Michael Ivan

The most important data link control protocol is HDLC (IS0 33009, IS0 4335). Not
only is HDLC widely used, but it is the basis for many other important data link
control protocols, which use the same or similar formats and the same mechanisms
as employed in HDLC. Accordingly, in this section we provide a detailed discussion
of HDLC. Section 6.5 surveys related protocols.
Basic Characteristics
To satisfy a variety of applications, HDLC defines three types of stations, two link
configurations, and three data-transfer modes of operation. The three station types
are :
Primary station. Has the responsibility for controlling the operation of the
link. Frames issued by the primary are called commands.
Secondary station. Operates under the control of the primary station. Frames
6.4 / HIGH-LEVEL DATA LINK CONTROL (HDLC) 177
issued by a secondary are called responses. The primary maintains a separate
logical link with each secondary station on the line.
Combined station. Combines the features of primary and secondary. A combined
station may issue both commands and responses.

The two link configurations are

Unbalanced configuration. Consists of one primary and one or more secondary
stations and supports both full-duplex and half-duplex transmission.
Balanced configuration. Consists of two combined stations and supports both
full-duplex and half-duplex transmission.

The three data transfer modes are

Normal response mode (NRM). Used with an unbalanced configuration. The
primary may initiate data transfer to a secondary, but a secondary may only
transmit data in response to a command from the primary.
Asynchronous balanced mode (ABM). Used with a balanced configuration.
Either combined station may initiate transmission without receiving permission
from the other combined station.
Asynchronous response mode (ARM). Used with an unbalanced configuration.
The secondary may initiate transmission without explicit permission of
the primary. The primary still retains responsibility for the line, including initialization,
error recovery, and logical disconnection.

NRM is used on mulitdrop lines, in which a number of terminals are connected
to a host computer. The computer polls each terminal for input. NRM is also
sometimes used on point-to-point links, particularly if the link connects a terminal
or other peripheral to a computer. ABM is the most widely used of the three modes;
it makes more efficient use of a full-duplex point-to-point link as there is no polling
overhead. ARM is rarely used; it is applicable to some special situations in which a
secondary may need to initiate transmission.

Frame Structure
HDLC uses synchronous transmission. All transmissions are in the form of frames,
and a single frame format suffices for all types of data and control exchanges.
Figure 6.10a depicts the structure of the HDLC frame. The flag, address, and
control fields that precede the information field are known as a header. The FCS
and flag fields following the data field are referred to as a trailer.
Flag Fields
Flag fields delimit the frame at both ends with the unique pattern 01111110. A single
flag may be used as the closing flag for one frame and the opening flag for the
next. On both sides of the user-network interface, receivers are continuously hunting
for the flag sequence to synchronize on the start of a frame. While receiving a frame, a station continues to hunt for that sequence to determine the end of the
frame. However, it is possible that the pattern 01111110 will appear somewhere
inside the frame, thus destroying frame-level synchronization. To avoid this, a procedure
known as bit stuffing is used. Between the transmission of the starting and
ending flags, the transmitter will always insert an extra 0 bit after each occurrence
of five Is in the frame. After detecting a starting flag, the receiver monitors the bit
stream. When a pattern of five 1s appears, the sixth bit is examined. If this bit is 0,
it is deleted. If the sixth bit is a 1 and the seventh bit is a 0, the combination is
accepted as a flag. If the sixth and seventh bits are both 1, the sender is indicating
an abort condition.
With the use of bit stuffing, arbitrary bit patterns can be inserted into the data
field of the frame. This property is known as data transparency.
Figure 6.11a shows an example of bit stuffing. Note that in the first two cases,
the extra 0 is not strictly necessary for avoiding a flag pattern, but is necessary for
the operation of the algorithm. The pitfalls of bit stuffing are also illustrated in this figure. When a flag is used as both an ending and a starting flag, a 1-bit error merges
two frames into one; conversely, a 1-bit error inside the frame could split it in two.

Address Field
The address field identifies the secondary station that transmitted or is to receive
the frame. This field is not needed for point-to-point links, but is always included
for the sake of uniformity. The address field is usually eight bits long but, by prior
agreement, an extended format may be used in which the actual address length is a
multiple of seven bits (Figure 6.10b). The least significant bit of each octet is 1 or 0,
depending on whether it is or is not the last octet of the address field. The remaining
seven bits of each octet form part of the address. The single-octet address of
11111111 is interpreted as the all-stations address in both basic and extended
formats. It is used to allow the primary to broadcast a frame for reception by all
secondaries.
Control Field
HDLC defines three types of frames, each with a different control field format.
Information frames (I-frames) carry the data to be transmitted for the user (the
logic above HDLC that is using HDLC). Additionally, flow- and error-control data,
180 CHAPTER 6 / DATA LINK CONTROL
using the ARQ mechanism, are piggybacked on an information frame. Supervisory
frames (S-frames) provide the ARQ mechanism when piggybacking is not used.
Unnumbered frames (U-frames) provide supplemental link control functions. The
first one or two bits of the control field serves to identify the frame type. The
remaining bit positions are organized into subfields as indicated in Figure 6.10~an d
d. Their use is explained below in the discussion of HDLC operation.
Note that the basic control field for S- and I-frames uses 3-bit sequence numbers.
With the appropriate set-mode command, an extended control field can be
used for S- and I-frames that employs 7-bit sequence numbers. U-frames always
contain an &bit control field.
Information Field
The information field is present only in I-frames and some U-frames. The field can
contain any sequence of bits but must consist of an integral number of octets. The
length of the information field is variable up to some system-defined maximum.
Frame Check Sequence Field
The frame check sequence (FCS) is an error-detecting code calculated from the
remaining bits of the frame, exclusive of flags. The normal code is the 16-bit CRCCCITT
defined in Section 6.2. An optional 32-bit FCS, using CRC-32, may be
employed if the frame length or the line reliability dictates this choice.
Operation
HDLC operation consists of the exchange of I-frames, S-frames, and U-frames
between two stations. The various commands and responses defined for these frame
types are listed in Table 6.1. In describing HDLC operation, we will discuss these
three types of frames.
The operation of HDLC involves three phases. First, one side or another initializes
the data link so that frames may be exchanged in an orderly fashion. During
this phase, the options that are to be used are agreed upon. After initialization, the
two sides exchange user data and the control information to exercise flow and error
control. Finally, one of the two sides signals the termination of the operation.
Initialization
Initialization may be requested by either side by issuing one of the six set-mode
commands. This command serves three purposes:
1. It signals the other side that initialization is requested.
2. It specifies which of the three modes (NRM, ABM, ARM) is requested.
3. It specifies whether 3- or 7-bit sequence numbers are to be used.
If the other side accepts this request, then the HDLC module on that end
transmits an unnumbered acknowledged (UA) frame back to the initiating side. If
the request is rejected, then a disconnected mode (DM) frame is sent.
Data Transfer
When the initialization has been requested and accepted, then a logical connection
is established. Both sides may begin to send user data in I-frames, starting with
sequence number 0. The N(S) and N(R) fields of the I-frame are sequence numbers
that support flow control and error control. An HDLC module sending a sequence
of I-frames will number them sequentially, modulo 8 or 128, depending on whether
3- or 7-bit sequence numbers are used, and place the sequence number in N(S).
N(R) is the acknowledgment for I-frames received; it enables the HDLC module to indicate which number I-frame it expects to receive next.
S-frames are also used for flow control and error control. The receive-ready
(RR) frame is used to acknowledge the last I-frame received by indicating the next
I-frame expected. The RR is used when there is no reverse-user data traffic (Iframes)
to carry an acknowledgment. Receive-not-ready (RNR) acknowledges an
I-frame, as with RR, but also asks the peer entity to suspend transmission of Iframes.
When the entity that issued RNR is again ready, it sends an RR. REJ initiates
the go-back-N ARQ. It indicates that the last I-frame received has been
rejected and that retransmission of all I-frames beginning with number N(R) is
required. Selective reject (SREJ) is used to request retransmission of just a single
frame.
Disconnect
Either HDLC module can initiate a disconnect, either on its own initiative if there
is some sort of fault, or at the request of its higher-layer user. HDLC issues a disconnect
by sending a disconnect (DISC) frame. The other side must accept the disconnect
by replying with a UA.
Examples of Operation
In order to better understand HDLC operation, several examples are presented in
Figure 6.12. In the example diagrams, each arrow includes a legend that specifies
the frame name, the setting of the PIF bit, and, where appropriate, the values of
N(R) and N(S). The setting of the P or F bit is 1 if the designation is present and 0
if absent.
Figure 6.12a shows the frames involved in link setup and disconnect. The
HDLC protocol entity for one side issues an SABM command to the other side and
starts a timer. The other side, upon receiving the SABM, returns a UA response
and sets local variables and counters to their initial values. The initiating entity
receives the UA response, sets its variables and counters, and stops the timer. The
logical connection is now active, and both sides may begin transmitting frames.
Should the timer expire without a response, the originator will repeat the SABM,
as illustrated. This would be repeated until a UA or DM is received or until, after a
given number of tries, the entity attempting initiation gives up and reports failure to
a management entity. In such a case, higher-layer intervention is necessary. The
same figure (Figure 6.12a) shows the disconnect procedure. One side issues a DISC
command, and the other responds with a UA response.
Figure 6.12b illustrates the full-duplex exchange of I-frames. When an entity
sends a number of I-frames in a row with no incoming data, then the receive
sequence number is simply repeated (e.g., I, 1, 1; I, 2, 1 in the A-to-B direction).
When an entity receives a number of I-frames in a row with no outgoing frames,
then the receive sequence number in the next outgoing frame must reflect the
cumulative activity (e.g., I, 1, 3 in the B-to-A direction). Note that, in addition to
I-frames, data exchange may involve supervisory frames.
Figure 6.12~sh ows an operation involving a busy condition. Such a condition
may arise because an HDLC entity is not able to process I-frames as fast as they are because it is out of order and sends an REJ with an N(R) of 4. This causes A to initiate
retransmission of all I-frames sent, beginning with frame 4. It may continue to
send additional frames after the retransmitted frames.
An example of error recovery using a timeout is shown in Figure 6.12e. In this
example, A transmits I-frame number 3 as the last in a sequence of I-frames. The
frame suffers an error. B detects the error and discards it. However, B cannot send
an REJ; this is because there is no way to know if this was an I-frame. If an error is
detected in a frame, all of the bits of that frame are suspect, and the receiver has no
way to act upon it. A, however, would have started a timer as the frame was transmitted.
This timer has a duration long enough to span the expected response time.
When the timer expires, A initiates recovery action; this is usually done by polling
the other side with an RR command with the P bit set, to determine the status of
the other side. Because the poll demands a response, the entity will receive a frame
containing an N(R) field and be able to proceed. In this case, the response indicates that frame 3 was lost, which A retransmits.
These examples are not exhaustive. However, they should give the reader a
good feel for the behavior of HDLC.

OTHER DATA LINK CONTROL PROTOCOLS
In addition to HDLC, there are a number of other important data link control protocols.
Figure 6.13 illustrates the frame formats, and this section provides a brief
overview.
LAPB
LAPB (Link Access Procedure, Balanced) was issued by ITU-T as part of its X.25
packet-switching network-interface standard. It is a subset of HDLC that provides
only the asynchronous balanced mode (ABM); it is designed for the point-to-point
link between a user system and a packet-switching network node. Its frame format
is the same as that of HDLC.
LAPD
LAPD (Link Access Procedure, D-Channel) was issued by ITU-T as part of its set
of recommendations on ISDN (Integrated Services Digital Network). LAPD provides
data link control over the D channel, which is a logical channel at the user-
ISDN interface.
There are several key differences between LAPD and HDLC. Like LAPB,
LAPD is restricted to ABM. LAPD always uses 7-bit sequence numbers; 3-bit
sequence numbers are not allowed. The FCS for LAPD is always the 16-bit CRC.
Finally, the address field for LAPD is a 16-bit field that actually contains two subaddresses:
one is used to identify one of possibly multiple devices on the user side
of the interface, and the other is used to identify one of possibly multiple logical
users of LAPD on the user side of the interface.
Logical Link Control (LLC)
LLC is part of the IEEE 802 family of standards for controlling operation over a
local area network (LAN). LLC is lacking some features found in HDLC and also
has some features not found in HDLC.
The most obvious difference between LLC and HDLC is the difference in
frame format. Link control functions in the case of LLC are actually divided
between two layers: a medium access control (MAC) layer, and the LLC layer,
which operates on top of the MAC layer.
Figure 6 . 1 3~sh ows the structure of the combined MACILLC frame; the
shaded portion corresponds to the fields produced at the LLC layer, and the
unshaded portions are the header and trailer of the MAC frame. The MAC layer
includes source and destination addresses for devices attached to the LAN. Two
addresses are needed as there is no concept of primary and secondary in the LAN
environment; therefore, both the sender and receiver must be identified. Error
detection is done at the MAC level, using a 32-bit CRC. Finally, there are some control functions peculiar to medium-access control that may be included in a MAC
control field.
At the LLC layer, there are four fields. The destination and source service
access points (DSAP and SSAP), identify the logical user of LLC at the source and
destination systems. The LLC control field has the same format as that of HDLC,
limited to 7-bit sequence numbers.
Operationally, LLC offers three forms of service. The connection-mode service
is the same as the ABM of HDLC. The other two services, unacknowledged
connectionless and acknowledged connectionless, are described in Part 11.
Frame Relay
Frame relay is a data link control facility designed to provide a streamlined capability
for use over high-speed packet-switched networks. It is used in place of X.25,
which consists of both a data link control protocol (LAPB) and a network-layer
protocol (called X.25 packet layer). Frame relay is examined in detail in Part 11.
The data link control protocol defined for frame relay is LAPF (Link Access
Procedure for Frame-Mode Bearer Services). There are actually two protocols: a
control protocol, which has similar features to HDLC, and a core protocol, which is
a subset of the control pyotocol.
There are several key differences between the LAPF control protocol and
HDLC. Like LAPB, LAPF control is restricted to ABM. LAPF control always uses
7-bit sequence numbers; 3-bit sequence numbers are not allowed. The FCS for
LAPF control is always the 16-bit CRC. Finally, the address field for LAPF control
is two, three, or four octets long, containing a 10-bit, 16-bit, or 23-bit DLCI (data
link connection identifier). The DLCI identifies a logical connection between a
source and destination system. In addition, the address field contains some control
bits that are useful for flow control purposes.
The LAPF core consists of the same flag, address, information, and FCS fields
as LAPF control. The difference is that there is no control field for LAPF core.
Thus, there is no means of doing flow and error control, which results in a more
streamlined operation.
Asynchronous Transfer Mode (ATM)
Like frame relay, ATM is designed to provide a streamlined data-transfer capability
across high-speed networks. Unlike frame relay, ATM is not based on HDLC.
Instead, ATM is based on a completely new frame format, known as a cell, that provides
minimum processing overhead.
The cell has a fixed length of 53 octets, or 424 bits. The details of the ATM cell
fields are discussed in Part 11

Protokol bluetooth menggunakan sebuah kombinasi antara circuit switching dan packet

Empty Life

Dia kembali menulis tentang kehidupannya, dimana dia merasa hidupnya benar-benar terasa kosong sekarang. Belum lama ini dia sempat menonton film drama seri, dan di film tersebut benar-benar mencerminkan kehidupannya yang sekarang ia rasakan. Kadang ia bertanya, bukan bahkan ia selalu bertanya kenapa ia terlahir dengan sifat sperti ini. Gengsi yang dimiliknya sangat tinggi yang mengakibatkan ia sering kehilangan something important in his life. Kenapa mulutnya sangatlah sulit untuk mengungkapkan isi hatinya, ia hanya bisa memendamnya bahkan membiarkan dirinya sakit karena sifatnya tersebut. Sekarang disaat seperti ini yang dia bisa lakukan hanya menyalahkan dirinya sendiri dan mengasihani dirinya yang memalukan tersebut. Hari ini dia bertemu dengan seseorang yang disebutkan dalam his fucking whole life was gone, tapi apa yang bisa dia perbuat?? Dia hanya terdiam tanpa dapat mengatakan apapun yang bisa mempertahankan his fucking whole life. Mengapa mulutnya sangatlah berat untuk mengucapkan kalimat yang diharapkan oleh his fucking whole life? yang sebenarnya juga diharapkan oleh dirinya. Namun semuanya telah berlalu, dia hanya bisa menyesalinya sekarang. His fucking whole life is really gone now, dengan seseorang yang tidak dicintainya. Disaat inilah dia percaya bahwa karma itu benar-benar ada, dah ia tidak ingin his fucking whole life tersebut merasakannya walaupun itu harus menyakiti hatinya sendiri. He really get an empty life now!!!

SISTEM

Sistem berasal dari bahasa Latin (systēma) dan bahasa Yunani (sustēma) adalah suatu kesatuan yang terdiri komponen atau elemen yang dihubungkan bersama untuk memudahkan aliran informasi, materi atau energi. Istilah ini sering dipergunakan untuk menggambarkan suatu set entitas yang berinteraksi, di mana suatu model matematika seringkali bisa dibuat.

Sistem juga merupakan kesatuan bagian-bagian yang saling berhubungan yang berada dalam suatu wilayah serta memiliki item-item penggerak, contoh umum misalnya seperti negara. Negara merupakan suatu kumpulan dari beberapa elemen kesatuan lain seperti provinsi yang saling berhubungan sehingga membentuk suatu negara dimana yang berperan sebagai penggeraknya yaitu rakyat yang berada dinegara tersebut.

Kata "sistem" banyak sekali digunakan dalam percakapan sehari-hari, dalam forum diskusi maupun dokumen ilmiah. Kata ini digunakan untuk banyak hal, dan pada banyak bidang pula, sehingga maknanya menjadi beragam. Dalam pengertian yang paling umum, sebuah sistem adalah sekumpulan benda yang memiliki hubungan di antara mereka.

Elemen dalam sistem

Pada prinsipnya, setiap sistem selalu terdiri atas empat elemen:

• Objek, yang dapat berupa bagian, elemen, ataupun variabel. Ia dapat benda fisik, abstrak, ataupun keduanya sekaligus; tergantung kepada sifat sistem tersebut.

• Atribut, yang menentukan kualitas atau sifat kepemilikan sistem dan objeknya.

• Hubungan internal, di antara objek-objek di dalamnya.

• Lingkungan, tempat di mana sistem berada.

Jenis sistem

Ada berbagai tipe sistem berdasarkan kategori:

• Atas dasar keterbukaan:

  • sistem terbuka, dimana pihak luar dapat mempengaruhinya.

  • sistem tertutup.

• Atas dasar komponen:

  • Sistem fisik, dengan komponen materi dan energi.

  • Sistem non-fisik atau konsep, berisikan ide-ide.

Sistem juga berkaitan dengan suatu jaringan kerja dari prosedur-prosedur yang saling berhubungan, berkumpul bersama-sama untuk melakukan suatu kegiatan atau untuk menyelesaikan suatu sasaran tertentu.

Esensinya sistem terdiri dari:

1. Komponen-komponen dalam sistem tersebut, mencakup

   - perangkat keras/,

   - perangkat lunak/software,

   - prosedur - prosedur/procedure,

   - perangkat manusia/brainware, dan

   - informasi/information itu sendiri;

2. Serta fungsi-fungsi teknologi di dalamnya yaitu:

   - input,

   - proses/process,

   - output,

   - penyimpanan/storage dan

   - komunikasi/communication.

Berikut ini adalah definisi sistem menurut definisi.net :

PENGERTIAN SISTEM

1. DEFINISI SISTEM

Sistem adalah sekumpulan unsur / elemen yang saling berkaitan dan saling mempengaruhi dalam melakukan kegiatan bersama untuk mencapai suatu tujuan.

Contoh :

Sistem Komputer terdiri dari :

- Software

- Hardware

- Brainware

Sistem Akuntansi

2. KARAKTERISTIK SISTEM

Suatu sistem mempunyai beberapa karakteristik yaitu :

a. Komponen / elemen (component)

b. Batas sistem (boundary)

c. Lingkungan luar sistem (environment)

d. Penghubung (interface)

e. Masukan (input)

f. Pengolah (process)

g. Keluaran (output)

h. Sasaran (objective) atau tujuan (goal)

i. Komponen / elemen (component)

Suatu sistem terdiri dari komponen yang saling berinteraksi , artinya saling bekerja sama membentuk satu kesatuan. Komponen - komponen dari suatu sistem biasanya dikenal dengan subsistem.

Subsistem ini mempunyai sifat-sifat dari sistem itu sendiri dalam menjalankan suatu fungsi tertentu dan mempengaruhi proses sistem secara keseluruhan.

Suatu sistem juga mempunyai sistem yang lebih besar yang dikenal dengan Suprasistem.

Contoh :

Jika suatu perusahaan dipandang sebagai suatu sistem , maka industri akan dipandang sebagai Suprasistem.

Batas Sistem (boundary)

Batas sistem merupakan daerah yang membatasi antara sistem yang satu dengan sistem lainnya atau dengan lingkungan luarnya. Dengan adanya batas sistem ini maka sistem dapat membentuk suatu kesatuan, karena dengan batas sistem ini fungsi dan tugas dari subsistem yang satu dengan lainnya berbeda tetapi tetap saling berinteraksi. Dengan kata lain batas sistem ini merupakan ruang lingkup atau scope dari sistem / subsistem itu sendiri.

Contoh :

Sistem Keuangan - Sistem Akuntansi

- Kasir

- Administrasi Keuangan

- Personalia

Lingkungan Luar Sistem (Environment)

Segala sesuatu diluar dari batas sistem yg mempengaruhi operasi dari suatu sistem disebut Lingkungan luar sistem (environment). Lingkungan luar sistem ini dapat bersifat menguntungkan atau merugikan.

Lingkungan luar yang bersifat menguntungkan harus dipelihara dan dijaga agar tidak hilang pengaruhnya , sedangkan lingkungan yang bersifat merugikan harus dimusnahkan dan dikendalikan agar tidak mengganggu operasi dari sistem.

Penghubung Sistem (Interface)

Penghubung Sistem merupakan suatu media penghubung antara satu subsistem dengan subsistem lainnya untuk membentuk satu kesatuan, sehingga sumber-sumber daya mengalir dari subsistem yang satu ke subsistem lainnya. Dengan kata lain melalui penghubung ini output dari suatu subsistem akan menjadi input sari subsistem lainnya.

Masukan(Input)

Energi yang dimasukkan ke dalam suatu sistem disebut INPUT. Masukan ini dapat berupa : - Masukan Perawatan (Maintenance Input)

Yaitu energi yang dimasukkan supaya sistem itu dapat beroperasi.

Contoh : Program untuk mengoperasikan komputer.

- Masukan Sinyal (signal input)

Yaitu energi yang diproses untuk diperolehnya suatu keluaran.

Contoh : Data

Pengolah (Process)

Suatu sistem mempunyai bagian pengolah yang akan mengubah input menjadi output.

Contoh : - CPU pada komputer

- Bagian produksi yang mengubah bahan baku menjadi barang jadi.

- Bagian akuntansi yang mengolah data transaksi menjadi laporan - laporan Keuangan.

Keluaran (Output)

Keluaran adalah hasil dari energi yang diolah. Keluaran ini dapat diklasifikasikan sebagai:

- Keluaran yang berguna

Contoh : Informasi yang dikeluarkan oleh komputer

- Keluaran yang tidak berguna yang dikenal sebagai sisa pembuangan

Contoh : panas yang dikeluarkan oleh komputer.

Sasaran sistem (Objective) dan Tujuan sistem (Goal)

Setiap sistem pasti mempunyai tujuan ataupun sasaran yang mempengaruhi input yang dibutuhkan dan output yang akan dihasilkan. Dengan kata lain, suatu sistem akan dikatakan berhasil kalau pengoperasian sistem itu mengenai sasaran atau tujuannya.

3. KLASIFIKASI SISTEM

Suatu sistem dapat diklasifikasikan sebagai:

Sistem ABSTRAK (Abstract system )

Sistem ini merupakan sistem yang tidak tampak secara fisik, karena hanya berupa pemikiran atau ide-ide.

Contoh :
Sistem Teologia yang merupakan suatu sistem yang menggambarkan hubungan Tuhan dengan manusia.

Sistem FISIK (Physical system)

Sistem fisik merupakan sistem yang tampak secara fisik sehingga setiap mahluk dapat melihatnya.

Contoh : Sistem Komputer

Sistem Akuntansi

Sistem Produksi

Sistem ALAMIAH (Natural system)

Sistem alamiah ini adalah sistem yang terjadi dari proses - proses alam dalam arti tidak dibuat oleh manusia.

Contoh : Sistem Geologi : sungai, pegunungan

Sistem Solar : galaxy, tata surya

Sistem buatan manusia (Human made system)

Sistem ini merupakan sistem yang dirancang & didisain oleh manusia.

Contoh : Sistem Informasi - manusia - komputer

Man - machine system / human-machine system

Interaksi antara manusia dan mesin

Sistem Deterministik (Deterministic System )

Sistem yang beroperasi dengan tingkah laku yg dapat diramalkan disebut sistem deterministik . Interaksi antar tiap-tiap bagian dapat dideteksi, sehingga outputnya juga dapat diramalkan.

Contoh : Sistem Komputer

Sistem Tak Tentu (Probabilistic System )

Sistem ini adalah sistem dimana kondisi masa depannya tak dapat diramalkan karena mengandung probabilitas.

Contoh : Sistem Manusia

Sistem Tertutup (closed system)

Sistem tertutup adalah sistem yang tidak berhubungan dan tidak dipengaruhi oleh lingkungan luarnya. Sebenarnya didunia ini tidak ada sistem yg benar-benar tertutup. Yang ada hanyalah sistem yang secara relatif tertutup (relatively closed system )

Sistem Terbuka (open system)

Sistem ini kebalikan dari sistem tertutup, karena sistem terbuka adalah sistem yang berhubungan dan dipengaruhi oleh lingkungannya. Oleh sebab itu sistem ini harus mempunyai suatu sistem pengendalian (control system) yang baik, agar yang masuk hanya pengaruh - pengaruh yang baik saja.

Contoh : sistem kebudayaan Indonesia

4. PENGERTIAN ANALISIS SISTEM

Suatu sistem akan dirancang oleh satu orang atau sekelompok orang yang membentuk tim. Orang yang merancang sistem ini disebut SISTEM ANALIS.

Ada yang mendefinisikan sistem analis sebagai

A. Seorang yang menggunakan pengetahuan aplikasi komputer yang dimilikinya untuk memecahkan masalah-masalah bisnis, dibawah petunjuk manajer sistem

B. Seorang yang bertanggung jawab menterjemahkan kebutuhan kebutuhan sipemakai sistem (user) kedalam spesifikasi teknik yang diperlukan oleh programmer dan diawasi oleh manajemen.

5. FUNGSI SISTEM ANALIS

FUNGSI SISTEM ANALIS :

1. Mengidentifikasikan masalah - masalah dari pemakai / user

2. Menyatakan secara spesifik sasaran yang harus dicapai untuk memenuhi kebutuhan user

3. Memilih alternatif - alternatif metode pemecahan masalah

4. Merencanakan dan menerapkan rancangan sistemnya sesuai dengan permintaan user

TUGAS -TUGAS UMUM DARI SISTEM ANALIS :

1. Mengumpulkan & menganalisis formulir, dokumen , file yang berkaitan dengan sistem yang berjalan.

2. Menyusun dan menyajikan laporan perbaikan (rekomendasi ) dari sistem yang berjalan kepada user.

3. Merancang suatu sistem perbaikan dan mengidentifikasikan aplikasi - aplikasi untuk penerapannya pada komputer.

4. Menganalisis & menyusun biaya-biaya & keuntungan dari sistem yg baru

5. Mengawasi semua kegiatan dalam penerapan sistem yang baru.

TUGAS -TUGAS TEKNIK DARI SISTEM ANALIS :

1. Menyiapkan gambaran kerja dalam menerapkan sistem baru.

2. Menyusun prosedur-prosedur untuk pengawasan.

3. Menyusun data flow diagram (DFD), Structured Analysis and Design Technique (SADT), dan sistem flowchart untuk merancang sistem baru secara detail.

4. Merancang pola pengawasan terhadap data yang bersifat sangat penting

5. Menyusun file-file untuk digunakan dalam komputer, agar sistem baru dapat berjalan efektif.

6. Merancang bentuk input/output agar mudah dibaca oleh user

7. Menyusun dokumentasi tentang pekerjaan yang dilakukan oleh sistem analis dalam merancang sistem yang baru.

PRIBADI SISTEM ANALIS

1. Mampu bekerja sama

2. Mampu berkomunikasi dengan baik

3. Mempunyai sopan santun

4. Mempunyai pendirian yang tegas

5. Mampu bersikap dewasa

6. Mampu bersikap tegas

7. Dapat bertindak secara metodik

8. Dapat bersikap akurat dalam memperhitungkan biaya-biaya

9. Mempunyai sifat kreatif

5 TAHAP LANGKAH KERJA SISTEM ANALIS

1. Tahap Mengidentifikasikan masalah kebutuhan user

2. Tahap Melaksanakan studi kelayakan

3. Tahap Analisis dan rancang sistem

4. Tahap Penerapan sistem

5. Tahap Evaluasi dan pemeliharaan

Contoh Sistem (Sistem fotosintesis pada tumbuhan)

H₂O + CO₂ + cahaya → C₆H₁₂O₆ (glukosa) + O₂

H2O = Air

CO2 = Karbondioksida

C6h1206 = glukosa

O2 = oksigen

Tumbuhan menyerap H2O (air/mineral dalam air), karbondioksida (CO2) dan cahaya matahari yang akan diproses didalam tubuh tumbuhan yang kemudian akan menghasilkan glukosa dan O2 (oksigen) pada tumbuhan.