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.