Subject: [rohc] Clarification required regarding the ECN_USED control filed in TCP Profile

From: Anil Maguluri <[email-masked]>
Date: Wed, 31 Mar 2010 10:12:57 +0530

Hi All,

Please clarify me whether my understanding is right or not.

As per my understanding, the ecn_used flag is enable whenever the TCP SYN packet
has ECE and CWR bits are set (ENC-SETUP SYN). This information is going to
send using TCP dynamic chain (tcp_ecn_flags) and set ecn_used flag in the TCP Dynamic chain
in the IR packet.

Decompressor receives the IR packet with ecn_used flag is set, update the ecn_used
flag in the context.

Whenever ecn_used flag is enable, compressor has to send TCP/IP ECN flags in the
irregular chain of the compressed packets and decompressor has to decode it from the
irregular chain to reconstruct the packet.

Please clarify the below queries.

è If the TCP flow started with ECN enable/supported, is it static the life time of the flow?

è If not, is TCP is going to send SYN packet again with disabling the ECE and CWR flags?

è How frequently TCP flow can change from ECN enable to non-ECN?

è If the TCP flow is changed from ECN capable to non-ECN, compressor has to inform

to decompressor while setting the ecn_used as zero. Right? So that, compressor no

need to sending TCP/IP ECN flags in the irregular chain.

Thanks for your support.

Regards,
Anil Kumar Maguluri

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