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New Member

HWIC-CABLE-D-2 ... DOCSIS 3 ?

We have an ISR 2801 with a HWIC-CABLE-D-2. Within 6 months we expect a DOCSIS 3 rollout to our area.

Is there any hope for a HWIC-CABLE-D-3 or another DOCSIS 3 compatible HWIC?

It would be even better if it was compatible with the ISR 2801.

I can't find any information on this except for a note stating that the HWIC-CABLE-D-2 will not be "upgraded" to be DOCSIS 3 compatible due

to the hardware not supporting channel-bonding. I assume this means a new HWIC would be needed, and not just an IOS upgrade (which is fine);

but does that imply a DOCSIS 3 HWIC will exist?

I know there are backbone devices that are DOCSIS 3 compatible, unfortunately they are not an option due to cost.

If we had to use an external DOCSIS 3 modem, and then use a short ethernet link to the 2801, what would be the downside?

I have a blind assumption that it would be a large performance hit to the router.

I know the DOCSIS protocol allows the ISP to have (in my opinion) strange restrictions and control over the modem.

Would we be able to route 3 IPs through the external modem like we are now?


Any information or even educated guesses on this front is very appreciated.

Thanks!

14 REPLIES
Hall of Fame Super Gold

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

Before worring so much about the router module, have you explicitely asked the cable company if they allow hardware not provided by them to be used as CPE on their network ?

Also note, there is no performance hit whatsoever by using a cable modem with eternet. That is what everybody is doing since 14 years and no issues.

New Member

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

>Before worring so much about the router module, have you explicitely asked the cable company if they allow hardware not provided by them to be used as CPE on their network ?

We are a little unconventional. dont-ask-dont-tell policy works well here.

I'd rather not pay extra to rent CPE from them when ours works perfectly well and provides more control. I really don't trust black boxes given to you as a consumer. It does make tech-support calls interesting, as there is something wrong with their end and if I had a traditional modem I would never know the difference. We used to have rented CPE and we got random 5 minute to 15 minute downtimes/disconnects, only once we started using the HWIC can we see the relevant negotiation failures. Now that we can see the failures we have scripted a fix to reduce the downtimes to about 30 sec to 1 minute.


>Also note, there is no performance hit whatsoever by using a cable modem with eternet. That is what everybody is doing since 14 years and no issues.

I find that difficult to believe, how are the following issues dealt with?

a) Latency caused by two additional interfaces in the path

b) Lack of modem configuration and congestion information to the 2801

c) Lack of capabilities to control the modem, like power-cycling

d) Additional point-of-failure and lack of diagnostics and logging / reporting

On the original question, do you have any information there?

I appreciate your interest in the obscure question.

Hall of Fame Super Gold

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

You can not connect your own device in place of SP-provided one to a cable network wihout they knowing.

It is not about regulations or policies, but simply due to very well enforced technical (security) reasons that exists in any DOCSIS revision.

And, is not like you can work around that by cloning the MAC addresses. It will simply not work, try yourself if you do not believe me.

Then regarding performance issues using an ethernet hop, I really do not have to explain you "why", you can find that yourself again testing.

Regarding you other concerns, I do agree that terminating the circuit directly in router is advantageous for many reasons and I do that myself as much as I can in designs for my clientes. However is some cases it is absolutely not possible, and your seem to be one of these. Fortunately, things works fine anyway.

New Member

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

Allright, so, for the sake of argument; they said it was fine, because it won't work if they didn't (and it does work).

I am also aware that you are unable (and it is bad practice anyway) to change MACs on a DOCSIS compatible device (defined in the specification), you cannot even run the command in IOS.

What about my original question about the availability of DOCSIS 3.0 HWIC devices?

New Member

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

forgive my intrusion:  I have no expertise on DOCSIS however there will be a performance 'hit' if you move up or down the ISORM from layer to layer or in the case of ethernet to docsis bridging; re-framing across a single layer.  the frame must be removed, interpreted, mappped and replaced in addition to the ingress and egress scheduling and queuing.  No matter if the processing is done in a RISC or a CISC machine, no matter how few clocks the instructions take and what the duty cycle is there will be increased latency impact.  It's all semantics but it may actually increase "performance" if your application needed the extra 100ns to avoid an overflow (just an abstract example of time and app).

One of the values I find in these forums in that the technical accuracy of the information is ultimately properly refined by the end of the thread.  It makes these forums valuable irrespective of formal academe.

you have provided great informational wealth and technical accuracy in a number of areas here (thank you) which is why I was surprised to see such a closed ended absolute statement being made.

I may be wrong but I might guess the intended message may be that; in your referenced experience of applications and reading, any performance degradation would be negligible.

Thanks again for your contributions!

Hall of Fame Super Gold

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

neharris, you are wrong about the performance hit, in abstract as in concrete.

The "overhead" when copying from a router to another over fast media, is so neglible that cannot be measured.

Meaning to be more clear: you measure transfer times, TCP. UDP, single session, multiple sessions: All the same result, no performance hit.

Thanks to expensive gear provided by Cisco, I did this kind of testing when I was working there.

Have you ever done the same ?

New Member

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

1) of course it's measurable.  equipment must not be sampling fast enough.  apply the nyquist

2) my post grad team built 4 routers from nothing, but alas this was before DOCSIS was ratified.  "no, I've never collected empirical data on DOCSIS to ethernet latency"

3) appears there's a preference to dictate rather than discuss and dismiss any commentary as though others come with nothing to the table

4) I'll leave so a return to the battle for the most forum posts can resume; sorry to see the response came only to the correction instead of the obvious compliment and gratitude for your responses.

regards

Hall of Fame Super Gold

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

neharris, I don't dictate anything. Neither I can (or want) to extend this debate beyond simple, practical networking.

When some will be able to prove that there is a measurable performance difference in real networking between:

connecting an ISP-provided cable-modem to a cisco router via fast ethernet

or

connecting a cisco router directly via cable module

I will be glad to say that I was wrong.

Again, the key facts supporting my statements:

1 - Going from slow media to fast media never slows down things no matter if there additional hops - try to believe.

2 - Measuring Cable internet performances is not the same as measuring a switch latency. What is important and measurable in one case, it is not in the other.

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

Maybe Paolo insists on his point of view simply because he is actually right.

I know nothing about DOCSIS, but here we are talking about modems and speeds in the order of 10Mbps or some multiples of 10 Mbps, right? When we say performance "impact", we are talking about a performance degradation that can be observed and in this case from the perspective of a typical user and not from the perspective of a single device in the path from source to destination.

Let's say you have $1000 and while you are not looking I take $1 away from you and immediately afterwards I put back $1000. You end up with $1999. Even if you actually saw me taking the $1 away, are you still thinking about that dollar? (ok, maybe you are, but, just to be clear, I'm not giving it back no matter what). If we improve the experience of a typical user by say doubling the bandwidth and we worsen some other negligible parameter, user will only observe an overall improvement.

In networking, latency typically consists of transmission, propagation and queueing/forwarding delay. In many cases, the dominating latency is the propagation delay, which depends on physical distance between source and destination and, in the best case, is determined by the speed of light in optical fiber. Propagation delay is usually in the order of milliseconds (roughly 100ms RTT for a transatlantic link). There is not much that can be done about this component of latency, except perhaps make some links have less length. We can't change the speed of light yet. When we are talking about speeds of 8 Mbps, it means we can transmit a 64-byte frame in 64 usec and larger frames will need more usecs. When you increase the transmission speed, say double it, you can cut the usecs in half. So, how many instructions are needed to forward a packet and how many usecs or msecs do they take? And what's the difference in that delay if we add some extra headers? Because those numbers are negligible compared to other delays, in low end devices you can have inexpensive types of DRAM in the forwarding path.

Since processor types were mentioned, Amdhal's Law/law of diminishing returns came to mind. So, if you wanted to improve the latency observed by a typical network user, would you reduce the number of local hops and number of headers (BTW: "local" means that the propagation delay is negligible in this case) or would you increase transmission speed?

Also, if user downloads a lot of stuff, then the pipe between source and destination becomes full and the delay observed by the user tends to depend on transmission speeds/available bandwidth only.

If we wanted to built a device that can forward packets at multiple Gbps of wire speed, then we would be discussing about high performance internal interconnects, SRAMs, CAMs, TCAMs, ASICs, etc and count instruction clock cycles. In practice, if the devices in a path from source to destination (routers, switches, optical equipment) can sustain the rates they are supposed to serve, then the dominating factor in the latency a typical user experiences is the physical distance from source to destination. If you actually do the math to calculate the delay from say South East Europe to London, you will see that the RTT measured by the ping program can be very close to the theoretical delay a theoretical direct fiber between endpoints would have despite of the numerous equipment between source and destination and the fact that fiber in practice doesn't follow a straight line between the endpoints. Of course, the transmission speeds/available bandwidth also matter.

In any case, a parameter that seems negligible in one context might gain significance in another. If we were discussing high performance networking and computing for specialized environments, then we would try to squeeze any delay component we can put our hands on. On the other hand, when we try to help a customer in their decision process to built a simple network we discuss the factors that really matter to them based on their needs and budget. I can buy the the best and most expensive laptop and DSL connection in the market, but what's the point if I only browse cisco.com ?

New Member

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

You both appear very passionate.  I'll leave one last piece behind on this thread: I believe teaching to be a noble profession, and not because my education cost more than most homes but because in order to be a successful teacher what the student hears must be placed ahead of what the teacher believes they are saying.  It has to have closed loop feedback.   I believe it's important to know what you know and what you do not, and to qualify information when it is presented from that teaching platform.  Whether it's authoritative, or just an assertion or educated guess are important facets to include.

I understood this thread to be about the question(s) Mr Morris brought to the table.  Regardless of his level of expertise, or anyone's for that matter, a choice was made to respond.  I hope that sincerity does not turn disingenuous, and addressing the question with the best answers possible remains paramount.

Cheers

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

My post was not meant to be passionate and I apologize if it looks that way. On the internet it's difficult to understand the tone of someone when they are telling you something. I just thought you wanted to discuss (based on your previous posts). So, I have put some effort to justify why Paolo was getting the results he reported because they sounded reasonable to me. If you think there is some mistake in my post, please post and I would be glad to be corrected. For most of us the participation in the forums is a learning experience and we also have learned to gracefully admit our mistakes.

Hall of Fame Super Gold

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

neharris wrote:

You both appear very passionate.  I'll leave one last piece behind on this thread: I believe teaching to be a noble profession, and not because my education cost more than most homes but because in order to be a successful teacher what the student hears must be placed ahead of what the teacher believes they are saying.  It has to have closed loop feedback.   I believe it's important to know what you know and what you do not, and to qualify information when it is presented from that teaching platform.  Whether it's authoritative, or just an assertion or educated guess are important facets to include.

I understood this thread to be about the question(s) Mr Morris brought to the table.  Regardless of his level of expertise, or anyone's for that matter, a choice was made to respond.  I hope that sincerity does not turn disingenuous, and addressing the question with the best answers possible remains paramount.

Cheers

neharris, please define "passionate" ? This is techical forum, and I just state technical facts here, nothing more. If in doing so, I am wrong, I will be happy to be corrected by one of my peers. While doing so, it is never my intention to offend anybody. Also, I am not a teacher, but I will try to benefit from your tips, if I will have to be one, so thank you for your partecipation.

Re: HWIC-CABLE-D-2 ... DOCSIS 3 ?

Hey Paolo, let's leave this here man. We agree that we disagree and that's it.

New Member

HWIC-CABLE-D-2 ... DOCSIS 3 ?

I know this is an old post... but did you ever find an answer to this?  They're mostly right that adding a single cable modem won't have much of a performance hit.  However, you potentially lose certain features, like you already mentioned.  I've never implemented this, but it seems like you have better control over congestion (and potentially QoS).  Check out this link:
http://www.cisco.com/en/US/prod/collateral/modules/ps5949/prod_qas0900aecd804b0669_ps3129_Products_Q_and_A_Item.html

One thing you do lose, is the potential to toss an ASA, IPS Module, or similar between the cable modem and your router.  If that isn't an issue to you then that's a different story.

Can't tell you about DOCSIS 3 unfortunately.  I'm curious to find out as well.

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