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DCCP: Transport Protocol with Congestion Control and Unreliability

DCCP: Transport Protocol with Congestion Control and Unreliability. Source ： Yuan-Cheng Lai IEEE Internet Computing ,2008 October Reporter : Chang, Yi Jui Student ID : M9756003. Outline. Introduction Packet format Connection Phases Connection establishment Data transfer

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DCCP: Transport Protocol with Congestion Control and Unreliability

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  1. DCCP: Transport Protocolwith Congestion Controland Unreliability Source：Yuan-Cheng Lai IEEE Internet Computing ,2008 October Reporter : Chang, Yi Jui Student ID : M9756003 國立屏東科技大學

  2. Outline • Introduction • Packet format • Connection Phases • Connection establishment • Data transfer • Connection termination • Congestion Control • CCID 2 • CCID 3 • Comparisons 國立屏東科技大學

  3. TCP Version • Tahoe • Reno • New Reno • SACK 國立屏東科技大學

  4. TCP behavior 2014/9/3 4 國立屏東科技大學

  5. Introduction-Why not use TCP? • IP phones, video conferencing, video on demand (VoD), and online games have consequently become extremely popular. • Real-time operation, delaysensitivity, and low reliability. 國立屏東科技大學

  6. Introduction-Why not use TCP? • TCP’s reliability mechanism retransmitslost packets, but retransmitting expiredpackets is redundant. • TCP reducesthe transmission rate on detecting packetloss, reducing quality of service (QoS) for theuser. • TCP executes a congestion-controlmechanism, it uses less than its fairshare of bandwidth when compared to UDP. 國立屏東科技大學

  7. Introduction • Multimedia applications have increased, UDP traffic has become widespread throughout the Internet, causing network congestion and threatening TCP traffic. • DCCP has two basic functions: • Establish,maintain, and tear down(or close) unreliable connections. • Utilize the congestion-controlmechanism for unreliable connections. 國立屏東科技大學

  8. Introduction • DCCP’s main characteristics： • Unreliable data transfer • Reliable connection establishment • Adequate packet options • Dynamic choice of congestion control • Dynamic adjustment of acknowledgment rate • Prevention of SYN flooding attack 國立屏東科技大學

  9. Packet format • The diagram shows • DCCP’s packet format. • (b) a DCCP generic header. • (c) the acknowledgment number sub-header. 國立屏東科技大學

  10. Packet format • CCval: indicates the congestioncontrol mechanism used (CCID 2 orCCID 3). • CsCov: (checksum coverage)determines what range thechecksum covers. • These two particular fields, CCval and CsCov, didn’t appear in previous protocols. 國立屏東科技大學

  11. Packet format • CCval lets theapplication dynamically adopt a suitablecongestion-control mechanismaccording to its requirement and network. • CsCov enhancesperformance on error-prone linksfor applications. • DCCP has defined 10packet types. 國立屏東科技大學

  12. Connection Phases • DCCP is a connection-oriented protocoland provides a bidirectionalconnection. • Connection establishment,data transfer, and connectiontermination. • DCCP has defined nine states that signify these phases’ processes: CLOSED, LISTEN, REQUEST,RESPOND, PARTOPEN, OPEN, CLOSEREQ,CLOSING, and TIMEWAIT. 國立屏東科技大學

  13. Connection establishment DCCP uses a three-way handshake to establish a connection. 國立屏東科技大學

  14. Connection establishment • Why not go to OPENstate？ Prevent a deadlock. • If a DCCPAck/DCCP-DataAck packet is lost,the server doesn’t enter the OPENstate and thus can’t send data. • Maximum segment lifetime(MSL) expires 4 times. 國立屏東科技大學

  15. Data transfer • The data packet exchange between the client and server is unreliable but restricted to congestion control. • During the transfer process,DCCPendpoints might use DCCP-Sync andDCCP-SyncAck packets forsynchronization. 國立屏東科技大學

  16. Data transfer DCCP can use DCCP-Sync and DCCP-SyncAck packets to synchronize the sequence numbers of both sides. 國立屏東科技大學

  17. Connection termination DCCP uses two- or three-way handshakes to terminate a connection. 國立屏東科技大學

  18. Congestion Control • CCID2: additive increase/ multiplicative decrease (AIMD) congestion-control mechanism whereby the sender adopts a congestion window to control the transmission rate. • Congestion window-based congestion control. 國立屏東科技大學

  19. Congestion Control • CCID3: TFRC(TCP-Friendly Rate Control) congestion control. The sender uses the loss event ratio the receiver measures, calculates the transmission rate T via the following formula, and accordingly adjusts its sending rate. • Rate-based congestion control. • T is transmission rate • S is packet size • RTT is round-trip time • tRTO is retransmission timeout • p is loss event ratio 國立屏東科技大學

  20. Comparisons 國立屏東科技大學

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