Hub An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub The main work of Hub is to receive incoming data signals, amplify them in the form of electrical signals and then send them to each connected device. A Hub may contain a number of ports. Minimum amount of ports that a hub can have is 4 and it can have up to 24 ports for connecting various devices and peripherals to it. 1. When referring to a network, a hub is the most basic networking device that connects multiple computers or other network devices together. Unlike a network switch or router, a network hub has no routing tables or intelligence on where to send information and broadcasts all network data across each connection. Most hubs can detect basic network errors such as collisions, but having all information broadcast to multiple ports can be a security risk and cause bottlenecks. 2. In general, a hub refers to a hardware device that enables multiple devices or connections to be connected to a computer. Another example besides the one given above is a USB hub, which allows multiple USB devices to be connected to one computer, even though that computer may only have a few USB connections. The picture to the right is an example of a USB hub. A common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets. What Hubs Do Hubs and switches serve as a central connection for all of your network equipment and handles a data type known as frames. Frames carry your data. When a frame is received, it is amplified and then transmitted on to the port of the destination PC. In a hub, a frame is passed along or "broadcast" to every one of its ports. It doesn't matter that the frame is only destined for one port. The hub has no way of distinguishing which port a frame should be sent to. Passing it along to every port ensures that it will reach its intended destination. This places a lot of traffic on the network and can lead to poor network response times. Passive, Intelligent and Switching Hubs A passive hub serves simply as a conduit for the data, enabling it to go from one device (or segment) to another. So-called intelligent hubs include additional features that enables an administrator to monitor the traffic passing through the hub and to configure each port in the hub. Intelligent hubs are also called manageable hubs. A third type of hub, called a switching hub, actually reads the destination address of each packet and then forwards the packet to the correct port. Types of Hub:On the basis of its working methods, the Hubs can be divided into three types, given as: Active Hub: As its name suggests, Active Hub is a hub which can amplify or regenerate the information signal. This type of bus has an advantage as it also amplifies the incoming signal as well as forward it to multiple devices. This Bus is also known as Multiport Repeater. It can upgrade the properties if incoming signal before sending them to destination. Passive Hub: Passive Hub works like a simple Bridge. It is used for just creating a connection between various devices. It does not have the ability to amplify or regenerate any incoming signal. It receives signal and then forward it to multiple devices. Intelligent Hub: This is the third and last type of Bus. It can perform tasks of both Active and Passive buses. Also, it can perform some other tasks like Bridging and routing. It increases the speed and effectiveness of total network thus makes the performance of whole network fast and efficient. Home and Small Business Hubs Hubs can be used as a standalone device or connected to compatible hubs and switches to form a larger network. Hubs are generally easy to install and maintain, making these devices a good option for home networking. A hub is also easily configured for small business branch office networking. Physical layer function A network hub is an unsophisticated device in comparison with a switch. As a multiport repeater it works by repeating bits (symbols) received from one of its ports to all other ports. It is aware of physical layer packets, that is it can detect their start (preamble), an idle line (interpacket gap) and sense a collision which it also propagates by sending a jam signal. A hub cannot further examine or manage any of the traffic that comes through it: any packet entering any port is rebroadcast on all other ports. A hub/repeater has no memory to store any data in – a packet must be transmitted while it is received or is lost when a collision occurs (the sender should detect this and retry the transmission). Due to this, hubs can only run in half duplex mode. Consequently, due to a larger collision domain, packet collisions are more frequent in networks connected using hubs than in networks connected using more sophisticated devices. Some Application of Networking Hub are given below: Hubs are used to create small Home Networks. Hubs are used for monitoring the networks. Hubs are used in Organizations and Computer Labs for connectivity. It Makes one device or peripheral available throughout the whole network. Advantage: Hub is less expensive product. It is used for connect the multiple devices. a hub can be able to support multiple users at the same time Diadvantages: It will broadcast to all the ports It runs half duplex If 10 Ports in a hub it will share bandwidth of 100 MbPs. So each port share 10 Mbps .It is a non intelligent connection switch A network switch (also called switching hub, bridging hub, officially MAC bridge) is a computer networking device that connects devices together on a computer network, by using packet switching to receive, process and forward data to the destination device. A network switch (also called switching hub, bridging hub, officially MAC bridge) is a computer networking device that connects devices together on a computer network, by using packet switching to receive, process and forward data to the destination device. Unlike less advanced network hubs, a network switch forwards data only to one or multiple devices that need to receive it, rather than broadcasting the same data out of each of its ports. A network switch is a multiport network bridge that uses hardware addresses to process and forward data at the data link layer (layer 2) of the OSI model. Switches can also process data at the network layer (layer 3) by additionally incorporating routing functionality that most commonly uses IP addresses to perform packet forwarding; such switches are commonly known as layer-3 switches or multilayer switches. Beside most commonly used Ethernet switches, they exist for various types of networks, including Fibre Channel, Asynchronous Transfer Mode, and InfiniBand. The first Ethernet switch was introduced by Kalpana in 1990. Switches manage the flow of data across a network by transmitting a received message only to the one or more devices for which the message was intended. Each networked device connected to a switch can be identified using a MAC address, allowing the switch to regulate the flow of traffic. This maximizes the security and efficiency of the network. Essentially, when replacing a repeater hub with an Ethernet switch, the single large collision domain is split up into smaller ones, reducing the probability and scope of collisions and, as a result, increasing the potential throughput. Because broadcasts are still being forwarded to all connected devices, the newly formed network segment continues to be a broadcast domain. Due to these features, a switch may be seen as more "intelligent" than a repeater hub, which simply retransmits messages out of every port of the hub but the receiving one, unable to distinguish different recipients, and greatly degrading the overall efficiency of the network. Applications The network switch plays an integral role in most modern Ethernet local area networks (LANs). Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office (SOHO) applications typically use a single switch, or an all-purpose converged device such as a residential gateway to access small office/home broadband services such as DSL or cable Internet. In most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may also include a telephone interface for Voice over IP (VoIP) protocol. Microsegmentation Segmentation involves the use of a bridge or a switch (or a router) to split a larger collision domain into smaller ones in order to reduce collision probability, and to improve overall network throughput. In the extreme case (i.e. microsegmentation), each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports. This allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex without collisions. Full-duplex mode has only one transmitter and one receiver per "collision domain", making collisions impossible. Layer 1 (hubs vs. higher-layer switches) A network hub, or a repeater, is a simple network device that does not manage any of the traffic coming through it. Any packet entering a port is flooded out or "repeated" on every other port, except for the port of entry. Since every packet is repeated on every other port, packet collisions affect the entire network, limiting its overall capacity. A network switch creates the layer 1 end-to-end connection only virtually, while originally it was mandatory. The bridging function of a switch uses information taken from layer 2 to select for each packet the particular port(s) it has to be forwarded to, removing the requirement that every node is presented with all traffic. As a result, the connection lines are not "switched" literally, instead they only appear that way on the packet level. There are specialized applications in which a network hub can be useful, such as copying traffic to multiple network sensors. High-end network switches usually have a feature called port mirroring that provides the same functionality. By the early 2000s, there was little price difference between a hub and a lowend switch. Layer 2 A network bridge, operating at the data link layer, may interconnect a small number of devices in a home or the office. This is a trivial case of bridging, in which the bridge learns the MAC address of each connected device. Single bridges also can provide extremely high performance in specialized applications such as storage area networks. Classic bridges may also interconnect using a spanning tree protocol that disables links so that the resulting local area network is a tree without loops. In contrast to routers, spanning tree bridges must have topologies with only one active path between two points. The older IEEE 802.1D spanning tree protocol could be quite slow, with forwarding stopping for 30 seconds while the spanning tree reconverged. A Rapid Spanning Tree Protocol was introduced as IEEE 802.1w. The newest standard Shortest path bridging (IEEE 802.1aq) is the next logical progression and incorporates all the older Spanning Tree Protocols (IEEE 802.1D STP, IEEE 802.1w RSTP, IEEE 802.1s MSTP) that blocked traffic on all but one alternative path. IEEE 802.1aq (Shortest Path Bridging SPB) allows all paths to be active with multiple equal cost paths, provides much larger layer 2 topologies (up to 16 million compared to the 4096 VLANs limit), faster convergence, and improves the use of the mesh topologies through increase bandwidth and redundancy between all devices by allowing traffic to load share across all paths of a mesh network. While layer 2 switch remains more of a marketing term than a technical term,  the products that were introduced as "switches" tended to use microsegmentation and full duplex to prevent collisions among devices connected to Ethernet. By using an internal forwarding plane much faster than any interface, they give the impression of simultaneous paths among multiple devices. 'Non-blocking' devices use a forwarding plane or equivalent method fast enough to allow full duplex traffic for each port simultaneously. Once a bridge learns the addresses of its connected nodes, it forwards data link layer frames using a layer 2 forwarding method. There are four forwarding methods a bridge can use, of which the second through fourth method were performance-increasing methods when used on "switch" products with the same input and output port bandwidths: Store and forward: the switch buffers and verifies each frame before forwarding it; a frame is received in its entirety before it is forwarded. Cut through: the switch starts forwarding after the frame's destination address is received. When the outgoing port is busy at the time, the switch falls back to store-and-forward operation. There is no error checking with this method. Fragment free: a method that attempts to retain the benefits of both store and forward and cut through. Fragment free checks the first 64 bytes of the frame, where addressing information is stored. According to Ethernet specifications, collisions should be detected during the first 64 bytes of the frame, so frames that are in error because of a collision will not be forwarded. This way the frame will always reach its intended destination. Error checking of the actual data in the packet is left for the end device. Adaptive switching: a method of automatically selecting between the other three modes. While there are specialized applications, such as storage area networks, where the input and output interfaces are the same bandwidth, this is not always the case in general LAN applications. In LANs, a switch used for end user access typically concentrates lower bandwidth and uplinks into a higher bandwidth. Layer 3 Within the confines of the Ethernet physical layer, a layer-3 switch can perform some or all of the functions normally performed by a router. The most common layer-3 capability is awareness of IP multicast through IGMP snooping. With this awareness, a layer-3 switch can increase efficiency by delivering the traffic of a multicast group only to ports where the attached device has signaled that it wants to listen to that group. Layer 4 While the exact meaning of the term layer-4 switch is vendor-dependent, it almost always starts with a capability for network address translation, but then adds some type of load distribution based on TCP sessions. The device may include a stateful firewall, a VPN concentrator, or be an IPSec security gateway. Layer 7 Layer-7 switches may distribute the load based on uniform resource locators (URLs), or by using some installation-specific technique to recognize application-level transactions. A layer-7 switch may include a web cache and participate in a content delivery network (CDN). Configuration options Unmanaged switches – these switches have no configuration interface or options. They are plug and play. They are typically the least expensive switches, and therefore often used in a small office/home office environment. Unmanaged switches can be desktop or rack mounted. Managed switches – these switches have one or more methods to modify the operation of the switch. Common management methods include: a command-line interface (CLI) accessed via serial console, telnet or Secure Shell, an embedded Simple Network Management Protocol (SNMP) agent allowing management from a remote console or management station, or a web interface for management from a web browser. Examples of configuration changes that one can do from a managed switch include: enabling features such as Spanning Tree Protocol or port mirroring, setting port bandwidth, creating or modifying virtual LANs (VLANs), etc. Two subclasses of managed switches are marketed today: Smart (or intelligent) switches – these are managed switches with a limited set of management features. Likewise "web-managed" switches are switches which fall into a market niche between unmanaged and managed. For a price much lower than a fully managed switch they provide a web interface (and usually no CLI access) and allow configuration of basic settings, such as VLANs, port-bandwidth and duplex. Enterprise managed (or fully managed) switches – these have a full set of management features, including CLI, SNMP agent, and web interface. They may have additional features to manipulate configurations, such as the ability to display, modify, backup and restore configurations. Compared with smart switches, enterprise switches have more features that can be customized or optimized, and are generally more expensive than smart switches. Enterprise switches are typically found in networks with larger number of switches and connections, where centralized management is a significant savings in administrative time and effort. A stackable switch is a version of enterprisemanaged switch. Advantages : 1) Reduces the number of Broadcast domains 2) Supports VLAN's which can help in Logical segmentation of ports[physical ports].Splitting up the broadcast domain. 3) Intellegent device[compared to Hub's] which can make use of CAM table for Port to MAC mapping 4) Compared to Bridges ,Switches are more H/w oriented therefore operations are less CPU intense[Basic operations] . 5) The cost to number of ports ratio is best .. ie For a cheaper cost you get switches with more number of ports available than Routers. Disadvantages : 1) Not as good as a router in limiting Broadcasts 2) Communication b/w VLAN's need interVLAN routing [Router] ,but these days there are a number of Multilayer switches available in the market. 3) Handling Multicast packets needs quite a bit of configuration & proper designing. 4) At times swtiches when in Promiscuos mode is a opening for Security attacks [Spoofing ip address or capturing Ethernet Frames using ethereal] I would definitely arguee with the interviewer that switches are designed for what they are & there is disadvatage as such unless it is compared to other layer devices.At Layer 2 it does what other devices of layer 2 cant do & it was initally meant to work at Layer 2,even though it works at multiple layers these days. ROUTER A router [a] is a networking device that forwards data packets between computer networks. Routers perform the "traffic directing" functions on the Internet. A data packet is typically forwarded from one router to another through the networks that constitute the internetwork until it reaches its destination node.
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