So what do we do if we need to have a dedicated point? The point connective ity? But we don't want to or we don't want to. You don't want I don't have that. We don't have the availability to actually get a dedicated least line Well, another option are a couple of the other up options available to us. Our frame relay, an asynchronous transfer mode
now Frame relay, an asynchronous transfer mode are both technologies that allow us to
take these. Take these different backbone lines, like R T. One E one E. T. Three and T three lines and utilize them but not utilize them as dedicated least lines. Instead, What we do is we utilize virtual circuits, so it
it to us looks like it's a dedicated point to point connection
from us to whichever other site we're trying to get to. But our Internet service provider is allowed to use whichever path they need in order to get from one point to another. We don't have a dedicated laid line just for us when we switch on our network, or if our network is all always on when our network is on
our Internet service, provider provider will use the best lines for them
to get from one dedicated point to another dedicated point.
Now these frame relay in asynchronous transfer modes that frame relay an asynchronous transfer mode connections. Again, we'll be able to use our tea and the lines without having to actually have a dedicated lease on them. But what we will do is we will sign an agreement with them,
say, stating that this will be what are our minimum.
Our minimum speeds will look like I will sign an S L. A with them standard lease agreement and say that at all times our speed should not drop below this, Um and then they'll provide us with a virtual connection from virtual point to point connection between one between point A and point B.
Now, with our frame relay as well as our secret, this transfer mode, we have virtual circuits and these virtual circuits. We have two different types. We have permanent virtual circuits and we have switched virtual circuits. Now a permanent virtual circuit is again a virtual circuit being a virtual
dedicated line, so back to our circuit switching type, connect it
connections. We have a dedicated when we need it connection between one point and another. We're not sharing with other people, but it's a virtual circuit because it can change, as the Internet service provider needs it, too.
If it's a permanent virtual circuit, that means it's always on for us. We have a always on connection between one site and another, or constantly flowing data between one side and another. So we always need that circuit to be available, whichever the Internet service provider may choose to go through for us.
And then our other option would be a switched virtual circuit
in a switch. Virtual circuit would be in as and on as needed connective ity. Maybe we don't always have the connection on between these two sites, for whatever reason. So instead of having a permanent virtual circuit, we would have a switched virtual circuit. So permanent virtual circuit is always on switched. First rule circuit is as needed,
but they both are virtual circuits.
So when they are on, we're not
using packet switching. We're use it using our circuit switching where we don't have that buffering connective ity that we're sharing with other people. We should have a dedicated connection according to our agreement with the Internet service provider.
So we have maximum transmission based on the lines that were using. Remember, we signed a minimum speed train speed agreement with our the provider of our frame relay circuit, but our men are maximum transmission is based on the type of lines that were going over.
We can't exceed a certain speed on the lines just based on based on
they're t one or E one or T wan t three or E three level of transmission or the line capabilities themselves.
now again so the Internet service provider can use whichever lines that it wants to to get us from one point to another. We don't lease a dedicated physical line, and with frame relay, we have a variable length frame. So we have different our frame that we're sending our sending data through
the how we're formatting, how we're framing our data
Eyes has variable lengths, and there's other individual specifications, and there's other types of frames that we can use with this frame. Relay technology
now are very similar asynchronous transfer mode. It also known as a T M. They'll confuse that with our automatic teller machines. But our asynchronous transfer mode is very similar to our frame relay are a secret is transfer mode is still going to let the Internet service provider use whichever,
whichever lines that needs to get from one point to another.
Our asynchronous transfer mode eyes going to use thes permanent virtual circuits as well as thes switched virtual circuits. But our asynchronous transfer mode does not have variable length frames are asynchronous transfer mode uses cells, which are fixed length frames are fixed length packets.
Now these packets are 53 bite packets that include a five bite header
and a 48 byte payload. The header Just giving us some information about what is in the payload and the payload is our actual data.
two other terms to be familiar with it with our asynchronous transfer mode is going to be our user network interface in our network node interface. So are you and I are in, and I are you and I are user network interface is going to be our connection between our asynchronous transfer mode switches to are in point.
So it's a T M switch, not the not the machine to get money out of.
But our asynchronous transfer mode switch to our in point is going to be our user network interface than our network node interface is the connection between our asynchronous transfer mode switches to another asynchronous transfer mode switches? So be aware of those two different distinctions there between our
user network interface and our network node interface.
So this is a recap. Remember that both are asynchronous transfer modes, and our frame relay are two different technologies to different ways. We format are different frames and packets that allow us to use certain backbone lines. Allow us to have a dedicated point to point connection
without actually having to have a dedicated least line.
We don't have to lease that line for on Lee us for all times. That's a dedicated point to point connection using virtual circuits. And then when we send our data over that virtual circuit, then our Internet service provider or whoever we got the agreement from,
will be able to actually use whichever lines are best for them or at least used for them
to get the data from one. Get our data from point A to point B