Metropolitan-area networks (MANs) are attracting the attention of enterprises and service providers alike. As enterprises fully comprehend the benefits in productivity afforded by increased connectivity and bandwidth extended from the local-area network (LAN) environment to the MAN, service providers drive toward new revenue streams enabled by the high-value data, voice, and video services their customers demand. Central to this dynamic and the current evolution of the MAN is the ubiquity of Ethernet in enterprises and the corresponding introduction of data to traditional time-division multiplexed (TDM) networks.
Multiple technology approaches exist today, which can bridge the gaps and
enable cost-effective Ethernet deployment over the MAN to drive productivity
for enterprises and profitability for service providers. Chief among these
are SONET/SDH, DWDM, and Ethernet switching. Several factors must be
considered in selecting the solution that best suits the service provider
and its enterprise customers and often it may be some combination of the
three that provides the optimal scenario to address the diverse needs of the
ENTERPRISE APPS OVER THE METRO It all begins with the needs of the enterprise; and primary among these
is the need for greater productivity. Foremost, enterprises want a way to
voice-network their branch offices together. Closely following that is the
need to create a seamless, high-bandwidth data network for information
sharing. Finally, outsourcing network operations, storage, and content
networking round out the list of major requirements. Due to a number of
challenges with regard to reliability, availability, efficiency, and
integration, enterprises have had to build separate parallel networks to get
these applications running. For example, the service enterprises have
received from their providers has been excellent for voice applications with
five-nines availability and reasonable tariffs. However, the bandwidth
available for data is typically 1.5 Mbps or 45 Mbps, compared to 1,000 Mbps
available inside the buildings. Additionally, two separate network
monitoring mechanisms as well as limited visibility beyond the LAN give rise
to difficulties instating and maintaining service level agreements (SLAs).
Finally, with two separate networks to support key applications, adding a
new site is cumbersome and often takes months.
From a business standpoint, if all applications were run over the same
network, it would result in tremendous capital and operational cost savings
as well as greater efficiency and productivity.
METRO SERVICE CHARACTERISTICS On the other side of this equation, service providers can now augment
revenue streams by offering data services in addition to TDM transport,
increasing service density and profitability in the metro. However,
established carriers face challenges in restructuring their business and
retooling their networks to deliver these benefits to their enterprise
An effective data service would allow the customer to increase bandwidth
in increments, add new sites to their network quickly and with little
effort, transparently extend the LAN network architecture at layer-2 or
layer-3, and effectively manage SLAs. Most importantly, the provider has to
offer data services at price points that are not out of line with current
These requirements pose specific challenges to existing service providers
and their SONET/SDH-based networks. When this service network connects to
the customerï¿½s data equipment, whether via LAN switch or a router, the
service network cannot manage the device. Additionally, increased data
bandwidth has to be provisioned throughout the service network, one node at
a time, which is very time consuming and prohibitive to an incremental
model. Lastly, bandwidth allocation models in TDM networks can often add to
the cost of service.
Clearly the carrier TDM networks must change to effectively deliver data
services and enable greater profitability for service providers. The optimal
network architecture is one that meets evolving requirements of service
delivery with minimal disruption to existing TDM service and revenue,
provides an Ethernet interface to the enterprise, and delivers scalability
to meet future requirements as demand increases.
SOLUTIONS ABOUND There are several technologies including SONET/SDH, DWDM, and Ethernet
switching that can pave the way for cost-effective Ethernet services in the
MAN. The exact formula depends on the unique requirements of a specific
provider, and often it may be a combination of several solutions that
provides the best infrastructure for current as well as future demands.
Metro SONET/SDH Networks Most existing service providers have SONET/SDH-based metro-area
networks. These networks are not traditionally optimized for data networking
but can evolve into very effective service delivery vehicles. As a first
step, these networks can be augmented at the metro edge with multiservice
provisioning platforms, or MSPPs, that support both traditional TDM and
offer Ethernet interfaces to customers. These multiservice platforms can map
Ethernet frames to SONET/SDH payloads. This technique creates effective
Ethernet services such as Ethernet private line offerings. As flexible MSPPs
continue to accelerate the ongoing evolution toward data-centric networks,
it appears that most existing providers are likely to deploy Ethernet ports
and data services over SONET/SDH networks in the near future.
Metro DWDM Networks Dense wavelength division multiplexing (DWDM) technology can be used
either as a bandwidth multiplier or as a service segregator. In the first
application, DWDM gear would be implemented underneath SONET/SDH to create
multiple virtual rings for additional bandwidth. For instance, if an OC-48
ring were fully utilized to deliver private line Ethernet service, the
provider could build more such rings over the same fiber using DWDM
equipment underneath MSPPs. In this case, each virtual network design would
be similar to the one described for Metro SONET/SDH. In the second case, a
wavelength can be allocated to a particular service offering, and different
wavelengths in the aggregate would create the complete provider network.
Such DWDM equipment would have a variety of service interfaces like ESCON,
FICON, Fibre Channel, and Gigabit Ethernet and traffic from each interface
would be mapped to a wavelength on the service ring.
Advances in technology would also allow the mapping of many services over
a single wavelength. It is also possible for these DWDM platforms to provide
functions like ring protection, separate communication channels, and ability
to carry TDM traffic without the use of SONET/SDH framing.
Metro Networks With Switched Ethernet Finally, it is quite possible for the service provider to build service
networks out of the same set of switches used by the enterprise to create
their LANs. These switches would implement both the customer virtual LAN or
VLAN control plane and the MPLS control plane to be able to interface with
the enterprise customer at layer-2 or layer-3. Using the VLAN control plane
would allow enterprises to extend their VLANs across the MAN. This would not
be a dominant design as most enterprises connect to the MAN/WAN using
layer-3, or IP technologies. An alternative for the provider would be to
implement an MPLS control plane in the network, and provide Ethernet, ATM,
and Frame Relay services to the enterprises at the edge. The benefit to an
Ethernet-switch-based network approach is the commonality between the
provider and the customer network, thereby easing the provisioning, and
management aspects of the data service.
Which Is The Right Solution? Perhaps a better question to ask is what network would an individual
provider want to choose, and when? Existing providers will be using all the
above technologies in their networks at various locations. For example,
parts of a network will run SONET/SDH for traditional voice services and in
other parts the SONET/SDH would be augmented with DWDM technologies for
additional bandwidth. Many of their edges would have Ethernet interfaces
mapping Ethernet frames to SONET/SDH while new build-outs in certain areas
may be comprised of packet switches and all traffic from customers would
converge over Ethernet frames. The key to prosperity for the service network
CONCLUSION Metro networks built over fiber will look very different from current
implementations. Ethernet will continue to gain prominence, and the new
metro service network will implement SONET/SDH, DWDM, and Ethernet switching
technologies in various parts of the network. The challenge for providers
will be to adopt these new technologies for cost-effective Ethernet
deployment and couple them with their proven business models and existing
revenue streams to create valuable data services that lead to increased
profitability and enable maximum productivity for their enterprise
Cecil Christie, is product manager, Optical Networking, at Cisco
Systems, Inc. Cisco Systems is a worldwide leader in networking for the
Internet. Information on Cisco can be found online at www.cisco.com.
As more and more of todayï¿½s businesses migrate to a ï¿½switched Ethernet-to-the-desktopï¿½ topology, which connects each desktop at speeds of up to 10 Mbps (or more), the issue of slow WAN (wide-area network) links is becoming especially important. Although transparent LANs (local-area network) are established technologies with multiple methods of transport delivery, they are usually connected to other building/campus environments through slower speed WAN connections. For instance, many companies with 1 Gbps LAN backbones are often connected by much slower WAN links, significantly affecting overall performance.
In the past, the solution to this problem has often required a private line facility between two locations. However, this introduces distance constraints that can often apply to native Ethernet. Until very recently, this could severely limit the range that can be bridged without a Layer 3 solution. And, a private line solution can be a very expensive dedicated access service. In fact, the premium pricing of private lines resulted, in some part, in the development of Frame Relay and ATM technologies as a way to achieve similar functionality at a lower cost.
Unfortunately, none of these incremental speeds have a one-to-one correspondence with LAN backbone speeds (10, 100, 1,000 Mbps), and therefore they are not easily adaptable to provide seamless transport from LAN to LAN.
Making Metro Ethernet The Standard To maximize the opportunity for enterprise businesses, some carriers have determined that metro Ethernet services should be a carrier-class, Layer 2 transport service delivering scalable, dedicated, protected, and guaranteed bandwidth.
Carriers that can provide all customer-premise transport equipment, while charging only a flat monthly fee for the service, provide a predictable pricing solution and may be the best option. These carriers can simplify the customerï¿½s network management and costs by frequently eliminating Layer 3 equipment that would be necessary to accomplish the transport requirement by directly connecting Layer 2 switches, all of which is transparent to the customer.
In addition, Gigabit Ethernet solutions have also become a way to simplify the provisioning of IP transport. A layer 3 solution, ï¿½GigEï¿½ is typically sold in denominations of 1 Mbps. However, this type of solution is more of an IP-VPN with Ethernet connections, which is very useful for general Layer 3 applications, but not necessarily for direct Layer 2 to Layer 2 connectivity. For instance, Layer 3 overhead and latencies will be higher, even if the IP networks are not oversubscribed.
Ability To Connect More Than Two Sites With metro Ethernet capabilities, carriers can easily solve the problem of connecting multiple sites by offering point-to-point and any-to-any connectivity options. With this, all locations can seamlessly communicate with each other.
The any-to-any option is an excellent managed solution for some customers, but the best approach depends on the customerï¿½s specific needs and current approach to network management. While any-to-any provides many benefits, including full duplex dedicated bandwidth without frame collisions and high efficiency between sites, some customers may prefer to manage their own site-to-site connectivity. In such cases, businesses can use point-to-point circuits that can be managed with the businessï¿½s own switching hardware.
Current demographic trends favor an increasing use of outsourced IT support, due to the difficulty in acquiring and retaining IT staff, and by delegating the transport management to the carrier, customers can spend more time on their core business.
Overall Cost Advantage Although Private Line, Frame Relay, and ATM transport have dominated connectivity in the past, the simple truth is that metro Ethernet services can be more cost effective for businesses on a price-per-bit basis. Customers can easily upgrade their dedicated bandwidth to LAN backbone speeds for less money, on a price-per-bit basis, than they would pay to connect through other methods of transport.
Many factors will contribute to the success of metro Ethernet services. In addition to the favorable economics of such a solution, metro Ethernet also provides scalable bandwidth that can be provisioned in days rather than months. Full-rate circuits often take as long as six months to provision, and usually at lower bandwidth capability, through traditional methods. Overall, metro Ethernet will provide strong competition for the existing installed base of private line, Frame Relay, and ATM.
Garrett Hess is a senior product manager of Ethernet Services at XO Communications. Please visit the companyï¿½s Web site at
Ethernet in the metro area is a technology ablaze. The tremendous growth
in worldwide data traffic has pushed the legacy SONET-based network
infrastructure to its limits, leaving a bottleneck in the metro and a need
for new technologies that can scale to accommodate this growth. Rapid
improvements in speed, network reach, and production costs make Ethernet,
which already serves 98 percent of all Internet end points, a logical choice
as the next ï¿½bottleneck-busterï¿½ technology. Metro Ethernet leverages a
massive installed base to offer the most cost-effective, scalable, and
reliable alternative to the current infrastructure.
Industry analysts are nearly unanimous in projecting that metro Ethernet
services will become a multi-billion dollar market within a very few years.
According to the Gartner report, The Ethernet MAN Service Opportunity,
issued August 23, 2001, ï¿½Ethernet is poised to do to metropolitan-area
networks (MANs) what it did to local-area networks (LANs) in the 1990s:
Ethernet-based MANs have the potential to overcome high-cost, extra-office
connectivity bottlenecks. A market inflection point could be emerging for
enterprise data telecommunications services in metropolitan areas around the
Metro Ethernet offers a host of advantages in optical access networks in
that they are more cost-effective, scalable, and reliable than competing
Cost-Effective Analysts at Dellï¿½Oro Group project that the cost advantage of Ethernet
equipment over legacy SONET gear will grow from about 7:1 today to 10:1 by
2004. Metro Ethernet allows for the rapid creation of new services, thus
expanding revenue-generating opportunities for the service provider. Metro
Ethernet also lowers operational costs because it is easier to provision,
requiring fewer truck rolls and less maintenance.
Metro Ethernet can scale instantly from 1 Mbps to 1,000 Mbps within the same
box, and offers more granularity than other technologies. The next
standards-based generation of 10 Gigabit Ethernet equipment will soon raise
this speed another order of magnitude. Because Ethernet is packet-based,
bandwidth can be utilized more effectively than legacy architectures
designed for voice services.
Industry vendors are rapidly bringing enterprise-oriented Ethernet equipment
up to carrier-class standards to support five-nines of reliability in fiber
Worcester Telegram & Gazette
The advantages of metro Ethernet are not merely theoretical; they are
demonstrated by numerous successful deployments at customers like the
Worcester Telegram & Gazette, the second largest newspaper in
Massachusetts. Immediately following the terrorist attacks of September 11,
2001, the paper needed a five-fold increase in Internet speed on a momentï¿½s
notice to meet critical operational requirements. Journalists and editors
were scrambling for news and background information on the Internet, and
production staff needed to upload huge volumes of text and photographs to
the paperï¿½s hosted Web site to meet the publicï¿½s demand for timely
information. Their baseline 2 Mbps metro Ethernet network, provided by Yipes
Communications (www.yipes.com), was
scaled instantly to deliver 10 Mbps. After the emergency, the paperï¿½s need
for extra service diminished, and they were able to control costs by
returning to their original bandwidth. The paper could not have met its
needs with legacy fixed-bandwidth services, such as T-1 lines, which take
weeks to provision and require customers to purchase and maintain extra
San Francisco-based Bang Networks (www.bangnetworks.com)
tells another successful metro Ethernet story. Faced with long lead times by
their local phone company, Bang Networks was looking for a solution that
could offer them scalability, flexibility, and short time-to-market. Telseon
(www.telseon.com) was able to provide a
cost-effective solution that has allowed Bang Networks to connect their
co-location facilities more effectively to multiple Internet Service
Providers in metro areas. This delivery of large amounts of bandwidth was
achieved using standard Ethernet technology instead of SONET-based services,
making it possible at much lower capital costs.
Wolverine Trading, L.P. (www.wolve.com),
one of the largest equity and equity options trading firms in the world is
also taking advantage of metro- and wide-area Ethernet. Replacing a legacy
network of T-1 lines, Wolverine now uses multi-megabit MAN services from
Yipes to connect its headquarters to the Chicago Stock Exchange, Chicago
Board Options Exchange, Chicago Mercantile Exchange, Chicago Board of Trade,
and its clearing firm, First Options. Wolverine has also connected its San
Francisco office over a 3 Mbps Yipes NAN (National-Area Network), a Layer 2
Ethernet service scalable from 1 Mbps to 1,000 Mbps in 1 Mbps increments. It
has contracted for similar NAN services to its New York and Philadelphia
offices. Wolverine communicates with its London office over a secure VPN,
using a 5 Mbps Yipes pipe to the Internet.
Optical Ethernet networks are leading a revolution that will truly enable
advanced Internet applications. As Charles Rutstein of Forrester Research
puts it, ï¿½This is one of those massive, fundamental shifts that come along
every several years ï¿½ the shift being the move from very complex, old
networking technologies to much simpler and much cheaper networking
Ron Young is chairman of the board and director for the Metro Ethernet
Forum, and co-founder and chief marketing officer for Yipes. For more
information, please visit www.metroethernetforum.org