Electronic interfaces/Network interfaces

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1 Network interfaces
2 References

Network interfaces

A network is a collection of computers or devices connected to each other with the ability to exchange data and or share resources.^[1] A network interface is the point of interconnection between a computer and a private or public network. Networks operate using serial communication. Examples of different networks are:

Local area network (LAN), which is usually a small network constrained to a small geographic area. Computers and devices are linked via Ethernet Cable, can be joined either directly or via a network router that allows multiple connections.
Wide area network (WAN) that is usually a larger network that covers a large geographic area. The largest and best example of a WAN is the Internet, which is a network comprised of many smaller networks. The Internet is considered the largest network in the world.^[2]. The PSTN (Public Switched Telephone Network) also is an extremely large network that is converging to use Internet technologies, although not necessarily through the public Internet.

Wireless LANs and WANs (WLAN & WWAN) are the wireless equivalent of the LAN and WAN.
An intranet is a private network within an organization that uses the same communications protocols as the Internet. When part of an intranet is made accessible to suppliers, customers or others outside the organization, that part becomes an extranet.
An internet (spelled with a lower case i) is a network that is composed of a number of smaller computer networks. The Internet (spelled with an upper case I) is the world-wide network of interconnected internets that operates using a standardized set of communications protocols called TCP/IP (transmission control protocol/Internet protocol), or the Internet protocol suite. This ultimate internet is vastly larger than any other internet and connects thousands of networks and hundreds of millions of computers throughout the world.

All networks are interconnected to allow communication with a variety of different kinds of media, including twisted-pair copper wire cable, coaxial cable, optical fiber, and various wireless technologies. The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the interconnections of the Internet).

History

In September 1940 George Stibitz used a teletype machine to send instructions for a problem set from his Model K at Dartmouth College in New Hampshire to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypes to computers was an interest at the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a working group he called the "Intergalactic Network". The first true computer network, the "Advanced Research Projects Agency Network" (ARPANET) was developed by the Advance Research Projects Agency (ARPA) designed for the United States Department of Defense. It is the precursor for today's internet. The first message ever to be sent over the ARPANET (sent over the first host-to-host connection) occurred at 10:30 PM on October 29, 1969. It was sent by UCLA student programmer Charley Kline and supervised by UCLA Professor Leonard Kleinrock. The message was sent from the UCLA SDS Sigma 7 Host computer to the SRI SDS 940 Host computer. The message itself was simply the word "login." The "l" and the "o" transmitted without problem but then the system crashed. Hence, the first message on the ARPANET was "lo". They were able to do the full login about an hour later.

Hardware

All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category_5_cable). Less common are microwave links (as in IEEE_802.11) or optical cable ("optical fiber").

Network Interface Cards: A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.
Repeaters: A repeater[1] is an electronic device that receives a signal and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair ethernet configurations, repeaters are required for cable runs longer than 100 meters away from the computer.
Hubs: A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub for transmission. When the packets are copied, the destination address in the frame does not change to a broadcast address. It does this in a rudimentary way: It simply copies the data to all of the Nodes connected to the hub.
Bridges: A network bridge connects multiple network segments at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments. Bridges inspect incoming traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects each incoming Ethernet frame - including the source and destination MAC addresses, and sometimes the frame size - in making individual forwarding decisions. Bridges come in three basic types:
- Local bridges: Directly connect local area networks (LANs)
- Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.
- Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
Switches: A switch is a device that performs switching. Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of each packet (based on the MAC address), and forwarding them appropriately. By delivering messages only to the connected device intended, a network switch conserves network bandwidth and offers generally better performance than a hub. As with hubs, Ethernet implementations of network switches are the most common. Mainstream Ethernet network switches support either 10/100 Mbps Fast Ethernet or Gigabit Ethernet (10/100/1000) standards.
Routers: Routers are networking devices that forward packets from one network to another. Based on internal routing tables, routers read each incoming packet and decide how to forward it. The destination address in the packets determines which line (interface) outgoing packets are directed to. In large-scale enterprise routers, the current traffic load, congestion, line costs and other factors determine which line to forward to. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Some DSL and cable modems, for home (and even office) use, have been integrated with routers to allow multiple home/office computers to access the Internet through the same connection. Many of these new devices also consist of wireless access points (waps) or wireless routers to allow for IEEE 802.11g/b wireless enabled devices to connect to the network without the need for cabled connections.

Ethernet

Ethernet is a physical and data link layer technology for local area networks (LANs)^[3]. Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. When first widely deployed in the 1980s, Ethernet supported a maximum theoretical data rate of 10 megabits per second (Mbps). Later, Fast Ethernet standards increased this maximum data rate to 100 Mbps. Today, Gigabit Ethernet technology further extends peak performance up to 1000 Mbps. Higher level network protocols like Internet Protocol (IP) use Ethernet as their transmission medium. Data travels over Ethernet inside protocol units called frames. The run length of individual Ethernet cables is limited to roughly 100 meters, but Ethernet can be bridged to easily network entire schools or office buildings. Most manufacturers now build the functionality of an Ethernet card directly into PC motherboards, obviating the need for installation of a separate network card.

Cables and Connectors

The currently most widely used twisted pair standards are 10BASE-T, 100BASE-TX, and 1000BASE-T (Gigabit Ethernet), running at 10 Mbit/s, 100 Mbit/s, and 1000 Mbit/s (1 Gbit/s) respectively. These three standards all use the same connectors. Higher speed implementations nearly always support the lower speeds as well, so that in most cases different generations of equipment can be freely mixed. They use 8 position modular connectors (8P8C), often called RJ45, based on the telecommunications standard TIA/EIA-568-B, which defines a hierarchical cable system architecture The cables usually used are four-pair or above twisted pair cable. Each of the three standards support both full-duplex and half-duplex communication. According to the standards, they all operate over distances of 'up to 100 meters'.

Category 5 cable

The specification for category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. These documents specified performance characteristics and test requirements for frequencies of up to 100 MHz. Category 5 cable includes four twisted pairs in a single cable jacket. This use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and other pairs (this latter form of interference is called crosstalk). It is most commonly used for 100 Mbit/s networks, such as 100BASE-TX Ethernet, although IEEE 802.3ab defines standards for 1000BASE-T - Gigabit Ethernet over category 5 cable. Cat 5 cable typically has three twists per inch of each twisted pair of 24 gauge copper wires within the cable.

Category 5e cable

Cat 5 e cable is an enhanced version of Cat 5 that adds specifications for far end crosstalk. It was formally defined in 2001 as the TIA/EIA-568-B standard, which no longer recognizes the original Cat 5 specification. Although 1000BASE-T was designed for use with Cat 5 cable, the tighter specifications associated with Cat 5e cable and connectors make it an excellent choice for use with 1000BASE-T. Despite the stricter performance specifications, Cat 5e cable does not enable longer cable distances for Ethernet networks: cables are still limited to a maximum of 100m (328ft) in length (normal practice is to limit fixed ("horizontal") cables to 90 m to allow for up to 5 m of patch cable at each end). Cat 5e cable performance characteristics and test methods are defined in TIA/EIA-568-B.2-2001.

TIA/EIA-568-B.1-2001 defines the pin/pair assignments for eight-conductor 100-ohm balanced twisted-pair cabling, such as Category 3, Category 5 and Category 6 unshielded twisted-pair (UTP) cables. These assignments are named T568A and T568B and they define the pinout, or order of connections, for wires in 8P8C eight-pin modular connector plugs and sockets.

8P8C Socket		8P8C Plug		T568A and T568B connector configuration
Pin	T568A Pair	T568B Pair	Wire	T568A Color	T568B Color
1	3	2	tip	white/green stripe	white/orange stripe
2	3	2	ring	green solid	orange solid
3	2	3	tip	white/orange stripe	white/green stripe
4	1	1	ring	blue solid	blue solid
5	1	1	tip	white/blue stripe	white/blue stripe
6	2	3	ring	orange solid	green solid
7	4	4	tip	white/brown stripe	white/brown stripe
8	4	4	ring	brown solid	brown solid

For a horizontal cable segment, the TIA/EIA 568 standard recommends the use of four-pair cables with all eight wires terminated in 8-position jack connectors at each end of the link. The entire twisted-pair cabling system should be wired "straight through." This means that pin 1 of the connector at one end of a horizontal cable is wired to pin 1 of the connector at the other end, and so on for all eight connections. This keeps the structured cabling system very simple and straightforward.
The words tip and ring are used to identify wires in a wire pair. Most single telephone circuits require just two wires to deliver what is known in the telephone industry as plain old telephone service (POTS). These two wires are identified as "tip" and "ring" by the industry. These names date from the earliest days of manual telephone switchboards, when operators made connections between telephone lines using patch cables with 1/4" phono plugs on the end. The plugs had a Tip (+) and a Ring (-) conductor, followed by the Sleeve (gnd); hence the names for the two wires still used to make a basic telephone connection. Each pair of wires in a modern communications cable is still considered to have a designated tip conductor and ring conductor, labeled T1 and R1 for the first pair, T2 and R2 for the second pair, and so on.
To help identify all the wires found in a multi-pair communications cable, the telephone industry has developed a widely used system of color coding. This system uses a pair of colors to identify the individual wires in each wire pair. The primary color group consists of white, red, black, yellow and violet. The secondary group uses the colors blue, orange, green, brown and slate. These colors are used to identify the wires in the majority of twisted-pair communications cables, from two-pair cables on up to larger cables. A primary color is paired with one of the secondary colors for each wire in the cable. For large cables, the primary color is used until it has been combined with each of the five secondary colors. Then the next primary color is paired with each of the five secondary colors, and so on. In a typical four-pair cable, the primary color is white, and no other primary color is needed, since there are only four pairs. Starting with the first wire in the first wire pair of a cable (T1), the insulation is given a base coat of the first primary color, white, with a stripe or dash of the secondary color blue. This is written as "white/blue" and is abbreviated as W-BL. The second wire in the first wire pair (R1) is given a base coat of the secondary color, blue, with a stripe or dash of the primary color white, written as "blue/white" and abbreviated as BL-W or sometimes just BL. In the first wire pair, then, the T1 wire is white with a blue stripe, and the R1 wire is blue with a white stripe. In the second wire pair, wire T2 is white with an orange stripe, and R2 is orange with a white stripe, etc.

Laboratory use

Ethernet interfaces are becoming more common in laboratory automation and instrumentation, although still not approaching the level of use of RS-232. Most laboratory instruments do not need the speed offered by Ethernet, but the ease of use and standardization of the modular connectors make the interface appealing. The cost of including an Ethernet connection in laboratory equipment has long been a barrier, especially compared to RS-232, but the widespread use of the network interface has significantly lowered the cost. Some instrument providers offer serial to network interfaces for their serial-equppped devices.^[4] Other laboratory equipment offers network capability as an optional add-on. ^[5]

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