Metro area networks have come a long way since the leased lines and SONET rings of yore. True, they are still widely deployed and extremely versatile technologies, but as user applications increasingly feature voice and data convergence and high-bandwidth/low-latency requirements, carriers are changing their metro area networks to support these applications. To understand how metro area networks are evolving, it makes sense to examine enterprise network architectures and the applications they need to support.
Enterprise WANs connect three distinct types of sites, according to Nemertes analyst Katherine Trost:
- Tier 1: Data centers
- Tier 2: Distributed offices
- Tier 3: Remote offices and users
Metro area networks are most commonly used to connect sites at the "top tier" of the WAN, which includes data centers, contact centers, administrative headquarters and some (but not all) distributed offices. These tier 1 sites are typically geographically close, and the applications located there generally move massive volumes of data. As a result, they need very low latency and very high reliability. Tier 1 WAN sites are perfect for metro area networks based on technologies including dedicated fiber, dense wave-division multiplexing (DWDM) and, more and more often, Carrier Ethernet.
Source: Nemertes Research
Carrier Ethernet suited for data center replication and call centers
Data center storage replication is one of the most common applications at this tier of the WAN. Enterprises continue to consolidate multiple data centers down to a handful, then use data center replication between two or three data centers to ensure reliability and redundancy. Often, two data centers will replicate synchronously over the metro area, typically using Fibre Channel as the core communications protocol. The theoretical maximum length of a synchronous Fibre Channel connection is on the order of 120 miles (depending on the bandwidth of the link). But latency is typically the primary gating factor, and the maximum practical distance for synchronous replication is roughly 30 miles.
Options for synchronous connection include Fibre Channel over SONET, Fibre Channel over DWDM and, potentially, Fibre Channel over Ethernet (FCOE). But future deployment of FCOE across the WAN will depend largely on the degree to which FCOE achieves acceptance within the data center, and here a large question mark remains. We found near-zero adoption of FCOE within data centers, with low planned usage for the next 24 months.
Another common metro-area application is connectivity into contact centers (call centers), which may handle hundreds of thousands of phone calls simultaneously. As enterprises move toward a converged voice and data architecture, incoming calls are carried across the WAN rather than across dedicated voice private lines, as they were previously. But ordinary WAN services such as Multi-protocol Label Switching (MPLS) may suffer from route-convergence problems: If a logical link fails, it may require multiple seconds for the network to re-establish connectivity. For most traffic, this isn't a problem, but an outage of several seconds is long enough to cause callers to a contact center to hang up in frustration.
With Carrier Ethernet, however, the connections can be engineered at layer 2, avoiding the route-convergence problem altogether. So service providers are increasingly turning to Carrier Ethernet and other technologies that support both voice and data and also can provide real-time redundancy.
The growth of high-bandwidth applications in the metro
Administrative headquarters often require metro-area connectivity, particularly in organizations (such as higher education institutions and state and local government) where many offices are in close proximity in a campus environment. Here, too, we see a greater-than-typical use of Carrier Ethernet (virtually all of the organizations Nemertes works with in both verticals have some degree of Ethernet in use in their metro-area networks). The use of Carrier Ethernet is likely to grow as high-bandwidth applications like video conferencing, telepresence, streaming video and distance learning increase.
The use of these applications is rising steeply today, driven by several related (but not identical) trends:
- Increasing acceptance of the "virtual workplace." Nearly 90% of organizations consider themselves "virtual workplaces" -- meaning that they actively encourage collaboration among employees or workers who are geographically separated.
- Travel restrictions (79% of organizations say travel restrictions have increased the use of video conferencing).
- Increased deployment of streaming video, particularly for training applications and distance learning.
The common theme across all these applications and WAN architectures is Ethernet. As voice and data converge, and as Ethernet becomes as widely deployed within data centers as Fibre Channel, Carrier Ethernet becomes the logical way to achieve high-bandwidth, low-latency links across the metro area. And those enterprises that deploy it, love it: Seventy-nine percent say they're "extremely happy" with their Ethernet deployments, and the vast majority say they expect to deploy more Carrier Ethernet in the near future (see graphic).
The bottom line is that we have seen the future of metro-area networks, and it's increasingly Carrier Ethernet. Low-latency, high-bandwidth, "cheap and cheerful" Ethernet services meet the needs of those tier 1 WAN sites that are close enough together to be served by a metro-area network.
About the author: Johna Till Johnson is the president and senior founding partner of Nemertes Research. She has decades of experience in IT structure, processes and organizations, and has worked closely with senior IT executives at leading organizations across a broad range of industries. A highly regarded expert, Ms. Johnson regularly speaks at trade shows, conferences and seminars.
