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March 13, 2017

Port Extender Technology Changes Network Switch Landscape

By George Hervey, Principal Architect, Marvell

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Our lives are increasingly dependent on cloud-based computing and storage infrastructure. Whether at home, at work, or on the move with our smartphones and other mobile computing devices, cloud compute and storage resources are omnipresent. It is no surprise therefore that the demands on such infrastructure are growing at an alarming rate, especially as the trends of big data and the internet of things start to make their impact. With an increasing number of applications and users, the annual growth rate is believed to be 30x per annum, and even up to 100x in some cases. Such growth leaves Moore’s law and new chip developments unable to keep up with the needs of the computing and network infrastructure. These factors are making the data and communication network providers invest in multiple parallel computing and storage resources as a way of scaling to meet demands. It is now common for cloud data centers to have hundreds if not thousands of servers that need to be connected together. 

Interconnecting all of these compute and storage appliances is becoming a real challenge, as more and more switches are required. Within a data center a classic approach to networking is a hierarchical one, with an individual rack using a leaf switch – also termed a top-of-rack or ToR switch – to connect within the rack, a spine switch for a series of racks, and a core switch for the whole center. And, like the servers and storage appliances themselves, these switches all need to be managed. In the recent past there have usually been one or two vendors of data center network switches and the associated management control software, but things are changing fast. Most of the leading cloud service providers, with their significant buying power and technical skills, recognised that they could save substantial cost by designing and building their own network equipment. Many in the data center industry saw this as the first step in disaggregating the network hardware and the management software controlling it. With no shortage of software engineers, the cloud providers took the management software development in-house while outsourcing the hardware design. While that, in part, satisfied the commercial needs of the data center operators, from a technical and operational management perspective nothing has been simplified, leaving a huge number of switches to be managed. 

The first breakthrough to simplify network complexity came in 2009 with the introduction of what we know now as a port extender. The concept rests on the belief that there are many nodes in the network that don’t need the extensive management capabilities most switches have. Essentially this introduces a parent/child relationship, with the controlling switch, the parent, being the managed switch and the child, the port extender, being fed from it. This port extender approach was ratified into the networking standard 802.1BR in 2012, and every network switch built today complies with this standard. With less technical complexity within the port extenders, there were perceived benefits that would come from lower per unit cost compared to a full bridge switch, in addition to power savings. 

The controlling bridge and port extender approach has certainly helped to drive simplicity into network switch management, but that’s not the end of the story. Look under the lid of a port extender and you’ll find the same switch chip being used as in the parent bridge. We have moved forward, sort of. Without a chip specifically designed as a port extender switch vendors have continued to use their standard chips sets, without realising potential cost and power savings. However, the truly modular approach to network switching has taken a leap forward with the launch of Marvell’s 802.1BR compliant port extender IC termed PIPE – passive intelligent port extender, enabling interoperability with a controlling bridge switch from any of the industry’s leading OEMs. It also offers attractive cost and power consumption benefits, something that took the shine off the initial interest in port extender technology. Seen as the second stage of network disaggregation, this approach effectively leads to decoupling the port connectivity from the processing power in the parent switch, creating a far more modular approach to networking. The parent switch no longer needs to know what type of equipment it is connecting to, so all the logic and processing can be focused on the parent, and the port I/O taken care of in the port extender. 

Marvell’s Prestera® PIPE family targets data centers operating at 10GbE and 25GbE speeds that are challenged to achieve lower CAPEX and OPEX costs as the need for bandwidth increases. The Prestera PIPE family will facilitate the deployment of top-of-rack switches at half the cost and power consumption of a traditional Ethernet switch. The PIPE approach also includes a fast fail over and resiliency function, essential for providing continuity and high availability to critical infrastructure.

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