Data Stream Kuliah Multimedia

Who Says What in Which Channel To Whom With What Effect Computer Network / Telecommunication Network Komunikator / Sender Komunikan / Receiver text gambar grafik audio video Independesi media Diskrit Kontinyu Kombinasi Integrasi Distribusi A multimedia system is characterized by computer-controlled, integrated production, manipulation, presentation, storage and communication of independent information, which is encoded at least through a continuous (time-independent) and a discrete (time independent) medium. Multimedia : Computing, Communication & Applications page 17

Transmisi data Pada multimedia yang terditribusi (distributed multimedia/network base multimedia) data disitribusikan melalui jaringan transmisi dan switching. Informasi yang ditransmisikan dibagi-bagi menjadi paket-paket data.

Apa itu Data Stream ? Data Stream is “A sequence of individual packet transmitted in a time-dependent fashion” (suatu barisan paket yang ditransmisikan dlm modus yang tergantung waktu) Sinonim dari Data Stream adalah Data FLow Paket data (atau disingkat paket atau juga message/pesan) membawa informasi baik dari data dalam medium diskrit atau kontinyu Paket mengindikasikan data sudah dalam bentuk representasi digital

Representasi Data Stream Dn Waktu (t) Data stream mengalir dari source ke destinasi Paket data yang tersusun secara beurutan Berbentuk sinyal digital

Data stream tradisional Terdapat 3 mode transmisi data stream: Mode transmisi Asynchronous Refers to events that are not synchronized, or coordinated, in time. The following are considered asynchronous operations. The interval between transmitting A and B is not the same as between B and C. The ability to initiate a transmission at either end. The ability to store and forward messages. Starting the next operation before the current one is completed. Mode transmisi Synchronous Refers to events that are synchronized, or coordinated, in time. For example, the interval between transmitting A and B is the same as between B and C, and completing the current operation before the next one is started are considered synchronous operations. Mode transmisi Isochronous Isochronous transmission transmits asynchronous data over a synchronous data link so that individual characters are only separated by a whole number of bit-length intervals. An isochronous message protocol assigns each data source a fixed amount of time to transmit (its "slot") within each cycle through the sources. That guarantees that each source will have regular opportunities to transmit the latest information. If a source has no more data to transmit, then the rest of its time slot is wasted. If it has more to send than will fit in its slot, it has to either store the excess data and transmit it in its next slot, or discard it. Isochronous communication suits applications where a steady data stream is more important than completeness and accuracy, e.g. video conferencing. http://encyclopedia2.thefreedictionary.com/isochronous

Karakteristik data stream tradisional Mode transmisi Asynchronous Tidak ada batasan waktu transmisi paket Paket yg dikirimkan cepat Kebanyakah digunakan untuk media diskrit (misalnya: Email, Ethernet) Jika digunakan untuk mentransmisikan media kontinyu dapat dikombinasikan dengan menambahkan pembatasan waktu Contoh : Modem Asinkron Mode transmisi Synchronous Maksimum waktu delay end-to-end ditentukan. Manfaatnya untuk menghindari paket data yang hilang. Setiap pakettidak memiliki garansi sampai ke penerima.Oleh karena itu perlu buffer/storage temporer. Misalnya maksimal data rate video 140 Mbps dan maksimal delay dalam 1 detik Contohnya modem Sinkronous (HDLC,SDLC) Mode transmisi Isochronous Maksimum dan minimum waktu delay end-to-end ditentukan dan dilakukan garansi pada tiap paket. http://www.versitron.com/synchronous.htm http://www.comptechdoc.org/independent/networking/cert/netmodems.html

Mode transmisi Asynchronous Mode transmisi Syncrhronous Mode transmisi Isochronous The interval between transmitting A and S is not the same as between S and Y. S Y N C (t) The interval between transmitting S and Y is the same as between Y and N I S O (t) Isochronous transmission transmits asynchronous data over a synchronous data link

Karakteristik data stream pada media kontinyu Variasi Interval waktu antar paket (time interval) Strongly periodic Weakly periodic Aperiodic Variasi besar paket (packet amount / data size) Strongly regular stream Weakly regular stream Irregular stream Variasi paket yang bersebelahan (contiguous packet) Continuous stream without intermediate gaps Discrete stream with gaps

Strongly periodic Weakly periodic Aperiodic Contoh : sinyal telepon Yang dikodekan secara PCM T D1 D2 D3 D4 (t) Strongly periodic : jika interval antar paket bersifat konstan T Contoh : sinyal datastream Video terkompresi MPEG T1 T2 T3 T1 T2 D1 D2 D3 D4 D5 D6 (t) Weakly periodic : jika interval antar paket bersifat konstan hanya pada waktu terbatas, tetapi dalam waktu keseluruhan tidak konstan Contoh : sinyal data posisi Mouse yang ditransmisikan T1 T2 T3 T4 T5 D1 D2 D3 D4 D5 D6 (t) Aperiodic : Bukan weakly dan bukan pula strongly periodik

Strongly regular stream Weakly regular stream Irregular stream D1 T D1 D1 D2 T D2 D3 D3 D1 ….. D2 D1 D3 Dn t t t Strongly regular : jika Ukuran data (data size) Konstan untuk seluruh Paket Misal : datastream tanpa kompresi Weakly regular : jika Ukuran data paket (data size) berubah secara periodik Misal :datastream Mpeg Irregular : jika Ukuran data paket (data size) berubah secara acak

Continuous stream without intermediate gaps Discrete stream with gaps Dn ……. (t) Continuous stream : paket di transmisikan tanpa ada Gap (disebut juga dg Connected data) Misal : ISDN B-channel dengan data audio 64 kbps T D D1 D2 D3 Dn ……. (t) Discrete stream : terdapat Gap-gap diantara paket (disebut juga dg UnConnected data) Misalnya : transmisi datastraem pada JPEG

Information Units / Satuan informasi Disebut dengan LDU (Logical Data Unit) : yaitu informasi yang dianggap paling kecil dan bermakna, misalnya : Audio : data sample, grup sample dst Video : film,clip,frame,block,pixel dst Jenis LDU berdasarkan durasinya : Close LDU : durasi ditentukan sebelumnya (predifined duration), misalnya sampel data stream audio di dalam komputer Open LDU : durasi tidak bisa ditentukan didepan, misalnya :datastream dikirim dari kamera dan mic menuju komputer

LDU pada data video FILM Clip Frame Blok Pixel

Pustaka tambahan http://encyclopedia2.thefreedictionary.com/isochronous http://www.versitron.com/synchronous.htm http://www.comptechdoc.org/independent/networking/cert/netmodems.html