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Embed code for: 02.2 Understanding Host-to-Host Communications
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02.2 Understanding Host-to-Host Communications
9/11/2016 Cisco ELearning for ICND1 v2.0 https://ondemandelearning.cisco.com/ciscosc/icnd1#/sections/2/pages/2 1/2 Understanding HosttoHost Communications Section 2: Understanding the HosttoHost Communications Model The main function of a network is to allow two endpoints to communicate with one another. Endpoints are often called hosts, so the communication between two endpoints is referred to as hosttohost communication. An end device or host is a computer that is connected to a network and that may offer information resources, services, and applications to users or other nodes on the network. A computer network, or simply a network, is a collection of computers and other hardware components that are interconnected by communication channels that allow sharing of resources and information. When two hosts communicate, one host is sending information and the other is receiving it. The sender is called the source, and the recipient is called the destination. Throughout the conversation between these devices, their roles alternate several times, because it is a twoway conversation. For example, Fred's PC sends a message to Sonya's PC, so Fred's PC is the source and Sonya's PC is the destination. However, when Sonya's PC sends a response, her PC is the source and Fred's is the destination. To ensure that both systems can communicate correctly, they have to speak the same language. This is achieved by the use of protocols. A protocol is a set of rules that determines how data is formatted and transmitted. Networking protocols describe the functions that occur during network communications. The most popular networking protocol is TCP/IP. Successful communication between hosts on a network requires the interaction of many different protocols. Early protocols and hosttohost communication models were proprietary. Each vendor controlled its own application and embedded communication software. An application that was written by one vendor would not function on a network that was developed by another vendor. Attempting to connect different networks resulted in the same communication problems that are faced by two people who speak different languages. It became obvious that common protocols that could be used across multivendor systems and software were required. 9/11/2016 Cisco ELearning for ICND1 v2.0 https://ondemandelearning.cisco.com/ciscosc/icnd1#/sections/2/pages/2 2/2 Developing a multivendor solution required that the communication process be divided into separate components, each corresponding to a particular network function. In the multivendor solutions that were eventually developed, the components were called layers. This layered approach required clearly defined rules or standards for interlayer interaction. Standardsbased layered models provide a number of benefits: Reducing complexity by breaking network communications into smaller, simpler parts Standardizing network components to allow different vendors to provide solutions for separate layers Facilitating modular engineering, allowing different types of network hardware and software to communicate with one another Ensuring interoperable technology and preventing changes in one layer from affecting the other layers Accelerating evolution, providing for effective updates and improvements to individual components without affecting other components or having to rewrite the entire protocol Simplifying teaching and learning Examples of standardsbased models include the OSI and TCP/IP models. Up Next: OSI Reference Model