Subject: [RMT] PGM and network layer independence

From: "Anumita Biswas" <[email-masked]>
Date: Thu, 07 Mar 2002 22:32:00 -0700

PGM does not appear to be completely network layer independent. The GSI
is calculated based on the DNS name to have network layer independence. 

But the packet formats themselves are not IPv6 compliant. Even though
there are fields like NLA AFI and NLA in the packets, the byte space
allocated allows only for 4 bytes of NLA. What is the need then for an
address family field ? And also it appears that "NLA" could as well be
called as IP(v4) address!

Probably, the issue here is even deeper... the fact that transport
layer headers carry network layer information which is mandated by the
very design of PGM protocol. 

Are my assumptions wrong here? Any comments? 

-AB

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From: Lorenzo Vicisano <[email-masked]>
Date: Fri, 8 Mar 2002 00:48:44 -0800

Anumita,

> called as IP(v4) address!

PGM does not specify NLAs to be 4 bytes. Their length is implicitly
determined by the AFI. Hence all the headers that contain one or more
NLAs have variable length. If any of the header specifications in
rfc3208 assumes that NLA is for bytes, then that's a bug in the
document (please let the authors know).

> very design of PGM protocol. 

All transport protocols need to identify network-layer endpoints
somehow. In PGM the choice was to communicate this information in-band and
to use NLAs directly, but note that NLAs are opaque to the transport
protocol.

Finally, further discussion concerning PGM specifically should be
carried out outside this mailing list.

	Thank you,
	Lorenzo