Schedule of Class Meeng

(1)

Mul$media Networking

#5 Real-‐Time Transport Protocol

Semester Ganjil 2012

(2)

(3)

Today’s Outline

• _RTP

–

_{protocol goals}

–

_{mixers and translators}

(4)

Real-‐Time Protocol (RTP)

• _{End-‐to-‐end protocol}

for applica$ons

(5)

RTP: Big Picture

Media Encapsula$on

RTP RTCP Applica$on

UDP

IPv4/6

Ethernet AAL5 ATM

ST-‐II

data

(6)

RTP: Big Picture

• _{Real-‐Time Transport Protocol (RTP) = data +}

control

• _data:

–

_$ming,

–

_{loss detec$on,}

–

_{content labeling,}

–

_{talk spurts,}

–

_encryp$on

• _control:

_(RTCP)

_

_{periodic with}

_T

∼

_popula$on

–

_{QOS feedback}

(7)

RTP: Goals

• _lightweight:

_{speciﬁca$on and implementa$on}

• _ﬂexible:

_{provide mechanism, don’t dictate}

algorithms

• _{protocol-‐neutral:}

_{UDP/IP,ST-‐II,IPX,ATM-‐AALx,...}

• _scalable:

_{unicast, mul$cast from 2 to O(107)}

• _{separate control/data:}

_{some func$ons may be}

taken over by conference control protocol

• _secure:

_{support for encryp$on, possibly}

(8)

RTP runs on top of UDP

Multmedia Networking

• _{Applica$on layer protocol}

• _{RTP libraries provide transport-‐layer interface}

that extends UDP:

• port numbers, IP addresses

• payload type iden$ﬁca$on

• packet sequence numbering

• $me-‐stamping

• Applica$ons that use RTP are:

• Less sensi$ve to packet loss

• Very sensi$ve to packet delays

• UDP provides key services:

• Mul$plexing

(9)

RTP Func$ons

• _{segmenta$on/reassembly done by UDP (or similar)}

• _{re-‐sequencing (if needed)}

• _{loss detec$on for quality es$ma$on, recovery}

• _{intra-‐media synchroniza$on: remove delay jiker}

through playout buﬀer

• _{intra-‐media synchroniza$on: driling sampling clocks}

• _{inter-‐media synchroniza$on (lip sync between audio}

and video)

• _{quality-‐of-‐service feedback and rate adapta$on}

(10)

opt.

timestamp

sequence number

synchronization source identifier (SSRC) M

contributing source identifiers (CSRC)

(11)

RTP header

number type time stamp

Synchronization Source ID

(12)

• _{mestamp ﬁeld (32 bits long):}*

_{sampling instant of}

(13)

• _P:

_{padding (for encryp$on)}

➠

_{last byte has}

padding count

• _M:

_{marker bit; frame, start of talk spurt}

➠

delay adjustment

• _CC:

_{content source count (for mixers)}

• _CSRC:

_{iden$ﬁers of those contribu$ng to}

(mixed into) packet

RTP header

payload type

sequence

(14)

RTP example

contains sequence

(15)

Today’s Outline

• _RTP

–

_{protocol goals}

–

_{mixers and translators}

(16)

RTP: Mixers and Translators

• _mixer:

– _{several media stream}➠_{one new stream (new encoding)} – _{reduced bandwidth networks (dial-‐up)}

– _{appears as new source, with own iden$ﬁer}

• _translator:

– _{single media stream}

– _may_{convert encoding}

– _{protocol transla$on (na$ve ATM ↔ IP), ﬁrewall} – _{all packets: source address = translator address}

(17)

RTP: Mixers and Translators

SSRC=39 SSRC=17

192.35.149.52

128.119.40.186

192.26.8.84 192.20.225.101

SSRC=5

DVI4

L16

GSM

GSM SSRC=5

translator end system

end system

mixer

(18)

Today’s Outline

• _RTP

–

_{protocol goals}

–

_{mixers and translators}

–

_{control: awareness, QOS feedback}

(19)

Control: awareness, QOS feedback

• _{Packet loss, conges$on, jiker, delivery $mes}

– _{Directly useful for control of adap$ve encodings} – _{Iden$fy if problems are local or global}

– _{Short-‐term and long-‐term sta$s$cal analysis}

• _{Self-‐adjus$ng network}

– _{Each par$cipant eventually knows about the other}

members

– _{Source descrip$on dynamically iden$ﬁes who is sending} – _{Ac$ve senders get more bandwidth}

– _{Session bandwidth kept constant by adjus$ng}

(20)

Real-‐Time Control Protocol (RTCP)

• _{works in conjunc$on}

with RTP

• _{each par$cipant in RTP}

session periodically

sends RTCP control

packets to all other

par$cipants

• _{each RTCP packet}

contains sender and/or

receiver reports

– _{report sta$s$cs useful to}

applica$on: # packets sent, # packets lost, interarrival jiker

• _{feedback used to control}

performance

– _{sender may modify its}

(21)

RTCP: packet types

• _{stackable packets, similar to data packets}

• _{sender report (SR):}

– _{bytes send}➠_{es$mate rate;} – _$mestamp➠_{synchroniza$on}

• _{recep0on reports (RR):}

– _{number of packets sent and expected}➠_{loss, avg. inter-‐}

arrival jiker, round-‐trip delay

• _{source descrip0on(SDES):}

– _{name, email, loca$on,...}

– _{CNAME (canonical name = user@host) iden$ﬁes user}

across media

• _{explicit leave (BYE):}

_{in addi$on to $me-‐out}

(22)

RTCP: packet structure

if encrypted: random 32-bit integer

(23)

RTCP: mul$ple mul$cast senders

 each RTP session: typically a single mul$cast address;

 every par$cipant: periodically mul$cast RTCP packet to same

group as data

 RTP, RTCP packets dis$nguished from each other via dis$nct port

numbers

 to limit traﬃc, each par$cipant reduces RTCP traﬃc as number of

conference par$cipants increases

RTCP RTP

RTCP RTCP

sender

(24)

RTCP: announcement interval

• _Goals:

–

_{es$mate current number of par$cipants & iden$$es}

of par$cipants – dynamic

–

_{source descrip$on (“SDES”)}

➠

_{who’s talking?}

–

_{quality-‐of-‐service feedback}

➠

_{adjust sender rate}

–

_{to O(1000) par$cipants, few % of data}

• ➠_{randomized response with rate ↓ as members ↑}

–

_{group size limited by tolerable age of status}

–

_{gives ac$ve senders more bandwidth}

(25)

RTCP: bandwidth scaling

RTCP aAempts to limit

its traﬃc to 5% of

session bandwidth

packet transmission period by calcula$ng avg RTCP

(26)

RTCP: bandwidth scaling

• sender period T:

T = # of senders

0_.25 _· 0_.05 _· _{session bw} · avg. RTCP packet size

• receivers:

T = # of receivers

0_.75 _· 0_.05 _· _{session bw} · avg. RTCP packet size

• next packet = last packet + max(5 s, T) · random(0.5. . . 1.5)

• randomization prevents “bunching”

(27)

RTCP sender reports (SR)

• _{SSRC of sender:}

_{iden$ﬁes source of data}

• _{NTP mestamp:}*

_{when report was sent}

• _{RTP mestamp:}*

_{corresponding “RTP $me”}

➠

lip sync

• _{sender’s packet count:}

_{total number sent}

• _{sender’s octet count:}

_{total number sent}

• _{followed by zero or more receiver report}

(28)

RTCP receiver reports (RR)

• _{SSRC of source:}

_{iden$ﬁes who’s being reported on}

• _{fracon lost:}*

_{binary frac$on}

• _{cumulave number of packets lost:}*

_{long-‐term loss}

• _{highest sequence number received}

_:

_{compare losses,}

disconnect

• _{inter-‐arrival jiAer:}

_{smoothed inter-‐packet distor$on}

• _LSR:

_{$me last SR heard}

(29)

RTCP: round trip delay es$ma$on

lsr =0xb705:2000 (46853.125 s) dlsr=0x0005.4000 ( 5.250 s)

(5.25 s)

DLSR

A 0xb710:8000 (46864.500 s)

DLSR −0x0005:4000 ( 5.250 s)

LSR −0xb705:2000 (46853.125 s)

delay 0x 6:2000 ( 6.125 s) ntp_sec =0xb44db705

ntp_frac=0x20000000 (3024992016.125 s)

(30)

(31)

= sync diﬀerent streams (audio, video,

RTCP: stream synchroniza$on

(32)

Today’s Outline

• _RTP

–

_{protocol goals}

–

_{mixers and translators}

–

_{control: awareness, QOS feedback}

(33)

Media Adapta$on

• _{Mul$media applica$ons can adjust their data rates:}

• _{Audio: (MPEG L3), encoding, sampling rate, mono/}

stereo

encoding

sampling rate

bit rate

LPC

8,000

5,600

GSM

8,000

13,200

DVI4

8,000

32,000

µ-law

8,000

64,000

DVI4

16,000

64,000

a range of DVI4 and MPEG L3

(34)

(35)

Applica$on Control

• _{networks without QoS or shared reserved link:}

– adapt applica$on to available bandwidth

– share bandwidth fairly with TCP?

– lowest common denominator

(36)

RTP/RTCP Does NOT

• _{Deﬁne media data formats or encodings}

–

_{Need media speciﬁc proﬁles}

• _{Handle connec$on setups}

–

_{Need other protocols like SIP or H.323}

• _{Handle resource reserva$on}

–

_{Need other protocols like RSVP}

• _{Guarantee $mely data delivery or Quality of}

Service

–

_{However, it does provide necessary data to}

(37)

References

• _{RFC 3550 -‐ hkp://tools.ie{.org/html/rfc1889} • _{RFC 3551 -‐ hkp://tools.ie{.org/html/rfc3551}

• _Wikipedia:

– _{RTP -‐ hkp://en.wikipedia.org/wiki/Real-‐$me_Transport_Protocol} – _{RTCP -‐ hkp://en.wikipedia.org/wiki/RTCP}

Schedule of Class Meeng

Mul$media Networking

#5 Real-­‐Time Transport Protocol

Semester Ganjil 2012

Today’s Outline

•

RTP

–

protocol goals

–

mixers and translators

Real-­‐Time Protocol (RTP)

•

End-­‐to-­‐end protocol

for applica$ons

RTP: Big Picture

RTP: Big Picture

•

Real-­‐Time Transport Protocol (RTP) = data +

control

•

data:

–

$ming,

–

loss detec$on,

–

content labeling,

–

talk spurts,

–

encryp$on

•

control:

(RTCP)



periodic with

T

∼

popula$on

–

QOS feedback

RTP: Goals

•

lightweight:

speciﬁca$on and implementa$on

•

ﬂexible:

provide mechanism, don’t dictate

algorithms

•

protocol-­‐neutral:

UDP/IP,ST-­‐II,IPX,ATM-­‐AALx,...

•

scalable:

unicast, mul$cast from 2 to O(107)

•

separate control/data:

some func$ons may be

taken over by conference control protocol

•

secure:

support for encryp$on, possibly

RTP runs on top of UDP

•

Applica$on layer protocol

•

RTP libraries provide transport-­‐layer interface

that extends UDP:

•

port numbers, IP addresses

•

payload type iden$ﬁca$on

•

packet sequence numbering

•

$me-­‐stamping

•

Applica$ons that use RTP are:

•

#5 Real-‐Time Transport Protocol

_RTP

_{protocol goals}

_{mixers and translators}

Real-‐Time Protocol (RTP)

_{End-‐to-‐end protocol}

_{Real-‐Time Transport Protocol (RTP) = data +}

_data:

_$ming,

_{loss detec$on,}

_{content labeling,}

_{talk spurts,}

_encryp$on

_control:

_(RTCP)

_

_{periodic with}

_T

_popula$on

_{QOS feedback}

_lightweight:

_{speciﬁca$on and implementa$on}

_ﬂexible:

_{provide mechanism, don’t dictate}

_{protocol-‐neutral:}

_{UDP/IP,ST-‐II,IPX,ATM-‐AALx,...}

_scalable:

_{unicast, mul$cast from 2 to O(107)}

_{separate control/data:}

_{some func$ons may be}

_secure:

_{support for encryp$on, possibly}

_{Applica$on layer protocol}

_{RTP libraries provide transport-‐layer interface}

$me-‐stamping

_{segmenta$on/reassembly done by UDP (or similar)}

_{re-‐sequencing (if needed)}

_{loss detec$on for quality es$ma$on, recovery}

_{intra-‐media synchroniza$on: remove delay jiker}

_{intra-‐media synchroniza$on: driling sampling clocks}

_{inter-‐media synchroniza$on (lip sync between audio}

_{quality-‐of-‐service feedback and rate adapta$on}

_{mestamp ﬁeld (32 bits long):}*

_{sampling instant of}