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Local Area Networks

Honolulu Community College

Cisco Academy Training Center

Semester 1

Version 2.1.1

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Overview Focus of this chapter is LAN devices. LANs:

high-speed, low-error data networks cover a relatively small geographic area.

Evolution of networking devices. How packets flow through each device and how

it relates to the layers of the OSI model. Basic steps in building LANs. LANs provide devices (usually PCs) with access

to high-bandwidth media.

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Physical Topology Topology defines the structure of the network. Physical topology is the actual layout of the wire

(media).

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Logical Topology Logical topology is how the hosts communicate

across the medium. Two most common logical topologies are

Broadcast and Token-passing. Broadcast topology - each host sends its data to

all other hosts on the network medium. Ethernet is a broadcast topology.

Token-passing controls network access by passing an electronic token sequentially to each host. Only host with token can send data on the network.

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Can you identify the topologies?

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LAN Devices - Hosts Hosts - devices that connect

directly to a network segment. Host devices are not part of

any layer. physical connection to the

network media with NIC. other OSI layer functions are

performed in software inside the host. they operate at all 7 layers of the OSI model, such

as encapsulation/decapsulation, run applications, code, segment.

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NIC - network interface card Layer 2 (Data link) device of the OSI model. Also called a network adapter. Controls access to the media.

In general, you need a NIC that has a specific connector to match the network media.

Transceivers can be used to connect between two different connection types.

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Media Layer 1 (Physical) components of LANs. Carry the flow of information through a LAN. This is the wiring or cabling.

Coax, UTP, STP, Fiber. principal medium in networking is Category 5

unshielded twisted-pair cable (CAT 5 UTP).

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Symbols for Media

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Repeaters Layer 1 (physical) device. Purpose is to regenerate and retime network

signals at the bit level to allow them to travel a longer distance on the media.

Repeaters are single-port "in" and single-port "out" devices.

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Hubs Are multi-port repeaters,

layer 1 (physical) device. Used to create a central connection point for the

wiring media (also called concentrator). Increases the reliability of the network.

Single wiring fault will not disrupt entire network. Active vs Passive hubs.

Active - regenerates, retime the signal. Passive - does not regenerate the signal.

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Bridges Layer 2 (data link) device

designed to connect two LAN segments. Purpose is to filter traffic based on MAC address.

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Switches Switch functions like

a multi-port bridge. Layer 2 (data link) device that filters based on

MAC addresses. “Switch" data only out the port to which the proper

host is connected. Switches keeps a switching table with MAC

addresses and ports, to perform switching. Concentrates connectivity (creates a virtual

connection between source and destination), making data transmission more efficient.

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Routers Layer 3 (network) device

makes decision based on network addresses (logical addresses).

Purpose: (1) choose the best path for packets; and (2) switch them out to the proper port.

Can connect different network technologies, such as Ethernet, Token-ring, and FDDI.

The most important traffic-regulating devices on large networks, backbone of the Internet.

Function of routers: 1) path determination and 2) packet switching.

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Cloud

Used to represent a collection of devices or networks, the details of which are unknown or not relevant.

Classified as a Layer 1-7 device.

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Network Segment A part of a network bounded by bridge, switch or

router.

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Evolution of Networking Devices Apple computer in 1978, & IBM PC in 1981. Early 1980’s - standalone computer use; why not

connect them? Repeaters -(device used by telephone networks)

was introduced to enable computer data signals to travel farther.

Hubs - multi-port repeaters, enables sharing files, servers and peripherals (workgroup network).

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Evolution of Networking Devices (cont.) As workgroup networks grew, there were larger

traffic jams. The bridge was invented to segment the network, to introduce some traffic control.

The best features of the hub (concentration or connectivity) and the bridge (segmentation) were combined to produce a switch.

In the mid-1980s, gateways (and then routers) were developed. These devices allowed the interconnection of separate LANs.

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Internetworks began in the 1980’s with the development of the router (gateway).

Cisco founded in 1984. 1990’s development of WWW (world wide web).

Exponential Growth of the Internet

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Networking Devices & OSI Layers Transceivers, repeaters, and hubs - Layer 1

devices, because they act only on bits. NICs - Layer 2 devices; location of the MAC

address; but since they handle signaling and encoding they are also Layer 1 devices.

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Networking Devices & OSI Layers (cont.) Bridges & switches - layer 2 devices; use layer 2

(MAC) address to determine whether or not to forward packets.

Routers - Layer 3 devices; use Layer 3 (network) addresses to choose best paths and to switch packets to the proper route.

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Networking Devices & OSI Layers (cont.) Clouds, which may include routers, switches,

servers, etc, involve Layers 1-7.

Routers

Bridges, Switches

Repeaters, Hubs

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Data Encapsulation Example

Session layer

Transport layer

Network layer

Data link layer

Physical layerCloud

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Packet Flow - Layer 1 Devices Layer 1 devices - work with bits (e.g. voltage

or light pulses), do not read headers. Passive vs Active devices.

Passive - no amplification (regeneration). plugs, connectors, jacks, patch panels, physical

media.

Active - regenerates signal (requires power). repeaters , hubs, transceivers.

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Packet Flow - Layer 2 Devices Layer 2 devices - NICs, bridges, & switches use

Data-Link (MAC) address information, i.e. they read the frame header.

Bridges checks MAC address of incoming frames. If MAC address is local (on the same segment as

the incoming port), frame is not forwarded. If MAC address is non-local (not on the same

segment as incoming port), frame is forwarded. Switches are like multi-port bridges.

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Packet Flow - Layer 3 Devices Layer 3 device - routers switch packets based

on layer 3 network addresses. Routers perform best path selection and actual

switching to the proper output port. After the proper port has been selected, the

router encapsulates the packet in a frame again to send the packet to its next destination.

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Packet Flow - Layer 1-7 Devices Some devices (e.g. your PC) are Layer 1-7

devices, they perform processes that can be associated with every layer of the OSI model. Encapsulation and decapsulation are two

examples of this. A gateway (essentially a computer which

converts information from one protocol to another) is also a Layer 1-7 device.

Clouds (may contain several kinds of media, NICs, switches, bridges, routers, gateways and other networking devices) operate at all levels of the OSI model, and is a Layer 1-7 device.

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Summary LAN devices, e.g. routers, switches, bridges,

hubs and repeaters. How data flows in a network, data encapsulation.

Two addresses - MAC and IP. Basics of building LANs - topologies, devices,

connections, etc.

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The End