Electrical gigabit transmission ?

M

Michael Weiss

Guest
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
 
In article <45bf1bb9$0$18833$9b4e6d93@newsspool4.arcor-online.net>,
"Michael Weiss" <maerchenprinz@arcor.de> 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.
 
"Michael Weiss" <maerchenprinz@arcor.de> wrote in message
news:45bf1bb9$0$18833$9b4e6d93@newsspool4.arcor-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....
Click to expand...

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


>
 
Tim McCaffrey wrote:
In article <45bf1bb9$0$18833$9b4e6d93@newsspool4.arcor-online.net>,
maerchenprinz@arcor.de 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
Click to expand...
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
 
Nick Maclaren wrote:
In article <45bf1bb9$0$18833$9b4e6d93@newsspool4.arcor-online.net>,
"Michael Weiss" <maerchenprinz@arcor.de> 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.
Click to expand...
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
 
In article <45bf1bb9$0$18833$9b4e6d93@newsspool4.arcor-online.net>,
maerchenprinz@arcor.de 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
Click to expand...
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
 
In article <epo5g1$32h$1@pcls6.std.com>,
jhallen@TheWorld.com (Joseph H Allen) writes:
|> In article <45bf1bb9$0$18833$9b4e6d93@newsspool4.arcor-online.net>,
|> Michael Weiss <maerchenprinz@arcor.de> 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.
 
In article <45bf1bb9$0$18833$9b4e6d93@newsspool4.arcor-online.net>,
Michael Weiss <maerchenprinz@arcor.de> 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)...?
Click to expand...
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 :)

--
/* jhallen@world.std.com 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:p%79-77?1:0:p<1659?79:0:p>158?-79:0,q?!a[p+q*2
]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817;)printf(q%79?"%c":"%c\n"," #"[!a[q-1]]);}
 
"Joseph H Allen" <jhallen@TheWorld.com> wrote in message
news:epoiig$d2v$1@pcls6.std.com...
OK so which technology is going to be cheaper for 100 G ethernet: fiber with
its expensive optical transceivers or all-electrical flexible waveguide?
Click to expand...
I'd wager there's a better chance that optical transceivers will become dirt
cheap before flexible waveguides do.
 
In article <epo6uv$9ua$1@gemini.csx.cam.ac.uk>,
Nick Maclaren <nmm1@cus.cam.ac.uk> wrote:

In article <epo5g1$32h$1@pcls6.std.com>,
jhallen@TheWorld.com (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.
Click to expand...
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...

--
/* jhallen@world.std.com 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:p%79-77?1:0:p<1659?79:0:p>158?-79:0,q?!a[p+q*2
]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817;)printf(q%79?"%c":"%c\n"," #"[!a[q-1]]);}
 
[trimmed the followups a bit...]

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...
Click to expand...
Unless you can get at least de facto agreement on a larger MTU the
whole thing is moot for the end systems at least. Unless the 100G NIC
can take advantage of a score of cores (or more) one isn't going to
get anywhere near 100G speeds anyway... And even then, the small
nature of most traffic (not all of course) makes even the de facto
larger MTU moot for anything other than netperf TCP_STREAM, FTP and
some other bulk transfer stuff.

rick jones
--
The glass is neither half-empty nor half-full. The glass has a leak.
The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...
 
On 2007-01-30 16:58:24 -0600, jhallen@TheWorld.com (Joseph H Allen) said:

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...
Click to expand...
Don't forget parallel copper. The cheapest version of 10GigE is CX4 and
will probably remain so. 100GigE could be 12 lanes of 10GHz over
copper, although people might not put up with the huge connectors.

--
Wes Felter - wesley@felter.org - http://felter.org/wesley/
 
"Wes Felter" <wesley@felter.org> wrote in message
news:45bff261$0$9000$4c368faf@roadrunner.com...
Don't forget parallel copper. The cheapest version of 10GigE is CX4 and will
probably remain so. 100GigE could be 12 lanes of 10GHz over copper, although
people might not put up with the huge connectors.
Click to expand...
Many of them would, I imagine... that's ~25 pins, right? -- which even in a
high-density D-sub is "game port" (traditional DB-15) sized, and denser
connectors (such as the newer parallel printer port connector) are readily
available.

I'm sure I'm not the only one who remembers some the truly enormous SCSI
connectors in years past.

Or 60 pin IDCs!
 
I'm sure I'm not the only one who remembers some the truly enormous SCSI
connectors in years past.
Click to expand...
SCSI connectors "truly enormous"? Surely not! Take a Massbus connector instead!

Jan
 
On 2007-01-30, Joel Kolstad <JKolstad71HatesSpam@yahoo.com> wrote:
"Joseph H Allen" <jhallen@TheWorld.com> wrote in message
news:epoiig$d2v$1@pcls6.std.com...
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.
Click to expand...
a flexible waveguide of the size required is little more than coaxial cable
without the inner conductor.

OTOH monomode fibre-optic cable is a waveguide too,...

Bye.
Jasen
 
On Tue, 30 Jan 2007 11:19:36 +0100, "Michael Weiss"
<maerchenprinz@arcor.de> 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)...?
Click to expand...
From the RF design point of view, one should remember that the power
is no longer transmitted with the conductors, but instead propagates
as a field between the conductor and ground plane (or between
conductors in a balanced system). Thus, the dielectric losses of the
PCB or coaxial cable insulation materials will be important, so
ordinary glass fiber boards and PE insulated cables may be
inappropriate at higher frequencies and more expensive materials may
have to be used.

Paul
 
In article <12s01ibq6bijg1b@corp.supernews.com>,
"Joel Kolstad" <JKolstad71HatesSpam@yahoo.com> writes:
|> "Wes Felter" <wesley@felter.org> wrote in message
|> news:45bff261$0$9000$4c368faf@roadrunner.com...
|>
|> > Don't forget parallel copper. The cheapest version of 10GigE is CX4 and will
|> > probably remain so. 100GigE could be 12 lanes of 10GHz over copper, although
|> > people might not put up with the huge connectors.
|>
|> Many of them would, I imagine... that's ~25 pins, right? -- which even in a
|> high-density D-sub is "game port" (traditional DB-15) sized, and denser
|> connectors (such as the newer parallel printer port connector) are readily
|> available.
|>
|> I'm sure I'm not the only one who remembers some the truly enormous SCSI
|> connectors in years past.
|>
|> Or 60 pin IDCs!

You ain't seen nothing yet, folks!


Regards,
Nick Maclaren.
 
"Jan Vorbrüggen" <jvorbrueggen@not-mediasec.de> wrote in message
news:52auu8F1n1fnaU1@mid.individual.net...
SCSI connectors "truly enormous"? Surely not! Take a Massbus connector
instead!
Click to expand...
Hmm... (Googles for Massbus connector imagine, finds it)... yeah, you're
right, that is worse!
 
Paul Keinanen wrote:
On Tue, 30 Jan 2007 11:19:36 +0100, "Michael Weiss"
maerchenprinz@arcor.de> 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)...?


From the RF design point of view, one should remember that the power
is no longer transmitted with the conductors, but instead propagates
as a field between the conductor and ground plane (or between
conductors in a balanced system). Thus, the dielectric losses of the
PCB or coaxial cable insulation materials will be important, so
ordinary glass fiber boards and PE insulated cables may be
inappropriate at higher frequencies and more expensive materials may
have to be used.
Click to expand...
PE is still a pretty good dielectric in the GHz range, but FR-4
substrate starts hurting by the time you gets to a GHz (Del Cecchi made
similar rude noises about FR-4 as well - wonder what he would think of
PVC...). The microwave guys have had a lot of experience with PCB
performance in the GHz range - dielectric loss will have a much worse
effect on a stripline filter than it will on a digital signal.

- Erik
 
Del Cecchi <delcecchiofthenorth@gmail.com> wrote:
+---------------
| QAM and other modulation schemes have been proposed but never really
| caught on. ... QAM only halves the baud or symbol rate compared to
| the data rate by encoding 2 bits per baud.
+---------------

True, QAM is seldom used in baseband copper, though note that GbE
uses PAM-5 (2 b/Baud + some slight coding). Where QAM *has* been
really pushed is in CATV RF nets, where QAM-64 (6 b/Baud) and
QAM-256 (8 b/Baud) are fairly common.

Of course, now that the RF nets (including RF-over-fiber) are being
displaced by digital fiber... ;-}


-Rob

-----
Rob Warnock <rpw3@rpw3.org>
627 26th Avenue <URL:http://rpw3.org/>
San Mateo, CA 94403 (650)572-2607
 
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