Introduction
I
remember installing Ethernet nearly two decades ago.
Over the years, Ethernet has killed off all of its
competitors in the LAN arena.
Now it is making inroads in the metro and long haul
networking space. With
Ethernet feeding the voice over IP frenzy, and MPLS delivering
ATM-like traffic engineering, could Ethernet finally kill ATM?
SONET? Circuit
switching? Although
these questions have been debated before, one simple truth
worth noting is that Ethernet’s low cost and simplicity
trumps technical advantages of higher cost alternatives.
This tutorial evaluates Ethernet’s place in metro and
long haul networks using optical interfaces.
Distance
Limitations: A Thing of The Past
Ethernet is now a full duplex,
point-to-point layer-two protocol that no longer has any
possibility of collisions. This means we can forget about
Carrier Sense Multiple Access Collision Detect (CSMA/CD).
Essentially, this means the distance limitation of the
Ethernet protocol is unrestricted. Of course, in practicality Gigabit Ethernet is restricted to
certain distances. This has nothing to do with the Ethernet
protocol and concerns optical transmission effects, such as
modal dispersion, chromatic dispersion, material dispersion,
waveguide dispersion, and attenuation, which are beyond the
scope of this article.
Multiple
Customer Support
If we are going to take Gigabit Ethernet seriously as a metro
architecture, it better be able to support multiple customers
on a single network. Users within the same company want to be
on the same network even though they may be spread out in
different buildings around a city.
Figure 1
This problem has been solved for quite some time.
It is called VLAN (Virtual LAN) and was intended to be an
enterprise solution. Metro
Ethernet service providers are now providing high-speed
connectivity using the VLAN concept (Yipes!). Is there a
security risk from this model? Couldn’t one company sniff
another company’s traffic? The answer is no, no, no!
Even though VLAN uses the same Ethernet backbone, each
customer’s frames are tagged as belonging to that specific
customer and are only forwarded to the Ethernet ports
belonging to that customer. This makes it impossible for one
company to sniff another company’s Ethernet traffic, unless
they get access to the Ethernet trunks, which of course must
be secured by the carrier.
There is no difference from any other statistical
multiplexing technology.
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