SIDE (IRT 3930) Põhipunktid. Loeng 12/2007 Meediavoo ülekanne Teema infotransport. Teenusetase (SLA) Hierarchical QoS. Telefoni vs datagrammi teenus

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1 SIDE (IRT 3930) Loeng 12/2007 Meediavoo ülekanne Teema infotransport Teenuse klassid ja kvaliteet Infotranspordi riskid Voogude moodustamine ja sünkroniseerimine Rakenduste nõuded Reaalaja ülekanne (RTP) Põhipunktid Avo Ots telekommunikatsiooni õppetool, TTÜ raadio- ja sidetehnika inst. Infotransport 397 Infotransport 398 Teenusetase (SLA) Infotransport 399 Infotransport 400 Hierarchical QoS Internet 10 GigE MPLS VPN Telefoni vs datagrammi teenus Ainult üks teenus: kõne Host on telefon Palju teenuseid Host tekitab mitu voogu VoIP VideoConf VideoStrea m p1 Internet Customer # 1 VLA N Cust n Cust 4 Cust 3 Cust 2 p2 Cust 1 MPLS Tunnel GigE Application Telephone Network () Link Telephone Telephone numbering, signaling, routing TDMA Application Transport Network () Link telnet, ftp, TCP, UDP IP 802.3, Infotransport 401 Infotransport 402 1

2 TCP Transport Liikluse (de)multipleksimine Application IP telnet HTTP ssh p1 p2 p1 p2 p3 p1 p2 A B C ports In TCP, a data stream is identified by a set of numbers: (Source Address, Destination Address, Source Port, Destination Port) Infotransport 403 Transpordiprotokolli funktsioonid Multiplexing/demultiplexing for multiple applications. Port abstraction Connection establishment. Logical end-to-end connection Connection state to optimize performance Error control. Hide unreliability of the network layer from applications Many types of errors: corruption, loss, duplication, reordering. End-to-end flow control. Avoid flooding the receiver Infotransport 404 Transmission Control Protocol (TCP) Reliable bidirectional inorder byte stream Socket: SOCK_STREAM Connections established & torn down Multiplexing/ demultiplexing Ports at both ends Error control Users see correct, ordered byte sequences End-end flow control Source Source Port Port Dest. Dest. Port Port Sequence Number Acknowledgment Number HL/Flags Advertised Win. Win. Checksum Urgent Urgent Pointer Pointer Options.. Infotransport 405 TCP lisaomadused ja lipud Sliding window protocol Use sequence numbers Bi-directional Each host can be a receiver and a sender simultaneously SYN: Synchronize Used when setting up connection FIN: Finish Used when tearing down connection Acknowledging received data Infotransport 406 Ühenduse loomine (TCP) Client SYN: SeqC : SeqC+1 SYN: SeqS : SeqS+1 Server Three-Way Handshake Each side notifies other of starting sequence number it will use for sending Each side acknowledges other s sequence number SYN-: Acknowledge sequence number + 1 Can combine second SYN with first Infotransport 407 SYN RCVD Send FIN TCP State Diagram: Setup Client D Server passive OPEN rcv SYN snd SYN rcv of SYN LISTEN rcv SYN snd ESTAB SEND snd SYN Rcv SYN, Snd delete TCB SYN SENT active OPEN Snd SYN Infotransport 408 2

3 Tearing Down Connection Either Side Can Initiate Tear Down Send FIN signal I m not going to send any more data Other Side Can Continue Sending Half open connection Must continue to acknowledge Acknowledging FIN Acknowledge last sequence number + 1 Infotransport 409 A FIN, SeqA, SeqA+1 FIN, SeqB, SeqB+1 B State Diagram: Tear-down send FIN FIN WAIT-1 FIN WAIT-2 rcv FIN snd Active Close send FIN rcv FIN snd rcv FIN+ snd ESTAB CLOSING TIME WAIT rcv FIN send rcv of FIN Timeout=2 MSL Passive Close WAIT snd FIN LAST- rcv of FIN D Infotransport 410 Retransmission Timeout () Initial Send Retry Ack Detect dropped packet Initial Send Ack Retry too short Time between sending & resending segment Challenge Too long: Add latency to communication when packets dropped Too short: Send too many duplicate packets General principle: Must be > 1 Round Trip Time (RTT) Infotransport 411 Round-trip Time Estimation Every /Ack pair gives new RTT estimate Sample Ack Can Get Lots of Short-Term Fluctuations Infotransport 412 TCP Round-trip Estimator Round trip times estimated as a moving average: New RTT = α (old RTT) + (1 - α) (new sample) Recommended value for α: for most TCP s Retransmit timer set to β RTT, where β = 2 Want to be somewhat conservative about retransmitting Sample RTT A RTT Sample Ambiguity Original transmission X retransmission B Sample RTT Ignore sample for segment that has been retransmitted A Original transmission retransmission B Infotransport 413 Infotransport 414 3

4 Ummistus võrgus Congestion Võrguliikluse koormus on suurem kui võrgu läbilaskevõime Kaasneb andmete kadu (ruuterites): Puhverdada saab ainult lõpliku hulga andmeid Transpordiprotokolli reaktsioon Ummistuse tagajärg Wasted bandwidth: retransmission of dropped packets Poor user service : unpredictable delay, low user goodput Increased load can even result in lower network goodput Switched nets: packet losses create lots of retransmissions Broadcast Ethernet: high demand -> many collisions Goodput congestion collapse Load Infotransport 415 Infotransport 416 Saatmiskiiruse valik Slow Start Send too slow: link sits idle wastes time Send too fast: link is kept busy but... queue builds up in router buffer (delay) overflow buffers in routers (loss) Many retransmissions, many losses Network goodput goes down Goodput safe operating point Load Congestion window 10 5 Congestion avoidance Slow start Threshold Congestion occurs Congestion avoidance Slow start 0 Infotransport 417 Round-trip times Infotransport Timeout 418 Voogude ootejärjestused Võrgujõudluse kasutus Infotransport 419 Infotransport 420 4

5 Ummistusest tekkinud viide Ummistuste haldamine Infotransport 421 Infotransport 422 ITU G.114 soovitus One Way Delay (msec)( Kõneviite piirid Description Acceptable for most user applications MPEG-2 Transport Strea m Multimeediavoo ülekanne Demux Presentation Time Sta mp (PTS) BPuhveruffer Puhver Video Monitor Encoder Acceptable provided that administrations are aware of the transmission time impact on the transmission quality of user applications Unacceptable for general network planning purposes however however It is recognized that in some exceptional cases this limit will be exceeded Program Clock Reference (PCR) Clock Recovery Coded Video Puhver Audio System Time Clock (STC) Infotransport 423 Infotransport 424 A Värin (jitter)ja sünkroniseerimine Andmevoog (stream) saatja vastuvõtja saatja 9 8 vastuvõtja Värin saabumisaja erinevus Sünkroniseerimine tegevuste ajastamine Infotransport 425 Paketid peavad jõudma kohale kindlal ajal kindlas järjestuses Kui ei jõua, siis vastu ei võeta Infotransport 426 5

6 RTP (Real Time Protocol) SP (554) DP (554) Len. CRC Payload type Timestamp Syncro Source Seq. No Maximum Bandwidth (Symmetric) 10Gbps 1Gbps 100Mbps 45Mbps 16Mbps 10Mbps 2Mbps EoPDH 45/32Mbps over T3/E3 EoPDH RFC 3518 or G /16Mbps over T1/E1 1000BASE-T (MMF) 100BASE-T (Cu Cat 5) 10BASE-T (Cu Cat5) Ethernet Access Ethernet over Copper Existing IETF and ITU-T standards 10GbE 1000BASE-LX (SMF) Existing IEEE standards Ethernet over Copper 100Base-L/BX10 (Single Mode Fiber) 1000Base B/L/PX10 Ethernet over Fiber 1000 Base- PX20 100m 500m 750m 2000m 2700m 5000m 10km 20km Minimum Reach Infotransport 427 Infotransport 428 End to End multimedia Voogude ja koormuse teke HDTV: SMPTE 260/274295/296M: 198 MB/s 1920 x 1080 (2640 x 1125), 10 Bit 4:2:2 YCbCr, 25FPS Cinema today: 2048 x 2048, 14 Bit RGB, 24 FPS: ~4 GB/s Cinema tomorrow: 4096 x 4096, 14 Bit RGB, 24 FPS: ~ 16 GB/s Infotransport 429 Infotransport 430 Video kiip Lõpulingid (12) System BUS Syntax Parser SDRAM I/F SDRAM Intra, Inter Prediction Entropy + 4x4/8x8 IDCT In/Post- Loop Filter Display I/F Display Engine Line-Pixel-Lookahead Slice Pixel SRAM Infotransport , ,00.html Infotransport 432 6