internet technologies and standards

(1)

Institute of Telecommunications Warsaw University of Technology 2015

internet technologies and standards

• Piotr Gajowniczek

• Andrzej Bąk

• Michał Jarociński

(2)

multimedia in the Internet

Voice-over-IP

(3)

multimedia networking: 3 application types

• streaming, stored audio, video



streaming: can begin playout before downloading entire file



stored (at server): can transmit faster than audio/video will be rendered (implies storing/buffering at client)



e.g., YouTube, Netflix, Hulu

• conversational voice/video over IP



interactive nature of human-to-human conversation limits delay tolerance



e.g., Skype

• streaming live audio, video



e.g., live sporting event (futbol)

(4)

multimedia: audio

• analog audio signal

sampled at constant rate



telephone: 8,000 samples/sec



CD music: 44,100 samples/sec

• each sample quantized, i.e., rounded



e.g., 28=256 possible quantized values



each quantized value represented by bits, e.g., 8 bits for 256 values

• various codec types

time

audio signal amplitude

analog signal quantized value of analog value quantization

error

sampling rate (N sample/sec)

(5)

• VoIP end-end-delay requirement: needed to maintain “conversational”

aspect

 higher delays noticeable, impair interactivity

 < 150 msec: good

 > 400 msec bad

 includes application-level (packetization,playout), network delays

• session initialization: how does callee advertise IP address, port number, encoding algorithms?

• value-added services: call forwarding, screening, recording

• emergency services: 911

Voice-over-IP (VoIP)

(6)

• network loss: IP datagram lost due to network congestion (router buffer overflow)

• delay loss: IP datagram arrives too late for playout at receiver

 delays: processing, queueing in network; end-system (sender, receiver) delays

 typical maximum tolerable delay: 400 ms

• loss tolerance: depending on voice encoding, loss concealment, packet loss rates between 1% and 10% can be tolerated

VoIP: packet loss, delay

(7)

constant bit rate transmission

time variable

network delay (jitter)

client

reception constant bit

rate playout at client

client playout delay

buffered data

• receiver attempts to playout each chunk exactly q msecs after chunk was generated.

 chunk has time stamp t: play out chunk at t+q

 chunk arrives after t+q: data arrives too late for playout: data “lost”

• tradeoff in choosing q:

 large q: less packet loss

 small q: better interactive experience

delay jitter

(8)

Real-Time Protocol (RTP)

• RTP specifies packet structure for packets carrying audio, video data

• RFC 3550

• RTP packet provides



payload type identification



packet sequence numbering



time stamping

• RTP runs in end systems

• RTP packets

encapsulated in UDP segments

• interoperability: if two VoIP applications run

RTP, they may be able to

work together

(9)

• payload type (7 bits): indicates type of encoding currently being used. If sender changes encoding during call, sender

• informs receiver via payload type field

 Payload type 0: PCM mu-law, 64 kbps

 Payload type 3: GSM, 13 kbps

 Payload type 7: LPC, 2.4 kbps

 Payload type 26: Motion JPEG

 Payload type 31: H.261

 Payload type 33: MPEG2 video

• sequence # (16 bits): increment by one for each RTP packet sent



detect packet loss, restore packet sequence

RTP header

payload type

sequence number

type

time stamp Synchronization Source ID

Miscellaneous fields

(10)

• timestamp field (32 bits long): sampling instant of first byte in this RTP data packet

 for audio, timestamp clock increments by one for each sampling period (e.g., each 125 usecs for 8 KHz sampling clock)

 if application generates chunks of 160 encoded samples, timestamp

increases by 160 for each RTP packet when source is active. Timestamp clock continues to increase at constant rate when source is inactive.

• SSRC field (32 bits long): identifies source of RTP stream. Each stream in RTP session has distinct SSRC

RTP header

payload type

sequence number

type

time stamp Synchronization Source ID

Miscellaneous fields

(11)

Real-Time Control Protocol (RTCP)

• works in conjunction with RTP

• each participant in RTP session periodically

sends RTCP control packets to all other participants

• each RTCP packet

contains sender and/or receiver reports



report statistics useful to application: #

packets sent, # packets lost, interarrival jitter

• feedback used to control performance



sender may modify its

transmissions based on

feedback

(12)

• what is SIP?

 IETF end-to-end call establishment and management protocol for multimedia services

 supports user location, presence, profiles

 allows call setup (with authorization)

 allows media media type, encoding negotiation

 supports session management (modification of session parameters, multiparty conferencing etc.)

 supports different forms of redirection (e.g. forking)

 supports WWW interaction/integration

• defines also

 SIP addressing (SIP URI; maps mnemonic identifier to current IP address)

 network servers architecture (registrar, proxy, redirect, location servers)

SIP: Session Initiation Protocol [RFC 3261]

(13)

• commands

 REGISTER – registration of physical address of the client; INVITE – call

setup/modification; ACK – ack. for the final response, BYE – ending session; CANCEL – breaking transaction; others: SUBSCRIBE, OPTIONS, INFO

• responses

 1xx - Provisional – request received and under processing; 2xx - Success; 3xx - Redirection; 4xx - Client Error – request cannot be processed (bad syntax, no

authorization etc.); 5xx - Server Error – serwer is unable to proces a (viable) request;

6xx - Global Failure

• transaction

 a command and all responses; non-INVITE scenario – command, sequence of

provisional responses and a final response; INVITE scenario – additional ACK command

SIP protocol

INVITE sip:[email protected] SIP/2.0 Via: argon.netlab.edu

From: sip:[email protected]; Tag=12 To: sip:[email protected]

Call-Id: [email protected] Cseq: 1 INVITE

Contact: sip:[email protected] Content-type ... Content-length ...

+SDP

200 OK SIP/2.0

Via: sipproxy.netlab.edu Via: argon.netlab.edu

From: sip:[email protected]; Tag=23 To: sip:[email protected]; Tag=12 Call-Id: [email protected] Cseq: 1 INVITE

Contact: sip:[email protected] Content-type ... Content-length ...

+ SDP

(14)

example: setting up call to known IP address

 Alice’s SIP invite message indicates her port number, IP address, encoding she prefers to receive (PCM mlaw)

 Bob’s 200 OK message indicates his port number, IP address, preferred encoding (GSM)

 SIP messages can be sent over TCP or UDP; here sent over RTP/UDP

 default SIP port number is

time time 5060

Bob's

terminal rings Alice

167.180.112.24

Bob

193.64.210.89

port 5060

port 38060

m Law audio

GSM

port 48753 INVITE [email protected]4.210.89

c=IN IP4 167.180.112.24 m=audio 38060 RTP/AVP 0

port 5060 200 OK

ACK

port 5060

(15)

INVITE sip:[email protected] SIP/2.0 Via: SIP/2.0/UDP 167.180.112.24 From: sip:[email protected]

To: sip:[email protected]

Call-ID: [email protected] Content-Type: application/sdp

Content-Length: 885

• Notes:

HTTP message syntax

sdp = session description protocol Call-ID is unique for every call

SIP INVITE

• Here we don ’ t know Bob ’ s IP address

intermediate SIP servers needed

• Alice sends, receives SIP messages using SIP default port 506

• Alice specifies in header that SIP

client sends, receives

SIP messages over

UDP

(16)

REGISTER sip:domain.com SIP/2.0 Via: SIP/2.0/UDP 193.64.210.89 From: sip:[email protected]

To: sip:[email protected] Expires: 3600

SIP registrar

 one function of SIP server: registrar

 when Bob starts SIP client, client sends SIP REGISTER message to Bob’s registrar server

register message:

(17)

• another function of SIP server: proxy

• Alice sends invite message to her proxy server

 contains address sip:[email protected]

 proxy responsible for routing SIP messages to callee, possibly through multiple proxies

• Bob sends response back through same set of SIP proxies

• proxy returns Bob’s SIP response message to Alice

 contains Bob’s IP address

• SIP proxy analogous to local DNS server plus TCP setup

SIP proxy

(18)

SIP example

1 1. Jim sends INVITE message to UMass SIP proxy.

2. UMass proxy forwards request to Poly registrar server

2 3. Poly server returns redirect response, indicating that it should try [email protected] 3

5. eurecom registrar

forwards INVITE to 197.87.54.21, which is running keith’s SIP client

5 4

4. Umass proxy forwards request to Eurecom registrar server

8 6

7

6-8. SIP response returned to Jim

9

9. Data flows between clients UMass

SIP proxy

Poly SIP registrar

Eurecom SIP registrar

197.87.54.21 128.119.40.186

(19)

multimedia in the Internet

video streaming

(20)

approaches to streaming

• HTTP download

• progressive download

• pseudostreaming

 relies on the ability of HTTP clients to seek to positions in the media file by performing byte range requests to the Web server (HTTP 1.1)

 keyframes are used as reference points, so the accuracy of seek depends on how the video was encoded

• dedicated server streaming

 requires streaming protocol for signalling (RTSP, RTMP)

• HTTP adaptive streaming (HAS)

(21)

• server:

 divides video file into multiple chunks

 each chunk stored, encoded at different rates

 manifest file: provides URLs for different chunks

• client:

 periodically measures server- to-client bandwidth

 consulting manifest, requests one chunk at a time

• chooses maximum coding rate sustainable given current bandwidth

• can choose different coding rates at different points in time (depending on available bandwidth at time)

HTTP Adaptive Streaming

• “intelligence” at client: client determines

 when to request chunk (so that buffer starvation, or overflow does not occur)

 what encoding rate to request (higher quality when more bandwidth available)

(22)

• all fragments with the same bitrate are stored in a single MP4 file

• when a client requests a specific source time segment from the IIS Web server, the server dynamically finds the appropriate Movie Fragment box within the MP4 file

• chunks are sent as a standalone files (full cacheability downstream possible)

Microsoft Smooth Streaming – MP4 container

RESTful URL:

http://video.sth.com/mediafile.ism/QualityLevels(400000)/Fragments(video=610275114)

(23)

26

DASH - Dynamic Adaptive Streaming over HTTP

(24)

DASH - Dynamic Adaptive Streaming over HTTP

Media Presentation Description

Stream segmentation