Topik bahasan. IF3291 Jaringan Komputer & Pengamanannya Physical layer. Dasar teori komunikasi data Jenis media transmisi. Contoh sistem komunikasi:

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IF3291 – Jaringan Komputer &

Pengamanannya

Physical layer

Achmad Imam Kistijantoro Semester II 2006/2007

Topik bahasan

• Dasar teori komunikasi data • Jenis media transmisi

– Media transmisi kabel – Media transmisi tanpa kabel – Komunikasi satelit

• Contoh sistem komunikasi:

– PSTN

– Sistem telpon mobile – TV Kabel

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6-Mar-07 IF-ITB/AI/Feb 07

IF3291 – Physical layer 3

Topik bahasan

• Dasar teori komunikasi data

• Jenis media transmisi

– PSTN

Dasar teori komunikasi data

• Informasi/data dikirimkan berupa sinyal, misalnya pada medium kabel, berupa

arus/tegangan sebagai fungsi dari waktu, g(t) • Setiap sinyal, selalu dinyatakan sebagai

komposisi dari gelombang sinusoida yang jumlahnya tak terhingga, dengan menggunakan formula fourier: ) 2 cos( ) 2 sin( 2 1 ) ( 1 1 nft b nft a c t g n n n n π

∑

π

∑

∞ = ∞ = + + =

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• Square wave: • Triangular wave: • Sawtooth wave:

Contoh

...) 5 cos 5 1 3 cos 3 1 (cos 4 − + − t t t A _ω _ω _ω π ...) 5 cos 25 1 3 cos 9 1 (cos 8 2 t+ t+ t+ A _ω _ω _ω π ...) 3 sin 3 1 2 sin 2 1 (sin 2 ₋ ₊ ₋ t t t A _ω _ω _ω π • Sinyal (c) adalah komposisi dari sinyal

– (a): sin( 2 ft ) – (b) 1/3 sin ( 2 (3f)t )

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• Dengan mengetahui frekuensi sinyal

komponennya, kita dapat menggambarkan sinyal yang sama dalam domain frekuensi

– (a) sinyal yang sama dengan slide sebelumnya – (b) sinyal berupa sebuah

kotak yang memiliki lebar x

Teori dasar komunikasi data

• Komponen sinyal yang diperlukan untuk membentuk sebuah sinyal tertentu dapat tak terbatas

• Setiap media memiliki keterbatasan dalam

mengirimkan sinyal. Umumnya hanya beberapa komponen frekuensi awal yang tidak mengalami pelemahan.

• Lebar frekuensi yang dapat diteruskan sebuah media tanpa mengalami pelemahan yang berarti disebut sebagai bandwidth

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Bandwidth-Limited Signals

A binary signal and its root-mean-square Fourier amplitudes.

(b) – (c)Successive approximations to the original signal.

Bandwidth-Limited Signals (2)

(d) – (e)Successive approximations to the original signal.

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Bandwidth-Limited Signals (3)

Hubungan antara data rate dengan harmonik untuk saluran yang memiliki bandwidth 3000 Hz (saluran telpon)

Topik bahasan

• Dasar teori komunikasi data

• Jenis media transmisi

– PSTN

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Guided Transmission Data

• Twisted Pair

• Coaxial Cable

• Fiber Optics

Twisted Pair

(a)Category 3 UTP.

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Twisted pair

• Twisting: menghindari kabel beroperasi sebagai antena • Cat 3: digunakan untuk komunikasi telpon (max 16 MHz) • Cat 5: digunakan untuk jaringan LAN/ethernet (max 100

MHz)

• Sinyal analog: memerlukan repeater setiap 5-6 km • Sinyal digital: memerlukan repeater setiap 2-3 km • murah

Coaxial Cable

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Coaxial cable

• Mampu menangani frekuensi lebih tinggi dibandingkan TP

• Kapasitas bandwidth dapat mencapai 1GHz • Analog: transmisi TV, telpon jarak jauh

(digantikan fiber sekarang)

• Digital: jaringan ethernet. Memerlukan repeater setiap < 1 km

Fiber Optics

(a)Side view of a single fiber.

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Fiber Optics

• Kapasitas besar, hingga ratusan GBps • Berukuran lebih kecil dan ringan

• Pelemahan sinyal tidak besar, memerlukan repeater setelah lebih dari puluhan km

Fiber Optics

(a)Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles.

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Transmission of Light through Fiber

Attenuation of light through fiber in the infrared region.

Fiber Cables (2)

A comparison of semiconductor diodes and LEDs as light sources.

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Wireless Transmission

• The Electromagnetic Spectrum

• Radio Transmission

• Microwave Transmission

• Infrared and Millimeter Waves

• Lightwave Transmission

The Electromagnetic Spectrum

The electromagnetic spectrum and its uses for communication.

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Radio Transmission

(a)In the VLF, LF, and MF bands, radio waves follow the curvature of the earth.

(b)In the HF band, they bounce off the ionosphere.

Politics of the Electromagnetic

Spectrum

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Lightwave Transmission

Convection currents can interfere with laser communication systems. A bidirectional system with two lasers is pictured here.

Communication Satellites

• Geostationary Satellites

• Medium-Earth Orbit Satellites

• Low-Earth Orbit Satellites

• Satellites versus Fiber

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Communication Satellites

Communication satellites and some of their properties, including altitude above the earth, round-trip delay time and number of

satellites needed for global coverage.

Communication Satellites (2)

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Communication Satellites (3)

VSATs using a hub.

Low-Earth Orbit Satellites

Iridium

(a)The Iridium satellites from six necklaces around the earth.

(b)1628 moving cells cover the earth.

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Globalstar

(a) Relaying in space.

(b) Relaying on the ground.

Topik bahasan

• Dasar teori komunikasi data • Jenis media transmisi

• Contoh sistem komunikasi:

– PSTN

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Public Switched Telephone System

• Structure of the Telephone System

• The Local Loop: Modems, ADSL and

Wireless

• Trunks and Multiplexing

• Switching

Structure of the Telephone System

(a)fully-interconnected network.

(b)Centralized switch.

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Structure of the Telephone System

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A typical circuit route for a medium-distance call.

Major Components of the

Telephone System

• Local loops

Analog twisted pairs going to houses and businesses

• Trunks

Digital fiber optics connecting the switching offices

• Switching offices

Where calls are moved from one trunk to another

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The Local Loop: Modems,

ADSL, and Wireless

The use of both analog and digital transmissions for a computer to computer call. Conversion is done by the modems and codecs.

Three major problems: attenuation, distortion & noise

Modem

• Digital signal requires a wide frequency

spectrum for transmission, which is unsuitable to be used on telephone line

• Modem translates digital data to/from analogue form for transmission over analogue media

• Codec: a software module that can also be used to translate between analogue and digital form • Modems are used for twisted pair, coaxial cable,

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Modems

(a) A binary signal

(b) Amplitude modulation

(c)Frequency modulation

(d)Phase modulation

Modems (2)

(a)QPSK: 1 symbol = 2 bit

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Modems (3)

(a)V.32 for 9600 bps. (TCM)

(b)V32 bis for 14,400 bps. (QAM-128)

(a) (b)

Modems (4)

• A modem/connection that allows traffic in both directions is called full duplex

• A connection that allows traffic either way, only one way at a time: half duplex

• A connection that allows traffic only one way is called simplex

• V.90 modem: capable of transmitting 33.6 kbps upstream & 56 kbps downstream

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Digital Subscriber Lines

Bandwidth versus distanced over category 3 UTP for DSL.

Digital Subscriber Lines

• DSL service criteria

– Work over existing cat 3 twisted pair local loops – Must not affect existing telephones and fax services – Much faster than 56 kbps

– Always on, no per-minute charge

• Initial solution:

– Dividing 1.1 MHz spectrum into 3 bands: POTS, upstream & downstream

• Better solution:

– Dividing 1.1 MHz into 256 channels of 4312.5 Hz each (Discrete multitone)

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Digital Subscriber Lines (2)

Operation of ADSL using discrete multitone modulation.

Digital Subscriber Lines

• Many providers choose to allocate more

bandwidth for downstream -> Asymmetric DSL • Use a modulation scheme similar to V.34, with sampling rate 4000 baud, and 15 bits per baud (symbol)

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Digital Subscriber Lines (3)

A typical ADSL equipment configuration.

Wireless Local Loops

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Trunks & Multiplexing

• Multiplexing allows the carrying of multiple signals on a single medium.

• e,.g. : frequency division multiplexing, time division multiplexing

Frequency Division Multiplexing

(a)The original bandwidths.

(b)The bandwidths raised in frequency.

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Frequency Division Multiplexing

• Filters are used at receiver to separate channels and remove carriers

• CCITT standards: 12 of 4 kHz voice channels are multiplexed into 60 kHz – 108 kHz called

group

• 5 groups (60 voice channels) form supergroup

• 5 supergroups form mastergroup

Wavelength Division Multiplexing

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Time Division Multiplexing

The T1 carrier (1.544 Mbps).

Analog signals are converted into digital by using PCM

Time Division Multiplexing (2)

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Time Division Multiplexing (3)

Multiplexing T1 streams into higher carriers.

Time Division Multiplexing (4)

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Time Division Multiplexing (5)

SONET and SDH multiplex rates.

Circuit Switching

(a)Circuit switching.

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Message Switching

(a)Circuit switching (b)Message switching (c) Packet switching

Packet Switching

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The Mobile Telephone System

• First-Generation Mobile Phones:

Analog Voice

• Second-Generation Mobile Phones:

Digital Voice

• Third-Generation Mobile Phones:

Digital Voice and Data

Analog voice: AMPS

• Dikembangkan oleh Bell Labs pada tahun 1982

• Menggunakan sistem cell: area geografis dibagi menjadi sel-sel kecil berukuran 10-20 km:

– Frequency reuse

– Handset dapat menggunakan daya lebih rendah untuk mengakses base station

• Pada setiap saatnya, seorang pengguna akan berada pada lokasi sel tertentu.

• Proses perpindahan pengguna dari satu sel ke sel lainnya pada saat terjadi percakapan aktif disebut sebagai hand-off.

• Soft hand-off: tanpa melalui pemutusan hubungan • Hard hand-off: hubungan dengan base lama terputus

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Advanced Mobile Phone System

(a)Frequencies are not reused in adjacent cells. Frequencies are reused for every 7 cells

(b)To add more users, smaller cells can be used.

Channel Categories

Frequency allocation: 824-849 MHz (mobile to base station), 869-894 MHz (base station to mobile) The 832 channels (30 kHz wide) are divided into

four categories:

• Control (base to mobile) to manage the system • Paging (base to mobile) to alert users to calls for

them

• Access (bidirectional) for call setup and channel assignment

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Channel allocation

• Control, access & paging dikelompokkan bersama menjadi control channel.

• 832 channel (full duplex) dibagi 2 (untuk 2 provider pada area yg sama), masing2 416 channel

• 21 channel digunakan untuk control (data/digital: 10 kbps) 1 channel untuk setiap sel, 395 untuk user (voice), dibagi per sel. Untuk alokasi sel dengan faktor 7, maka per sel mendapat 395/7 = 57 channel

Call management

• Saat handset dinyalakan: scan 21 control channel untuk mencari sinyal terkuat (memilih sel)

• Handset kemudian mengirim informasi serial number handset & nomor telpon

• MTSO mencatat informasi pengguna & lokasinya • Untuk memanggil: handset mengirimkan nomor tujuan

via access channel. Jika ada channel tersedia, base station mengalokasikan channel data tersebut, dan handset mendengarkan channel untuk melakukan panggilan