[ndnSIM] [EXT]Re: Adding new field in Interest Packet.

[Junxiao Shi]

Hi DJEMAA


If the packet length doesn't matter in your configuration, I advise you to
> add a Tag instead of a new Field to your packet, since according to ndnSIM
> design, the tag resides only in the memory.
> Also, a Tag can be easily managed directly in the NFD machinery (forwarder
> class), contrary to a new field in either Interest or Data packets which
> are generally static objects.
>

ndnSIM doesn't support ns3::Tag (the kind described in ns-3 model library
https://www.nsnam.org/docs/release/3.33/models/html/packets.html#adding-and-removing-tags
).
Subclasses of ndn::Tag are completely different from ns3::Tag. This
includes the HopCountTag. They must be encoded into the packet buffer to
have any effect.


>> The main problem is that if i have the following topology
>> A--B--C--D
>> (Where A is the Consumer and D is the Producer, and B and C are routers)
>> Then by the solution given in the above link the custom field set in A's
>> generated Interest packet is reset to default value by B when it forwards
>> the interest to C.
>> How can I make it carry the value intended by A?
>>
>
A *forwarded* Interest is actually a different packet from the original:
Name, CanBePrefix, MustBeFresh, ApplicationParameters are copied over,
InterestLifetime, Nonce, HopLimit are modified, and other fields may be
discarded.

As I said previously, it's best to include the information as part of the
Name or ApplicationParameters, which is supported universally.

While NDN protocol allows having unrecognized non-critical fields in the
Interest packet, the protocol is vague on whether and what to preserve
during forwarding.
So far, as long as Name, CanBePrefix, MustBeFresh, ApplicationParameters,
and any fields that appear after ApplicationParameters are preserved, the
forwarder implementation would be interoperable.

Yours, Junxiao
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