From: Scott Morris (swm@emanon.com)
Date: Sun Apr 11 2004 - 22:16:00 GMT-3
It's a perception thing... But you're correct, it's not really acurate.
T-1 is 24 channels ta 64k each. 24 * 64000 = 1,536,000 of raw perceived
data.
When you run your T1 in ESF mode, you are assembling "frames" together.
There are 8000 samples per second done with voice stuff at 8 bits a piece.
When you combine 24 separate channels worth of frames together you have 192
bits of information.
There's actually 1 bit stuck in there for good measure in setting
separation/signalling information stuff. So that means you have 193 bits of
information * 8000 of these superframes per second.
That leftover 1-bit is your extra 8k! (193 bits * 8000 = 1,544,000). That
extra 1 bit is not really usable by data, so the fact that you 'say' you
have 1.544M of data transfer, it really doesn't work that way. :) It just
depends on your router/IOS to which value is used.
The clockrate is the rate at which things are sent between two DSU's or
devices on the line. The bandwidth or perceived bandwidth is really just a
thing that your router does to make it, or you, feel better. The router
will make calculations and decisions based on this perceived number. So if
your clockrate is 64000, your line is really operating at 64000 bps, but
unless you do something to change the default bandwidth, everything
calculated will be done based on 1.544M (or 1.536M depending on your
router/IOS).
In the grand scheme of things, 8k isn't going to amount to all that much of
a bandwidth difference... Take a look at your EIGRP topology table and see
what values are set at. This is the thing that will give you indication as
to the variance you need to do. The other method "fixing" the calculation
would be to apply an offset list where necessary. You need to think like
the router thinks though. That will give you all the information you need!
If your clockrate is set to 640000, set your bandwidth to 64. That'll make
things at least accurate. :) It would stand to reason that the more
accurate your depiction of the network is, the more accurate your routers
can calculate things correctly. Less tweaking that admins need to do.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, CISSP,
JNCIS, et al.
IPExpert CCIE Program Manager
IPExpert Sr. Technical Instructor
swm@emanon.com/smorris@ipexpert.net
http://www.ipexpert.net
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Ahmed Mustafa
Sent: Sunday, April 11, 2004 4:28 PM
To: ccielab@groupstudy.com
Subject: Bandwidth 1544 vs 1536
What is the correct way to interpret Serial interface bandwidth. Usually,
it is said that by default Serial interface bandwidth is equivalent to T1
bandwidth.
It doesn't seem to be correct since the T1 bandwidth is 1536000 64000KB x
24 Channels, and the serial port bandwidth is 1544000.
Two Questions:
1) If the tasks states the T1 bandwidth so should we change the serial port
bandwidth from 1544 to 1536 or leave it alone.
2) In a lab environment, we usually use DCE/DTE cable and whatever the
clockrate is configured for it that fast the link would be then. If I
configure my clock rate 64000KB then it is obvious that the DCE/DTE would be
sending bits at the rate of 64000 bits per second regardless of what the
bandwidth parameters are set for.
I am confused how I would actually configure unequal cost load-balancing for
EIGRP.
The task states to use the T1 bandwidth so I must change the default serial
bandwidth from 1544 to 1536, but the clock rate I configured is only
64000KB.
The question how should I go about configuring load-balancing by keeping
everybody happy.
Regard,
Ahmed
This archive was generated by hypermail 2.1.4 : Mon May 03 2004 - 19:48:46 GMT-3