Datornätverk A – lektion 6 Kapitel 7: Transmissionsmedia Kapitel 8: Kretskoppling Bredbandsinfrastruktur Kapitel 9: Bredbandsaccesstekniker: DSL, Cable Modem.

Chapter 7 Transmission Media

Figure 7.2 Classes of transmission media

Figure 7.3 Twisted-pair cable (TP)

Figure 7.4 UTP (Unshielded TP) and STP (Shielded TP)

Table 7.1 Categories of unshielded twisted-pair cables Category Bandwidth Data Rate Digital/Analog Use 1 very low < 100 kbps Analog Telephone 2 < 2 MHz 2 Mbps Analog/digital T-1 lines 3 16 MHz 10 Mbps Digital LANs 4 20 MHz 20 Mbps 5 100 MHz 100 Mbps 6 (draft) 200 MHz 200 Mbps 7 (draft) 600 MHz 600 Mbps

Figure 7.5 UTP connector

Figure 7.7 Coaxial cable

Table 7.2 Categories of coaxial cables Category Impedance Use RG-59 75 W Cable TV RG-58 50 W Thin Ethernet RG-11 Thick Ethernet Ledningens karaktäristiska impedans är den impedans (eller resistans) ledningen skulle ha om den vore oändligt långt.

BNC-Bayonet Neill Concelman Figure 7.8 BNC connectors BNC-Bayonet Neill Concelman T-koppling

Ledningsreflektioner Se animering. Ledningsreflektioner kan orsaka s.k. stående vågor, som innebär att vissa frekvenser släcks ut i vissa punkter på ledningen. Reflektioner kan uppstå: om ledningar med olika karaktäristisk impedans kopplas samman, om en ledning får t.ex. en kläm- eller fuktskada, om långa ledningar parallellkopplas (t.ex. om man stoppar in en ledning mellan T-kopplingen och datorn som är längre än halva våglängden), eller om en ledning inte avslutas med en termineringsresistor som har samma resistans som ledningens karaktäristiska impedans.

Ledningsreflektioner (Forts) Viktigt vid bussnät baserade på koaxialkablar. Vid bussnät är nätverkskortet högohmigt, dvs avbrott. I ledningens båda ändar behövs en terminering på samma impedans som ledningen karaktäristiska impedans, t.ex. 50 Ohm vid Ethernet koaxialkabel. Vid TP-kablar innehåller Ethernetkortet en termineringsresistor, dvs det är lågohmigt. Därmed behövs ingen extra termineringsresistor. Men därför är det inte möjligt att ansluta flera datorer till samma TP-kabel, utan att det uppstår reflektioner. Datorerna måste anslutas till ett nätnav (hub) eller en växel (switch), och således bilda ett fysiskt eller logiskt stjärnnät.

Kabeltyper för Ethernet 10BASE5=Tjock Ethernet, 10Mbps, 500m avstånd, koaxial. 10BASE2=Tunn Ethernet, 10Mbps, 200m, koaxial. 10BASE-T, 10Mbps, 100m, TP=Tvinnad parkabel, hubnät. 100BASE-T=Fast Ethernet, 100Mbps, 100m, TP, hubnät. 1000BASE-T, 1000Mbps, TP, hubnät.

Kontaktdon för Ethernet

Figure 7.13 Modes

Figure 7.15 Fiber-optic cable connectors

Figure 7.16 Optical fiber performance

Figure 7.9 Coaxial cable performance

Figure 7.2 Classes of transmission media

Figure 7.17 Electromagnetic spectrum for wireless communication

Våglängd och frekvens Ju högre frekvens desto kortare våglängd.

Vågutbredning av radio- och mikrovågor Exempel: Radio-LAN använder ofta frekvensen 2.4GHz, dvs våglängden 300/2400 =0.125m. Radioskugga kan uppstå bakom föremål med storlek några våglängder (några dm i vårt exempel). Radiovågor dämpas kraftigt av metallnät, t.ex. armeringsjärn, med mindre hål än en halv våglängd (ca 6 cm i vårt fall). Metallnätet utgör då Faradays bur.

Kort avstånd eller line-of-sight 300 – 400GHz Line-of-sight Figure 7.19 Wireless transmission waves 30kHz – 2GHz 2 – 300GHz Kort avstånd eller line-of-sight 300 – 400GHz Line-of-sight Fjärrstyrning IRDA Broadcasting (radio och TV), Mobiltelefoni Mikrovågslänkar (två parabolantenner på två hus eller master) Satellitkommunikation Radio-LAN Korthållskommukation (t.ex. Bluetooth)

Används ofta vid radiovågor Figure 7.20 Omnidirectional antennas Används ofta vid radiovågor

Note: Radio waves are used for broadcast communications, such as radio and television, and paging systems.

Används ofta vid mikrovågslänkar och satellitkommunikaton Figure 7.21 Unidirectional antennas Används ofta vid mikrovågslänkar och satellitkommunikaton

Note: Infrared signals can be used for short- range communication in a closed area using line-of-sight propagation.

Circuit Switching and Telephone Network Chapter 8 Circuit Switching and Telephone Network

Telephone network – Local Switch The telephone network uses switches Every subscriber ( telephone jack in a house) has a twisted-pair wire connected to the closest telephone exchange. They are called local switches or local exchanges.  switch subscriber This cannot provide connection to subscribers connected to another local switch.

Switches What is a switch? A central device usually used with a star topology Can be built in hardware and/or software Used to provide temporary connections between any two devices connected to the switch A network of switches can be made if a very large number of devices spread in a large geographic space need to be connected

A Circuit Switch  Device with a number of inputs and outputs Creates temporary physical connection between an input and output link  Subscribers connected to the same swich The local switch can connect each telephone with each other

Figure 8.2 A circuit switch

Circuit Switching Three phases of the connection: Circuit establishment Data transfer Circuit disconnect The bandwidth is guaranteed during the connection The bandwidth cannot be used by anyone else, even if it is not needed at certain moment (no flexibility)

Figure 8.4 Crossbar switch

Figure 8.5 Multistage switch Space switching

Figure 8.6 Switching path

Figure 8.7 Time-division multiplexing, without and with a time-slot interchange

Figure 8.8 Time-slot interchange

Figure 8.10 TST switch (Time-Space-Time)

Characteristics of the Switches Space switches The advantage is that if a cross point is available, the connection is almost instantaneous The disadvantage is the need for many cross points which is expensive Time switches Advantage is that it does not need cross points Limited by the maximum data rate of one line. Introduces a fixed delay. Combined switches combine the advantages of both types

Figure 8.11 A telephone system Accessnät (Spridningsnät)

Hierarchy of the Telephone Network International network International gateway exchange National tandem exchanges regional tandem exchanges trunk network Tandem offices local tandem exchanges local network local exchanges (toll offices) subscriber lines (local loops)

Bredbandsaccess- tekniker Chapter 9 Bredbandsaccess- tekniker

Bredbands- infrastruktur Ethernet-LAN används ofta i flerfamiljshus

9.1 DSL Technology ADSL Other DSL Technologies

Note: ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses.

The existing local loops can handle bandwidths up to 1.1 MHz. Note: The existing local loops can handle bandwidths up to 1.1 MHz.

Note: ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop line.

Figure 9.2 Bandwidth division

Dicrete Multi-tone Modulation Figure 9.1 DMT Dicrete Multi-tone Modulation - Många långsamma modulatorer, var och en på olika underbärvågsfrekvens. Syfte: - Vid störningar på vissa frekvenser kan antal bit per symbol minskas endast på dem. - Långa symboler ger mindre känslighet för intersymbol-interferens.

ADSL Frequency Spectrum Divides the bandwidth into 256 x 4.3K channels 1 (ch 0) POTS, 5 (ch 1-5) not used, 1 upstream control, 1 downstream control Typical 6-30 for upstream, rest for downstream Each 4.3K channel 4K baud sample, V.34 QAM modulation, up to 15 bits per baud 4K * 15 = 60 Kbps per channel

Figure 9.3 ADSL modem

Figure 9.4 DSLAM

Other DSL Technologies SDSL (Symmetric DSL) divides frequencies evenly HDSL (High-rate DSL) provides DS1 bit rate in both directions Short distances Four wires VDSL (Very high bit rate DSL) provides up to 52 Mbps Very short distance Requires Optical Network Unit (ONU) as a relay

9.2 Cable Modem Traditional Cable Networks HFC Network Sharing CM and CMTS DOCSIS

Figure 9.5 Traditional cable TV network

Communication in the traditional cable TV network is unidirectional. Note: Communication in the traditional cable TV network is unidirectional.

Figure 9.6 HFC network

Communication in an HFC cable TV network can be bidirectional. Note: Communication in an HFC cable TV network can be bidirectional.

Figure 9.7 Coaxial cable bands

Downstream data are modulated using the 64-QAM modulation technique. Note: Downstream data are modulated using the 64-QAM modulation technique.

Upstream data are modulated using the QPSK modulation technique. Note: Upstream data are modulated using the QPSK modulation technique.

Figure 9.8 Cable modem

CMTS = Cable Modem Terminating System Figure 9.9 CMTS CMTS = Cable Modem Terminating System

Optical Hierarchies SONET (Synchronious Optical NETwork) A standard for TDM used in United States SDH (Synhronous Digital Hierarchy) A standard for TDM in Europe Both use synhronous communication Digital telephony systems use clocking for synchronous data delivery Synchronous network moves data at a precise rate

Note: SONET and SDH are synchronous TDM systems controlled by a master clock.

Figure 9.10 A SONET

Figure 9.11 Frame format

Table 9.1 SONET rates STS OC Rate (Mbps) SPE (Mbps) User (Mbps) STS-1 51.84 50.12 49.536 STS-3 OC-3 155.52 150.336 148.608 STS-9 OC-9 466.56 451.008 445.824 STS-12 OC-12 622.08 601.344 594.432 STS-18 OC-18 933.12 902.016 891.648 STS-24 OC-24 1244.16 1202.688 1188.864 STS-36 OC-36 1866.23 1804.032 1783.296 STS-48 OC-48 2488.32 2405.376 2377.728 STS-192 OC-192 9953.28 9621.604 9510.912

Figure 9.12 Data rate

Figure 9.13 VT types

Figure 9.14 STS multiplexing