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Forum: µC & Digital Electronics 10gbase kr with sfp 10gbase t sfp+ pluggable?


von teasnakl (Guest)


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hi is it possible to connect a 10 gbase  kr phy via 10 gbase t sfp+ 
pluggable to another 10gbase t sfp+  pluggable in a pc which supports 
different protocols (i hope also kr) ?
or should i use a 10gbase-cu sfp+ cable?

thank you

von teasnakl (Guest)


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or is the 10gbase KR not used anymore?
it says https://standards.ieee.org/standard/802_3ap-2007.html is 
replaced?
or not more active?

von Gerd E. (robberknight)


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teasnakl wrote:
> hi is it possible to connect a 10 gbase  kr phy via 10 gbase t sfp+
> pluggable

10GBASE-T and SFP+ are two different things.

10GBASE-T is the standard for transmitting 10 GBit Ethernet over 4 pairs 
of twisted pair copper.

SFP+ is the socket you can plug in 10 GBit fiber modules or direct 
attach cables.

I guess with "10 gbase t sfp+ pluggable" you mean a SFP+ direct attach 
cable, correct?

> pluggable to another 10gbase t sfp+  pluggable in a pc which supports
> different protocols (i hope also kr) ?
> or should i use a 10gbase-cu sfp+ cable?

10GBASE-KR is a standard explicitly for backplanes. You can't directly 
connect it to any of the other 10 Gbit Ethernet standards. So if you 
have a PHY for 10GBASE-KR, then you need another 10GBASE-KR PHY on the 
other side of the connection. If you want to connect it to a PC, you'd 
need some media converter that has a 10GBASE-KR connection on one side 
and for example a SFP+ slot on the other side.

von tja (Guest)


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Gerd E. wrote:
> 10GBASE-KR is a standard explicitly for backplanes. You can't directly
> connect it to any of the other 10 Gbit Ethernet standards. So if you
> have a PHY for 10GBASE-KR, then you need another 10GBASE-KR PHY on the
> other side of the connection. If you want to connect it to a PC, you'd
> need some media converter that has a 10GBASE-KR connection on one side
> and for example a SFP+ slot on the other side.

in my opinion this is not true.
10GBASE-KR is for backplane application and has improvements on signal 
quality and an optional forward error correction. But everything is 
automatically handled with auto-negotation. If the phy does additionally 
support you can connect it directly to a SFP+ module via the so called 
SFI interface.

So, what phy are you using? this will help a lot to answer your 
question.

von teasnakl (Guest)


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tja wrote:
> So, what phy are you using? this will help a lot to answer your
> question.

vsc8489
Datasheet explain modes:
1
1111: 10BASE-T (not supported)
2
1110: 100BASE-TX (not supported)
3
1101: 1000BASE-KX
4
1100: 1000BASE-T (not supported)
5
1011: 10GBASE-KR
6
1010: 10GBASE-KX4 (not supported)
7
1001: 10GBASE-T (not supported)
8
1000: 10GBASE-LRM
9
0111: 10GBASE-SR
10
0110: 10GBASE-LR
11
0101: 10GBASE-ER
12
0100: 10GBASE-LX-4
13
0011: 10GBASE-SW
14
0010: 10GBASE-LW
15
0001: 10GBASE-EW
16
0000: Reserved

Gerd E. wrote:
> SFP+ is the socket you can plug in 10 GBit fiber modules or direct
> attach cables.

yes and 10 GBase T for "standard" RJ45 Twisted Pair

Gerd E. wrote:
> 10GBASE-KR is a standard explicitly for backplanes. You can't directly
> connect it to any of the other 10 Gbit Ethernet standards. So if you
> have a PHY for 10GBASE-KR, then you need another 10GBASE-KR PHY on the
> other side of the connection. If you want to connect it to a PC, you'd
> need some media converter that has a 10GBASE-KR connection on one side
> and for example a SFP+ slot on the other side.

thank you

yes this is what i suspected, actually the pc-card maybe supports the 
KR-protocol,  but even the ethtool doesnt say it xD

For a first test i could change my phy to SR mode, which is supported by 
my pc-card.

I dont need SFP+ Fiber dont I? I can do it with SFP+ 10GBase T?
I will check it :)

von teasnakl (Guest)


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> I dont need SFP+ Fiber dont I? I can do it with SFP+ 10GBase T?
> I will check it :)

PHY( SR Mode) -> SFP+ for 10GBase T-> SFP+ for 10GBase T-> Ethernet Card

I dont really know if this makes sense.

von tja (Guest)


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teasnakl wrote:
> PHY( SR Mode) -> SFP+ for 10GBase T-> SFP+ for 10GBase T-> Ethernet Card

this is absolutely fine and will work. So the TO don't need the KR 
option.

von teasnakl (Guest)


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Hi thank you.
tja wrote:
> the TO

What is the T0?
And do you know why this is ok? Will the SFP transceiver just to the 
translation?

von tja (Guest)


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TO = thread opener ;-)

the interface between phy and sfp+ is specified and called SFI. Any SFP+ 
module has absolutely the same electrical interface standard. So in 
general for the phy it isn't important what type connected: 10GBASE-SR, 
10GBASE-ER, 10GBASE-LR, 10GBASE-T, etc.

So connection between phy and SFP+ is fine.

Next step:
10GBASE-T at your hardware and 10GBASE-T at your network adapter in your 
PC. Between them there is the electrical interface standard with a PAM 
(pulse amplitude coding). Buter after the SFP+ there is the SFI 
interface with NRZ coding again.

You can believe it or not, but it will work. And when you don't believe 
then take the datasheet, literate especially you should read the IEEE 
802.3 specification where everything is described in detail.

Good luck

von teasnakl (Guest)


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Hi tja,

I still don't understand the compability yet, but SFI might be a good 
solution!

Thank you :D

I will/need-to check out SFI,SerDes,IEEE and so on!


Until then i ask myself:

E.g. 10GBase-T descirbes twisted pair cable. When plugging a SFP+ 
inside, the SFI should transform the twisted pair signals to SFP+... and 
e.g. 10GBase CX4 also to SFP+.

...
I mean:

phy(some ethernet standard)->sfi->sfp+-> cable


I found these books which maybe tells something about it. Hadn't time to 
read into it now.
https://www.google.de/books/edition/High_Speed_Serdes_Devices_and_Applicatio/Cx3r0H-4AhEC?hl=de&gbpv=1&dq=serdes+frame+interface&pg=PA204&printsec=frontcover

https://www.google.de/books/edition/Network_Infrastructure_and_Architecture/YVQID9pY1rIC?hl=de&gbpv=1&dq=serdes+frame+interface&pg=PA250&printsec=frontcover

von tja (Guest)


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von teasnakl (Guest)


Attached files:

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Thank you,
I began to check the IEEE standards. Starting with PMA ...
I just got maybe 10% of understanding.
It looks like the PMA is directly connected to the Pins. E.g. at 10GBase 
T the 4 differential pairs...
I will check more :D

von teasnakl (Guest)


Attached files:

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oh this is why it also confusing a PMD is not "mandotory" everywhere.

von teasnakl (Guest)


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I am still not 100 % sure. If my PHY is only able to do Clause 73 
Auto-Negotiation. Because if the SFP+ does some translation but has no 
intelligence two systems won't fit like Backplane Ethernet (KR,Kr and so 
on, but no 10GBaseT)  and my 10GbE Ethernet NIC(no KR and stuff my PHY 
supports.)
... But a 16 ms signal-burst-signal should be sent be each of them 
right?

Check this out, in Clause 73 it says:

>"While implementation of Auto-Negotiation is mandatory for Backplane >Ethernet 
PHYs, the use of
>Auto-Negotiation is optional. Parallel detection shall be provided for >legacy 
devices that do not support
>Auto-Negotiation."


And whatever that means:
>"If Clause 37 Auto-Negotiation is performed after Clause 73 >Auto->Negotiation, 
then the
>advertised abilities used in the Clause 37 Auto-Negotiation shall match >those 
advertised abilities used in the
>Clause 73 Auto-Negotiation."

von teasnakl (Guest)


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sry for bad quotations

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