TCP / IP Introduction to OSI Layer

 TCP / IP Introduction to OSI Layer

By the time we start the step into the science of computer network, the first thing we learn is usually TCP / IP. TCP / IP can be in such language analogy. When humans exchange information, people will speak in a language that can be understood by speakers and listeners. So is the case with the host computer or in a network. Communication and exchange of information in order to be well established, it takes the same language. Although different brands of the network host - different, the host can still communicate with other hosts because it uses the same communication standard, namely TCP / IP. Internet Protocol was first designed in the 1980s. But in the 1990's where the internet is increasingly popular and more and more hosts, ranging bemunculan protocol that can only be used by certain circles, or protocol made by certain manufacturers that are not necessarily compatible with other protocols from other plants as well. So in the end the body the International Standards Organization (ISO) to standardize protocols that are currently known to the protocol of the Open Systems Interconnection or OSI abbreviated. The OSI reference model is widened and the basic concepts of a theory of how the protocol. In the development of TCP / IP is used as a de facto standard.

OSI Layer
When the ISO (International Standard Organization) to standardize the protocol, it creates a standard reference model containing the workings of the protocol. Reference model which was then called the Open Systems Interconnection (OSI). Based on the document recommendation X.200, the OSI standard has 7 layers. Each layer has a different function definitions.

Layer 7: Application Layer
Is the layer where the interaction with the end user interface applications that work using the network functionality, make arrangements of how the application works using the network resources, to then memberika message when an error occurs. Some of the services and protocols that are in this layer as HTTP, FTP, SMTP, etc..

Layer 6: Presentation Layer
This layer works to translate the data format to be transmitted by the application over the network, into a format that can be transmitted by the network. In this layer the data will be encrypted or in-description.

Layer 5: Session Layer
Session layer defines how connections can be made, maintained, or destroyed. In this layer there are protocols Name Recognition, NFS and SMB.

Layer 4: Transport Layer
This layer will split data into packets of data and provide the serial number on the data packets that can be rearranged when it came to the side of the goal. In addition, at this level, will determine the protocol that will be used to transmit the data, eg TCP protocol. This protocol will transmit data packets, as well as to ensure that the packet received successfully (acknowledgment), and retransmit the packets that are lost or damaged on the way.

Layer 3: Network Layer
Network layer will make header for packets that contain IP information, both the sender's IP data and IP destination data. Under certain conditions, this layer will also perform routing through the use of internetworking routers and layer 3 switches.

Layer 2: The data-link layer
Befungsi to determine how the data bits are grouped into a format called a frame. In addition, at this level of error correction, flow control, addressing hardware (such as the Media Access Control address (MAC address)), and determine how the network devices such as hubs, bridges, repeaters, and a layer 2 switch operates. IEEE 802 specification, dividing it into two levels level children, the layer Logical Link Control (LLC) layer and the Media Access Control (MAC).

Layer 1: Physical Layer
Layer Physcal work by defining the network transmission media, signaling method, bit synchronization, network architectures (such as Ethernet or Token Ring), network topology and cabling. In addition, this level also defines how the Network Interface Card (NIC) can interact with cable or radio media.

The process of sending data can pass through each layer analogy like when we send a letter. The letter is the data that will be sent (layer 7 -> 5). Then, according to standard delivery, we put the letter into an envelope (layer - 4). So that we can sent the letter, we need to add the address where the mail is sent, as well as who the sender of the letter was (Layer - 3). Furthermore, the letter we submitted to the expedition, and the expedition we will be sending a letter earlier (layer - 2 & 1).

Packet Header
In the previous review we discuss how a process of data transmitted, now we will try to unload data. What's in sebiah data so that data can be transmitted. analogy when we send data on the Internet is like sending a POS, it can be said that the data is the contents of the letter, then the packet headers is an envelope, stamp, address, and other equipment. Packet header provides some additional information. If we surgical ditrasnmisikan a data packet using ipv4, then the contents of the data packets can be seen as shown below:

IPVer: Storing information used IP version (IPv4 or IPv6).
IHL (IP Header Leght): Information overall length of the data packet header. The minimum length of the IP header is 20 bits, and the maximum length is 24 bits.
TOS: It is a field in the IPv4 header has a length of 8 bits and is used to indicate the type of Quality of Service (QoS) that is used by the datagram in question to be submitted to the internetwork routers. Implementation of this TOS is usually when we do the limitations of HIT in the web proxy service proxy or VOIP.
Bit 16 Total Length: 16 bits The contents of this gives the overall size information packet (fragment) including header and data. Information is displayed in a format bytes
16 Bit Identification, Fragment Offset Flag / Length: At the time of ip packet goes on the internet, this pack will probably pass some routers can not handle the size of the packet, for example, the value of Maximum transmission unit (MTU) that is smaller than its IP datagram size, then The package will be broken or fragmented packets - smaller package would then be reassembled later. These parameters will be used for fragmentation and rearrangement.
TTL: There is the possibility of an IP packet wander aimlessly in the Internet network. Case example of an error routing or routing loops. In order for this package is not circling the Internet forever, the TTL value will be deducted each time a data packet passes through a router. When the TTL value of a packet of data has been exhausted or has a value of 0, then the packet is dropped or discarded.
Protocol: Contains information what protocol is used to transmit data.
16 Bit Header checksum: information is calculated based on the calculation of the value of the IP header content. Used to determine if there is an error at the time of transmission of the data.
32 Bit Source IP Address: 32 bits data packet source IP information.
Bit 32 Destination IP Address: 32 bits IP destination information of data packets.
Options (if any): This parameter includes rarely used, has a variable length, from 0 to a multiple of 32 bits. This parameter can be used to store a value for the security option, Record Route, Time Stamp, etc..
Data: Contains the data that is transmitted.

From the packet header information above, at the end of a data can be sent from one host to another.

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Wiring

Wiring

At the time we speak, we say that the voice could reach the ear associates that we are speaking, it takes a trasnmisi media, in this case air. Each computer also requires a network transmission medium. Transmission medium there are many computer networks, can use the media cable, radio waves / wireless, infrared, bluetooth, or the current popular media uses light (fiber optic). Most of the transmission medium used today are the type of cable. Each type of cable typically have different capabilities and specifications, therefore, made the introduction of cable types.

Twisted Pair Cables

Twisted-pair cable is a type of cable used for telephone communications and most modern Ethernet networks. A pair of wires forming a path to transmit data. The pair made kebel entwined to provide protection against "crosstalk" or interference generated by the pair of adjacent wires. When an electric current flows through a wire, will create small circular magnetic field around the wire. When two wires in an electrical circuit are placed close together, and their magnetic fields are opposite of each other, thus the two magnetic fields will cancel out each other. The cable pair will also eliminate any magnetic field from the outside wires. By turning the cable will be able to enhance the effects of magnetic fields cancel each other out and effectively be able to provide protection to the cable network. There are two general types on the type of twisted-pair cable, unshielded twisted pair (UTP) and shielded twisted pair (STP)

UTP

UTP cable is a transmission medium that consists of 4 pairs of wires. UTP cables are used in a variety of tissues. Each of the eight individual copper wires in UTP cable is covered by an insulating material. In addition, in each pair of wires that are wrapped around each other.

UTP cables are often combined with the use of Registered Jack 45 (RJ-45) connector. RJ-45 connector eight cable is typically used to connect a computer to a local-area network (LAN), especially Ethernet.

UTP cable has four pairs of copper wire with a size 22 or 24 gauge (gauge is the standard cable pengurkuran). One factor that distinguishes other UTP cable with one cable UTP cable has an impedance of 100 ohms. although formerly UTP cable is said to have a slow transfer speed, but in its development are now able to pass traffic up to 1 Gbps. Maximum UTP cable length is 100 meters.

STP

Almost the same with just any pair UTP wire wrapped with metal foil. These four pairs of comrades will be wrapped again with metal foil or metal fibers. The goal is around to reduce noise disturbances such as electric, magnetic fields, etc.. STP can be combined with STP Data Connector or it could be with RJ45. STP maximum cable length is 100 meters. Because it is more resistant than noise, STP cable is more widely used for outdoor applications, such as cable leading to the AP on the tower.

Standard Wiring

Each wire in the cable networks have different functions so that we can not crimping origin. There are two wiring standards most commonly used are: EIA / TIA 568A and EIA / TIA 568B, by way of cable sususan sort by color.

EIA / TIA 568A

The composition of the cable with a standard EIA / TIA 568A begins with green white cable. the cable arrangement would be as follows:

1. The White Green
2. Green
3. White Orange
4. Blue
5. White Blue
6. Orange
7. White Chocolate
8. Brown

EIA / TIA 568B

The composition of the cable with a standard EIA / TIA 568B begins with orange and white colors. Complete sequence of the cable with the standard as follows:

1. The White Orange
2. Orange
3. White Green
4. Blue
5. White Blue
6. Green
7. White Chocolate
8. Brown

Cross Cable & Straight

By the time we talk about sorting pin cable network, of Crossover and Straight designations often we hear.   Straight cable is a cable that ends with the beginning of the end of the end of the cable has the same pin order. Examples of straight cable with standard sequencing pin EIA / TIA 568B

And then end with the back end of the same - the same pin arrangement EIA / TIA 568B. Then for a cross cable, as its name means opposite pin arrangement, or the opposite.

Straight and cross cable is the same - just connect the device to other devices in a computer network, but a device that can be associated with each - each of these different types of cables. Derikut table devices to be connected and cables needed:

Auto MDI / MDI-X

The latest devices today typically supports Auto MDI / MDI-X. Devices that already support Auto MDI / MDI-X can be connected by a straight cable and cross cable. The device will detect whether the connection requires a crossover, and it will automatically use the MDI or MDIX configuration to match the opponent's connection.

Wiring

Before doing the wiring, there are several considerations that must be done first, such as how many computers will be connected. Then the distance between the nodes.

Equipment Needed

to do the wiring, prepare some of the following tools:

• Cable UTP / STP, specify how long the cable, and the amount of wiring required. Cable quality is also different in each brand.
• RJ45, which will be used as a cable connector.
• Crimping Tool, for installing konekstor RJ45 cable to UTP / STP, usually disebit crimping.
• LAN Tester, when the network cable manufacturing process has been completed, the last thing you need to do is testing. LAN tester is used to perform tsting on the cable network. Indication of whether the cable berfungdi normally be of indicators buyi LAN tester beeps or it could be from the LED lights.

Wiring Method

1. Peel the end of the UTP cable, approximately 2 cm.
2. Open the cable strands, straighten and urutankan compliant cables TIA / EIA 368B
3. Once the order is according to the standard, cut and flatten the ends of the cable, input cable is straight and aligned into the RJ-45 connector, and make sure all cables are correct position.
4. Perform using crimping tools crimping, press crimping tool and make sure all the pins (brass) on the RJ-45 connectors already "bite" of each cable. Once finished at the other end, do it again at the other end.
5. The final step is check the cable pulled you created earlier by using the LAN tester, how to enter each end of the cable (RJ-45) masing2 to an available port on the LAN tester, make sure all the lights turn on and the LED lights up in accordance with the order of cable we make.

Make sure the end of the UTP cable that has an RJ-45 connector is attached properly, the cable sheath (blue) also took a bit get into the connector.

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Selection of Frequency Band & Implementation Wireless In

Selection of Frequency Band & Implementation Wireless In

For those who've never tried to implement wireless, will usually encounter some obstacles that sometimes confuse. However, current wireless technologies are widely applied, especially with the range of reasons. Wireless technology is quite helpful especially to reach areas far / wide. Instead of having to build a network cable to connect remote devices, it will be easier and more efficient if you use wireless. But behind these advantages, there are factors that make the application of wireless is not as easy as using a cable. When using a cable, we stayed plug from one port to another. If the remote could use a Fiber Optic. But when implementing a wireless, connect one device to another will be influenced by many factors. Among other things, LoS (Line of sight), site 1 to site that should be able to see each other and without a hitch.

Band

Selecting the band is a standard way to specify the protocol to be used by wireless interfaces. In addition to determining the standard protocol, the band also specify the data rates that can be missed, channel frequencies and channel widths. There are few bands in mikrotik router.

• 2GHz-b, working at a frequency of 2.4 GHz. Using 802.11b protocol with a maximum data rate of 11 Mbit / s.
• 2GHz-b / g, also works at a frequency of 2.4 GHz. Using 802.11b and 802.11g protocols. 802.11g protocol is almost the same as 802.11b but is transmitting with a base such as 802.11a OFDM 802.11g protocol that can reach 54 Mbit / s.
• 2Ghz-b/g/n, working at a frequency of 2.4 GHz. Using 802.11b, 802.11g and 802.11n. The development of the standard 802.11 protocol, coupled with the ability of multiple-input multiple-output (MIMO). With the addition of the MIMO feature, the maximum theoretically achievable data rate is 300 Mbit / s.
• 2GHz-only G, working at a frequency of 2.4 GHz, just use the 802.11g protocol.
• 2GHz-only N, working at a frequency of 2.4 GHz, just use the 802.11n protocol.
• 5GHz-a, working at a frequency of 5 GHz. Using the 802.11a protocol, the maximum data rate that can be achieved is 54 Mbit / s.
• 5GHz-a / n, working at a frequency of 5 GHz. Using 802.11a and 802.11n protocol.
• 5GHz-only N, working at a frequency of 5 GHz and only using 802.11n protocol.

If we look, there are several options that the band uses more than one protocol. If we set a wireless interface with a band that uses more than one protocol, then the wireless interfaces provide options to the client, where the protocols that support the client device.

Frequency

Wireless LAN uses a radio frequency propagation medium that also need to be clean and without interruption. Interference can be obstacles such as trees, buildings, walls, glass or frequency interference from other devices in the vicinity.

In order to form a good wireless link, this disorder should be avoided. The first thing to do is to do a site survey first to determine the physical condition of the field and the use of existing frequencies. For example, the presence of obstructions such as hills, buildings, trees, walls, glass, etc. should be avoided. We also need to know the frequency - a frequency that is around. its use will be avoided so that no interference / overlapping.

The allocation of frequencies is set in the regulations in each region and country. In Indonesia, for the purposes already dalokasikan wireless LANs in the ISM band at 2.4 GHz and 5.8 GHz. More details her, to 2.4 GHz is divided into several channels with each channel width - 22MHz respectively.

So also with the 5GHz. 5GHz frequency is also divided into several channels.

In the proxy, each channel is displayed with its midpoint frequency. For example in the 2.4 GHz band, channel1 = 2412, etc..

Back to the interference problem. In proxy there are several tools that can be used to perform the scanning frequency.

• Scanner Tool, double-click the wlan interface> set mode = station band and frequency> click scan.

• Snooper tool, double-click the wlan interface> set mode = station band and frequency> click snooper.

• Usage Frequency Tool, double-click the wlan interface> set mode = station band and frequency> click Freq. Usage

From these survey results, we can determine the frequency of use on our devices so as not to interfere with the other. Based on the distribution channel at 2.4 GHz, with a standard width of the channel, can be seen there are several mutually overlapping channels. This is what should be avoided so as not to interfere with each other and with well established wireless links. For example, the results of the scan turns out many are using the 2412 frequency (channel 1), then we can use the 2437 frequency (channel 6). Why not use 2417 (Ch.2) alone? not 2412 (Ch.1) and 2417 (Ch.2) are different.? Take a look at the image-sharing channel earlier, between 2412 (Ch.1) and 2417 (Ch.2) was still overlapping, mutually interfere. If pictured again, so as not to interfere with each other can use 2412 (Ch.1), 2437 (Ch. 6), 2462 (Ch. 11)

Well, if for freq 2484 (Ch.14) is a channel that is not standard. Devices like gadgets, laptops usually do not support.

Proxy support for 2484 (ch.14). But we still should not use these frequencies in vain. Although technically support devices, but the use of a clear allocation of frequencies outside violate the rules. So let's use the appropriate frequency of existing regulations. In order not to interfere with each other at other frequencies.

Tips for selection on the frequency of use of the 2.4 GHz band. How to 5GHz?. Most devices such as laptops, gadgets previously was only support for 2.4 GHz only. However, some gadgets now support 5GHz. Similarly to link wireless LAN devices today many are turning to 5GHz. In contrast to the distribution channel at 2.4 GHz, the distribution channel in the 5GHz no overlapping each other. To cover a laptop or gadget, can use the frequency 5725 - 5785 MHz. Most of today's gadgets support at these frequencies. Mikrotik product also has support for both 2.4 GHz and 5GHz bands. Support also for custom and custom channel width freq. But once again, the frequency of use wisely. Do not violate the regulation.

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Selection of Type of VPN

Selection of Type of VPN

 VPN is a method to build a network of links between network nodes in a safe / encrypted by using the public network (Internet / WAN). An example implementation is when you manage a network that consists of several offices in different locations. Would require substantial costs if we then establish a wireless link or fiber optic inter-office but could be located in the city or even a different island. With a VPN, we can establish a link between the office by utilizing the existing internet network. Links are formed secured with encryption to minimize the possibility of data will be accessible by people who are not responsible. Mikrotik VPN support several methods such as PPTP, L2TP, SSTP, and OpenVPN. Given some of these options, we need to select the type of VPN is suitable for our network. In general, all of these types have the same function. The difference is the authentication and encryption in use.

PPTP (Point to Point Tunnel Protocol)
PPTP VPN is one of the simplest type in the configuration. It is also flexible. The majority of operating systems already support the PPTP Client, both the operating system on a PC or gadgets like android. Communication PPTP uses TCP port 1723, and use the IP protocol for packet encapsulation 47/GRE data. In the PPTP settings, we can determine the network security protocol used to authenticate PPTP on Mikrotik, such as pap, chap, MSCHAP and mschap2. Then after the tunnel is formed, the transmitted data will be encrypted using Microsoft Point-to-Point Encryption (MPPE). Encryption process will usually make the transmitted packet header size will increase. If we are monitoring, traffick which passes through the PPTP tunnel will have overhead ± 7%.

L2TP (Layer 2 Tunnel Protocol)
L2TP is an extension of PPTP L2F plus. Network security and encryption protocol used to authenticate the same with PPTP. However, for communication, L2TP uses UDP port 1701. Usually for keamaanan better, combined with IPSec L2TP, L2TP/IPSec be. Examples for the Windows operating system, by default Windows OS using L2TP/IPSec. However, the consequences of course configuration that must be done is not that simple PPTP. The client side must already support IPSec when applying L2TP/IPSec. In terms of encryption, the encryption on L2TP/IPSec certainly have a higher level of security than PPTP uses MPPE reply. Traffick L2TP tunnel that passes overhead will have ± 12%.

SSTP (Secure Socket Tunneling Protocol)
To establish a method SSTP VPN with SSL certificates required in each device, unless both using RouterOS. SSTP communications using TCP port 443 (SSL), its the same thing as the website is secure (https). You have to make sure the clock is in conformity with the real time when using a certificate. Manyamakan time with real-time router can with NTP Client feature. Unfortunately not all OS Support VPN with SSTP method. Traffick SSTP tunnel that passes overhead will have ± 12%.

OpenVPN
VPN is usually used when needed on high data security. By default, OpenVPN uses UDP port 1194 and required certificate on each device to be connected. For compatibility client, OpenVPN can be built almost on all Operating Systems with the help of third-party applications. OpenVPN uses the sha1 and md5 algorithm for the authentication, and using some cipher that is blowfish128, AES128, AES192 and AES256. Traffic passing through the OpenVPN tunnel will have ± 16% overhead.

Keep in mind, that the more we need a secure network, the more complex configuration needs to be applied, as well as the use of hardware resources, the higher the encryption used, resource usage, especially CPU will also rise. The conclusion that we can take, if you want a VPN client that dg better device compatibility, then PPTP could be an option. In addition, PPTP can also be an option if you do not want too much trouble to do the configuration. But if you want a VPN with better security, use L2TP/IPsec or OpenVPN. Typically for windows OS, by default using L2TP/IPSec, so stay diseusuaikan on the server side. If your device supports it and you need a high security on the path that your VPN, L2TP/IPSec could be an option. One thing to note, the use of a VPN can not increase the bandwidth (more precisely reduce your bandwidth because there are additional headers), depending on the bandwidth of your subscription.

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