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Minimum CIR Required for TCP/IP

Posted on 2001-07-27
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Can you tell me what is the minimum CIR on Frame Relay that is required for:

a) TCP/IP

b) MPLS switching

c) VPN's

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Question by:bpadda
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SteveJ earned 50 total points
ID: 6335949
First, you can't get a frame relay circuit at less than 56k, so there's your minimum physical circuit. Second, you can get a 0k CIR, which means essentially that every frame you place on the network has the Discard Elegible bit set. So there's your minimum CIR: zero.

If this is a homework question and you are really asking "what would the minimum CIR need to be to GUARANTEE that a TCP frame or an IP datagram will be delivered?" then you need to rephrase the question because you are mixing the concepts of "circuit capacity" and "rate of delivery." Without knowing the ratio of overhead to data, your question is really impossible to answer . . .

Last, you may need to spend a little more time understanding the different vendor offerings of frame relay. You won't find that in a text book or an RFC.

Properly sizing the CIR and the physical circuit requires knowing more than just the transport protocol. If you get a more specific answer to this question, you'd be well advised to ignore it.

Good luck.
Steve
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by:crieman
ID: 6336520
zero  :)
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by:SteveJ
ID: 6477647
Earth to bpadda . . .
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by:learath
ID: 7504663
In theory?  ~9600 for TCP/IP, not quite sure on MPLS, and VPN would be around 14,400.    In practice?  I'd recommend around 768k for a useable setup with MPLS & a VPN.
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by:voids
ID: 7651856
It all to do with header and frame size. CIR must account for PAYLOAD and well as HEADER.
Therefore if still matters the TRAFFIC you will send, and not what flavour (VPN, MPLS, TCP/IP)

You need to estimate what traffic you will be sending, then look at about 5-10% more for the VPN headers (depends on if your using IPSEC over MPLS, or simply using MPLS which is a VPN technology in it self.

From working with major Telco's, get a small CIR ie 16K but get a large EIR 64K. This works out much cheaper than 32k CIR and 64K EIR. You should get most of the time up to the 64K anyway, particularly if the passport switch for the NTU is not in heavly use by other customer.

This should be enough for an office of about 20 people using the network moderately for email and general web browsing (no large downloads). You can then use MRTG or get IT advise to monitor the Bandwidth, and upgrade the CIR as required (or throttle down the downloads etc. to avoid congestion)
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by:lrmoore
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G'day, bpadda
There has been no activity on the question for 138 days, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area for this question:

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per recommendation

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