An introduction to TCP and its modeling By: Amin PourRostami

Internet Protocol (IP) Unreliable Unreliable Best-Effort Best-Effort End-to-End End-to-End Data-link protocols Data-link protocols

IP Protocol stack fragmentation fragmentation time-to-live time-to-live type-of-service type-of-service Datagram Datagram length length 4-bitVersion4-bit Header length 8-bit Type of service 16-bit Total length 16-bitIdentification3-bitFlags13-bit Fragment offset 8-bit Time to live 8-bitProtocol16-bit Header checksum 32-bit Source IP address 32-bit Destination IP address Options Data

Transmission Control Protocol (TCP) Multiplexed Multiplexed Duplex Duplex Connection-oriented Connection-oriented Reliable Reliable Flow-controlled Flow-controlled Byte-stream Byte-stream

TCP Protocol Stack 16-bit Source port number 16-bit Destination port number 32-bit Sequence number Sequence number 32-bit Acknowledgement number 4-bit Header length Reserved (6 bits) U UURGRGUURGRG ACKACKACKACKPSHPSTSYNFIN16-bit Window size 16-bit TCP checksum 16-bit Urgent pointer options data

Flow Control Open-Loop Open-Loop Conflicting requirements Conflicting requirements Traffic descriptors Traffic descriptors Peak and average rates Peak and average rates Linear bounded arrival processes Linear bounded arrival processes Closed-Loop Closed-Loop … sinksource RTT µλ B 0 First generation (match sending rate to destination service rate) On-OffStop-and-Wait Static window Second generation( match sending rate to destination and network service rate) State measurement Choice of control Point of control Explicit Dynamic window End-to-End Implicit Dynamic rate Hop-by-Hop

Flow Control Closed-loop Cntd. Closed-loop Cntd. ExplicitImplicit Dynamic window Dynamic rate Dynamic window Dynamic rate End-to-EndDeCbit ATM Forum EERCTCP-TahoeTCP-RenoTCP-VegasNETBLTPacket-pair Hop-by-HopCredit-basedMishra/Kanakia

TCP Flow Control TCP-Tahoe TCP-Tahoe Detects losses using timeouts Detects losses using timeouts Decreases the flow control window to 1 Decreases the flow control window to 1 Ssthresh =, slow-start, congestion-avoidance Ssthresh =, slow-start, congestion-avoidance TCP-Reno TCP-Reno Detects losses using both timeouts and three duplicate ACKs Detects losses using both timeouts and three duplicate ACKs Timeout -> Tahoe Timeout -> Tahoe Fast retransmit ->congestion-avoidance->continues even if D- ACKs received Fast retransmit ->congestion-avoidance->continues even if D- ACKs received Exponential back-off Exponential back-off TCP-SACK TCP-SACK Selective ACKs Selective ACKs TCP-Vegas TCP-Vegas Described later Described later …

TCP-Reno modelling Fast retransmit Congestion avoidance Exponential backoff Slow start

TCP-Vegas Modelling Adaptive scheme Adaptive scheme