Computer Network & Internet (MBA)

There are a large number of ways we can classify networks, depending on what we're interested in. Most of these are orthogonal...

Regular vs. Irregular

A regular network topology is defined in terms of some sort of regular graph structure (such as rings, meshes, hypercube, etc); an irregular topology isn't. We tend to talk more about regular topologies, since it's possible to analyze them reasonably; even discovering the topology of an irregular network can be a challenge. Regular topologies are used in applications such as parallel processors and small LANs; irregular topologies are used in larger LANs and in internets (the Internet is extraordinarily irregular -- and there are even tools out there for attempting to discover the topology of the internet near your site!).

Static vs. Dynamic

There are two basic ways to construct a network: we can use the processors themselves as the routing nodes, or we can let the processors and memory sit ``outside'' the network and have specialized switching nodes transfer the messages. The former is a static network; the latter is a dynamic network (the idea is that with a static network you can only send a message to your neighbors, while in a dynamic network you can drop a message with routing information and the network can get it anywhere). As it turns out, we can easily find examples of both dynamic and static networks for nearly any topology we care to come up with.

Circuit Switching vs. Packet Switching

Second, there are two basic ways to set up the communication paths in a network: we can put each packet on the net with either routing information or just information about its destination, or else we can set up all the switches once and let all the packets follow the path that was established. The first way is called packet switching, the second is circuit switching. Historically the phone system used circuit switching; now just about everything uses packet switching.

Note: while just about everything today is packet-switched, the way it is normally presented to the user is through virtual circuits.

Source-based routing vs. others

We also have a choice of sending a packet along with just the destination address, leaving the network to figure out how to get the data to its destination, or actually specifying the full route in the header. The old Usenet bang-paths specifying e-mail addresses were an example of source-based routing. Today, we almost never see source-based routing; we always let the network links do the routing (note: the term ``source-based'' routing has been recycled in recent years to refer to making routing decisions based on the source of a packet. This is a completely different and unrelated use of the term, and is in fact used in an environment that is not source-based as we are using it here).

Store-and-forward vs. Wormhole routing

Normally, we think of data being shipped through a network a packet at a time: we send the packet to the first intermediate node, then on to the second, and so forth. This is called store-and-forward routing. An alternative which has become popular recently is wormhole routing. Remember that ordinarily, a packet contains a header with routing information followed by a payload containing the actual data, probably followed by a checksum or something to guarantee integrity. This implies that once the header has arrived at a node, it's possible to make routing decisions and pass it along immediately, rather than waiting for the entire packet to arrive first. This is called wormhole routing, in analogy with a worm crawling through a wormhole. Wormhole routing dramatically reduces latency, but creates new possibilities for deadlock.

Blocking vs. non-blocking vs. re-arrangeable

In a dynamic network, a question that arises is whether it's possible to realize any transformation of the sources and destinations. If not, it's a blocking network; if so, it's non-blocking. One last, somewhat counterintuitive to my mind, possibility is that it's possible to have a network in which there is more than one possible path from sources to and you have to find the right one to take to avoid blocking. This is called a rearrangeable network, because you can rearrange your paths to fix blocking.

·       Subnetting

A subnet allows the flow of network traffic between hosts to be segregated based on a network configuration. By organizing hosts into logical groups, subnetting can improve network security and performance.

Subnet Mask

Perhaps the most recognizable aspect of subnetting is the subnet mask. Like IP addresses, a subnet mask contains four bytes (32 bits) and is often written using the same "dotted-decimal" notation. For example, a very common subnet mask in its binary representation

11111111 11111111 11111111 00000000

is typically shown in the equivalent, more readable form

255.255.255.0

Applying a Subnet Mask

A subnet mask neither works like an IP address, nor does it exist independently from them. Instead, subnet masks accompany an IP address and the two values work together. Applying the subnet mask to an IP address splits the address into two parts, an "extended network address" and a host address.

For a subnet mask to be valid, its leftmost bits must be set to '1'. For example,

00000000 00000000 00000000 00000000

is an invalid subnet mask because the leftmost bit is set to '0'.

Conversely, the rightmost bits in a valid subnet mask must be set to '0', not '1'. Therefore,

11111111 11111111 11111111 11111111

is invalid.

All valid subnet masks contain two parts: the left side with all mask bits set to '1' (the extended network portion) and the right side with all bits set to '0' (the host portion), such as the first example above.

Classes of IP Addresses, IP Broadcast and IP Multicast

IPv4 Address Classes

The IPv4 address space can be subdivided into 5 classes - Class A, B, C, D and E. Each class consists of a contiguous subset of the overall IPv4 address range. With a few special exceptions explained further below, the values of the leftmost four bits of an IPv4 address determine its class as follows:

Class	Leftmost bits	Start address	Finish address
A	0xxx	0.0.0.0	127.255.255.255
B	10xx	128.0.0.0	191.255.255.255
C	110x	192.0.0.0	223.255.255.255
D	1110	224.0.0.0	239.255.255.255
E	1111	240.0.0.0	255.255.255.255

All Class C addresses, for example, have the leftmost three bits set to '110', but each of the remaining 29 bits may be set to either '0' or '1' independently (as represented by an x in these bit positions):

110xxxxx xxxxxxxx xxxxxxxx xxxxxxxx

Converting the above to dotted decimal notation, it follows that all Class C addresses fall in the range from 192.0.0.0 through 223.255.255.255.

IP Address Class E and Limited Broadcast

The IPv4 networking standard defines Class E addresses as reserved, meaning that they should not be used on IP networks. Some research organizations use Class E addresses for experimental purposes. However, nodes that try to use these addresses on the Internet will be unable to communicate properly.

A special type of IP address is the limited broadcast address 255.255.255.255. A broadcast involves delivering a message from one sender to many recipients. Senders direct an IP broadcast to 255.255.255.255 to indicate all other nodes on the local network (LAN) should pick up that message. This broadcast is 'limited' in that it does not reach every node on the Internet, only nodes on the LAN.

Technically, IP reserves the entire range of addresses from 255.0.0.0 through 255.255.255.255 for broadcast, and this range should not be considered part of the normal Class E range.

IP Address Class D and Multicast

The IPv4 networking standard defines Class D addresses as reserved for multicast. Multicast is a mechanism for defining groups of nodes and sending IP messages to that group rather than to every node on the LAN (broadcast) or just one other node (unicast).

Multicast is mainly used on research networks. As with Class E, Class D addresses should not be used by ordinary nodes on the Internet.

IP Loopback, IP Private Addresses, and IPv6 Address Types

IP Loopback Address

127.0.0.1 is the loopback address in IP. Loopback is a test mechanism of network adapters. Messages sent to 127.0.0.1 do not get delivered to the network. Instead, the adapter intercepts all loopback messages and returns them to the sending application. IP applications often use this feature to test the behavior of their network interface.

As with broadcast, IP officially reserves the entire range from 127.0.0.0 through 127.255.255.255 for loopback purposes. Nodes should not use this range on the Internet, and it should not be considered part of the normal Class A range.

Zero Addresses

As with the loopback range, the address range from 0.0.0.0 through 0.255.255.255 should not be considered part of the normal Class A range. 0.x.x.x addresses serve no particular function in IP, but nodes attempting to use them will be unable to communicate properly on the Internet.

Private Addresses

The IP standard defines specific address ranges within Class A, Class B, and Class C reserved for use by private networks (intranets). The table below lists these reserved ranges of the IP address space.

Definition: Intranet is the generic term for a collection of private computer networks within an organization. An intranet uses network technologies as a tool to facilitate.

·       The Difference Between Hubs, Switches and Routers

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.

Switch

In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs.

Router

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 (Internet Control Message Protocol) to communicate with each other and configure the best route between any two hosts.

The Differences Between Hubs, Switches, and Routers on the Network

The functions of a router, hub and a switch are all quite different from one another, even if at times they are all integrated into a single device. Let's start with the hub and the switch since these two devices have similar roles on the network. Each serves 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. The big difference between these two devices is in the method in which frames are being delivered.

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.

A switch, however, keeps a record of the MAC addresses of all the devices connected to it. With this information, a switch can identify which system is sitting on which port. So when a frame is received, it knows exactly which port to send it to, without significantly increasing network response times. And, unlike a hub, a 10/100Mbps switch will allocate a full 10/100Mbps to each of its ports. So regardless of the number of PCs transmitting, users will always have access to the maximum amount of bandwidth. It's for these reasons why a switch is considered to be a much better choice then a hub.

Routers are completely different devices. Where a hub or switch is concerned with transmitting frames, a router's job, as its name implies, is to route packets to other networks until that packet ultimately reaches its destination.

A router is typically connected to at least two networks, commonly two Local Area Networks (LANs) or Wide Area Networks (WAN) or a LAN and its ISP's network . for example, your PC or workgroup and EarthLink. Routers are located at gateways, the places where two or more networks connect. Using headers and forwarding tables, routers determine the best path for forwarding the packets. Router use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

All routers have a WAN Port that connects to a DSL or cable modem for broadband Internet service and the integrated switch allows users to easily create a LAN. This allows all the PCs on the LAN to have access to the Internet and Windows file and printer sharing services.

Some of the more high-end or business class routers will also incorporate a serial port that can be connected to an external dial-up modem, which is useful as a backup in the event that the primary broadband connection goes down, as well as a built in LAN printer server and printer port.

So, in short, a hub glues together an Ethernet network segment, a switch can connect multiple Ethernet segments more efficiently and a router can do those functions plus route TCP/IP packets between multiple LANs and/or WANs; and much more of course.

·       Switching Techniques

Circuit Switching

This method involves the physical interconnection of two devices. A good example of circuit switching involves the Public phone network. A data example would be the classic A/B switch!

Packet Switching

Packet Switching techniques switch packets of data between destinations. Traditionally, this applied to X.25 techniques, but this also applies to TCP/IP and IPX/SPX routers also. Proprietary Frame Relay switches can switch voice signals.

Message Switching

Message Switching techniques were originally used in data communications. An example would be early "store and forward" paper tape relay systems. E-Mail delivery is another example of message switching. In voice systems, you can find Voice Mail delivery systems on the Internet. The classic "forward voice mail" capability in some voice mail systems is another example.

Cell Switching

Cell Switching is similar to packet switching, except that the switching does not necessarily occur on packet boundaries. This is ideal for an integrated environment and is found within Cell-based networks, such as ATM. Cell-switching can handle both digital voice and data signals.

·       Circuit Switching vs. Packet Switching

In circuit-switching, this path is decided upon before the data transmission starts. The system decides on which route to follow, based on a resource-optimizing algorithm, and transmission goes according to the path. For the whole length of the communication session between the two communicating bodies, the route is dedicated and exclusive, and released only when the session terminates.

In packet-switching, the packets are sent towards the destination irrespective of each other. Each packet has to find its own route to the destination. There is no predetermined path; the decision as to which node to hop to in the next step is taken only when a node is reached. Each packet finds its way using the information it carries, such as the source and destination IP addresses.

Packets

To be able to understand packet-switching, you need to know what a packet is. The Internet Protocol(IP), just like many other protocols, breaks data into chunks and wraps the chunks into structures called packets. Each packet contains, along with the data load, information about the IP address of the source and the destination nodes, sequence numbers and some other control information. A packet can also be called a segment or datagram.

Once they reach their destination, the packets are reassembled to make up the original data again. It is therefore obvious that, to transmit data in packets, it has to be digital data.

Brief comparison

• Circuit switching is old and expensive, and it is what PSTN uses. Packet switching is more modern.
• When you are making a PSTN call, you are actually renting the lines, with all it implies. See why international calls are expensive? So if you speak for, say 10 minutes, you pay for ten minutes of dedicated line. You normally speak only when your correspondent is silent, and vice versa. Taking also into consideration the amount of time no one speaks, you finally use much less than half of what you are paying for. With VoIP, you actually can use a network or circuit even if there are other people using it at the same time. There is no circuit dedication. The cost is shared.
• Circuit-switching is more reliable than packet-switching. When you have a circuit dedicated for a session, you are sure to get all information across. When you use a circuit which is open for other services, then there is a big possibility of congestion (which is for a network what a traffic jam is for the road), and hence the delays or even packet loss. But you actually have other protocols giving a helping hand in making packet-switching techniques to make connections more reliable. An example is the TCP protocol. Since voice is to some extent tolerant to some packet loss (unless text - since a comma lost can mean a big difference), packet-switching is finally ideal for VoIP.

OSI 7 Layers Reference Model

These 7 layers further divide the tasks of moving the data across the network into subtask and hence complete one communication cycle between two computers or two network devices. Each layer is assigned a task and the task is completed independently. The OSI layers have the clear and independent characteristics and tasks.

The 7 layers of the OSI models can be divided into upper and lower layers. I have defined the characteristics, tasks and features of each layer separately.

Layer 7: Application Layer

The application layer defines the interfaces for communication and data transfer. This layer also provides and support services such as job transfer, handles network access, e-mail, supports user applications and error recovery.

Protocols: FTP, DNS, SNMP (simple network management protocol), SMTP (simple message transfer protocol), FINGER (which gives user profile information), TELNET (terminal access protocol), TFTP (trivial ftp), BOOTP and SMB protocol are operated on the application layer.

Network Devices: Gateway network device is operated on the application layer.

Layer 6:Presentation Layer

The presentation layer presents the data into a uniform format and masks the difference of data format between two dissimilar systems. It also translates the data from application to the network format. Presentation layer is also responsible for the protocol conversion, encryption, decryption and data compression. Presentation layer is a best layer for cryptography.

Network Devices: Gateway Redirector is operates on the presentation layer.

Layer 5: Session Layer

Session layer establish and manages the session between the two users at different ends in a network. Session layer also manages who can transfer the data in a certain amount of time and for how long. The examples of session layers and the interactive logins and file transfer sessions. Session layer reconnect the session if it disconnects. It also reports and logs and upper layer errors.

Protocols: The protocols that work on the session layer are NetBIOS, Mail Slots, Names Pipes, RPC

Network Devices: Gateway

Layer 4: Transport Layer

Transport layer manages end to end message delivery in a network and also provides the error checking and hence guarantees that no duplication or errors are occurring in the data transfers across the network. Transport layer also provides the acknowledgement of the successful data transmission and retransmits the data if no error free data was transferred.

It also provides and error handling and connectionless oriented data deliver in the network.

Protocols: These protocols work on the transport layer TCP, SPX, NETBIOS, ATP and NWLINK.

Network Devices: The Brouter, Gateway and Cable tester work on the transport layer.

Layer 3: Network Layer

The network layer determines that how data transmits between the network devices. It also translates the logical address into the physical address e.g computer name into MAC address. It is also responsible for defining the route, managing the network problems and addressing. Router works on the network layer and if a sending device does not break the data into the similar packets as the receiving device then network layer split the data into the smaller units and at the receiving end the network layer reassemble the data.

Network layer routes the packets according to the unique network addresses. Router works as the post office and network layer stamps the letters (data) for the specific destinations.

Protocols: These protocols work on the network layer IP, ICMP, ARP, RIP, OSI, IPX and OSPF.

Network Devices: Network devices including Router, Brouter, Frame Relay device and ATM switch devices work on the network layer.

Layer 2:Data Link Layer

Defines procedures for operating the communication links

Frames packets

Detects and corrects packets transmit errors

Protocols: Logical Link Control

• error correction and flow control

• manages link control and defines SAPs

802.1 OSI Model

802.2 Logical Link Control

Media Access Control

• communicates with the adapter card

• controls the type of media being used:

802.3 CSMA/CD (Ethernet)

802.4 Token Bus (ARCnet)

802.5 Token Ring

802.12 Demand Priority

Network Devices: Bridge

Switch

ISDN Router

Intelligent Hub

NIC

Advanced Cable Tester

Layer 1: Physical Layer

Physical layer defines and cables, network cards and physical aspects. It defines raw bit stream on the physical media. It also provides the interface between network and network communication devices. It is also responsible for how many volts for 0 and how many for 1. Physical layer also checks the number of bits transmitted per second and two ways or one way transmission. Physical layer also dealing with the optical, mechanical and electrical features.

Protocols: Protocols that work on the physical layer are ISDN, IEEE 802 and IEEE 802.2

Network Devices: Hubs, Repeaters, Oscilloscope and Amplifier works on the network devices.

Layer 1+2 protocols

• Ethernet
• GFP ITU-T G.7041 Generic Framing Procedure
• OTN ITU-T G.709 Optical Transport Network also called Optical Channel Wrapper or Digital Wrapper Technology

Layer 2 protocols (Data Link Layer)

• ARCnetre Attached Resource Computer NETwork
• ARP Address Resolution Protocol
• RARP Reverse Address Resolution Protocol
• CDP Cisco Discovery Protocol
• DCAP Data Link Switching Client Access Protocol
• Dynamic Trunking Protocol
• Econetr
• FDDI Fiber Distributed Data Interface
• Frame Relay
• ITU-T G.hn Data Link Layer
• HDLC High-Level Data Link Control
• IEEE 802.11 WiFi
• IEEE 802.16 WiMAX
• LocalTalk
• L2F Layer 2 Forwarding Protocol
• L2TP Layer 2 Tunneling Protocol
• LAPD Link Access Procedures on the D channel
• LLDP Link Layer Discovery Protocol
• LLDP-MED Link Layer Discovery Protocol - Media Endpoint Discovery
• PPP Point-to-Point Protocol
• PPTP Point-to-Point Tunneling Protocol
• Q.710 Simplified Message Transfer Part
• NDP Neighbor Discovery Protocol
• RPR IEEE 802.17 Resilient Packet Ring
• SLIP Serial Line Internet Protocol (obsolete)
• StarLANr
• STP Spanning Tree Protocol
• Token ring is not a protocol but is a topology
• VTP VLAN Trunking Protocol

Layer 2+3 protocols

• ATM Asynchronous Transfer Mode
• Frame relay, a simplified version of X.25 welcome
• MPLS Multi-protocol label switching
• X.25

Layer 1+2+3 protocols

• MTP Message Transfer Part
• NSP Network Service Part

Layer 3 protocols (Network Layer)

• CLNP Connectionless Networking Protocol
• EGP Exterior Gateway Protocol
• EIGRP Enhanced Interior Gateway Routing Protocol
• ICMP Internet Control Message Protocol
• IGMP Internet Group Management Protocol
• IGRP Interior Gateway Routing Protocol
• IPv4 Internet Protocol version 4
• IPv6 Internet Protocol version 6
• IPSec Internet Protocol Security
• IPX Internetwork Packet Exchange
• SCCP Signalling Connection Control Part
• AppleTalk DDP

Layer 3 protocols (Network Layer management)

• IS-IS Intermediate System-to-Intermediate System
• OSPF Open Shortest Path First
• BGP Border Gateway Protocol
• RIP Routing Information Protocol
• ICMP Router Discovery Protocol: Implementation of RFC 1256
• Gateway Discovery Protocol (GDP) is a Cisco protocol similar to IRDP

Layer 3.5 protocols

• HIP Host Identity Protocol

Layer 3+4 protocol suites

• AppleTalk
• DECnet
• IPX/SPX
• Internet Protocol Suite
• Xerox Network Systems

Layer 4 protocols (Transport Layer)

• AH Authentication Header over IP or IPSec
• ESP Encapsulating Security Payload over IP or IPSec
• GRE Generic Routing Encapsulation for tunneling
• IL Originally developed as transport layer for 9P
• SCTP Stream Control Transmission Protocol
• Sinec H1 for telecontrol
• SPX Sequenced Packet Exchange
• TCP Transmission Control Protocol
• UDP User Datagram Protocol

Layer 5 protocols (Session Layer)

• 9P Distributed file system protocol developed originally as part of Plan 9
• NCP NetWare Core Protocol
• NFS Network File System
• SMB Server Message Block
• SOCKS "SOCKetS"

Other protocols

• Controller Area Network (CAN)

Layer 7 protocols (Application Layer)

• ADC, A peer-to-peer file sharing protocol
• AFP, Apple Filing Protocol
• BACnet, Building Automation and Control Network protocol
• BitTorrent, A peer-to-peer file sharing protocol
• BOOTP, Bootstrap Protocol
• CAMEL, an SS7 protocol tool for the home operator
• Diameter, an authentication, authorization and accounting protocol
• DICOM includes a network protocol definition
• DICT, Dictionary protocol
• DNS, Domain Name System
• DHCP, Dynamic Host Configuration Protocol
• ED2K, A peer-to-peer file sharing protocol
• FTP, File Transfer Protocol
• Finger, which gives user profile information
• Gnutella, a peer-to-peer file-swapping protocol
• Gopher, a hierarchical hyperlinkable protocol
• HTTP, Hypertext Transfer Protocol
• IMAP, Internet Message Access Protocol
• Internet Relay Chat (IRC)
• ISUP, ISDN User Part
• XMPP, an instant-messaging protocol
• LDAP Lightweight Directory Access Protocol
• MIME, Multipurpose Internet Mail Extensions
• MSNP, Microsoft Notification Protocol (used by Windows Live Messenger)
• MAP, Mobile Application Part
• NetBIOS, File Sharing and Name Resolution protocol - the basis of file sharing with Windows.
• NNTP, News Network Transfer Protocol
• NTP, Network Time Protocol
• NTCIP, National Transportation Communications for Intelligent Transportation System Protocol
• POP3 Post Office Protocol Version 3
• RADIUS, an authentication, authorization and accounting protocol
• Rlogin, a UNIX remote login protocol
• rsync, a file transfer protocol for backups, copying and mirroring
• RTP, Real-time Transport Protocol
• RTSP, Real-time Transport Streaming Protocol
• SSH, Secure Shell
• SISNAPI, Siebel Internet Session Network API
• SIP, Session Initiation Protocol, a signaling protocol
• SMTP, Simple Mail Transfer Protocol
• SNMP, Simple Network Management Protocol
• SOAP, Simple Object Access Protocol
• STUN, Session Traversal Utilities for NAT
• TUP, Telephone User Part
• Telnet, a remote terminal access protocol
• TCAP, Transaction Capabilities Application Part
• TFTP, Trivial File Transfer Protocol, a simple file transfer protocol
• WebDAV, Web Distributed Authoring and Versioning
• DSM-CC Digital Storage Media Command and Control

·       TCP/IP model

The types of services performed and protocols used at each layer within the TCP/IP model are described in more detail in the following table.

 

Layer	Description	Protocols
Application	Defines TCP/IP application protocols and how host programs interface with transport layer services to use the network.	HTTP, Telnet, FTP, TFTP, SNMP, DNS, SMTP, X Windows, other application protocols
Transport	Provides communication session management between host computers. Defines the level of service and status of the connection used when transporting data.	TCP, UDP, RTP
Internet	Packages data into IP datagrams, which contain source and destination address information that is used to forward the datagrams between hosts and across networks. Performs routing of IP datagrams.	IP, ICMP, ARP, RARP
Network interface	Specifies details of how data is physically sent through the network, including how bits are electrically signaled by hardware devices that interface directly with a network medium, such as coaxial cable, optical fiber, or twisted-pair copper wire.	Ethernet, Token Ring, FDDI, X.25, Frame Relay, RS-232, v.35

.

Impact of Computer Networks on Society & Business

Computer networks are becoming a very important tool in successfully linking people together for a variety of reasons. The internet has revolutionized communications and methods of commerce by allowing various computer networks around the world to interconnect. There are a multitude of advantages associated with computer networks. Some areas which are successfully using this system are industry associations, corporations, professional societies, government, and education.

Computer networks have opened the flood gates of information and enables instant access to information – “anywhere, anytime and any format”. The immense wealth of information floating in the cyber world is accessible though these well connected global networks. Networks have ushered in a digital society which now affects everyday life, groups, personal identity, culture, safety, and virtually all aspects of existence. The digital society has become so pervasive that recognizing the impacts of such technologies on us as individuals as well as the societal repercussions is gaining importance. Networks now contribute to the globalization of production and capital markets by reducing the cost of information and communication. These technologies have made it easier for multinationals and other companies to spread production facilities all over the world, to co-ordinate international marketing campaigns, and to ease collaboration in projects taking place on different continents.

Computer networks support human communication via electronic mail (e-mail), “chat rooms,” newsgroups, and audio and video transmission and allow people to work collaboratively at many different locations. It supports access to digital information by many applications, including the World Wide Web. The Internet has proved to be a spawning ground for a large and growing number of “e-businesses” that carry out most of their sales and services over the Internet. Wireless services enable applications not previously possible in any economical fashion. For example, global positioning systems (GPS) combined with wireless Internet access would help mobile users to locate alternate routes, generate precise accident reports and initiate recovery services, and improve traffic management and congestion control. In addition to wireless laptop computers and personal digital assistants (PDAs), wearable devices with voice input and special display glasses are under development. Higher backbone and network access speeds enabled through fiber optic networks will simultaneously carry multiple signals—data, voice, and video.

The Internet is offering the possibility of creating an environment or virtual reality in which individuals might work, socially interact with others, and perhaps even live out their lives. People can now go online and search for information on subjects as diverse as politics, gardening, health, technology and online shopping. The information superhighway can be tapped to send across breaking news as it happens during catastrophic disasters. Internet can be a medium to mobilize people and engage in social interactions. Online gaming is a part of the rapidly growing virtual economies some of which exceed the GNP of countries in Africa and Asia. The use of Wikipedia and social networking tools such as Facebook, MySpace and LinkedIn has created online communities where constant exchange of information takes place. Internet dating sites and pornography appeal to particular niche groups. Advertising is a huge revenue source for many companies. E-commerce now includes retail shopping, banking, stocks, auctions, real estate transactions, airline booking, and movie rentals – nearly anything you can imagine in the real world. Enterprise applications deployed over networks bring in efficiencies and cost savings.

Computer networks have created vast resources for people to enhance their learning skills. People can now browse through catalogs, periodicals, websites, blogs and databases and increase their knowledge. The Internet has become an invaluable and discipline-transforming environment for scientists and scholars. Scientific databases and electronic publishing help the scientific community to exchange ideas and resources. Free speech has been made possible by networks where an individual can freely express his ideas and thoughts without fear of prosecution. Online political campaigns are now an integral part of any elections. Candidates can now galvanize volunteer campaign workers and raise significant sums from many small donations.

While the benefits outweigh any negative implications, people are still worried about privacy, trust, security, and now, reliability. There are also concerns about access, reputation, participation, sustainability, responsibility, authenticity, authorship, ownership, surveillance and control, cultural health (digital literacy) and distinctiveness. Issues about data ownership, systems vulnerability, information manipulation, false propaganda/rumors, plagiarism and malware need to be tackled. Computer networks are revolutionizing information and entertainment delivery, transforming social life and behavior, even political institutions and the role of citizens within them. Some of the social/political changes will be liberating, some will have little social effect, but others may be harmful or even socially and politically explosive. We should all be vigilant about the benefits and consequences of rapidly proliferating computer networks.

·        Remote Monitoring Techniques

Network monitoring is the information collection function of network management and The purpose of network monitoring is the collecting of useful information from various parts of the network (for problems caused by overloaded and/or crashed servers, network connections or other devices..etc). so that the network can be managed and controlled using the collected information and most of the network devices are located in remote locations (may be in www). These devices do not usually have directly connected terminals so that network management application cannot monitor their statuses easily. Thus, network monitoring techniques are developed to allow network management applications to check the states of their network devices. As more and more network devices are used to build bigger networks, network monitoring techniques are expanded to monitoring networks as a whole and the commonly measured metrics are response time and availability

Performance monitoring

Performance monitoring deals with measuring the performance of the network. There are three important issues in performance monitoring.

1. performance monitoring information is usually used to plan future network expansion and locate current network usage problems.

2. the time frame of performance monitoring must be long enough to establish a network behavior model.

3. choosing what to measure is important. There are too many measureable things in a network. But the list of items to be measured should be meaningful and cost effective.

Fault monitoring

Fault monitoring deals with measuring the problems in the network. There are two important issues in fault monitoring.

1. fault monitoring deals with various layers of the network. When a problem occurs, it can be at different layers of the network. Thus it is important to know which layer is having problem.

2.fault monitoring requires establishing a normal characteristics of the network in an extended period of time. There are always errors in the network but when there are errors, it does not mean the network is having persistent problems. Some of these errors are expected to occur. For example, noise in a network link can cause transmission errors.

Account monitoring

Account monitoring deals with how users use the network. The network keeps a record of what devices of the network are used by users and how often they are used. This type of information is used for billing user for network usage, and for predicting future network usage

A good network monitoring system must have the functions

IP SLA Reports ,Logical Grouping, Trending ,Trend Prediction, Auto Discovery ,Agent ,SNMP ,Syslog,Plugins, Triggers / Alerts, WebApp ,Distributed Monitoring ,Inventory ,Data Storage Method, Maps, Access Control ,IPv6

Polling is a CAM (channel access method). In a master/slave scenario, the master queries each slave device in turn as to whether it has any data to transmit. If the slave answers yes then the device is permitted to transmit its data. If the slave answers no then the master moves on and polls the next slave device. The process is repeated continuously.

• Class of Service (CoS)

Class of Service (CoS) is a way of managing traffic in a network by grouping similar types of traffic (for example, e-mail, streaming video, voice, large document file transfer) together and treating each type as a class with its own level of service priority. Unlike Quality of Service (QoS) traffic management, Class of Service technologies do not guarantee a level of service in terms of bandwidth and delivery time; they offer a "best-effort." On the other hand, CoS technology is simpler to manage and more scalable as a network grows in structure and traffic volume. One can think of CoS as "coarsely-grained" traffic control and QoS as "finely-grained" traffic control.

here are three main CoS technologies:

• 802.1p Layer 2 Tagging
• Type of Service (ToS)
• Differentiated Services (DiffServ)

802.1p Layer 2 Tagging and ToS make use of three bits in the layer 2packetheader that can be used to specify priority.

Differentiated Services uses a different approach to managing packets than simple priority labeling. It uses an indication of how a given packet is to be forwarded, known as the Per Hop Behavior (PHB). The PHB describes a particular service level in terms of bandwidth, queueing theory, and dropping decisions. Based on application requirements, traffic is prioritized at the connection endpoint by setting the Differentiated Services (Diff-Serv) code in the header of an IP data packet. Letting users manage network traffic, Diff-Serv, together with other MPLS protocols, is used to prioritize data traffic in both IP and ATM networks.

·       Quality of Service

Quality of Service (QoS) refers to the ability of a network to provide higher priority services, including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics, to selected network traffic over various WAN, LAN and Man technologies. At the same time, making sure that providing priority for one class of traffic does not make other flows fail.

Typically, there are three levels / classes of QoS:

• Best-effort servicebasic connectivity with no guarantees of traffic delivery, and speed and order of delivery.
• Differentiated service (Class of Service) - Some traffic is treated better than the rest (faster handling, more average bandwidth, and lower average loss rate). This is a statistical preference, not guaranteed service, which is typically provided by classification of traffic.
• Guaranteed service -This is an absolute reservation of network resources for specific traffic. This is provided through QoS tools RSVP in the packet network. The traditional PSTN network uses circuit switch with guaranteed link connection and bandwidth allocation to ensure QoS.

QoS technologies covers the following three areas:

• QoS identification and marking techniques for coordinating QoS from end to end between network elements, which is accomplished through packet/traffic classification and bandwidth reservation. Common methods of identifying flows include access control lists (ACLs), policy-based routing, committed access rate (CAR), and network-based application recognition (NBAR).
• QoS within a single network element: which includes technologies of congestion management, queue management, link efficiency, and shaping/policing tools provide QoS within a single network element.
• QoS policy, management, and accounting functions to control and administer end-to-end traffic across a network: this includes baseline the network with devices such as RMON probes, Deploy QoS techniques when the traffic characteristics have been obtained and an application(s) has been targeted for increased QoS and Evaluate the results by testing the response of the targeted applications to see whether the QoS goals have been reached.

CSMA/CD

CSMA/CD (Carrier Sense Multiple Access / Collision Detection) is the protocol used in Ethernet networks to ensure that only one network node is transmitting on the network wire at any one time.

Carrier Sense means that every Ethernet device listens to the Ethernet wire before it attempts to transmit. If the Ethernet device senses that another device is transmitting, it will wait to transmit.

Multiple Access means that more than one Ethernet device can be sensing (listening and waiting to transmit) at a time.

Collision Detection means that when multiple Ethernet devices accidentally transmit at the same time, they are able to detect this error.

 

How Collisions Occur under CSMA/CD

Imagine a very simple Ethernet network with only two nodes.

Each node, independently, decides to send an Ethernet frame to the other node.

Both nodes listen to the Ethernet wire and sense that no carrier is present.

Both nodes transmit simultaneously, causing a collision.

Both nodes detect the collision and each node waits a random amount of time before transmitting again.

Collisions are normal on an Ethernet network. A small amount of collisions are expected in the protocol design.

If too many nodes are transmitting on an Ethernet network the number of collisions can rise to an unacceptable level. This can reduce the amount of available bandwidth on an Ethernet network because so much bandwidth is lost in retransmission.

Ethernet switches greatly reduce the already minor difficulties experienced with the CSMA/CD protocol.

Token Ring

Token Ring is a local area networking system originally conceived in the late 1960s by IBM and patented in 1981, with IBM promoting its use throughout most of the 1980s. Although initially very successful, it was eventually displaced by Ethernet as the favored technology and architecture for local area networks (LAN); although IBM undertook a valiant effort to compete, this was not successful and IBM itself eventually stopped using token ring as its LAN standard.

How Token Ring Works

The token ring network is simple in design and conceptual operation.

The key to the system is a 'token' – which is actually a data frame or container for storing data that is to be transmitted down a 'ring' of computers connected to the network. A simple analogy is to imagine a clock with each number on the clock face representing one computer on a network; 12 numbers, 12 computers.

A 'free' (or empty) token is released into the network, moving around the network, 'stopping off' at each computer to check if it is needed. Assume that computer 3 wants to send a data package to computer 9. When the free token 'stops off' at computer 3, it is grabbed and the data is 'injected' into the empty vessel and then sent on its way. The token passes each computer in the sequence (e.g. computer 4, 5, 6 and so on); each computer notes that the packet is not addressed to it and 'rejects' it, in effect, "passing" it on to the next computer in the series.

Once the packet or token reaches computer 9 (to which the data is addressed), it is 'grabbed' again and an exchange of data occurs – the data is released to computer 9, and the computer 'injects' an acknowledgement receipt into the token. The token (with the acknowledgement receipt) is released back into the network, proceeding down the chain (e.g. moving to computers 9, 10 and so on) with each one again 'rejecting' the token since it is not addressed to them.

Once the token reaches Computer 3 (which was the 'sender' of the data packet), the token is again 'grabbed,' with the acknowledgement message being read; in a sense, the token is emptied of its contents by the original sending computer and sent on its way, ready for use by another computer.

Token Ring Operating Speed and Popularity

Although the process may seem to be cumbersome, the speed of data transmission is exceedingly fast and movement of the token is measured in microseconds. The token ring also has a built-in recovery and management system to ensure the system does not give way to faults or problems.

Although the Token Ring networking system appears to be reliable and fast, its early development stages were hit with problems and issues which made it appear to be less reliable and efficient than the Ethernet networking system. These led to its subsequent decline, with Ethernet now in place in an estimated 70 percent of LAN setups worldwide.

Different Layer Switching

Layer 2: refers to the Data Link layer of the commonly-referenced multilayered communication model, Open Systems Interconnection (OSI). The Data Link layer is concerned with moving data across the physical links in the network. In a network, the switch is a device that redirects data messages at the layer 2 level, using the destination Media Access Control (MAC) address to determine where to direct the message.

The Data-Link layer contains two sublayers that are described in the IEEE-802 LAN standards:

• Media Access Control (MAC) sublayer
• Logical Link Control (LLC) sublayer

The Data Link layer ensures that an initial connection has been set up, divides output data into data frames, and handles the acknowledgements from a receiver that the data arrived successfully. It also ensures that incoming data has been received successfully by analyzing bit patterns at special places in the frames.

Layer 3 Switch:- Layer 3 switch is a network device that forwards traffic based on layer 3 information at very high speeds. Layer 3 switch uses the same routing algorithms as traditional routers do. However, Layer 3 switch performs its operations using application specific integrated circuit (ASIC) hardware, while a router does it using software in a microprocessor. A Layer 3 switch goes beyond the Layer 2 MAC addressing and routing. The Layer 3 switch looks at the incoming packet's networking protocol. Layer 3 switching is more effectively used to segment a LAN than to provide a WAN connection. Traditionally, routers, which inspect layer 3, were considerably slower than layer 2 switches.

Layer 4 Switch:- Layer 4 switch, based on the OSI "transport" layer, allows for policy-based switching such as limiting different types of traffic on specific end-user switch ports, or for prioritizing certain packet types, such as database or application server traffic. Layer 4 switches also offer a powerful combination of Network Address Translation (NAT) with higher-layer address screening. Actually, layer 4 switch may make forwarding decisions based upon information at any OSI layer from 4 through 7, depending upon the particular product. In fact, some of the so-called "Layer 4 Switches" even monitor the state of individual sessions from beginning to end, just as firewalls do, in which case they're referred to as "session switches." Therefore, it is called Layer 4 - 7 switch.

Layer 7 Switch:- A Layer 7 Switch performs wire-speed processing of packet header content, not only at Layer 2 or Layer 3, but also at the transport layer (Layer 4) up through the application layer (OSIs Layer 7). Layer 7 switch integrates routing and switching by forwarding traffic at layer 2 speed using layer 7 information. For example, an XML switch can analyze the XML tags at the application level and make forwarding decisions.

Fast Ethernet and Gigabit Ethernet

Fast Ethernet supports a maximum data rate of 100 Mbps. It is so named because original Ethernet technology supported only 10 Mbps. Fast Ethernet began to be widely deployed in the mid-1990s as the need for greater LAN performance became critical to universities and businesses.

A key element of Fast Ethernet's success was its ability to coexist with existing network installations. Today, many network adapters support both traditional and Fast Ethernet. These so-called "10/100" adapters can usually sense the speed of the line automatically and adjust accordingly. Just as Fast Ethernet improved on traditional Ethernet, Gigabit Ethernet improves on Fast Ethernet, offering rates up to 1000 Mbps instead of 100 Mbps.

Gigabit Ethernet is an extension to the family of Ethernet computer networking and communication standards. The Gigabit Ethernet standard supports a theoretical maximum data rate of 1 Gbps (1000 Mbps).

At one time, it was believed that achieving Gigabit speeds with Ethernet required fiber optic or other special cables. However, Gigabit Ethernet can be implemented on ordinary twisted pair copper cable (specifically, the CAT5e and CAT6 cabling standards).

Migration of existing computer networks from 100 Mbps Fast Ethernet to Gigabit Ethernet is happening slowly. Much legacy Ethernet technology exists (in both 10 and 100 Mbps varieties), and these older technologies offers sufficient performance in many cases.

Today, Gigabit Ethernet can only be found mainly in research institutions. A decrease in cost, increase in demand, and improvements in other aspects of LAN technology will be required before Gigabit Ethernet surpasses other forms of wired networking in terms of adoption.

Also Known As: 1000 Mbps Ethernet

Synchronous Optical Network (SONET)

SONET is the American National Standards Institute standard for synchronous data transmission on optical media. The international equivalent of SONET is synchronous digital hierarchy (SDH). Together, they ensure standards so that digital networks can interconnect internationally and that existing conventional transmission systems can take advantage of optical media through tributary attachments.

SONET provides standards for a number of line rates up to the maximum line rate of 9.953 gigabits per second (Gbps). Actual line rates approaching 20 gigabits per second are possible. SONET is considered to be the foundation for the physical layer of the broadband ISDN (BISDN).

Asynchronous transfer mode runs as a layer on top of SONET as well as on top of other technologies.

SONET defines a base rate of 51.84 Mbps and a set of multiples of the base rate known as "Optical Carrier levels (OCx)."

• Internet Protocol version 6 (IPv6)

It is the next-generation Internet Protocol version designated as the successor to IPv4, the first implementation used in the Internet that is still in dominant use currently. It is an Internet Layer protocol for packet-switched internetworks. The main driving force for the redesign of Internet Protocol is the foreseeable IPv4 address exhaustion. IPv6 was defined in December 1998 by the Internet Engineering Task Force (IETF) with the publication of an Internet standard specification.

Features and differences from IPv4

In most regards, IPv6 is a conservative extension of IPv4. Most transport- and application-layer protocols need little or no change to operate over IPv6; exceptions are application protocols that embed network-layer addresses, such as FTP or NTPv3 (Network Time Protocol).

Larger address space

The most important feature of IPv6 is a much larger address space than that of IPv4: addresses in IPv6 are 128 bits long, compared to 32-bit addresses in IPv4.

The very large IPv6 address space supports a total of 2¹²⁸ (about 3.4×10³⁸) addresses—or approximately 5×10²⁸ (roughly 2⁹⁵) addresses for each of the roughly 6.5 billion (6.5×10⁹) people alive in 2006.

Stateless address auto configuration

IPv6 hosts can configure themselves automatically when connected to a routed IPv6 network using ICMPv6 router discovery messages. When first connected to a network, a host sends a link-local multicast router solicitation request for its configuration parameters; if configured suitably, routers respond to such a request with a router advertisement packet that contains network-layer configuration parameters.

If IPv6 stateless address auto configuration is unsuitable for an application, a network may use stateful configuration with the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) or hosts may be configured statically.

Multicast

Multicast, the ability to send a single packet to multiple destinations, is part of the base specification in IPv6. This is unlike IPv4, where it is optional (although usually implemented).

IPv6 does not implement broadcast, which is the ability to send a packet to all hosts on the attached link. The same effect can be achieved by sending a packet to the link-local all hosts multicast group. It therefore lacks the notion of a broadcast address—the highest address in a subnet (the broadcast address for that subnet in IPv4) is considered a normal address in IPv6.

TCP/IP Network Model

The Internet Protocol Suite also known as TCP/IP is the set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard. IP networking represents a synthesis of several developments that began to evolve in the 1960s and 1970s, namely the Internet and LANs (Local Area Networks), which emerged in the mid- to late-1980s, together with the advent of the World Wide Web in early 1990s.

The main differences between the two models are as follows:

1. OSI is a reference model and TCP/IP is an implementation of OSI model.

2.TCP/IP Protocols are considered to be standards around which the internet has developed. The OSI model however is a "generic, protocol independent standard."

3. TCP/IP combines the presentation and session layer issues into its application layer.

4. TCP/IP combines the OSI data link and physical layers into the network access layer.

5. TCP/IP appears to be a simpler model and this is mainly due to the fact that it has fewer layers.

6. TCP/IP is considered to be a more credible model- This is mainly due to the fact because TCP/IP protocols are the standards around which the internet was developed therefore it mainly gains creditability due to this reason. Where as in contrast networks are not usually built around the OSI model as it is merely used as a guidance tool.

7. The OSI model consists of 7 architectural layers whereas the TCP/IP only has 4 layers.

The figures describes the same.

Diagram of the TCP/IP Model

THE TCP/IP MODEL

The TCP/IP model does not exactly match the OSI model. There is no universal agreement regarding how to describe TCP/IP with a layered model but it is generally agreed that there are fewer levels than the seven layers of the OSI model. The four layer structure of TCP/IP is built as information is passed down from applications to the physical network layer. When data is sent, each layer treats all of the information it receives from the layer above as data and adds control information to the front of that data. This control information is called a header, and the addition of a header is called encapsulation. When data is received, the opposite procedure takes place as each layer removes its header before passing the data to the layer above.