1. Ensuring the Reliability of Data Delivery © 2004 Cisco Systems, Inc. All rights reserved. Establishing a TCP Connection INTRO v2.0—6-1

2. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-2 Outline Overview Establishing a Connection with a Peer System Flow Control Acknowledgement Windowing TCP Sequence Number and Acknowledgement Numbers Summary Lab Exercise 6-1: TCP Establishment Process

3. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-3 Establishing a Connection

4. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-4 Three-Way Handshake ctl = which control bits in the TCP header are set to 1

5. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-5 Flow Control

6. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-6 TCP Acknowledgment

7. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-7 Fixed Windowing

8. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-8 TCP Sliding Windowing

9. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-9 TCP Sequence and Acknowledgement Numbers

10. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-10 Summary Using TCP as the transport layer protocol, before applications can transfer data, both the sending and the receiving applications inform their respective operating systems that a connection will be initiated. Once synchronization has occurred, the two end systems have established a connection and data transfer can begin. Flow control avoids the problem of a transmitting host overflowing the buffers in the receiving host and slowing network performance. TCP provides sequencing of segments with a forward reference acknowledgment. When a single segment is sent, receipt is acknowledged and the next segment is then sent.

11. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—6-11 Summary (Cont.) The TCP window size decreases the transmission rate to a level where congestion and data loss do not occur. The TCP window size allows for a specified number of unacknowledged segments to be sent. A fixed window is a window with an unchanging size that can accommodate a specific flow of segments. A TCP sliding window is a window that can change size dynamically to accommodate the flow of segments. TCP provides the sequencing of segments by providing sequence numbers and acknowledgement numbers in the TCP headers.