[ih] IP over wireless [was: booting linux on a 4004]

[Brian E Carpenter]

On 28-Nov-24 06:39, Greg Skinner via Internet-history wrote:
> I read some of the discussions about mobility and wireless networks that took place on the nimrod and big-internet lists during the early to mid-1990s.  My impression was that people felt it was important to support both, but priority needed to be given to the address exhaustion and routing table space issues.

As a member of the original IPng directorate, I believe that is correct. But also, several of us had been severely burned by multicast storms on large bridged Ethernets. So the implicit assumption was that there wouldn't be any more of those, since moderately priced routers were coming to market, and that it was therefore safe to use link-layer multicast for neighbour discovery. And that is still true on modestly sized Ethernets and Wi-Fi networks. Where it goes horribly wrong is on *large* WiFis. I've done tests at an IETF meeting where at most 10% of link-layer multicasts were delivered to a host sitting on the same table as the sender. Don't put a thousand hosts on the same BSS.

    Brian

> 
> --gregbo
> 
> On Nov 24, 2024, at 9:20 PM, Barbara Denny <b_a_denny at yahoo.com> wrote:
>>
>> ----- Forwarded Message -----
>> From: Barbara Denny <b_a_denny at yahoo.com>
>> To: Brian E Carpenter <brian.e.carpenter at gmail.com>
>> Sent: Sunday, November 24, 2024 at 07:50:05 PM PST
>> Subject: Re: IP over wireless [was: booting linux on a 4004]
>>
>> I don't think I ever sent this due to mistakenly thinking I would have time to review it in a couple days.  I did trim this thread a little bit just now because my first attempts to sending the email didn't succeed..
>>
>> ***************************************
>>
>> Thanks for the thoughtful feedback. It is a long time ago but I would like to provide some recollections and my personal feelings on this topic as best as I can remember.
>>
>>   I think you agree that the IPv6 specification was done without much input regarding wireless. (i.e. too early for WiFi).  However, packet radio type networks had been of interest  to the military long before IPv6, and of course there were satellite links in the Internet as well. . These were the two kinds of networks, besides the ARPAnet, that first used the IP protocols. Other early wireless offerings were even available to the public ( e.g. WaveLAN and Ricochet) before the IPv6 and WiFi specs.  I am also sure most people on the Internet history list are aware that packet radio networks were part of the Internet story long before the IETF existed and the prevalence of Ethernet.
>>
>> In 1995, or perhaps early 1996,  I also gave a talk regarding DARPA's Global Mobile (GloMo) program to a small group of researchers.   It included the history of DARPA's packet radio projects, an overview of GloMo participants and the technology areas in their proposals,  and suggestions of possible challenges facing the Internet with wireless mobile participation. The bottom line message was that a wireless, mobile world is coming and the Internet might need to make changes to enable their full potential. The meeting was in the Bay Area and the audience was mostly DARTnet researchers as well as people like Barry Leiner (who had returned to DARPA) and Jon Postel.  One of the people present was Steve Deering as he was part of DARTnet.  As you know he was heavily involved in IPv6 in the IETF.  I feel one goal of this meeting and my talk was to establish contacts and hopefully start a dialogue between the two communities (wired and wireless).
>>
>> This DARPA sponsored meeting wasn't the only place I brought up wireless and mobility in the Internet.  A little later (1997? or may have been in 1996), there was a white paper request for Internet2 topics. I don't remember much about this white paper request but I think  the selected papers were going to be discussed at an upcoming Internet2 meeting.  I did submit a paper regarding wireless and probably mobility.  I never heard any feedback and I discovered much later which topics had been selected for a meeting.   To me,  the papers reflected the topics of the day (for example, supporting policy).
>>
>> The concern I have/had is I don't ever remember hearing about any engagement with people who were creating, or had created, these wireless networks to see if the new IPv6 effort was meeting their needs or perhaps creating potential pain as in the adaptation layer assumption (I left SRI in 1996 and went to 3COM). I was disappointed at the time that this kind of dialogue didn't seem to be happening. I also personally felt IPv6 should have looked at changes that perhaps could support mobility better.  The opportunity to revisit the IP protocol spec is rare.
>>
>> Here are some other thoughts I would like to mention.
>>
>> 1) My impression when I heard about the creation of the IETF was it was going to address immediate and near term technical and operational issues facing the Internet, so a broader scope than the interest of commercial companies and dominant networking technology. Five years sticks out in in my mind as the time frame but it could have been longer.
>>   
>> 2) I also think I heard that a design goal for the Internet was not to place any requirements on the constituent networks. So let's revisit the 576 byte packet length in IPv4. I don't remember hearing the rationale for this size so my guess is performance and memory constraints in the gateways at the time.  ( IPv4  has packet fragmentation and reassembly but gateways do not reassemble packets if I remember correctly). At the time, I thought the 576 byte packet size specification was made because of the need to participate in Internet routing in v4: not to support the idea that the Internet required an adaptation layer if the native packet size of a network was considered too small.  This required 576  packet size was well known to people in the early 80s as far as I can remember. Of course routing being able to scale was a concern and brought up but I don't think it was viewed as a show stopper for this packet size due to the anticipated Internet size at the time. Any issues needed to meet the 576 byte requirement had been met in the existing networks for the Internet as far as I knew in the early 80s. Keeping IPv6 at 576 bytes therefore would have been fine (as reflected in RFC 1883, the original IPv6 spec). This size did not cause problems for the networks in existence or in the pipeline that I knew about at the time.
>>
>> BTW, the last time I worked on a packet radio type network was in early 2000.  There were 2 teams working on a DARPA contract. Part of the effort involved new radios.  The team I worked with briefly did have the intention to eventually produce a radio they could sell to the military based upon this project . The use of IPv6 was on their radar screen but all the demos, etc. were done with v4. Meeting the 1280 IPv6 packet size requirement natively was not possible with these radios, especially under certain operating conditions. I don't know if they ever found, defined, and tested a workaround. (Sorry I feel I have to be vague here).
>>
>> If you can provide a reference you like to the multicast problem in large WiFi networks I would appreciate it.
>>
>> barbara
>>
>> On Tuesday, October 15, 2024 at 01:12:30 PM PDT, Brian E Carpenter <brian.e.carpenter at gmail.com> wrote:
>>
>>
>> Barbara,
>>
>> I've been communing with myself about how to reply to this. When I was trying to explain to students why Ethernet is like it is, of course like everybody I started with Aloha before talking about yellow cable and CSMA/CD. That is of course largely irrelevant today, but we still use the same frame format. Ethernet (partly because it descended from Aloha) natively supports broadcast.
>>
>> Then there is Wi-Fi which has the goal of emulating Ethernet, so must support broadcast even though it's disastrous to do so and has many bad consequences. Short explanation: if you run a large enough Wi-Fi network, it will end up saturated by multicast traffic.
>>
>> We don't even have that properly documented in an RFC today, but it's on its way:
>>
>> https://www.ietf.org/archive/id/draft-ietf-6man-ipv6-over-wireless-06.html
>>
>> That said, because IPv6 was designed in the Ethernet era, IPv6 over Wi-Fi works in a relatively simple way, and 1500 byte packets are the norm. So small Wi-Fi networks are fine.
>>
>> Then there is the whole topic of low-power wireless networks where 1500 bytes is certainly not the norm and some kind of adaptation layer is needed. (I'm no expert in that area, but as far as I can tell all the effort has gone into IPv6 rather than IPv4.) You'll find references to that work in the above draft, but I think the key one is RFC 4944 about IPv6 over IEEE 802.15.4. There's a whole section about the adaptation layer:
>> https://www.rfc-editor.org/rfc/rfc4944.html#section-5
>>
>> So, the wireless people have simply accepted the magic 1280 rule and adapted to it.
>>
>> As to the origin of that magic rule, there's one view of its origin at
>> https://mailarchive.ietf.org/arch/msg/int-area/Wpv1jT6UQt6KlzrdIoZSSLF-7XA
>>
>> (RFC 1883 specified 576 bytes in 1995. RFC 2460 raised it to 1280 in 1998.)
>>
>> Regards
>>      Brian Carpenter
>>
>> On 11-Oct-24 10:09, Barbara Denny via Internet-history wrote:
>>>   Thanks Brian.  I could see how the number was perhaps derived. I don't know how much it was  vetted with different types of networking folks.   To me the assumption of an adaptation layer just handling this is something that comes more from people who are used to wired networks than wireless.
>>>
>>> As I am sure you know,  there were issues about IPv6  discussions when they started in the IETF.  I experienced it when I had an opportunity to be at an IETF meeting at the time.  For those who don't know this history and are interested, I am sure Steve Deering relayed his experience at the time.
>>>
>>> barbara
>>>
>>>       On Thursday, October 10, 2024 at 01:49:41 PM PDT, Brian E Carpenter <brian.e.carpenter at gmail.com <mailto:brian.e.carpenter at gmail.com>> wrote:
>>>   
>>>   Barbara,
>>>
>>> If you mean how the 1280 bytes minimum MTU size for IPv6 was chosen, it was 1500 minus N, where N was an abitrary choice of how many levels of IPv6-in-IPv6 encapsulation would be possible within one 1500 byte packet, plus a bit of spare. So there was some hand waving involved.
>>>
>>> It was always assumed that lower layers that couldn't carry 1280 natively would provide an adaptation layer.
>>>
>>> We are still very sad that PMTUD doesn't work reliably, because that means that the lowest common denominator of 1280 is often used when we could do much better.
>>>
>>> Regards
>>>       Brian Carpenter
>>>
>>> On 11-Oct-24 06:55, Barbara Denny via Internet-history wrote:
>>>>     Just a FYI
>>>> I can see how IPv6 requirements in this area might be problematic for packet radio networks. I will admit my knowledge is old so  things may have changed.
>>>>      I also don't know how the numbers in the IPV6 specification were selected.
>>>>
>>>> barbara
>>>>         On Thursday, October 10, 2024 at 09:56:26 AM PDT, Barbara Denny via Internet-history <internet-history at elists.isoc.org <mailto:internet-history at elists.isoc.org>> wrote:
>>>>     
>>>>       Reminds me of how much effort went into selecting a packet size and the coding at the link layer in a packet radio environment.  If you are interested, I think Mike Pursley (Clemson) might have done the analysis for us (SRI) when we were working on porting the Packet Radio protocols to the SINCGARs radio.  I looked recently to see if I could  find a writeup but couldn't find anything quickly regarding this particular effort (Our discussion regarding MTU got me thinking on this topic).  The web page for him at Clemson does mention his current research is network coding for packet radio networks. :-)
>>>> barbara
>>
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