized as ITU-T G.984. GPON offers downstream speeds of 1.25 Gbps and 2.5 Gbps. Upstream speeds supported are 155 and 622 Mbps, plus 1.25 and 2.5 Gbps.

The EPON or Ethernet Passive Optical Networking standard is supported by IEEE 802.3ah and offers 1.25 Gbps both upstream and downstream.

Now comes 10 Gbps GPON offering 10 Gbps of passive optical networking or 4x the capacity of GPON. There is also a 10GEPON. That's 10 Gigabit Ethernet Passive Optical Networking now in development under IEEE 802.3av. Seems like that should be enough for now, but with 100 Gbps core networks being demonstrated and 40 Gbps being deployed by long haul carriers, 100 Gbps GPON may not be that far in the future.

The mad dash for fiber optic deployment is having a beneficial effect of reducing the cost per Mbps for Ethernet WAN business users as well as residential broadband/television/telephone users. Just in time, too, as video and other high bandwidth application are sucking up packet speed as fast as it becomes available.

Click to check pricing and features or get support from a Telarus product specialist.

Follow Telexplainer on Twitter