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2.1 Definition of Computer Networks
A computer network is a collection of two or more computers that are interconnected with each other to communicate data using a communication protocol via a communication medium (cable or wireless), so that these computers can share information, data, together. In this case data communication that can be done through a computer network can be in the form of text, images, video and sound. (Kustanto & Daniel T Saputro: 2008)Meanwhile, according to Oetomo in (Linto, 2003) a computer network is an autonomous group that uses communication protocols through communication media so that they can share data, information, application programs and hardware such as printers, scanners, CD drives or hard drives, and allow them to communicate with each other online. electronic.
2.2 Classification of Computer Networks
The following is a classification of computer networks based on their scale and function.
2.2.1 Network Type Based on Scale
Iwan Sofana (2007) states that, Computer networks can be grouped based on the area that can be reached or served. In general, computer networks are divided into 4 types, namely Personal Area Networks (PAN), Local Area Networks (LAN), Metropolitan Area Networks (MAN), and Wide Area Networks (WAN).
Below are some types of networks based on their scale.
a. Personal Are Network (PAN)
Personal Are Network (PAN) is a computer network formed by several computers or between computers and non-computer equipment (such as printers, fax machines, cellular phones, PDAs, mobile phones). The coverage area of a PAN is very limited, which is around 9-10 meters. A PAN can be built using wire and wireless network technology. PAN wire technology can be connected with USB and FireWire. Meanwhile, wireless PAN can be connected with Bluetooth, WiFi, and Infrared technology.
b. Local Area Networks (LAN)
Local Area Network is a computer network that only covers a small area. such as campus computer networks, buildings, offices, in homes, schools or smaller ones. Currently, most LANs based on IEEE 802.3 Ethernet technology use switch devices, which have data transfer rates of 10, 100, or 1000 Mbps. In addition to Ethernet technology, currently 802.11b technology (or commonly called Wi-fi) is also often used to form LANs.
c. Metropolitan Area Network (MAN)
The technology used by MAN is similar to LAN. It's just that the area is bigger and the computers connected to the MAN network are far more than the LAN. MAN is a computer network that covers an area the size of a city or a combination of several LANs connected into a large network. The MAN network can be a combination of computer networks from several schools or several campuses. MAN can be implemented on a wire or wireless network.
d. Local Area Network (WAN)
Wide Area Network is a computer network that covers a large area (wide). An example is a computer network between regions, cities or even countries, or it can also be defined as a computer network that requires routers and public communication channels. WAN is used to connect one local network with another local network, so that users or computers in one location can communicate with users and computers in other locations.
2.2.2 Network Type Based on Function
Based on the operating pattern or function of each computer, the computer network can be divided into:
a. Peer to peer
Peer to peer is a type of computer network where each computer can be both a server and a client. Each computer can receive and provide access from or to other computers.
b. Client servers
Client server is a computer network where one computer functions as a server. Such as server computers at the Head Office of PT. Semen Baturaja which provides access to the Web, e-mail, files and intranet applications that run on clients via a browser.
2.3 Computer Network Topology
Topology is a structure of a network. There are two kinds of topology, namely:
1. Physical Topology - Describes the actual conditions of the existing network
2. Logical Topology - Describes how a host communicates through the medium.
2.3.1 Physical Topology
Linto (2008) Explains Physical Topology in general there are 5 models, namely Bus, Ring, Star, Extended Star and Mesh.
1. Bus topology
This topology uses a single backbone cable to connect one node to another in a network.
Figure 3.1 BUS Topology
The star toology connects all nodes to a single central node. These nodes are usually hubs or switches.
Figure 3.2 Star Topology
This topology connects one node to another where the last node is connected to the first node so that the connected nodes form a network like a ring.
Figure 3.3 Ring Topology
This toology allows nodes with one or more other nodes connected in the network without a certain pattern.
2.3.2 Logical Topology
The logical topology describes how the media is accessed by the host to send data. In general, there are two types of logical topologies, namely:
In this topology, all hosts can send data to all others via the media in the network. The principle of this topology is First Come First Serve.
b. Token Pass
The token passing topology controls network access by passing electronic tokens to each host in turn. When the host receives the token. Then the host can send data. If no data is sent then the token is passed to the next host and this process repeats continuously. The use of token passing can be found in Token Ring and Fiber Distributed Data Interface (FDDI).
2.4 The Osi Layer Model
The OSI Reference Model for open networking or the OSI open network reference model is a network architectural model developed by the International Organization for Standardization (ISO) in Europe in 1977 (Sofana, 2008). OSI itself stands for Open System
This model is also called the "OSI seven layer model" (OSI seven layer model). The OSI model was created to overcome various internetworking constraints due to differences in network architectures and protocols. In the past, communication between computers from different vendors was very difficult to do. Foreign - each vendor uses different protocols and data formats. So that the International Organization for Standardization of Communications (ISO) made known as an Open System Interconnection (OSI) architecture model that defines standards for connecting computers from different vendors. This reference model was originally intended to develop network protocols. However, the idea failed to materialize.
The following is a table that explains the function of each layer along with examples of the appropriate protocols for each layer.
Protocol Example Function Layer
Application Provides services for various
network applications NNTP, H7, Modbus,
SIP, SSI, DHCP, FTP, Gopher, HTTP, NFS, NTP, RTP, SMPP, SMTP, SNMP, Telnet
Presentation Manages conversion and translation
various data formats, such as data compression and data encryption TDI, ASCII, EBCDIC,
MIDI, MPEG, ASCII7
Session Set the session (session) that
includes estabilishing (starting a session), maintaining (maintaining a session) and terminating (ending a session) between entities owned by the SQL presentation layer, X Windows,
Named Pipes (DNS), NetBIOS, ASP, SCP, OS Scheduling, RPC, NFS, ZIP
Transport Provide end to end
communications protocol. This layer is responsible for "data safety", such as: managing flow control, error detection and correction, data sequencing, and size.
of the packet (packet size) TCP, SPX, UDP, SCTP,
Network Determines the route passed by
data. This layer provides logical addressing and path determination IPX, IP, ICMP, Ipsec,
ARP, RIP, IGRP, BGP, OSPF, NBF, Q.931
Data Link Specifies the physical address
(hardware address), error notification (error detection), frame flow control, and network topology.
There are two sublayers to the data link, namely: Logical Link Control (LLC) and Media Access Control (MAC).
The LLC manages communications, such as error notifications and flow control.
While the MAC regulates the physical address used in the communication process between 802.3 (Ethernet) adapters,
802.11a/b/g/n MAC/LLC, 802.1Q (VLAN), ATM, CDP, HDP, FDDI, Fiber
Channel, Frame Relay, SDLC, HDLC, ISL, PPP, Q.921, Token Ring
This Physical Layer defines the problem
electricity/waves/fields and various procedures/functions related to the physical link, such as the amount of voltage/electrical current, the maximum length of the transmission medium, phase change, cable types and connectors RS-232, V.35, V.34,
I.430, I.431, T1, E1,
10BASE-T, 100BASE-TX, POTS, SONET, DSL, 802.11a/b/g/n
PHY, hubs, repeaters, fiber, optics
Table 2.4 OSI Layers
2.5 VLAN (Virtual Local Area Networks)
In Sofana (2008) explains that, Virtual Local Area Network or abbreviated VLAN is a group of devices on one or more LANs that are configured (using management software) so that they can communicate as if these devices were connected to the same line, even though the devices are actually on a number of different LAN segments.(Wikipedia)
One of the problems faced by (Traditional) LANs is that there is no flexible regulatory mechanism. Administrators will find it quite difficult to group each host based on a certain category. Like grouping some
hosts based on work groups, based on departments, applications or services provided.
To overcome this, we can create a VLAN or Virtual LAN. VLANs can overcome some of the difficulties that traditional LANs cannot solve. For example, we can group several hosts located in four different buildings into one group, for example, lecturer groups, student groups, and others.
When viewed from the membership side, VLANs can be divided into two:
a. Static VLAN
Static VLAN is the most commonly used and most secure VLAN type. Each member of a VLAN is assigned a switch port number. Membership will remain that way until we decide otherwise. Usually by moving the network cable to another port. Sometimes static VLANs are referred to as port based VLANs.
b. Dynamic VLAN
In dynamic VLAN, membership will be determined automatically using software installed on a central server, called the VLAN management Policy Server (VMPS).
2.6 Computer Network Devices
Sofana (2008) describes the devices used in computer networks:
Routers have the capability of passing IP packets from one network to another which may have multiple paths between the two. Routers that are connected to each other in the internet network participate in a distributed routing algorithm to connect to each other in the internet network to determine the best path for IP packets to pass from one system to another.
Routers can be used to connect a number of LANs (Local Area Networks) so that traffic generated by a LAN is well isolated from traffic generated by other LANs. If two or more LANs are connected by a router, the LANs are considered as distinct subnetworks. Similar to bridges, routers can connect different network interfaces.
Routers that are generally used consist of two types, dedicated routers (manufactured for example Cisco http://www.cisco.com, BayNetwork
http://www.baynetwork.com) and PC routers. A PC can function as a router as long as it has more than one network interface, is able to forward IP packets, and runs programs to manage packet routing.
In order for a LAN to connect to other LANs, special hardware and software is needed, called a bridge. There are three types of bridges, namely internal bridges, external bridges and remote bridges. The internal bridge is the bridge that contains the server computers for the two LANs to be connected. An external bridge is a bridge that requires a specific PC each to be set up as a bridge on the two LANs to be connected. Remote bridge is a bridge that allows the formation of WAN. This remote bridge is actually the same as an external bridge with the difference in the distance between the PCs used so that the bridges are far apart. The connection between the PC bridge is done via a modem and a telephone line.
Similar to a router, a switch divides a large network into smaller segments, reducing the number of users consuming network resources and bandwidth. Switches are very useful for preventing collisions between data packets and reducing competition between workstations thereby increasing network performance. But on the other hand, it is different from a router, a switch allows certain bandwidth to be assigned to each device on the network. The switch also provides a Virtual Local Area Network (VLAN) that allows the creation of a small group of users within an existing network without costly architectural modifications.
Switches are also useful for combining several hubs in a dispersed network, because the incoming data speed does not decrease even though many resources are connected.
Hubs can function as connecting cables of the same or different types, as repeaters or amplifiers or intelligent hubs. Hub is a device where several workstations and servers are connected via cables to form a LAN and allow data exchange. The term hub is usually used for ethernet networks, while for token ring networks the term MAU (Multistation Access Unit) or concentrator is used.
There are two types of hubs namely active and passive hubs. Passive hubs only provide a wired connection that connects each workstation to the server without amplifying the data signal, so passive hubs are not suitable for long-distance connections. Meanwhile, active hubs besides being able to be a long-distance data connection also have an electrical circuit that filters and amplifies the data signal that passes through it. Hubs can also be referred to as repeaters because of their ability to retransmit data packets received from various resources.
2.6.5 NIC (Network Interface Card)
Network Interface Card is a card that is needed by every PC computer, both server and workstation computers, so that they can be combined into a network. On each card there is a connector for connection with a cable. There are several types of cards depending on the network topology used.
Ethernet cards have higher speeds and of course cost more than other cards. The type of ethernet card according to the bus used:
2. Ethernet with ISA bus.
3. Ethernet with PCI bus.
4. Ethernet in the form of a PCMCIA card.
2.7 Data Transmission Media
2.7.1 Copper media (copper media)
Copper media is all data transmission media made of copper known as cable. Data sent through cables in the form of electrical signals. Example of cable specification.
1. 10BASE-2 (Thin Ethernet)
2. 10BASE-5 (Thick Ethernet)
The types of cables used for data transmission on the network
The advantage of using coaxial cable is that it is cheap and the range is quite far. The drawback is that it's difficult to install
Gambar 2.7.1 Kabel Koaksial
Figure 2.7.2 Thin Ethernet (left) and Thick Ethernet (right)
The advantage of using STP (Shielded Twisted Pair) cables is that they are more resistant to electromagnetic wave interference from both inside and outside. The drawbacks are that it is expensive, difficult to install (especially grounding problems), and the range is only 100m
Figure 2.7.3 STP (Shielded Twisted Pair) Cable
STP (Screened Twisted Pair) is a twisted pair cable that is balanced and covered by metal braid, a layer of tin (which is called a screen), or both, and bundled together in a single cable sheath. This cable has immunity to noise but the price is more expensive when compared to UTP (Unshielded Twisted Pair).
Figure 2.7.8 ScTP Cable (Screened Twisted Pair)
UTP (Unshielded Twisted Pair) is a type of cable media that does not have a protective layer (shield) and is only protected by the outermost layer (outer jacket). The advantage of using UTP cable is that it is cheap and easy to install. The drawback is that it is susceptible to electromagnetic wave interference, and its range is only 100m. The specifications of the UTP cable, among others:
1. Cat 1 : Voice Only (Kabel Telpon RJ-11)
2. Cat 2 : 4 Mbps
3. Cat 3 : 10 Mbps
4. Cat 4 : 16 Mbps
5. Cat 5 : 100 Mbps
6. Cat 5e : 100 – 1000 Mbps
7. Cat 6 : 1 Gbps
Figure 2.7.9 UTP Cable (Unshielded Twisted Pair)
2.7.2 Optical Media
The basic material of optical media is glass with a very small size (micron scale). Usually known as fiber optic (fiber optic). Data is passed on this medium in the form of light (laser or infrared) with a fairly high data transmission speed. This type of media also has a range of more than 3 km.
Figure 2.7.10 fiber optic
2.7.3 Wireless Media
Wireless transmission media use high frequency radio waves. Usually electromagnetic waves with a frequency of 2.4 GHz and 5 GHz. Digital data sent via wireless will be modulated into these electromagnetic waves. Various types of wireless networks or wireless networks, namely:
a. Wireless Personal Area Network (WPAN)
Wireless Personal Area Network is a computer network used to communicate between computer devices (including telephones and Personal Digital Assistants (PDAs)) to one person. The range for the Personal Area Network is only a few meters. Technologies that use WPAN, for example, are Bluetooth and infrared.
b. Wireless Local Area Networks (WLAN)
Wireless Local Area Network uses radio to transmit data between computers on a LAN network. The types of WLAN are:
i. Wi-Fi, usually using a wireless network in a computer system that can connect to the internet or other machines that have Wi-Fi functionality.
ii. Fixed Wireless Data, is a type of wireless data network that can be used to connect two or more buildings simultaneously to expand or share network bandwidth without using cables (physically) in buildings.
iii. Wireless Metropolitan Area Network (WMAN)
This connection can cover a very wide range, such as in a city or country, through several antennas or satellite systems used by telecommunications service providers. This WMANs technology is known as the 2G (second generation) system. The core of the 2G system includes the Global System for Mobile Communications (GSM), Cellular Digital Packet Data (CDPD) and Code Division Multiple Access (CDMA). Henceforth, a transition is being made from 2G to 3G (third generation) technology which will become a global standard and will also have global roaming features.
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