[Sis-dtn] [EXTERNAL] RE: New version of LTP Corrigendum

Wed May 31 17:58:34 UTC 2023

Good people have written good stuff.  Glad to have it available!

From: sburleig.sb at gmail.com <sburleig.sb at gmail.com> 
Sent: Wednesday, May 31, 2023 1:57 PM
To: Robert C Durst <durst at mitre.org>; Cerf, Vinton <vint at google.com>
Cc: 'Sipos, Brian J.' <Brian.Sipos at jhuapl.edu>; 'Sanchez Net, Marc (US 332H)' <marc.sanchez.net at jpl.nasa.gov>; Jeremy.Mayer at dlr.de; 'Torgerson, J. Leigh (US 332C)' <jordan.l.torgerson at jpl.nasa.gov>; Felix.Flentge at esa.int; keithlscott at gmail.com; sis-dtn at mailman.ccsds.org
Subject: RE: [Sis-dtn] [EXTERNAL] RE: New version of LTP Corrigendum

Excellent digging, Bob.

From: Robert C Durst <durst at mitre.org <mailto:durst at mitre.org> > 
Sent: Wednesday, May 31, 2023 10:54 AM
To: sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> ; Cerf, Vinton <vint at google.com <mailto:vint at google.com> >
Cc: 'Sipos, Brian J.' <Brian.Sipos at jhuapl.edu <mailto:Brian.Sipos at jhuapl.edu> >; 'Sanchez Net, Marc (US 332H)' <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; Jeremy.Mayer at dlr.de <mailto:Jeremy.Mayer at dlr.de> ; 'Torgerson, J. Leigh (US 332C)' <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >; Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> ; keithlscott at gmail.com <mailto:keithlscott at gmail.com> ; sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> 
Subject: RE: [Sis-dtn] [EXTERNAL] RE: New version of LTP Corrigendum

Thanks, Scott!

Indeed, fragmentation and reassembly are (and have always been) challenging, sometimes necessary, and the source of many bad words.

For the near-ish term future, it’s reasonable to assume that BPAs know or can be informed of the limitations of the CLAs in the system.  And still, design matters.  These two excerpts from RFC 7122 are relevant, and perhaps the RID response should point to this section of RFC7122:    

3.1. How and Where to Deal with Fragmentation

The Bundle Protocol allows bundles with sizes limited only by node

resource constraints. In IPv4, the maximum size of a UDP datagram is

nearly 64 KB. In IPv6, when using jumbograms [RFC2675], UDP

datagrams can technically be up to 4 GB in size [RFC2147], although

this option is rarely used. (Note: RFC 2147 was obsoleted by RFC

2675.) It is well understood that sending large IP datagrams that

must be fragmented by the network has enormous efficiency penalties

[Kent87]. The Bundle Protocol specification provides a bundle

fragmentation concept [RFC5050] that allows a large bundle to be

divided into bundle fragments. If the Bundle Protocol is being

encapsulated in DCCP or UDP, it therefore SHOULD create each fragment

of sufficiently small size that it can then be encapsulated into a

datagram that will not need to be fragmented at the IP layer.

IP fragmentation can be avoided by using IP Path MTU Discovery

[RFC1191] [RFC1981], which depends on the deterministic delivery of

ICMP Packet Too Big (PTB) messages from routers in the network. To

bypass a condition referred to as a black hole [RFC2923], a newer

specification is available in [RFC4821] to determine the IP Path MTU

without the use of PTB messages. This document does not attempt to

recommend one fragmentation avoidance mechanism over another; the

information in this section is included for the benefit of

implementers.

And

3.1.2. UDP

When an LTP CL is using UDP for datagram delivery, it SHOULD NOT

create segments that will result in UDP datagrams that will need to

be fragmented, as discussed above.

3.2. Bundle Protocol over a Datagram Convergence Layer

In general, the use of the Bundle Protocol over a datagram CL is

discouraged in IP networks. Bundles can be of (almost) arbitrary

length, and the Bundle Protocol does not include an effective

retransmission mechanism. Whenever possible, the Bundle Protocol

SHOULD be operated over the TCP Convergence Layer or over LTP.

Best,

Bob

From: sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com>  <sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> > 
Sent: Wednesday, May 31, 2023 1:35 PM
To: Cerf, Vinton <vint at google.com <mailto:vint at google.com> >; Robert C Durst <durst at mitre.org <mailto:durst at mitre.org> >
Cc: 'Sipos, Brian J.' <Brian.Sipos at jhuapl.edu <mailto:Brian.Sipos at jhuapl.edu> >; 'Sanchez Net, Marc (US 332H)' <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; Jeremy.Mayer at dlr.de <mailto:Jeremy.Mayer at dlr.de> ; 'Torgerson, J. Leigh (US 332C)' <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >; Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> ; keithlscott at gmail.com <mailto:keithlscott at gmail.com> ; sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> 
Subject: RE: [Sis-dtn] [EXTERNAL] RE: New version of LTP Corrigendum

The convergence layer adapter is expected (7.2 of RFC 9171) to notify the BPA when it fails to forward the bundle, for whatever reason; among those reasons might well be “bundle is too big for this CL protocol”.  Depending on implementation, the BPA might respond to this notice by fragmenting the bundle; ION currently does this for the UDP CLA.  But certainly another implementation expedient might be for the BPA to know in advance the limitations of all available CLAs and choose the CLA for a given bundle on that basis.

Reassembly of a bundle from fragments, at the destination endpoint node, is certainly somewhat complicated.  But we discussed the alternatives at length, and what’s in the RFC is what we agreed on.  Reassembly of segmented LTP blocks and reassembly of fragmented IP packets is likewise complicated.  Ideally you always want this to be Somebody Else’s Problem.

Scott

From: Vint Cerf <vint at google.com <mailto:vint at google.com> > 
Sent: Wednesday, May 31, 2023 9:55 AM
To: Robert C Durst <durst at mitre.org <mailto:durst at mitre.org> >
Cc: Sipos, Brian J. <Brian.Sipos at jhuapl.edu <mailto:Brian.Sipos at jhuapl.edu> >; Sanchez Net, Marc (US 332H) <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; Jeremy.Mayer at dlr.de <mailto:Jeremy.Mayer at dlr.de> ; sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> ; Torgerson, J. Leigh (US 332C) <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >; Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> ; keithlscott at gmail.com <mailto:keithlscott at gmail.com> ; sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> 
Subject: Re: [Sis-dtn] [EXTERNAL] RE: New version of LTP Corrigendum

briefly, fragmentation, re-transmission, alternative convergence layers can result in non-uniform and overlapping receipt of fragmented bundles. That can make for a pretty messy reassembly at bundle layer. Of course, alternative routing through different CLAs can also result in partially reassembled bundles or bundle fragments at the receiving end of a CLA. We've encountered a lot of that in the Internet in its various incarnations. 

Is is a good assumption that the bundle maker layer knows about limitations of the CLA with regard to maximum bundle size to avoid fragmentation?

v

On Wed, May 31, 2023 at 12:39 PM Robert C Durst via SIS-DTN <sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> > wrote:

Folks, on a note that’s somewhat related to Brian’s message below, so far I’ve received precisely one Agency RID on BPv7, which is attached, FYI.  It deals with the BPv7 Minimum Supported Bundle Size (sec 3.6):

3.6 MINIMUM SUPPORTED BUNDLE SIZE

Conformant CCSDS implementations shall be able to forward and/or deliver bundles whose total size, including all extension blocks, is less than or equal to 10*220 bytes (10 MB).

NOTE - Disposition of larger bundles is implementation-specific.

The RID says:    

“Add details that show considerations for minimum size have been considered for network implementation.  

The Note that disposition of larger bundles is implementation-specific needs to be augmented to show that 

the impacts of this large bundle size have been considered for the various ways that networks could meet 

this requirement with the convergence layers.  It’s difficult to understand how an UDP or SPP Convergence-Layer

would satisfy this requirement.  It would be helpful to provide examples based on the CLAs specified in this document.”

In Normative Annex B, we specify 5 CLAs, and assert that a compliant BP implementation shall implement at least one of them.  As a result, a compliant implementation need implement no more than one of them.  By implication, since any of the CLAs specified might be the only CLA available, the requirement from Section 3.6 must be able to be met by any of the CLAs.

B2.1.2:  TCP CL – stream-oriented CL; no inherent limitations on Bundle Size.

B2.1.3:  UDP CL – Note on B2.1.3.2 says “It is desirable that BP agents endeavor to send bundles of such a size as not to require fragmentation by the IP (Internet Protocol) layer. In practice this generally means keeping the size of the IP datagram (including the IP and UDP headers, plus the bundle) to no more than 1500 bytes.”  

Probably not the answer he wants, particularly in the context of a 10MB bundle.  How does a UDP CL meet the requirement specified in 3.6?  If the UDP CL *cannot* meet the requirement specified in 3.6, how should we proceed?  Must the Bundle be fragmented into some number of fragmentary bundles that fit into a sequence of 150+ 65507-byte UDP payloads (or 6700+ 1472-byte UDP payloads)?  

B2.1.4:  LTP CL – is there a length limitation on LTP ADUs (Blocks)? I didn’t see one in the RFC or the Blue Book

B2.1.5:   SPP – B2.1.5.1 notes that the maximum size of a bundle is <= 65535.  Is Bundle fragmentation therefore the only way to accommodate the requirement of section 3.6?

B2.1.6:  EPP – 4GB MTU meets the section 3.6 requirement.

So, for TCP, LTP, and EPP there’s no issue with the requirement in 3.6.  For UDP and SPP, is Bundle Fragmentation the only feasible approach?  

RFC 9171 section 5.9 permits in-transit reassembly (“an ADU also be reassembled at some other node on the path to the destination.”).  The motivator for that might be to remove redundant bundle headers in order to reduce overhead before forwarding a large bundle over a (potentially not-yet-available) constrained link.

Is it the sense of this group that this is correct?  Would an appropriate response to the RID be to add to the note on 3.6 a sentence to the effect of the following:  “…is implementation-specific.  For CLAs that have maximum size limits that are less than this 10MB requirement (e.g., UDP, B2.1.3 and SPP, B2.1.5), Bundle Fragmentation and Reassembly (refer to RFC 9171 sections 5.8 and 5.9) are available to mitigate the limitation.” 

Any sense of the reaction to this not-so-satisfying response?

Thanks,
Bob   

From: SIS-DTN <sis-dtn-bounces at mailman.ccsds.org <mailto:sis-dtn-bounces at mailman.ccsds.org> > On Behalf Of Sipos, Brian J. via SIS-DTN
Sent: Wednesday, May 31, 2023 11:04 AM
To: Sanchez Net, Marc (US 332H) <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; Jeremy.Mayer at dlr.de <mailto:Jeremy.Mayer at dlr.de> ; sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> ; Torgerson, J. Leigh (US 332C) <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >; Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> ; keithlscott at gmail.com <mailto:keithlscott at gmail.com> 
Cc: sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> 
Subject: Re: [Sis-dtn] [EXTERNAL] RE: New version of LTP Corrigendum

Marc, for my own purposes the one reason for using unreliable LTP is to take advantage of the segmentation of larger-than-MTU blocks. It’s a useful thing on its own separate from other capabilities of LTP. Similar to some of these other recommendations, it would be helpful for implementations to know “if you are able to choose block sizes then here is a recommendation … Otherwise if you are using green block segmentation then here are some considerations (about timing and resource leaks) …”

I think it’s better for an designer/implementer to be aware of potential issues and head them off than to try to ignore or impose restrictions on the service which would prohibit existing use cases.

From: SIS-DTN <sis-dtn-bounces at mailman.ccsds.org <mailto:sis-dtn-bounces at mailman.ccsds.org> > On Behalf Of Sanchez Net, Marc (US 332H) via SIS-DTN
Sent: Wednesday, May 31, 2023 8:55 AM
To: Jeremy.Mayer at dlr.de <mailto:Jeremy.Mayer at dlr.de> ; sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> ; Torgerson, J. Leigh (US 332C) <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >; Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> ; sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> ; keithlscott at gmail.com <mailto:keithlscott at gmail.com> 
Subject: [EXT] Re: [Sis-dtn] [EXTERNAL] RE: New version of LTP Corrigendum

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I am unconvinced either way, to be honest. I agree with Jeremy forcing the LTP engine to know the contact plan is not great, but having another “stale session timeout” seems an equally non-ideal solution. Would all these problems “go away” if we force in the spec that a green block always be transmitted as a single green segment? But then the block size must be matched to the underlying link MTU (or transmission size used by the mission) which is <=65 kB for transfer frames, I believe. Would that be too restrictive if we sent streaming video over LTP green?

-----------------------------------------------------------------------------------------------------------------------

Marc Sanchez Net (332H)

Telecommunications Engineer

Jet Propulsion Laboratory

Cell:  <mailto:(617)%20953-7977> (617) 953-7977 | Email:  <mailto:marc.sanchez.net at jpl.nasa.gov> marc.sanchez.net at jpl.nasa.gov

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From: Jeremy.Mayer at dlr.de <mailto:Jeremy.Mayer at dlr.de>  <Jeremy.Mayer at dlr.de <mailto:Jeremy.Mayer at dlr.de> > 
Sent: Wednesday, May 31, 2023 1:05 AM
To: sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> ; Sanchez Net, Marc (US 332H) <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; Torgerson, J. Leigh (US 332C) <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >; Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> ; sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> ; keithlscott at gmail.com <mailto:keithlscott at gmail.com> 
Subject: RE: [Sis-dtn] [EXTERNAL] RE: New version of LTP Corrigendum

Hi,

Realistically, I agree, the LTP engine should probably be aware of either the contact plan OR the status of the downlink. That being said, I don’t think that’s a dependency which we want to force, due to the “perpetual downlink” use-case (ISS). There’s nothing stopping me from running a single LTP link from now until the end of time, unaware of the status of the underlying link. Of course, there’s the caveat that green sessions may be transmitted into the void, never to be seen again.

That being said, the “last green block” problem is insidious: In a nominal downlink (e.g. with minimal out-of-order arrival and loss), we can use the EOB as a signal that the block should be delivered. However, if the EOB is out-of-order, there’s a problem: the application shouldn’t have to expect that data from the same session may arrive twice. The only way to really deal with this in the face of out-of-order/missing arrivals is to track the completeness of a green session. If the EOB block is delivered while data is still missing, we ignore it and “hold” the session until a user-specified timeout. In LTPv2, we called this the “stale session timeout”. If more data is delivered into one of these pending sessions, it can still be enqueued and delivered upon timeout. This allows us to treat out of order sessions and those where the EOB is missed in the same way.

Thanks,

Jeremy

From: SIS-DTN <sis-dtn-bounces at mailman.ccsds.org <mailto:sis-dtn-bounces at mailman.ccsds.org> > On Behalf Of sburleig.sb--- via SIS-DTN
Sent: Tuesday, May 30, 2023 11:55 PM
To: 'Sanchez Net, Marc (US 332H)' <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; 'Torgerson, J. Leigh (US 332C)' <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >; 'Felix Flentge' <Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> >; 'Dr. Keith L Scott via SIS-DTN' <sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> >; keithlscott at gmail.com <mailto:keithlscott at gmail.com> 
Subject: Re: [Sis-dtn] [EXTERNAL] RE: New version of LTP Corrigendum

Marc, good question.  My thought on this is that LTP needs to be aware of the “contact plan” in order to know when to pause and resume the “red” timers.  Given this, the LTP engine should be able to infer that cessation of green block segment reception is due to the termination of the pass.  At that point we have a matter of policy.  If it’s known that green block transmission is always supposed to happen far enough before the end of the pass to enable complete reception, then the end of the pass signifies that any currently incomplete block is not going to be completed and the block’s current incomplete contents can be delivered.  If not, then maybe the current state of that incomplete final block should be sustained until the start of the next pass enables further reception of that block’s segments.

Of course, sticking to small green blocks that are transmitted in single green segments makes the whole issue go away.

Scott

From: Sanchez Net, Marc (US 332H) <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> > 
Sent: Tuesday, May 30, 2023 1:18 PM
To: sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> ; Torgerson, J. Leigh (US 332C) <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >; 'Felix Flentge' <Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> >; 'Dr. Keith L Scott via SIS-DTN' <sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> >; keithlscott at gmail.com <mailto:keithlscott at gmail.com> 
Cc: Gao, Jay L (US 332C) <jay.l.gao at jpl.nasa.gov <mailto:jay.l.gao at jpl.nasa.gov> >; Richard, Nate J (US 332C) <nathaniel.j.richard at jpl.nasa.gov <mailto:nathaniel.j.richard at jpl.nasa.gov> >
Subject: RE: [EXTERNAL] RE: [Sis-dtn] New version of LTP Corrigendum

All,

A quick update to the draft LTP corrigendum with a few more items to make sure some of the issues being brought up in this email chain don’t fall through the cracks. 

Also, a minor note on Scott’s comment that “the arrival of the first segment of the next “green” block is a simpler and perhaps more accurate (configuration-free) means of determining that it is time to deliver the current block”: How does the receiving LTP engine handle the very last LTP block of a pass? Without a timer, would it ever be released to the application? I hate to add new timers, but I do not see how to get around it in this this corner case.

-----------------------------------------------------------------------------------------------------------------------

Marc Sanchez Net (332H)

Telecommunications Engineer

Jet Propulsion Laboratory

Cell:  <mailto:(617)%20953-7977> (617) 953-7977 | Email:  <mailto:marc.sanchez.net at jpl.nasa.gov> marc.sanchez.net at jpl.nasa.gov

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From: sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com>  <sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> > 
Sent: Tuesday, May 30, 2023 8:13 AM
To: Torgerson, J. Leigh (US 332C) <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >; 'Felix Flentge' <Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> >; Sanchez Net, Marc (US 332H) <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; 'Dr. Keith L Scott via SIS-DTN' <sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> >
Cc: Gao, Jay L (US 332C) <jay.l.gao at jpl.nasa.gov <mailto:jay.l.gao at jpl.nasa.gov> >; Richard, Nate J (US 332C) <nathaniel.j.richard at jpl.nasa.gov <mailto:nathaniel.j.richard at jpl.nasa.gov> >
Subject: RE: [EXTERNAL] RE: [Sis-dtn] New version of LTP Corrigendum

Guys, a thought on this.

In “red” transmission you expect out-of-order segment arrival on a routine basis, because every retransmitted bundle will arrive out of order.  There are timers in the protocol to support the operation of the retransmission procedures.

In “green” transmission you cannot have out-of-order segment arrival if you size your blocks in such a way that each block is transmitted in a single segment.  I believe users will typically adopt this model, as “green” data will normally be data for which minimized delay is more important than reliability (otherwise they would use “red” transmission).

In “green” transmission where the blocks are large enough to require transmission in multiple segments you have to wait for an entire block to arrive – or until you are confident that any missing segments were actually lost rather than simply forwarded out of order – before delivering the contents of the block.  But there’s no re-transmission to avoid, because the transmission is “green”, right?  If you wanted retransmission you would have used “red”.

So in that event I would suggest that the arrival of the first segment of the next “green” block is a simpler and perhaps more accurate (configuration-free) means of determining that it is time to deliver the current block – complete or incomplete – and let the application figure out what to do about the missing data.

Scott

From: Torgerson, J. Leigh (US 332C) <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> > 
Sent: Tuesday, May 30, 2023 7:54 AM
To: Felix Flentge <Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> >; sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> ; Sanchez Net, Marc (US 332H) <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; 'Dr. Keith L Scott via SIS-DTN' <sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> >
Cc: Gao, Jay L (US 332C) <jay.l.gao at jpl.nasa.gov <mailto:jay.l.gao at jpl.nasa.gov> >; Richard, Nate J (US 332C) <nathaniel.j.richard at jpl.nasa.gov <mailto:nathaniel.j.richard at jpl.nasa.gov> >
Subject: Re: [EXTERNAL] RE: [Sis-dtn] New version of LTP Corrigendum

Thanks Felix – 

Agreed - A statement warning about how implementations should be wary of out-of-order deliveries would be useful in the corrigendum..

regards,

Leigh

From: Felix Flentge < <mailto:Felix.Flentge at esa.int> Felix.Flentge at esa.int>
Date: Monday, May 29, 2023 at 11:47 PM
To: "Torgerson, Jordan L (332M)" < <mailto:jordan.l.torgerson at jpl.nasa.gov> jordan.l.torgerson at jpl.nasa.gov>, " <mailto:sburleig.sb at gmail.com> sburleig.sb at gmail.com" < <mailto:sburleig.sb at gmail.com> sburleig.sb at gmail.com>, "Sanchez Net, Marc (US 332H)" < <mailto:marc.sanchez.net at jpl.nasa.gov> marc.sanchez.net at jpl.nasa.gov>, "'Dr. Keith L Scott via SIS-DTN'" < <mailto:sis-dtn at mailman.ccsds.org> sis-dtn at mailman.ccsds.org>
Cc: "Gao, Jay L (US 332C)" < <mailto:jay.l.gao at jpl.nasa.gov> jay.l.gao at jpl.nasa.gov>, "Richard, Nate J (US 332C)" < <mailto:nathaniel.j.richard at jpl.nasa.gov> nathaniel.j.richard at jpl.nasa.gov>
Subject: RE: [EXTERNAL] RE: [Sis-dtn] New version of LTP Corrigendum

Hi Leigh,

Yes, we also have systematic out-of-order in EO or L2 missions as different physical channels may be used (with maybe different rates and different PDU sizes). With ‘implementation issue’ I don’t mean that it is not important but I would like to avoid making it normative as we want to avoid ‘changing the standard’ which would require interop testing.

By any means, we should have a statement that in case you may have out-of-order delivery it is recommended to implement timer to wait for out-of-order segments to avoid re-transmission (we will add a similar statement to CFDP for the next release).

Regards,

Felix

From: Torgerson, J. Leigh (US 332C) <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> > 
Sent: Thursday, May 25, 2023 6:22 PM
To: Felix Flentge <Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> >; sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> ; Sanchez Net, Marc (US 332H) <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; 'Dr. Keith L Scott via SIS-DTN' <sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> >
Cc: Gao, Jay L (US 332C) <jay.l.gao at jpl.nasa.gov <mailto:jay.l.gao at jpl.nasa.gov> >; Richard, Nate J (US 332C) <nathaniel.j.richard at jpl.nasa.gov <mailto:nathaniel.j.richard at jpl.nasa.gov> >
Subject: Re: [EXTERNAL] RE: [Sis-dtn] New version of LTP Corrigendum

Thanks Felix – 

One comment is that in deep space use of DTN, we would expect that out-of-order delivery would be the rule, rather than the exception – if it takes 40 min RTT to recover a missing segment from Mars, waiting for it to ensure in-order delivery to some application would make ops impossible. (One must design one’s applications to be “aware” of the operational environment of course..)

We haven’t used both LTP red/green at the same time in our testing and real-world ops as far as I know, but I suspect that recommending that red and green be in different sessions would be a good idea, if nothing else but to make troubleshooting easier!  (Nate and Jay may have some thoughts based on our lunar ops with KPLO so I cc:d them..)

regards

Leigh

From: Felix Flentge < <mailto:Felix.Flentge at esa.int> Felix.Flentge at esa.int>
Date: Thursday, May 25, 2023 at 4:56 AM
To: " <mailto:sburleig.sb at gmail.com> sburleig.sb at gmail.com" < <mailto:sburleig.sb at gmail.com> sburleig.sb at gmail.com>, "Sanchez Net, Marc (US 332H)" < <mailto:marc.sanchez.net at jpl.nasa.gov> marc.sanchez.net at jpl.nasa.gov>, "'Dr. Keith L Scott via SIS-DTN'" < <mailto:sis-dtn at mailman.ccsds.org> sis-dtn at mailman.ccsds.org>
Cc: "Torgerson, Jordan L (332M)" < <mailto:jordan.l.torgerson at jpl.nasa.gov> jordan.l.torgerson at jpl.nasa.gov>
Subject: [EXTERNAL] RE: [Sis-dtn] New version of LTP Corrigendum

Hi,

I agree with the modifications below.

Some additional points:

*         I would propose to also deprecate Service Data Aggregation (it is currently mandatory). Unless, I am overlooking something, it is not an interoperable mechanism as there is no generic way to determine the length of a client data capsule. Also, for BP/LTP the updated BP standard will describe an aggregation mechanism (CBOR length information + bundle IIRC).

*         Should we discourage use of mixed sessions (on the other hand LTP green is optional anyway)?

*         For the two additional issues, we could add that this is an implementation issue and that implementation may want to introduce these additional timers in case they (routinely) expect out-of-order delivery

Regards,

Felix

From: SIS-DTN <sis-dtn-bounces at mailman.ccsds.org <mailto:sis-dtn-bounces at mailman.ccsds.org> > On Behalf Of sburleig.sb--- via SIS-DTN
Sent: Thursday, May 18, 2023 1:23 AM
To: 'Sanchez Net, Marc (US 332H)' <marc.sanchez.net at jpl.nasa.gov <mailto:marc.sanchez.net at jpl.nasa.gov> >; 'Dr. Keith L Scott via SIS-DTN' <sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> >
Cc: 'Torgerson, J. Leigh (US 332C)' <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >
Subject: Re: [Sis-dtn] New version of LTP Corrigendum

Marc, FWIW, I agree about deprecating LTP security and I am likewise skeptical that adding more timers is a good idea; that sounds like a way to work around a design element that hasn’t been thought through completely.

Scott

From: SIS-DTN <sis-dtn-bounces at mailman.ccsds.org <mailto:sis-dtn-bounces at mailman.ccsds.org> > On Behalf Of Sanchez Net, Marc (US 332H) via SIS-DTN
Sent: Tuesday, May 16, 2023 7:05 PM
To: Dr. Keith L Scott via SIS-DTN <sis-dtn at mailman.ccsds.org <mailto:sis-dtn at mailman.ccsds.org> >
Cc: Torgerson, J. Leigh (US 332C) <jordan.l.torgerson at jpl.nasa.gov <mailto:jordan.l.torgerson at jpl.nasa.gov> >
Subject: [Sis-dtn] New version of LTP Corrigendum

All,

Please find attached a new version of the LTP corrigendum with some modifications including:

*         Comparison between LTP and "the new protocol" has been reduced. This in part motivated by the fact that we have demonstrated ~4 Gbps rates with ION's LTP implementation, which is more than sufficient for deep space links (e.g., even in future trunk lines between Earth and Mars, data rates of 4 Gbps are never exceeded).

*         I have added two possible additions to the technical corrigendum based on work done by Brian and people at GRC. They are all optional (MAY) statements and I believe can be implemented without additional managed parameters (and timers).

*         Brian has commented on two additional issues (see here <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/22__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33vk9LEw4$>  and here <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> ), but those seem to require additional timers that would need to be managed, so I am unconvinced it is worth the extra complexity. Brian, please correct me if I am wrong.

Finally, I think the note at the beginning of Section 3.9 of the current CCSDS LTP spec should be modified to explicitly state that LTP security should not be used and, instead, implementers should rely on security mechanisms provided by other parts of the CCSDS protocol stack, be it SDLS or BPSec. Thoughts on this point? 

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> Defer data retransmission with out-of-order report segments · Issue #24 · nasa/HDTN

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> When the network is causing out-of-order segment reception it is possible that one or more synchronous reception reports are received either out-of-order or within a short time window, possibly fol...

github.com <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> 

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> Defer synchronous reception report with out-of-order data segments · Issue #22 · nasa/HDTN

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> When red part data is segmented and delivered to the receiving engine out-of-order, the checkpoint(s) and EORP can be received before the earlier-in-block data segments. If a synchronous report is ...

github.com <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> 

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$>  

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> Thanks,

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> -----------------------------------------------------------------------------------------------------------------------

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> Marc Sanchez Net (332H)

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> Telecommunications Engineer

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> Jet Propulsion Laboratory

 <https://urldefense.us/v3/__https:/github.com/nasa/HDTN/issues/24__;!!PvBDto6Hs4WbVuu7!J3wEpyPHlAiGcXO0VDc8uO1zb9BOrpYLw3dw6BHPigpmcy0Q4f8gxX6hHLnQOqg_AVxEg_MYrByNRr1urhAp-KViTuP33uBoiHHY$> Cell: (617) 953-7977 | Email: marc.sanchez.net at jpl.nasa.gov

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