NETWORK DEVICES
INTRODUCTION
Network Devices is a machine or component that is attached to a computer. Examples of device include disk drive,printers,mice and DSL cable . These particular devices fall into the category of peripheral devices because they are separate from the main computer. Most devices, whether peripheral or not, require a program called a device driver that acts as a translator, converting general Commands from an applications into specific commands that the device understands.
Types of Network Devices: ─
1. Hub
2. Switch
3. Router
4. Repeater
5. Network card
6. Bridge
7. Gateways
HUB
As its name implies, a hub is a center of activity. In more specific network terms, a hub, or concentrator, is a common wiring point for networks that are based around a star topology. Arcnet, 10base-T, and 10base-F, as well as many other proprietary network topologies, all rely on the use of hubs to connect different cable runs and to distribute data across the various segments of a network. Hubs basically act as a signal splitter. They take all of the signals they receive in through one port and redistribute it out through all ports.
Ø Hub works on Physical Layer of OSI model.
SWITCH
A Switch is a devicethat provides a central connection point for cables from workstations, servers, and peripherals. In a star topology, twisted-pair wire is run from each workstation to a central switch/hub. Most switches are active, that is they electrically amplify the signal as it moves from one device to another. Switches no longer broadcast network packets as hubs did in the past, they memorize addressing of computers and send the information to the correct location directly. Switches are:
Ø Usually configured with 8, 12, or 24 RJ-45 ports
Ø Switch works on Data-Link Layer of OSI model.
Ø Often used in a star or star-wired ring topology
Ø Sold with specialized software for port management
Ø Usually installed in a standardized metal rack that also may store net dsl modem,bridges or royters.
Switches subdivide larger networks and prevent the unnecessary flow of network traffic from one segment to another, or in the case of cross-segment traffic, switches direct the frames only across the segments containing the source and destination hosts.
This ensures the integrity of our data; it does nothing to increase overall network speed. Switches help to ensure additional network access opportunities for attached devices (increasing speed and reducing traffic) by restricting data flows to local segments unless frames are destined for a host located on another segment. The switch examine the destination address and forward the requisite frames only across the destination segment, leaving all additional segments attached to that switch free from that particular broadcast and (theoretically) able to facilitate local-segment traffic. Rather than being a passive connection between multiple segments, the switch works to ensure that network traffic burdens the fewest number of segments POSSIBLE.
Difference between a hub and a switch
Hubs and switches are different types of network equipment that connect devices. They differ in the way that they pass on the network traffic that they receive. Switches differ in some ways. They can be of the store-and-forward type, storing each incoming packet in an internal buffer before forwarding it, or cut-through, beginning to forward packets already after their header is in and before the rest of the packet has been received. Hubs repeat everything they receive and can be used to extend the network. However, this can result in a lot of unnecessary traffic being sent to all devices on the network. Hubs pass on traffic to the network regardless of the intended destination.
In a small network (less than 30 users), a hub (or collection of hubs) can easily cope with the network traffic generated and is the ideal piece of equipment to use for connecting the users.
When the network gets larger (about 50 users), you may need to use a switch to divide the groups of hubs, to cut down the amount of unnecessary traffic being generated.
Network Interface Cards
The network interface card (NIC) provides the physical connection between the network and the computer workstation. Most NICs are internal, with the card fitting into an expansion slot inside the computer. Some computers, such as Mac Classics, use external boxes which are attached to a serial port or a SCSI port. Laptop computers can now be purchased with a network interface card built-in or with network cards that slip into a PCMCIA slot.
Network interface cards are a major factor in determining the speed and performance of a network. It is a good idea to use the fastest network card available for the type of workstation you are using.
The three most common network interface connections are Ethernet cards, Local Talk connectors, and Token Ring cards. According to a International Data Corporation study, Ethernet is the most popular, followed by Token Ring and Local Talk.
TOPOLOGY
The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations.
Main Types of Topologies:─
The following sections discuss the topologies used in networks .
Ø Linear Bus
Ø Star
Ø Star-Wired Ring
Ø Tree
Linear Bus
A linear bus topology consists of a main run of cable with a terminator at each end. All nodes (file server, workstations, and peripherals) are connected to the linear cable. ethernet and local talk networks use a linear bus topology
Star
A star topology is designed with each nodes (file server, workstations, and peripherals) connected directly to a central network Hub on a star network passes through the hub before continuing to its destination. The hub manages and controls all functions of the network. It also acts as a Repeater for the data flow. This configuration is common with Twisted paired cable & also used with Coaxial cable or fiver optical cable.
Tree
A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable.
PROTOCOLS
A protocol is a set of rules that governs the communications between computers on a network. These rules include guidelines that regulate the following characteristics of a network: access method, allowed topologies, types of cabling, and speed of data transfer.
The most common protocols are:
♦Ethernet
♦Token ring
♦FDDI
♦Atm
♦IP protocol
♦TCP protocol
Ethernet
The Ethernet protocol is by far the most widely used. Ethernet uses an access method called CSMA/CD (Carrier Sense Multiple Access / Collision Detection). This is a system where each computer listens to the cable before sending anything through the network. If the network is clear, the computer will transmit. If some other node is already transmitting on the cable, the computer will wait and try again when the line is clear.
Sometimes, two computers attempt to transmit at the same instant. When this happens a collision occurs. Each computer then backs off and waits a random amount of time before attempting to retransmit. With this access method, it is normal to have collisions. However, the delay caused by collisions and retransmitting is very small and does not normally effect the speed of transmission on the network.
The Ethernet protocol allows for linear bus, star, or tree topologies. Data can be transmitted over twisted pair, coaxial, or fiber optic cable at a speed of 10 Mbps up to 1000 Mbps.
Fast Ethernet
To allow for an increased speed of transmission, the Ethernet protocol has developed a new standard that supports 100 Mbps. This is commonly called Fast Ethernet. Fast Ethernet requires the use of different, more expensive network hubs and network interface cards.
Token Ring
The Token Ring protocol was developed by IBM in the mid-1980s. The access method used involves token-passing. In Token Ring, the computers are connected so that the signal travels around the network from one computer to another in a logical ring. A single electronic token moves around the ring from one computer to the next. If a computer does not have information to transmit, it simply passes the token on to the next workstation. If a computer wishes to transmit and receives an empty token, it attaches data to the token. The token then proceeds around the ring until it comes to the computer for which the data is meant. At this point, the data is captured by the receiving computer.
The Token Ring protocol requires a star-wired ring using twisted pair or fiber optic cable. It can operate at transmission speeds of 4 Mbps or 16 Mbps. Due to the increasing popularity of Ethernet, the use of Token Ring in school environments has decreased.
IP Addressing
The IP addressing scheme is integral to the process of routing IP data gram through an internet work. Each IP address has specific components and follows a basic format. These can be sub divided and used to create addresses for sub networks. Each host on a TCP/IP network is assigned a unique 32-bit logical address that is divided into two main parts: the network number and the host number. The network number identifies a network and must be assigned by the Internet Network Information Center (InterNIC) if the network is to be part of the Internet
