What makes a successful MAN?: The successful delivery of high-speed services across the MAN will be dependent on the combined implementation of new metro technologies - Value-added services - Brief Article

Until recently, the development of the metropolitan area network (MAN) had been restricted by the incumbent technology of mid-capacity synchronous digital hierarchy (SDH) rings. But now, technical advances in optical infrastructure equipment are breaking the bandwidth bottleneck and bringing high-speed connectivity to the metro.

These new technical developments in the MAN have a critical role to play in the delivery of services to end-users. From basic e-mail, remote access, videoconferencing, hosted applications and virtual private networks (VPNs), the growing array of networking applications demands that providers offer tiered levels of services so that their customers can buy the right one for each offering. To deliver these services, providers need highly granular control over the quality of service (QoS) they deliver to each customer or application. To do this, they will have to rely on the developments of optical technologies - namely dense wavelength division multiplexing (DWDM), 10 gigabit ethernet, multi protocol label switching (MPLS) and resilient packet rings (RPRs).

The promise of DWDM

The greatest advances in optical networking have been made in the long-haul core. In this area, it is difficult to understate he significance of dense wavelength division multiplexing (DWDM) technology. DWDM holds great future promise for optical networking in the metropolitan envionment because it allows more efficient use of fibre already in place by simultaneously transmitting multiple wavelengths over a single one. Indeed, most metro areas have an existing fibre infrastructure which makes the implementation of a DWDM solution into an upgrade of existing deployments (more specifically, replacing SDH signalling equipment) a reasonably easy task, This is a critical factor in the metro environment because obtaining the necessary rights-of-way for new deployments can be difficult in densely populated areas. The provision of DWDM bandwidth, however, is fast and flexible.

DWDM, though, does have its problems. The most notable being that DWDM equipment is extremely expensive. These costs have previously been easy to justify on the long-haul network, where the greatest costs come from laying fibre and regeneration tools over significant distances. But in the MAN, the length from one point to another is much shorter and signal generation equipment costs predominate. In addition, DWDM continues a share some of the limitations of SDH technology. In particular, it lacks service awareness capability. This creates a need for an extra overlay to provide the tiered services for different application flows that are increasingly sought after in the metro environment. WDM wavelengths also present special switching and routing challenges. While DWDM is a technology with bright long-term prospects in the MAN, it will probably be a solution that comes in gradually in conjunction with other optical networking solutions.

Indeed, over the last year, 10 gigabit ethernet, MPLS and RPRs have also emerged at the forefront f metro networking. Each of these technologies individually adds features to MANs that are currently lacking but little attention has been focused on the question of how they ore meant to work together. There is no debate that they will co-exist and need to interoperate with each other (along with legacy technologies), but there is an unfortunate tendency to describe each one individually as the 'magic bullet' which will relieve all service provider concerns. But the combination of these technologies, however, could be the answer to the future of metro networking.

10 gigabit ethernet

Today's network-based applications are business-critical and include corporate local area network (LAN) connection, backend server connections, real-time streaming and telecommuting. Beyond the obvious need for higher bandwidth, all of these applications have several requirements in common, such as the need to be feature-rich, work across converged networks, and be accessible and reliable. Ethernet meets these requirements but it has so far lacked the scalability to serve the MAN.

The development of 10 gigabit ethernet promises to remove this restriction and offer a new option for data transport over dark fibre or DWDM. Driven by the desire to interconnect ethernet LANs that may now be operating at 10Mbps, 100Mbps or even 1 Gbps, standards for 10 gigabit ethernet are being developed by The Institute of Electrical and Electronics Engineers (IEEE) and will be promoted in the marketplace by The 10 Gigabit Ethernet Alliance (10GEA). Drafts are now available and the formal standard is expected in early 2002, with conforming products and deployments arriving shortly afterwards. In the meantime, there are now some proprietary products that can support existing ethernet networks in the MAN. The forthcoming 10 gigabit ethernet standard will carry distances of up to 40km over singlemode fibre with a physical media dependent layer for 1550 nanometer serial lasers, rated at up to 80km.

by Richard Benwell