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<!doctype html>
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<title>Advanced Networking - Module 1 Chapter 4 - Network Access</title>
<meta name="description" content="Abilitante alle certificazioni Cisco CCENT e CCNA">
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<div class="slides">
<section>
<h1>Advanced Networking</h1>
<h2>Routing & Switching:</h2>
<h2>Introduction to Networks</h2>
<h3>Chapter 4: Network Access</h3>
<small><a href="http://hlcs.it">Hacklab Cosenza</a> / Centro di Ricerca su Tecnologia e Innovazione</small>
</section>
<section>
<h2>Getting Connected</h2>
<p>To use a network, you must first choose a <strong>way to connect</strong> to it.
Wirings and wireless are popular choices.</p>
<p>Thanks to <strong>Integrated Service Routers (ISR)</strong> and their included multiple ports switch plus a Wireless <em>Access Point</em>, you have increasing flexibility.</p>
<img src="http://i.imgur.com/FTorMBU.jpg">
</section>
<section>
<h2>Purpose of Physical Layer</h2>
<p>Physical Layer <strong>takes the frame resulting from all of the above layers and encodes</strong> the bit into a series of signals for transmitting.</p>
<p>The destination physical layer decodes the signal <strong>and restore the bit representing the frame</strong>, and passes it to upper layers.</p>
</section>
<section>
<h2>Common Media for Physical Layer</h2>
<ul>
<li><strong>Copper</strong>: represents bits through electricity.</li>
<li><strong>Fiber-optic</strong>: represents bits through light patterns.</li>
<li><strong>Wireless</strong>: represents bits through radio waves.</li>
</ul>
</section>
<section>
<section>
<h2>L1 Fundamentals: Physical Components</h2>
<p>Every physical layer involves by definition at least some <strong>physical components involved in generating and trasmitting</strong> the signals, such as cables, connectors, network interfaces, ports.</p>
<img src="http://i.imgur.com/kdClDxZ.jpg">
</section>
<section>
<h2>L1 Fundamentals: Signaling</h2>
<p><strong>The signaling method is the method of representing bits</strong>.</p>
<p>Common signaling methods in networking are changes in electromagnetics fields, voltage variations, or waves <em>modulation</em>.</p>
<img src="https://upload.wikimedia.org/wikipedia/commons/a/a4/Amfm3-en-de.gif">
<p>Signals can be <em>asynchronous</em> or <em>synchronous</em>. The difference is in the presence of an associated <strong>clock signal</strong>.</p>
</section>
<section>
<h2>L1 Fundamentals: Encoding</h2>
<p><strong>The encoding method is how you decide to use signals to represent information</strong>.</p>
<p>Bits need to be sent in a <strong>specific pattern that is recognizable</strong> at both ends. This is called a <em>code</em>.</p>
</section>
<section>
<h2>Signal vs Code: Morse Code</h2>
<ul>
<li><strong>Signaling</strong>: the signal can be sound, light, pulses ("clicks").</li>
<li><strong>Encoding</strong>: Patterns of "lines" and "dots".</li>
</ul>
</section>
</section>
<section>
<h2>Bandwidth and Throughput</h2>
<p>Data transfer speed is usually discussed in terms of</p>
<ul>
<li><strong>Bandwidth</strong>: (maximum) <u>theoretical</u> capacity of a medium to carry data. It's a <u>fixed</u> value.</li>
<li><strong>Throughput</strong>: it's the <u>actual</u> measure of how many bits flow across the media in a period of time. It's a <u>variable</u> value.</li>
</ul>
<p>They are measured in <strong>bps</strong> (bit per seconds) and multiples.</p>
<p>A lot of factor contributes to <strong>throughput not being able to reach theoretical bandwidth</strong>: physics, media quality, amount and type of traffic, latency (delay).</p>
<p>Throughput can only be <strong>as fast as the slowest link</strong>.</p>
</section>
<section>
<h2>Copper Cabling</h2>
<ul>
<li>Copper media is <strong>great for networking</strong> because it's <u>cheap</u>, <u>easy</u> to deploy and has <u>low resistance</u> to current. But...</li>
<li>... it also suffers from <strong>signal attenuation</strong> over long distances, so you have a maximum distance to respect.</li>
</ul>
<p>Copper cabling can suffer from 2 kinds of <strong>interferences</strong>:</p>
<ul>
<li><strong>Electromagnetic</strong> (EMI) or <strong>radiofrequency</strong> (RFI) interferences from other sources.</li>
<li><strong>Crosstalk</strong> from one wire to an adjacent one.</li>
</ul>
<p>There are <strong>countermeasures</strong>: metallic shielding, cable twisting, twisting rate disparity, sensible cable-laying.</p>
</section>
<section>
<h2>Copper Cabling: UTP</h2>
<img src="http://i.imgur.com/WYs133P.jpg" style="float: right;">
<p><strong>Unshielded twisted-pair</strong> (UTP) is the most common network media. They are terminated by <strong>RJ45 connectors</strong>.</p>
<p>They are composed by:</p>
<ul>
<li>An outer jacket the protects the wire.</li>
<li>Twisted pairs of wires to transmit the signal.</li>
<li>Color-Coded insulation.</li>
</ul>
</section>
<section>
<h2>Copper Cabling: STP</h2>
<img src="http://i.imgur.com/CXmQuwd.jpg" style="float:right">
<p>They cost more, and are more difficult to install, but <strong>shielded twisted-pair</strong> cable provide better interference protection.</p>
<p><strong>They combine shielding and crosstalk protection</strong> with special connectors (that can make the cable act like an antenna if unproperly grounded).</p>
<p><strong>Shielding (a metallic foil)</strong> on STP cabling can be applied:</p>
<ul>
<li>On the wire bundle</li>
<li>On the wire bundle and on each wire separately</li>
</ul>
</section>
<section>
<h2>Copper Cabling: Coaxial</h2>
<img src="http://i.imgur.com/1Tq2an1.jpg"><img src="https://i.imgur.com/5qM90qF.jpg" style="width: 25%; height: 25%;">
<p>In coaxial cables there are <strong>only two concentric conductors</strong>, separated by plastic insulation. The second, <strong>outer conductor act as a shield</strong> for the inner one.</p>
<p>Coaxial cables have <strong>many type of connectors</strong>, among the popular choices are BNC, N-type, F-type, RP-SMA.</p>
<p>Nowadays in networking they are mostly used for <strong>attaching antennae</strong> to wireless devices and for broadband.</p>
</section>
<section>
<h2>Copper Cabling: Safety</h2>
<p>Copper cabling hasn't a very good resistance to <strong>ignition</strong>.</p>
<p>The main thing you have to do with copper cabling, aside from assuring integrity, is to <strong>correctly ground them</strong>.</p>
<p>Incorrect grounding can result in <strong>parasitic currents</strong> flowing in a device chassis (exposed to individuals) and the cable providing a possible path to <strong>lightnings</strong>.</p>
</section>
<section>
<section>
<h2>UTP Cabling Standards</h2>
<img src="https://i.imgur.com/rCvsp1Q.png">
<!--<img src="https://i.imgur.com/Hr9UTGZ.jpg">-->
<p>The <strong>TIA/EIA-568 standards</strong> specifies cable <strong>categories</strong>, lengths, connector, pinouts, cable termination, and testing method for LAN cable installations.</p>
</section>
<section>
<h2>UTP Cabling Standards</h2>
<p><strong>RJ45 is the 8P8C physical connector used by the Ethernet standard</strong> (and many others). Proper termination of cables at the RJ45 connectors is extremely important.</p>
<p><strong>UTP cables are certified</strong> by IEEE into categories when they met certain requirements. Cat 5e is the minumum acceptable for LAN nowadays.
<ul>
<li><strong>Cat. 3</strong>, for voice/phone lines.</li>
<li><strong>Cat. 5 and 5e</strong>, up to 100 Mb/s and 1 Gb/s respectively.</li>
<li><strong>Cat. 6 and 6a</strong>, up to 10 Gb/s (55m and 100m respectively).</li>
</ul>
</section>
<section>
<h2>RJ45 Connectors</h2>
<img src="https://i.imgur.com/qxk9bQ7.jpg">
<ul>
<li><strong>Left</strong>: Front/Up side on an UTP RJ45 8P8C Connector.</li>
<li><strong>Right</strong>: Bottom side of UTP and FTP RJ45 8P8C Connector.</li>
</ul>
</section>
<section>
<h2>RJ45 Socket</h2>
<img src="https://i.imgur.com/sEHKUOH.jpg" style="width: 50%; height: 50%;">
<p>RJ45 8P8C female socket plug and wiring process, which uses a tool called <em>punch-down</em>.</p>
</section>
<section>
<h2>UTP Wiring Conventions</h2>
<p>The <strong>pinouts</strong> (wiring order and corresponding pins) of UTP cables varies according to the use case.</p>
<ul>
<li><strong>Straight-Through</strong>: same convention at both ends, it's the most common type of cable for networking and it's used for host-to-switch and switch-to-router connections.</li>
<li><strong>Crossover</strong>: different conventions at each end of the cable, it's used for connecting two similar devices, like two hosts, two switches, two routers.</li>
<li><strong>Rollover</strong>: Cisco proprietary for console port usage.
</ul>
<p>No damage can happen by <strong>using the wrong cable</strong>, but unless there's some auto-sensing mechanism, no communication will occur. It's the first thing to check!
</section>
<section>
<h2>UTP Cable Testing</h2>
<img src="http://i.imgur.com/NSbPbev.jpg" style="float: right; width: 50%; height: 50%;">
<p>For anything other than simple functional tests, such as a <em>wire map</em>, a <strong>UTP Cable tester</strong> should be used.</p>
<p>For more advanced measurements such as cable length, signal attentuation, crosstalk, a <strong>cable certifier/verifier</strong> is required.</p>
</section>
</section>
<section>
<section>
<h2>Fiber Optic Cabling</h2>
<img src="https://i.imgur.com/9PX5UHT.jpg" style="float: right; height: 33%; width: 33%;">
<p><strong>Optical fiber</strong> is a flexible and extremely thin transparent wire of pure glass. <strong>It acts as a guide for light impulses</strong> to which bits are encoded.</p>
<p>Fiber Optics allows for <strong>longer distances and higher data rates</strong> than any other media. It is also <strong>immune to any electromagnetic interference</strong>. It is used for:</p>
<ul>
<li>Backbone applications</li>
<li>Broadband delivery (FTTN/B/H)</li>
<li>Long distances networks</li>
<li>Submarine networks</li>
</ul>
</section>
<section>
<h2>Fiber Optic Cabling: Design</h2>
<img src="http://i.imgur.com/jPmApfP.jpg">
<p>Fiber optic cables have a simple but hi-tech structure:</p>
<ul>
<li><strong>Core</strong> - the glass through which the light is transmitted.</li>
<li><strong>Cladding</strong> - it is the glass that surrounds the core. It acts as a mirror, reflecting the light trying to escape the core, keeping it in.</li>
<li><strong>Jacket</strong> - A stengthened PVC enclosure that protects the glass.</li>
</ul>
</section>
<section>
<h2>Fiber Optic Cabling: Types</h2>
<p>The lights travelling through a fiber optic cable can be <strong>generated by lasers or by LEDs</strong>. Photodiodes will catch the light at the other end and convert it to data frames.</p>
<p>Fiber optics cables are mainly of two categories:</p>
<ul>
<li><strong>Single-Mode (SMF)</strong>: very expensive, it uses laser and a very small core to produce a single ray that can travel very long distances with minimal losses.</li>
<li><strong>Multi-Mode (MMF)</strong>: LED emitting through a larger core, entering the fiber at various angles. Up to 500m@10Gb/s.</li>
</ul>
<p>You need <strong><em>patch cords</em></strong> to connect fiber infrastructure devices. <strong>Standard colors</strong> are yellow for SMF, orange/aqua for MMF.</p>
</section>
<section>
<h2>Fiber Optic Connectors</h2>
<img src="http://i.imgur.com/L2UbGss.jpg">
<ul>
<li><strong>ST</strong>: bayonet-style (open/close with a twist) for MMF.</li>
<li><strong>SC</strong>: it's the "standard" connector, used for SMF and MMF. It has a push-pull mechanism that keeps it in place.</li>
<li><strong>LC</strong>: smaller sized connector, used mainly for SMF but also supports MMF. It's probably the most popular nowadays.</li>
</ul>
<p>In fiber cabling <strong>light travels only in one direction</strong>. You need two bundled cables to be able to tx/rx simultaneously (even better: a <strong>Duplex Multimode LC Connector</strong>).</p>
<p>Unused fiber cables should be protected with a plastic cap.</p>
</section>
<section>
<h2>Fiber Optic Cabling: Testing</h2>
<p>Terminating and cutting fiber-optic cables is definitely not as easy as with copper. <strong>It requires special equipment and skills</strong>.</p>
<p>Typical errors in termination and splicing (joining) are:</p>
<ul>
<li><strong>Misalignment</strong> of two joined fibers.</li>
<li><strong>End gap</strong>, the media does not touch at the connection point.</li>
<li><strong>End finish</strong>, the media has not a precise termination and presents some dirt.</li>
</ul>
</section>
<section>
<h2>Copper vs Fiber</h2>
<small>
<table>
<tr>
<td><strong>Implementation issues</strong></td>
<td><strong>Copper media</strong></td>
<td><strong>Fiber optics</strong></td>
</tr>
<tr>
<td><strong>Bandwidth supported</strong></td>
<td>10 Mb/s - 10 Gb/s</td>
<td>10 Mb/s - 100 Gb/s</td>
</tr>
<tr>
<td><strong>Distance</strong></td>
<td>Relatively short (up to 100 m)</td>
<td>Relatively high (up to 100 Km)</td>
</tr>
<tr>
<td><strong>Immunity to EMI/RFI</strong></td>
<td>Low</td>
<td>High (completely immune)</td>
</tr>
<tr>
<td><strong>Immunity to electical hazards</strong></td>
<td>Low</td>
<td>High (completely immune)</td>
</tr>
<tr>
<td><strong>Media and connector costs</strong></td>
<td>Lowest</td>
<td>Highest</td>
</tr>
<tr>
<td><strong>Installation skills</strong></td>
<td>Lowest</td>
<td>Highest</td>
</tr>
</table>
</small>
</section>
</section>
<section>
<section>
<h2>Wireless Standards</h2>
<p>Wireless transmissions that we commonly encounter includes:</p>
<ul>
<li><strong>IEEE 802.11</strong> - Wireless LAN (WLAN), we call it <u>Wi-Fi</u>.</li>
<li><strong>IEEE 802.15</strong> - Wireless Personal Area Network (WPAN), commonly known as <u>Bluetooth</u>.</li>
<li><strong>IEEE 802.16</strong> - WiMAX, uses a PtMP topology and was specifically developed to provide broadband access.</li>
</ul>
<p>Each standard dictates parameters such as techniques for <strong>encoding of data</strong> of data into radio waves, transmission <strong>power</strong>, usable <strong>frequencies</strong>, <strong>antenna</strong> design, and many more.</p>
</section>
<section>
<h2>Wireless LAN</h2>
<p>To <strong>connect wirelessly</strong> to a LAN you need:</p>
<ul>
<li>a <strong>Wireless Access Point</strong> (WAP or AP) that signals the availability of a wifi connection and aggregates the signals, connecting user to an existing wired infrastructure.
<li>a <strong>Wireless NIC adapter</strong>, providing wireless capabilities to individual hosts.
</ul>
</section>
<section>
<h2>Timeline of Wireless Standards</h2>
<p>802.11 family of standards has evolved a lot in 15 years:</p>
<img src="http://i.imgur.com/743EZBs.gif">
</section>
</section>
<section>
<h2>Data Link Layer</h2>
<p>The Data Link layer performs two <strong>functions</strong> at its core:
<ul>
<li>It takes L3 PDUs and <strong>generates data units called frames</strong>, that are ready for transmission over the media.</li>
<li>It <strong>controls media access</strong>, that is how, when and whose data is placed on the media, and also performs error detection.
</ul>
<p>In essence it <strong>hides the specifics of the media</strong> from every upper layer, which they don't need to know about.</p>
</section>
<section>
<h2>Data Link Sublayers: LLC & MAC</h2>
<img src="http://i.imgur.com/fW4YTuA.jpg">
<ul>
<li>The <strong>Logical Link Control (LLC)</strong> is the <strong>interface to the Network Layer</strong> in the stack, it identifies which L3 protocol is in use and de/multiplexes it into/from the frame.</li>
<li>The <strong>Media Access Control (MAC)</strong> is the <strong>interface to the hardware</strong>, it generates the frame, attaching data link addresses and delimitations, and then physically coordinates with the hardware to send it.</li>
</ul>
<p>LLC is software (the NIC driver), while MAC is implemented in hardware.</p>
</section>
<section>
<h2>Media Access Control</h2>
<p>The <strong>media access control method is the technique used for placing the frame on and off the media</strong>.</p>
<p>Examples of MAC methods are CSMA, TDMA, Polling, etc. They <strong>depend on the (logical) topology</strong> and whether the media is to be <strong>contented or not</strong>.</p>
<p>While L3 protocols may stay largely the same, we are bound to see <strong>many different data link and media transitions</strong> over a remote communication.</p>
<p><strong>Routers de-encapsulate and re-encapsulate</strong> properly according to L1 and L2 protocols of that network segment.</p>
</section>
<section>
<h2>Data Link Layer Standards</h2>
<p>Because of the close relationship between L2 and L1, <strong>many Data Link standards actually defines both</strong>.</p>
<img src="http://i.imgur.com/MQJ1hQu.jpg">
</section>
<section>
<section>
<h2>Layer 2 Frame Structure</h2>
<p>A L2 frame contains <strong>the PDU of L3 plus control informations</strong>, that is information that allows the protocol to carry on its functions.</p>
<p>A L2 frame is composed by:</p>
<ul>
<li>An <strong>Header</strong> at the beginning, containing addressing information.</li>
<li>then <strong>Data</strong>, in the form of the L3 PDU.</li>
<li>and at the end, a <strong>Trailer</strong> containing other control infos like error detection.</li>
</ul>
</section>
<section>
<h2>A Generic L2 Frame</h2>
<img src="http://i.imgur.com/ElcQ6yY.png">
<p>Structure of frame and fields contained in header and trailer <strong>vary according to the DLL protocol. There can't be a single one</strong> because needs of transportation across media types are very different.</p>
</section>
</section>
<section>
<section>
<h2>Physical WAN Topologies</h2>
<h3>Point-to-Point</h3>
<img src="http://i.imgur.com/rBfJeU9.png">
<p>Permanent link between only 2 end points.</p>
</section>
<section>
<h2>Physical WAN Topologies</h2>
<h3>Hub and Spoke</h3>
<img src="http://i.imgur.com/BSI4ALs.png">
<p>A central node interconnecting many PtP links.</p>
<p>It's the WAN equivalent of the LAN "Star" topology.</p>
</section>
<section>
<h2>Physical WAN Topologies</h2>
<h3>Mesh</h3>
<img src="http://i.imgur.com/USADL5c.jpg">
<p>Every node is PtP interconnected to every other node (<em>full mesh</em>) or multiple other nodes (<em>partial mesh</em>).</p>
</section>
</section>
<section>
<h2>Physical vs. Logical PtP</h2>
<p>When two nodes are physically connected in a PtP topology, <strong>media sharing is not a concern, and so isn't addressing</strong>. DLL protocols can therefore be much more simple.</p>
<p>However when they don't have a direct physical connection, it can be possibile to establish <strong>a logical PtP connection though a virtual circuit</strong> and other intermediate devices.</p>
<p><strong>In logical PtP, the MAC method and the DLL still operate</strong> as if the connection was physical.</p>
</section>
<section>
<section>
<h2>Physical LAN Topologies</h2>
<h3>Star</h3>
<img src="http://i.imgur.com/ESpljwG.jpg">
<p>End devices connected to a central device, that used to be an hub but now is a switch. Most common LAN topology.</p>
</section>
<section>
<h2>Physical LAN Topologies</h2>
<h3>Extended Star</h3>
<img src="http://i.imgur.com/Zlo9GrA.jpg" style="width: 40%; height: 40%;">
<p>Several star topologies are interconnected together through other star topologies (<em>Extended Star</em>) or through a bus (<em>Hybrid</em>).</p>
</section>
<section>
<h2>Physical LAN Topologies</h2>
<h3>Bus</h3>
<img src="http://i.imgur.com/pIC5oUK.gif" style="background: white;">
<p>No intermediary device required, all end systems chained toghether on the same main cable (the <em>bus</em>) in some form or another.</p>
</section>
<section>
<h2>Physical LAN Topologies</h2>
<h3>Ring</h3>
<img src="http://i.imgur.com/EsRCGRK.gif">
<p>Each end device is connected to its neighbours, forming a ring.</p>
</section>
</section>
<section>
<h2>Half and Full Duplex</h2>
<p>The communication between 2 devices, regarding its direction, can be:</p>
<ul>
<li><strong>Half-Duplex</strong>: both can TX/RX, but not simultaneously. This mandates for <strong>conflict resolution</strong> about media usage.</li>
<ul>
<li>Star topologies using hubs; bus topologies; WLANs.</li>
</ul>
<li><strong>Full-Duplex</strong>: both can TX/RX and can do that at the same time. This means the media is <strong><u>assumed uncontended</u></strong> by the DLL.</li>
<ul>
<li>Enabled by Ethernet switches.</li>
</ul>
</ul>
</section>
<section>
<h2>Sharing media on LAN topologies</h2>
<p>When multiple nodes access the network through a common medium, it's called a <strong><em>multi-access network</em></strong>.</p>
<p>There are many MAC methods for such networks, but the two basic fall in these 2 categories:</p>
<ul>
<li><strong>Contention-based access</strong>: the medium is contested (hosts can send data when it has them), but nodes know what to do if a collision happens.</li>
<li><strong>Controlled access</strong>: each node has its own allocated time (or turn) for medium usage.</li>
</ul>
</section>
<section>
<h2>Carrier Sense Multiple Access</h2>
<p>The more nodes there are the less probable is to be able to use the media without collisions.</p>
<p>CSMA is used in contention-based medium access to <strong>detect if there's a signal (carrier) on the media</strong> before transmitting. It works in combination with a <strong>collision resolution method</strong>:</p>
<ul>
<li><strong>CSMA/CD</strong> for Ethernet 802.3: if another signal is perceived while transmitting, colliding devices will stop to try later.</li>
<li><strong>CSMA/CA</strong> for 802.11: doesn't detect collisions, instead it sends notification of intent to use media and wait for clearance.</li>
</ul>
<p>Switched Ethernet operates as <strong><u>not contention-based</u></strong>.</p>
</section>
<section>
<h2>[A] Controlled Access</h2>
<p><strong>Devices access the medium one after the other</strong>, and then have to wait for their turn again.</p>
<p>A device must first <strong>acquire the token</strong> to be able to so. When it has one and wants to transmit, it fills the token with data and send it.</p>
<p><u>No other device can transmit until the frame has arrived and the token got released</u>.</p>
<p>Examples: <strong>Token Ring</strong> (IEEE 802.5) and <strong>Fiber Distributed Data Interface</strong> (FDDI).</p>
</section>
<section>
<h2>[A] Ring Topology</h2>
<p>It is a <strong>multi-access topology</strong>, because every frame is <u>received by each node</u> (on the path between source and destination), but <u>addressed only by the intended destination</u>.</p>
<p>If a node receives a message that is <strong>not destined to it, it relays it</strong> to the next node.</p>
<p>Using a token is the most common MAC method for ring topologies.</p>
</section>
<section>
<h1>End of Lesson</h1>
</section>
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