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 6-Mar-07
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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 6-Mar-07
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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: g (t ) =
6-Mar-07
∞ ∞ 1 c + ∑ an sin(2πnft ) + ∑ bn cos(2πnft ) 2 n =1 n =1
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Contoh • Square wave: 4A
1 1 (cos ωt − cos 3ωt + cos 5ωt − ...) π 3 5
• Triangular wave: 8A
π
2
(cos ω t +
1 1 cos 3ω t + cos 5ω t + ...) 9 25
• Sawtooth wave: 2A
π 6-Mar-07
(sin ω t −
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1 1 sin 2ω t + sin 3ω t − ...) 2 3 5
• 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
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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 6-Mar-07
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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. 6-Mar-07
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Bandwidth-Limited Signals (2)
(d) – (e) Successive approximations to the original signal. 6-Mar-07
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Bandwidth-Limited Signals (3)
Hubungan antara data rate dengan harmonik untuk saluran yang memiliki bandwidth 3000 Hz (saluran telpon) 6-Mar-07
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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 6-Mar-07
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Guided Transmission Data • Twisted Pair • Coaxial Cable • Fiber Optics
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Twisted Pair
(a) Category 3 UTP. (b) Category 5 UTP. 6-Mar-07
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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
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Coaxial Cable A 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
6-Mar-07
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Fiber Optics
(a) Side view of a single fiber. (b) End view of a sheath with three fibers. 6-Mar-07
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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
6-Mar-07
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Fiber Optics
(a) Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles. (b) Light trapped by total internal reflection. 6-Mar-07
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Transmission of Light through Fiber
Attenuation of light through fiber in the infrared region. 6-Mar-07
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Fiber Cables (2)
A comparison of semiconductor diodes and LEDs as light sources. 6-Mar-07
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Wireless Transmission • • • • •
6-Mar-07
The Electromagnetic Spectrum Radio Transmission Microwave Transmission Infrared and Millimeter Waves Lightwave Transmission
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The Electromagnetic Spectrum
The electromagnetic spectrum and its uses for communication. λf = c 6-Mar-07
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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. 6-Mar-07
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Politics of the Electromagnetic Spectrum The ISM bands in the United States.
6-Mar-07
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Lightwave Transmission
Convection currents can interfere with laser communication systems. A bidirectional system with two lasers is pictured here. 6-Mar-07
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Communication Satellites • • • •
6-Mar-07
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. 6-Mar-07
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Communication Satellites (2)
The principal satellite bands. 6-Mar-07
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Communication Satellites (3)
VSATs using a hub. 6-Mar-07
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Low-Earth Orbit Satellites Iridium
(a)
(b)
(a) The Iridium satellites from six necklaces around the earth. (b) 1628 moving cells cover the earth. 6-Mar-07
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Globalstar
(a) Relaying in space. (b) Relaying on the ground. 6-Mar-07
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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 6-Mar-07
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Public Switched Telephone System • Structure of the Telephone System • The Local Loop: Modems, ADSL and Wireless • Trunks and Multiplexing • Switching
6-Mar-07
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Structure of the Telephone System
(a) fully-interconnected network. (b) Centralized switch. (c) Two-level hierarchy. 6-Mar-07
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Structure of the Telephone System (2)
A typical circuit route for a medium-distance call. 6-Mar-07
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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 6-Mar-07
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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 6-Mar-07
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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, fibre optics, radio and satellite transmission 6-Mar-07
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Modems
(a) A binary signal (c) Frequency modulation (b) Amplitude modulation IF-ITB/AI/Feb(d) 6-Mar-07 07 Phase modulation 41 IF3291 – Physical layer
Modems (2)
(a) QPSK: 1 symbol = 2 bit (b) QAM-16: 1 symbol = 4 bit (c) QAM-64: 1 symbol = 6 bit 6-Mar-07
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Modems (3)
(a)
(b)
(a) V.32 for 9600 bps. (TCM) (b) V32 bis for 14,400 bps. (QAM-128) 6-Mar-07
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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 • V92: 48 kbps upstream & 56 kbps downstream 6-Mar-07
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Digital Subscriber Lines
Bandwidth versus distanced over category 3 UTP for DSL. 6-Mar-07
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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) 6-Mar-07
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Digital Subscriber Lines (2)
Operation of ADSL using discrete multitone modulation. 6-Mar-07
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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)
6-Mar-07
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Digital Subscriber Lines (3)
A typical ADSL equipment configuration. 6-Mar-07
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Wireless Local Loops
Architecture of an LMDS system. 6-Mar-07
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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
6-Mar-07
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Frequency Division Multiplexing
(a) The original bandwidths. (b) The bandwidths raised in frequency. (b) The multiplexed channel. 6-Mar-07
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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
6-Mar-07
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Wavelength Division Multiplexing
Wavelength division multiplexing. 6-Mar-07
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Time Division Multiplexing
The T1 carrier (1.544 Mbps). Analog signals are converted into digital by using PCM
6-Mar-07
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Time Division Multiplexing (2)
Delta modulation. 6-Mar-07
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Time Division Multiplexing (3)
Multiplexing T1 streams into higher carriers. 6-Mar-07
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Time Division Multiplexing (4)
Two back-to-back SONET frames. 6-Mar-07
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Time Division Multiplexing (5)
SONET and SDH multiplex rates. 6-Mar-07
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Circuit Switching
6-Mar-07
(a) Circuit switching. (b) Packet IF-ITB/AI/Feb switching. 07
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Message Switching
(a) Circuit switching (b) Message switching (c) Packet switching 6-Mar-07
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Packet Switching
A comparison of circuit switched and packet-switched networks. 6-Mar-07
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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
6-Mar-07
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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 dahulu, sebelum tersambung ke base station baru 6-Mar-07
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Advanced Mobile Phone System
(a) Frequencies are not reused in adjacent cells. Frequencies are reused for every 7 cells 6-Mar-07 (b) To add more users,IF-ITB/AI/Feb smaller07cells can be used.
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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 • Data (bidirectional) for voice, fax, or data 6-Mar-07
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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 6-Mar-07
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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
6-Mar-07
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D-AMPS Digital Advanced Mobile Phone System
(a) A D-AMPS channel with three users. (b) A D-AMPS channel with six users. 6-Mar-07
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GSM Global System for Mobile Communications
GSM uses 124 frequency channels, each of which uses an eight-slot TDM system 6-Mar-07
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GSM (2)
A portion of the GSM framing structure. 6-Mar-07
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CDMA – Code Division Multiple Access
(a) Binary chip sequences for four stations (b) Bipolar chip sequences (c) Six examples of transmissions (d) Recovery of station C’s signal 6-Mar-07
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Third-Generation Mobile Phones: Digital Voice and Data Basic services an IMT-2000 network should provide • High-quality voice transmission • Messaging (replace e-mail, fax, SMS, chat, etc.) • Multimedia (music, videos, films, TV, etc.) • Internet access (web surfing, w/multimedia.) 6-Mar-07
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Cable Television • • • • •
6-Mar-07
Community Antenna Television Internet over Cable Spectrum Allocation Cable Modems ADSL versus Cable
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Community Antenna Television
An early cable television system. 6-Mar-07
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Internet over Cable
Cable television 6-Mar-07
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Internet over Cable (2)
The fixed telephone system. 6-Mar-07
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Spectrum Allocation
Frequency allocation in a typical cable TV system used for Internet access 6-Mar-07
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Cable Modems
Typical details of the upstream and downstream channels in North America. 6-Mar-07
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