Subject: RE: [NSIS] layer split summary? opinions?

From: "Georgios Karagiannis (ELN)" <[email-masked]>
Date: Thu, 30 Jan 2003 14:21:05 +0100

Dear Henning

Please see my comments in line:
[georgios-previous] Features such as segmentation, congestion
[georgios-previous] control, non duplication of signaling messages, etc.
[georgios-previous] are specific and needed for some NSLP type, 
[georgios-previous] but not for all NSLP types.

[Henning] Can you identify the types that need it and the types 
          that don't?

For the moment I would want to mention that the NTLP that I need 
to use does not need such features.

[Henning] Are you advocating that NSLP become a full-fledged transport protocol 
[Henning] for 'some' NSLP types, essentially an application-layer TCP or SCTP?

No, if an application needs TCP or SCTP features, then these applications 
should probably use the TCP or SCTP protocols, e.g., below NTLP.

Best Regards,
Georgios

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From: Henning Schulzrinne <[email-masked]>
Date: Thu, 30 Jan 2003 08:50:03 -0500

> to use does not need such features.

I'm afraid I can't parse this.

> should probably use the TCP or SCTP protocols, e.g., below NTLP.

That's what I've been advocating. Part of the discussion problem seems 
to be that some people say "NTLP" and mean "whatever 'transport' layer 
NSIS invents including the transport below", others mean "whatever sits 
on top of either IP or TCP/SCTP". We should agree on one definition.

A different way of phrasing the confusion is that some people see NTLP 
as an interface to the higher layer (NSLP) above - it describes all of 
the services that the NSIS-new-stuff adds plus any underlying existing 
transport protocol offers.

Other people, possibly guided by the 'P' at the end, see it as a 
protocol, i.e., describe only the services that this layer adds on top 
of whatever L3/L4 mechanism is below.

The re-use of the word transport can't help but add to 
misunderstandings, but we probably lack the language supply to fix that 
particular problem. (We have used the term messaging layer in one 
context, but that term has its own set of problems.)

However, your statement does add a requirement to NTLP: namely, that it 
should be able to use either 'raw' IP or an existing transport 
mechanism, such as UDP, TCP or SCTP (or possibly one of the emerging 
UDP-like, congestion-controlled protocols being discussed in TSVAREA).