FEATURE SDN
configure each and every entry in each and every forwarding table in each and every switch, however you want, at any time,’ says Chris Janz, vice president of market development at Ciena. ‘Conventional protocols don’t allow you to do that.’ Te three-layer SDN architecture applies to the
data centre and to transport SDN. But whereas the data centre is packet-based, the carrier’s data plane includes packet and transport layers (see SDN architecture). Te ONF’s Optical Transport Working Group,
set up in March, is investigating the extensions needed to enable OpenFlow to also control the transport layers (see box, Extending OpenFlow for Transport SDN). ‘SDN and optical networking go nicely
together, making up an end-to-end overall framework,’ says Uwe Fischer, CTO at Coriant. Optical layer developments such as new modulation formats and bandwidth virtualisation using super-channels and flexible
SDN ARCHITECTURE
The ONF SDN architecture separates the network into management/applications, control, and data layers. The uppermost level –
management/applications – includes such components as customer management, services, billing systems, cloud orchestration, and portals so customers can configure services using
SDN. The middle, control, layer is where the SDN controller resides. The controller has a centralised view of the network and sends commands to the underlying networking elements. OpenFlow is an SDN controller protocol to configure and control the forwarding behaviour of equipment.
The direct and abstract model associated with the Optical Transport Work Group’s extension work
Application 1
Orchestration layer Application N
Transport SDN Management
Control Physical
Source: Fibre Systems, OIF
Data Centre Management
Control Physical
OpenFlow is one
approach by which the middle-layer software communicates with the network. Others include the RESTful application programming interface and proprietary ones. The ONF’s work is network
focused whereas the OIF’s remit is looking at how SDN can be used to optimise all
Application Layer Business Applications Business Applications Control Layer
Southbound Interface (Direct Mode)
SDN Network Controller
Infrastructure Layer Network Device Network Device
SDN Client Controller Function Business Applications Business Applications Northbound Interface SDN Client Controller
SDN Network Controller Mediation/Virtualisation
Abstracted Network Model
Southbound Interface (Abstracted Mode)
resources: network, and processing and storage that reside in the data centre. Accordingly, the OIF has
added an orchestration layer that bestrides the data centre and WAN SDN architectures to enable such optimisation. Application software then resides above the orchestration layer, communicating with it and
the underlying IT and telecom infrastructure via a programmable interface. ‘The orchestration layer
will coordinate the data centre and transport network activities and give, northbound, easy access to new applications,’ says Hans-Martin Foisel, chair of the OIF’s Carrier Working Group.
grid, are no longer discussed from a physical perspective only, he says, but also in the context of an SDN framework. ‘When you have a multi-layer network, you
want to choose the most appropriate path for the traffic because that will yield the lowest cost-per- bit, and the most efficient use of your resources,’ says Liou. Having a centralised application overseeing all the multi-layer information will help streamline operational issues, like automating the turning up of links, he says. It can take weeks to turn up an IP link,
especially when an operator’s IP operation group requests bandwidth from the transport group. ‘Carriers have visions of automating some of these processes through some higher level SDN concept that can orchestrate and optimise resource allocation, ideally without much human intervention,’ says Liou. ADVA Optical Networking undertook a field
trial with Juniper Networks and operator Telefonica. Te trial explored the use of SDN
@fibresystemsmag |
www.fibre-systems.com
technology to set up optical links to carry IP traffic when it could be offloaded from the routers. A greater than 30 per cent equipment saving resulted, due to the more efficient usage of the IP-over-WDM network. Centralised control also promises to aid the
day-to-day running of a network. An operator can divert traffic from sites requiring maintenance. ‘Te SDN approach is much more command-based, with the SDN controller having a view of the network,’ says Elbers.
Challenges
Carriers will choose SDN deployments carefully, given the complexity of their networks and their need to gain confidence using the technology. System vendors say they are all working closely
with carriers and content service providers about how best to use SDN, and have seen interest grow significantly in the last year. Ciena, working with partners, is building a testbed research network to boost carrier
Network Device Network Device
Network Device Network Device
Network Device Network Device
20
FIBRE SYSTEMS Issue 1 • Autumn 2013
ONF
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