ATM, Frame Relay, and MPLS – CompTIA Network+ N10-006 – 1.4
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ATM, Frame Relay, and MPLS – CompTIA Network+ N10-006 – 1.4

October 9, 2019


ATM stands for
asynchronous transfer mode. It is a protocol that used Sonet
as it’s transport mechanism, and it was designed use
these 53-byte cells, 48 bytes would be your
data, and then there would be a 5-byte routing
header just before the data was sent over the ATM network. This was designed
to constantly send these cells, which
means that we had a very high speed, high
throughput network, that allowed us to use
real time protocols, and communicate using
voice, or video, or data, over that
same Sonet mechanism, using this ATM protocol. We got maximum speeds of
OC-192, and at the time, these were very, very
high speed networks. We had to limit the speeds
because every time you would pull the data off
of the ATM network it had to be segmented
to put on, and reassemble when it came off. So there was a bit of
overhead associated with that. ATM did not really catch
on, as we thought it might. We ended up having higher speed
ethernet take over on the LAN, and ATM really was never able to
make the jump on the WAN side. On our wide area networks,
we used to put up circuits from one point to the other in
these point-to-point T1 or T3 links were nailed up and we’d
have them up and running all the time, whether we were
sending traffic over that link or not. We started to replace
these point-to-point T1s with something that was
a little more flexible called Frame Relay. In Frame Relay, we
encapsulated our LAN traffic into these frame relay
frames, and we sent them into what we called
a frame relay cloud. We called it a cloud because our
local router would put traffic into the cloud. And this was all
the providers world. We didn’t exactly know how the
data was getting from one point to the other. All we knew was we would
put traffic into the cloud, and then, magically, it would
show up on the other side. And it was the responsibility
of the provider in the middle to be able to make sure the
data was traversing from one end to the other. Now we didn’t exactly
understand what happened inside of the cloud, but
we knew that we were using the bandwidth
in the best possible way. Because if we weren’t
using the connection, somebody else was
using that connection, and that kept the cost down. Certainly less than paying
for a T1 or T3 connection that was always being connected,
all the time, whether we were putting data over it or not. The speeds generally
range from 64 kilobits per second, through these
T3, DS3 type speeds. So we were getting pretty
good throughput, for the time, over these wide area
networks using frame relay. Ultimately, we were getting
better speeds and more flexibility through MPLS. So these days most of
our frame relay networks have evolved and migrated
into MPLS networks. With MPLS, we took
the best part of ATM, and the best part
of Frame Relay, and we put all those
things together to come up with a brand new
wide area network mechanism. This allowed us to
package up data, send it across the network, and
we were able to direct where the traffic goes, based on
something called an MPLS label. This also made it very easy
for the end devices on the MPLS network to know exactly
where the traffic was going because it had a
very easy to follow label. This allowed us to put
really anything inside of this transport mechanism. We could put IP information,
we could put a ATM cells, we could put ethernet
frames, and we were able to run this across
a very common MPLS network. So that really isn’t layer
two, it’s not layer three, it’s somewhere in
the middle if we’re looking to figure out where
MPLS goes on in OSI model. You’re going to find
MPLS in many places this is really the default for
wide area networks these days. If you’re not running just
a standard metro ethernet, it’s very common to
see an MPLS network. This routing process
on an MPLS network is called pushing and popping. When we’re putting information
onto an MPLS network, we push a label onto it, and
we put it into the MPLS cloud. This is a good example
of taking information coming from a
customer edge router, connecting to the first
provider edge router on the MPLS network, and pushing the
route onto that connection. It then finds its way
through the MPLS network, and on the outside,
it pops off the labels and provides the
regional traffic back to the customer edge router,
and the process is repeated to go to the other side. Although we don’t see
much native ATM or Frame Relay on our network
any longer, we can really find the best parts
of both of those contained in our MPLS wide area networks.

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  1. The Frame Relay use the "DLCI" to provide reference of routing, not "magically" go to anther side as you said in this video.

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