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).