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occurs when receiver gap-acks data and later discards the data without having delivered it to the receiving application
is discouraged but permitted (Receiver’s OS might need to reclaim buffer space) by definition, does NOT occur on data that has been delivered to the receiving application
Acknowledgment Types Cumulative Acknowledgment (ACK) – cum-ack n : (TCP) acks all data up to but not including byte n, (SCTP) acks all TSNs up to and including TSN n Selective Acknowledgment (SACK) – gap-ack : acks data received out-of-order Duplicate SACK (D-SACK) : acks data received multiple times
Reneging
SACK Limitations SCTP’s data receiver has no mechanism to inform a data sender about out-of-order data that has
been delivered (and therefore cannot be reneged) SCTP’s data receiver has no mechanism to inform a data sender about out-of-order data that has
not been delivered and will never be reneged
References ● P. Natarajan, P. Amer, E. Yilmaz, R. Stewart, J. Iyengar. Non-Renegable Selective Acknowledgments for SCTP,
IETF Internet Draft: draft-natarajan-tsvwg-sctp-nrsack (in-progress)
● E.Yilmaz, N. Ekiz, P. Natarajan, P. Amer, F.Baker. Performance analysis of SCTP Non-Renegable Selective Acknowledgements(NR-SACKs) (in-progress)
● P. Natarajan. Leveraging Innovative Transport Layer Services for Improved Application Performance, PhD Dissertation, CIS Department, University of Delaware
● Preethi Natarajan, Nasif Ekiz, Ertugrul Yilmaz, Paul D. Amer, Janardhan Iyengar and Randall Stewart, Non-Renegable Selective Acknowledgments (NR-SACKs) for SCTP, International Conference on Network Protocols (ICNP) 2008, Orlando, October 2008.
-send buffer size = 8
-send buffer size = 5
TSN 11 TSN 12 TSN 13 TSN 14
TSN 11
C=8; O=5 C=8; O=4 C=8; O=3 C=8; O=2 C=8; O=1
C=8; O=5 C=8; O=5 C=4; O=4 C=4; O=4
C=5; O=4
15, 14, 13, 12, 11 14, 13, 12, 11
13, 12, 11 12, 11
11
16, 15, 14, 13, 11 17, 16, 15, 14, 11
17, 16, 15, 11 18, 17, 16, 11
21, 20, 19, 18
TSN 15
TSN 17 TSN 16
TSN 18
TSN 19 TSN 20
19, 18, 17, 11 20, 19, 18, 11 C=4; O=4
C=4; O=4
TSN 21 TSN 22
22, 21, 20, 19, 18 C=5; O=5
SCTP with SACKs
SCTP with NR-SACKs
-send buffer size = 8
TSN 11 TSN 12 TSN 13 TSN 14
TSN 11
C=8; O=8 C=8; O=7 C=8; O=6 C=8; O=5 C=8; O=4 C=8; O=3 C=8; O=2 C=8; O=1
C=8; O=7 C=8; O=6 C=4; O=5 C=4; O=4 C=4; O=3 C=4; O=2 C=4; O=1
C=4; O=1
17, 16, 15, 14, 13, 12, 11 18, 17, 16, 15, 14, 13, 12, 11
16, 15, 14, 13, 12, 11 15, 14, 13, 12, 11
14, 13, 12, 11 13, 12, 11
12, 11 11
18, 17, 16, 15, 14, 13, 12, 11 18, 17, 16, 15, 14, 13, 12, 11 18, 17, 16, 15, 14, 13, 12, 11 18, 17, 16, 15, 14, 13, 12, 11 18, 17, 16, 15, 14, 13, 12, 11 18, 17, 16, 15, 14, 13, 12, 11 18, 17, 16, 15, 14, 13, 12, 11
19
TSN 15 TSN 16 TSN 17 TSN 18
TSN 19 TSN 20 TSN 21 TSN 22
20, 19 21, 20, 19
22, 21, 20, 19
C=4; O=2 C=4; O=3 C=4; O=4
TSN 11 TSN 12 TSN 13 TSN 14
TSN 11
C=8; O=8 C=8; O=7 C=8; O=6 C=8; O=5 C=8; O=4 C=8; O=3 C=8; O=2 C=8; O=1
C=8; O=8 C=8; O=8 C=4; O=7 C=4; O=6 C=4; O=5 C=4; O=4 C=4; O=4
C=5; O=4
17, 16, 15, 14, 13, 12, 11 18, 17, 16, 15, 14, 13, 12, 11
16, 15, 14, 13, 12, 11 15, 14, 13, 12, 11
14, 13, 12, 11 13, 12, 11
12, 11 11
19, 18, 17, 16, 15, 14, 13, 11 20, 19, 18, 17, 16, 15, 14, 11
20, 19, 18, 17, 16, 15, 11 20, 19, 18, 17, 16, 11
20, 19, 18, 17, 11 20, 19, 18, 11 21, 20, 19, 11
24, 23, 22, 21
TSN 15 TSN 16 TSN 17 TSN 18
TSN 20 TSN 19
TSN 21
TSN 22 TSN 23
22, 21, 20, 11 23, 22, 21, 11 C=4; O=4
C=4; O=4
TSN 24 TSN 25
25, 24, 23, 22, 21 C=5; O=5
send buffer blocking
Sponsors:
Performance Analysis of SCTP Non-Renegable Selective Acknowledgments (NR-SACKs)
Protocol ● Engineering ● Laboratory University of Delaware
Prof. Paul Amer, Ertugrul Yilmaz, Nasif Ekiz, Preethi Natarajan, Jonathan Leighton,
Fred Baker, Randall Stewart, Janardhan Iyengar
SCTP Network Topology
CMT Network Topology
out-of-order data is non-renegable either when the data has been delivered to the application, or when the receiver takes responsibility for delivery of the data
NR-SACKs enable data receiver to convey the renegable vs. non-renegable nature of out-of-order data. When out-of-order data is non-renegable, the data sender is no longer responsible for the data and can remove the data from its retransmission queue
NR-SACKs
Throughput Gain In SCTP
Narrower “region of gain” for larger send buffers. Higher peak throughput gain for smaller send buffers.
Throughput Gain In CMT
0% 10% 20% 30% 40% 50% 60% 70%
0%
50%
100%
150%
200%
250%
300%
0% 2% 4% 6% 8%
10% 12% 14% 16%
0% 1% 2% 3% 4% 5% 6%
Thro
ughp
ut G
ain
Loss Rate
SCTP 64K SCTP 32K SCTP 8K
SCTP SENDER 8K, 32K, 64K, 128K SCTP RECEIVER
100Mbps, 45ms
10Mbps, 45ms 100Mbps, 5ms
100Mbps, 450ms
CMT SENDER 128K, 256K CMT RECEIVER
Path 1
Path 2
loss rate: 0.08%
loss rates: 0.08%, 1.5%, 3.5%, 8.5%
100Mbps 5ms
450ms 45ms
* 100Mbps, 45ms
0% 10% 20% 30% 40% 50% 60% 70% 80%
0% 1% 2% 3% 4% 5% 6%
Thro
ughp
ut G
ain
Loss Rate
SCTP 32K 100Mbps 5ms SCTP 32K 100Mbps 45ms SCTP 32K 10Mbps 45ms SCTP 32K 100Mbps 450ms
BW has no effect on throughput gain (given BDP>SB). Shorter delay allows better throughput gain in SCTP.
Effects of BW and Delay in SCTP
0%
20%
40%
60%
80%
100%
120%
140%
0% 1% 2% 3% 4% 5% 6% 7% 8% 9%
Thro
ughp
ut G
ain
Path-2 Loss Rate
CMT 128K 5ms CMT 128K 45ms CMT 128K 450ms CMT 256K 5ms CMT 256K 45ms CMT 256K 450ms
Higher throughput gain as paths get more asymmetric. Smaller send buffer results in higher throughput gain. Shorter delay allows better throughput gain in CMT.
