Undergraduate
Student: Estella
Kang
Graduate Student: Matt
Powers
Professor: David
Starobinski
SC441 Introduction to Computer
Networks
Boston University
Metropolitan Ethernet Networks:
The demand for more reliable, cost-effective, and high-speed
networks rises as more businesses and individuals seek for high-quality
voice, video, and data transfers. Currently, the predominant architecture
SONET/SDH (Synchronous Optical Network/Synchronous Digital Hierarchy)
deployed in MAN (Metropolitan Area Network) is expensive, lacks scalability,
and has limited bandwidth capability. To improve the current technology
in MAN, the existing Ethernet, the best technology for carrying IP traffic
and usually implemented in LAN (Local Area Network), has been coupled
with carrier-class control DWDM (Dense Wavelength Division Multiplexing)
equipment to reduce cost, increase speed, and create network flexibility.
The main advantage of the Ethernet MAN is its cost-effectiveness.
Due to the widespread acceptance of its protocol, the Ethernet interface
itself is very inexpensive. This technology was developed 30 years ago
and is now the predominant technology connecting computers on a corporate
network. According to the Federal Communications Commission, Ethernet
equipment can cost anywhere from 40% to 50% less than its counterparts,
such as SONET/SDH and ATM (Asynchronous Transfer Mode). In addition, service
and operational cost is reduced because when updating systems over time,
traditional SONET/SDH service require technicians to be on site, whereas
Metro Ethernet upgrades can be done remotely using software.
In addition, many Metro Ethernet providers allow their
subscribers to add bandwidth as needed, by segregating traffic of different
users and delivering the particular service level each user purchases.
Traffic segregation is accomplished by marking each user’s traffic
with a virtual LAN tag as it enters the network, and keeps this traffic
separated as it crosses the network. This scalability can range from 1Mbps
to 10Gbps, and even to ultra high speeds of 100Gbps. These speeds allow
video broadcast and conferencing, storage and disaster recovery, as well
as business telephony. One challenge is to increase the number of possible
VLAN tags from thousands to millions.
Other advantages include fewer protocol conversions,
better network management, more skilled professionals in the field. Also,
customers can mix voice and data traffic on one medium, and thus cutting
overhead cost.
Also, because Ethernet MAN is implemented over existing
Ethernet infrastructure, network resiliency and protection should be improved.
Recovery rate from link failures has reduced from 45 seconds to mere seconds.
Nevertheless, SONET/SDH, which is deployed in fiber rings, is able to
detect and recover from link errors within 50 ms. Ethernet does not have
correction features, hence it relies on Ethernet protocols to restore
service. This has resulted in vendors layering Ethernet on top of SONET/SDH
technology, enabling carriers to use their existing infrastructure.
In conclusion, even though each technology has its advantages/disadvantages
in different areas, Ethernet benefits of flexibility and simplicity outweigh
its weaknesses. SONET/SDH has long been the predominant architecture but
it was designed for slow-growing, constant-rate voice traffic –
not for the present rapidly growing data traffic. Its rigidity and lack
of scalability make it an expensive solution that is difficult to manage
in an environment where bandwidth demands are continually increasing.
However, the Ethernet MAN adds traffic engineering and management capabilities
carriers need, and integrates these with optical networking to deliver
the distances and speeds required to traverse metropolitan areas.
