Packet optical transport: Hollowing the network core
Wednesday, October 20, 2010 at 5:02PM Intune Networks has developed an optical packet switching and transport (OPST) system that effectively turns fibre into a distributed switch.
The platform enables a fully-meshed metropolitan network
Intune Networks' CEO, Tim Fritzley (right) and John Dunne, co-founder and CTO with software support for web-based services, claims the Irish start-up.
“What we have designed allows for the sharing of the same fibre switching assets across multiple services in the metro,” says Tim Fritzley, Intune’s CEO.
The company is in talks with several operators about its OPST system, which is being used for a nationwide network in Ireland. The system is also part of an EC seventh framework project that includes Spanish operator Telefónica.
OPST architecture
Intune’s OPST system, dubbed the Verisma iVX8000, uses dense wavelength division multiplexing (DWDM) technology but with a twist. Each wavelength is assigned to a particular destination port, over which the data is transmitted in bursts. The result is an architecture that uses both wavelength-division and time-division multiplexing.
To enable the approach, Intune has developed a control algorithm that can switch and lock a tunable laser’s wavelength “in nanoseconds”. Such rapid laser switching enables wavelength addressing - assigning a dedicated wavelength to each destination port.
As packets arrive at the iVX8000, they are ‘coloured’ and queued before being sent on the required wavelength to their destination. In effect packets are routed at the optical layer, in contrast to traditional systems where traffic is packed onto a lightpath that has a fixed predefined point-to-point optical path.
The packets are sent in bursts based on their class-of-service. Intune uses a proprietary framing scheme for transmission, with Ethernet frames restored at the destination. At the input port, all the packets are queued based on their wavelength and class-of-service. The scheduler, which composes the bursts, picks bits to transmit from the queues based on their class, with the bits sent without having to be aligned with a frame’s boundaries.
“Instead of assigning an electrical address to a fixed wavelength, we are assigning electrical addresses to dynamic wavelengths”
Tim Fritzley, Intune Networks
Intune also uses dynamic bandwidth allocation: any bandwidth unused by the higher classes of service is assigned to lower priority traffic. This achieves over 80 percent utilisation of the Ethernet switching and the fibre, says Fritzley.
“You are responding to the dynamic loading of the traffic as it comes in, on a destination-by-destination, colour-by-colour basis,” says Fritzley “Instead of assigning an electrical address to a fixed wavelength [as with traditional systems], we are assigning electrical addresses to dynamic wavelengths.”
The result is a fully meshed architecture with any transponder able to talk to any other transponder on the network, says Fritzley.
System’s span
The network architecture is arranged as a ring with up to a 300km span. The ring connects up to 16 iVX8000 nodes each comprising four 10 Gigabit-per-second (Gbps) ports and switching hardware. Each port is assigned a particular wavelength, equating to a total switch capacity of 640Gbps.
Intune has an 80-wavelength design even though only 64 are used. Indeed it uses two optical rings in parallel. The two rings run in opposite directions, providing optical protection for each port and effectively doubling overall capacity.
For the client side interfaces, the iVX8000 uses four 10 Gigabit Ethernet ports. Since transmissions are in bursts, multiple ports can transmit data to the same destination port even though they share the same wavelength.
The system’s 300km span is an artificial value set by Intune to guarantee “plug-and-play” performance. If the individual chassis are less than 65km apart and the total ring is 300km or under, Intune guarantees no DWDM engineering is required. “We auto-discover all the optical paths and nodes in the network; we automatically adjust all the amplification and set up the dispersion compensation,” says Fritzley. “This saves thousands of engineer-hours and truck rolls.”
Intune points out that it has engineered a 700km network but claims that for distances beyond 1,000km, point-to-point links connecting regions make more sense.
John Dunne, co-founder and CTO of Intune, claims the metro architecture simplifies networking greatly when connecting the network edge to the IP core. “It is different to what is there today because there are no routeing decisions to be made,” says Dunne. “All of the routes pre-exist, and that is because the tunable lasers contain all the colours of all the ports on the ring.”
As a result, setting up a flow of packets between the edge and core involves using a single interface to the ring. “You don’t have to talk to all the [ring’s] elements, you just talk to the ring,” says Dunne. “The ring is pre-engineered so it knows it’s a ring; it also knows how to guarantee the latency, the bandwidth, the jitter of any flow.”
This is the system’s main merit, says Dunne, the pre-engineered ring hides all the difficulty of building a control layer on top of a dynamic optical and layer-two switching system.
Bringing the web into the network
Intune realised that traditional telecom software would struggle to make best use of its distributed optical packet switch architecture. The company has adopted the representational state transfer (REST) software approach for its architecture instead.
“REST is the heart of web services,” says Fritzley. “The reason we did this is that there are hundreds of thousands of programmers that understand how to program it, so you are not into the arcane telecom languages of SNMP and TL1.” Adopting a 'RESTful' approach, claims Intune, reduces code development by 70 percent.
Moreover, REST by its nature is distributed such that it lends itself to supporting distributed transactions across Intune’s switch. “We have put a mini-http server on every card; we do not centralise control inside a node,” says Fritzley. “Every card peers with all of its peer-functions on the ring.”
In terms of the switch's operation, high-level XML commands are used instead of sending low-level instructions to numerous elements. “For example you ask the ring - set up this flow of packets with this bandwidth, this jitter and this delay,” says Dunne. “The ring replies that it can set this up and it performs the low-level stuff internal to the ring."
Such a capability will ultimately enable a machine to provision bandwidth for services, and enable machine-to-machine communications, says Intune. It will also enable third-party application developers to use the switch for service provisioning. This isn’t possible today because there is a lack of control, says Dunne.
“We have a full suite of XML-based interface commands,” he says. “All [the interface commands] would go to the carrier, the carrier would expose a subset to the Googles, the Googles would expose a subset to their application writers, and the application writers would expose a subset to the consumer.” Were the consumer to send a command to request some bandwidth, the call would be passed through the various layers directly into the switch, all in a controlled manner.
Provisioning of bandwidth in such an automated fashion is possible because Intune’s underlying network is bounded and predictable, says Dunne, with the optical path pre-engineered to work with the data path.
Meanwhile until XML becomes more commonplace, Intune uses a code translator that converts the XML code to SNMP or TL1 to interface to existing systems.
“The ring is pre-engineered so it knows it’s a ring; it also knows how to guarantee the latency, the bandwidth, the jitter of any flow”
John Dunne, Intune Networks
Applications
The iVX8000 is being targetted at applications such as cloud computing services and the moving of virtualised environments between data centres. But the real target is using the platform to support multiple services – 3G and 4G wireless backhaul, on-demand IP TV as well as cloud. “No-one can do traffic planning anymore around such services,” says Fritzley.
The platform addresses what one large European operator calls ‘hollowing the core’. The operator wants to simplify its metro network by moving such networking elements as broadband remote access servers (BRASs) to the network edge. These will be connected using a simpler layer-two network that lessens the use of large, expensive IP core routers.”All the IP processing is on the edge and you go edge-to-edge on a flat layer two,” says Fritzley.
Market developments
Intune is using its system to enable the Exemplar network in Ireland. Backed by the Irish Government, the company’s systems will be used to build a nationwide network. The first phase involves a lab for application development and testing. So far 40 multi-nationals have signed up to use the network. Starting next year, a ring network will be up and running around Dublin to be followed with a nationwide roll-out in 2013.
The Irish start-up is also part of an EC Seventh Framework research project called MAINS. The project, which started in January, involves Telefónica which is using the iVX8000 to move virtualised resources between data centres depending on user demand and latency requirements. The project uses XML commands to call for bandwidth from the networking layer.
Meanwhile, Intune says that it is “deeply engaged” with four to five of the largest operators in North America and Europe.
Reader Comments (1)
It is good to see that optical burst switching is taking off on the market. It is time for the telecoms industry to get rid of the rigidity and inefficiency of currently used fixed pipes and adopt felxible and easily reprogrammable networking technologies. Simply substituting 10G fixed pipes by 100G fixed pipes may bring more bandwidth in the network, but will still keep the rigidity and inefficiencies that are at the root of the problems today.