Geoff
A fine name it is indeed :) I opted myself for Optical Coax Unit (OCU) to
have some similarity to ONU and OLT and CNU names.
I am also curious as to what extent this " small amount of logic required to
couple PHYs back-to-back" could be extended to do some more intelligent
things, including reporting coax plant conditions to the OLT to make sure
that data rates towards CNUs are adapted accordingly. I'd really like this
BOX to be a little bit smarter, something in between a pure repeater and MAC
bridge ... hence I wonder whether this "duplex repeater" could be that
missing link between repeaters and MAC bridges
Marek
-----Original Message-----
From: Geoff Thompson [mailto:thompson@xxxxxxxx]
Sent: 03 March 2012 08:33
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] What is the problem with the EPoC converter, and
what is the CLT?
All-
This reply is primarily to respond to Jorge's message time stamped Fri,
2 Mar 2012 05:12:46 +0000
and Ed's message below.
I hope I provide some guidance that will settle us on some common
terminology.
I believe that I have the history in 802 and 802.3 to provide the most
authoritative guidance here.
What Jorge was asking for in his message as a "converter" is not a "bridge"
by any definition of a "bridge" used in 802.
A "bridge" is:
- A device that operates at Layer 2 above the MAC
- A device that couples multiple MACs together
- Is something that relays packets
- Is a packet store and forward device
- Can accommodate differences in speeds between ports
- Has two or more ports
- Has a relay functionality between the ports that is standardized in 802.1
(and is thus outside the scope of 802.3) Crossing a "bridge" with an
EPON/EPoC on either side would constitute 2 entirely separate TDMA domains
that were isolated and separated by the bridge, not an extension of one
domain across the device.
There are a number of devices on the market that are called "media
converters" (most often "converting" between fiber and twisted pair).
These days (unlike days of yore) these are most often two port non-filtering
bridges. 802.1 has done some work to support such devices.
802.1 calls the piece of such a device that is within their scope a "2 Port
MAC Relay (2PMR)"
A "media converter" is a product that is historically unspecified in 802.
The products sold under this name had a wide variety of performance features
and ills. It has always been felt in 802.3 that because of this, it would be
a bad idea to use that term for a standardized device.
As Ed mentioned, there was a device once upon a time in the history of
802.3 that was much closer to Jorge's ask. That was the 802.3 10 Mb/s
repeater (see clause 9 of the standard). In fact, in its earliest
incarnation, it was used to do "media conversion" between coax and fiber. It
doesn't match the functionality of what we want now because it was a
half-duplex device that actually participated in the CSMA/CD contention
resolution process.
We need a full duplex device. Once upon a time there was such a device
defined in the FDDI Standards work. It was:
- Called PHY-REP (Physical Layer Repeater)
- The small amount of logic required to couple PHYs back-to-back
- Full duplex
- A bit store and forward device
- Provides bit level retiming
- Was same bit and clock rate on each side We certainly could explore
developing and standarizing such a device for use in a hybrid EPo
environment. Whether we could come up with a reasonable box has a lot of
issues. Some of these were set forth by Mr.
Yao. Another might be a mismatch of clock rates and encoding on copper vs.
fiber
Whether such a device is feasible for us certainly a reasonable topic for
discussion. I would propose calling such a device a "duplex repeater".
Hopefully these messages will help us more forward with greater common
understanding.
Best regards to all,
Geoff Thompson
On 23//12 2:59 PM, Ed (Edward) Boyd wrote:
Hi Jorge and all,
The IEEE 802.3 can define the EPOC PHY with the Ethernet MAC above it.
The IEEE has the definition for the bridge in 802.1. The definition of a
bridge between EPON and EPOC should be handled by these standards. I agree
that it isn't really a CLT since we think of the CLT has a shelf with many
blades. It is a 2 port bridge. I think that we could modify our drawings
to show a 2 port bridge between EPON and EPOC. We should come up with a
nice acronym for it. Maybe ECB "EPON Coax Bridge". I don't think that a
bridge is what Jorge had in mind.
Media converters are not normally defined in 802.3 but they have been
standardized. 802.3 defined Ethernet Repeaters long ago when we had half
duplex. Repeaters were connections between Ethernet PHYs which is
essentially what you are asking for today. The repeater disappeared with
full duplex. Media Converters have standards in Japan and other places.
They have not been defined by 802.3 to my knowledge. I agree that we should
show the media converter or repeater application in our system drawings
since it has great value to the operators. As Mark suggested, we should
keep the media converter (repeater) in mind when we define the PHY. I'm not
sure if we can define it here in 802.3 with the EPOC PHY. Maybe Glen or
Howard can comment where in IEEE, where it would get defined. Do we ask for
a repeater project in 802.3 or a media converter in SIEPON or somewhere
else?
For reference, I will mention that an Ethernet media converter is simple
to build and it can handle different rate PHYs. You can find them for sale
on-line. Some people use higher data gigabit optics as the transport but
they are connecting to 100BT Ethernet devices. The media converter has
buffering for a single packet. It will get the packet off of the GMII and
put it on the XGMII. If there is 100BT on both sides of the media
converter, there is no packet drop. If the MAC isn't controlled to 100BT
rate, packets will be dropped.
In the case of EPOC, we will have a similar issue. In the Ethernet in the
first mile, the MAC was required to delay the transmission of packets to the
PHY to meet the data rate of the PHY. I'm sure Howard can shine more light
on this approach. If we connect the EPOC PHY to the EPON MAC, the EPOC MAC
must regulate the frames to the PHY's auto-negotiated data rate. In the
case of the media converter, the EPON MAC in the OLT would need to regulate
the transmission of data as if it was directly connected to the EPOC PHY.
I hope this was helpful,
Ed....
-----Original Message-----
From: Marek Hajduczenia [mailto:marek.hajduczenia@xxxxxxxxx]
Sent: Friday, March 02, 2012 8:35 AM
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] What is the problem with the EPoC converter, and
what is the CLT?
Bill,
That is one of the reasons why I agree with Jorge: there is need for
it, and we need to look at providing this specific feature so there is
no doubt and finger-pointing later on.
Marek
-----Original Message-----
From: Trubey, Bill [mailto:bill.trubey@xxxxxxxxxxx]
Sent: 02 March 2012 16:31
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] What is the problem with the EPoC converter,
and what is the CLT?
Let's make sure the "bridging" IWF performs and is defined with no
ambiguities- as we saw long ago between two dissimilar media, FDDI and
Ethernet. We as consumers had to deal with several (large) vendors
pointing fingers at each other on who interpreted the IEEE standards
"correctly" .
_____________________________
Bill Trubey, Time Warner Cable
bill.trubey@xxxxxxxxxxx, (720) 279-2819
From: "Mudugere, Satish"
<satish.mudugere@xxxxxxxxx<mailto:satish.mudugere@xxxxxxxxx>>
Reply-To: "Mudugere, Satish"
<satish.mudugere@xxxxxxxxx<mailto:satish.mudugere@xxxxxxxxx>>
Date: Fri, 2 Mar 2012 11:12:58 -0500
To:
"STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx<mailto:STDS-802-3-EPOC@xxxxxxxxxxxx
E.ORG>
"
<STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx<mailto:STDS-802-3-EPOC@xxxxxxxxxxxx
E.ORG>
Subject: Re: [802.3_EPOC] What is the problem with the EPoC converter,
and what is the CLT?
I agree with Vally. We have to define the content of the converter box
in detail. I would suggest to use the word 'EPoC bridge' than
'converter'. The EPoC bridge needs to be clarified with input and
output interfaces along with the exact funcationality expected from
the device. There is no packet loss frame loss associated with bridge.
The EPoC bridge acts a mediator for OLT to treat ONU and CNU in same way.
Thx,
Satish
Intel Corporation
From: Valentin Ossman [mailto:Valentin_Ossman@xxxxxxxxxxxxxx]
Sent: Thursday, March 01, 2012 11:33 PM
To:
STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx<mailto:STDS-802-3-EPOC@xxxxxxxxxxxxx
.ORG>
Subject: Re: [802.3_EPOC] What is the problem with the EPoC converter,
and what is the CLT?
Hi Jorge,
I totally understand your concern and tried to raise this in the past
meeting in Long Beach.
The conversion box in your description is simply called a bridge and
is already defined by 802. That bridge has 2 interfaces, EPON for the
fiber and an new one for the Coax.
The challenge, as you correctly formulated, is to be able to manage
and provide the CNUs form the OLT. I completely agree with this
statement and want to see this on the EPOC objectives.
As a side note, there've been discussions about "media converters" or
"black magic box" between EPON (fiber) and EPOC (coax). Defining those
boxes as PHY layer "media converter" is incorrect in the 802 jargon as
it implies that every bit of information from one side is converted to
the other side. To be more specific, there is no packet filtering in
the media converter as the PHY can't analyze a data packet (that's done in
the MAC).
I propose that we move away from the self-imposed limitation of "media
converter" and PHY only protocol and, have a solid discussion on a
practical solution that is able to provide a manageable data service
between the OLT and the ONU, taking advantage of EPON and the most
efficient technologies available for Coax at this time.
We should not impose unnecessary technical and physical limitation on
the coax just to have a protocol identical to EPON but we must ensure
that whatever we define, can work with and be manageable from existent
EPON OLT equipment.
We must also completely define those "black magic boxes". There is no
point in defining an architecture that relays on an element that is
not standardized. I propose we use the well defined functionality of
Ethernet switches/bridges for that element.
---
Valy Ossman
Principal System Architect
FTTH BU
www.PMC-Sierra.com
From: Salinger, Jorge [mailto:Jorge_Salinger@xxxxxxxxxxxxxxxxx]
Sent: Thursday, March 01, 2012 9:13 PM
To:
STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx<mailto:STDS-802-3-EPOC@xxxxxxxxxxxxx
.ORG>
Subject: [802.3_EPOC] What is the problem with the EPoC converter, and
what is the CLT?
Paul, David, Howard, and EPoC Study Group members,
I'm expanding a discussion that I had with Marek, Ed, and Mark to the
entire team. I know this will get unruly, but I see this as a "white
elephant in the room" for what seems like some sort of philosophical
argument, so might as well get it out in the open. Also, I recognize
that this was a subject of discussion during the meeting in Newport
Beach, but I did not understand it then and thought it might not be
important. I see now that it is a key problem that if not resolved
will haunt us forever. So, let's see if we can discuss it via Email
and see if we can resolve it before the meeting in Hawaii.
My initial statement of the problem to Ed, Mark and Marek, expanded
for clarity, is: I struggle with what the CLT is, and what is the
problem with the converter that we need to define. I see the EPON and
EPoC systems containing these components:
EPON:
OLT<=== Fiber =====================================> ONUs
EPoC:
OLT<=== Fiber ====> converter<=== HFC network ====> CNUs
The bottom line is that I want to buy a standard OLT, and buy ONUs for
customers I can connect via fiber. And, when I can't run fiber to
customers, I want to buy a converter between the fiber and the HFC
network so I can use the same standard OLT, and use CNUs (an RF
version of the ONU) for those customers attached to the HFC network.
The FIRST KEY POINT here is that I want to use the same OLT.
The SECOND KEY POINT is that I want to buy a passthrough device that
will be invisible to the OLT, which will take the optical EPON signals
and convert them into RF signals. This passthrough device must be
flexible in several ways, such as allowing me to use different
portions of the RF spectrum, including more and less spectrum as
available.
The THIRD KEY POINT is that I want the CNU to be functionally
equivalent to the ONU so that the OLT does not know the difference.
I think that I want the RF PHY that the converter and the CNU will use
to be defined at IEEE because that should make it easier for the
vendors that will implement the converter and the CNU to develop it.
But people tell me that this will be a problem because, from what I
understand, the IEEE does not specify converters or some such rationale.
Because of that we have to talk about a CLT instead of the OLT, to
hide the converter inside the OLT (if I understood correctly).
I hope I was able to keep the definition of the problem simple and
clean enough to have a straightforward discussion of why we can't do
what I, and my esteemed MSO colleagues, need.
So, what is the problem with the converter, and why is there a need to
instead define a CLT which is something I don't want to have?
Thanks!
Jorge
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