The HARDWARE 2 course: server, network and communication

2. Network introduction

2.1. Introduction - 2.2. OSI model network - 2.3. Model TCP/IP - 2.4. Types of connected computers - 2.5. Networks applications - 2.6. Types of servers - 2.7. Characteristic of a network - 2.8. Safety and administration

2.1. Introduction

Before attacking us with the infrastructures networks, in general let us take again some basic concepts on the data-processing network.

The networks make it possible to share resources between several computers: data or peripherals (printer, safeguard on tapes, modem, scanner...). The first part of this course takes again all information making it possible to connect these computers between-them. As this processing training is typically hardware, I will be interested mainly only in this aspect. The other aspects of a network are included in the other trainings of technician PC networks, in particular "Base network", "Initiation with systems LINUX & UNIX", "Network software"...

The transmission of information between 2 data-processing programs out of 2 different machines passes by two models: the OSI model or model TCP/IP. These two standards make it possible each part of the communication to dialogue. Each model includes several layers. Each layer must send (and receive for the other PC) a comprehensible message by the two parts, compatibility of information. The following chapter (transmission network bases) will treat communication in its details. 

2.2. OSI model

Other technicians PC / network courses on the networks spoke to you about the various layers of OSI model (Open System Interconnection Model). This ideal model defines in 1977 governs the communication between 2 information processing systems according to 7 layers. With each layer, the 2 systems must communicate "compatible". You reassure, I am not a follower of this matter to proceed. If they are mentioned, they do not form really part of the formation "hardware network". In hardware we use only the sub-bases. The use of Novell Netware, Microsoft Windows NT, Windows 2000, Linux or any other manager of network does not intervene significantly on the hardware, with share for the drivers.

The OSI is a basic model which was defined by the International Standard Organization. This organization returns regularly for standardized various concepts, as well in electronics as in data processing. This model defines 7 levels different for transport from data. These levels are also called layers.

Level 7: level application, manages the transfer of information between programs.

Level 6: level presentation, occupies itself of the data preparation, possibly of in encoding and the compression of the data, for example formatted of the texts, images and videos.

Level 5: the session layer, is occupied of the establishment, the management and coordination of the communications

Level 4: the transport layer, manages the correct handing-over of information (management of the errors), uses in particular the UDP and the TCP/IP

Level 3: the network layer, determines the roads of transport and is occupied of the treatment and the transfer of messages: manage IP and ICMP

Level 2: the data link layer, defines the interface with the board network: hubs, switch...

Level 1: the physical layer, manages the material connections, defines the way in which the data are converted into numerical signals

With each one of these levels OSI, one encapsulates a heading and an end of message which comprises information necessary while following the rules defined by the protocol used. This protocol is the language of communication for the transfer of the data (TCP/IP, NetBui, IPX are the principal ones). On the diagram below, the part which is added on each level is the part on white zone. The part on grayed bottom is that obtained after encapsulation of the preceding level. The last screen, that which one obtains after having encapsulated the physical layer, which is that will be sent on the network.

In hardware, we are interested only in the first three levels of OSI model (until the routers and switch the top-of-the-range one), possibly on level 4 for the firewall. The road bases are reserved for the other courses of the technician PC Networks training, in particular bases network and protocol TCP/IP.

2.3. Model TCP/IP

Model TCP/IP is inspired by OSI model . It takes again the modular approach (use of modules or layers) but contains of them only four:

On each level, the package of data changes aspect, because one adds a heading to him, thus names change according to the layers:

• The package of data is called message on the level of the application layer
• The message is then encapsulated in the form of segment in the transport layer. The message is thus cut out of piece before sending.
• The segment once encapsulated in layer Internet takes the name of datagrams
• Lastly, one speaks about screen on the level of the layer access network

   Layers TCP/IP are more general than in OSI model

2.3.1. level application

The Application Layer includes the standards applications of the network:

• Smtp: "Simple Mall protocol Transport", management of the malls 

• Telnet: protocol allowing to connect itself on a distant machine (server) as a user

• Ftp: "File Protocol Transfer", protocol allowing to exchange files via Internet 

and others less current.

2.3.2. level transport

The transport Layer ensures the routing of the data and the mechanisms making it possible to know the state of the transmission

The protocols of the following layers make it possible to send information of a machine to another. The transport layer makes it possible to identify the applications which communicate. To facilitate the communication, one A not defines names of applications, but of the wearing of communication (varying number from 0 to 65535, 2¹⁶) specific to each application.

The transport layer manages 2 protocols of delivery of information, independently of the type of borrowed network:

TCP ensures the control of the data, directed connection (checks the sending of data by signals of acknowledgement of delivery -acknowledge - of the recipient), he ensures the control of the data thus

UDP, antiquated and not directed connection, does not ensure any control of transmission of the data.

    These 2 types (directed connection or not) are a concept used for the firewall. Indeed, when you closed a port in TCP, the sending of a message does not return signal of return (acknowledge), making believe that address IP is not used. On the other hand, in UDP, the closed port not returning information makes believe that address IP is used. Indeed, the UDP returns a message only if the port is in error (does not answer)

2.3.3. level Internet

Layer Internet is charged to provide the package of the data. It defines the datagrams and manages the decomposition/recombining of the segments.

Layer Internet contains 5 protocols (the 3 first are most important):

1. Protocol IP: manage the destinations of the messages, addresses of the recipient

2. Protocol ARP (Address Protocol Resolution): manage the addresses of the network boards. Each board has its own address of identification coded on 48 bits.

3. Protocol ICMP (Internet Control Message Protocol) manages information relating to the errors of transmission. ICMP does not correct the errors, but announces to the other layers that the message contains errors.

4. Reverse Address Resolution Protocol (Reverse Address Resolution Protocol) manages address IP for the equipment which cannot get of them one by reading of information in a file of configuration. Indeed, when a PC starts, the configuration network reads the address IP which it will use. This is not possible in certain equipment which does not have hard disks (final primarily)

5. Protocol IGMP (Internet Group Protocol Management) makes it possible to send the same message to machine forming part of a group. This protocol also makes it possible these machines to subscribe or to be stopped subscribing of a group. This is used for example in the video conference with several machines, sending of vidéos... The principal HARDWARE application of the IGMP is found in the SWITCH manageables. This protocol makes it possible to gather stations.

2.3.4. Access network sleep

The layer Access network specifies the form in which the data must be conveyed, whatever the type of network used.

It deals with the following concepts:

• Routing of the data on the connection

• Coordination of the data transmission (synchronization)

• Format of the data

• Conversion of the signals (analogic/numeric) for modems

• Control errors with the arrival

24. Types of connected computers and networks

A network makes it possible to connect computers whatever the type: PC, Mac, Hand Frames (host computer)... between-them to share resources.

One determines two types of computers connected on the network: servers and customers. The servers share their resources (files, peripherals of storage, peripherals of impression...). The customers use these shared resources.

One distinguishes three types of networks:

1. the networks "Peer to Peer" or points at points. In these small networks, the connected computers are at the same time customers and servers. A network Peer to current Peer consists of PC under Windows 95 /98 put in networks. This term is also used by extension for the division of music and various files between PC connected on Internet, a nightmare for the administrators networks and an excellent fault of safety for the hackers.
2. The networks known as heavy use a host computer (called server) which shares its resources. In this case, the levels of access of the users allow of protected the data. The various peripherals connected on this server increase further this safety (backup, UPS...). Management is made by a specific operating system of type "Server" such as for example Linux, Windows NT server, Windows 2000 server or Netware Novell.
3. The networks Wan (World  Area Network) are international networks making it possible to inter-connect networks of the heavy type. Internet is a network of this type. A Wan is not distance related, but well to the type of interconnection between two networks.

The applications, the costs and the difficulties of implementation and management are proportional. Safety is inevitably proportional.

Us will not be interested too much in these concepts. Indeed, with share for connections, the considerations Peer To Peer, servers or Wan are determined by the operating system and the use that by the machines.

. Win 95/98/me/ Xp home for Peer To Peer

. Win NT, 2000 server, XP pro, Windows 2003 server, Linux or Netware for the heavy networks

. Unix system or owners (specific to the manufacturer) for the others, even if Wan is configured more and more using gathering of heavy networks. Internet does not make departures from the rule.

2.5. The networks applications.

To connect network computers is not used for large thing without applications. The use of a network allows:

1. Plays. The setting in computer network makes it possible to play several at the same time if the plays includes this possibility. In this case, a simple network Peer to Peer of the Win98 type is sufficient.
2. File sharing. According to the level of desired safety and centralized administration, one can choose either a network Peer To Peer, or for a heavy network. In a Peer To Peer network, safety and the administration are almost null but the installation is relatively easy and flexible. Moreover, it is easier to carry out a safeguard of only one computer (the server) that on all the connected PC. The peer to peer are not thus used that for a restricted number of PC. You can also use a NAS to replace a server.
3. Central application. In business applications, one calls upon a program managing one (or several) data bases. These programs generally require a heavy server. This makes it possible several PC to work on the same basis of data at the same time starting from different PC (accountancy, management of manufacture, invoicing and stock management...). Safety is done on two levels: access to the files and limitations of the rights of access in the program itself. Let us take an example, a company uses a commercial management (invoicing, inventory control...). If the secretary should not have access to the data base, its access server will not include the access to the file. In the same way, the person in charge for the purchases will be limited to the level for the program not to have the access to the invoices of exits or only in consultation. This requires particularly muscular servers with generally an operating system dedicated server.
4. Share connection Internet. To connect itself simultaneously on Internet starting from each PC via their own connection costs in the long term very much. The setting in network of the computers makes it possible to share only one connection (modem, ADL or high speed). This possibility passes by a division of connection Internet under Win98 and higher or by the use of a router or an application software for more professional uses.
5. Divide peripherals. To use a printer by PC allows a flexibility in use. Nevertheless, the simultaneous use of only one printer of large capacity can prove to be profitable with the purchase of a faster printer (generally, more the printer is expensive, less expensive is the page price).

This list is not exhaustive.

2.6. Servers Types.

In the preceding chapter, we spoke about servers in the broad sense. In data processing, one distinguishes three types of servers:

• A file-sharing server stores and distributes data shareable by the users of the local area network. It results from a combination of hardware and software which can be specific. They are also used as print servers.
• An application server makes it possible to exploit an application (a program) on a server starting from all the customers. This is typical with the applications based on data bases (management of manufacture, commercial management, accountancy...). It makes it possible for example to invoice, manage stocks... starting from several PC at the same time in a commercial management. These applications must be dedicated to this mechanism of division. The configuration of these servers are generally definitely more muscular. The server permanently sends the parts of program and data towards each station, which increases the traffic network clearly. The servers of this type are in world PC multiprocessors. The program must be conceived for like application centralized. Indeed, a file (text, table...) can be used only by one program (1 PC customer in our case) at the same time. This poses problems for the safeguards when the server works for example. In the case of the data bases, the dedicated program allows simultaneous work on the same data base. To avoid the risks of errors (modification of the same recording by 2 users at the same time and corruption of the data), the dedicated program will block each recording used by a station. For recall, in the data bases, the recording of a modification is done with fact, without need to use the order to record small file. On the other hand, if the base of data is used, it is impossible to safeguard the base of data. Safety (access control, safeguards,..) is however facilitated bus centralized.
• A printer server makes it possible to divide printers connected on only one PC. Certain printers networks can be directly connected on the network without passing by a PC, specific cases can also be used.

In practice, a server often gathers the three applications. The configurations (powers) are different for each application, the servers of applications are most powerful.

2.7. Network characteristics.

 The local area networks (LAN) are complex infrastructures and not only cables between workstations. If one enumerates the list of the components of a local area network, one will be surprised to find of it a quantity larger than envisaged:

1. Wiring constitutes the physical infrastructure, with the choice between telephone pair, coaxial cable and optical fiber. This choice determines the type of concentrators (switch, HUB) of the network. Those constitute the interns in the case of distribution systems star. In this course, the links microwave (without wire) are seen like a particular wiring.
2. The access method describes the way in which the network referee communications of the various stations on the cable: order, time speaking, organization of the messages. It depends closely on the topology and thus on the space organization of the stations the ones compared to the others. The access method is primarily materialized in the interface boards, which connect the stations to the cable.
3. The protocols of networks are software which "turns" at the same time on the various stations and their interface boards networks. It is the language of communication. So that two structures connected on the network, they must "speak" the same protocol.
4. The server network operating system, often named administrative of the network, is installed on the servers. It manages the divisions, right of access... For Microsoft, one finds Windows NT server, Windows 2000 server, Windows 2003 (NET). They are specific versions. Linux is used under various versions servers. Novell Netware is a mainly effective system dedicated like file server.
5. The system of safeguard is an essential element which functions in various ways either by recopying all the files systematically of the servers, or by making regular safeguards, possibly automated.
6. A bridge, a router or gateway constitutes the means of communication which allow one its users "to leave" the local area network to reach other local area networks or distant servers.
7. The system of management and administration of the network sends alarms in the event of incidents, enters the traffic, memorizes the activity of the network and assistance the supervisor to envisage the evolution of its network. This part is typically software.

2.8. Safety and administration.

    One of the important aspect of a heavy network is the centralization of the administration of the data. This makes it possible to safeguard and make safe the data on only one machine, reducing the wastes of time related to this unpleasing but obligatory aspect of data processing.

Safety gathers a whole of measurements: intrusion and right of access, virus, safeguard of the data, continuity of the application (not of stops)...

There are no ideal solutions for the safety of the networks (and for the computer security in general). Three solutions are possible: material solutions that we will see, of the solutions based on Linux and the solutions based on Windows or the programs added on these Windows stations. The mixture of several solutions is possible in certain cases. Certain solutions are complementary besides. On a large "significant" network, to put a VPN hardware is not sufficient. A complementary software safety including access controls to the level administration server (server, file, right of access) and software of safety measures checking the traffic on the internal network is not superfluous.

• The routers can be replaced by the WinGate software or specific applications in Linux on a dedicated PC for example
• The servers proxy are sometimes integrated in the routers
• The firewall anti-intrusion are integrated in certain routers but software provides (almost) equivalent functions (e.g..: Symantec, Zonealarm)
• The integrated private networks (VPN) allowing an access to a heavy network by Internet are included in certain software or operating systems.
• The antivirus generally software, but are sometimes included in the routers who have their own antivirus software. These equipments directly return all messages containing a virus to its shipper.

According to the application, the originator of the network will use one or the other or a combination of both. The software solutions are reserved for the other courses of the technician PC/networks training. Other control network programs make it possible to manage traffics, users... They are specifically software. The rights of access can be blocked of a station towards a server in its entirety, not on the level of the resources. In light, by hardware, you can block the complete access to a server, by software, to authorize only one part of the resources of a server.

1. Network hardware course - 2. Introduction to communication - 3. Base of transmission -  4. Ethernet cards - 5. Switch, router, ... Ethernet - 6. High speed Internet connections - 7. Networks servers - 8. Special hard drive: SCSI, SAS, RAID - 9. Backup and storage - 10. Hardware Security - 11. Wireless and Wifi - 12. UPS, Inverter, Power Supply - 13 . Corporate network - 14. Other network technologies - 15. Touch Screen, video projector 17. Exercise: connecting hardware firewall

Hardware 1 course: PC and peripherals, Hardware 2 course: Network, servers and communication.

All the hardware training