Pengantar – Komunikasi Data (1)

Transcription

TUJUAN
•
Berevolusi dan selalu berkembang sejak pertama kali adanya Computing
•
Mempelajari konsep-konsep dasar dan terminologi yang berhubungan dengan
komunikasi data dan jaringan komputer
•
Mempelajari beberapa teknik yang dipergunakan untuk melakukan transfer data
antara dua computer
e.g. dua komputer dalam satu ruangan atau dibedakan dengan jarak dan terhubung
melalui jaringan telepon
•
Mempelajari bermacam-macam fungsi dan protokol jaringan berdasarkan referensi
dari ISO Reference Model
•
Mempelajari dasar-dasar teori yang berhubungan dengan transmisi digital
2
KOMUNIKASI DATA
•
Pertukaran data antara dua perangkat (komputer)
•
Terhubung melalui beberapa macam media transmisi
SISTEM KOMUNIKASI DATA
•
Kombinasi dari hardware dan software
•
Memungkinkan terjadinya pertukaran komunikasi data
KOMPONEN-KOMPONEN:
3
Komponen - komponen sistem komunikasi data
•
Pesan (Message):
¾ Informasi (data) yang akan dikirim
¾ Dapat berupa teks, gambar, suara dll
•
Pengirim/Penerima (Sender/Receiver):
¾ Perangkat untuk mengirim/menerima pesan data (data message)
¾ Dapat berupa komputer, kamera video dll
¾ Membuat istilah “end system atau host” yang mengacu pada keduanya
•
Medium:
¾ Lintasan fisik di mana data/pesan bergerak dari pengirim menuju penerima
¾ Dapat berupa kabel, gelombang radio dll
4
Komponen - komponen sistem komunikasi data
•
Protokol:
¾ Peraturan-peraturan yang mengatur komunikasi data
¾ Menggambarkan kesepakatan antara perangkat-perangkat komunikasi
¾ Tanpa protokol, dua perangkat mungkin mungkin untuk saling terhubung, tetapi
tidak saling berkomunikasi
Sebagai contoh adalah dua orang yang berbicara dengan bahasa yang
berbeda, tidak dapat mengerti satu dengan yang lainnya
Hubungan antara perangkat - perangkat komunikasi
•
Konfigurasi sambungan:
¾ Mendefinisikan bagaimana cara dua atau beberapa perangkat komunikasi
tersambung pada link
•
Mode transmisi:
¾ Mendefinisikan arah alur sinyal antara dua perangkat yang terhubung
5
Materi Kuliah (1)
2. Pengantar
– Jaringan komunikasi data: Beberapa tipe dari jaringan komunikasi data
– Standar-standar: Evolusi, Beberapa badan international
3. Pengantar
– OSI model arsitektur: Lapisan dan stuktur model, Fungsi setiap lapisan
4. Komunikasi Data Interface
– Media transmisi: Beberapa macam tipe fisik media transmisi yang dipergunakan
untuk data transmisi, Karakteristik dan limitasi dari setiap tipe
– Tipe-tipe sinyal: Beberapa tipe sinyal yang digunakan dalam komunikasi data,
Sumber sinyal
– Sumber redaman dan distorsi: Beberapa tipe redaman dan distorsi, pengaruh
redaman dan distorsi pada sinyal
– Delay propagasi: Pengaruhnya pada sinyal
– Standar interface lapisan fisik: Standar yang digunakan untuk menghubungkan
peralatan komunikasi
6
Materi Kuliah (2)
5. Transmisi Data
– Dasar transmisi data: Beberapa tipe mode transmisi
– Transmisi sinkron dan asinkron: Perbedaan dua tipe kontrol transmisi
– Teknik deteksi kesalahan
– Kompresi data: Beberapa tipe algoritma kompresi data
– Kendali transmisi: Perbedaan dua tipe kontrol transmisi
– Kendali komunikasi: Beberapa tipe perangkat komunikasi kendali
6. Dasar-dasar Protokol
– Kendali kesalahan: pengertian-pengertian dasar dalam kendali kesalahan
– Idle RQ: prinsip kerja, arsitektur, spesifikasi, penggunaan
– Continuous RQ: prinsip kerja, arsitektur, penggunaan
– Manajemen Link
7
Materi Kuliah (3)
7. Protocol TCP/IP
– Karakteristik
– Fungsi tiap lapisan
8. Data Link Control
– Protokol character-oriented
– Protokol bit-oriented
– Standar interface lapisan kendali link
9. Multiplexing
– FDM - Frequency-Division Multiplexing
– Synchronous TDM (Time-Division Multiplexing)
– Statistical TDM
10. Multiple Access
– FDMA – Frequency Division Multiple Access
– TDMA – Time Division Multiple Access
– CDMA – Code Division Multiple Access
– Random Access
8
Jaringan Komunikasi Data (1)
¾ Point-to-point
• wire link
• other link: PSTN (Public Switched Telephone Network) & Modem
A
B
A
B
PSTN
modem
modem
9
¾ LAN (Local Area (data) Network)
• More than 2 computers involved in an application
• A switched communication network facility used to enable all the
computers to communicate with one another at different times
• If all the computers are distributed around single office/building, it is
possible to install one single LAN
• Otherwise, a few LAN is connected through a link (site-wide
(backbone) LAN)
10
• More than 2 computers involved in an application
A
LAN 1
B
Technical
and office
automation
LAN 2
C
LAN 3
Site-wide (backbone) LAN
Mainframe or minicomputer, advanced workstation or personal computer
Bridge
11
Manufactoring cells
Factorywide (backbone) LAN
Intracell LAN
Manufactoring automation
12
¾ WAN (Wide Area (data) Network)
• when computers are located in different establishments
(sites), and then used public carrier facilities
• Different types depend on the nature of applications
e.g.:
• Enterprisewide Private Network: when computers belong to the
same enterprise and having a requirement to transfer some amounts
of data between sites by leasing transmission lines (circuits) from
the public carriers and install a private switching system at each site
• PSDN – Public Switched Data Network: similar as above, where
public carrier network is used
• ISDN – Integrated Services Digital Networks: similar, with ability
to transmit data without modems
13
•
Enterprisewide Private Network:
14
computer
•
PSDN:
computer
TC
PSDN
computer
computer
PSDN = Public Switched Data Network
TC
TC = Terminal Controller
= Interface standards
= Communication subsystem (hardware and software)
15
•
ISDN:
voice handset
voice handset
NTE
NTE
computer
computer
ISDN
voice handset
NTE
NTE
computer
voice handset
computer
NTE = Network termination equipment
ISDN = Integrated Services Digital Network
16
¾ Internetwork or Internet; where communication facility include multiple
networks such as LAN-WAN-LAN
¾ Broadband Multiservice Networks
• Connect workstations that support desktop video telephony,
videoconferencing and more general multimedia services
• ‘Broadband’ means of its high transmission bit rates
¾ ATM (Asynchronous Transfer Mode)
• An approach for transmission and switching within the networks
• Used to distinguish data communication & speech and video
communication
17
•
Worldwide interwork:
Site-wide
LAN
Site-wide
LAN
National
PSDN
Ground station
Satellite
Site-wide
LAN
National
PSDN
Ground station
= Gateway
Site-wide
LAN
18
¾ MAN (Metropolitan Area Network)
• A new network with the interconnection of ATM LANs; and data-only
LANs are distributed around a town or city
ATM
LAN
Data-only
LAN
ATM
MAN
ATM
WAN
ATM
MAN
Data-only
LAN
ATM
LAN
Data-only workstation / server
Multimedia workstation /
server
19
Standards (1)
¾ Evolution:
• 1970s – Mainframe, PSTN
• 1980s – Network computing, separate data and voice networks
• 1990s – Personal computing, workstations, LAN, ISDN, Internet
• 2000s – Global integrated multimedia infomedia network
¾ Provides a model for development
¾ Allows a product to work regardless of the individual manufacturer
¾ Developed by cooperation among standards organizations, e.g. ISO, ITU-T,
IEEE, IETF
20
Standards (2)
¾ Documented agreements containing technical specifications
• To be used consistently as rules, guidelines, or definitions of
characteristics of a system
• To ensure that adhered systems are fit for their purposes
¾ Standards contribute to
• Making life simpler
• Open systems
• Ensure compatibility
• Bring costs down by encouraging competition
¾ Most telecom related standards are international
21
Standards (3)
¾ Enhanced product quality and reliability
¾ Simplification for improved usability
¾ Increased distribution efficiency, and ease of maintenance
¾ Ensure compatibility and interoperability
¾ Encourage competition
• Bring costs down
• Ensure stable supply
¾ Developed by cooperation among standards organizations, e.g. ISO, ITU-T,
IEEE, IETF
22
Standards (4)
¾ ISO: International Standards Organization
• A worldwide federation of national standards bodies from some 100
countries, one from each country
• A multinational organization dedicated to worldwide agreement on
international standards in a variety of fields
• Established in 1947
• Example of standards: ISO OSI Reference Model
23
Standards (5)
¾ ITU-T: International Telecommunications Union – Telecommunication
Standards Sector
• United Nations organization that develops standards for
telecommunication
• Headquartered in Geneva, Switzerland
• International organization whithin which governments & private
sectors coordinate global telecom networks and services
• Activities include:
‣ Coordination, development, regulation and standardization of
telecommunication
‣ Organization of regional & world telecom events
24
Standards (6)
¾ ITU-T: International Telecommunications Union – Telecommunication
Standards Sector (cont)
• Example of standards:
‣ V-series: define data transmission over phone line
‣ X-series: define transmission over public digital networks
¾ IEEE: Institute of Electrical and Electronics Engineers
• A non-profit, technical professional association of more than 377,000
individual members in 150 countries.
• Largest national profession group
• Example of standards: IEEE 802 series
25
Standards (7)
¾ IETF: Internet Engineering Task Force
• Standards body for the Internet itself
• A large open international community of network designers, operators,
vendors, and researchers concerned with the evolution of the Internet
architecture and the smooth operation of the Internet
• Develops and reviews specification intended as Internet Standards
• The actual technical work is done in its working groups, which are
organized by topic into several areas (e.g. routing, network
management, security, etc.)
• Most of the work is handled via mailing list, however, IETF also holds
meetings three times per year
• Example of standards: RFC 2616 – HTTP protocol
26
Standards (8)
¾ ISOC: Internet Society
• International organization for global cooperation and coordination for
the Internet and its internetworking technologies and applications
• Its members reflect the breadth of the entire Internet community and
consist of individuals, corporations, non-profit organizations, and
government agencies
• Its principal purpose is to maintain and extend the development and
availability of the Internet and its associated technologies and
applications – both as an end in itself, and as a means of enabling
organizations, professions, and individuals worldwide to more effective
collaborate, cooperate, and innovate in their respective fields and
interests
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Komunikasi Data
Pengantar – kuliah ke 2
•
OSI model arsitektur
¾ Lapisan dan struktur model
¾ Fungsi setiap lapisan
1
ISO Reference Model
•
•
•
ISO has taken a model to overcome difficulties to test and modify
softwares; since the software for a communication subsystem, were often
based on a single, complex, unstructured program, (written in assembly
language) with many interacting components
The communication subsystem here consists of a complex piece of
hardware and software
ISO Reference Model has taken a layered approach, where the complete
communication subsystem is broken down into a number of layers, each of
which performs a well-defined function
Conceptually, each layers can be considered as performing generic
functions:
¾ Network-dependent functions
¾ Application-oriented functions
2
ISO Reference Model
•
Three different operational environments:
¾ Network environment: concern with the protocols and standards
relating to the different types of underlying data communication
networks
¾ OSI environment; include the network environment and adds additional
application-oriented protocols and standards to allow end systems
(computers) to communicate with one another in an open way
¾ Real systems environment; build on the OSI environment and
concerned with a manufacturer’s proprietary software and services;
have been developed to perform a particular distributed information
processing task
3
ISO Reference Model
Diagram environment:
Computer A
Computer B
AP
AP
Application-oriented
functions
Application-oriented
functions
Network-dependent
functions
Network-dependent
functions
Data network
Network environment
OSI environment
Real systems environment
4
ISO Reference Model
•
Network-dependent and application-oriented (network-independent)
components of the OSI model are implemented as a number of layers
•
Each layer performs a well-defined function in the context of the overall
communication subsystems; and has a well-defined interface with the
layers immediately above and below
•
The function of each layer is specified formally as a protocol that defines
the set of rules and conventions used by the layer to communicate
(exchanging messages, both user data and additional control information),
with a corresponding (similar) peer layer in another (remote) system
•
The implementation of a particular protocol layer is independent of all
other layers
5
ISO Reference Model
The logical structure of ISO Reference Model:
Computer A
Computer B
AP
AP
Application layer
AL (7)
Presentation layer
PL (6)
Session layer
SL (5)
Transport layer
TL (4)
Network layer
NL (3)
Link layer
LL (2)
Physical layer
PL (1)
Data network
Network environment
OSI environment
Real systems environment
6
ISO Reference Model
•
The network-dependent layers (three lowest layers) are concerned with the
protocols associated with the data communication network being used to
link the two communicating computers
•
The application-oriented layers (three upper layers) are concerned with the
protocols that allow two end-user application processes to interact with
each other, normally through a range of services offered by the local
operating system
•
The intermediate transport layer (4) masks the upper application-oriented
layers from the detailed operation of the lower network-dependent layers; it
develops the services provided by providing the application-oriented layers
with a network-independent message interchange service
7
Function of each layer of the OSI model:
End-user application process
Distributed information services
File transfer, access and management, document and
message interchange, job transfer and manipulation
Application layer
Syntax-independent message
interchange services
Transfer syntax negotiation,
data representation transformations
Dialog and synchronization
control for application entities
Presentation layer
Session layer
Network-independent message
interchange services
End-to-end message transfer (connection management,
error control, fragmentation, flow control)
Network routing, addressing, call set-up, and clearing
Data link control (framing, data transparency, error control)
Mechanical and electrical network interface definitions
Transport layer
Network layer
Link layer
Physical layer
Physical connection to
network termination equipment
Data communication network
8
ISO Reference Model
•
Each layer provides a defined set of services to the layer immediately
above; also uses the services provided by the layer immediately below it to
transport the message units associated with the protocol to the remote peer
layer
example: transport layer provides a network-independent message transport
service to the session layer above it and uses the service provided by
network layer below it to transfer a set of message units associated with the
transport protocol to a peer transport layer in another system
9
ISO Reference Model
•
Network-dependent layers
¾ Physical layer
¾ Link layer
¾ Network layer
•
Application-oriented layers
¾ Transport layer
¾ Session layer
¾ Presentation layer
¾ Application layer
10
ISO Reference Model
Physical layer
•
Concern with the physical and electrical interfaces between the user
equipment and the network terminating equipment
•
Provide the link layer with a means of transmitting a serial bit stream
between two equipments
•
Examples: wires, connectors, voltages, data rates
11
ISO Reference Model
Link layer
•
Develop a physical connection provided by the particular network to
provide network layer with a reliable information transfer facility
•
Responsible for functions such as error detection and retransmission
messages (if there is a transmission error)
•
Examples: physical addressing, network topology, error notification, flow
control
•
Two types of services:
¾ Connectionless, treats each information frame as a self-contained entity
that is transferred using a best-try approach. If errors are detected in a
frame, then the frame is simply discarded
¾ Connection oriented, try to provide an error-free information transfer
facility
12
ISO Reference Model
Network layer
•
Responsible for establishing and clearing a network wide connection
between two transport layer protocol entities
•
It includes functionality as network routing (addressing) and, flow control
across the computer-to-network interface
•
In internetworking, it provides various harmonizing functions between the
inter-connected networks
13
ISO Reference Model
Transport layer
•
Interface between the higher application-oriented layers and the underlying
network-dependent protocol layers
•
Provide the session layer (one layer above) with a message transfer facility
that is independent of the underlying network type; therefore transport layer
hides the detailed operation of the underlying network from the session
layer
•
It offers a number of classes of service to compensate for the varying
quality of service (QOS) provided by the network layers associated with the
different types of network
•
Five classes of services ranging from class 0 (provides only basic functions
needed for connection establishment and data transfer) to class 4 (provides
full error control and flow control procedures
14
ISO Reference Model
Session layer
•
Interhost communication: establishes, manages and terminates sessions
between applications
•
Allows two application layer protocol entities to organize and synchronize
their dialog and manage their data exchange
•
Responsible for setting up (& clearing) a communication (dialog) channel
between two communicating application layer protocol entities
(presentation layer protocol entities in practice) for the duration of the
complete network transaction
•
A number of optional services provided:
¾ Interaction management; data exchange associated with a dialog may
be duplex or half-duplex (where each protocol here provides facilities
for controlling the exchange of data/dialog units in a synchronized
way)
15
ISO Reference Model
Session layer
•
A number of optional services provided:
¾ Synchronization; for lengthy network transactions, the user (through
the services provided by the session layer) may choose periodically to
establish synchronization points associated with the transfer.
If a fault develops during a transaction, the dialog may be restarted at
an earlier synchronization point
¾ Exception reporting; non-recoverable exceptions arising during a
transaction can be signaled to the application layer by the session layer
16
ISO Reference Model
Presentation layer
•
Concerned with the representation (syntax) of data during transfer between
two communicating application processes
•
Data security; encrypted/enciphered (using a key) data sent is (hopefully)
known only by the intended recipient presentation layer, and later the key is
used to decrypts (deciphers) the received data before passing it onto the
intended recipient
17
ISO Reference Model
Application layer
•
Provides the user interface (an application program/process) a range of
network wide distributed information services
examples: file transfer access and management, general document and
message interchange services (e-mail)
•
The layer provides other services as:
¾ Identification of the intended communication partner by name or by
address
¾ Determination of the current availability of an intended communication
partner
¾ Establishment of authority to communicate
¾ Agreement on privacy (encryption) mechanism
18
ISO Reference Model
Application layer
•
The layer provides other services as:
¾ Authentication of an intended communication partner
¾ Selection of the dialog discipline, including the initiation and release
procedures
¾ Agreement on responsibility for error recovery
¾ Identification of constraints on data syntax (character sets, data
structures, etc.)
19
Data Encapsulation
20
Data Encapsulation
21
ISO vs TCP/IP Reference Model
22
TCP/IP Reference Model
The importance of TCP/IP
Although the OSI model is universally recognized, the historical and
technical open standard of the Internet is TCP/IP (Transmission
Control Protocol/Internet Protocol)
The TCP/IP model and the TCP/IP protocol stack make data
communication possible between any computers, anywhere in the
world
Four layers in TCP/IP model:
Application; Transport; Internet; Network
23
Application layer
• The designer felt that the higher level protocols should include the
session and presentation layer details
• They created this layer that handles high-level protocols, issues of
representation, encoding and dialog control
• The TCP/IP combines all application-related issues into one layer,
and assumes this data is properly packaged for the next layer
24
Transport layer
• It deals with the quality of service issues of reliability, flow control
and error correction
• One of its protocols, the transmission control protocol (TCP), is a
connection-oriented protocol that provides excellent and flexible
ways to create reliable, well-flowing, low-error network
communications
• It dialogues between source and destination while packaging
application layer information into units called segments
25
Internet layer
• It governs by the Internet protocol (IP)
• Send source packets from any network on the internetwork and have
them arrive at the destination independent of the path and networks
they took to get there
• Best path determination and packet switching
• Example: when we mail a letter, we do not know how it gets there
(various possible routes), but we do care that it arrives
26
Physical layer
• It also called the host-to-network layer
• Concerned with all issues that an IP packet requires to actually make
a physical link
• This includes a LAN and WAN technology details, and all the
details in the OSI physical and data link layers
27
28
Comparing TCP/IP with OSI
• TCP/IP combines the presentation and session layer issues into its
application layer
• TCP/IP combines the OSI data link and physical layers into one
layer
• TCP/IP appears simpler because it has fewer layers
• TCP/IP protocols are the standards around which the internet
developed, so the TCP/IP model gains credibility just because of its
protocols.
29
TRANSMISI DATA &
MEDIA TRANSMISI
TERMINOLOGI (1)
Network Devices
Terminologi (2)
Terminologi (3)
Frekuensi, Spektrum dan
Bandwidth
Sinyal-Sinyal Kontinu dan
Diskrit
Sinyal Periodik
Gelombang Sinus
Keragaman Gelombang Sinus
Panjang Gelombang
(Wavelength)
Frequency Domain Concepts
Add Frequency Component
Frequency Domain
Analog And Digital Data
Transmission
Data
Acoustic Spectrum
Signal
Data & Signal
Media on PC

Ethernet
Modem
PC Card (WLAN)
DVB
Ethernet - Architecture
Ethernet – IEEE 802.3

10Base5 – Thick wire coaxial
10Base2 – thin wire coaxial / cheaper
net
10BaseT – Twisted Pair
10BaseF – Fiber Optics
100BaseT – Fast Ethernet
Ethernet – 10Base5
Ethernet – 10Base2
Ethernet – 10BaseT
NIC Connector type

Coaxial Cable
{

Twisted Pair Cable
{

Bayonet Nut Connector (BNC)
RJ-45 (8 wire)
Fiber Optics
{
SMA connectors
Modem

Allows modems of different vendors to
operate together
Define How modems operate:
{
{
{
Modulation techniques
Data compression technique
Error detection strategy
Modem – Analog vs Digital

Analog
{
{
{
{

Infinite number of levels
Conform to voice pattern
Times from highest to lowest and back to the
highest point in one second is the frequency
Can be transmitted over long distance
Digital
{
{
{
Only two levels (high and low)
Conforms to how computers operate
Cannot transmitted over long distance
Modem - Connection
Modem – Internal/External
PC Card – WLAN (802.11)

Bypassing last mile
PC Card (WLAN) - 1
PC Card (WLAN) - 2
PC Card (WLAN) – Indoor
Antena
DVB – DVB/IP Tech

The Digital Video Broadcast over Internet
Protocol (DVB/IP) system is functionally an
IP-over-Ethernet simplex satellite service
that incorporates frame-relay type traffic
management. At its core, DVB is a modemon-a-chip, plus an intelligent multiplexer.
The antenna is typically a CATV dish, 2.4 3.8 meters in diameter (for C-band), or 0.6 1.8 meters (for Ku-band).
DVB – DVB/IP Routing
DVB - Adaptability
DVB – DVB Card
Media Transmisi

Wired
{
{
{

Twisted Pair – UTP
Coaxial
Fiber
Wireless
{
{
Microwave
Satellite
Twisted Pair

Two wired wrapped in
a twisted fashion
{
{

Designed to reduce
cross-talk due
inductance
Still subject to
interference from stray
signal
Primarily used for local
loop connections and
LANs
Comparatively narrow
bandwidth
UTP – Unshielded Twisted
Pair

Pair 1
{
{

Pair 2
{
{

{
White/Green
Green
Pair 4
{
{

White/Orange
Orange
Pair 3
{

White/blue
Blue
White/Brown
Brown
RJ45 Connector
UTP – Straight Cable
Wo/O Wg/B Wb/G Wbr/Br
UTP – Cross Cable
Wg/G Wo/B Wb/O Wbr/Br
UTP - Category
Category
CAT 1
Maximum Data Rate
Less than 1 Mbps
Usual Application
Analog voice (POTS),
Integrated Services Digital Network Basic Rate Interface in ISDN
Doorbell wiring
CAT 2
4 Mbps
Mainly used in the IBM Cabling System for token ring networks
CAT 3
16 Mbps
Voice and data on 10BASE-T Ethernet
CAT 4
20 Mbps
Used in 16 Mbps Token Ring
Otherwise not used much
CAT 5
100 Mbps
100 Mbps TPDDI (100BASE-T or Fast Ethernet)
1000 Mbps (4 pair)
155 Mbps ATM
Gigabit Ethernet
CAT 5E
100 Mbps
100 Mbps TPDDI (100BASE-T or Fast Ethernet)
155 Mbps ATM
CAT 6
200-250 MHz
Super-fast Broadband Applications.
Coaxial

Center lead conducts the signal
{

Protected by insulation and braded wire
Used mostly for television and connections to
antenna
Larger Bandwidth but large in size
Fiber Optical

Signal transmitted by photos rather than electrons
Dramatically higher bandwidth
Used mostly for backbone communication
connections, very high speed LANs and fast
network connections
Fiber Optical
Wireless Transmission
Microwave – Antenna (1)

Omni
2.4GHz 8dBi

Sectoral
14dBi 180deg

Sectoral
17dBi 90deg

Direct (Grid)
2.4 GHz 24dB
Microwave – Power AMP
Satellite - Broadband
Media Comparison
Multiplexer

HUB
Switch
Bridge
Router
Hub versus Switch

Hub provide connection to all ports (i.e. in
one port and out all other ports).
{
{

Passive hub – no signal regeneration
Active hub – provide signal regeneration
Switch direct the message from appropriate
port (directs a message from the input port
to the desired output port).
{
More expensive but better bandwidth utilization
Hub versus Switch
LAN Hub device
Hub
LAN Switch device
Switch
Bridge – Access Point (WLAN)
Router

Connecting different segment
Have different interfaces (Ethernet,
WAN-Serial, Fiber, etc)
Table Routing
Router
Komunikasi Data
Interface Komunikasi & Transmisi Data – kuliah ke 4
Interface komunikasi
– Sumber redaman dan distorsi
¾ Beberapa tipe redaman dan distorsi
¾ Pengaruh redaman dan distorsi pada sinyal
– Delay propagasi - pengaruhnya pada sinyal
Transmisi Data
– Dasar transmisi data: beberapa tipe mode transmisi
– Transmisi sinkron dan asinkron: persamaan & perbedaan
– Teknik deteksi kesalahan: beberapa metode pendeteksian
– Kompresi data: beberapa tipe algoritma kompresi
1
Attenuation & Distortion
Various attenuation &
distortion effects that affects
any signal carried on a
transmission medium:
•
Attenuation
•
Limited bandwidth
•
Delay distortion
•
Noise
2
Attenuation
•
Signal attenuation - if a signal that propagates along a transmission
medium (line) gets an amplitude decreasing
•
A limit is set on the length of cable that can be used to ensure that
receiver can detect and interpret the received attenuated signal
correctly
•
If longer cable is needed, one or more amplifiers (=repeaters) are
inserted at intervals along the cable to restore the received signal to its
original level
3
Attenuation
•
Signal attenuation increases as a function of frequency; since signal
consists of a range of frequencies
•
Solutions:
– By designing amplifiers to amplify different frequency signals by
varying amounts
– By using equalizers to equalize the attenuation across a defined
band of frequencies
4
Attenuation
•
Measurement of attenuation and amplification (also known as gain) is
in decibels (dB)
P1
Attenuation = 10 log10 dB
P2
Amplification = 10 log10
P2
dB
P1
where P1 is the transmitted signal power level & P2 is the received power;
both in watts.
•
Therefore, decibels are dimensionless and simply a measure of the
relative magnitude of the two power levels
•
The use of logarithms means that the overall attenuation/amplification of
a multisection transmission channel can be determined by summing
together the attenuation/amplification of the individual sections
5
Attenuation
•
Each signal element can represent more than a single binary digit; e.g.
when binary informations are transmitted over a limited-bandwidth
channel such as the PSTN, we often use more than two signal levels.
•
If the number of signal levels is M, then the number of bits per signal
element m, is given by:
m = log 2 M
•
The rate of change of the signal is known as the signaling rate (Rs);
measured in baud.
R = Rs log 2 M
6
Limited bandwidth
•
Any communications channel/transmission medium has a defined
bandwidth associated with it; which specifies the band of sinusoidal
frequency components that will be transmitted by the channel
unattenuated
•
Therefore, when transmitting data over a channel, it is needed to
quantify the effect of the channel bandwidth on the transmitted data
signal
•
From the fourier analysis, it is known that any periodic binary sequence
is made up of an infinite series of sinusoidal signals including the
fundamental frequency component, f0, and its harmonic components.
7
Limited bandwidth
•
When a binary signal is transmitted over a channel, only those
frequency components that are within the channel bandwidth will be
received
•
From the figure: the larger the channel bandwidth, the higher-frequency
components are received and the closer is the received signal to the
original (transmitted) signal
•
The maximum information transfer rate of noiseless transmission
channel C, is given by Nyquist expression as:
C = 2W log 2 M
Where W is the bandwidth of the channel in Hz, and M is the number of
levels per signaling element
8
9
Limited bandwidth
•
In practice, with binary data, extra bits are added for transmission
control purposes; therefore the useful data rate is often less than the
actual bit rate
•
When information are transmitted over a communications channel,
three rates are involved: the signaling rate, the bit rate, and the data
rate; all of which may be the same or different
•
Since the duration of each bit, Tb (in sec.), is the reciprocal of the bit
rate, R, (in bps), then the bandwidth efficiency of a transmission
channel, B, that defined as R/W, can be derived as :
1
R
m
bps Hz-1
B= =
=
W WTs WTb
10
Limited bandwidth
•
From the expression, it can be assumed that the higher the bit rate,
relative to the available bandwidth, the higher bandwidth efficiency
•
Typical values of B range from 0.25 to 3.0 bps Hz-1
where the first corresponding to a low bit rate relative to the available
bandwidth, and the second a high bit rate that requires a relatively high
signaling rate
•
In general, the higher the bandwidth efficiency, the stricter are the
design parameters of the associated equipment and hence the higher
cost
11
Delay distortion
•
When a digital signal is transmitted, the various frequency components
making up the signal arrive at the receiver with varying delays. This
results in delay distortion of the received signal
•
The amount of distortion increases as the bit rate of the transmitted
data increases, since some of the frequency components associated
with each bit transition are delayed and start to interfere with the
frequency components associated with a later bit
•
It also called intersymbol interference, since the received signal, that is
normally sampled at the nominal center of each bit cell, can lead to
incorrect interpretation of the received signal as the bit rate increases
12
Noise
•
Line noise level, a random perturbations that present on the line even
when no signal is being transmitted
•
Signal-to-noise ratio (SNR) is the ratio of the average power in a
received signal S, to the power in the noise level N; normally
expressed in decibels; given as:
SNR
= 10 log
10
⎛ S ⎞
⎟ dB
⎜
⎝N ⎠
13
Noise
•
High SNR means a high power signal relative to the existing noise
level, resulting a good-quality received signal; on the other hand, a
low SNR means a low-quality received signal
•
Shannon-Hartley law is the expression to determine the theoretical
maximum information (data) rate of a transmission channel related
to the SNR ratio; given as:
S ⎞
⎛
C = W log 2 ⎜ 1 + ⎟
N⎠
⎝
bps
where C is the information (data) rate [bps], W is the bandwidth of the
line channel [Hz], S is the average signal power [watts] and N is the
random noise power [watts]
14
Noise examples:
•
Near-end crosstalk (NEXT) or self-crosstalk, caused by the strong
signal output by a transmitter circuit being coupled and interfered with
the much weaker signal at the input to the local receiver input
•
Impulse noise, caused by impulses of electrical energy associated with
external activity or equipment being picked up by a signal line. Ex:
switching circuits in old telephone exchanges (loud clicks on the line,
etc)
•
Thermal noise, caused by the thermal agitation of electrons associated
with each atom in the device or transmission line material.
- present in all electronic devices and transmission media
- all transmission media experience this noise at all temperatures above
absolute zero
15
Noise examples:
•
- this noise is also known as white noise, since it is made up of random
frequency components (across the complete frequency spectrum) of
continuously varying amplitude
¾ In practice, it is important to determine the minimum signal level that
must be used (relative to the noise level), to achieve a specific
minimum bit error rate ratio
¾ bit error rate ratio is an acceptable low probability that a single bit
will be misinterpreted by the receiver over a defined period
ex: a bit error rate ratio of 10-4 means that, on average, 1 bit in every
104 received will be misinterpreted
16
Noise
•
The energy per bit in a signal, Eb is given by:
E b [joules] = ST b =
S
[watt - second]
R
where S is the signal power [watts] and Tb is the time period for 1 bit
[seconds], R is the data transmission rate that is equal to 1/T
•
The noise power density [watts Hz-1], the level of (thermal) noise in a
bandwidth of 1 Hz in any transmission line is given by:
N 0 = kT [watt Hz
-1
]
where k is Boltzmann’s constant (1.3803 x 10-23 joule K-1) and T is the
temperature [K]
•
From these, to quantify the effect of noise, the energy per bit Eb is
expressed as a ratio of the noise energy per Hz, N0 :
17
Noise
•
The effect of noise, the energy per bit Eb is expressed as a ratio of the
noise energy per Hz, N0 :
S
S
Eb
= R= R
kT
N0 N0
Or in decibels:
Eb
⎛S ⎞
[dB] = 10 log 10 ⎜ ⎟ − 10 log 10 (kT )
N0
⎝R ⎠
•
It can be seen that, to achieve an acceptable Eb / N0 ratio (hence
minimum bit error rate), the signal power level S is needed with
increasing of the temperature T and bit rate R
18
Noise
•
Since N0 is the noise power density [watts Hz-1] and a channel of
bandwidth is W Hz, the noise power in a received signal N given by
N = W N0 then
E
S W
b
N
•
0
=
N R
Or in decibels:
Eb
⎛S ⎞
[dB] = 10 log 10 ⎜ ⎟ + 10 log 10 W − 10 log 10 R
N0
⎝N ⎠
19
Propagation delay
•
There is always a short but finite time delay for a signal (electrical,
optical or radio) to propagate (travel) from one end of a transmission
medium to the other; known as the transmission propagation delay, Tp
of the medium
•
Round-trip delay is the time delay between the first bit of a block being
transmitted by the sender and the last bit of its associated
acknowledgement being received
The function is not only of the time taken to transmit the frame at the
link bit rate (known as the transmission delay, Tx) but also of the
propagation delay of the link Tp
•
The relative weighting of the two varies for different types of data link
and hence the two times varies for different are often express as a ratio
a:
20
Propagation delay
•
The relative weighting of the two varies for different types of data link
and hence the two times varies for different are often express as a ratio
Tp
a:
a=
Tx
Tp =
where
physical separation S in meters
velocity of propagation V in meters per second
and
Tx =
number of bits to be transmitted N
link bit rate R in bits per second
•
If a < 1: the round trip delay is determined primarily by the transmission
delay
•
If a = 1: both delays have equal effect
•
If a > 1: the propagation delay dominates
21
Data Transmission
•
In data communication, the term ‘data’ is reserved for describing a
set/a block of one/more digitally encoded alphabetic and numeric
characters that being exchanged between two devices
•
When a data communication facility is used to transfer this type of
data, the two communicating parties (DTEs) must also exchange
control messages (i.e. to overcome the effect of transmission errors)
within the communication facility
Coded bit patterns:
codewords
Encode
Keyboard
- EBCDIC (Extended
Binary Coded Decimal
Interchange Code)
- ASCII (American
Standards Committee for
Information Interchange)
Decode
Printer
22
Data Transmission
•
Transfer modes:
– Parallel transmission mode: multiple wires connected to each
subunit, and separate wire carries each bit of data; results in
minimal delays
– Serial transmission mode: use a single pair of lines; the data is
transmitted in a single bit of time using a fixed time interval for
each bit
23
Data Transmission
•
Communication modes:
– Simplex: used when data is to be transmitted in one direction only;
i.e. in a data logging system in which a monitoring device returns a
reading at regular intervals to the data gathering facility
– Half-duplex: used when the two interconnected devices wish to
exchange information (data) alternately; i.e. if one of the devices
returns some data only in response to a request from the other. The
two devices must be able to switch between send and receive
modes after each transmission
– Duplex/full-duplex: used when data is to be exchanged between
the two connected devices in both directions simultaneously; i.e. if
for throughput reasons data can flow in each direction
independently
24
Data Transmission
•
For the receiving device to decode and interpret the pattern correctly, it
must be able to determine:
– The start of each bit cell period (in order to sample the incoming
signal in the middle of the bit cell): bit or clock synchronization
– The start and end of each element (character or byte): character or
byte synchronization
– The start and end of each complete message block (frame): block
or frame synchronization
•
Transmission modes: synchronization method determined whether the
transmitter and receiver clocks are independent (asynchronous) or
synchronised (synchronous)
25
Data Transmission
•
Two different transmission modes:
– Asynchronous transmission: each character (byte) is treated
independently for clock (bit) and character (byte) synchronization
purposes and the receiver resynchronizes at the start of each character
received
– Synchronous transmission: the complete frame (block) of characters is
transmitted as a contiguous string of bits and the receiver endeavors to
keep in synchronism with the incoming bit stream for the duration of
the complete frame (block)
26
Data Transmission
•
Error control:
– Need mechanism to detect when a bit is in error (parity bits, block
checksums, etc)
– parity bit: used in an asynchronous transmission, where a binary
digit (bit) is added within each transmitted character
– error check sequence: used in a synchronous transmission, where
possible transmission errors on the complete frame, as the basic
unit of transmission is in frame
– Another schemes are exist to enable the receiver to obtain another
copy of the original transmission when errors are detected
27
Data Transmission
•
Flow control:
– The receiver may not be able to handle all the information sent due
to limited processing power, buffer space, etc.
– the control of the flow information between two DTEs when the
two devices operate at different data rates; i.e. control of the mean
output rate of the faster device, to prevent the communication
network becomes congested
– need when two devices are communicating through an
intermediate network, as often the network will buffer only a
limited amount of data
– method to control the flow data transfer to ensure that the receiver
does not lose any of the transmitted data because the receiving
device has insufficient storage
28
Data Transmission
•
Data link protocols
– protocol: a set of conventions or rules that must be adhered to by
both communicating parties to ensure that information being
exchanges across a serial data link is received and interpreted
correctly
– defines: error and flow control;
data format (number of bits per element and type of encoding
scheme being used);
type and order of messages that are to be exchanged in order to
achieve reliable (error free and no duplicates) information transfer
between two communicating parties.
29
Asynchronous Transmission
•
Use when the data to be transmitted is generated at random intervals;
i.e. a user at a keyboard communicating with a computer
•
Each transmitted character/byte is encapsulated between an
additional start bit and one or more stop bits
•
The polarity of the start and stop bits is different; to ensures that
there is always a minimum of one transition (1Æ0Æ1) between each
successive characters
30
•
Baud: the number of line signal transitions per second; if each
transmitted signal can be in one of two states, baud and bits per
second (bps) are equivalent.
•
In general, signaling rate is more general to use, since it avoid
confusion. The data or information transfer rate represents the
number of data bits per second (bps).
I.e. a signaling rate of 300 baud with 4 bits per signaling element
would yield a data rate of 1200 bps.
•
To achieve bit and character synchronization, the receiving
transmission control circuit must be set to operate with the same
characteristics as the transmitter in terms of the number of bits per
character and the bit rate being used
31
Bit synchronization
•
The receiver clock runs asynchronously with respect to the incoming
signal. In order for the reception process to work reliably, a scheme
whereby the local receiver clock samples the incoming signal as near
to the center of the bit cell as possible
32
Bit synchronization
•
Since the receiver clock (RxC) is running asynchronously with
respect to the incoming signal (RxD), the relative positions of the
two signals can be anywhere within the single cycle of the receiver
clock.
•
The higher the clock rate ratio, the nearer the sampling instant will
be to the nominal bit cell center.
•
The maximum bit rate normally used with this transmission is 19.2
kbps.
33
Character synchronization
•
The receiving transmission control circuit is programmed to operate
with the same number of bits per character and the same number of
stop bits as the transmitter.
•
After the start bit has been detected and received, the receiver
achieves character synchronization simply by counting the
programmed number of bits.
•
It then transfers the received character (byte) into a local buffer
register and signals to the controlling device (e.g. microprocessor)
that a new character (byte) has been received.
•
It then awaits the next line signal transition that indicates a new start
bit (and character) is being received
34
Frame synchronization
•
Here, the receiver must be able to determine the start and end of
each frame
•
Example of transmitting blocks of printable characters encapsulated
by the complete block between two special (nonprintable)
transmission control characters: STX (start-of-text; indicates the start
of a new frame after an idle period) and ETX (end-of-text; indicates
the end of the frame)
•
In transmitting binary data, the two transmission control characters
STX and ETX are each preceded by a third transmission control
character DLE (data link escape)
35
Frame synchronization
•
Character/byte stuffing: On receipt of each byte after the DLE-STX
start-of-frame sequence, the receiver determines the next
character/byte. If it is a DLE, the receiver processes the next byte to
determine whether that is another DLE or ETX. If it is a DLE, the
receiver discards it and awaits the next byte. If it is an ETX, this is
taken as the end of the frame.
36
Synchronous Transmission
•
Use in transmission of large blocks of data at higher bit rates; the
complete block or frame of data is transmitted as a contoguous bit
stream with no delay between each 8-bit element.
•
To enable the receiving device to achieve the various level of
synchronization:
– The transmitted bit stream is suitable encoded so that the receiver
can be kept in synchronism
– All frames are preceded by one or more reserved bytes/characters
for byte/character synchronization (to ensure the receiver reliably
interprets the received bit stream on the correct byte/character
boundaries
– The contents of each frame are encapsulated between a pair of
reserved character/byte synchronization
37
Synchronous Transmission
•
During the period between the transmission of successive frames,
either synchronous idle characters/bytes are continuously transmitted
to allow the receiver to retain bit and byte synchronism; or each frame
is preceded by two or more special synchronizing bytes or characters
to allow the receiver to regain synchronism
38
Error Detection
•
The concept behind error control is the prevention of delivery of
incorrect messages (bits) to a higher level in the communication
hierarchy
•
Two factors that determine the type of error-detection techniques:
– Bit Error Rate (BER); whether the errors occur as random singlebit errors
– Burst Error; whether the errors occur as groups of contiguous
strings of errors
•
The BER is the probability P of a single bit being corrupted in a
defined time interval. BER of 10-13 means that, on average, 1 bit in 103
will be corrupted during a defined time period
39
Error Detection
•
Two approaches to achieve a copy of (hopefully) correct information:
– Forward error control; each transmitted character/frame contains
additional (redundant) information so that the receiver can not only
detect when errors are present but also determine where in the
received bit stream the errors are. The correct data is obtained by
inverting these bits. In practice, the number of additional bits,
required to achieve reliable forward error control, increases rapidly
as the number of information bits increases
– Feedback (backward) error control; each character/frame includes
only sufficient additional information to enable the receiver to
detect when errors are present but not their location. A
retransmission control scheme is used to request that another copy
of information be sent
40
Error Detection
•
Widely used error detection schemes: parity, check sum, cyclic
redundancy check
Parity
•
Extra bit at the end of a character (5-7 bits) specifying how many of
the bits are 1’s
•
The parity bit is said to be even if it is set to make the total number of
1’s even, and oddif it is set to make the total number of 1’s odd.
•
Can detect all odd numbers of bit errors in the message
•
Can not detect even numbers of bit errors – error cancellation
•
Hamming distance: number of bits in which two words differ
•
Typically used in asynchronous transmission, since timing and spacing
between characters is uncertain.
41
Error Detection
•
Typically used in asynchronous transmission, since timing and spacing
between characters is uncertain.
42
Error Detection
Parity
43
Error Detection
Block Sum Check
•
Block error rate: the probability of a block containing an error
•
Block (sum) check character check the error by using a vertical parity
check that calculates parity over the same bit of multiple characters.
•
Used in conjunction with longitudinal parity check.
•
Overhead is related to number of bits and can be large
44
Error Detection
Cyclic Redundancy Check (CRC)
•
Parity bits still subject to burst noise, uses large overhead (potentially)
for improvement of 2-4 orders of magnitude in probability of detection
•
CRC is based on a mathematical calcilation performed on message.
The following terms will be used:
– M – message to be sent (k bits)
– F – Frane check sequence (FCS) to be appended to message (n
bits)
– T – Transmitted message includes both M and F Æ (k+n bits)
– G – a (n+1) bit pattern (called generator) used to calculate F and
check T
45
Data Compression
•
Mainly done in applications that involve public transmission facilities,
such as PSTN, where charges are based on time (duration) and
distance. If the time to transmit each block of data can be reduced, it
will reduce the call cost
•
In practice, a range of compression algorithm can be applied, each
suited to a particular type of data
•
Some modems (intelligent modems) now offer an adaptive
compression feature which selects a compression algorithm to suit the
type of data being transmitted
•
Some common types of data compression algorithm:
46
Data Compression
Packed decimal
•
Used to compress a frame contain only numeric characters
•
It reduces the number of bits per character from seven (ASCII) to four
by using a binary-coded-decimal (BCD); all have 011 in their three
high-order bit positions
47
Data Compression
Relative encoding
•
Send only the magnitude difference between each value together with
a known reference value
•
Effective for data logging applications; ex. monitoring the water level
of a river
•
In general, binary values with a bit-oriented protocol produce the
largest saving
48
Data Compression
Character suppression
•
A variation of the relative encoding scheme; use in a more general way
to compress other character types
•
In transmitting frames contain printable characters, there are often
sequences in the frame when the same character repeats; e.g. the space
character. The control device at the transmitter scans the frame
contents prior to transmission and, if a contiguous string of three or
more characters is located, replaces these with the three-character seq.
49
Data Compression
Huffman coding
•
Exploits the property that not all symbols in a transmitted frame occur
with the same frequency e.g. in a frame comprising strings of
characters, certain characters occur more often than others.
•
Instead of using a fixed number of bits per character, a statistical
encoding scheme is used, where the most common characters are
encoded using fewer bits than less frequent characters.
•
The character string to be transmitted is analyzed and the character
types and their relative frequency is determined. The coding operation
then creates an unbalanced tree with some branches (as codewords)
shorter than others. The degree of imbalance is a function of the
relative frequency of occurrence of the characters; the larger the
spread, the more unbalanced is tree Æ huffman code tree
50
Data Compression
Huffman coding
•
Huffman (code) tree is a binary tree with branches assigned the value
0 or 1. The base of the tree (at geometric top), is known as root node,
and the point where a branch divides is a branch node. The termination
point of a branch is known as a leaf node, where the symbols being
encoded are assigned.
•
The theoretical minimum average number of bits per codeword to
transfer message string is known as the entropy, H, of the message.
•
The formula to calculate H is derived by Shannon:
n
H = ∑ Pi log 2 Pi
(bits per codeword)
i =1
Where n is the number of characters in the message and Pi is the
probability of character (i) occuring in the message.
51
Data Compression
Huffman coding
•
It is most efficient when frequency distribution of the characters being
transmitted is wide and long character strings are involved; it is not
suitable for the transmission of binary-coded computer data since the
8-bit bytes generally occur with about the same frequency
52
Data Compression
Dynamic Huffman Coding
•
Problem with basic Huffman encoding is that transmitter and receiver
must know the code tree; here, updates Huffman tree dynamically.
•
With this method, if the character to be transmitted is currently present
in the tree, its codeword is determined and sent in the normal way. If
the character is not present (its first occurrence), the character I
transmitted in its uncompressed form.
•
The encoder updates its Huffman tree either by incrementing the
frequency occurrence of the transmitted character or by introducing the
new character into the tree.
•
This means that the savings in transmission bandwidth start only when
characters begin to repeat themselves; I.e. in transmitting the text files
53
Data Compression
Fascimile compression
•
Effective for data logging applications
•
In general, binary values with a bit-oriented protocol produce the
largest saving
54

Pengantar – Komunikasi Data (1)

Transcription

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