Re: [manet-dlep-rg] Slight issue with Data items

"Taylor, Rick" <Rick.Taylor@cassidian.com> Mon, 10 March 2014 17:25 UTC

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From: "Taylor, Rick" <Rick.Taylor@cassidian.com>
To: "Stan Ratliff (sratliff)" <sratliff@cisco.com>, Rick Taylor <rick@tropicalstormsoftware.com>
Thread-Topic: [manet-dlep-rg] Slight issue with Data items
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Date: Mon, 10 Mar 2014 17:25:16 +0000
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Subject: Re: [manet-dlep-rg] Slight issue with Data items
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> I'll offer up a slight modification of the "London Rule" :  Experimental Data
> Items (and Vendor-specific TLVs) that are not supported by an
> implementation should be parsed (e.g. "stepped over') and silently dropped.
> Data Item TLVs that are not *understood* (e.g. TLV number not registered,
> or "reserved"), OR are out-of-context (like a Version TLV in a destination
> update message) should cause PEER_TERMINATION and closure of TCP
> session.

That will rely on a clear list of every suitable data item TLV used with each signal, which might turn into an O(N^2) documentation nightmare.

I was wondering about adding an 8bit context field to the TLV header: 8bit Type, 8bit Context, 16bit Length (seems to align nicely).

Context: 1 = Discovery Data Item, 2 = Session Initiation/Termination Data Item, 3 = Peer Data Item, 4 = Link Data Item, plus the classic experimental and reserved spaces.

This might be easier to specify, and reduces the London Rule to "Any data item received with a context field that does not match the context of the enclosing signal MUST result in PEER_TERMINATION", then all that is needed is to define the context of each signal, back to O(N) for those of you familiar with big-O notation.

I know this seems like adding error checking to the protocol, but with Vendor Extensions and experimental TLVs a bit of error checking is no bad thing, just think of it as an FEC code...

Alternatively you could consider Type and Context as one little endian 16bit value... or swap them around to make CTLV...

Rick

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