tailieunhanh - CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 52

Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 52 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | Page 479 Tuesday May 20 2003 2 53 PM Understanding the TCP IP Transport Layer 479 Figure 9-2 Transport Layer Role in Communication Between Network Devices The transport layer provides the following basic services Segmenting upper-layer application data Establishing end-to-end operations Sending segments from one end host to another end host Ensuring flow control provided by sliding windows Ensuring reliability provided by sequence numbers and acknowledgments The transport layer assumes that it can use the network as a cloud to send data packets from source to destination. The cloud deals with issues of which of several paths is best for a given route. This starts to illustrate the role that routers perform in this process. TCP IP is a combination of two individual protocols TCP and IP. IP is a Layer 3 protocol a connectionless service that provides best-effort delivery across a network. TCP is a Layer 4 protocol a connection-oriented service that provides flow control as well as reliability. Pairing the protocols enables them to provide a wider range of services. The TCP IP protocol suite is made up of many protocols but TCP and IP are the key ones. TCP IP is the protocol suite on which the Internet is based. Flow Control As the TCP transport layer protocol sends data segments it can ensure the integrity of the data. One method of doing this is called flow control. Flow control avoids the problem of a transmitting host overflowing the buffers in the receiving host. Overflows can present serious problems because they can result in the loss of data. Transport layer services enable reliable data transport between hosts and destinations. To obtain such reliable transport of data a connection-oriented relationship is used Page 480 Tuesday May 20 2003 2 53 PM 480 Chapter 9 TCP IP Transport and Application Layer between the communicating end systems. Reliable transport can accomplish the following Ensure that segments delivered will be acknowledged to