Transcript PPT Version

NR-SACKs for SCTP
(Non-Renegable SACKs)
draft-natarajan-tsvwg-sctp-nrsack-00
Preethi Natarajan
Paul Amer
Ertugrul Yilmaz (slides)
Randall Stewart
Janardhan Iyengar
Reneging and SCTP
• SCTP SACK chunk carries cum ack, gap acks
• Receiver may reneg on gap-acked data
– due to buffer overbooking
– sender does not discard gap-acked data
• Receiver cannot reneg on delivered / cum-acked
data
– sender can discard cum-acked data
2
Eg: Using SCTP multistreaming
56
789
sent from application
objects in send buffer
stream 1
delivered to application
cum-ack 9
1 ;
8
Gap-ack 2-7
2-2
2-3
2-4
2-5
2-6
receive buffer
retransmission
loss
stream 2
stream 3
SCTP association
Web server
Web client
Now with NR-SACKs
56
789
sent from application
objects in send buffer
delivered to application
cum-ack
1;gap-ack
2-4
2-5
cum-ack
1;gap-ack
cum-ack
1 ;2-7
8
9
2-6
receive buffer
nr-gap-ack
4-4
nr-gap-ack
4-5
nr-gap-ack
4-7
4-6
Gap-ack 2-3
2-2
stream 1
retransmission
loss
stream 2
stream 3
SCTP association
Web server
Web client
draft-natarajan-tsvwg-sctpnrsack-00
• Proposal:
– Negotiate NR-SACK capability at INIT time
– Replace SACKs with NR-SACKs
– Sender can use NR-SACK info to free
buffer
– (see draft for more on structure and use
cases)
• Is this draft ready to be a wg item?
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