• United States

OTN offers transparent service delivery

Feb 06, 20062 mins

* Optical Transport Network addresses two major WAN issues

OTN offers transparent service delivery

By Steve Alexander

The global migration to IP/Ethernet applications is forcing enterprises to address two major WAN issues – converging TDM and packet networks to reduce expenses, and improving network and service management to support bandwidth-intensive, delay-sensitive applications.

A new global standard is addressing these challenges – ITU G.709, commonly called Optical Transport Network (OTN) or digital wrapper technology. While digital wrapper technology has been around for a few years, standards have been in various states of completion, and only in the past year has true OTN equipment become available to make network deployments in the United States and Europe a reality.

Today, OTN is primarily offered at two rates, OTU1 and OTU2. OTU1 is defined as a 2.7Gbps signal designed to transparently carry a SONET OC-48 or synchronous digital hierarchy (SDH) STM-16 signal. OTU2 is defined to carry a 10.7Gbps signal to transparently transport an OC-192, STM-64 or 10Gbps WAN physical layer entity (PHY) as well as 10Gbps Fibre Channel.

Unlike SONET/SDH, OTU2 can be modified for special bit rates so it also can carry a 10G LAN PHY from IP/Ethernet switches and routers at full line rate. This is important, because LAN PHY typically includes proprietary overhead that increases the data rate beyond 10Gbps, making it too large for a 9.953Gbps SONET/SDH payload. The OTU3 (40Gbps) standard easily extends these networks to support future higher-bandwidth requirements. Click here to read more.

Alexander is CTO for Ciena. He can be reached at