| Overview

Routers use the Internet Protocol (IP) address information in an IP packet header to determine which interface the packet should be switched to in order to move closer its destination. Because IP does not provide any services to help insure that the packet actually reaches the destination, it is described as an unreliable, connectionless protocol, using best-effort delivery. If packets are dropped in route, arrive in the wrong order, or are transmitted faster than the receiver can accept them, IP alone cannot correct the problem. To address these problems, IP relies upon Transmission Control Protocol (TCP). This module describes TCP and its functions and introduces UDP, another important Layer 4 protocol. Each layer within the OSI networking model has various functions. These functions are independent of the other layers. Each layer expects to receive services from the layer beneath it, and each layer provides certain services to the layer above it. The application, presentation, and session layers of the OSI model, which are all considered to be part of the application layer in the TCP/IP model, access the services of the transport layer through logical entities called ports. This module will introduce the concept of ports and will explain the critical importance of ports and port numbers in data networking. Students completing this module should be able to: Describe TCP and its function Describe TCP synchronization and flow control Describe UDP operation and processes Identify common port numbers Describe multiple conversations between hosts Identify ports used for services and clients Describe port numbering and well known ports Understand the differences and the relationship between MAC addresses, IP addresses, and port numbers