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Electrical gigabit transmission ?

 
 
Michael Weiss
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      01-30-2007
Hi all,

I wonder what is curently state-of-the art in serial high-speed transmission
and what are the prevailing data rates? I know about some SerDes in the
gigabit-per-second range but I cannot imagine if 10 Gbps are really a
challenge or the applied method or if it's 1 Gbps (or something in
between)...?
I recently heard about some 60 GHz in the mobile communication sector and 10
Gbit Ethernet but as far as I know there are those multi-level modulation
methods (like QAM for example) that are able to provide 10 Gbit bandwidth
with a bitrate of some Mbps (is that correct?).
I'm not interested so much in those higher modulation methods (nor in
optical transmission) but in the baseband communication where bitrate =
clockrate, i.e. the line rate. What can be efficiently transmitted today
electrically (over wire or PCB)? What is the prevailing technology of those
circuits, is it CMOS or are there alternatives?
I am a senior electrical engineer and unfortunately did not manage to keep
up-to-date. After googling all night I'm really depressed because I finally
couldn't find an unambiguous answer.
Maybe some guys in the silicon-business or practitioners know the anser and
are willing to share there knoledge with me?

Best regards
Geronimo


 
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Nick Maclaren
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      01-30-2007

In article <45bf1bb9$0$18833$(E-Mail Removed)-online.net>,
"Michael Weiss" <(E-Mail Removed)> writes:
|>
|> I wonder what is curently state-of-the art in serial high-speed transmission
|> and what are the prevailing data rates? I know about some SerDes in the
|> gigabit-per-second range but I cannot imagine if 10 Gbps are really a
|> challenge or the applied method or if it's 1 Gbps (or something in
|> between)...?

Oh, it's a challenge, all right. I went to a very interesting talk on
it, and heard about the issues. The worst problem seems to be cross-talk,
but losses are pretty bad, too. It's feasible, for short distances, but
is a lot harder than 1 Gbps. One of the reasons that 60 Gbps is being
touted is that some people are doubtful about being able to get to 100
Gbps in a realistic timescale for a feasible cost.

|> I am a senior electrical engineer and unfortunately did not manage to keep
|> up-to-date. After googling all night I'm really depressed because I finally
|> couldn't find an unambiguous answer.

Unfortunately, I am not, so I can merely tell you the above; there is
little point in me trying to go into details of what I remember, as I
will probably get them wrong.

What I am certain of is that an optoelectronic breakthrough (and there
are several possibilities) would kill medium distance, high speed
electrical transmission dead - almost overnight. As 'they' have spent
a couple of decades putting serious money into optoelectronic research,
I am not holding my breath. But, as with flat screens, it could happen
at any time.

Unfortunately, none of that gets you a lot further


Regards,
Nick Maclaren.
 
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Del Cecchi
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Posts: n/a
 
      01-30-2007

"Michael Weiss" <(E-Mail Removed)> wrote in message
news:45bf1bb9$0$18833$(E-Mail Removed)-online.net...
> Hi all,
>
> I wonder what is curently state-of-the art in serial high-speed
> transmission and what are the prevailing data rates? I know about some
> SerDes in the gigabit-per-second range but I cannot imagine if 10 Gbps
> are really a challenge or the applied method or if it's 1 Gbps (or
> something in between)...?
> I recently heard about some 60 GHz in the mobile communication sector
> and 10 Gbit Ethernet but as far as I know there are those multi-level
> modulation methods (like QAM for example) that are able to provide 10
> Gbit bandwidth with a bitrate of some Mbps (is that correct?).
> I'm not interested so much in those higher modulation methods (nor in
> optical transmission) but in the baseband communication where bitrate =
> clockrate, i.e. the line rate. What can be efficiently transmitted
> today electrically (over wire or PCB)? What is the prevailing
> technology of those circuits, is it CMOS or are there alternatives?
> I am a senior electrical engineer and unfortunately did not manage to
> keep up-to-date. After googling all night I'm really depressed because
> I finally couldn't find an unambiguous answer.
> Maybe some guys in the silicon-business or practitioners know the anser
> and are willing to share there knoledge with me?
>
> Best regards
> Geronimo

I'll go along with the crosspost this time....

You are talking about what is called "NRZ" or "not return to zero" and
the state of the art for commercial products is in the 10-12 Gbit/second
range for copper wires on backplanes or short cables. These
serializer/deserializer (serdes) products are usually done in CMOS.

QAM and other modulation schemes have been proposed but never really
caught on. Likewise, advanced coding schemes like trellis or viterbi
coding and forward error correction such as are used in long haul
optical and in disk drives haven't caught on in the copper world. QAM
only halves the baud or symbol rate compared to the data rate by encoding
2 bits per baud.

People use CMOS because it is the cheapest, although some of the chips
involved with optics are made with more exotic materials.

del cecchi


>



 
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Tim McCaffrey
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Posts: n/a
 
      01-30-2007
In article <45bf1bb9$0$18833$(E-Mail Removed)-online.net>,
http://www.velocityreviews.com/forums/(E-Mail Removed) says...
>
>Hi all,
>
>I wonder what is curently state-of-the art in serial high-speed transmission
>and what are the prevailing data rates? I know about some SerDes in the
>gigabit-per-second range but I cannot imagine if 10 Gbps are really a
>challenge or the applied method or if it's 1 Gbps (or something in
>between)...?
>I recently heard about some 60 GHz in the mobile communication sector and 10
>Gbit Ethernet but as far as I know there are those multi-level modulation
>methods (like QAM for example) that are able to provide 10 Gbit bandwidth
>with a bitrate of some Mbps (is that correct?).
>I'm not interested so much in those higher modulation methods (nor in
>optical transmission) but in the baseband communication where bitrate =
>clockrate, i.e. the line rate. What can be efficiently transmitted today
>electrically (over wire or PCB)? What is the prevailing technology of those
>circuits, is it CMOS or are there alternatives?
>I am a senior electrical engineer and unfortunately did not manage to keep
>up-to-date. After googling all night I'm really depressed because I finally
>couldn't find an unambiguous answer.
>Maybe some guys in the silicon-business or practitioners know the anser and
>are willing to share there knoledge with me?
>
>Best regards
>Geronimo
>
>

The fastest signaling over copper that I'm (being a software guy, and not
involved in bleeding edge hardware development) aware of (in production) is
3Gig SAS/SATA cables. I'm not sure what the "baud" of the protocol is.

Perhaps Infiniband is faster?

- Tim

 
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PeteS
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Posts: n/a
 
      01-30-2007
Tim McCaffrey wrote:
> In article <45bf1bb9$0$18833$(E-Mail Removed)-online.net>,
> (E-Mail Removed) says...
>> Hi all,
>>
>> I wonder what is curently state-of-the art in serial high-speed transmission
>> and what are the prevailing data rates? I know about some SerDes in the
>> gigabit-per-second range but I cannot imagine if 10 Gbps are really a
>> challenge or the applied method or if it's 1 Gbps (or something in
>> between)...?
>> I recently heard about some 60 GHz in the mobile communication sector and 10
>> Gbit Ethernet but as far as I know there are those multi-level modulation
>> methods (like QAM for example) that are able to provide 10 Gbit bandwidth
>> with a bitrate of some Mbps (is that correct?).
>> I'm not interested so much in those higher modulation methods (nor in
>> optical transmission) but in the baseband communication where bitrate =
>> clockrate, i.e. the line rate. What can be efficiently transmitted today
>> electrically (over wire or PCB)? What is the prevailing technology of those
>> circuits, is it CMOS or are there alternatives?
>> I am a senior electrical engineer and unfortunately did not manage to keep
>> up-to-date. After googling all night I'm really depressed because I finally
>> couldn't find an unambiguous answer.
>> Maybe some guys in the silicon-business or practitioners know the anser and
>> are willing to share there knoledge with me?
>>
>> Best regards
>> Geronimo
>>
>>

> The fastest signaling over copper that I'm (being a software guy, and not
> involved in bleeding edge hardware development) aware of (in production) is
> 3Gig SAS/SATA cables. I'm not sure what the "baud" of the protocol is.
>
> Perhaps Infiniband is faster?
>
> - Tim
>


Well, one of the architects of InfiniBand posted right above you

The 1.2 spec has details for 2.5, 5 and 10Gb/s signaling per pair,
although as I recall from the discussions we had 10Gb/s was not easily
realisable on 'ordinary' materials at the time the 1.2 spec was being
written.

Cheers

PeteS
 
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PeteS
Guest
Posts: n/a
 
      01-30-2007
Nick Maclaren wrote:
> In article <45bf1bb9$0$18833$(E-Mail Removed)-online.net>,
> "Michael Weiss" <(E-Mail Removed)> writes:
> |>
> |> I wonder what is curently state-of-the art in serial high-speed transmission
> |> and what are the prevailing data rates? I know about some SerDes in the
> |> gigabit-per-second range but I cannot imagine if 10 Gbps are really a
> |> challenge or the applied method or if it's 1 Gbps (or something in
> |> between)...?
>
> Oh, it's a challenge, all right. I went to a very interesting talk on
> it, and heard about the issues. The worst problem seems to be cross-talk,
> but losses are pretty bad, too. It's feasible, for short distances, but
> is a lot harder than 1 Gbps. One of the reasons that 60 Gbps is being
> touted is that some people are doubtful about being able to get to 100
> Gbps in a realistic timescale for a feasible cost.
>
> |> I am a senior electrical engineer and unfortunately did not manage to keep
> |> up-to-date. After googling all night I'm really depressed because I finally
> |> couldn't find an unambiguous answer.
>
> Unfortunately, I am not, so I can merely tell you the above; there is
> little point in me trying to go into details of what I remember, as I
> will probably get them wrong.
>
> What I am certain of is that an optoelectronic breakthrough (and there
> are several possibilities) would kill medium distance, high speed
> electrical transmission dead - almost overnight. As 'they' have spent
> a couple of decades putting serious money into optoelectronic research,
> I am not holding my breath. But, as with flat screens, it could happen
> at any time.
>
> Unfortunately, none of that gets you a lot further
>
>
> Regards,
> Nick Maclaren.


Optics are expensive compared to copper - very expensive. I designed a
4x InfiniBand optical interface board some 3 years ago using POP4
transceivers and although it worked great, it was too expensive for any
sort of large installation.

Cheers

PeteS
 
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Joseph H Allen
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Posts: n/a
 
      01-30-2007
In article <45bf1bb9$0$18833$(E-Mail Removed)-online.net>,
Michael Weiss <(E-Mail Removed)> wrote:
>Hi all,


>I wonder what is curently state-of-the art in serial high-speed transmission
>and what are the prevailing data rates? I know about some SerDes in the
>gigabit-per-second range but I cannot imagine if 10 Gbps are really a
>challenge or the applied method or if it's 1 Gbps (or something in
>between)...?


10 Gb/sec is commonplace (we're close to every PC having a 10 G port). 40
Gb/sec is available (Cisco sells 40 G line cards today). 40 G exists
because it was mostly developed during the bubble. Development has leveled
off since then...

The main disadvantage of these high speed serial and optical interfaces is
heat and the size of the optical modules. They use much more power than the
equivalent bandwidth parallel interface.

There are challenges at every level for these interfaces, but here's one
example: at 10 G, the packet rate for packet-over-SONET is 25 M packets /
sec. This means you need to make a routing decision at this rate, and that
you need random access from you buffer at this rate. So for example, RLDRAM
can do 50 M random accesses / sec, which supports one 10 G interface (25 M
for the write side, and 25 M for the read side). The raw bandwidth is an
easier problem because you can always do muxing (either wavelength division
muxing or electrical SONET-level muxing). The disadvantage of MUXing is
that you can then not support a single flow greater than any one input to
your mux.

It does not help that the internet protocols (for example HDLC) were design
for a word size of one byte (which is better than the previous standards of
one bit, but a word size of 64-bits would be much easier).

Now at 40 G, the packet rate is 100 M / sec for POS... you can see where
this is going

--
/* (E-Mail Removed) AB1GO */ /* Joseph H. Allen */
int a[1817];main(z,p,q,r){for(p=80;q+p-80;p-=2*a[p])for(z=9;z--q=3&(r=time(0)
+r*57)/7,q=q?q-1?q-2?1-p%79?-1:0%79-77?1:0<1659?79:0>158?-79:0,q?!a[p+q*2
]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817printf(q%79?"%c":"%c\n"," #"[!a[q-1]]);}
 
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Nick Maclaren
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Posts: n/a
 
      01-30-2007

In article <epo5g1$32h$(E-Mail Removed)>,
(E-Mail Removed) (Joseph H Allen) writes:
|> In article <45bf1bb9$0$18833$(E-Mail Removed)-online.net>,
|> Michael Weiss <(E-Mail Removed)> wrote:
|>
|> >I wonder what is curently state-of-the art in serial high-speed transmission
|> >and what are the prevailing data rates? I know about some SerDes in the
|> >gigabit-per-second range but I cannot imagine if 10 Gbps are really a
|> >challenge or the applied method or if it's 1 Gbps (or something in
|> >between)...?
|>
|> 10 Gb/sec is commonplace (we're close to every PC having a 10 G port). ...

However, that doesn't help without affordable, reliable and usable cables
and connectors - and they are the problem.


Regards,
Nick Maclaren.
 
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Joseph H Allen
Guest
Posts: n/a
 
      01-30-2007
In article <epo6uv$9ua$(E-Mail Removed)>,
Nick Maclaren <(E-Mail Removed)> wrote:

>In article <epo5g1$32h$(E-Mail Removed)>,
>(E-Mail Removed) (Joseph H Allen) writes:


>|> >I wonder what is curently state-of-the art in serial high-speed transmission
>|> >and what are the prevailing data rates? I know about some SerDes in the
>|> >gigabit-per-second range but I cannot imagine if 10 Gbps are really a
>|> >challenge or the applied method or if it's 1 Gbps (or something in
>|> >between)...?


>|> 10 Gb/sec is commonplace (we're close to every PC having a 10 G port). ...


>However, that doesn't help without affordable, reliable and usable cables
>and connectors - and they are the problem.


OK so which technology is going to be cheaper for 100 G ethernet: fiber with
its expensive optical transceivers or all-electrical flexible waveguide? TE
propogation at 100 GHz is a waveguide cut-off size on the order of just 1.5
mm...

--
/* (E-Mail Removed) AB1GO */ /* Joseph H. Allen */
int a[1817];main(z,p,q,r){for(p=80;q+p-80;p-=2*a[p])for(z=9;z--q=3&(r=time(0)
+r*57)/7,q=q?q-1?q-2?1-p%79?-1:0%79-77?1:0<1659?79:0>158?-79:0,q?!a[p+q*2
]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817printf(q%79?"%c":"%c\n"," #"[!a[q-1]]);}
 
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Joel Kolstad
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Posts: n/a
 
      01-30-2007
"Joseph H Allen" <(E-Mail Removed)> wrote in message
news:epoiig$d2v$(E-Mail Removed)...
> OK so which technology is going to be cheaper for 100 G ethernet: fiber with
> its expensive optical transceivers or all-electrical flexible waveguide?


I'd wager there's a better chance that optical transceivers will become dirt
cheap before flexible waveguides do.



 
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