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Does SCTP support out of band data

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  Does SCTP support out of band data ittium <ittium@gmail.com> - 2011-09-09 11:24 +0530
    Re: Does SCTP support out of band data Volker Birk <bumens@dingens.org> - 2011-09-09 10:40 +0000
    Re: Does SCTP support out of band data Stephane CHAZELAS <stephane_chazelas@yahoo.fr> - 2011-09-09 12:48 +0000
      Re: Does SCTP support out of band data ittium <ittium@gmail.com> - 2011-09-10 12:31 +0530

#1238 — Does SCTP support out of band data

Group,
This may be a very basic question. I did some googling but could not 
find definitive answer
Does SCTP support out of band data ?
thanks
Ittium

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#1240

ittium <ittium@gmail.com> wrote:
> This may be a very basic question. I did some googling but could not 
> find definitive answer
> Does SCTP support out of band data ?

To help you where to search:

<https://www.rfc-editor.org/rfc/rfc4960.txt>
| SCTP is a reliable transport protocol operating on top of a
| connectionless packet network such as IP.  It offers the following
| services to its users:
| [...]
|    --  sequenced delivery of user messages within multiple streams,
|        with an option for order-of-arrival delivery of individual
|        user messages,

The /recommended/ implementation of SCTP using a BSD socket API is
defined here:

<https://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-15>

And in this documentation, you will not find MSG_OOB.

If this was followed strictly, or if you have something else is
depending on the implementation of your operating system. You should be
able to find the answer in the documentation of your OS.

To explain:

"Out of bad data" is a term which is not specified in SCTP, but in BSD
socket API. The wording "the underlying protocol must also support
``out-of-band'' data." in send(2) does not mean, that there must be "out
of band data" explicitely defined in the protocol description, but in
the documentation about the implementation of the protocol.

So to answer your question quickly, you could search the documentation
of the SCTP implementation of your operating system for MSG_OOB. If
there is nothing like that:

Nope.

Yours,
VB.
-- 
Wenn Du für eine Leistung nichts bezahlst,
bist Du nicht der Kunde, sondern die Ware.

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#1241

2011-09-09, 11:24(+05), ittium:
[...]
> Does SCTP support out of band data ?
[...]

An SCTP association can have several streams, so you can use
one stream for "in-band" data, another for "out-of-band" data if
you like.

Message assembly and reordering in one stream doesn't affect
other streams. Messages can also be sent with an "unordered"
flag which can make their delivery faster in case of packet loss
or out of order delivery on the network.

So I suppose there's no point in having something similar as
TCP's "URGENT" flag there.

-- 
Stephane

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#1244

On 09-09-2011 PM 06:18, Stephane CHAZELAS wrote:
> 2011-09-09, 11:24(+05), ittium:
> [...]
>> Does SCTP support out of band data ?
> [...]
>
> An SCTP association can have several streams, so you can use
> one stream for "in-band" data, another for "out-of-band" data if
> you like.
>
> Message assembly and reordering in one stream doesn't affect
> other streams. Messages can also be sent with an "unordered"
> flag which can make their delivery faster in case of packet loss
> or out of order delivery on the network.
>
> So I suppose there's no point in having something similar as
> TCP's "URGENT" flag there.
>

thanks Stephane and Volker.

I am quoting this from RFC 4960

    "An SCTP endpoint can indicate that no ordered delivery is
    required for a particular DATA chunk transmitted within the stream by
    setting the U flag of the DATA chunk to 1.

    When an endpoint receives a DATA chunk with the U flag set to 1, it
    must bypass the ordering mechanism and immediately deliver the data
    to the upper layer (after reassembly if the user data is fragmented
    by the data sender).

    This provides an effective way of transmitting "out-of-band" data in
    a given stream.  Also, a stream can be used as an "unordered" stream
    by simply setting the U flag to 1 in all DATA chunks sent through
    that stream."

thanks
Ittium

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