IT220 Network Standards & Protocols. Unit 4: Chapter 4 Transmitting Bits

Transcription

1 1 IT220 Network Standards & Protocols Unit 4: Chapter 4 Transmitting Bits

2 Objectives Differentiate among major types of LAN and WAN technologies and specifications and determine how each is used in a data network. Explain basic security requirements for networks. Install a network (wired or wireless), applying all necessary configurations to enable desired connectivity and controls. 2

3 3 Objectives Explain the fundamentals of electrical circuits. Identify different types of physical cabling. Identify wireless network communication needs. Distinguish among the different needs for wired and wireless networks.

4 4 Objectives Classify Layer 2 networking components used in a typical LAN. Compare and contrast advantages and disadvantages of network media. Use basic troubleshooting techniques to ensure network connectivity at Layers 1 and 2.

5 Transmitting Bits General idea of how a TCP/IP network forwards IP packets from one host to another: Nodes (routers in this example) each make a choice of where to send the packet next so the data arrives at the correct destination. Always keep the big goal of the network in mind: Delivering data from the source to the destination. Sending Data Through a Network of Nodes and Links 5 Figure 4-1

6 Sending Bits with Electricity and Copper Wires Electrical circuit must exist as complete loop of material (medium) over which electricity can flow. Direct Current (DC) electrical circuits Electrical current: Amount of electricity that flows past single point on circuit (amount of electron flow in circuit). Current always flows away from negative (-) lead in circuit and towards positive (+) lead. Powering a Light Bulb with a DC Circuit 6 Figure 4-3

7 Sending Bits with Electricity and Copper Wires DC circuit (on left) and AC circuit (on right) both use 1 volt. DC shows constant +1 volt signal. AC circuit slowly rises to +1 volt, falls to 0 then falls to -1 volt (1 volt, but in opposite direction), repeating over time. Resulting AC wave: Sine wave Graphs of 1 Volt (Y-Axis) over time: DC (Left) vs AC (Right) 7 Figure 4-4

8 Sending Bits with Electricity and Copper Wires To send data, networking Physical layer standards can change amplitude, frequency, phase, period of AC electrical signal. Graphs of AC Circuit: Amplitude, Period, Frequency 8 Figure 4-5

9 Sending Bits with Electricity and Copper Wires Most commonly used in networking encoding schemes. One signal used by encoding scheme means binary 0, other means binary 1. Encoding Options: Frequency, Amplitude, and Phase Shifts 9 Figure 4-6

10 Sending Bits with Electricity and Wave Feature Amplitude Frequency Phase Period Definition of the Graph Copper Wires Maximum height of the curve over the centerline. Number of complete waves (cycles) per second (in Hertz). Single location in repeating wave. Time (width on x-axis) for one complete wave to complete. Electrical Feature it Represents Voltage Speed with which current alternates directions. Voltage jumps, which makes signal graph jump to new phase. Time for voltage to change from maximum positive voltage back to same point again. Common Features Used by Encoding Schemes 10 Table 4-1

11 Network Cabling Before a node can send data, it needs to create a circuit between itself and the destination node. Copper cable has outer plastic cover (jacket) that holds wires (conductors). Sending/receiving nodes use a pair of wires connected at their ends to create circuit. Photo of Wires Inside a Networking Cable 11 Figure 4-7

12 Network Cabling Cable has 4 pairs of wires: 2 used, 2 unused. Hardware of each node must agree which wires to use and which to ignore. For wires chosen to use, nodes loop ends together to create a circuit. Physical Components to Create an Electrical Circuit Between Two Nodes 12 Figure 4-8

13 Network Cabling Loop (circuit) can t create circuit by itself: something has to create electrical current. Transmitting node creates electrical signal, changing signal over time to encode different bit values. Transmitter: Part of node that sends data. Receiver: Part that listens for signal of incoming bits. Transmitter Generating a Current to Send; Receiver Sensing Current to Receive 13 Figure 4-9

14 Circuit Bit Rates Bit rate (link speed): Defines number of bits sent over link per second (bps). Impacts how nodes send data over circuit. Example of how bit rate and encoding scheme work together: Bit rate = 10 bps; encoding scheme states that binary 1 should be +2 volts and binary 0 as +1 volts. Example where Encoder Changes Signal Every Bit Time 14 Figure 4-10

15 Encoding Scheme Works like language: Defines electrical equivalent of 1 s and 0 s. Different frequencies represent binary 1 s and 0 s. Example sending 1010: Lower frequency represents binary 1, higher frequency represents binary 0. Frequency Shift Keying: Low Frequency = 1, High Frequency = 0 15 Figure 4-11

16 Manchester Encoding Used on some early Ethernet networks. Does not choose one electrical signal at beginning of bit time, instead changes signal in middle of bit time. Follows this logic: To encode 0: Start high, and transition low in the middle of bit time. To encode 1: Start low, and transition high in the middle of bit time. Manchester Encoding: 0 = High-to-Low, 1 = Low-to-High 16 Figure 4-12

17 Using Multiple Circuits Simplex transmissions are one way: If encoding scheme works in only one direction (on single circuit): Devices must take turns using that circuit or Devices must use different circuits for each direction. Half-duplex transmissions take turns: Node1 sends while Node2 listens; when Node1 finishes, Node2 sends while Node1 listens. Full duplex transmissions can send/receive simultaneously: Both endpoints can send at same time because they use multiple wire pairs. Full Duplex Using Two Pair, One for Each Direction 17 Figure 4-13

18 18 Problems with Electricity Noise: Electro-Magnetic Interference (EMI) Cables help prevent effects of EMI in many ways, including shielding. Twisting of wire pairs creates cancellation effect to help stop EMI effect. Attenuation: Signals fade away over distance to point where devices can t interpret individual bits Ethernet standards limit copper links to 100 meters. Very important when designing network.

19 Unshielded Twisted Pair (UTP) 10Base-T, 100Base-T & 1000Base-T uses Unshielded Twisted Pair (UTP). Cable contains twisted pairs of wires and no added shielding materials. Twisting reduces EMI effects between pairs in same jacket and in nearby cables. Lack of shielding makes cables less expensive, lighter, easier to install. Supports full-duplex. Note: Twisted pair cables with shielding are called Shielded Twisted Pair (STP). 19

20 LAN Standards Progression IEEE standardized Ethernet in standard in early 1980s. Has added many more Ethernet standards since then. Each standard took years to grow in marketplace and eventually drive prices down. Timeline of the Introduction of Ethernet Standards 20 Figure 4-14

21 RJ-45 Connectors (Ports) Ethernet standards allow use of RJ-45 connectors on twisted pair cable and matching RJ-45 ports (sockets) on NICs, switch ports, and other devices. Again, RJ-45 connectors and ports accommodate 8 wires (pins) in single row. Example RJ-45 Connectors and Sockets 21 Figure 4-15

22 Cable Pinouts Pinouts: How each wire in cable should be connected to each pin in connector according to Ethernet standards. Wires must be in correct order so correct wires in twisted pair send to correct direction. Wires, Connector Pin numbers, and Socket Pin Numbers 22 Figure 4-16

23 Cable Pinout Standards Ethernet uses TIA (Telecommunications Industry Association) 568 standards to define specific wires to use for pinouts. UTP cables have four pairs of wires, each using a different color: green, blue, orange, brown. Each pair has 1 wire with solid color and other one with white stripe. Ethernet uses following rules for creating circuits: One pair at pins 1 and 2 One pair at pins 3 and 6 TIA Cable Pinouts T568A On Each End Creates a Straight-Through Cable 23 Figure 4-18

24 Cable Pinout Standards 568A/568B NOTE: 568B switches green and orange wires. TIA Cable Pinouts T568A On Each End Creates a Straight-Through Cable 24 Figure 4-18

25 25 Break Take 10

26 Sending Bits with Fiber Optic Cables Fiber optics transmission use light to signify bits: ON = Light, OFF = No light. Endpoints agree to use same speed and same basic encoding scheme. Encoding Bits Using Light On/Off 26 Figure 4-20

27 Sending Bits with Fiber Optic Cables Fiber cables contain several parts that wrap around glass or plastic fiber core. Core is about as thin as human hair. Fiber breaks easily without some type of support. Core and cladding have direct effect on how light travels down cable. Optical transmitter (laser or LED) shines light into core to transmit data. Components of a Fiber Optic Cable 27 Figure 4-21

28 Sending Bits with Fiber Optic Cables Cladding surrounds core for entire length of cable. Reflects light back into core Light waves reflect off cladding back into core until light waves reach other end of cable Fiber optic cables work well to send light in one direction at time, but not two. Cable acts like dark tunnel so nodes can easily see light coming through cable. Cladding Reflecting the Light Back into the Fiber Optic Cable s Core 28 Figure 4-22

29 Sending Bits with Fiber Optic Cables Most fiber links use pair of cables for full-duplex. Each fiber NIC, port, interface, etc., has interface with two sockets: One for send cable, one for receive cable. Each node s transmit socket must connect to same cable as other node s receive socket. NOTE: In addition to sending data using light over cables, fiber technology also includes free space optics (e.g., TV remote) which sends light through air; requires line-of-sight. 29 Figure 4-23

30 Optical Transmitters LEDs shine light in multiple directions; lasers shine in one direction. Fiber cables come in two major categories: Multimode (MM), single mode (SM). Multimode have larger cores and work best with LED transmitters. Single mode have smaller diameter cores and work best with laser transmitters. LEDs with Multiple Modes (Angles), and Lasers, with a Single Mode (Angle) 30 Figure 4-24

31 Optical Ethernet LANs Fiber cables not affected by EMI. Fiber links more secure. Example: Typical campus LAN has employees in two buildings in office park that sit 150 meters apart, which exceeds Ethernet standards for copper cabling. Need to use multimode links as they can run 200 meters. Typical Use of Fiber Optics in a LAN: Links Between Neighboring Buildings 31 Figure 4-25

32 Optical WAN Links Example: Fiber that connects equipment in CO to other Telco sites (called core sites). COs sit at edge sites of Telco network and have links to core sites. Physical locations include office buildings with server rooms. In this figure, all links use fiber except links from CO to customer router which use copper. Fiber Links Used to Help Create a Telco Network 32 Figure 4-27

33 Optical WAN Links: SONET Synchronous Optical Network (SONET): One of longer-established standards for WAN links. Defines Physical layer standards for data transmission over optical Name links. Uses hierarchy of speeds that are multiples of base speed (51.84 Mbps) plus some overhead. OC-1 OC-3 OC-12 OC-24 OC-48 OC-96 OC-192 (Rounded) Line Speed 52 Mbps 155 Mbps 622 Mbps 1244 Mbps 2488 Mbps 4976 Mbps 9952 Mbps SONET Optical Carrier (OC) Names and (Rounded) Line Speeds Table

34 Wireless Networks Basics Example: Radio stations Signals broadcast so anyone near enough to station s antenna (radio tower) can receive them. Radio tower sends electricity through antenna to create radio waves. More electrical power creates stronger radio waves that can travel longer distances. Radio tower sends signals upward because radio waves bounce off ionosphere (one of layers of Earth s atmosphere). Bouncing radio waves off ionosphere sends radio waves to wider area. A Radio Station Broadcasting a Radio Signal to a Car Radio Figure

35 Wireless Networks Basics A Radio Station Broadcasting a Radio Signal to a Car Radio Figure

36 A Radio Station Broadcasting a Radio Signal to a Car Radio Figure Wireless Networks Basics Electromagnetic radiation (ER): Described using electromagnetic (EM) spectrum ER energy travels as waves Each wave has specific wavelength Spectrum categorizes energy based on wavelength Examples: Radio waves, visible light, X-rays, microwaves Radio waves work well for networking because can be changed (modulated) over time to send data.

37 A Radio Station Broadcasting a Radio Signal to a Car Radio Figure Wireless Networks Basics Key points about why radio can be used to wirelessly send data: 1. Radio waves have energy level that moves up and down over time, so when graphed, waves look like sine wave. 2. Radio waves can be changed and sensed by networking devices, including changes to frequency, amplitude, phase, period, wavelength. 3. EM energy does not need physical medium to move.

38 Major Components in the Mobile Phone Network Model Figure Wireless WANs Mobile Phones & Voice Mobile network provider creates its own network. But most phone users want to communicate with more phones than just those on same mobile company s network, as well as landline phones. Enter the Public Switched Telephone Network (PSTN)

39 Connecting a Mobile Phone Call through a Radio Tower to the Telco Network Figure Wireless WANs Mobile Phones & Voice Most mobile phones act as digital phones. Send and receive digits (bits) that represent voice traffic. To transmit bits, phones use wireless radio technology. Phone sends bits encoded as radio waves to nearby radio antenna on tower owned by mobile phone company.

40 40 Wireless WANs Mobile Phones & Voice Steps to place call on mobile phone: 1. Person speaks creating sound waves (as usual). 2. Phone converts sound waves into bits. 3. Phone sends (encodes) bits as radio waves through air towards cell tower. 4. Radio equipment at tower receives (decodes) radio waves back into original bits. 5. Rest of trip uses various technology (details not included).

41 Smart Phone: Using Radio to Forward Bits to the Tower, and then to the Internet Figure Wireless WANs Mobile Phones & Data Radio link on phone supports data service just as it does for voice. When sending or receiving data, phone passes bits using radio waves between itself and radio tower. Phone encapsulates data. To support data applications, mobile network connects to Internet and any other networks that support data apps requested by user. Mobile network forwards data to correct destination in Internet, not through PSTN.

42 42 Wireless WANs Mobile Phones & Data Steps in accessing Internet via mobile phone: 1. Person types URL or taps hyperlink. 2. Phone encapsulates HTTP request into IP packet, then Data Link layer frame. 3. Phone sends (encodes) frame s bits as radio waves towards cell tower. 4. Radio equipment at tower receives (decodes) radio waves back into original bits. 5. Equipment near cell tower forwards bits into Internet as for any IP packet.

43 Wireless WAN Standards Gen Umbrella Standard Other Terms Related to Generation Standards Body 2G GSM (Global System for Mobile Communications) TDMA, CDMA ETSI 3G IMT-2000 (International Mobile Telecommunications- 2000) UTMS ITU 4G IMT-Advanced (International Mobile Telecommunications - Advanced) LTE, Wi-Max ITU, ETSI, IEEE Mobile Wireless Standards and Terms Table

44 A Small Wireless LAN with One Access Point (AP) Figure Wireless LANs Devices & Topology Wireless LAN devices need wireless NIC. Gives PC ability to connect WLAN Uses radio antenna that allows NIC to send and receive data Most WLANs use Access Points (AP) which are small devices that acts like small radio tower. All wireless user devices communicate through AP.

45 A WLAN AP Bridges Between the WLAN and an Ethernet LAN Figure Wireless LANs Devices & Topology WLAN with AP creates a WLAN Basic Service Set (BSS). In a BSS, all communications happen with the AP, much like it does in the wireless WAN model.

46 Amplitude and Phase Shift Basic Examples Figure Wireless LANs Sending Data For most WLAN standards, the encoding scheme uses some form of amplitude shift keying or phase shift keying, which changes the amplitude or phase (respectively) to represent a 0 or 1.

47 A WLAN with Possible Sources of Interference Figure Wireless LANs Typical Problems AP sits under metal desk (radio waves do not pass through metal very well). AP sits next to other equipment and cables that interfere (EMI). AP sits on wrong side of interior wall away from end user devices.

48 CSMA/CA Process Figure Wireless LANs Transmission Wireless LANs take turns by using rules called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). This technology is similar to wired Ethernet s CSMA/CD.

49 IEEE WLAN Standard Wireless LAN Standards Maximum Stream Rate (Mbps) Frequency Range Number of Nonoverlapping Channels b GHz a 54 5 GHz g GHz n 72 5 GHz n* GHz ac** 1000 Plus 5 GHz 12 * When using bonded 40 MHz channel, instead of 20 MHz channel (as used by other standards outlined in table). ** WLAN Standards and Speeds Table

50 Enterprise LAN Example: Wired & Wireless Many corporate campus LANs have both wired and wireless LAN support on each floor. The WLAN connects to the same Ethernet network as the wired network does so all devices in the two building can communicate. Campus LAN: Wireless Devices, Wired Desktops, and Fiber Trunks Figure

51 Summary, This Chapter Looked at the details of how to move bits from one node to the next node in a network. Focused on moving bits over a single link. Looked at how to move bits using copper wires and electricity. Explained the fundamentals of how electricity can be graphed. Discussed fiber optics. Compared and contrasted the two common types of fiber optic transmitters and two general categories of fiber optic cables.

52 52 Summary, This Chapter Listed common reasons for using fiber optic cables instead of copper cables in networks. Drew a diagram of the relationships between mobile phones, mobile phone radio towers, the mobile network, the worldwide telephone network, the Internet, home telephones, and web servers in the Internet. Concluded by introducing the basics of Wireless LANs.

53 53 Summary, This Chapter Compared and contrasted mobile phones, mobile company radio towers, wireless LAN NICs, and wireless LAN Access Points. Created an example demonstrating how devices share a wireless LAN using CSMA/CA.

54 Questions? Comments? 54