Embed Size (px)
Citation preview
2
Networked multimedia applications: timing and tolerance of data loss
Delay-sensitive and loss-tolerant Streaming stored audio and video
– Stored media– Streaming: avoids having to download the entire file before begi
nning playout. Realplayer, QuickTime and Media Player– Continuous playout
Streaming live audio and video– Not stored, not fast-forward– Use the IP multicast
3
Real-time interactive audio and video– Real-time– Interactive– Internet phone– For voice, 150 msec, 150-400 msec, 400 msec
Hurdles for multimedia– End-to-end delay for a packet– Variation of packet delay, packet jitter– Packet loss
Supporting multimedia better in Internet– Reservation approach– Laissez-faire approach: ISP, CDN, multicast overlay networks– Differentiation approach
4
Audio and video compression– 1024 pixels * 1024 pixels with each pixel encoded into 24 bits => 3 Mbyt
e– 7 Min over a 64 kbps link– If the image is compressed at 10:1,
Audio compression– 8000 samples per second -> quantization with 256 values (8bits)-> 64,0
00 bits/second– Pulse code modulation– GSM, G.729, MPEG 1 layer 3(MP3),…
Video compression– MPEG 1, 2, 4, H.261
5
Real-time streaming protocol (RTSP)– User interactivity– RealPlayer and Media Player– Decompression, jitter removal, and correction– Fig 6.2
Streaming stored audio and video
6
Fig 6.3
7
RTSP– Control the playback of continuous media– No related with compression schemes, encapsulation in packets,
transportation, buffering– Out-of-band protocol– Over either TCP or UDP– Pause/resume, playback, fast-forward, and rewind
8
Fig 6.5
9
Every 20 msec over UDP Packet loss, end-to-end delay, and packet jitter Removing jitter at the receiver for audio
– With a sequence number, a timestamp or – delaying playout at the receiver
Internet phone
10
Fig 6.6
11
RTP– For sound and video– On UDP– RTP header: the type of audio encoding, a sequence number, a
nd a timestamp– Sequence number: detect packet loss – Timestamp: synchronous playout at the receiver– Synchronization source identifier (SSRC): identify the source of t
he RTP stream– Fig 6.9
Protocols for real-time interactive applications
12
Table 6.1 and 6.2
13
Developing software applications with RTP
Fig 6.10 and 6.11
14
RTP control protocol (RTCP)– In conjunction with RTP– Report statistics including number of packets sent, number of pa
ckets lost, and interarrival jitter.– RTP traffic vs RTSP traffic grows linearly with the number of rec
eivers (5 % of the session bandwidth).– Fig 6.12
15
SIP– Establish calls between a caller and a callee over an IP network– Caller determines the current IP address of the callee– Call management– Fig 6.13
16
SIP– SIP proxy and registrar (cf. DNS)– Fig 6.14
17
H.323– Fig 6.15
18
FIFO– Fig 6.21
Priority queuing using ToS– Fig 6.23
Scheduling and policing mechanisms
19
Round robin and weighted fair queuing (WFQ)– WFQ differs from round robin in that each class may receive a di
fferential amount of service in any interval of time.– Fig 6.26
Priority queuing using ToS– Fig 6.23
20
Policing: the leaky bucket– Policing criteria: average rate, peak rate, and burst rate– Polices a traffic flow– At most b tokens in the bucket = max burst size for leaky-bucket-
policed flow– Long-term average rate = Max number of packets entering the n
etwork in time t = rt + b– Fig 6.27
21
Individual applications sessions– Reserved resources– Call setup
Steps– Traffic characterization and specification of the desired QoS– Signaling for call setup– Per-element call admission– Fig 6.29
Integrated services
22
– Fig 6.30
23
Resources– Link bandwidth– Router buffers
Characteristics– Reservations for bandwidth in multicast trees– Receiver-oriented– Not specify how the network provides the reserved bandwidth to
the data flow -> provisioning done with the scheduling mechanisms
– Not a routing protocol– Signaling protocol
RSVP
24
Example– Video and audio be encoded in layers– The receiver pick out the layers that are appropriate for their rec
eiving rates.– Multicast routing protocol -> multicast tree -> rsvp– Fig 6.32
25
Difficulties of the Interserv– Scalability: per-flow using RSVP– Flexible service models: limited service classes
Architecture– Edge function: packet classification with marking and traffic cond
itioning, behavior aggregate– Core function: forwarding, per-hop behavior– Fig 6.34
Differentiated service
26
Fig 6.35
Fig 6.36
27
– Traffic profile– Metering function: compare the incoming packet flow with the
negotiated traffic profile and determine whether a packet is within the negotiated traffic profile.
– Fig 6.37
28
per-Hop behaviors– Expedited forwarding:– Assured forwarding
Criticisms of differentiated services– Multiple ISPs– How to police and authenticate
