Cost Effective Ethernet Passive Optical Network

Aaron Patzer
Electrical and Computer Engineering, Duke University
atp3@duke.edu
Advisors:  David Brady and Rick Jones

April 8, 2002

Abstract:

An Ethernet passive optical network (EPON) is a point-to-multipoint (1:N) optical access network.  EPONs leverage the low cost, high performance curve of Ethernet chipsets to provide reliable data, voice, and video to end users at bandwidths far exceeding current access technologies.  This paper details an EPON created at Duke University's Fitzpatrick Center for Photonic Communications using inexpensive off the shelf components.  The 1:4 EPON created achieved full 100Mbps Fast-Ethernet transmission over bidirectional optical links.  Other performance metrics such as latency, link budget, transmitter power and passband, receiver sensitivity, and distance reachable were measured.  It is concluded that by using components costing no more than $250 per optical network unit (ONU), a 1:32 EPON with a bandwidth of 100Mbps and a range of 10-15km can be constructed.

I.  Introduction

The access network resides between the individual subscriber and network carrier's central office (CO).  With the ever increasing demand for network bandwidth driven by Internet usage, videoconferencing, storage networks, and large file transfers, the installed base of copper twisted pair and coaxial cable are insufficient for demand.  Falling costs of fiber, CO optical line terminal (OLT) equipment, and end user optical network units (ONUs) will soon bring Gigabits/sec to what has long been called the "last mile" bottleneck.

The Ethernet passive optical network (EPON) is a point-to-multipoint optical access architecture designed to bridge the last mile.  By exploiting the superior price/performance curve of Ethernet ports - along with low-cost, low-maintenance passive components in the network - the EPON is economical and fast.  In contrast to ATM or SONET based networks, EPONs ensure that IP/Ethernet packets begin and end their life as IP/Ethernet packets without expensive and time consuming protocol conversion, or circuit setup.

Figure 1:  An Ethernet passive optical network.

II.  Results

A bidirectional EPON was constructed using $215 Versitron Fast-Ethernet optical modems to simulate the user premise ONU, while Lucent Allwave Metro equipment was used to simulate the carrier's central office.  Bidirectional transmission of 10 km was acheived using TCP/IP at a rate of 90.5 Mbits/sec.  System jitter including optical modem, NIC, protocol stack, and OS was measured to be submillisecond, with latencies well under 10 ms.  These parameters are sufficient for reliable voice and video communication with plenty of bandwidth for fast data transmission.

The link budget for downstream transmission was calculated at 30 dB, while the upstream link budget was 15 dB.  Link budgets for downstream transmission need to be much higher due to the split loss inherent in the point-to-multipoint nature of an EPON.  This is sufficient for ranges of up to 15 km and splits of 1:32.

The EPON system created may now be used as a high-speed access network, optical interconnect medium, or teaching laboratory.

Full documentation of EPON project may be found at www.duke.edu/~atp3/research/optics/epon.htm