Sometimes the most innovative products are simple, but not obvious combinations of existing products.

The emergence of Ethernet as a mass-market service requires re-thinking and re-engineering Ethernet services from the costly point-to-point model to point-to-multipoint architecture. Whether in the access network, the data center, or premise distribution wiring, Ethernet (E)PON technology continues to grow in installed base. 

In the access network EPON is implemented with an optical line terminal (OLT), passive optical distribution network and an optical network unit (ONU) at the customer premise. The ONU is both the EPON access device and a bridge with 10/100/1000Mbps copper Ethernet ports on the customer side. While suitable for a single port and simple multi-port Ethernet service, it is challenging for more complex services requiring many ports or a variety of services such as voice, data, and emulated TDM circuits.

Service providers install an ONU in series with a customer access router or switch. This is so typical in business services that it represents the majority implementations outside of the SOHO and some SMB business markets.

Form factors

About ten years ago, equipment and optics vendors in the Ethernet industry began developing multi-source agreements (MSAs).

These multi-lateral contracts provide a common set of requirements for the packaging of optical subsystems and assemblies for the benefit of a defined and simplified market for the optical component suppliers and their customers, the equipment vendors. The most widely used pluggable MSAs are the small form-factor pluggable (SFP) for Gigabit Ethernet and the XFP for 10GigE.

In EPON systems there are SFPs available for both 10km and 20km optics on the OLT side of the network. At the ONU side, most optics are packaged as small form-factor fixed (SFF). The SFF is similar to an SFP, but comes in a form to be fixed to a circuit board, instead of the pluggable SFP form. Some optical component vendors offer SFPs for the ONU optics. This is useful for a single ONU to support either of the two EPON optics power budgets (10km and 20km optics).

What about taking the SFP to a new level by integrating the ONU optical, electronics, processor, and software functions into an SFP form factor?

One company that has done so, Broadway Networks, has brought to market a single SFP that terminates the EPON, acts as an ONU and Ethernet bridge and provides a standard SFP interface. Broadway’s ‘‘EPON stick,” also known as SFP-ONU, embeds the ONU inside an SFP so that no external ONU is necessary. With this technology, a service provider can plug the SFP-ONU into any SFP MSA-compliant interface and use EPON as a substitute for baseband copper or optical GigE or coarse wavelength division multiplexing (CWDM).

CPE, data center, enterprise

The SFP-ONU works the same way that other types of SFPs work. The customer premise equipment sees an 802.3 interface looking backwards into the SFP and the EPON is invisible.

On the service provider’s side the ONU is visible and managed from the OLT using a dedicated and secure channel separate from customer traffic, as defined in the IEEE 802.3ah EPON standard. In business services applications, the EPON stick eliminates an entire ONU box and all of the associated capital and operational costs.

In the data center, EPON eliminates an Ethernet switch and shares the cost of a 1Gig port across multiple servers (many servers use SFP interface). In the enterprise, the SFP-ONU brings GigE performance to the desktop for a fraction of the capital and premise fiber installation costs of 1000BaseSX.  

(For related illustrations, see February issue of Communications Technology, page 26.)

–Victor Blake

The Daily


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