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-----
> > > From: Subramanian Nallasivam [mailto:[EMAIL PROTECTED]]
> > > Sent: Tuesday, July 11, 2000 3:54 PM
> > > To: Ole Drews Jensen
> > > Cc: [EMAIL PROTECTED]
> > > Subject: Re: Some ISDN PRI questions
> > >
> > > Hi,
> > >
> > > I am new to ISDN concepts, but here they are....
> > >
> > > We have 23 DSO for carrying data. Each channel carries 8 bit word or
> > > something. So
> > >
> > > 23 * 8 = 184
> > >
> > > One channel is used for carrying signal . So the number comes out to be
> > >
> > > 184 + 8 = 192
> > >
> > > Since 8000 samples are sampled per second , the calculation comes to be
> > >
> > > 192 * 8000 = 1536 Kbps.
> > >
> > > T1 uses in-band signalling ( uses same data channel for signalling also)
> > > where
> > > as ISDN PRI uses out-band signalling (uses seperate channels for signals).
> > >
> > > I am new to ISDN cocepts. If I am wrong please correct me.
> > >
> > > Thanks,
> > > -Subbi.
> > >
> > > Ole Drews Jensen wrote:
> > >
> > > > The ISDN BRI has two 64 kbps B channels and one 16 kbps D channel. That
> > > > gives us a maximum of 128 kbps bandwidth for data which makes sense.
> > > >
> > > > The ISDN PRI has twenty three 64 kbps B channels and one 64 kbps D
> > > channel.
> > > > That should give us a maximum of 1472 kbps bandwidth for data, and not
> > > 1536
> > > > kbps as normally specified unless it is possible to use the D channel
> >for
> > > > data too ???
> > > >
> > > > The ISDN PRI in Europe has thirty 64 kbps B channels and one 64 kbps D
> > > > channel. That should give us a maximum of 1920 kbps for data, and not
> >2048
> > > > kbps as normally specified even if the D channel is used for data too.
> > > >
> > > > Are these numbers just used because it's easier to remember the 1536 and
> > > > 2048 values, or is there a hidden factor here???
> > > >
> > > > A last question: I sometimes hear people refer to an ISDN PRI as a T1.
> >The
> > > > T1 has the same amount of channels and bandwidth, so the question is -
> >are
> > > > there really a big difference between these two specifications, or is it
> > > > more or less the same???
> > > >
> > > > Some or all of these questions might be answered later on in my book,
> >but
> > > I
> > > > can't wait any longer - I want to know NOW :-)
> > > >
> > > > Thanks for any comments on this.
> > > >
> > > > Ole
> > > >
> > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > Ole Drews Jensen
> > > > Systems Network Manager
> > > > CCNA, MCSE, MCP+I
> > > > RWR Enterprises, Inc.
> > > > [EMAIL PROTECTED]
> > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > >
> > > > ___________________________________
> > > > UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html
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> >
> >
> >___________________________________
> >UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html
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>
> **************************************************
> Adam Quiggle
> Senior Network Engineer
> MCI Worldcom/BP Amoco
> CCNA, MCNE, MCSE
> [EMAIL PROTECTED]
> **************************************************
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