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FEATURE SOFTWARE-DEFINED NETWORKING
Trains, planes and software-defined multilayer networks
Jonathan Homa examines the benefits of taking a more holistic view of network optimisation
I
magine you are in charge of your country’s public transportation. You have three divisions, busses, trains, and aeroplanes. Each division shares patterns of passenger
traffic with each other, but otherwise operate independently. Te population is generally satisfied with the level of service, even when switching between modes of transport, but you know that this is primarily due to the fact that your budgets have been generous enough to allow each division to build sufficient route capacity and frequency. You are now informed that, sorry, your
budget is being cut by 20 per cent, and by the way, you better keep the same level of customer satisfaction because there is an election next year. You know that if you cut services across the board by 20 per cent that things will quickly fall apart. What do you do? Aſter consulting with operational planners,
economists, and other savants, you decide to build a sophisticated model and develop accompanying algorithms that looks at the totality of passenger traffic and all three modes of transport, simultaneously. Te fortunate result, you discover, is that you can provide travellers essentially the same level of service. While you need to give up excess capacity (there won’t be many open seats), by carefully planning routes and schedules among all three divisions, you can get people to their destinations in line with their current experience. Moreover, you can translate the algorithms
underlying the new scheduling into apps that enable travellers to plan their routes with higher precision, and decide among options
with different transit times and costs. And if a problem develops with a route, then the application notifies travellers in real-time and immediately suggests alternatives. Tis is the essence of multilayer
optimisation. To understand why this is so urgently needed today for telecommunications networks, we need to turn back the clock.
Our predicament: parallel evolution A scant 25 years ago, telecommunications networks were planned and optimised for fixed-rate voice traffic. Networks employed SDH/SONET technologies which mapped this traffic onto optical channels. In essence, we had a single layer network. Ten along came data services traffic for
computer networking and the budding world wide web. Tis was packet traffic based on
statistical multiplexing principles. Te packet engineers built their own overlay networks of Layer 3 Internet Protocol routers and Layer 2 Ethernet switches, but always came knocking on the door of the established and robust SDH/ SONET networks to hitch a ride for transport. SDH/SONET didn’t mind so long as the
packet traffic sat, figuratively, at the back of the bus and didn’t complain. Over time, however, the strength of packet
grew and the two worlds of fixed-rate ‘bell heads’ and statistical multiplexing ‘data heads’ evolved in wary co-existence. SDH/SONET transport was displaced by packet-friendly OTN, which was also needed to support faster optical line rates. Transport gear also began incorporating some Layer 2 packet-switching functionality, creating a new breed of packet-optical transport equipment.
Issue 15 • Spring 2017 FIBRE SYSTEMS 25
Stockphoto mania/
Shutterstock.com
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