· The network interface card (NIC)
· The hub
· The switch
· The bridge
· The router
· The gateway
NIC
A network interface card, more commonly referred to as a NIC, is a device that allows computers to be joined together in a LAN, or local area network. Networked computers communicate with each other using a given protocol or agreed-upon language for transmitting data packets between the different machines, known as nodes. The network interface card acts as the link for the machine to both send and receive data on the LAN.
The most common language or protocol for LANs is Ethernet, sometimes referred to as IEEE 802.3. A lesser used protocol is Token Ring. When building a LAN, a network interface card must be installed in each computer on the network and all NICs in the network must be of the same architecture. For example, all must either be Ethernet cards, Token Ring cards, or an alternate technology.
An Ethernet network interface card is installed in an available slot inside the computer. The NIC assigns a unique address called a MAC (Media Access Control) to the Machine. The MACs on the network are used to direct traffic between the computers. The back plate of the network interface card features a port that looks similar to a phone jack, but is slighter larger. This port accommodates an Ethernet cable, which resembles a thicker version of a standard telephone line. Ethernet cable must run from each network interface card to a central hub or switch. The hub or switch acts like a transmit, passing information between computers using the MAC addresses and allowing resources like printers and scanners to be shared along with the data.
When buying components for a LAN, make sure the NICs and hub or switch have the same capabilities. The entire network must be either wired or wireless, so a wireless network interface card cannot talk to a wired switch or hub. In addition, newer versions of hardware will likely support more features and/or greater speeds than older versions. Make sure your central switch or hub can utilize the highest capabilities of the network interface card under consideration.
Hub
The networking hub (concentrator device) is a junction box with several ports in the back for receiving the Ethernet cables that are plugged into each computer on the LAN. With Ethernet cables going from each NIC to the hub, all computers are connected to the hub.
With a group of computers wired to the hub and the software installed, the computers can talk to each other. Networking hubs will broadcast all traffic that comes through the hub to all machines or nodes connected to the LAN. Each computer/node on the LAN will have its own addresses, called a MAC address. Each node will ignore any traffic not addressed to its MAC address.
Networking hubs are simple devices that are fine for home use in most cases, but not considered best for workplace environments. Networking hubs can only operate in half-duplex mode - - a computer cannot receive and send transmissions at the same time. Another drawback is that networking hubs broadcast traffic indiscriminately to all machines on the LAN. This opens the door to security issues, making it easy to use so-called packet sniffers, for instance, to snoop on all network traffic.
Switch
A networking switch is the central device in a wired or wireless LAN (local area network). It receives signals from each computer on the network via Ethernet cables in a wired network or radio waves in a wireless LAN. In both cases, the networking switch directs traffic across the LAN, enabling the computers to talk to each other and share resources.
If the NIC is wireless, the card will feature a small antenna instead of an Ethernet port. The antenna transmits signals to the wireless networking switch, which also bears an antenna rather than ports. Whether wireless or wired, the networking switch acts as a link, reading traffic packets as they arrive from the various machines and directing the packets to the proper MAC address.
A networking switch runs in full-duplex mode, meaning a machine on the LAN can receive and transmit data simultaneously. This is much faster than a networking hub, an alternate device that serves the same purpose as a switch but operates in half-duplex mode, allowing each machine or node either to send or receive at any given time. Another key difference between a networking switch and a hub is that the switch sends traffic discriminately, using addresses to direct traffic packets exactly where they are supposed to go. Conversely, a networking hub broadcasts all traffic on the network to all nodes, relying in filters within each machine to discard packets not addressed to it. This makes networks that use a hub particularly vulnerable packet sniffers or eavesdropping. Ananti-sniffing software can be installed on a switched network to detect packet sniffers.
Bridge
In telecommunication networks, a bridge is a product that connects a local area network (LAN) to another LAN that uses the same protocol (for example, Ethernet or Token Ring). You can envision a bridge as being a device that decides whether a message from you to someone else is going to the LAN in your building or to someone on the LAN in the building across the street. A bridge examines each message on a LAN, passing those known to be within the same LAN, and forwarding those known to be one of the interconnected LAN (or LANs).
Bridging networks are generally always interconnected LAN since broadcasting every message to all possible destinations would flood a larger network with unnecessary traffic. For this reason, router networks such as the Internet use a scheme that assigns addresses to nodes so that a message or packet can be forwarded only in one general direction rather than forwarded in all directions.
A bridge reads the outermost section of the data on the data packet, to tell where the message is going. It reduces the traffic on other network segments, since it does not send all packets. Bridges can be programmed to reject packets from particular networks. Bridging occurs at the data link layer of the OSI model, which means the bridge cannot read the IP addresses, but only the outermost hardware address of the packet. In our case the bridge can read the Ethernet data which gives the hardware address of the destination address, not the IP address. Bridges forward all broadcast messages. Only a special bridge called a translation bridge will allow two networks of different architectures to be connected. Bridges do not normally allow connection of networks with different architectures. The hardware address is called MAC address. To determine the network segment a MAC address belongs to, bridges use one of:
· Transparent Bridging –They build a table of addresses (bridging table) as they receive packets. If the address is not in the bridging table, the packet is forwarded to all segments other than the one it came from. This type of bridge is used on Ethernet networks.
· Source route bridging – The source computer provides path information inside the packet. Thus it is used on Token Ring networks.
Router
If you have little idea about computer networks or even if you are using Internet, you must have come across the word router. Now the question arises what is router and of course what is routing?
We all know that in any computer network data is transported from one location to another location. This transportation of data is known as routing.
Internet is a worldwide network of computer networks. It is an interconnection of large and small networks around the globe. To connect one network to another we need some sort of the linkage, this linkage provided by an electronic device, work of this device is to connect two or more networks and routes incoming data packets to the appropriate network. The well-known term for such device is router.
When we send any data across the network, it flows in the form of packet, besides containing data itself these packets contains two addresses. One which is assigned to the machine sending data i.e. source address and other assigned to the machine receiving data i.e. destination address. The addresses which we are talking about are known as IP addresses. IP stands for Internet Protocol. All computers across the internet are assigned a globally unique identifier called IP address. IP addresses are used as street addresses so other computers can locate them, these addresses takes the form of four numbers separated by dots e.g. 124.45.68.89. In future the IP numbers will be in the form of six numbers like 192.168.222.212.10.111 known as IPv6 (IP version 6).
Function of router is to take out the destination IP address from the packet and determines the next network point to which a data packet should be forwarded towards its destination. Before reaching the destination from source, packet may have to follow a long path, in between it may go through many routers, like first router may send it to second and so on . . . number may rise up to 10 to 20 routers . . . or even more.
When ultimately packet reaches to the destination machine, that machine uses the source IP address of the packet to send acknowledgement indicating that packet has arrived. This may also happen that packet may not arrive due to some reasons, in that case error will be sent to the source machine.
One very important function played by router is acting as firewall. When our PC is directly connected to the Internet, a unique address is assigned to our PC by the Internet Service Provider (ISP). For example, you are now connected to the Internet, your PC will be having a globally unique IP address, this address is very public i.e. it can be known to anyone anywhere on the internet. In such cases, anyone can use the IP address of user machine to do some mischievous work, for example anyone can install some software to keep track of user activities. One of the software known as spyware can be installed in user machine that covertly gathers user information through the user’s internet connection without his or her knowledge.
In such cases router can act as hardware firewall, it does not allow computer’s IP address to directly expose to the Internet. Now the question arises how it does so?
What happens in such cases the IP address is assigned to the router by ISP and not to the PC, now it’s the work to assign private address to the PC. When we send any packet, router removes the source IP address and attaches its own public IP address, in turn stores the information about all the changes which were made. When any packet comes to the PC, router gets information which it has stored and accordingly routes the packet to the source machine. In this way our PC is not visible on the net, but our PC can see the Internet . . . isn’t it great.
Gateway
A gateway is any hardware and software combination that connects dissimilar network environments. Gateways are the most complex of network devices because they perform translations at multiple layers of the OSI model.
For example, a gateway is the device that connects a LAN environment to a mainframe environment. The two environments are completely different. LAN environments use distributed processing, baseband communications, and the ASCII character set. Mainframe environments use centralized processing, broadband and baseband communications, and the EBCDIC character set. Each of the LAN protocols is translated to the mainframe counterpart by the gateway software.
Another popular example is the e-mail gateway. Most LAN-based e-mail software, such as Novell’s GroupWise and Microsoft’s Exchange, can’t communicate directly with Internet mail servers without the use of a gateway. This gateway translates LAN-based mail messages into the SMTP format that Internet mail uses.
Posted By: Chaudhary Amit V.
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