How to connect "into" a Frame Relay??

[dannydanny]

Hi,

Could someone please clear up some confusion I have with FR?

When I buy into a frame relay circuit, do I need to provide a connecion into the providers T1 line? Is this line leased, private?

What is the speed of the line? Does the speed of this line have to match that of the CIR I am buying from my provider?

Thanks for any info.
Danny

 

[StarTAC]

frame relay is usually provided over POTS lines or a fibre network.. the issues is not what type of medium is coming to your premises, but where it's being routed to...

T-1s are basically circuit-switched, dedicated leased line connections, and will traditionally end up at the telcos circuit switched main frame.. frame relay, on the other hand, is a packet-switched network, and will terminate into a frame relay switch or frame relay aggregator... along with the rest of the telcos frame relay connections...

frame relay will run from as low as 64Kbps, to as high as 45Mbps.... if u're using a Cisco router, your serial interface will, by default, support up to 1.544Mbps, unless u're using a router lower than a 1600 series, such as an 805 series router...

the same line coming to your premises can easily be converted to a T-1 as well.. it's all about the telco simply cross-connecting your line to the right DCE equipment at their end, and u have a solution.... the medium can handle whichever layer 2 protocol u request from the telco.. be it frame relay or HDLC...

line speed doesn't have to match CIR.. if u have a fibre connection coming into your office, u can have up to 2.5Gbps of bandwidth, but only 512Kbps will be provided to u by the telco, if u go frame relay, and depending on what u request... speed of line is generally dictated by the DCE equipment and what u've been provisioned, not by the actual line..

good luck..

 

[dannydanny]

Thanks for the explanation StarTAC.

If I may ask, what is meant by a PVC of 256k with a CIR of 128k? Thats the specifications of our Frame Relay that my boss has given me.

Does it mean that the max line speed we have subscribed to is 256k, but the minimum guaranteed is 128k?, Or is it the line speed from our office into the FR is 256k, with the FR company sending the data at a guaranteed speed of 128k?

Thanks in advnace for any clarification.
Danny

 

[darinhamilton]

Your frame relay service is made up of five basic components at each end of the connection:

1. router
2. CSU/DSU
3. local loop
4. frame relay port
5. frame relay PVC

The local loop is likely 256K, which is actually fractional T1 or E1 (depending on where you are in the world).

The port is likely 256K, which is your maximum possible data rate into the provider's network (this normally equals the speed of the local loop, but this is not necessarily the case).

The PVC is made up of the following:
1. CIR (Committed Information Rate, or your minimum committed throughput) plus
2. EIR (Excess Information Rate, or your burst capacity)

CIR + EIR = AIR (Available Information Rate, or your maximum throughput)

If your provider tells you your PVC is 256K he means your AIR. Therefore you ahve the following:

CIR = 128K (min.)
EIR = 128K
AIR = 256K (max.)

Hope that helps

Darin, CCNA
Infonet Canada

http://www.infonet.com

 

[dannydanny]

Excellent explanation there! Much appreciated Darin.

So, if the line speed of the local loop is, say, 56k, but our CIR is 128k, then there is almost no chance of breaching the CIR, right?

In this case, is it common to find that companies try to match the line speed of the local loop to the AIR? Wouldn`t this be the optimal speed because you can never over submit data...or is the optimal line speed into the FR, the same as the CIR you`ve subscribed to? Cause then you would never have to burst and all data is guaranteed to flow and not be dropped?

Thanks in advance for any info.
Danny

 

[StarTAC]

if your line speed were 56Kbps, there would be no point in getting a 128Kbps CIR, because u'd pay for something u'd never use.. in some parts of the world, u don't have to worry about line speed.. the line could be twisted pair copper, or fibre..

all the telco tells u is they'll give u 64Kbps CIR, regardless of the medium u are using.. they will take care of having enough capacity on their network to give you your 64Kbps access to their frame relay switch...

saying that, CIR is just that, committed.. it means if u attempt to go over your CIR, your packets will get become DE [Discard Eligible] which means the bits are always on on all packets.. DE is a method of congestion control.. it can be broken down further to include FECN or BECN[Forward/Backward Explicit Congestion Notification]..

FECN tells the destination router that the path that has just been traveresed by the packet is congested, so take note.. and BECN tells the transmitting router to reduce its rate of data transmission, as the link is congested...

usually, u will start feeling congestion on a 64Kbps as u approach 61Kbps utilisation.. on a 128Kbps circuit, u will start feeling the pinch when at about 125Kbps.. u usually leave 2-3Kbps for overhead...

good luck..