"Mark" wrote in message
...
On Thu, 13 Jan 2011 15:57:18 +0000, The Natural Philosopher
wrote:

Timothy Murphy wrote:
Huge wrote:

The manufacturer calls the device attached to the internet a "modem",
They're wrong.

I think a manufacturer probably knows better than you what he is making.

well it is a modem, but its not just a modem

Typically a basic NAT router is a modem, a bridge, a router, a NAT
engyne, a stateful firewall machine, a DHCP server a proxy DNS server
and..a web server . To name just a few. Its probably alos a log server
and may have an snmp server in it too. Oh and a wireless bridge.

And it may also be a Network Switch too.

and a file server, print server.

Mine is a Linux machine in a a box as are a lot of others.

Note the ;? ..

I'm used to ;-? for that... ;-)

Had this very conversation the other month with Two BT exchange engineer
types.. one argued that it was a digital system the other argued that it was
not.. I presume the actual modulation scheme in use would determine that..

They could well both be right on different lines. One has old-fashioned
copper from the DSLAM in the exchange to the street box, the other has
fibre to a DSLAM in the box. When they finally roll out fibre to the
home, then it'll be digital all the way. Inside your current
Modem/Router is an analogue line driver, though.

The feed into your house consists of a number of modulated narrowband HF
carriers, which are phase and/ or amplitude modulated, I can't remember
which, and an analogue baseband signal for your normal phone.

Yes digital modulation system perhaps;?...
--
Tony Sayer

In article , The Natural Philosopher
scribeth thus
tony sayer wrote:
In article , John Williamson johnwilli
scribeth thus
Timothy Murphy wrote:
Clive George wrote:

On 13/01/2011 15:28, Timothy Murphy wrote:
Huge wrote:

The manufacturer calls the device attached to the internet a "modem",
They're wrong.
I think a manufacturer probably knows better than you what he is making.
I'd rather hope the manufacturer knows exactly what they're making.
However their marketing department may choose to use a different name
when describing it to consumers in order to sell more stuff.
According to Wikipedia, "A modem is a device or program
that enables a computer to transmit data over, for example,
telephone or cable lines."

You obviously have a different definition.
What is it; and do you have some authority to back your definition?


The Modem is the bit that turns the stream of digital bits into analogue
signals.


Umm ... where are the analogue signals in a lets say router that you'd
use for a ADSL Broadband service in the UK;?..



On the telephone line.

Would you like to explain that a -bit- further;?..
--
Tony Sayer

tony sayer wrote:
Note the ;? ..

I'm used to ;-? for that... ;-)

Had this very conversation the other month with Two BT exchange engineer
types.. one argued that it was a digital system the other argued that it was
not.. I presume the actual modulation scheme in use would determine that..

They could well both be right on different lines. One has old-fashioned
copper from the DSLAM in the exchange to the street box, the other has
fibre to a DSLAM in the box. When they finally roll out fibre to the
home, then it'll be digital all the way. Inside your current
Modem/Router is an analogue line driver, though.

The feed into your house consists of a number of modulated narrowband HF
carriers, which are phase and/ or amplitude modulated, I can't remember
which, and an analogue baseband signal for your normal phone.

Yes digital modulation system perhaps;?...

Of an analogue carrier. The signal on the line is *not* a simple on/off,
it uses a combination of phase and amplitude modulation of multiple
carriers. What controls the modulation is digital, the modulated carrier
is analogue.

To aid in your understanding, *all* signals passing along the local loop
(AKA the "Last mile") are analogue.

Digital signals are transmitted by encoding onto a carrier, and then
decoded by comparing the transmitted signal with a stable reference, as
in a FM or AM radio set. The output from this decoder to your computer
is digital, the input to the decoder from the line is analogue. In the
days of 75 baud modems, the digital data was transmitted by switching an
audio tone on and off, and later, the tone was switched between two
frequencies, which allowed faster transmission. Later still, advances in
design and manufacture permitted the use of combinations of level and
phase variation of the carrier to allow the transmission of more than
one bit of data per cycle of carrier. Broadband basically just uses a
number of these phase and amplitude modulated carrier signals coming
down the same line.

Now, either you're trying to wind me up, or you *really* don't
understand the difference between the analogue and digital parts of a
modem. If the latter, then I'd suggest studying the Wiki reference
given, and follow the links in the article to the bits you don't
understand. You might also like to study amplitude, frequency and phase
modulation schemes for radio transmission.

--
Tciao for Now!

John.

In article , John Williamson johnwilli
scribeth thus
tony sayer wrote:
Note the ;? ..

I'm used to ;-? for that... ;-)

Had this very conversation the other month with Two BT exchange engineer
types.. one argued that it was a digital system the other argued that it was
not.. I presume the actual modulation scheme in use would determine that..

They could well both be right on different lines. One has old-fashioned
copper from the DSLAM in the exchange to the street box, the other has
fibre to a DSLAM in the box. When they finally roll out fibre to the
home, then it'll be digital all the way. Inside your current
Modem/Router is an analogue line driver, though.

The feed into your house consists of a number of modulated narrowband HF
carriers, which are phase and/ or amplitude modulated, I can't remember
which, and an analogue baseband signal for your normal phone.

Yes digital modulation system perhaps;?...

Of an analogue carrier. The signal on the line is *not* a simple on/off,
it uses a combination of phase and amplitude modulation of multiple
carriers. What controls the modulation is digital, the modulated carrier
is analogue.

To aid in your understanding, *all* signals passing along the local loop
(AKA the "Last mile") are analogue.

Digital signals are transmitted by encoding onto a carrier, and then
decoded by comparing the transmitted signal with a stable reference, as
in a FM or AM radio set. The output from this decoder to your computer
is digital, the input to the decoder from the line is analogue. In the
days of 75 baud modems, the digital data was transmitted by switching an
audio tone on and off, and later, the tone was switched between two
frequencies, which allowed faster transmission. Later still, advances in
design and manufacture permitted the use of combinations of level and
phase variation of the carrier to allow the transmission of more than
one bit of data per cycle of carrier. Broadband basically just uses a
number of these phase and amplitude modulated carrier signals coming
down the same line.

Now, either you're trying to wind me up, or you *really* don't
understand the difference between the analogue and digital parts of a
modem. If the latter, then I'd suggest studying the Wiki reference
given, and follow the links in the article to the bits you don't
understand. You might also like to study amplitude, frequency and phase
modulation schemes for radio transmission.


No John, thats the day job in Radio of a few types!, its just where do
you draw the demarcation line in a digital or analogue system.

Two senior BT engineering types couldn't agree on this.

I'll see what a Professor I know at the Uni sez. Be interesting..

--
Tony Sayer

tony sayer wrote:

No John, thats the day job in Radio of a few types!, its just where do
you draw the demarcation line in a digital or analogue system.

I draw it at the point where the digital data is turned into an analogue
signal by the modulator and vice versa.

Though, I might *call* it digital all the way through, if I were talking
to someone who doesn't know a lot about it......

To draw a (Maybe not perfect) analogy, the "digital" sound recording I
made the other day was analogue from the microphone up to the point
where the signal met the ADC, then it was digital all through the chain
until it met the DAC just before the amplifier. Then it was analogue
again. If I published it, it would be classified as DDD on a CD, as all
the recording, editing and distribution was done in the digital domain.
Both ends of the reproduction chain must be analogue, though. Unless
you've got digital vocal chords and ears. It's still *called* a digital
recording, though.

--
Tciao for Now!

John.

On 15/01/2011 16:02, John Williamson wrote:

tony sayer wrote:
Yes digital modulation system perhaps;?...

Exactly so. xDSL uses discrete multi-tone modulation (DMT), a variation
on the theme of OFDM used for digital radio and TV. These are
undoubtedly *digital* modulation schemes.

Of an analogue carrier.

Of a large number of (suppressed) carriers, in fact. The resulting
electrical signal has a time variation of amplitude that looks similar
to white Gaussian noise, but you shouldn't think of it as being
analogue. The amplitude is not a direct representation of a
continuously varying quantity an the way that the analogue speech signal
on the line represents sound pressure.

The signal on the line is *not* a simple on/off,

So what? A digital representation doesn't have to be binary. Digital
data - that could, for example, represent an audio signal after sampling
and A/D conversion - is frequently transmitted over wires or radio
channels as a sequence of 'symbols' each symbol representing one *or
more* bits. Increasing the number of bits per symbol generally allows
more data to be sent over a given spectral bandwidth but the signal
remains digital - each symbol represents one of a finite number of
discrete states.

To aid in your understanding, *all* signals passing along the local loop
(AKA the "Last mile") are analogue.

The speech signal is analogue. The xDSL signal is digital.

[...]

Now, either you're trying to wind me up, or you *really* don't
understand the difference between the analogue and digital parts of a
modem.

Both sides of a modem can be digital.

If the latter, then I'd suggest studying the Wiki reference
given, and follow the links in the article to the bits you don't
understand. You might also like to study amplitude, frequency and phase
modulation schemes for radio transmission.

And you might like to try these:

http://en.wikipedia.org/wiki/Digital
http://en.wikipedia.org/wiki/Discret...one_modulation
http://en.wikipedia.org/wiki/Digital...lation_methods

The last one's interesting. Like you it starts by referring to an
"analog carrier", but then goes on to say:

"According to one definition of digital signal, the modulated signal is
a digital signal, and according to another definition, the modulation is
a form of digital-to-analog conversion. Most textbooks would consider
digital modulation schemes as a form of digital transmission, synonymous
to data transmission; very few would consider it as analog transmission."

--
Andy

Andy Wade wrote:
On 15/01/2011 16:02, John Williamson wrote:

tony sayer wrote:
Yes digital modulation system perhaps;?...

Exactly so. xDSL uses discrete multi-tone modulation (DMT), a variation
on the theme of OFDM used for digital radio and TV. These are
undoubtedly *digital* modulation schemes.

Of an analogue carrier.

Of a large number of (suppressed) carriers, in fact. The resulting
electrical signal has a time variation of amplitude that looks similar
to white Gaussian noise, but you shouldn't think of it as being
analogue. The amplitude is not a direct representation of a
continuously varying quantity an the way that the analogue speech signal
on the line represents sound pressure.

No, the phase and amplitude of the (suppressed) analogue carrier
compared to a reference are controlled by the digital signal. Taking the
simplest case, is an FM or AM radio signal modulated by a square wave
analogue or digital?

The signal on the line is *not* a simple on/off,

So what? A digital representation doesn't have to be binary. Digital
data - that could, for example, represent an audio signal after sampling
and A/D conversion - is frequently transmitted over wires or radio
channels as a sequence of 'symbols' each symbol representing one *or
more* bits. Increasing the number of bits per symbol generally allows
more data to be sent over a given spectral bandwidth but the signal
remains digital - each symbol represents one of a finite number of
discrete states.

I know about that. It's how a 56Kbps modem gets its data along a phone
line that can't carry an audio frequency of more than about 4KHz. The
more steps you can distinguish the faster the data can be transferred,
relative to the bandwidth. The more steps you try to distiguish, the
greater the error rate. The faster you transit, the greater the error
rate. The Nyquist limit dictates how much information you can shift
through a particular link.

[...]

Now, either you're trying to wind me up, or you *really* don't
understand the difference between the analogue and digital parts of a
modem.

Both sides of a modem can be digital.

? MODulator/ DEModulator implies an analogue carrier in the transmission
medium. If both sides are digital, then surely it's just a line driver?

If the latter, then I'd suggest studying the Wiki reference
given, and follow the links in the article to the bits you don't
understand. You might also like to study amplitude, frequency and phase
modulation schemes for radio transmission.

And you might like to try these:

http://en.wikipedia.org/wiki/Digital
http://en.wikipedia.org/wiki/Discret...one_modulation
http://en.wikipedia.org/wiki/Digital...lation_methods

Thanks, I have.

The last one's interesting. Like you it starts by referring to an
"analog carrier", but then goes on to say:

"According to one definition of digital signal, the modulated signal is
a digital signal, and according to another definition, the modulation is
a form of digital-to-analog conversion. Most textbooks would consider
digital modulation schemes as a form of digital transmission, synonymous
to data transmission; very few would consider it as analog transmission."

The last two articles both mention conversion of digital data to and
from analogue form for transmission.

"In digital modulation, an analog carrier signal is modulated by a
digital bit stream" is a quote from the first paragraph of the Digital
Modulation article.

The discrete multitone modulation article block diagram shows an ADC/
DAC pair in the chain, before and after the transmission medium. Part of
the DAC function is to convert inexact analogue levels in the
transmission into steps for digital decoding.

I would say that the *signal* on the line is analogue, with the levels
partly dictated by analogue mechanisms such as AGC and interference,
while the information transmitted is digital.

I suspect we're looking at the same thing from different angles.

--
Tciao for Now!

John.

On 15 Jan,
Andy Wade wrote:

So what? A digital representation doesn't have to be binary. Digital
data - that could, for example, represent an audio signal after sampling
and A/D conversion - is frequently transmitted over wires or radio
channels as a sequence of 'symbols' each symbol representing one *or
more* bits. Increasing the number of bits per symbol generally allows
more data to be sent over a given spectral bandwidth but the signal
remains digital - each symbol represents one of a finite number of
discrete states.

Several symbols (carriers) are usually used simultaneusly (together with the
baseband audio signal) The signal is analogue -- any amplification etc. has
to be (analogue) linear or the quality (BER) is reduced by crosstalk and
intermodulation.

It may represent binary digits, but it must be treated as an analogue signal.

--
B Thumbs
Change lycos to yahoo to reply

On Fri, 14 Jan 2011 15:11:48 +0000, The Natural Philosopher wrote:

You also need to know that only ports have IP address's not
devices.

No., *interfaces* have *one* IP address and up to 64,000 PORTS.

In my book an "interface" can have more than one physical connection,
each phyical connection is a "port", as in the ports of an interface
card in a PABX or comms matrix.

Isn't language interesting?

--
Cheers
Dave.

tony sayer wrote:
Note the ;? ..

I'm used to ;-? for that... ;-)

Had this very conversation the other month with Two BT exchange engineer
types.. one argued that it was a digital system the other argued that it was
not.. I presume the actual modulation scheme in use would determine that..

They could well both be right on different lines. One has old-fashioned
copper from the DSLAM in the exchange to the street box, the other has
fibre to a DSLAM in the box. When they finally roll out fibre to the
home, then it'll be digital all the way. Inside your current
Modem/Router is an analogue line driver, though.

The feed into your house consists of a number of modulated narrowband HF
carriers, which are phase and/ or amplitude modulated, I can't remember
which, and an analogue baseband signal for your normal phone.

Yes digital modulation system perhaps;?...
No. Somes sort of FSK IIRC.

tony sayer wrote:
In article , John Williamson johnwilli
scribeth thus
tony sayer wrote:
Note the ;? ..

I'm used to ;-? for that... ;-)

Had this very conversation the other month with Two BT exchange engineer
types.. one argued that it was a digital system the other argued that it was
not.. I presume the actual modulation scheme in use would determine that..

They could well both be right on different lines. One has old-fashioned
copper from the DSLAM in the exchange to the street box, the other has
fibre to a DSLAM in the box. When they finally roll out fibre to the
home, then it'll be digital all the way. Inside your current
Modem/Router is an analogue line driver, though.

The feed into your house consists of a number of modulated narrowband HF
carriers, which are phase and/ or amplitude modulated, I can't remember
which, and an analogue baseband signal for your normal phone.

Yes digital modulation system perhaps;?...
Of an analogue carrier. The signal on the line is *not* a simple on/off,
it uses a combination of phase and amplitude modulation of multiple
carriers. What controls the modulation is digital, the modulated carrier
is analogue.

To aid in your understanding, *all* signals passing along the local loop
(AKA the "Last mile") are analogue.

Digital signals are transmitted by encoding onto a carrier, and then
decoded by comparing the transmitted signal with a stable reference, as
in a FM or AM radio set. The output from this decoder to your computer
is digital, the input to the decoder from the line is analogue. In the
days of 75 baud modems, the digital data was transmitted by switching an
audio tone on and off, and later, the tone was switched between two
frequencies, which allowed faster transmission. Later still, advances in
design and manufacture permitted the use of combinations of level and
phase variation of the carrier to allow the transmission of more than
one bit of data per cycle of carrier. Broadband basically just uses a
number of these phase and amplitude modulated carrier signals coming
down the same line.

Now, either you're trying to wind me up, or you *really* don't
understand the difference between the analogue and digital parts of a
modem. If the latter, then I'd suggest studying the Wiki reference
given, and follow the links in the article to the bits you don't
understand. You might also like to study amplitude, frequency and phase
modulation schemes for radio transmission.


No John, thats the day job in Radio of a few types!, its just where do
you draw the demarcation line in a digital or analogue system.

Two senior BT engineering types couldn't agree on this.


there is in the limit no distinction.

Digital signals are approximated by analogue electronics which have at
their heart digital atomic electron transitions as the core element.

If you like an analogue signal is in fact a digital approximation done
by counting electrons.

The sound of each electron hitting, is the noise.



I'll see what a Professor I know at the Uni sez. Be interesting..

Andy Wade wrote:
On 15/01/2011 16:02, John Williamson wrote:

tony sayer wrote:
Yes digital modulation system perhaps;?...

Exactly so. xDSL uses discrete multi-tone modulation (DMT), a variation
on the theme of OFDM used for digital radio and TV. These are
undoubtedly *digital* modulation schemes.

Of an analogue carrier.

Of a large number of (suppressed) carriers, in fact. The resulting
electrical signal has a time variation of amplitude that looks similar
to white Gaussian noise, but you shouldn't think of it as being
analogue. The amplitude is not a direct representation of a
continuously varying quantity an the way that the analogue speech signal
on the line represents sound pressure.

The signal on the line is *not* a simple on/off,

So what? A digital representation doesn't have to be binary. Digital
data - that could, for example, represent an audio signal after sampling
and A/D conversion - is frequently transmitted over wires or radio
channels as a sequence of 'symbols' each symbol representing one *or
more* bits. Increasing the number of bits per symbol generally allows
more data to be sent over a given spectral bandwidth but the signal
remains digital - each symbol represents one of a finite number of
discrete states.

To aid in your understanding, *all* signals passing along the local loop
(AKA the "Last mile") are analogue.

The speech signal is analogue. The xDSL signal is digital.


No, it's not - its amplitude and phase modulated carriers.

Dave Liquorice wrote:
On Fri, 14 Jan 2011 15:11:48 +0000, The Natural Philosopher wrote:

You also need to know that only ports have IP address's not
devices.
No., *interfaces* have *one* IP address and up to 64,000 PORTS.

In my book an "interface" can have more than one physical connection,
each phyical connection is a "port", as in the ports of an interface
card in a PABX or comms matrix.


That is exactly correct for TCP/IP

An interface can have many many connections, some even to the same port.

They just aren't 'physical'

That's the whole beauty of TCP/IP. Many virtual connections can exist
over the same physical piece of wire.


Isn't language interesting?

In article o.uk,
"Dave Liquorice" writes:
On Tue, 11 Jan 2011 14:20:35 +0100, Timothy Murphy wrote:

It seems to me that a modem should be able to re-connect
without external help;
I wonder if there are ADSL modems around that do this?

Yes, mine does. It also has a configuration setting to not do this.

What is your modem.

ZyXEL P660R-61C

I have ZyXEL P660R-D1 (basic modem with NAT) and ZyXEL P660HW-T1 V2
(more advanced modem with NAT, Firewall, WiFi), and both auto reconnect.

Still have a couple of old Dynamode R-ADSL-C1 modems. These also
reconnect, but do periodically lockup for other reasons and so are
regularly checked and if necessary rebooted by a computer on site.
Eventually they die completely.

Also still have a very old BT-badged Alcatel modem as a spare, which
reconnects without any problems. These are infamous for the internal
mains PSU dying, but mine's still OK.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 15/01/2011 22:22, John Williamson wrote:

[...] Taking the simplest case, is an FM or AM radio signal modulated
by a square wave analogue or digital?

It could be either. If the modulation represents a continuously varying
quantity (e.g. as in PAM or PWM) it's analogue. If the modulation
represents discrete states from a finite set (e.g. OOK, ASK or FSK) it's
digital. Even plain old OOK morse ('CW') is essentially digital,
although you could argue that subtle timing variations in the sender's
'fist' is additional analogue information:~)

The essential characteristics to consider are these:

Analogue
--------
- transmitted signal has continuous variation, representing an input
signal with similar variation;

- imperfections such as noise and many types of distortion arise in
transmission and are always present in the received signal to some extent;

- the original input can never be perfectly reconstructed for
retransmission. In a chain of relays there will be cumulative
deterioration;

- tendency to gradual deterioration with degrading S/N ratio in the channel.

Digital
-------
- transmitted signal represent discrete states;

- received & decoded signal can have a vanishingly small probability of
error. Provided the channel parameters are within certain limits, the
original input can be reconstructed free of added noise and distortion;

- no cumulative deterioration in long chains or relays;

- tendency to rapid deterioration with degrading S/N ratio in the
channel (digital cliff effect).

MODulator/ DEModulator implies an analogue carrier in the transmission
medium.

That's a carry-over from thinking of all RF systems as analogue. Really
a carrier is just a sinusoidal signal; it's neither analogue nor
digital. How you modulate it determines that.

If both sides are digital, then surely it's just a line driver?

Not if significant signal processing is performed, as is very much the
case for digital modulation schemes like xDSL and COFDM. A line driver
doesn't do things like multi-carrier FDM, interleaving, FEC coding and
I-Q modulation.

[...]
The discrete multitone modulation article block diagram shows an ADC/
DAC pair in the chain, before and after the transmission medium. Part of
the DAC function is to convert inexact analogue levels in the
transmission into steps for digital decoding.

Point taken, but that's just part of the electrical signal processing in
the modem chain. In fact it's normal to use DACs to create the I and Q
baseband components that are multiplied by the carrier in a balanced
modulator, and ADCs after downconversion at the receiving end. The
baseband waveforms are certainly 'analogue-like' (no 'square' waves here
as they're band-limited) but that doesn't make the modulated signal
analogue, in my view. Call it analogue signal processing within a
digital system if you like.

I would say that the *signal* on the line is analogue, with the levels
partly dictated by analogue mechanisms such as AGC and interference,
while the information transmitted is digital.

Would you consider Ethernet on twisted pair analogue or digital? It's
certainly influenced by electrical issues like attenuation, frequency
response and crosstalk. DACs and ADCs could be used to send and receive
the actual line signals.

And what about high-speed data buses in computers? Noise, overshoot &
ringing and transmission line issues such as reflections and impedance
matching are all relevant. Are these buses analogue or digital
transmission systems?

I suspect we're looking at the same thing from different angles.

Definitely :-)

--
Andy

On 15/01/2011 23:32, wrote:

Several symbols (carriers) are usually used simultaneusly

'Symbols' are not 'carriers'.

A symbol (one ore more bits) is the basic unit of data transmitted.
Symbols are transmitted in time sequence to send a data stream.
http://en.wikipedia.org/wiki/Symbol_%28data%29

The number of carriers (one or many) is quite separate. Multi carrier
FDM systems like DMT and (C)OFDM are used so that a fast stream can be
broken into many slower ones, each with a correspondingly slower symbol
rate. This, within limits, can make a system much more tolerant to
multipath reflections occurring in the transmission channel.

--
Andy

Andy Wade wrote:
On 15/01/2011 22:22, John Williamson wrote:

[...] Taking the simplest case, is an FM or AM radio signal modulated
by a square wave analogue or digital?

It could be either. If the modulation represents a continuously varying
quantity (e.g. as in PAM or PWM) it's analogue. If the modulation
represents discrete states from a finite set (e.g. OOK, ASK or FSK) it's
digital. Even plain old OOK morse ('CW') is essentially digital,
although you could argue that subtle timing variations in the sender's
'fist' is additional analogue information:~)

The essential characteristics to consider are these:

Analogue
--------
- transmitted signal has continuous variation, representing an input
signal with similar variation;

- imperfections such as noise and many types of distortion arise in
transmission and are always present in the received signal to some extent;

- the original input can never be perfectly reconstructed for
retransmission. In a chain of relays there will be cumulative
deterioration;

- tendency to gradual deterioration with degrading S/N ratio in the
channel.

Digital
-------
- transmitted signal represent discrete states;

- received & decoded signal can have a vanishingly small probability of
error. Provided the channel parameters are within certain limits, the
original input can be reconstructed free of added noise and distortion;

- no cumulative deterioration in long chains or relays;

- tendency to rapid deterioration with degrading S/N ratio in the
channel (digital cliff effect).

MODulator/ DEModulator implies an analogue carrier in the transmission
medium.

That's a carry-over from thinking of all RF systems as analogue. Really
a carrier is just a sinusoidal signal; it's neither analogue nor
digital. How you modulate it determines that.

If both sides are digital, then surely it's just a line driver?

Not if significant signal processing is performed, as is very much the
case for digital modulation schemes like xDSL and COFDM. A line driver
doesn't do things like multi-carrier FDM, interleaving, FEC coding and
I-Q modulation.

[...]
The discrete multitone modulation article block diagram shows an ADC/
DAC pair in the chain, before and after the transmission medium. Part of
the DAC function is to convert inexact analogue levels in the
transmission into steps for digital decoding.

Point taken, but that's just part of the electrical signal processing in
the modem chain. In fact it's normal to use DACs to create the I and Q
baseband components that are multiplied by the carrier in a balanced
modulator, and ADCs after downconversion at the receiving end. The
baseband waveforms are certainly 'analogue-like' (no 'square' waves here
as they're band-limited) but that doesn't make the modulated signal
analogue, in my view. Call it analogue signal processing within a
digital system if you like.

I would say that the *signal* on the line is analogue, with the levels
partly dictated by analogue mechanisms such as AGC and interference,
while the information transmitted is digital.

Would you consider Ethernet on twisted pair analogue or digital? It's
certainly influenced by electrical issues like attenuation, frequency
response and crosstalk. DACs and ADCs could be used to send and receive
the actual line signals.

And what about high-speed data buses in computers? Noise, overshoot &
ringing and transmission line issues such as reflections and impedance
matching are all relevant. Are these buses analogue or digital
transmission systems?

all analogue of course.

All computers are in fact analogue, only the DATA is held in digital format.

Never the SIGNALS.





I suspect we're looking at the same thing from different angles.

Definitely :-)

In article , John Williamson johnwilli
scribeth thus
tony sayer wrote:

No John, thats the day job in Radio of a few types!, its just where do
you draw the demarcation line in a digital or analogue system.

I draw it at the point where the digital data is turned into an analogue
signal by the modulator and vice versa.

Though, I might *call* it digital all the way through, if I were talking
to someone who doesn't know a lot about it......

To draw a (Maybe not perfect) analogy, the "digital" sound recording I
made the other day was analogue from the microphone up to the point
where the signal met the ADC, then it was digital all through the chain
until it met the DAC just before the amplifier. Then it was analogue
again. If I published it, it would be classified as DDD on a CD, as all
the recording, editing and distribution was done in the digital domain.
Both ends of the reproduction chain must be analogue, though. Unless
you've got digital vocal chords and ears. It's still *called* a digital
recording, though.


Yes indeed, 'tho not as digital as might be thought.

We have a Digital FM transmitter .. work then one out;!..
--
Tony Sayer

Andrew Gabriel wrote:

Still have a couple of old Dynamode R-ADSL-C1 modems. These also
reconnect, but do periodically lockup for other reasons and so are
regularly checked and if necessary rebooted by a computer on site.

Thanks for your info.
But how do you reboot the modem by computer, as a matter of interst?
In my case when the modem goes down I cannot access it from the desktop
(to which it is connected by ethernet).

--
Timothy Murphy
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland

tony sayer wrote:
In article , John Williamson johnwilli
scribeth thus
tony sayer wrote:
No John, thats the day job in Radio of a few types!, its just where do
you draw the demarcation line in a digital or analogue system.

I draw it at the point where the digital data is turned into an analogue
signal by the modulator and vice versa.

Though, I might *call* it digital all the way through, if I were talking
to someone who doesn't know a lot about it......

To draw a (Maybe not perfect) analogy, the "digital" sound recording I
made the other day was analogue from the microphone up to the point
where the signal met the ADC, then it was digital all through the chain
until it met the DAC just before the amplifier. Then it was analogue
again. If I published it, it would be classified as DDD on a CD, as all
the recording, editing and distribution was done in the digital domain.
Both ends of the reproduction chain must be analogue, though. Unless
you've got digital vocal chords and ears. It's still *called* a digital
recording, though.


Yes indeed, 'tho not as digital as might be thought.

We have a Digital FM transmitter .. work then one out;!..
What you all need to appreciate is the data may be digital, electronics
is always analogue.

To get a digital data transferred over an analogue channel takes a modem.

even a line driver is a sort of modem

In article ,
Timothy Murphy writes:
Andrew Gabriel wrote:

Still have a couple of old Dynamode R-ADSL-C1 modems. These also
reconnect, but do periodically lockup for other reasons and so are
regularly checked and if necessary rebooted by a computer on site.

Thanks for your info.
But how do you reboot the modem by computer, as a matter of interst?
In my case when the modem goes down I cannot access it from the desktop
(to which it is connected by ethernet).

I can still get to the web interface, and hence select reboot.
I used to have one on a site with computer controlled power outlets,
so I could power cycle it, but it eventually completely died and has
been replaced with a ZyXEL P660R-D1 which has been completely
trouble-free, and I no longer even poll with the computer.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 16/01/2011 11:47, The Natural Philosopher wrote:

all analogue of course.

All computers are in fact analogue, only the DATA is held in digital
format.

Never the SIGNALS.

Hmm, that's a rather unorthodox view. It amounts to saying that there's
no such thing as a digital signal. That flies in the face of
established usage, and the IEV which gives the following definitions for
"signal" and "digital signal":

Signal:
- physical quantity, one or more parameters of which carry information
about one or more quantities
NOTE €“ These parameters are referred to as €œinformation parameters€�.

[IEV number 351-21-51]


Digital signal:
- signal whose information parameter may assume one out of a set of
discrete values.

[IEV number 351-21-54]

--
Andy

Andy Wade wrote:
On 16/01/2011 11:47, The Natural Philosopher wrote:

all analogue of course.

All computers are in fact analogue, only the DATA is held in digital
format.

Never the SIGNALS.

Hmm, that's a rather unorthodox view. It amounts to saying that there's
no such thing as a digital signal. That flies in the face of
established usage, and the IEV which gives the following definitions for
"signal" and "digital signal":

Signal:
- physical quantity, one or more parameters of which carry information
about one or more quantities
NOTE €“ These parameters are referred to as €œinformation parameters€�.

[IEV number 351-21-51]


Digital signal:
- signal whose information parameter may assume one out of a set of
discrete values.


Information parameter == DATA

What that is saying is that e.g. the information parameter held as 0 or
1 may be expressed by e.g. voltages above below 0.5v and or above say 3v.


It doesn't say that 2v has meaning. Which is why you have a clock..to
say 'don't look at me while I am changing, darling'

Neither does it say that the voltages or the circuitry associaed with
them are in fact anything other than analogue devices, and they are.

When we talk about 'digital electronics' what we mean is 'analogue
electronics that processes digital data'


[IEV number 351-21-54]

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember (Andrew
Gabriel) saying something like:

I have snip and ZyXEL P660HW-T1 V2

I've got the v3, as supplied by my ISP.
Total pita it is, as it keeps filling the log entries with 'total number
of sessions per user exceeded' or somesuch, then craps out, but a reset
sorts it for two days.
In the Network/NAT settings, it has "Maximum number of NAT/firewall
sessions for the router is blah. To remove the per user limit, set to
4096". I've done just that, but it makes no difference.

Hohum, I can see a Netgear DG834G in my future.

In article ,
Grimly Curmudgeon writes:
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember (Andrew
Gabriel) saying something like:

I have snip and ZyXEL P660HW-T1 V2

I've got the v3, as supplied by my ISP.
Total pita it is, as it keeps filling the log entries with 'total number
of sessions per user exceeded' or somesuch, then craps out, but a reset
sorts it for two days.
In the Network/NAT settings, it has "Maximum number of NAT/firewall
sessions for the router is blah. To remove the per user limit, set to
4096". I've done just that, but it makes no difference.

Are you running something that generates lots of network connections
or cycles through network connections rapidly?
On mine, it's set to 512 NAT/Firewall Session Per User. Not sure what
a "user" is in this case - maybe each internal IP address? However, I've
not seen what you describe and I've heard no complaints from the users.

Hohum, I can see a Netgear DG834G in my future.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Tue, 18 Jan 2011 23:57:26 +0000 (UTC),
(Andrew Gabriel) wrote:

In article ,
Grimly Curmudgeon writes:
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember (Andrew
Gabriel) saying something like:

I have snip and ZyXEL P660HW-T1 V2

I've got the v3, as supplied by my ISP.
Total pita it is, as it keeps filling the log entries with 'total number
of sessions per user exceeded' or somesuch, then craps out, but a reset
sorts it for two days.
In the Network/NAT settings, it has "Maximum number of NAT/firewall
sessions for the router is blah. To remove the per user limit, set to
4096". I've done just that, but it makes no difference.

Are you running something that generates lots of network connections
or cycles through network connections rapidly?
On mine, it's set to 512 NAT/Firewall Session Per User. Not sure what
a "user" is in this case - maybe each internal IP address? However, I've
not seen what you describe and I've heard no complaints from the users.

I had one similar Zyxel router (probably the V2) and also did not
experience this problem. This is no help to GC though. Sometimes
things just don't work for a few people.

Hohum, I can see a Netgear DG834G in my future.

Don't hear much good about these nowadays, except for the ones with
the Broadcom chipset.
--
(\__/) M.
(='.'=) Due to the amount of spam posted via googlegroups and
(")_(") their inaction to the problem. I am blocking some articles
posted from there. If you wish your postings to be seen by
everyone you will need use a different method of posting.

Mark wrote:

Hohum, I can see a Netgear DG834G in my future.

Don't hear much good about these nowadays, except for the ones with
the Broadcom chipset.

What do you hear about Linksys routers?
I have a Linksys WRT54GL (running wrt-dd)
which has worked perfectly for me for a number of years;
I'm wondering if this is still the best Linksys offering?

--
Timothy Murphy
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland

On Wed, 19 Jan 2011 12:24:08 +0000, Timothy Murphy
wrote:

Mark wrote:

Hohum, I can see a Netgear DG834G in my future.

Don't hear much good about these nowadays, except for the ones with
the Broadcom chipset.

What do you hear about Linksys routers?
I have a Linksys WRT54GL (running wrt-dd)
which has worked perfectly for me for a number of years;
I'm wondering if this is still the best Linksys offering?

I don't use Linksys routers myself but I believe they are fairly good
as a whole.
--
(\__/) M.
(='.'=) Due to the amount of spam posted via googlegroups and
(")_(") their inaction to the problem. I am blocking some articles
posted from there. If you wish your postings to be seen by
everyone you will need use a different method of posting.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Mark
saying something like:

On Tue, 18 Jan 2011 23:57:26 +0000 (UTC),
(Andrew Gabriel) wrote:

In article ,
Grimly Curmudgeon writes:
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember (Andrew
Gabriel) saying something like:

I have snip and ZyXEL P660HW-T1 V2

I've got the v3, as supplied by my ISP.
Total pita it is, as it keeps filling the log entries with 'total number
of sessions per user exceeded' or somesuch, then craps out, but a reset
sorts it for two days.
In the Network/NAT settings, it has "Maximum number of NAT/firewall
sessions for the router is blah. To remove the per user limit, set to
4096". I've done just that, but it makes no difference.

Are you running something that generates lots of network connections
or cycles through network connections rapidly?
On mine, it's set to 512 NAT/Firewall Session Per User. Not sure what
a "user" is in this case - maybe each internal IP address? However, I've
not seen what you describe and I've heard no complaints from the users.

Ah; it might be utorrent. I'll try it without for a couple of days and
see what happens, thanks.


I had one similar Zyxel router (probably the V2) and also did not
experience this problem. This is no help to GC though. Sometimes
things just don't work for a few people.

Hohum, I can see a Netgear DG834G in my future.

Don't hear much good about these nowadays, except for the ones with
the Broadcom chipset.

Noted, ta.

In article ,
Grimly Curmudgeon writes:
On Tue, 18 Jan 2011 23:57:26 +0000 (UTC),
(Andrew Gabriel) wrote:

In article ,
Grimly Curmudgeon writes:
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember (Andrew
Gabriel) saying something like:

I have snip and ZyXEL P660HW-T1 V2

I've got the v3, as supplied by my ISP.
Total pita it is, as it keeps filling the log entries with 'total number
of sessions per user exceeded' or somesuch, then craps out, but a reset
sorts it for two days.
In the Network/NAT settings, it has "Maximum number of NAT/firewall
sessions for the router is blah. To remove the per user limit, set to
4096". I've done just that, but it makes no difference.

Are you running something that generates lots of network connections
or cycles through network connections rapidly?
On mine, it's set to 512 NAT/Firewall Session Per User. Not sure what
a "user" is in this case - maybe each internal IP address? However, I've
not seen what you describe and I've heard no complaints from the users.

Ah; it might be utorrent. I'll try it without for a couple of days and
see what happens, thanks.

Did it make any difference?
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember (Andrew
Gabriel) saying something like:

Ah; it might be utorrent. I'll try it without for a couple of days and
see what happens, thanks.

Did it make any difference?

utorrent's not been downloading for the past few days, only seeding, and
the router's not choked up, so it looks like that was it.

In message , Grimly
Curmudgeon writes
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember (Andrew
Gabriel) saying something like:

Ah; it might be utorrent. I'll try it without for a couple of days and
see what happens, thanks.

Did it make any difference?

utorrent's not been downloading for the past few days, only seeding, and
the router's not choked up, so it looks like that was it.

Yup, I've had problems with routers choking after sometime with the
number of connections from uttorent. In my case a Zyxel and a Netgear.
The O2 supplied one, some variety of Thomson doesn't seem to suffer the
same problem.
--
Chris French

In article ,
chris French writes:
In message , Grimly
Curmudgeon writes
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember (Andrew
Gabriel) saying something like:

Ah; it might be utorrent. I'll try it without for a couple of days and
see what happens, thanks.

Did it make any difference?

utorrent's not been downloading for the past few days, only seeding, and
the router's not choked up, so it looks like that was it.

Yup, I've had problems with routers choking after sometime with the
number of connections from uttorent. In my case a Zyxel and a Netgear.
The O2 supplied one, some variety of Thomson doesn't seem to suffer the
same problem.

The problem will be with the volume of stateful information it needs to
keep. The limit(s) could be in the firewall and/or NAT function (although
not the router function as that's probably stateless in an ADSL modem).

If you want to run what ammounts to a server, then you probably don't
want to front it with what ammounts to a low capacity client NAT/firewall
in an ADSL modem. I actually use the NAT/firewall functions inside the
server which will handle millions of connections if necessary (although
not necessary for me).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]