TCP Flow Control and Data Transfer

TCP Flow Control

TCP Data Transfer

• Selective Repeat ARQ with Positive ACK
• Window slides a byte basis instead packet basis
• Dynamically advertising the window size

TCP Window Flow Control

TCP Connection Management

• Select initial sequence numbers (ISN) to protect against segments from prior connections (delayed duplicates)
• Use local clock to select ISN sequence number
• Time for clock to go through a full cycle should be greater than the maximum lifetime of a segment (MSL); Typically MSL=120 seconds
• High bandwidth connections pose a problem

Sequence Number Wraparound

• 2^32 = 4.29x10^9 bytes = 34.3x10^9 bits
  • High bandwidth poses a problem; At 1 Gbps, sequence number wraparound in 34.3 seconds (< MSL that is 120 seconds).
• Timestamp option: Insert 32 bit timestamp in header of each segment
  • Timestamp + sequence no → 64-bit seq. no
  • Timestamp can be in TCP option clock must: