[Sls-slp] RE: TC commanding

Shames, Peter M (3130) peter.m.shames at jpl.nasa.gov
Mon Oct 19 18:02:54 UTC 2009

True enough.  SLE is an application layer protocol that provides a link layer tunnel.  Not unlike a VPN application layer service in that regard.

Cheers, Peter

On 10/19/09 7:18 AM, "L.Wood at surrey.ac.uk" <L.Wood at surrey.ac.uk> wrote:

Minor nit in the below - SLE isn't a transport. SLE runs over TCP, which
provides reliable transport (while limiting overall throughput) - though
you'd have to read the SLE specification quite closely to notice that it
runs over TCP.

SLE is really an application-layer protocol.

-----Original Message-----
From: sls-slp-bounces at mailman.ccsds.org on behalf of Hooke, Adrian J (9000)
Sent: Mon 2009-10-19 13:09
To: Shames, Peter M (3130); SLS-SLP WG
Subject: [Sls-slp] RE: TC commanding

Peter wrote:

> Actually, according to the definition of "Network Layer" in the ISO BRM, 7498,

> the SPP is NOT a network layer service since it does not exhibit most of the

> properties defined in a network layer. ......

> Accordingly the SPP should either be:

> A) Treated as the application layer data structure that it actually is, or

> B) Be redefined and extended to include all of the attributes that a true network layer service must have.

> Doing A) makes sense.

Absolutely right. The SPP is an Application layer protocol and should remain as such. We have actually tied to use it as an Application support service (APID, length delimitation, sequence are of significance to the application), as a Transport service (sequence count), as a Network service ("Path ID") and as a Link multiplexing service (APID = link port ID, length delimitation). As a consequence we have over-used and under-specified it. It's time to run it as an Application service over underlying Transport, Network and Link services.

In the Forward Space Packet configuration, the SPP runs over SLE and IP as its Transport and Network layers in order to get to the space Link terminus. If there is then just a single hop into space, this sort of works. However, if there is more than one hop then the SPP is "naked" and can't go any further without a Network layer. So why don't we just get it over with and put one in for all SPP data transfers??



Peter Shames
Manager - JPL Data Systems Standards Program
InterPlanetary Network Directorate
Jet Propulsion Laboratory, MS 301-230
California Institute of Technology
Pasadena, CA 91109 USA

Telephone: +1 818 354-5740,  Fax: +1 818 393-0584

Internet:  Peter.M.Shames at jpl.nasa.gov
"We shall not cease from exploration, and the end of all our exploring
will be to arrive at where we started, and know the place for the first time"

                                                                                             T.S. Eliot

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