Kent,
If you are using RBS it is because you are using ISDN PRI.
Subsequently, you have 24 channels running at 56Kbps for
data throughput. This means your bandwidth is as follows:
24channels * 56Kbps/Channel = 1344Mbps
If you are worried that because you are using ESF versus
SF with RBS that you have less bandwidth, then the answer
is no. Because we are missing one bit from two of our
channels with RBS, then we can't use that extra bit in any
of our channels, it literally goes wasted. ESF just uses more
of those wasted bits than does SF.
Does this answer your question?
AQ
At 09:55 AM 7/12/2000, Kent wrote:
>Adam,
>
>If the 6th, 12th, 18th and 24th bit of the
>extended superframe are robbed, does this mean the
>data part of a T1 will be 20x64k+4x56k=1504K(1.504M)
>in stead of 1.536M?
>Hope I am not missing something here.
>
>Thanks
>
>Kent
>
>--- Subramanian Nallasivam <[EMAIL PROTECTED]> wrote:
> > Hi Adam,
> >
> > Thanks for your clarification . I am having one
> > more doubt. Where comes the
> > concept of red and yellow alaram.
> >
> > Thanks,
> > -Subbi.
> >
> > Adam Quiggle wrote:
> >
> > > Hey Ole,
> > >
> > > It really is 8000 samples. The number 8000 comes
> > from Nyquist's
> > > theorem which in a nutshell states that in order
> > to properly represent
> > > an analog signal in digital form we must sample
> > twice the frequency
> > > range. Since an analog signal is represented from
> > 0-4Khz we must sample
> > > an analog signal (2*4000) times a second in order
> > to transport it with
> > > minimal loss. Thus we get 8000 samples a second.
> > Each sample is encoded
> > > with 8 bits to represent an analog signal at
> > anyone time, thus we get:
> > >
> > > 8 bits/samples * 8000 samples/sec = 64,000
> > bits/sec (look familiar?)
> > >
> > > Now, if we look at a single frame of a channelized
> > T1 we can see that
> > > we have twenty-four 8-bit timeslots plus a single
> > bit for framing or:
> > >
> > > Data Channels (23B+1D)
> > > 24 channels * 8 bits/sample * 8000 samples/second
> > = 1,536,000bps
> > >
> > > Framing Bit
> > > 1 bit/sample * 8000 samples/second = 8000 bps
> > >
> > > So, we can see that for data we have 1,536,000 bps
> > and 8,000 bps for framing,
> > > which equals 1,544,000 bps. This is why people
> > think of a T1 as 1.544Mb
> > > but it's true throughput is only 1.536Mb.
> > >
> > > So, what is the framing bit used for? Framing
> > allows the CSU/DSU to find
> > > the timeslots in the channelized T1. Remember,
> > that 8000 T1 frames are
> > > flying out of the circuit every second, and the
> > CSU/DSU must know how
> > > to find the T1 frames in this circuit (don't ask
> > me why, but I can't stop
> > > thinking of Lucille Ball in the bon/bon episode
> > :-)
> > >
> > > In order to maintain sync, the CSU/DSU must grab
> > every 193rd bit off of
> > > the line, string them together and see if it forms
> > the "pattern" it is looking
> > > for. The type of framing used describes the
> > pattern to look for.
> > >
> > > When using Superframing twelve of these bits are
> > strung together and must
> > > form the following pattern of "100011011100". If
> > it doesn't form this
> > > pattern, the CSU/DSU is said to slip and it must
> > then resync its
> > > timing to the signal.
> > >
> > > Extended Superframing is an extension of
> > Superframing and instead of
> > > trying to collect twelve of these framing bits, it
> > collects 24 of these
> > > bits for syncing to the signal.
> > >
> > > So, what about robbed bit signaling (RBS)? RBS is
> > not a function of
> > > what type of framing you are using. RBS also
> > known as Channel Associated
> > > Signaling (CAS) is a technique in which
> > supervisory and signaling information
> > > is sent by removing the 8th bit of the 6th and
> > 12th Superframe or the
> > > 8th bit of the 6th, 12th, 18th and 24th bit of the
> > extended superframe.
> > >
> > > The overall affect for those using Channel
> > Associated Signaling is that you
> > > don't need a D channel, however all your B
> > channels use 56kbps.
> > >
> > > You can find more information on the following
> > topics in McGraw Hill BCRAN:
> > >
> > http://www.bookpool.com/.x/p9zwbh4yt6/sm/0072124806
> > >
> > > Channelized T1/E1 frame format: 208-213
> > > Framing and linecoding: 226-228
> > > Robbed bit signaling/Channel Associated Signaling:
> > 230-231
> > >
> > > The purpose of this book was to go beyond the
> > Ciscopress material, which
> > > focuses on the BCRAN exam material only and add
> > information that seems
> > > to have been ignored by Ciscopress's BCRAN. You
> > will note that in this
> > > book, when
> > > a topic is not covered on the BCRAN exam, there is
> > a note indicating such,
> > > so that you don't review material not required for
> > the exam....ok shameless
> > > plug over... :-)
> > >
> > > Adam Quiggle
> > >
> > > At 05:31 PM 7/11/00, Ole Drews Jensen wrote:
> > > >Hi Subbi,
> > > >
> > > >You are dragging me out in orbit now, but I'll
> > try to hang on.
> > > >
> > > >To get back to the ISDN PRI...
> > > >
> > > >The 8000 samples, are you sure that it's not 8
> > k-samples (8*1024) = 8192
> > > >samples???
> > > >
> > > >That would make sense since the 192 bits (24*8)
> > multiplied with 8192 equals
> > > >1572864 which again equals 1536 kbps
> > (1572864/1024). That brings us back to
> > > >24 channels where the last one is only used for
> > signaling - not data.
> > > >
> > > >Ole
> > > >
> > > >~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > Ole Drews Jensen
> > > > Systems Network Manager
> > > > CCNA, MCSE, MCP+I
> > > > RWR Enterprises, Inc.
> > > > [EMAIL PROTECTED]
> > > >~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > >
> > > >-----Original Message-----
> > > >From: Subramanian Nallasivam
> > [mailto:[EMAIL PROTECTED]]
> > > >Sent: Tuesday, July 11, 2000 4:14 PM
> > > >To: Ole Drews Jensen
> > > >Cc: [EMAIL PROTECTED]
> > > >Subject: Re: Some ISDN PRI questions
> > > >
> > > >
> > > >Hi Ole,
> > > >
> > > > Let me take the case of T1. In T1 all
> > the 24 channel are used for
> > > >sending data. There will be one framing bit which
> > constitiute to 193 bits.
> > > >So
> > > >193 * 8000 = 1544 kbps. And one bit from every
> > sixth frame in case of
> > > >superframe(which consists of 12 T1/DS1 frames)
> > will be robbed for
> > > >signalling.
> > > >The robbed bit will be the least significant bit
> > and this concept is known
> > > >as
> > > >robbed-bit signalling. If I am wrong then please
> > correct me.
> > > >
> > > >Thanks,
> > > >-Subbi.
> > > >
> > > >
> > > >Ole Drews Jensen wrote:
> > > >
> > > > > Hi Subbi,
> > > > >
> > > > > That would still only leave 184 * 8000 =
> > 1472000 bps or (1472000/1024)
> > > > > 1437.5 kbps for data.
> > > > >
> > > > > Ole
> > > > >
> > > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > Ole Drews Jensen
> > > > > Systems Network Manager
> > > > > CCNA, MCSE, MCP+I
> > > > > RWR Enterprises, Inc.
> > > > > [EMAIL PROTECTED]
> > > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > >
> > > > > -----Original Message-----
> >
>=== message truncated ===
>
>
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*******************************
Adam Quiggle
Sr. Network Engineer
BP-Amoco/MCI Worldcom
CCNA, MCNE, MCSE
[EMAIL PROTECTED]
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