Hub

What is a Hub?

A hub is used in a wired network to connect Ethernet cables from a number of devices together. The hub allows each device to talk to the others. Hubs aren't used in networks with only wireless connections, since network devices such as routers and adapters communicate directly with one another.
Hubs are such simple devices — they require no configuration, and have no manuals — that their function is now included in other devices such as routers and modems.  NETGEAR no longer sells stand-alone hubs.  If you require a stand-alone appliance, use a switch instead.  Switches provide better performance and features than hubs.
Examples of hubs.

What is switch?

A network switch or switching hub is a computer networking device that connects network segments.
The term commonly refers to a network bridge that processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (layer 3 and above) are often referred to as Layer 3 switches or multilayer switches.
The term network switch does not generally encompass unintelligent or passive network devices such as hubs and repeaters.
                                                               Amitabh Kumar (9015123133, 9811006683)
                                                                                    www. ITRD.CO.IN, AmitSintu@Gmail.com

Router and Switch definition

A router is a device in computer networking that forwards data packets to their destinations, based on their addresses. The work a router does it called routing, which is somewhat like switching, but a router is different from a switch. The latter is simply a device to connect machines to form a LAN.

A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP??s network. Routers are located at gateways, the places where two or more networks connect.
Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.
Very little filtering of data is done through routers.
See "Common Router Settings" in the Quick Reference section of Webopedia.
See also Webopedia's "Did You Know... Routers, Switches and Hubs: What's the Difference?"

How a Router Works

When data packets are transmitted over a network (say the Internet), they move through many routers (because they pass through many networks) in their journey from the source machine to the destination machine. Routers work with IP packets, meaning that it works at the level of the IP protocol.

Each router keeps information about its neighbors (other routers in the same or other networks). This information includes the IP address and the cost, which is in terms of time, delay and other network considerations. This information is kept in a routing table, found in all routers.

When a packet of data arrives at a router, its header information is scrutinized by the router. Based on the destination and source IP addresses of the packet, the router decides which neighbor it will forward it to. It chooses the route with the least cost, and forwards the packet to the first router on that route.

Do I need a router?

If you have a LAN and want to connect it to the Internet, then you need a router. If you are deploying VoIP on your LAN, then you need one. If you have a simple phone system, then choose an ATA.

                                               

                                      Amitabh Kumar (9015123133,9811006683)

                                      Amitsintu@Gmail.com,  www.itrd.co.in

Difference between an Ethernet hub and switch

What is the difference between an Ethernet hub and switch?

Although hubs and switches both glue the PCs in a network together, a switch is more expensive and a network built with switches is generally considered faster than one built with hubs.  Why?

When a hub receives a packet (chunk) of data (a frame in Ethernet lingo) at one of its ports from a PC on the network, it transmits (repeats) the packet to all of its ports and, thus, to all of the other PCs on the network.  If two or more PCs on the network try to send packets at the same time a collision is said to occur.  When that happens all of the PCs have to go though a routine to resolve the conflict.  The process is prescribed in the Ethernet Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.  Each Ethernet Adapter has both a receiver and a transmitter.  If the adapters didn't have to listen with their receivers for collisions they would be able to send data at the same time they are receiving it (full duplex).   Because they have to operate at half duplex (data flows one way at a time) and a hub retransmits data from one PC to all of the PCs, the maximum bandwidth is 100 Mhz and that bandwidth is shared by all of the PC's connected to the hub. The result is when a person using a computer on a hub downloads a large file or group of files from another computer the network becomes congested.  In a 10 Mhz 10Base-T network the affect is to slow the network to nearly a crawl.  The affect on a small, 100 Mbps (million bits per scond), 5-port network is not as significant.
Two computers can be connected directly together in an Ethernet with a crossover cable.  A crossover cable doesn't have a collision problem.  It hardwires the Ethernet transmitter on one computer to the receiver on the other.   Most 100BASE-TX Ethernet Adapters can detect when listening for collisions is not required with a process known as auto-negotiation and will operate in a full duplex mode when it is permitted. The result is a crossover cable doesn't have delays caused by collisions, data can be sent  in both directions simultaneously, the maximum available bandwidth is 200 Mbps, 100 Mbps each way, and there are no other PC's with which the bandwidth must be shared.
An Ethernet switch automatically divides the network into multiple segments, acts as a high-speed, selective bridge between the segments, and supports simultaneous connections of multiple pairs of computers which don't compete with other pairs of computers for network bandwidth.  It accomplishes this by maintaining a table of each destination address and its port.  When the switch receives a packet, it reads the destination address from the header information in the packet, establishes a temporary connection between the source and destination ports, sends the packet on its way, and then terminates the connection.
Picture a switch as making multiple temporary crossover cable connections between pairs of computers (the cables are actually straight-thru cables; the crossover function is done inside the switch).  High-speed electronics in the switch automatically connect the end of one cable (source port) from a sending computer to the end of another cable (destination port) going to the receiving computer on a per packet basis.  Multiple connections like this can occur simultaneously.  It's as simple as that. And like a crossover cable between two PCs, PC's on an Ethernet switch do not share the transmission media, do not experience collisions or have to listen for them, can operate in a full-duplex mode, have bandwidth as high as 200 Mbps, 100 Mbps each way, and do not share this bandwidth with other PCs on the switch.  In short, a switch is "more better."

Question:  What is the difference between a router and hub or switch?

Answer: A router is a more sophisticated network device than either a switch or a hub. Like hubs and switches, network routers are typically small, box-like pieces of equipment that multiple computers can connect to. Each features a number of "ports" the front or back that provide the connection points for these computers, a connection for electric power, and a number of LED lights to display device status. While routers, hubs and switches all share similiar physical appearance, routers differ substantially in their inner workings.

Traditional routers are designed to join multiple area networks (LANs and WANs). On the Internet or on a large corporate network, for example, routers serve as intermediate destinations for network traffic. These routers receive TCP/IP packets, look inside each packet to identify the source and target IP addresses, then forward these packets as needed to ensure the data reaches its final destination.

Routers for home networks (often called broadband routers) also can join multiple networks. These routers are designed specifically to join the home (LAN) to the Internet (WAN) for the purpose of Internet connection sharing. In contrast, neither hubs nor switches are capable of joining multiple networks or sharing an Internet connection. A home network with only hubs and switches must designate one computer as the gateway to the Internet, and that device must possess two network adapters for sharing, one for the home LAN and one for the Internet WAN. With a router, all home computers connect to the router equally, and it performs the equivalent gateway functions.

Additionally, broadband routers contain several features beyond those of traditional routers. Broadband routers provide DHCP server and proxy support, for example. Most of these routers also offer integrated firewalls. Finally, wired Ethernet broadband routers typically incorporate a built-in Ethernet switch. These routers allow several hubs or switches to be connected to them, as a means to expand the local network to accomodate more Ethernet devices.

In home networking, hubs and switches technically exist only for wired networks. Wi-Fi wireless routers incorporate a built-in access point that is roughly equivalent to a wired switch. 

Amitabh Kumar(9015123133,9811006683)
Amitsintu@Gmail.com

www.itrd.co.in