7.4.4. Network Devices

The Internet is one big network of internal networks, related to that purpose designed devices, with the edge of which are end users. Generally each network system must meet some requirements regarding functionality that could be considered in two categories.

End-user devices allow the user to use a variety of applications regarding the use of various Internet services and network device, enabling the exchange of information between users devices over the connecting lines of various types. Physical connection to the network is achieved by merging with a specially designed card that is inserted into the computer, and allows modem or Ethernet communications. It is good that these cards for this action have their own processor to the less debited processor of computer. An increasing number of cases in which both functions are implemented on the motherboard of your computer (especially for notebooks) which is not good because they are usually cheaper circuits. In professional purposes, for example, better quality upgrade NIC in a PC and turn off the integrated onto the motherboard. Logical connection to the network using standard called PROTOCOLS.

The protocol is a formal set of rules and conventions that are used in the work of the network devices. The connection to the Internet can be achieved by using multiple types of protocols, but TCP / IP protocol suite basis of the modern Internet. Network devices connected user devices, including the network, into a single functional unit. A company that is in the design of network devices in the world's most respected Cisco and will continue to use their symbols to explain the basic network devices. Besides Cisco's worldwide enable opening 'Cisco Networking Academy' where students learn how to interconnect all together into a unique whole that works. After completion of the training program CCNA (basic program) or CCNP (advanced program) students can take the exams, which are the starting point for further education offered by Cisco. So many of them, the picture is here and there is all finely written (no commercial advertising, education is very, very useful).

REPEATER - The bus topology can happen that two users connected at opposite ends of the confirmation (Figure 3.6.4) can not communicate because the digital signal is distorted over time and is no longer a well recognizable. Therefore, the input device that has two-way communication and perform restoration of digital signals. Thus increasing the quality of communication and can be achieved by extending the scope of the network. However, this expansion can not go on forever. Standards for Ethernet provides much should be no longer than the time required to exchange frames are between two end users (Round-trip delay time). If you add up the delays that enters regenerator and delay per meter length of the 'journey' through the signals will guide how to get the maximum distance between two transaction confirmations. Regenerator divided into two physical network segment, but it still remains one collision domain. How not processed FRAME belongs to the devices of the first layer of the OSI model.

HUB - Not used bus topology, which is cheap and not too happy about network administrators. Any interruption or impairment of coaxial cable leads to termination of the network functionality. Therefore, devices have been developed that are on their port's connection (RJ45) could accommodate one user device. The physical topology is a star, but it is still the Ethernet technology. HUB boosts the signal, regenerates it, and performs matching between the port and the NIC, and if there is little 'intelligence' knows how will disable the port on which the faulty NIC. In Figure 3.6.8 shows how can be connecting two HUB's. But usually connect more HUB's done so that one of the HUB port's proclaim UP-LINK (link to the master) and that port's are connected to some 'central' HUB. Such a structure would be expanded star. HUB does not share a collision domain and not processed FRAME belongs to the devices of the first layer of the OSI model. Number RJ45 port's usually in the range of 4 to 24 different options are installed electronics and thus prices. Communication between the user and the Half-Duplex, which is clear if you can assist, and the principle of 'I give you, so you give me,' because otherwise it can not because of CSMA / CD.

BRIDGE - Repeater as such could not reduce the amount of collisions on the network, and in order that developed a device that separates the two physical network segment, but by listening to traffic learns and remembers the MAC address of the device for each segment separately in the MAC address table in working memory. So know that you miss in the second FRAME segment or not. Therefore, creating two smaller collision domains, perform filtering and distribution of traffic and increases the throughput of the network. According to the above devices belong to the second layer of the OSI model. But his role is not to be just that. If you need to connect two networks of different technologies such as Ethernet and Token-Ring or Ethernet network and Wireless network must know the make and protocol conversion. In this case, they will run at the higher layers of the OSI model, and of course it will be much more expensive. If the power goes out randomly lose all data from the working memory and must re-learn the (miserable).

SWITCH - With the idea to take advantage of the good properties of the bridge, switch is developed, a device which usually has 4-48 RJ45 ports and features in addition to remember the MAC address, and port number assigned to MAC address. These data are stored in working memory in a data set called the CAM table. Of course, during the work switch learning about connections and if the power goes out must again learn. Connect it to the UPS! With the help of software and embedded electronics can make a separate connection between two users based on their memory of the MAC address (L2 switch) so that those with the handling of interpersonal communication does not bother anyone else. If anyone does not bother NO collisions. Each port is a separate collision domain and because of this quality, it is possible to achieve full-duplex traffic. Of course, need to have a 'smart' NIC in your computer that will know how to use it. How to speak with a MAC address belongs to the devices of the second layer of the OSI model. But the development of technology and falling prices has enabled the development of switches that can be used for communication and the IP address of the packet (L3 switch), and in that the devices fall into the third layer of the OSI model. Of course, much more complex and more powerful, and more expensive. Often they are modular and can be upgraded with optical transducers (transceiver) and between them can achieve reliable and fast communication. Certain species and allow for connecting wireless devices.

ACCESS POINT - Wireless connections are now a reality. Hence, and this type of device found in this group. Act as a central hub that connects via special adapters for the switch. Communication is achieved by CSMA / CA principle. This is an example where the analog signal is modulated by the digital to achieve radio transmission. Using frequencies of 2.4 GHz and 5 GHz. Because of the principle of propagation of electromagnetic waves in all directions 'safety' is one of the major problems. These devices can also serve as a bridge, especially when you want to link two physically separated spaces. Then they will have a symbolic image jumper charted 'twist' as it is in this picture. With directional antennas, it is possible to interconnect a pretty remote places, like islands in Croatia.

ROUTER - With NIC of device it is the crucial, the most important of all network devices. Has knowledge about the availability of all parts of the network. When used within the local network the basic task is to share the broadcast domain. But when configuring it can be set to miss a particular type of traffic on any IP addresses or the type of traffic (protocol field in the header). This means that work on the third layer of the OSI model. In order to direct traffic to the destination of the read packet header is used to support the relevant software and algorithms and protocols (routing protocols) such as RIP, OSPF and others. Operate using a network mask to all computers connected to it via switch or hub grouped into a single IP address - NETWORK ADDRESS. When the router directs FRAME based on readings IP addresses and network masks entered (by the administrator) decide on which port to forward the frame. This network device does not leak PRIVATE network traffic, which generally means that it can enable NAT and DHCP services. The local network serves as a link between the local network and the Internet.

GATEWAY - It's nothing more than a router with some additional modules. The most complex device because it allows regeneration of the signal, the concentration of multiple connections, data conversion and data flow management. When connected as an output device local network must know converting Fast Ethernet communication at a relatively slow serial communication (depending on the type). On the Ethernet side uses the MAC address on the output side of the IP address. That MAC address of its Ethernet port is the default output address for the computer and called DEFAULT GATEWAY (Windows XP). If the network protocol is converted then this device is the fourth layer of the OSI model. Modern routers and switches and their protocols to allow one single network address can be divided into multiple subnets, which are yet to see the world as one. The network is divided into virtual LANs (VLAN - 802.1Q protocol), and certain types of traffic can be restricted to specific VLAN's and the communication between them, which contributes to security of the local network. In addition to directing traffic, from the aspect of a home user, it is a SOHO device that serves as the link between the local network and the Internet.

FIREWALL - By function capability is expanded gateway. Expansion refers primarily to prevent unauthorized access to the network in general. The above means that this device provides control network traffic between boarding school and local area networks in a way that all incoming Internet traffic to the firewall rules defined filters and ducts in the local network and vice versa. Since this is the internal supply unit operates on the same level of the OSI model as a gateway. In addition to traffic filtering to define access rules (ACL - Access Control Lists), the most important is the ability to define the IP address of the local network as a private network, and mechanism of NAT (Network Address Translation) to translate incoming IP address in the local private IP addresses and vice versa. Then the usual support and DHCP (Dynamic Host Configuration Protocol) mechanism automatically assign an IP address to a computer on the local network. Communications initiated outside the firewall are disabled. Although they can be configured via the HTTP protocol with built-in Web server for this purpose, as all modern devices previously mentioned, this does not mean that the device belongs to the highest level. Allow you to set and monitor VPN (Virtual Private Network) traffic and, depending on the purpose and PPPoE (Point-to-Point Protocol over Ethernet) if it is designed as a SOHO device. Such devices, often home, usually support Ethernet and Wireless communication with them and their communication devices connected to the aforementioned ways. Increasing 'mess' on the Internet implies a growing need for this device.

MODEM - Modem is basically described in Chapter 3.6.5, but it relates to modems that are used at home for connection to Internet Service Providers (CARNet, T-Com, Iskon, Globalnet and others). But there are other kinds of devices to connect to a local area network to an ISP (Internet Service Provider). So that we can implement DSL - ADSL, ISDN device, cable modem and other devices with some additional devices allow the user PC or over a local network to communicate with the Internet. Hence, network devices there's more. There's a whole bunch. So far, the bases for understanding the work of any other. Basically this or a similar symbol is used wherever connects the user or the LAN to an ISP.

INTERNET - Internet as a concept does not belong to any device, but it is full of network devices that combine in a single functional unit, with users on the one side and service providers on the other side, as we were in communication with each other through the network devices that are found in their local networks, which enable them to access to the Internet, which are interconnected network devices that is only intended to connect the network. It is therefore a great variety in the design and characteristics of network devices. The variety of services that it offers a very large and diverse group of one so commonly described as a cloud which has everything, including malicious users to a greater or lesser extent, simply harming the entire Internet community. This is favored by, among other things, increasing the speed of communication between network devices, so for example the appearance of a malicious virus in the U.S. means almost simultaneously its expansion in Europe. Any progress apparently has its price, which in this case is reflected in the increasing investment in security.

So, all network devices are not working at all levels of the OSI model as nearly according to the scheme shown below:

Figure* 7.4.8 Scheme of data processing by device type / Examples of devices. ( + / - )

Two final destination point as computers, which handle data across all seven layers of the OSI model in order to monitor its users communicate with each other. To make the data come from one user to another, process them some protocols of individual layers in a way that the data processing and delivery from a higher to a lower layer adds a header (a procedure called encapsulation), and upon receipt of data when moving from lower to higher layer header lower layer is subtracted (a procedure called decapsulation). Specified animation illustrates in Figure 7.4.6.

Network devices, depending on the application are not designed to carry all the headers to interpret the data, but only those for which they are designed, which maps the schema in Figure 7.4.8. But there are exceptions; core network switches are designed to be interpreted so that the pieces of information of the third layer, such as IP addresses from which achieves greater efficiency regarding distributed transactions, but this is not a router or switch can take over its function. Also when to an SOHO device access to the Internet can be accessed regarding configuration through a web interface, it does not mean it belongs to the devices of the highest layer of the OSI model. Examples of devices, mainly for installation in network cabinets, are shown in sub-Figure 7.4.8b.

The network furniture, often called the network switching cabinets or closets or 'rack', is an integral part of network equipment without which the design of a network system is unthinkable. Whether to working on small home versions, that look more like the cupboards for shoes, or a professional wardrobe with ventilation, they showed that the network device in them creating noise. Therefore, such cabinets in larger communities placed in separate rooms, which monitors the temperature of the air conditioner that is able to remember the settings if power fails, and my own new work. The unit measures the height of the cabinet is the height of an average power supply unit (1U), and the width is generally standardized. Will you have a glass door or not or is it a lock for their lock or some specific supplements depending on the needs of the user. A typical example of their arrangement is shown in Figure 7.5.2. Network cabinets need not contain only network devices, anything can be placed in them, from servers, UPS to the network access point, and the like. Depending on the needs of users, network design, and available technology and content closet can be very diverse. Server as the device can not be strictly considered a more network devices, because the primary task of the routing network devices and network traffic monitoring. How will it all work together depends on how it is designed according to the design of all linked together in a patch closets and between cabinets