Lec49-TCP services | Computer Networks

Key Concepts

• Process-to-process communication
• Sending and receiving buffers
• Segments (data transfer units)
• Full-duplex communication
• Multiplexing and demultiplexing
• Connection-oriented service (establishment, data transfer, termination)
• Reliable service (acknowledgement-based)

Services Provided by Transmission Control Protocol (TCP)

1. Process-to-Process Communication

• Definition: TCP facilitates communication between specific application processes running on different hosts.
• Details:
  • Operates within the client-server paradigm.
  • Application layer programs send data to the transport layer (TCP suite).
  • The transport layer then delivers the data to the appropriate application layer program on the server side.
  • Each process is identified by a port number: a source port number at the sender and a destination port number at the receiver.
• Example: A web browser (client) communicating with a web server.

2. Buffering (Sending and Receiving)

• Definition: TCP utilizes buffers at both the sender and receiver sides to store data.
• Details:
  • Sending Buffer: Located at the client, it stores bytes received from the application layer before they are transmitted. Can be visualized as a circular array.
  • Receiving Buffer: Located at the server, it stores bytes received from the sender before they are delivered to the application layer.
• Function: Buffers help manage data flow and accommodate differences in processing speeds between the application and transport layers.

3. Segmentation

• Definition: Data is transmitted in units called segments.
• Details:
  • A segment consists of multiple bytes.
  • Each byte within a segment is assigned a byte number.
  • Example: A segment might contain 1000 bytes. If the first byte in the segment has a byte number of 601, the last byte will have a byte number of 1601 (601 + 1000).
• Importance: Segmentation allows TCP to break down large data streams into manageable units for transmission.

4. Full-Duplex Communication

• Definition: TCP supports full-duplex communication, meaning data can be sent in both directions simultaneously.
• Details:
  • Both the client and server can act as both senders and receivers.
  • Requires both the client and server to maintain both sending and receiving buffers.
• Benefit: Enables efficient two-way communication.

5. Multiplexing and Demultiplexing

• Definition: TCP handles multiple application processes concurrently through multiplexing and demultiplexing.
• Details:
  • Multiplexing (Sender Side): Multiple processes at the application layer send data to a single transport layer (TCP). Many-to-one relationship.
  • Demultiplexing (Receiver Side): The transport layer receives data and directs it to the appropriate application process. One-to-many relationship.
• Analogy: Similar to how a post office sorts mail to different recipients.

6. Connection-Oriented Service

• Definition: TCP is a connection-oriented protocol, requiring a connection to be established before data transfer.
• Details:
  • Three Phases:
    1. Connection Establishment: A handshake process to ensure both sender and receiver are ready.
    2. Data Transfer: Data is sent in a stream of bytes within segments.
    3. Connection Termination: The connection is closed after data transfer is complete.
• Contrast with UDP: UDP is connectionless; data is sent without prior connection establishment.
• Use Case: TCP is suitable for long messages and reliable data transfer, where data integrity is crucial.

7. Reliable Service

• Definition: TCP provides a reliable data transfer service, ensuring data reaches the destination correctly.
• Details:
  • Acknowledgement (ACK): The receiver sends an acknowledgement to the sender upon successful receipt of a segment.
  • Error Control: TCP includes mechanisms to detect and retransmit lost or corrupted segments.
• Contrast with UDP: UDP does not guarantee delivery or provide error control.
• Importance: Reliability is essential for applications where data loss is unacceptable.

Synthesis/Conclusion

TCP provides a comprehensive set of services that ensure reliable and ordered data delivery between applications. Its connection-oriented nature, combined with features like segmentation, buffering, full-duplex communication, multiplexing/demultiplexing, and reliable data transfer through acknowledgements, makes it suitable for a wide range of applications requiring data integrity and guaranteed delivery. While UDP is suitable for small messages, TCP is designed for long messages and ensures that the stream of bytes reaches the receiver successfully.