3.6.4. Network Interface Card

The circuit, which together with connectors and wiring, creates physical performance protocols and the OSI model is the interface between the computer and Circuit Embedded communication system, called the Network Interface Card - NIC. What network card quality makes its own processor that takes care of how to integrate a network of media and communication. If most of these fundamental tasks left to the microprocessor, allows the design of cheaper network cards, which is acceptable for computer users but not for the server. Program support, which takes account of the protocols, along with the card constitutes an interface between the computer and communications subnet.

IEEE (The Institute of Electrical and Electronics Engineering) has established a number of ways in which network cards transmit information through the media, mostly various types of lines, adopted by ISO and relate to a variety of computing platforms.

Standards are known under the designation 802.1 to 802.11 onwards that essentially define different topology and data transfer methods, in general:

• 802.1
  Defines the relationship between the IEEE and ISO standards model.
• 802.2
  MAC (Medium Access Control) sublayer and LLC (Logical Link Control) protocols; Standard of communication layer connection and connectivity. Describing the medium access control mechanism and logical data and their reception and transmission (transfer). Standards continue to describe the physical layers of the OSI model.
• 802.3
  CSMA / CD (Carrier Sense Multiple Access / Collision Detection); Bus standards, protocols in which stations listen transmission medium that is what they are doing other stations and depending on the data sent or not, and the mechanism of availability of testing media networks, and if the medium is busy not accessed the network to avoid the collision, the most commonly used in ETHERNET.
• 802.4
  Token Bus; Mechanism for transmitting packets from station to station in the sender has 'put' information and address (code) of the destination station and a destination that takes a package (sometimes called 'tokens') comes up to him and when the address is in the package agreed with the destination address. The order of transmitting stations is random.
• 802.5
  Token Ring; Mechanism similar to the previous except that 'tokens' constant travels in a circle in the same direction. Use the type of ring topology.
• 802.6
  DQDB (Distributed Queue Dual Bus); Standard that supports communication through light fibers, support networks of type MAN (Metropolitan Area Network) and WAN (Wide Area Network), and the city and state-transnational networks.
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• 802.11
  DSSC (Direct Sequence Spread Commission); Used CSMA / CA Technology (Carrier Sense Multiple Access / Collision Avoidance). Type and speed of communication can be recognized by standard which indicates the following suffix (a, b, g, n, ac, ax). Standard that supports wireless communications developed several versions of the operating frequency of 2.4 GHz and 5 GHz at speeds of 1-150 Mbps (up to n standard) or up to 1.7 Gbps for four-channel standard (standard ac). This standard belong to Wi‑Fi devices that work according to the specifications established for better interoperability which adheres to a couple of hundred companies (3Com, Cisco ...). Standard mechanism used positive confirmation of connection (ACK - explicit acknowledgment packet), which requires that you first examine the state of the media in order to determine its availability.
  
  
  • 802.11g (Wi‑Fi 3) In 2002 and 2003, WLAN products supporting a newer standard called 802.11g emerged on the market. 802.11g attempts to combine the best of both 802.11a and 802.11b. 802.11g supports bandwidth up to 54 Mbps, and it uses the 2.4 GHz frequency for greater range. 802.11g is backward compatible with 802.11b, meaning that 802.11g access points will work with 802.11b wireless network adapters and vice versa.
    
    
  • 802.11n (Wi‑Fi 4) Sometimes known as Wireless N, was designed to improve on 802.11g in the amount of bandwidth it supports, by using several wireless signals and antennas (called MIMO technology) instead of one. Industry standards groups ratified 802.11n in 2009 with specifications providing for up to 600 Mbps of network bandwidth. 802.11n also offers a somewhat better range over earlier Wi‑Fi standards due to its increased signal intensity, and it is backward-compatible with 802.11a/b/g gear.
    
    
  • 802.11ac (Wi‑Fi 5) The generation of Wi‑Fi that first signaled at 2014 popular use, 802.11ac uses dual-band wireless technology, supporting simultaneous connections on both 2.4 GHz and 5 GHz Wi‑Fi devices. 802.11ac offers backward compatibility to 802.11a/b/g/n and bandwidth rated up to 1'300 Mbps on the 5 GHz band plus up to 450 Mbps on 2.4 GHz. Most home wireless routers are compliant with this standard.
    
    
  • 802.11ax (Wi‑Fi 6) Branded as Wi‑Fi 6, the 802.11ax standard went live in 2019 and will replace 802.11ac as the de facto wireless standard. Wi‑Fi 6 maxes out at 10 Gbps, uses less power, is more reliable in congested environments, and supports better security.
    
    
  • 802.11ax (Wi‑Fi 6E) The improved version of 802.11ax was launched in 2020, in which the upper limit of the 5 GHz range was increased from 6 GHz to 7 GHz, so it has a frequency range of 2.4 GHz and an extended frequency range of 5-7 GHz.
    
    
  • 802.11be (Wi‑Fi 7) Uses Flexible Channel Utilization. Technology advancement is based on preamble puncturing to avoid channels with interference, resulting in an ability to use wider channels also in the face of interference. Wi‑Fi 7 can deliver massive throughput gains thanks to a wider channel and capacity gains from 6 GHz spectrum. Wi‑Fi 7 can deliver peak rates of over 40 Gbps, a 4X increase over Wi‑Fi 6E.
    
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• 802.16
  WiMAX (Worldwide Interoperability for Microwave Access); Wireless technology that enables wireless broadband access within the frequency range of 2-11 GHz. Providing broadband access without the need to create a direct line of sight, LOS - Line of Sight between the transmitting and receiving antenna. Within a radius of 8 km is provided to beneficiaries for the joint use of total throughput capacity of over 75 Mbps. Therefore, the available resources are divided into the number of users currently present within the geographical area of operation. By the way, the part of the working frequency ranges and microwave ovens that 'cooked dinner' :-). Defines two standards, one for the fixed wireless network and the other for the mobile network. Over time, both versions evolve using additional frequency spectrum and more advanced communication standards, which is particularly interesting for the introduction of 5G technology for Home Mobile Internet (Homebox) and smartphones.
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The card is to connect computers in the same network topology. Connect different network topologies can be done by inserting multiple cards for different configurations of the server each 'serving' their topological manifold. Of course, the network needs to support software for a variety of network systems. NetWare network type system in its structure has implemented support for the server to perform the task of bridge and router and is diverse enough to insert the card.

PC network card is configured for one of the most common types of I / O bus (ISA, VLB or PCI) and usually supports ISA, PCI, or PCI-E bus, which fully meet the requirements concerning network communications. The network card on the front will have one or more types of connections:

             1.) THIN ETHERNET (thin coaxial cable) - bus topology with
                 'transceiver' (hand-transmitter) installed on the card.
                 Coaxial cable via BNC-T by binding directly to the card;
                 has greater immunity to noise, typical for bus topology.
                 The solution is cheap, but does not tolerate poor grounding.
                 Interruption or damage to the cable causes
                 the complete dysfunction of the entire network.
				 
             2.) TWISTED-PAIR (twisted four pairs of wires) - star
                 topology with the hub (traffic center) and RJ45
                 PTT connector type for the phone. Can be shielded STP and
                 UTP-unshielded, are cheaper and easier to install.
                 Increasing popularity not only gets the relatively
                 cheap connecting wiring but also due to the large fall
                 in the price of active network equipment. Network reliability
                 is significantly higher compared to the Bus topology.

             3.) THICK ETHERNET (thick coaxial cable + TRANSCEIVER) - Device
                 that connects to the network card using 'transceiver' cable
                 (15-pin AUI connector). The solution is generally no longer
                 use, and looking for quality grounding.
                 Interruption or damage to the cable causes
                 the complete dysfunction of the entire network.

Card that contains several types of connections commonly called combined (combo) network card.

Figure* 3.6.17 Bracket of 'Combo' PC NIC / NIC Examples. ( + / - )

Of course, it is not possible to simultaneously use multiple ways of connecting the network card to the network, but only one of them. In the configuration file card should define what kind of connection with the card to work. NIC when no appropriate connector for connecting portable media, the AUI (Attachment Unit Interface) connector that allows connection to a variety of media with appropriate transceiver's (converters). Transceiver is basically a receiver-transmitter, and can and do transform the signal into another one of nature (electrically in the optical and vice versa). As the receiver-transmitter default is to have two-way communication. In addition, the network card can be active at the same time (configured) in a single network, regardless of the protocol used.

Cards with multiple interfaces, as shown in the previous Figure, usually called 'combo'-combined. Function of transceiver with 10Base2 and 10Base-T does electronics incorporated on the printed board network card.

Particularity about this are:

             4.) FIBER-OPTIC (fibers) - the cable has two or more
                 optical fiber because fiber only supports one-way
                 communication. Provide good security for resistance
                 external electromagnetic influences and high speed transfer
                 data, but they are very expensive. Network card of this type
                 systems are used to store huge amounts of data.

             5.) WIRELESS (based on the use of electromagnetic waves) - Everyday
                 all prevalent types of communication that enables connection
                 PC via PCI or PCMCIA network card.
                 There are also versions of USB devices that serve as a wireless
                 communication device or even contain converter for converting
                 wireless communication in a wired communication. Commonly
                 used in notebook computers.

There is widespread use of RJ45 connections and star network architectures. Namely price drop HUB and SWITCH devices in fully displacing a thin Ethernet cable to the network configurations because of the unreliability of the bus network topology. Thick Ethernet cable is used only in the old systems if they are to function. Besides better HUB or SWITCH is able to identify which network interface card or cable are not correct and that port is automatically disconnected from the system. SWITCH has additional features, better described in the Chapter of Intranet.

Each network adapter hardware device is assigned a unique number (MAC address - Media Access Control) which is given command of the OS can be read as a hex notation, for example 08:00:20:7B:2B:36 (48 bits), if the computer involved and active on the network. Special international organization assigns a set number of manufacturers of network cards so that no two cards in the world with the same hardware number. In this way they avoid the 'differences' between the cards in the network traffic. Hexadecimal first 6 digits MAC address indicates the manufacturer, and the next 6 unique card number of manufacturers. As there is no legal obligation on the registration network cards sold this information is not helpful in detecting 'naughty' users. Since the paper uses the NIC MAC address belongs to the L2 layer of the OSI model, of course with the L1 layer circuits. Transceiver (receiver-transmitter) is one L1 devices layer because it works only with signals is not addresses.

NIC has the following functional parts:

• Module of transmitting-receiving
  In essence they are transmitting and receiving circuits of signals with data.
• Module of encoding-decoding
  Allows the insertion of the synchronization bit sequence in the data just before the transmission, in order to maintain synchronization in receiving and transmitting, and extract the data when it receives.
• Medium Access Module (MAC)
  The most important module generates a transmission destination address, control and CRC field of FRAME, while receiving treatment addresses of FRAME and its reception, and error detection and procedure in the event of a fault. The algorithm of the module allows for this purpose provides processor designed with the associated memory in which the registered MAC algorithm.
• Buffer for FRAME
  A cache in which it is entered FRAME before transmitting or kept just received FRAME. It measured from a few kB to MB.
• Interconnection towards the bus (computer)
  Presents circuits which will send data to the computer in the bus to him recognizable form or vice versa. Therefore, they are designed for ISA, EISA, MC and other types of buses. This means that the card for one type of computer can not be used in another.

NIC hardware settings are:

• Number of interrupt
  When NIC receives data informs the CPU becomes the arrival information via a signal interrupts - IRQ. Upon receipt of the interruption signal stops the current CPU task, writing where it left off, examining where the wire interruption occurred, and the number of stops and starts interruption vector table corresponding service software routine that knows how to process the received packets and which passes control to the CPU. Selection is usually IRQ 5, it is rarely used by computers LPT2, or PnP (Plug and Play - Insert and Work) if the NIC, BIOS and OS support it.
• DMA or DMM (Direct Memory Mapping - Shared Memory)
  NIC may use one of the DMA channels to transfer data from the buffer and the NIC in the computer memory or memory mapped buffers in the NIC memory area in the range of 640 kB-1 MB. Then you have to specify a starting address of the NIC buffer and its size.
• I / O port address
  I / O address must be chosen that does not conflict with existing devices, such as 300H or will ask itself if the NIC, BIOS and OS type PnP (Plug and Play).

By the speed of data transmission in computer DMM is the fastest, followed by the I / O port, and DMA. It is possible to use, and combinations thereof.

Each card that is inserted into the slot motherboard should be granted free IRQ number and address (e.g. IRQ=5, I / O address=300H) and bridging specify which type of connectors used, the presence of BOOT ROM for stations without OS disk and so forth. If the slot's computer input multiple cards each must be individually configured in various interruptions and address since it is essentially more devices. This simplifies the task of using a PnP card is a new generation who are in communion with the BIOS and OS of the new generation automatically all adjusted.

Most modern motherboards for computers have built UTP network card, and when it comes to portable computers (laptops) often have a modem port (RJ11), UTP port (RJ45), and wireless connectivity for CSMA / CA technology to Wi‑Fi 802.11x standard for connections to approximately 100 m and BLUETOOTH technology (radio link at 2.4 GHz) for close links to 10 m. Over greater distances (WAN), over 10 km, is designed for WiMax wireless technology based on the 802.16 standard, which is not a substitute for Wi‑Fi standard that the example uses the SOHO environment. So, types of network interface card are very different regards to its purpose, protocol and interface.

In relation to the block diagram shown in Figure 7.4.9, the wireless card has additional devices that perform the modulation and demodulation of high-frequency signal with a signal from digital receiver and transmitter of network card to encrypt the content with regard to its protection from reading and network access security mechanism.

SUMMARY:

Undoubtedly a network card is a very important communicational device. If you look closely at the network card in Figure 3.6.1c, it may be noted that some have a large chip mounted on a printed board, as shown on the card in the Figure 4.6.48d. This means that they have their own processor (according to the diagram in Figure 7.4.9) that monitors communication, and uses their own DMA channel (Remote DMA - RDMA). In computing, remote direct memory access (RDMA) is a direct memory access from the memory of one computer into that of another without involving either one's operating system. This permits high-throughput, low-latency networking.

RDMA supports networking by enabling the network adapter to transfer data directly or from a cache memory, eliminating the need to copy data between the memory used by software of the operating system and the data interface. Such transfers do not require work by the processor, interface, or switches, and the transfer of data takes place in parallel with other operations of the operating system. When an RDMA program reads or writes a request, the data is delivered directly to the network, which reduces latency and enables fast transmission of messages.

Therefore, a quality network card has its own receiver (RX) and transmitter (TX) according to standards for the TCP / IP communication protocol set, and possibly some additional (such as IPX / SPX). Network cards embedded on the motherboard generally do not have the aforementioned feature, and for communication purposes are used CPU resources and capabilities of the operating system.