The Transport Layer

• The purpose of the transport layer is to mask from the application any failures of the network. The transport layer provides reliable end-to-end delivery of messages.
• The service -- the transport layer as seen by the user processes
  • Connection Establishment
  • Data Transfer
  • Connection Release
• OSI and TCP approaches
• The protocol -- the transport layer inside - how it operates to provide the services
  • Connection Establishment
    • Problem: Unreliable networks may hinder connection establishment
    • ISO Connection Establishment Protocol
    • TCP Connection Establishment Protocol
  • Data Transfer
    • Error Detection
    • Error Correction
      • Stop and Wait
      • Go Back n
    • Data Unit Ordering
    • Flow Control
      • Slow Start and Congestion Avoidance
      • Recipient's window size is its means of flow control
      • Sender uses missing acks to notice congestion and uses slow start and congestion to respond.
    • TCP and TP4
  • Connection Release

OSI Transport Services

• Calling transport SAP
• Called transport SAP
• Responding Address
• Expedited Data
• Quality of Service
• User Data

TCP Connection Establishment Services:

• ACTIVE_OPEN
• ACTIVE_OPEN_WITH_DATA
• FULL_PASSIVE_OPEN
• UNSPECIFIED_PASSIVE_OPEN
• OPEN_ID
• OPEN_SUCCESS
• OPEN_FAILURE
• OPEN_RECEIVED