Computer Networks

Network in other words, you can say is a ‘web’. So, Computer Network becomes ‘web of computers’. This special kind of web of computers should be designed so intelligently that there should be no mess, not much expensive, secure, efficient and quick in communicating with each other.

For computers to communicate with other computers there should be some devices which are able to send data (according to its nature) in medium. Network devices are the components used to connect computers or electronic devices to communicate in a network of computers.

“Network devices are those devices which are used to interconnect two or more than two computers with each other to share data, information, voice, resources and to communicate with each other.”

Network devices are the hardware responsible to send data on medium and some software, which helps in making a secure and efficient network. And the software is also used to monitor the traffic of the network device.

The network devices and its components which you use in a network depend on the type of need of the network with efficiency, speedy, secure and cheap. 

Basic Network Devices

Basic network devices are components used to connect computers or other electronic devices together, so that they can share files or resources efficiently.

Router

Router is a layer 3 (works on network layer according to the OSI model), smartest and most complicated device. It connects more than one device with the network (also connects sub-networks) and it is a protocol dependent device. The primary function of the router is to connect networks together, providing Network Access Translation (NAT) and limited firewall functionality. It has RAM, ROM and processor.

 Fig. 1.1 : Linkysys WRT54GL Wireless-G Router

Router has build-in software which calculates minimum time required to forward received packet to its next network port according to the state of the network (called ‘forwarding decision’). On receiving a packet, router reads the packet information at network layer and decides for the packet to forward (process of reading information at the network layer for network address is called ‘routing’). Router records and maintains a table (called ‘routing table’) with distance and cost algorithms to judge the best route for the packet to pass.

For high-speed Internet connections such as cable, satellite or DSL, a router also acts as a firewall for the computer. Router provides better protection to the attached computers against hacking than computer firewall software does. Because your IP is not directly exposed to the Internet (it makes ports scanning impossible). Also router does not require extra resources of your computer as computer firewall software does. Commercially manufactured routers are cheap, easy to install and use.

Fig. 1.2 : Internal Labeled Linkysys WRT54GL Wireless-G Router

Those companies which manufacture router include Cisco, Juniper, D-Link, Datasys, Nortel (Bay Networks), Redback, Lucent, 3Com, HP, TP-Link, Motorola, Juniper Networks Inc., Huawei and much more.

Advantages of Rouoter:

• It limits the collision domain
• It gives services to LAN and WAN
• It can connect with different media architectures
• It determines the best path for the data packets to route
• It provides security for networks with the help of Access Control List (ASL) and Network Address Translation (NAT)

Disadvantages of Router:

• It is more expensive than hub and switch.
• It only work with routable protocol
• Routing table updates consume bandwidth
• It increases latency due to greater degree of packet filtering
• Signals adversely affected by climatic conditions such as thunderstorms
• As, wi-fi signals use high power consumption compared to some other standards

Access point

An access point differs from the wireless router, it extends the range of your network by placing it at dead spot (where signal is weak. It can be in different room or floor). Access points act as a central transmitter and receiver of WLAN radio signals. Access points which are used in home or small business, a dedicated built-in hardware devices like network adapter, antenna and radio transmitter. Access points support Wi-Fi communication standards.

Not like the router, it does not work has firewall to protect local network against threats from Internet.

But like the router, access point allow your workstations to access the network and Internet without running wires.

WAP610N Wireless-N Access Point

Those companies which manufacture router include Cisco, D-Link, Netgear.

Advantages of Access point:

• It is easier to add workstations
• It is easier to provide connectivity in areas where it is difficult to lay cable. Usually in dynamic environment requiring frequent moves and changes
• Access to the network can be from anywhere within range of an access point
• Reduced the mess of cables. Ideal for temporary network setups
• Implementation cost is minimum

Disadvantages of Access point:

• Increase in the number of users in the network will decrease in the data transfer rate to each user. Number of users and data transfer rate is inversely proportional to each other
• Security is more difficult to guarantee and requires configuration. For example, hacker’s laptop could be the your access point in an unknown location, due to which hacker can access your private data
• Signals adversely affected by climatic conditions such as thunderstorms
• As, wi-fi signals use high power consumption compared to some other standards
• Free access points can be used by the malicious to anonymous to initiate an attack that would be extremely difficult to track beyond the owner of the access point

Bridge

Bridge is a layer 2 device (works on data link layer according to the OSI model) used to connects multiple network segments.

A bridge is a network device that is to connect two separate network segments and prevents the data of one network segment from crossing over to the other network segment, unless the data is for other side. In other words, bridge filters traffic at boundary of network segment. It reduces the amount of traffic on a LAN by dividing it into two segments. It inspect incoming traffic and decide whether to forward it or discard it.

Example of Bridge

Bridges interpret data frames, records the MAC address to make bridging table for each associated MAC address to a port on the bridge. If incoming frame has unknown MAC address, then the bridge floods the frame to all ports.

Bridges are much slower than hubs, because they store frames to read them before forwarding it.

Those companies which manufacture router include NetGear, Cisco, D-Link, TRENDnet, Motorola, TP-Link, 3Com, Shenzhen etc.

Bridging is useful when you need to:

1. Maintain a flat topology
2. Reduce traffic travelling between segments or reduce the number of hosts on a segment
3. Extend the cable length of a particular LAN segment
4. Forward frames based on MAC address only

Advantages of Bridge:

• Simple bridges are inexpensive
• Simple configuration modes
• Isolate collision domains with micro-segmentation
• It increase network length
• Access control and network management capabilities
• Bandwidth scales as network grows

Disadvantages of Bridge:

• Does not limit the scope of broadcast
• Does not scale to extremely large networks
• Extremely large networks cannot rely on bridges
• Buffering and processing introduces delays

Switch

Switch is a layer 2 device (works on data link layer according to the OSI model). It forwards traffic intelligently and the function of the switch is transparent to the network.

Similar to bridge, with variety of higher level techniques to improve latency, reduce errors and collisions. Network switches connect multiple workstations and sends data only to the source and destination workstations (in Ethernet LAN, switch decide where incoming packets are transferred to, based on the NIC’s 48-bit address).

Some newer switches also perform routing functions (layer 3 or network layer functions in OSI model) and sometimes called IP switches.

Those companies which manufacture router include HP, Cisco, Dell, Telenet, Phoenix, Intel, Acer, Dynex Products, ATEN Technology, 3Com, Belkin, Linksys, Shenzhen, ConSentry etc.

Advantages of Switch:

• User performance increases. As, it gets only its belonging data addressed to its NIC
• High throughtput, because only relevant traffic is sent down any given network port. This means a switch can manage a large volume of data at any given time
• Bandwidth wastage is minimal. Multiple devices sharing bandwidth
• Switches are full duplex
• Most switches don not require any prior configuration

Disadvantages of Switch:

• In comparison with routers, switches are less sophisticated and less intelligent

Hub

Hubs work on layer 1 (physical layer – as hubs only repeat the electric pulses to every computer connected) of OSI model. It is a non-intelligent device which performs some extra functions than just connecting wires together. When a frame arrives at one port, it is copied to all other ports.

A hub connects multiple Ethernet devices together, making them act as a single segment. So, it is a networking component which acts as a convergence point of a network.

Hubs provide ports to the network to extend the workstations of a network. It is used where performance is not critical factor on the network.

Powered hubs also function as repeater, boosting signals and cleaning digital signals.

 

Main reason for purchasing hub rather than switch is its low cost. Those companies which manufacture router include Belkin, Linksys, Sun Systems, Cisco etc.

Hub is least expensive, least intelligent, least complicated and it is ignorant about the data being transmitted (regardless of the intended destination). As, hubs repeat everything they receive which results in lot of un-necessary traffic being sent to all devices on the network.

Advantages of Hub:

• Comparatively least cheaper device
• Least complicated

Disadvantages of Hub:

• It is dumb and non-intelligent device which broadcast signals to all ports
• Hubs are half-duplex devices
• Least secure
• Bandwidth is shared by all the PC’s connected to the hub

Repeater

All repeaters work on physical layer, layer 1 of the OSI mode and do not interpret the data being transmitted. Repeater just regenerates incoming electrical, wireless or optical signals.

A Repeater amplifies the signal between two physically distant networks, due to which distance of the network extends.

Those companies which manufacture router include Ultralink, QVS, IBM, Omnitron, Cisco, Gefen, Avocent Corporation, Tripp Lite, Kramer Electronics etc.

Advantages of Repeater:

• Simplest way to establish network interconnection
• Cheapest way to regenerate and retransmit the signal its original strength
• It is used to exceed the size limit of a single cable segment

Disadvantages of Repeater:

• It has no method of isolating traffic

Transceiver

Transceiver is a short name of ‘transmitter-receiver’, a device that transmits and receives analog or digital signals. It is a component in local area network (LAN) that applies signals onto the network wire and detects signals passing through the wire.

In other words, transceiver is a single package of combination of transmitter and receiver.

It is used in certain types of networks to transfer 5 volts data signals into the appropriate signals for the network. In Ethernet, 10/100/1000 twisted pair networks, the transceiver is part of the Network Interface Card. In Ethernet networks, a transceiver is also called a Medium Access Unit (MAU).

Network transceivers are of two types: half-duplex and full-duplex. A half-duplex transceiver can transmit or receive a signal at a time. While full-duplex can transmit and receive signals simultaneously.

Those companies which manufacture router include 3Com, Apple, IBM, Huawei Technologies Co. Ltd., Aruba Networks Inc., Quantum Corporation, Belkin, SMC Networks, Lucent Technologies, Nortel Networks, Shenzhen etc.

In Satellite communications, networks often use full duplex transceivers at the surface based subscriber points. The transmitted signal (transceiver-to-satellite) is called uplink and the received signal (satellite-to-transceiver) is called down-link.

Hybrid Network Devices

A hybrid network is local area network (LAN) containing a mix of both wired and wireless client devices. Usually in home network, wired computers and other devices generally connect with Ethernet cables, while wireless devices normally use wireless technology.

Multilayer Switch

A multilayer switch is like an ordinary network switch and provides extra functions on higher OSI layers. These switches can perform packet switching up to ten times faster than a pure layer 3 router.

Multilayer switch can perform tasks of both, layer 2 (switching) and layer 3 (routing). A received packet must be routed first, allowing the switching engine to cache the IP traffic flow. After this cache is created, subsequent packets destined for that flow can be switched and not routed, reducing latency. This concept is known as ‘route once, switch many’.

Cisco implemented this ‘route once, switch many’ concept as NetFlow switching or route-cache switching. But now, inspite of NetFlow switching, Cisco Express Forwarding (CEF) is used.

HP A7502 Switch L4-L7 managed rack-mountable

Those companies which manufacture router include HP, Cisco etc.

Protocol converter

Protocol converter is a device used to convert the protocol of one device into the other device protocol which is suitable for it to communicate on standards. Protocols are software installed on the routers which convert the data formats, data rate and protocol of one network into the protocols of the network in which data is navigating.

General Architecture of Protocol Converter

Those companies which manufacture router include Shenzhen etc.

Bridge router

A hybrid device ‘Bridge router’ are also known as ‘Brouter’. Brouters can operate as either a switch or a bridge. Unlike, a bridge which can only accept frames, read MAC address and make bridging table, and a router which can only accepts packets, read IP address and make routing table. While a brouter can read both frames and packets, and forward it accordingly.

Brouters are used as connecting devices in the networking system, so it act as bridge in a network and as a router in an internetwork. In other words, brouter is used when some packets need to be bridged, while other packets need to be routed.

Hardware and Software components in Network

A network operation needs those devices that are designed to handle certain network functions. Those devices could be internal or external, hardware or software, so collectively you can say network components.

Proxy

When you browse the Internet, means you are compromising on your information which your IP address sends from your computer to the Internet. You may wonder why certain sites know where you are. This is because your IP is traceable. So, usually companies track you IP address for advertisement purpose.

A proxy uses a mask on your real IP address to hide it from the Internet. It protects your IP from tracing. It also provides a secure gateway to Internet. The network proxy preference tool enables you to configure how your system connects to the Internet.

Web proxies are commonly used for cache web pages from web server. A content filtering web proxy server provides administrative control over the content to ensure that Internet usage conforms to acceptable use policy. It also produces logs, either to give detailed information about the URLs accessed by specific users, or to monitor bandwidth usage statistics. Some common methods used for filtering include: URL, DNS blacklist, URL regex filtering, MIME filtering or content keyword filtering.

In another context, proxy is a computer network service which allows clients to make indirect connection to other network services.

Firewall

Network firewalls are systems that enforce access policy between an organization’s network and the Internet for security purposes. Firewall draws the line which separates internal and external networks. It is the most basic security element to hide your network from the outside and control all external ports. It is used to prevent unauthorized Internet users from accessing private networks. Firewalls play a vital role in network security grows in parallel with the constant increase in cyber attacks for the purpose of stealing/corrupting data, planting viruses etc.

It prevents unauthorized access like hackers, viruses etc. inbound and outbound traffic in a network by blocking the data according to rules set up in its configuration. It is a device which restricts network transmission.

You can build a list of rules that meets your unique needs: control traffic by protocol, source address or port, destination address or port, and set default actions. Firewall evaluates traffic travelling across your network by applying your rules and then either it blocks or allows it to pass through to your computer.

It can be installed either software or hardware. The hardware or devices are also used as firewall service like Cisco ASA server or hotbricks.

Cisco ASA server

Hotbrick

Other manufacturers are IBM, ESET Smart Security, McAfee, Cisco, AVG, Barracuda Networks, Juniper Networks, Symentec, Norton, Zone Alarm etc.

Today’s market is dominated by two types of firewall: Application proxies and Packet filtering gateways.

Windows Firewall: It is a default Microsoft software as a firewall present in Windows XP, Vista and other products.

Network Address Translator

Network address translator is a network service provided as hardware or software that converts internal to external network addresses. Network administrators create a NAT table that does the global-to-local and local-to-global IP address mapping. NAT can also be used in conjunction with policy routing. The main use of NAT is to limit the number of public IP addresses for both economy and security purposes.

NAT serves three main purposes:

• Provides a type of firewall by hiding internal IP addresses
• Enables a company to use more internal IP addresses. Since they are used internally only, there is no possibility of conflict with IP addresses used by other companies and organizations
• Allows a company to combine multiple ISDN connections into a single Internet connection

Gateway

A Gateway device combines the functions of a simple two-network router and a switch, and it is used to connect two different networks (usually LAN and the Internet). So, the activities of a gateway are more complex than that of the router or switch as it communicates using more than one protocol.

In other words, network gateways interconnect networks with different, incompatible communication protocols. Network gateways can operate at any level of the OSI model.

Gateways can help different email systems to communicate with each other, translate voice data to data packets and vice versa, or work as a firewall. These are software which run on computers, servers or routers.

Those companies which manufacture router include NetComm, GammaLink, NetGear, Symantec, AT&T, Cisco, D-Link, Adtran Inc., Avaya Inc., Watchguard Inc., TrueCafe etc.

Other hardware for establishing networks or dial-up connections

Multiplexer

Multiplexer is a device that combines several electrical signals into a single signal which carries several communications channels by means of some multiplex technique. It is used in local area network (LAN), metropolitan area network (MAN) and wide area network (WAN). They may also use a number of different transport mechanisms, including fiber optic and wireless.

Multiplexer by Penril Communications

At a minimum, network multiplexers a single output and an input control. The number of input controls is based on the relationship between inputs and outputs.

TS3L501E - 16-bit to 8-bit multiplexer/de-multiplexer gigabit Ethernet LAN switch with power down mode

Those companies which manufacture router include Cisco, Transition Networks Inc., Allied Telesyn, Omnitron, NovaTec, Adtran Inc., Penril Communications etc.

Network Interface Card (NIC)

Network Interface Card (Network Interface Card also known as network interface controller, network adapter, LAN adapter) is a piece of computer hardware to allow the attached computer to communicate with network. In other words, NIC provides the hardware interface between a computer and a network. According to OSI model, network interface card is layer 1 (physical layer) and layer 2 (data link layer) device, as it provides physical access to a networking medium and provides a low-level addressing system through the use of MAC addresses.

Network Interface Card for connection of a computer to an Ethernet Network

A network interface card is usually installed inside a workstation in a PCI slot and provides for access to a 10/100/1000 twisted pair Ethernet network.

The NIC (Network Interface Card) is part of the host computer. It contains the MAC address which uniquely identifies the machine on the network. The NIC contains the data link network layer logic, and performs other basic functions of detecting and processing network communications at lowest level.

Each network interface card is assigned an Ethernet source address by the manufacturer of the network interface card (normally it is stored in PROM on the network interface card). The addresses are globally unique and are assigned in blocks of 16 (or 8) million addresses to the Ethernet interface manufacturers, according to a flat addressing structure (ensures that no two Ethernet network interface card will ever have the same sources address).

Example of Network Interface Card

Those companies which manufacture router include IBM, Kingston, Novel, Intel, 3Com, LinkSys, Realtek etc.

Advantages of Network Interface Card:

• NIC is often cheap
• Troubleshooting is easy
• Newer NIC can reach speeds of up to 2000 Mbps

Disadvantages of Network Interface Card:

• It must be configured properly
• NIC must match with the speed of the network switch that is connected for it to work properly
• A wired connection is required for NIC to work
• In NIC, data is not secured, can be hacked

Modem

Modem is a device that modulates an analog ‘carrier’ signal to encode in digital information and that also demodulates a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. These signals can be transmitted over telephone lines and demodulated by another modem at the receiver side to recover the digital data. The modem provides the connection interface to the Internet service provider.

Modem

You need a working modem in your computer and that is connected to a working phone line to create a dial-up connection with Internet. It requires username, password, then checks the both, if correct your connection will be completed and you will see a notification on your toolbar showing that you are connected and at what speed your connection is made. Your connection speed will vary depending on the quality of your modem, your phone line and Internet providing vendor service.

Example of cable modem

Those companies which manufacture router include Intel, Motorola, Compaq, Omnitron, Star Tech, Watchguard Inc., ZyXel Communication Corp., Canary Communications etc.

Advantages of Modem:

• More useful in connecting LAN with the Internet
• Speed depends on the cost (line charges)
• High bandwidth

Disadvantages of Modem:

• Acts just as an interface between LAN and Internet
• No traffic maintenance is present
• With increasing number of users the amount of bandwidth decreases and makes the connection slower

ISDN terminal adapter

Integrated Services Digital Network (ISDN) is set of communication standards for simultaneous digital transmission of voice, video, data and other network services over the traditional circuits of the Public Switched Telephone Network (PSTN). ISDN is a circuit-switched telephone network system, which also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in potentially better voice quality than an analog phone can provide.

Analog telephones and fax machines are used over ISDN lines, but their signals are converted into digital by the ISDN terminal adapter. It plugs into the serial port of the computer or into an expansion slot. Some terminal adapters sue the parallel port for higher speed. The adapter may also include a regular data or fax/modem and switch automatically between analog and digital depending on the type of call.

The ISDN Terminal Adapter connects a PC to the Internet or to dial-up locations for web surfing, email access or telecommunicating over ISDN. It takes full advantage of ISDN capacity, making your time much more productive compared with using conventional modems. It is an older technology that provides higher speed data (Internet) traffic over 2 times faster than dial-up connection.

ISDN service is not available from telephone companies in all areas and also the terminal adapter is not usually built into a computer. You purchase and install it when you sign up for ISDN service. Some manufacturers and telephone companies use the term ISDN modem, instead of ISDN terminal adapter.

NETGEAR XM128 ISDN Modem

Those companies which manufacture router include NetGear, Norstar etc.

Line Driver

Line driver is a device to increase transmission distance by amplifying the analog or digital signal at its source, in base band networks only.

Example of Line driver

Those companies which manufacture router include Consec, Blitz etc.


Feel free to comment with your questions and suggestions regarding the post content...!