CCNA Introducing Networks

CCNA Guide to Cisco Networking Fundamentals Chapter 1 Introducing Networks

Objectives Identify and describe the functions of each of the seven layers of the OSI reference model Identify the reasons why the networking industry uses a layered model Define and explain the conversion steps of data encapsulation Define and describe the function of a MAC address Describe connection-oriented network service and connectionless network service, and identify the key differences between them CCNA Guide to Cisco Networking Fundamentals

Introduction to Networking Computer network, or simply network Refers to the connection of two or more computers by some type of medium You can connect computer using the following: Public telephone system Wire cable Fiber-optic cable Infrared equipment Radio equipment CCNA Guide to Cisco Networking Fundamentals

Origin of Networking Industry experts find it difficult to date the precise origin of networking Because many devices have been networked throughout history Mainframe computers were sometimes connected to each other by cables Today, systems that are part of a network do not have to be identical A modern network can include a wide variety of computers, peripheral components, and even other networks CCNA Guide to Cisco Networking Fundamentals

Why Do We Use Networks? This question can be answered in one word: convenience People expect interoperability from electronic devices Computer networks allow: For the transfer of files, data, and even shared applications without copying anything to floppy disk Computers to share items such as printers, scanners, fax machines, processors, disk drives, and other resources Networked computers can share data and peripherals CCNA Guide to Cisco Networking Fundamentals

Networking Terminology Media Refers to the wire cabling that form the connections in most networks Some networks use wireless transmission media, such as infrared or radio signals Client/server networks Servers host the resources for the clients to use and provide security A client is the computer that requests resources from the server CCNA Guide to Cisco Networking Fundamentals

Networking Terminology (continued) Client/server networks (continued) Types of servers include: Print server File server Database server Remote access server (RAS) Web server Peer-to-peer network When every computer on a network acts as both a client and a server Also known as “workgroups” CCNA Guide to Cisco Networking Fundamentals

Networking Terminology (continued) LAN, WAN, MAN, SAN Local area network (LAN) is contained within a company or department and located in a single geographic area Wide area network (WAN) spans multiple geographic areas and is usually connected by common telecommunication carriers Metropolitan area network (MAN) refers to the intermediate stage between a LAN and a WAN CCNA Guide to Cisco Networking Fundamentals

Networking Terminology (continued) LAN, WAN, MAN, SAN (continued) Storage area network (SAN) refers to a series of storage devices that are networked together to provide very fast data storage for a network or subnetwork Network Operating System (NOS) Allows communication, security, and distribution of data, files, and applications over a network Network Interface Card (NIC) A device that allows a computer or other device to connect to a network through the media CCNA Guide to Cisco Networking Fundamentals

Networking Terminology (continued) Networking hardware Describes all the physical components of a network, such as the NIC, cable, hub, switch, router, and any related connectors or devices Networking software The programs used to run a network Virtual private networks Network that uses a public communications infrastructure (like the Internet) to facilitate private communication between a company LAN and remote employees CCNA Guide to Cisco Networking Fundamentals

Networking Terminology (continued) Virtual private networks (continued) Extranet is the part of the company’s network that allows access to nonemployees Intranet is the part of the company’s network that allows access to employees CCNA Guide to Cisco Networking Fundamentals

Understanding the OSI Model Open Systems Interconnection (OSI) model Presented in 1984 by the International Organization for Standardization (ISO) Based on examination of existing protocols, ISO recommended a seven-layer network model Allows vendors to implement networks that permit communication among the wide variety of network implementations The OSI model is not an absolute standard for computer networks Used as a reference model CCNA Guide to Cisco Networking Fundamentals

Reasons for Layering Advantages Simplifies the networking model Enables programmers to specialize in a particular level or layer Provides design modularity Encourages interoperability Allows networking vendors to produce standardized interfaces CCNA Guide to Cisco Networking Fundamentals

CCNA Guide to Cisco Networking Fundamentals

Reasons for Layering (continued) Protocol Defined method for communicating between systems Computers must use a common protocol to communicate properly Examples: TCP/IP and IPX/SPX CCNA Guide to Cisco Networking Fundamentals

Peer OSI Communication Peer communication Each layer will only talk to its peer on the opposite side of the communications process Each layer is unaware of the activities of all other layers of the model Allows error checking to occur on two separate layers simultaneously Each layer does provide services to the layer above it and receives services from the layer below it Layers do not acknowledge these services in any way CCNA Guide to Cisco Networking Fundamentals

Layer Functions The OSI model was developed as an industry standard For companies to use when developing network hardware and software to ensure complete compatibility Each layer in the OSI model performs a specific function in the transmission process Most modern networks do not implement the OSI model exactly as it is defined CCNA Guide to Cisco Networking Fundamentals

Layer Functions (continued) Physical (Layer 1) responsibilities Defines the physical characteristics of the network hardware, including cable and connectors Represents binary digits as voltages (encoding) Transmits signals on the wire CCNA Guide to Cisco Networking Fundamentals

Layer Functions (continued) Data Link (Layer 2) responsibilities NIC software functions, including the identification of the source and destination nodes via their physical addresses (Media Access Control addresses) Definition of how data is packaged for transport in smaller units known as frames Error notification The Data Link sublayers: Logical Link Control (LLC) layer Media Access Control (MAC) layer CCNA Guide to Cisco Networking Fundamentals

Layer Functions (continued) CCNA Guide to Cisco Networking Fundamentals

Layer Functions (continued) Network (Layer 3) functions Software/logical addressing for data packets , such as IP, IPX, and AppleTalk Data routing and connectivity Best path selection Protocols at the Network layer allow computers to route packets to remote networks using a logical address CCNA Guide to Cisco Networking Fundamentals

Layer Functions (continued) Transport (Layer 4) responsibilities End-to-end, error-free transmission and delivery between the ultimate sender and ultimate receiver Flow control Data segmentation into maximum transmission unit (MTU) size Messaging service for the Session layer Protocols that reside at the Transport layer can be connection-oriented or connectionless Data sent by a connectionless transport is called a datagram CCNA Guide to Cisco Networking Fundamentals

Layer Functions (continued) Session (Layer 5) services Control for data exchange (full or half duplex) Clocking or timing Failure recovery Initial link setup and link termination when communications complete The Session layer allows the transfer of a large set of data across the network Examples of Session layer protocols include NetBIOS, SQL, RPC, and X-Windows CCNA Guide to Cisco Networking Fundamentals

Layer Functions (continued) Presentation (Layer 6) responsibilities Data translation Data formatting Data syntax restructuring Data encryption Data compression This layer also provides encryption services when data encryption is used in network communications CCNA Guide to Cisco Networking Fundamentals

Layer Functions (continued) Application (Layer 7) responsibilities Initiating the request for network services Providing network services to applications such as e-mail and Web browsers This layer is concerned with user interaction with the computer and the network Contains many protocols and utilities, such as telnet, FTP, HTTP, DNS, SMTP, and SNMP CCNA Guide to Cisco Networking Fundamentals

Layer Functions (continued) Data encapsulation Data is sent from one computer to another in a data packet Each layer in the protocol stack may add a protocol data unit (PDU) to the data as it is passed down the layers The addition of a header and/or trailer is called encapsulation CCNA Guide to Cisco Networking Fundamentals

Summary Two or more computers connected by media form a network Before computers were networked, file transfers were usually conducted by users physically walking copies of data to another computer The ISO developed the OSI model in the mid-1980s to standardize networking models Data transmission can be connection-oriented or connectionless The OSI networking model has seven layers CCNA Guide to Cisco Networking Fundamentals

Summary (continued) The Physical layer handles the physical transmission of data across the network The Data Link layer, the second layer of the OSI model, interacts with the networking hardware The Network layer supports logical addressing and routing of data packets The Transport layer segments data that is to be sent out on the network into MTUs The Session layer, the fifth layer, establishes and maintains connections between computers during data transfers CCNA Guide to Cisco Networking Fundamentals

Summary (continued) The Presentation layer, the sixth layer, handles data translation, encryption, and formatting for transmission on the network or for interpretation by the Application layer The Application layer, the seventh and highest layer, handles the interface between the network and the user When the network user sends data to the network, it goes through a five-step data encapsulation process CCNA Guide to Cisco Networking Fundamentals

CCNA Introducing Networks

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CCNA Introducing Networks