[tcpdump-workers] Request for link-layer header type (XRA)

Bruno Verstuyft bruno.verstuyft at gmail.com
Thu Jan 4 08:47:25 EST 2018


Hi,

are any more clarifications needed for the XRA header spec?

Best regards,

Bruno

2017-12-12 11:17 GMT+01:00 Bruno Verstuyft <bruno.verstuyft at gmail.com>:

>
>
> 2017-12-11 22:31 GMT+01:00 Guy Harris <guy at alum.mit.edu>:
>
>> On Dec 5, 2017, at 4:47 AM, Bruno Verstuyft <bruno.verstuyft at gmail.com>
>> wrote:
>>
>> > 2017-12-04 22:21 GMT+01:00 Guy Harris <guy at alum.mit.edu>:
>> >
>> >> On Nov 16, 2017, at 1:21 AM, Bruno Verstuyft <
>> bruno.verstuyft at gmail.com>
>> >> wrote:
>> >>
>> >>> we put the specification of the XRA header online.
>> >>
>> >> The MAC document speaks of "logical" upstream and downstream channels;
>> are
>> >> those what the "Downstream Channel ID" and "Upstream Channel ID" TLVs
>> refer
>> >> to?
>> >>
>> > Yes, from the MULPI spec:
>> > Logical (Upstream) Channel: A MAC entity identified by a unique channel
>> ID
>> > and for which bandwidth is allocated by an
>> > associated MAP message. A physical upstream channel may support multiple
>> > logical upstream
>> > channels. The associated UCD and MAP messages completely describe the
>> > logical channel.
>>
>> You might want to say "ID of downstream *logical* channel" in the remarks
>> for "Downstream Channel ID"; the remarks for "Upstream Channel ID" already
>> say "logical upstream channel" (is it best to say "logical XXX channel" or
>> "XXX logical channel"?).
>>
>
> In the DOCSIS specs, there is no occurence of the term downstream logical
> channel, since there are only physical downstream channels.
> In the upstream, a physical upstream channel (channel around a center
> frequency) can be divided into multiple logical channels. This division is
> time based.
> More information can be found  in 5.2.1.1.3.1 "Downstream Data Forwarding
> in a MAC Domain" and 5.2.1.1.3.2 " Upstream Data Forwarding in a MAC
> Domain" in the DOCSIS MULPI spec.
>
> It is best to say logical upstream channel, since this is the term used in
> the DOCSIS specs.
>
>
>
>>
>> >> To what do the start and stop minislots in the "Minislot ID" TLV refer?
>> >
>> > These are the minislots, relative in an OFDMA frame. The minislot with
>> the
>> > lowest subcarriers has id 0.
>>
>> So those are the minislots from section 7.4.1 "Signal Processing
>> Requirements" of the PHY specification?
>>
>
> Yes, updated in the Xra Header spec.
>
>>
>> >> What do the "Symbol ID", "Burst ID", and "Subplot ID" TLVs contain?
>> >
>> > Symbol ID is a number assigned to each symbol by our hardware. This is
>> > mainly used for timing calculations. It can also be used to visualize
>> the
>> > correlation between NCP (Next Codeword Pointers) and the corresponding
>> > downstream data packets.
>>
>> So to which symbol in the packet does that refer?
>>
>
> The first symbol of the packet. Updated in the spec.
>
>>
>> > Burst ID is used to map mac frames to the corresponding databurst. A
>> > databurst can e.g. contain a segment:(see MULPI 7.2.4
>> > Continuous Concatenation and Fragmentation). This means a segment can
>> > contain multiple Mac frames, or a Mac frame can be spread over multiple
>> > segments. In our sniffer, we extract these Mac frames from the
>> segments. To
>> > save the information of which Mac frame belongs to which segment (or
>> > multiple segments), we use the Burst ID: each data burst gets a unique
>> > Burst ID. In the Mac Frame the "Burst Info"/"Burst ID reference" is
>> used to
>> > reference these Burst IDs.
>>
>> So your sniffer assigns the Burst IDs?
>>
>> There's a variable-length "Burst ID" field and a "Burst ID Reference"
>> field.  Does the "Burst ID" field contain a single burst ID?  If so, to
>> which burst was that ID assigned?  And what does the "Burst ID Reference"
>> field contain?
>>
>> Added extra explanation in the spec.
>
>
>> >> Does the SID TLV contain the Service Identifier for the service flow in
>> >> which the packet was sent?
>> >
>> > Yes
>>
>> You might want to spell out "Service Identifier" in the remarks.
>>
>
> Updated in spec.
>
>
>>
>> >> Does the IUC TLV contain the Interval Usage Code for the burst if the
>> >> packet is a burst?
>> >
>> > Yes
>>
>
> You might want to spell out "Interval Usage Code" in the remarks.
>>
>>
> Updated in spec
>
>


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