Modeling RTP Streams over ATM AAL5

Transcription

1 ENSC 835 Modeling RTP Streams over ATM AAL5 Kevin Ko Naomi Ko

2 Outline of Presentation Project Overview Background Information Theory and Methodology OPNET Implementation Conclusion References 2

3 Project Overview and Objectives End-to-end duplex system RTP streams over ATM Model system and simulate in OPNET Verification and analysis Topic chosen out of personal interest ATM Forum contribution by AT&T Labs (A. Fraser, P. Onufryk, K.K. Ramakrishnan) 3

4 Background Information: Real-Time Transport Protocol RFC1889 Standard for conveying real-time media streams Typically over UDP/IP Applications in VoIP telephony, multimedia conferencing RTP sessions with multiple context sessions or RTP streams defined by source/destination IP addresses, UDP ports, and RTP Synchronization Source (SSRC) 4

5 Background Information: Asynchronous Transfer Mode ITU-I.361 Circuit-switched network technology Fixed-size cells ATM Adaptation Layer type 5 (ITU-I.363.5) Simple and efficient adaptation layer (SEAL) Used for IP data 5

6 Theory and Methodology End-to-end system RTP/UDP/IP Generator/ Sink RTP/UDP/IP Header Compressor/ Decompressor RTP-ATM encapsulator/ decapsulator ATM Network IP Network RTP/UDP/IP Generator/ Sink RTP/UDP/IP Header Compressor/ Decompressor RTP-ATM encapsulator/ decapsulator 6

7 Theory and Methodology: RTP/UDP/IP Header Compression/Decompression RFC2508 Based on TCP/IP header compression Most header fields stay constant or change by fixed amount Requirement: Link layer handles error detection Our focus on IPv4 7

8 Theory and Methodology: RTP/UDP/IP Header Compression/Decompression (cont d) Regularly changing field values in red Version IHL TOS Total Length Identification Flags Fragment Offset IPv4 Header TTL Protocol Source IP Address Destination IP Address Header Checksum Options and Padding [ optional ] UDP Header RTP Header Source Port Length V P X CC M Payload Type Sequence Number Timestamp Synchronization Source (SSRC) Identifier Destination Port Checksum Contributing Source (CSRC) Identifiers [ optional ]... RTP Payload... 8

9 Theory and Methodology: RTP/UDP/IP Header Compression/Decompression (cont d) Field values that must be sent in red Version IHL TOS Total Length Identification Flags Fragment Offset IPv4 Header TTL Protocol Source IP Address Destination IP Address Header Checksum Options and Padding [ optional ] UDP Header RTP Header Source Port Length V P X CC M Payload Type Sequence Number Timestamp Synchronization Source (SSRC) Identifier Destination Port Checksum Contributing Source (CSRC) Identifiers [ optional ]... RTP Payload... 9

10 Theory and Methodology: RTP/UDP/IP Header Compression/Decompression (cont d) Compressed packets must carry 8 or 16-bit Context Identifier (CID) Identifies context session 4-bit link sequence Detects packet loss 10

11 Theory and Methodology: RTP/UDP/IP Header Compression/Decompression (cont d) 3 packet formats sent from compressor COMPRESSED_RTP COMPRESSED_UDP FULL_HEADER 11

12 Theory and Methodology: RTP/UDP/IP Header Compression/Decompression (cont d) COMPRESSED_RTP Compresses RTP/UDP/IP headers if 16-bit CID if non-zero in context if encapsulated M S MSB of CID (if 16-bit CID) T I Link Seq UDP Checksum "RANDOM" fields LSB of Session Context ID if MSTI = 1111 M' S' T' I' CC Delta IPv4 ID if I or I' = 1 if S or S' = 1 Delta RTP Sequence Delta RTP Timestamp if MSTI = 1111 and CC non-zero Contributing Source (CSRC) Identifiers if X set in context RTP Header Extension... RTP Payload... 12

13 Theory and Methodology: RTP/UDP/IP Header Compression/Decompression (cont d) COMPRESSED_UDP Compresses UDP/IP header only if 16-bit CID if non-zero in context if encapsulated if I or I' = MSB of CID (if 16-bit CID) I Link Seq Payload Type Delta IPv4 ID UDP Checksum "RANDOM" fields LSB of Session Context ID... UDP Payload... (which may be RTP) 13

14 Theory and Methodology: RTP/UDP/IP Header Compression/Decompression (cont d) FULL_HEADER No compression Either UDP or IP header cannot be compressed Version IHL TOS Total Length Identification Flags Fragment Offset TTL Protocol Source IP Address Destination IP Address Header Checksum Options and Padding [ optional ] Source Port Length Destination Port Checksum V P X CC M Payload Type Sequence Number Timestamp Synchronization Source (SSRC) Identifier Contributing Source (CSRC) Identifiers [ optional ]... RTP Payload... 14

15 Theory and Methodology: RTP/UDP/IP Header Compression/Decompression (cont d) Context information shared by compressor and decompressor Header Compressor Header Decompressor Packet Generator RTP/UDP/IP IP header UDP header IP header Compressed RTP IP header UDP header IP header RTP/UDP/IP Packet Sink IP ident IP ident RTP seq num RTP seq num RTP timestamp RTP timestamp last link seq sent last link seq rcv'd 15

16 Theory and Methodology: ATM Encapsulator/Decapsulator UNI must support RTP/UDP/IP formats AAL5 Service Specific CS Common Part CS SAR ATM encapsulation AAL Common Part AAL SAP Service Specific CS (SSCS) Primitives Common Part CS (CPCS) Primitives SAR SAR CS ATM SAP 16

17 Theory and Methodology: ATM Encapsulator/Decapsulator (cont d) Common Part Convergence Sublayer (CPCS) 40 bytes 8 bytes Payload (RTP/UDP/IP packet) AAL5 Trailer CPCS-UU MBZ Length CRC 1 byte 1 byte 2 bytes 4 bytes X 1 bit Seq # 7 bits Real-time AAL5 Encapsulation Packet (Voice over ATM to the Desktop) 17

18 Theory and Methodology: ATM Encapsulator/Decapsulator (cont d) ATM encapsulation VC assignment based on CID CID=1 = destn= => VC=0/32 CID=3 = destn= => VC=0/32 IP addr: RTP session 1: port 200 stream 1: CID=1 stream 2: CID=4 IP addr: RTP session 1: port 100 stream 1: CID=1 stream 2: CID=4 RTP session 2: port 101 stream 1: CID=2 stream 2: CID=3 VPI/VCI=0/32 ATM Network CID=1? => IP= CID=3? => IP= IP addr: RTP session 2: port 201 stream 1: CID=2 stream 2: CID=3 18

19 OPNET Implementation RTP/UDP/IP Generator/ Sink RTP/UDP/IP Header Compressor/ Decompressor RTP-ATM encapsulator/ decapsulator ATM Network IP Network RTP/UDP/IP Generator/ Sink RTP/UDP/IP Header Compressor/ Decompressor RTP-ATM encapsulator/ decapsulator 19

20 OPNET Implementation: RTP Generator/Sink 20

21 OPNET Implementation: RTP Generator/Sink (cont d) 21

22 OPNET Implementation: RTP/UDP/IP Header Compression/Decompression 22

23 OPNET Implementation: ATM Encapsulator/Decapsulator 23

24 OPNET Implementation: ATM Encapsulator/Decapsulator (cont d) 24

25 OPNET Implementation: Assumptions Session setup / termination RTP session: SIP (RFC 2543), H.323 ATM: PVC vs. SVC Ideal network One RTP session, multiple RTP streams IPv4 only 25

26 OPNET Implementation: Verification Methods Stage by stage accuracy Collection of packet information at symmetrical stages of transmission packet stream 0 packet stream 1 packet stream 2 time 26

27 Conclusion Compression and encapsulation of RTP/UDP/IP packet Implementation in OPNET Programming in OPNET Knowledge of RTP, ATM protocols 27

28 References [1] Casner, S., Frederick, R., Jacobson, V., and Schulzrinne, H., RTP: A Transport Protocol for Real-Time Applications, RFC1889, GMD Fokus, Precept Software, Inc., Xerox Palo Alto Research Center, Lawrence Berkeley National Laboratory, January [2] Casner, S. and Jacobson, V., Compressing IP/UDP/RTP Headers for Low-Speed Serial Links, RFC2508, Cisco Systems, February [3] Cisco Systems, Inc. Guide to Cisco Systems VoIP Infrastructure Solution for SIP Version 1.0, pp 1-8., [4] Cisco Systems, Inc. Asynchronous Transfer Mode (ATM) Switching. February 25, [5] Fraser, A., Onufryk, P., and Ramakrishnan, K., Encapsulation of Real-Time Data Including RTP Streams over ATM, ATM Forum/SAA , AT&T Labs. Research, February [6] Heinanen, J., Multiprotocol Encapsulation over ATM Adaptation Layer 5, RFC1483, Telecom Finland, July [7] International Telecommunication Union. B-ISDN ATM layer specification. ITU-T I.361, February [8] International Telecommunication Union. B-ISDN ATM Adaptation Layer specification: Type 5 AAL, ITU-T I.363.5, August [9] Jacobson, V. Compressing TCP/RTP Headers for Low-Speed Serial Links, RFC1144, LBL, February [10] Webopedia, RTP, March 14,

29 Modeling RTP Streams over ATM AAL5 Thank You for listening so attentively Questions? Kevin Ko Naomi Ko 29