Re: [mpls] Another way...

[[e-mail]]

Tony,

Tnx! Yes, that is what I (vaguely) remember too.

In that case, a terminology question.


Looking at e.g. a Format B LSE:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Opcode    |        Data             |R|IHS|S| Res |U|  NASL |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 2: LSE Format B: The initial opcode


Is that 31 bits ISD or just 13 bits, i.e. does "ISD" relate to the field
"Data" only or to the entire LSE (minus s-bit)?

Tony writes that there is a benefit to having ISD so we can indicate the
presence of PSD, I read that as the entire LSE is ISD.


/Loa


>
> [WG chair hat: off]
>
> Loa,
>
> My memory says that there was no reason to preclude it and some benefit
> for actually having ISD if PSD was present, so that we could indicate that
> PSD was present.
>
> T
>
>
>> On Mar 22, 2024, at 1:06 PM, [e-mail] wrote:
>>
>> Jags, all,
>>
>> I remember that we discussed whether a packet could carry both ISD and
>> PSD, but I don't remember if we reached a consensus either way.
>>
>> Anyone remember?
>>
>> /Loa
>>
>>
>>> Hello Jie,
>>>
>>>   I was mentioning an option of using the PSD offset opcode as an
>>> indicator for the PSD presence.
>>>
>>>   In case PSD offset opcode is encoded in the Format-B, then it is in
>>> the
>>> same level as proposed "P" bit, so I did not see any reason why this
>>> approach always consumes additional LSE.
>>>   I agree that if anyone wishes to encode an ISD opcode using Format-B
>>> along with a PSD, it may require an additional LSE beyond what the
>>> current
>>> approach entails
>>>
>>>
>>> Thanx,
>>> Jags
>>>
>>>> On Wed, Mar 20, 2024 at 8:24 PM Dongjie (Jimmy)
>>>> <[e-mail]>
>>>> wrote:
>>>>
>>>> Hi Jags,
>>>>
>>>>
>>>>
>>>> Thanks for sharing opinion on this.
>>>>
>>>>
>>>>
>>>> In my understanding the PSD offset opcode is optional and is not
>>>> needed
>>>> when PSD follows immediately after the EOS.  Making it mandatory for
>>>> PSD
>>>> would always consume one LSE and would reduce the space available for
>>>> ISD.
>>>>
>>>>
>>>>
>>>> Another point is the position of the PSD offset opcode in NAS is not
>>>> fixed, which means for a node which only supports PSD, it may need to
>>>> parse
>>>> the preceding ISDs to find the indicator of PSD. This is not efficient
>>>> in
>>>> implementation, and also makes the implementation of PSD coupled with
>>>> ISD.
>>>>
>>>>
>>>>
>>>> Best regards,
>>>>
>>>> Jie
>>>>
>>>>
>>>>
>>>> *From:* mpls <[e-mail]> *On Behalf Of *Jaganbabu
>>>> Rajamanickam
>>>> *Sent:* Wednesday, March 20, 2024 8:44 AM
>>>> *To:* [e-mail]
>>>> *Cc:* mpls <[e-mail]>
>>>> *Subject:* Re: [mpls] Another way...
>>>>
>>>>
>>>>
>>>> Hello All,
>>>>
>>>>
>>>>
>>>>    In the PSD case, we may need a new ISD opcode to indicate the
>>>> offset
>>>> of the start of PSD if PSD is not encoded immediately after the EOS.
>>>>
>>>>    In section 6.1 of our PSD draft (
>>>> https://datatracker.ietf.org/doc/draft-jags-mpls-ps-mna-hdr/ ). We
>>>> already have mentioned that the new ISD opcode will be allocated with
>>>> the
>>>> format option of Format-B or Format-C.
>>>>
>>>>
>>>>
>>>>    I think we could use the same opcode to indicate the presence of
>>>> PSD
>>>> as well. The offset could be zero or Non-Zero value.
>>>>
>>>>
>>>>
>>>>    If we use a reserved bit in the Format-B to indicate the presence
>>>> of
>>>> PSD and in case we encode the new PSD offset, then still we need to
>>>> add
>>>> an
>>>> additional opcode to be encoded.
>>>>
>>>>
>>>>
>>>> Thanx,
>>>>
>>>> Jags
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>> On Thu, Mar 14, 2024 at 12:58 AM <[e-mail]> wrote:
>>>>
>>>> All,
>>>>
>>>> I have been thinking about using an OpCOde for a while, but have been
>>>> reluctant to propose it. Several reasons, but mainly as the encoding
>>>> grows
>>>> more complicated we would either need a general encoding document or
>>>> include this in the framework. Until we make up our minds there is
>>>> some
>>>> time and that delays progress of the other drafts.
>>>>
>>>> Another reason is that sometimes it is an entire LSE, and sometimes it
>>>> is not.
>>>>
>>>> If we have just one OpCode after the Format A LSE (Opcode P (for PSD)
>>>> it
>>>> is no big deal.
>>>>
>>>> Example:
>>>>
>>>>    0                   1                   2                   3
>>>>    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>   |      MNA-Label=bSPL (TBA)             | TC  |S|    TTL        |
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>   |   Opcode P  |        Data             |R|IHS|S| Res |U| NASL=0|
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>
>>>> and
>>>>
>>>>    0                   1                   2                   3
>>>>    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>   |      MNA-Label=bSPL (TBA)             | TC  |S|    TTL        |
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>   |   Opcode X  |        Data             |p|IHS|S| Res |U| NASL=0|
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>
>>>> Is roughly equivalent :) (I said roughly).
>>>>
>>>> However if there is another OpCOde
>>>>
>>>>
>>>>    0                   1                   2                   3
>>>>    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>   |      MNA-Label=bSPL (TBA)             | TC  |S|    TTL        |
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>   |   Opcode X  |        Data             |R|IHS|S| Res |U| NASL=1|
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>   |   Opcode P  |       Ancillary Data          |0|  AD   | NAL=0 |
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>
>>>> Is less efficient than
>>>>
>>>>    0                   1                   2                   3
>>>>    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>   |      MNA-Label=bSPL (TBA)             | TC  |S|    TTL        |
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>   |   Opcode X  |        Data             |p|IHS|S| Res |U| NASL=0|
>>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>>
>>>>
>>>>
>>>>
>>>> Note: The discussion we have now about "changing" the format would
>>>> potentially affect the Framework. Or even motivate a general MNA
>>>> encoding document.
>>>>
>>>> Since both the OpCode and the p-bit are ISD, I think they should be
>>>> assigned in draft-ietf-mpls-mna-hdr.
>>>>
>>>>
>>>> /Loa
>>>>
>>>>>
>>>>> In fact, it’s not a whole label.  If we’re talking
>>>>> about
>>>> PSD, it’s
>>>>> very likely that there’s nothing in ISD except for the PSD
>>>> indication
>>>>> and this opcode would fit in the Format B LSE without any additional
>>>>> overhead.
>>>>>
>>>>> One could, in principle, generalize this to make the entire Format B
>>>> data
>>>>> space into extension bits of various flavors, with PSD being only
>>>>> one.
>>>>>
>>>>> We have many extension mechanisms, not just reserved bits.
>>>>>
>>>>> T
>>>>>
>>>>>> On Mar 13, 2024, at 11:36 AM, Haoyu Song
>>>> <[e-mail]>
>>>>>> wrote:
>>>>>>
>>>>>> I think this is very inefficient. While only a single bit is
>>>> sufficient
>>>>>> to server the purpose, why dedicate a whole label?
>>>>>>
>>>>>> Haoyu
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: mpls <[e-mail]> On Behalf Of Tony Li
>>>>>> Sent: Wednesday, March 13, 2024 8:29 AM
>>>>>> To: Loa Andersson <[e-mail]>
>>>>>> Cc: mpls <[e-mail]>
>>>>>> Subject: [mpls] Another way...
>>>>>>
>>>>>>
>>>>>> [WG chair hat: off]
>>>>>>
>>>>>> Hi Loa,
>>>>>>
>>>>>> It occurred to me that another way of indicating the presence of PSD
>>>>>> would be to allocate an opcode to serve this purpose.
>>>>>>
>>>>>> This requires no reserved bits and no pre-definition of any value so
>>>> it
>>>>>> intrinsically cannot disappear.
>>>>>>
>>>>>> Tony
>>>>>>
>>>>>> _______________________________________________
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>>>>>
>>>>>
>>>>
>>>>
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>>>
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>>
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