Service chaining is not a new concept, but the trend has taken on a new importance with the rise of SDN and Network...
Functions Virtualization (NFV).
A service chain simply consists of a set of network services, such as firewalls or application delivery controllers (ADCs) that are interconnected through the network to support an application. But SDN and NFV can make the service chain and application provisioning process a whole lot shorter and simpler.
In the past, building a service chain to support a new application took a great deal of time and effort. It meant acquiring network devices and cabling them together in the required sequence. Each service required a specialized hardware device, and each device had to be individually configured with its own command syntax. The chance for error was high, and a problem in one component could disrupt the entire network.
Moving network functions into software means that building a service chain no longer requires acquiring hardware.
Adding to the difficulty, application loads often increase over time, so building a chain that would not have to be immediately reconfigured meant estimating future demand and over-provisioning to support growth. Devices needed to be sized to support the maximum level of demand -- something which might only occur at particular times of the year. Yet extra capacity has meant extra capital investment.
The effort required to construct a chain also meant that chains were often built to support multiple applications. As a result, data sometimes passed through unnecessary network devices or servers and consumed extra bandwidth and CPU cycles.
SDN and NFV simplify service chains
Two recent developments -- SDN and NFV -- now enable network managers to quickly and inexpensively create, modify and remove service chains.
SDN moves management functions out of the hardware and places it in controller software that executes in a server. A standardized configuration protocol between the controller and network devices replaces proprietary device configuration languages. As a result, entire service chains can be provisioned and constantly reconfigured from the controller. In that scenario, the chance for error is much smaller since the controller software has an overall view of the network, reducing the chance for inconsistent device configurations.
NFV moves network functions out of dedicated hardware devices and into software. Functions that in the past required specialized hardware devices can now be performed on standard x86 servers. Specialized packet handling hardware has been added to standard servers to make this possible.
Moving network functions into software means that building a service chain no longer requires acquiring hardware. Network functions typically execute as virtual machines under control of a hypervisor. When more bandwidth is required, an additional virtual machine can be provisioned to take part of the load, or the initial VM can be moved to a higher capacity server or to one that is less heavily loaded by other applications. There's no need to overprovision since additional server-based capacity can be added when needed.
Connections between service chain components may be contained within a single virtualized server or may cross network links between servers. Traffic may be contained within a VLAN or by one of the technologies being developed by vendors to address VLAN limitations, such as VXLAN tunneling.
SDN and NFV service chains change the service provider model
Because communications service providers and public cloud providers carry such a wide variety of data types and applications, SDN and NFV-driven service chaining can improve their business models just by simplifying the service chain provisioning process.
Cloud providers must host enterprise applications that access databases and make bulk data transfers to and from customers' private networks constantly; meanwhile, communications service providers carry email, voice, video, Web traffic and downloads. Each data type benefits from specific types of related services. With SDN and NFV, providers can create service chains tuned to each data type and ensure the level of service each customer purchases as a result. What's more, they can do this provisioning more quickly and for less money.
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For service providers, a service chain may consist of an edge router at the customer premises, followed by deep packet inspection (DPI). The DPI service determines the type of traffic and signals the controller software to create a service chain for that packet stream and that customer.
An email service chain, for example, would include virus, spam and phishing detection and could be routed through connections offering no delay and with jitter guarantees. Web traffic would be routed through a chain that includes virus scanning and an ADC. The chain created for video and voice traffic would include traffic shaping, so that traffic would be routed over links with the level of delay and jitter guarantees purchased by each customer. Each type of stream would receive only the services needed, skipping the unnecessary ones.
SDN or NFV service chaining also makes the process of network upgrade simpler. Communications service providers, for example, have networks that are geographically distributed, so upgrading equipment requires travel. In addition, a single error can bring down the entire network and cause outages on interconnecting providers' networks. But with SDN and NFV, providers can create new chains that increase the efficiency and the capacity of their networks without radically changing hardware.
Finally, service providers can use new service chaining techniques to generate revenue from applications. Until now third parties have delivered services such as video on demand over service provider networks, while service providers themselves have been unable to enter these markets because of the complications involved in provisioning. But service chaining enables them to more efficiently embed applications and related services in the network itself, placing them at an advantage over the third party provider.
SDN and NFV and their use in building service chains are very recent developments. Vendors have begun exploring the technology and developing management tools that will simplify their use. As experience with the techniques accumulates and network managers see their benefits, service chains based on SDN and NFV will become a standard component of clouds and service provider networks.
About the author:
David B. Jacobs of The Jacobs Group has more than twenty years of networking industry experience. He has managed leading-edge software development projects and consulted to Fortune 500 companies as well as software start-ups.