3
model utama yang menjadi acuan dalam mendesain Sistem Terdistribusi
Physical models
are the most explicit way in which to describe a system; they capture the
hardware composition of a system in terms of the computers (and other devices,
such as mobile phones) and their interconnecting networks.
Architectural models describe a system in terms of the computational and communication
tasks performed by its computational elements; the computational elements being
individual computers or aggregates of them supported by appropriate network
interconnections.
Fundamental models take an abstract perspective in order to examine individual aspects of
a distributed system. Fundamental models examine three important aspects of
distributed systems: interaction models; failure models; security models.
tiga generasi perkembangan dari
Model Fisik Sistem Terdistribusi
Early distributed systems: In the late 1970s - 1980s in response to the emergence of local area
networking technology, usually Ethernet. These systems typically consisted of
between 10 and 100 nodes interconnected by a local area network, with limited
Internet connectivity and supported a small range of services such as shared
local printers and file servers as well as email and file transfer across the
Internet.
Internet-scale distributed systems: Building on this foundation, larger-scale distributed systems started
to emerge in the 1990s in response to the dramatic growth of the Internet. They
incorporate large numbers of nodes and provide distributed system services for
global organizations and across organizational boundaries (Enterprise Level).
The level of heterogeneity in such systems is significant in terms of networks,
computer architecture, operating systems, languages employed and the
development teams involved. This has led to
an increasing emphasis on open standards
and associated middleware technologies
Model Arsitektur pada Sistem Terdistribusi adalah The architecture of a system is its structure in terms of separately specified components and their interrelationships
Perbedaan antara network dan internetwork
Network,
identik dengan jaringan Local Area Network (LAN). LAN merupakan hubungan
komunikasi data antara berbagai device maupun perangkat komputer dalam suatu
jaringan lokal. Disebut jaringan lokal, karena hubungan tersebut berada dalam
satu Subnet yang sama. Bukan antar Subnet. Dalam hubungan semacam
ini tidak diperlukan mekanisme Routing Protocol yang terdefinisi.
Perangkat jaringan yang digunakan umumnya merupakan perangkat jaringan lokal,
yang bekerja pada layer 1 dan layer 2 dari protokol jaringan.
Contohnya dalam hal ini adalah Hub, Switch, Bridge maupun Repeater.
Internetwork, identik dengan jaringan Wide
Area Network (WAN). WAN merupakan hubungan komunikasi data antara berbagai device
maupun perangkat komputer antar Subnet. Dalam hubungan ini
diperlukan mekanisme Routing Protocol yang terdefinisi. Perangkat
jaringan yang digunakan umumnya merupakan perangkat jaringan yang bekerja pada layer
3 dari protokol jaringan. Contohnya dalam hal ini adalah Router.
Perbedaan
antara Personal Area Network (PAN), Local Area Network (LAN), Wide
Area Network (WAN) dan Metropolitan Area Network (MAN)
Personal Area
Networks (PANs), are a subcategory of local networks in which the
various digital devices carried by a user are connected by a low-cost,
low-energy network. Wireless personal area networks
(WPANs) are of increasing importance due to the number of personal
devices such as mobile phones, tablets, digital cameras, music players and so
on that are now carried by many people. Usually technology used is Bluetooth WPAN
Local area
networks (LANs) carry
messages at relatively high speeds between computers connected transmission
media, such as twisted copper wire, coaxial cable or optical fibre including
wireless channel. No routing of messages is required
within a segment. Larger local networks, such as those that serve a
campus or an office building, are composed of many segments interconnected by
switches or hubs. The total system bandwidth is high
and latency is low, except when message traffic is very high. Ethernet emerged as the dominant technology for wired
local area networks, with a bandwidth of 10 Mbps (million bits per second) and
extended to 100 Mbps, 1000 Mbps (1 gigabit per second) and 10 Gbps. Ethernet
technology lacks the latency and bandwidth guarantees needed by many multimedia
applications. ATM networks were developed to
fill this gap, but their cost has inhibited their adoption in local area
applications. Instead, high-speed Ethernets
have been deployed in a switched mode that overcomes these drawbacks to a
significant degree, though not as effectively as ATM.
Wide Area
Networks (WANs) carry at
lower speeds between nodes that are often in different
organizations and may be separated by large
distances. The communication medium is a set of communication circuits
linking a set of dedicated computers called routers.
They manage the communication network and route
messages or packets. Total latency for the transmission of a message
depends on the route that it follows and the traffic loads in the various
network segments. In current networks these latencies can be as high as 0.1 to
0.5 seconds. Speeds of 1–10 Mbps are more typically experienced for bulk
transfers of data.
Metropolitan
Area Networks (MANs), is
based on the highbandwidth copper and fibre optic
cabling recently installed in some towns and cities for the transmission
of video, voice and other data over distances of up to 50 kilometres. A variety
of technologies have been used to implement the routing of data in MANs,
ranging from Ethernet to ATM.
Layer-layer yang terdapat pada
model OSI beserta fungsinya
Application
Designed to interface to a service.
Presentation
Handles encryption & changes to
syntax
Session
Reliability and adaptation
measures, such as detection of failures and automatic recovery.
Transport
Provide reliable or best-effort
delivery of messages.
Data link
Responsible for transmission of
packets between nodes that are directly connected by a physical link.
Physical
It transmits sequences of binary
data by analogue signalling
The term protocol is used to
refer to a well-known set of rules and formats to be used (for communication
between processes).
Contoh: Penggunaan bahasa yang
dapat dimengerti bersama.
Perbedaan Header dengan Protocol Data Unit
(PDU)
PDU
(Protocol Data Unit) merupakan unit data yang berada pada layer protokol
tertentu (layer ke-N). Di dalamnya sudah termasuk Protocol Header (PCI) dan SDU
(Service Data Unit). Sedangkan Protocol Header atau bisa dikatakan dengan
sebutan Header saja, merupakan informasi tambahan yang diperlukan saat
dilakukan enkapsulasi terhadap PDU layer ke-N ke layer bawahnya (N-1) agar
diperoleh kontruksi PDU yang baru (PDU ke N-1).
Enkapsulasi
adalah proses kontruksi PDU ke N-1 dari PDU ke N dengan cara menambahkan header
pada PDU ke N
Deenkapsulasi
adalah proses pemecahan kontruksi PDU ke N dari PDU ke N-1 dengan cara
memisahkan SDU dengan header-nya
Circuit switching
Suatu
mekanisme switching (penyambungan) di mana jaringan diduduki terus-menerus
selama service diperoleh melalui mekanisme set up (dialing). Susunan jaringan
yang terbentuk saat penyambungan terbentuk adalah tetap.
Packet switching
Disebut juga mekanisme store-and-forward. Di mana message
diubah dalam bentuk paket-paket, dan dikirim melalui jaringan. Susunan jaringan
yang terbentuk dapat berubah-ubah sesuai kondisi di mana paket di-deliver. Dan
switching (penyambungan) tidak perlu secara terus-menerus diduduki manakala
service diperoleh. Service untuk mengirimkan paket, diperoleh tanpa perlu
melakukan mekanisme set up terlebih dahulu.
There
are two approaches to the delivery of packets by the network layer:
Datagram Packet Delivery
The
essential feature of datagram networks is that the delivery of each packet is a
‘one-shot’ process; no setup is required, and once the packet is delivered the
network retains no information about it. Packets transmitted by a single host
to a single destination may follow different routes. Every datagram packet
contains the full network address of the source and destination hosts. Datagram
delivery is the concept on which packet networks were originally based, and it
can be found in most of the computer networks in use today.
Virtual Circuit Packet Delivery
A virtual circuit must be set up before packets can pass
from a source host A to destination host B. The establishment of a virtual
circuit involves the identification of a route from the source to the
destination, possibly passing through several intermediate nodes. Once a
virtual circuit has been set up, it can be used to transmit any number of
packets. Each network-layer packet contains only a virtual circuit number in
place of the source and destination addresses. The addresses are not needed,
because packets are routed at intermediate nodes by reference to the virtual
circuit number. When a packet reaches its destination the source can be
determined from the virtual circuit number.
Apakah fungsi
pengalamatan layer 4 yang berupa port ? Mengapa pengalamatan layer 3
yang berupa IP dianggap tidak mencukupi
?
Ports
IP supports communication between pairs of computers must
provide process-to-process communication. This is accomplished by the use of
ports. (proses yang membutuhkan layanan (service) yang spesifik).
IP hanya digunakan sebagai pengalamatan saat pengiriman
paket. Belum sampai pada inter-process communication dari message-nya sendiri
yang membutuhkan layanan (service) yang bersifat spesifik.
|
z
|
Media
|
MTU (bytes)
|
Internet IPv4 Path MTU
|
At least 68[4]
|
Internet
IPv6 Path MTU
|
At least 1280[7]
|
1500[9]
|
|
1492[10]
|
|
Ethernet Jumbo Frames
|
1500-9000
|
7981[11]
|
|
4464
|
|
4352[5]
|
