Optik 125 (2014) 6739–6745 Contents lists available at ScienceDirect Optik jo ur nal homepage: www.elsevier.de/ijleo A novel algorithm to integrate synchronous digital hierarchy networks into Optical Transport Network using mixed line rates Maninder Singh ∗ , Maninder Lal Singh Department of Electronics Technology, Guru Nanak Dev University, Amritsar 143005, India a r t i c l e i n f o Article history: Received 24 November 2013 Accepted 5 July 2014 Keywords: Optical Transport Network (OTN) Routing Mixed line rates (MLR) SDH Integer Linear Programming (ILP) model a b s t r a c t In this era of high data transfer speeds and new age technologies, Optical Transport Network (OTN) along with its newly introduced Optical Transport Hierarchy (OTH) has provided a lease of life to legacy low rate networks. It has provided a common backbone for multiple data rates to coexist on same fiber along with the enhanced transmission reach. The cost effective Optical Transport Network design has always been a complex issue due to the presence of multiple variables like number of fibers on each link, available data rates on each fiber, the wavelength count, transmission reach at each data rate, etc. In this paper an Integer Linear Programming (ILP) model has been presented to solve Routing problem for Synchronous Digital Hierarchy (SDH) over OTN over DWDM design. Optical Transport Hierarchy (OTH) has been used to integrate heterogenous SDH/SONET operating at different rates (STM-16, STM-64 and STM-256) into a single network supporting mixed line rates. These rates can coexist in a same fiber but each rate carries different cost with it. The objective function aims at finding the least cost routing solution by looking at different tradeoffs between the Capital Expenditure and the operational expenditure. Certainly different variables like the number of fibers and wavelengths, transmission reach, etc. are a factor in it. A mechanism has been put to monitor the Bit Error Rate (BER) levels as well. For evaluating the ILP model, 18 Node 38 Link European Optical Network was considered as the reference model and two ordering techniques, namely, full ILP and highest rate first (HRF) were used for deriving the results. The ILP model was designed with minimum of decision variables so in spite of big reference network it converges much faster. Under the given conditions, full ILP gave least cost network whereas HRF ordering took least time for ILP to converge. © 2014 Elsevier GmbH. All rights reserved. 1. Introduction In the last decade the worldwide Internet traffic figures have achieved an unprecedented levels. This deep surge in demand can be attributed to the advent of vast array of new services such as video on demand, network computing and IPTV, along with the ever increasing number of people getting the broadband access. As the trend is quite likely to continue in future as well, so a need for transport networks upgradation was long felt. As a huge amount of Capital Expenditure (CAPEX) is required to build backbone trans- port networks, their complete replacement is not a viable option at all. This makes out a strong case in which any technological upgra- dation for transport networks should attempt to use the existing physical layer along with providing the added capacities to carry ∗ Corresponding author. Tel.: +91 9878700816. E-mail addresses: manindr.singh@hotmail.com (M. Singh), mlsingh7@gmail.com (M.L. Singh). the increased traffic demands. ITU-T G.872 and G.709 Optical Trans- port Network (OTN) is one such interfacing protocol which offers high speed data transfers along with the capabilities to integrate lower speed networks [1,2]. The basic philosophy behind OTN was to provide a common high speed backbone platform which can be used by all sort of networks. From its initial inception in 1990’s, OTN evolved to include a well defined mapping procedure called the Optical Transport Hierarchy (OTH) through which payload of heterogenous networks work- ing at multiple data rates can be mapped into an OTN frame and are further carried over a common physical network. So any routing and wavelength assignment problem involving OTN nec- essarily becomes a mixed line rate (MLR) problem. In this paper we have presented an optimization framework in the form of an Integer Linear Programming (ILP) model for solving the rout- ing and wavelength assignment problem for integrating legacy networks like STM-16, STS64 and STS256 into the OTN environ- ment using mixed line rates. In most of the existing literature, OTN and MLR networks were studied separately. To our wisdom, we http://dx.doi.org/10.1016/j.ijleo.2014.08.062 0030-4026/© 2014 Elsevier GmbH. All rights reserved.