Switch: Switches work at layer 2 of OSI model, which is Data Link Layer. A switch looks at the destination MAC address before forwarding a frame. It may be noted that there are some layer 3 switches. Though these devices are called switches, they typically do the routing. When we say switches, we mean layer 2 switches (or simple switches). A switch uses OSI layer 2 address (MAC Addresses) for forwarding frames. A switch can be used to reduce network traffic by dividing the broadcast domains of a network. Switches are the connectivity points of an Ethernet network. Devices connect to switches via twisted-pair cabling, one cable for each device
The main function of a content switch is to inspect the network data that it receives so that it can decide where on the network that data (or request) needs to be forwarded to.
Router: The following are true about routers:
Hub: Hubs are simple devices that direct data packets to all devices connected to the hub, regardless of whether the data packet is destined for the device. This makes them inefficient devices and can create a performance bottleneck on busy networks.
The difference between hubs and switches is in how the devices deal with the data they receive. Whereas a hub forwards the data it receives to all the ports on the device, a switch forwards it to only the port that connects to the destination device. It does this by the MAC address of the devices attached to it and then by matching the destination MAC address in the data it receives.
Hubs and switches have two types of ports:
The two types of ports differ in their wiring. As the X implies, an MDI-X port's wiring is crossed; this is because the transmit wire from the connected device must be wired to the receive line on the other. Rather than use a crossover cable, you can use the more simple straight-through cable to connect systems to the switch or hub.
Three different types of hubs are widely known. These are:
Passive hubs do not amplify the electrical signal of incoming packets before broadcasting them out to the network.
Active hubs, on the other hand, amplify the received signal before sending them out. Some people use the terms concentrator when referring to a passive hub and multiport repeater when referring to an active hub.
An intelligent (also called smart) hub typically is stackable (built in such a way that multiple units can be placed one on top of the other to conserve space). It also typically includes remote management capabilities via SNMP and virtual LAN (VLAN) support.
A network hub operates at the physical layer of the OSI model. A router operates at the network layer of the OSI model. A Wireless bridge operates at the data link layer of the osi model. A NIC and Access Point operates at the data link layer of the osi model. There are two main types of switches. Layer-2 switches operate at the data-link layer of the OSI model and are based on bridging technologies. They establish logical connections between ports based on MAC addresses. Layer-3 switches operate at the layer 3(network layer) of the OSI model and are based on routing technologies. They establish logical connections between ports based on network addresses. Layer-3 switches are sometimes called routing switches or multilayer switches.
Firewall: A firewall can be implemented either as a hardware device or using software. A software implementation of firewall typically resides on top of the operating system, and controls the network traffic. A hardware implementation sits separately away from the computer box. One main advantage of hardware firewall is its speed, where as the main advantage of software firewall is its low cost.
The following are the commonly used FireWall technologies:
1. Access Control Lists (ACL): Access Control List (ACL) refers to a list of ports and services that are available on a host (or a network device such as router), each with a list of hosts and/or networks permitted to use the service. Both nodes (work stations or servers) as well as routers can have access lists. Access lists are used to control both inbound and outbound traffic.
2. Packet Filters: This is also known as static packet filtering. Access to a network is controlled by analyzing the incoming and outgoing packets and "allow" or "deny" them based on the IP addresses of the source and destination. Dynamic packet filtering uses stateful inspection. Static packet filter just uses the header information for packet filtering. The main draw back of static packet filter is spoofing.
3. Dynamic Packet Filters: Also referred to as Stateful Inspection, DPF, unlike static packet filters, monitors each session and makes sure they are valid. Note that a static packet filtering uses only the header information in a packet traversing the FireWall, whereas a Dynamic Packet Filter inspects all the interfaces based on a state table. CheckPoint's FireWall-1 uses stateful inspection.
4. Protocol Switching: We know that TCP/IP is the protocol used on the Internet. By using a different protocol on the private network that is connected to the public Internet through a Firewall, we can improve the security of the private network.
An analog modem, usually just referred to as a modem (short for modulator/demodulator), is a device that converts the digital signals generated by a computer into analog signals that can travel over conventional phone lines. The modem at the receiving end converts the signal back into a format that the computer can understand. Modems can be used as a means to connect to an ISP or as a mechanism for dialing up a LAN.
Wireless accesspoint:
Wireless LANs consist mainly of two entities: clients or end-user devices and Access Points (AP). Clients' are equipped with devices that allow the user to use the RF medium to communicate with other wireless devices. AP functions like a regular switch or router in wired network for the wireless devices. Moreover, it represents a gateway between the wireless devices and a wired network. The basic structure of a Wireless LAN is called BSS (Basic Service Set) shown in below fig, in which the network consists of an AP and several wireless devices. When these devices try to communicate among themselves they propagate their data through the AP device. In order to form the network, AP keeps broadcasting its SSID (Service Set Identifier) to allow others to join the network.
If the BSS did not have an AP device, and the wireless devices were communicating with each other directly, this BSS is called an Independent BSS and works in mode called "ad hoc mode". Group of BSSs (either BSS or IBSS) can be combined to form an ESS (Extended Service Set). This set is created by chaining this group of BSSs to a single backbone system.
There are three main categories of antennas:
Omni-directional - Omni-directional antennas radiate RF in a fashion similar to the way a table or floor lamp radiates light. They are designed to provide general coverage in all directions.
Semi-directional - Semi-directional antennas radiate RF in a fashion similar to the way a wall sconce is designed to radiate light away from the wall or the way a street lamp is designed to shine light down on a street or a parking lot, providing a directional light across a large area. Yagi antenna is an example of this type of antennas.
Highly-directional - Highly-directional antennas radiate RF in a fashion similar to the way a spotlight is designed to focus light on a flag or a sign. Each type of antenna is designed with a different objective in mind. Phased array antenna is an example of this type of antenna.
