Convergence in Optical Transport Networks

Abstract

Optical transport networks interconnect switches and routers in the network core, or connect high-speed, typically business/enterprise, users to the network (access). These networks are almost entirely based on the Synchronous Digital Hierarchy (SDH) standards today (or the equivalent Synchronous Optical Network (SONET) standard in North America).

Traditionally, SDH has been the sole transport network and thus has carried all of the telecommunication service provider's traffic, including voice and data. So, SDH has, in a sense, provided “converged” transport, all along. However, the interfaces provided by SDH equipment for the first 10 years or so (since about 1990 to 2002) were restricted to the rates used by the older plesiochronous digital hierarchy (PDH) systems, namely, 2/34/140 Mbps, or the standard SDH rates, 155/622/2488 Mbps. Data typically originates within an enterprise local area network (LAN), invariably Ethernet at 10, 100 or 1000 Mbps, and had to adapted to a “standard” PDH or SDH data rate, typically using a router within the enterprise. (This application of a router is so prevalent that the PDH interface on a router is called the wide- area network, WAN, interface.)

The first step that the SDH standards, and equipment vendors, took to support a data-friendly network was to provide Ethernet interfaces (10/100/1000 Mbps) on the SDH equipment in addition to PDH and SDH interfaces. The provision of Ethernet interfaces on SDH equipment is based on the Generic framing Procedure (GFP), Virtual Concatenation (VCAT) and Link Capacity Adjustment Scheme (LCAS) standards that were published and refined in 2001–03, and which are collectively referred to as the “Ethernet-over-SDH/SONET” or EoS standards. “Next-generation” SDH equipment supporting these EoS standards has been deployed since early 2003; Tejas' first shipment of standards-based EoS equipment to carry commercial traffic was in January 2003.

Additional information

Notes on contributors

Jishnu A

Jishnu A is Sr R&D Engineer in Network Design team at Tejas Networks India Limited.

He has a BTech degree in electronics and communication from REC, Calicut 1988–2001 and MSc (Engg) from IISc, Bangalore 2002–2004.

Sarath Kumar

Sarath Kumar is Group Director of Ethernet Products at Tejas Networks India Limited, responsible for adding data capabilities to the next generation SDH systems. He also heads the Network Design team and the Ethernet product development team at Tejas.

Prior to this, he was with Bell Labs 1995–2000, Lucent Technologies, New Jersey, USA working on design, architecture and performance analysis of Wireless networks. He has a BTech in Electrical Engineering from IIT, Kanpur 1984–88, MTech also in Electrical Engineering from IIT, Mumbai 1988–90 and a PhD, from the University of Pennsylvania, Philadelphia in 1990–93 in Communications and Signal Processing.

Kumar N Sivarajan

Kumar N Sivarajan obtained the BTech degree in Electrical Engineering (Electronics) from the Indian Institute of Technology, Madras, and the MS and PhD degrees in Electrical Engineering from the California Institute of Technology, Pasadena.

From 1990–1994, Sivarajan was with IBM Thomas J Watson Research Center, Yorktown Heights, NY From 1994–2000, Sivarajan was with the Electrical Communication Engineering Department, Indian Institute of Science, Bangalore. Since May 2000, he is Chief Technology Officer of Tejas Networks, Bangalore.

Sivarajan is co-author of the book 'Optical Networks: A Practical Perspective published by Morgan Kaufmann Publishers, February 1998. He is a Fellow of the Indian National Academy of Engineering, an Associate of the Indian Academy of Sciences, a recipient of the Young Engineer Award from the Indian National Academy of Engineering, and the Swamajayanti Fellowship from the Department of Science and Technology, Government of India. He is also a recipient of the IEEE Charles LeGeyt Fortescue Fellowship, the IEEE Communications Society William R Bennett Prize Paper Award, and the IEEE W R G Baker Prize Paper Award.