Local Area Networks

Local Area Networks Honolulu Community College Cisco Academy Training Center Semester 1 Version 2.1.1

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.

Physical Topology • Topology defines the structure of the network. • Physical topology is the actual layout of the wire (media).

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.

Can you identify the topologies?

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.

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.

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).

Symbols for Media

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.

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.

Bridges • Layer 2 (data link) device designed to connect two LAN segments. • Purpose is to filter traffic based on MAC address.

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.

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.

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.

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

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).

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.

Exponential Growth of the Internet • 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).

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.

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.

Networking Devices & OSI Layers (cont.) • Clouds, which may include routers, switches, servers, etc, involve Layers 1-7. Routers Bridges, Switches Repeaters, Hubs

Data Encapsulation Example Session layer Transport layer Network layer Data link layer Physical layer Cloud

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.

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.

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.

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.

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.

The End

Local Area Networks