Chapter Three The Highways and Byways of the Network

Objectives You will get a review of binary. You’ll examine different communications models. Here you’ll learn about different physical media types used to build networks. You’ll learn about wireless media as well.

Reviewing Binary Computers only know 0 and 1 –On and off –Yes and no –Open and closed Based on the studies of George Boule

Terms of Binary Bit –A single 1 or 0 Nibble –4 bits transmitted as a unit Byte –8 bits used to generate a single character

AM versus FM Amplitude modulation (AM) –Data encoded by varying the relative strength (known as amplitude) of the signal Frequency modulation (FM) –Data encoded by varying how many times per second the signal oscillates

Communications Models Simplex –A device can either send or receive, but not both. Half-duplex –A device can both send and receive, but not at the same time. Full duplex –A device can send and receive at the same time.

Bounded Media Fixed cable of some sort –Twisted pair –Coaxial –Fiber optics

Twisted Pair (1 of 2) Eight strands of wire carry the signals (or are null). Strands are separated into four pairs that are twisted around each other to reduce crosstalk. Unshielded twisted pair (UTP) has no external armor. Shielded twisted pair (STP) is protected by a metal foil (or similar) wrapping. Twisted pair cable is defined by its category.

Pair 1 Orange -- white/orange striped Pair 2 Green --white/green striped Pair 3 Blue -- white/blue striped Pair 4Brown -- white/brown striped Twisted Pair (2 of 2)

Some Twisted Concepts Limited to 100 meters without a repeater Bandwidth limitations defined by category Terminated by RJ-45 connector

CategoryFrequency SupportedUsage 1Voice only, no dataTelephone only 24MhzLocaltalk/ISDN 316MhzEthernet 420MhzToken ring 5100MhzFast Ethernet 5e400Mhz Gigabit Ethernet/ATM to 622MB/sec 6550Mhz Gigabit Ethernet/ATM to 2.4GB/sec

EIA/TIA Wiring Standards Pin No.Signal Carried568B568A 1Transmit (+)White/OrangeWhite/Green 2Transmit (-)OrangeGreen 3Receive (+)White/GreenWhite/Orange 4Not UsedBlue 5Not UsedWhite/Blue 6Receive (-)GreenOrange 7Not UsedWhite/Brown 8Not UsedBrown

Coaxial Cable Thinnet –RG-58 –Terminated with BNC connector –10Mb/s throughput –180M maximum run Thicknet –RG-8 –Terminated with vampire clamp –10Mb/s throughput –500M maximum run

Fiber Optics Single mode –Very thin strands of fiber –Single signal transmitted over each fiber –Signals only travel in one direction Multimode –Thicker strands carry multiple signals Each one on a different frequency

Unbounded Media Infrared Laser Radio Microwave

Infrared Line of sight –Two communicating devices must have an unblocked path between them –Used for linking peripherals to computers or a laptop to a desktop or a TV/VCR remote Scatter infrared –Limited range –Used for small office/home office (SOHO) networks

Laser Line of sight –Requires precise alignment of transmitter and receiver Capable of high speeds (155Mb/s to 622Mb/s) Useful for creating pseudo-WAN links between offices

Radio Public band radio limited in range –Frequency ranges are 902Mhz t0 928Mhz and 5.72Mhz to 5.85Mhz. Other frequencies monitored by FCC and require a license

Single Frequency Low power single frequency (LPSF) –Used in the public bands –Small networks with relatively low speeds High power single frequency (HPSF) –Generally allows for line of sight communications –Atmospheric bounce can extend range

Spread Spectrum Signal bounced over multiple frequencies to increase security Direct sequence spread spectrum –A specific pattern of frequency hops followed Frequency hopping spread spectrum –Signal bounces between frequencies in a pseudo-random order for higher security

Microwave Terrestrial microwave –All line of sight –Range limited by the horizon –Relay stations can extend range Satellite microwave –Global coverage –Expense can be prohibitive