changes in rtp multi-stream...2015/03/24 · slide title 70 pt capitals slide subtitle minimum 30...

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Changes in RTP Multi-stream draft-ietf-avtcore-rtp-multi-stream-07

Magnus Westerlund (Ericsson) Jonathan Lennox (Vidyo) Colin Perkins (University of Glasgow) Qin Wu (Huawei)

https://datatracker.ietf.org/doc/draft-ietf-avtcore-rtp-multi-stream/













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text in the footer area draft-ietf-avtcore-rtp-multi-stream-07 | IETF 92 AVTCORE WG | Magnus Westerlund | 2015-03-12 |

› Changes

– Scheduling algorithm change

– Limit for transmission of initial RTCP compound packets

– Recommendation for mitigating legacy avg_rtcp_size calculation

– Piggybacking Feedback Packets on other SSRCs’ transmission

– Rules for determining point to point behavior vs. multiparty

– Intend no example configurations

› Next Step

Outline

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› Variables as used in RFC3550 and RFC4585

– tp: Time of previous RTCP transmission

– tc: Current Time

– tn: Time of next scheduled RTCP transmission

– Td: Deterministic transmission interval

› When aggregating: set tp variable to intended transmission

time (tt) rather than tc

– Intended transmission time is derived by calculating tn and doing

consideration and updating tn until allowed to send.

– To ensure maintaining bandwidth allocation

Previous algorithm

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› Simulations of RTP session where the number of SSRCs

per endpoint is reduced uncovered an issue:

– The tp value can drift into the future

› Example: ~2% of the tp values are more than 1.5*Td from tc

– Reverse Reconsideration was applied

– RTCP sender may go dormant for many reporting intervals

Issue with Previous Algorithm

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Previous Algorithm

Previous Algorithm

(tp-tc)/Td

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› When the number of SSRCs on an endpoint is more than what

can be aggregated in one RTCP compound packet:

– Then an SSRC with tn further into the future is skipped in the current

packet

– But, that SSRC is likely to be sender in the next, thus updating tp to tc

– Thus drift unlikely

› When the number of SSRCs all fit in one aggregate:

– Algorithm picks the SSRC(s) that gets low random number * Td

– A SSRC not picked for a couple of cycles can get tp further than

1.5/1.21828*Td and will never be picked

› Issue arises when the SSRC or SSRCs picked are removed

– Then tp for the remaining SSRCs is far into the future

Issue depends on #SSRCs

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› Set tp to the average of all

aggregated SSRCs’ transmission

time (tt)

– SSRC triggering transmission

has tt = tc

– Other SSRCs calculate tt =

intended transmission time

› Maintains bandwidth

consumption

› Ensures that tp is worst case set

to tc + 1.5/1.21828*Td

– This prevents drift

Proposed change

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New Algorithm

New Algorithm

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Comparison: tp distributions

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Transmission interval

Average

AVPF 0.639

Previous

Algorithm 0.589

New

Algorithm 0.591

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0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 2,2 2,4 2,6 2,8 3 3,2 3,4 3,6 3,8 4

PreviousAlgorithm

NewAlgorithm

AVPF

t (s)

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› Changes

– Scheduling algorithm change

– Limit for transmission of initial RTCP compound packets

– Recommendation for mitigating legacy avg_rtcp_size calculation

– Piggybacking Feedback Packets on other SSRCs’ transmission

– Rules for determining point to point behavior vs. multiparty

– Intend no example configurations

› Next Step

Outline

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› When an endpoint joins an “unicast” session it may use a

zero delay before sending the initial compound RTCP

packet.

› We propose a limit to this behaviour to a maximum of

4 RTCP compound packets

– These RTCP compound packets can be aggregates

› Limit chosen based on the TCP Initial Window

Limit initial transmission

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› Legacy endpoint that doesn’t calculate avg_rtcp_size as in

this document:

– Will arrive on a Td value that is N times longer

– N is the number of reporting SSRCs in each compound packet

› Results in lower reporting rate

› Timeout modification should prevent timeout as long as

non-legacy has Td no larger than 1 second

› For cases where legacy endpoints are likely

– Limit aggregation to two SSRCs per compound, or

– Turn off aggregation

Legacy avg_rtcp_size

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› When an FB packet can’t trigger early transmission of the

SSRC(s) that is suitable to report

– AVPF says schedule regular RTCP, if that is prior to

T_max_fb_delay, else

– Drop FB packet

› We propose that it can be queued to be included

(piggybacked) on the first of any other SSRCs’ compound

packet which may be sent within T_max_fb_delay.

– Source of FB packet will still be suitable SSRC (Section 5.4.1)

Piggyback FB packets

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› Provide clear rule for how to judge Point-to-point vs.

Multiparty in scheduling algorithm

– Not based on number of SSRCs

› If Reporting groups are used:

– If only one external reporting group then P2P, else multiparty

› Else if number of endpoint external CNAMEs seen on

Media sending SSRCs are:

– Only one then P2P, else multiparty

› Will classify mixer cases as P2P

– Ok: Mixer will insulate the other legs or multiparty domain from

endpoint.

P2P vs. Multiparty

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› We have for a while considered configuration examples

– Was a TBD in Section 6.2.2

› In the interest of completing this work we intended to skip

this.

Skipping Examples

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› Please review!

› Intended to request WG last call soon

– Giving you some time to review and consider changes

› Related documents are ready for WG last call:

– draft-ietf-avtcore-multi-media-rtp-session-07

– draft-ietf-avtcore-rtp-multi-stream-optimisation-05

Next Step

https://datatracker.ietf.org/doc/draft-ietf-avtcore-multi-media-rtp-session/















https://datatracker.ietf.org/doc/draft-ietf-avtcore-rtp-multi-stream-optimisation/















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BACKUP SLIDES

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› 2 Endpoint, each starts with 16 SSRCs each

› RR: 15000 bps, RS: 10000 bps, T_rr_int = 0, transport delay between endpoints 100 ms (Static: no jitter)

› Simulation loop 1. Send 300 RTCP packets

2. Remove one SSRC per endpoint

3. Perform reverse reconsideration due to the local SSRC

4. Sample the values of tp

5. Goto 1 unless there is only one SSRC per Endpoint

› The shown plots contains all sample values over 50000 repetitions of the above – For the old algorithm, the furthest drift that occurred in a specific run

was 75,6*Td

Simulation Setup

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SSRCs 1 2 3 4 5 8 12 16 24 31 32 64 128 256

AVPF 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

AVPF-AGG 0.37% -9.52% -8.64% -8.56% -7.11% -4.00% -1.96% 0.43% -0.17% -0.02% 0.33% 0.03% -0.28% -0.10%

AVPF-RG 17.16% -21.48% -40.46% -52.22% -59.99% -73.04% -81.07% -85.37% -85.26% -85.31% -84.53% -84.04% -83.32% -81.44%

AVPF-RG-AGG 17.38% -30.72% -49.37% -60.18% -67.11% -78.66% -85.42% -88.76% -88.27% -87.30% -86.49% -85.54% -83.98% -81.91%

Gain Matrix

• Reduction in average reporting interval compared to AVPF

• Report groups for endpoints with many SSRCs (>16):

• Under utilize bandwidth

• Reason is IIR filtering of avg_rtcp_size

• Example: AVPF-RG with 64 SSRCs per endpoint

• Packets with Reporting is 2.85% of total number of packets

• Report packets are ~8 times bigger (big report blocks)

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