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COMPUTER NETWORKING
By,SAVIN SHETTYBHARAT SHETTYANKITA SHETTYPOOJA SHETTYNIKITA RAI
INDEX
TOPICS COVERED BY
INTRODUCTION SAVIN SHETTY
TYPES OF TOPOLOGY ANKITA SHETTY
TYPES OF SERVES NIKITA RAI
TYPES OF NETWORKS BHARAT SHETTY
COMPONENTS OF NETWORKS
POOJA SHETTY
OSI MODEL SAVIN SHETTY
BIBLIOGRAPHY -
What is Computer networking?
Networking is the word basically relating to computers and their connectivity. It is very often used in the world of computers and their use in different connections. The term networking implies the link between two or more computers and their devices, with the soul purpose of sharing the data stored in the computers, with each other. The networks between the computing devices are very common these days due to the launch of various hardware and computer software which aid in making the activity much more convenient to build and use. Networking is the word basically relating to computers and their connectivity. It is very often used in the world of computers and their use in different connections. The term networking implies the link between two or more computers and their devices, with the soul purpose of sharing the data stored in the computers, with each other. The networks between the computing devices are very common these days due to the launch of various hardware and computer software which aid in making the activity much more convenient to build and use.
Computer networking is then categorized into several different areas and uses, such as the most common ones like LAN and WAN.
Computer networking is also based on different network designs. The two basic classification categories of the network design are the client-server and peer-to-peer. The client-server networking refers to the computer servers that are centralized, which are mainly used in storing emails, web pages, files and applications. The peer-to-peer network is the most commonly used and all the computers mainly support its functions. The Client server is used extensively in the business functions, whereas the peer-to-peer server is for home use.
Every network requires a topology to work through which the data flows and the computers can communicate with each other. The most common types of topologies are bus, star, ring, and mesh.
Networking also involves a special communication language used by the computer devices. These languages are called network protocols, and most of the computers use a range of protocols which they support. The most common network in the Internet and home networks is the TCP/IP.
Networking can be either wired or wireless. The most common wired networks like Ethernet cables were extensively used but now wireless networking have emerged and the new computer networks mainly support this feature.
With the increasing use of the computers and the networking the local area network of the LAN is one such network type which links the two computers in a connection.
For this connection a Local area network card or the LAN card is required which enables the connection of the computers in a network. It is a piece of hardware which is connected inside the PC linking the computer network.
What is Network Topology?
Computer network topology is the way various components of a network (like nodes, links, peripherals, etc) are arranged. Network topologies define the layout, virtual shape or structure of network, not only physically but also logically. The way in which different systems and nodes are connected and communicate with each other is determined by topology of the network. Topology can be physical or logical.Physical Topology is the physical layout of nodes, workstations and cables in the network; while logical topology is the way information flows between different components.
Types of Physical Network Topologies
Bus Topology
Star Topology
Ring Topology
Mesh Topology
BUS TOPOLOGY :
Bus Topology is the simplest of network topologies. In this type of topology, all the nodes (computers as well as servers) are connected to the single cable (called bus), by the help of interface connectors. This central cable is the backbone of the network and is known as Bus (thus the name). Every workstation communicates with the other device through this Bus.
A signal from the source is broadcasted and it travels to all workstations connected to bus cable. Although the message is broadcasted but only the intended recipient, whose MAC address or IP address matches, accepts it. If the MAC /IP address of machine doesn’t match with the intended address, machine discards the signal.
A terminator is added at ends of the central cable, to prevent bouncing of signals. A barrel connector can be used to extend it.
Advantages of Linear Bus Topology :
1) It is easy to set-up and extend bus network.
2) Cable length required for this topology is the least compared to other networks.
3) Bus topology costs very less.
4) Linear Bus network is mostly used in small networks. Good for LAN.
Disadvantages of Linear Bus Topology :
1) There is a limit on central cable length and number of nodes that can be connected.
2) Dependency on central cable in this topology has its disadvantages. If the main cable (i.e. bus ) encounters some problem, whole network breaks down.
3) Proper termination is required to dump signals. Use of terminators is must.
4) It is difficult to detect and troubleshoot fault at individual station.
5) Maintenance costs can go higher with time.
6) Efficiency of Bus network reduces as the number of devices connected to it increases.
7) It is not suitable for networks with heavy traffic.
8) Security is very low because all the computers receive the sent signal from the source.
STAR TOPOLOGY:
In Star topology, all the components of network are connected to the central device called nodes were connected to central cable, here all the workstations are connected to central device with a point-to-point connection. So it can be said that every computer is indirectly connected to every other node by the help of “hub”.
All the data on the star topology passes through the central device before reaching the intended destination. Hub acts as a junction to connect different nodes present in Star Network, and at the same time it manages and controls whole of the network. Depending on which central device is used, “hub” can act as repeater or signal booster. Central device can also communicate with other hubs of different network. Unshielded Twisted Pair (UTP) Ethernet cable is used to connect workstations to central node.
Advantages of Star Topology :
1) As compared to Bus topology it gives far much better performance, signals don’t necessarily get transmitted to all the workstations. A sent signal reaches the intended destination after passing through no more than 3-4 devices and 2-3 links. Performance of the network is dependent on the capacity of central hub.
2) Easy to connect new nodes or devices. In star topology new nodes can be added easily without affecting rest of the network. Similarly components can also be removed easily
3) Centralized management. It helps in monitoring the network.
4) Failure of one node or link doesn’t affect the rest of network. At the same time it’s easy to detect the failure and troubleshoot it.
Disadvantages of Star Topology :
1) Too much dependency on central device has its own drawbacks. If it fails whole network goes down.
2) The use of hub, a router or a switch as central device increases the overall cost of the network.
3) Performance and as well number of nodes which can be added in such topology is depended on capacity of central device.
RING TOPOLOGY:
In Ring Topology, all the nodes are connected to each-other in such a way that they make a closed loop. Each workstation is connected to two other components on either side, and it communicates with these two adjacent neighbors. Data travels around the network, in one direction. Sending and receiving of data takes place by the help of TOKEN.
Token Passing: Token contains a piece of information which along with data is sent by the source computer. This token then passes to next node, which checks if the signal is intended to it. If yes, it receives it and passes the empty to into the network, otherwise passes token along with the data to next node. This process continues until the signal reaches its intended destination.The nodes with token are the ones only allowed to send data. Other nodes have to wait for an empty token to reach them. This network is usually found in offices, schools and small buildings.
Advantages of Ring Topology :
1) This type of network topology is very organized. Each node gets to send the data when it receives an empty token. This helps to reduces chances of collision. Also in ring topology all the traffic flows in only one direction at very high speed.
2) Even when the load on the network increases, its performance is better than that of Bus topology.
3) There is no need for network server to control the connectivity between workstations.
4) Additional components do not affect the performance of network.
5) Each computer has equal access to resources.
Disadvantages of Ring Topology:
1) Each packet of data must pass through all the computers between source and destination. This makes it slower than Star topology.
2) If one workstation or port goes down, the entire network gets affected.
3) Network is highly dependent on the wire which connects different components.
4) Multistation Access Unit, and network cards are expensive as compared to Ethernet cards and hubs.
MESH TOPOLOGY:
In a mesh network topology, each of the network node, computer and other devices, are interconnected with one another. Every node not only sends its own signals but also relays data from other nodes. In fact a true mesh topology is the one where every node is connected to every other node in the network. This type of topology is very expensive as there are many redundant connections, thus it is not mostly used in computer networks. It is commonly used in wireless networks. Flooding or routing technique is used in mesh topology.
Advantages of Mesh topology:
1) Data can be transmitted from different devices simultaneously. This topology can withstand high traffic.
2) Even if one of the components fails there is always an alternative present,So data transfer doesn’t get affected.
3)Expansion and modification in topology can be done without disrupting other nodes.
Disadvantages of Mesh topology
1) There are high chances of redundancy in many of the network connections.
2) Overall cost of this network is way too high as compared to other network topologies.
3) Set-up and maintenance of this topology is very difficult. Even administration of the network is tough.
SERVERS
What are Servers?
Server is a computer or a device that manages network resources such as file, printer, and user group as well as network traffic on the network.
During the server selection two parameter are very important to consider that is server specification and processor specification.
There are also some more specification to be consider are memory, storage, connectivity, operating system support specifications.
Servers in a data center. Several servers are mounted on a rack and connected to a KVM switch.
Servers often provide essential services across a network, either to private users inside a large organization or to public users via the Internet.
Types of servers
In a general network environment the following types of servers may be found.
1.)Application Server:
An application server is a server that provides software applications with services such as security, data services, transaction support, load balancing, and management of large distributed systems.
The term is often used for web servers that support the Java Platform, Enterprise Edition; however its use isn't restricted to Java.
2.) Catalog Server:
A catalog server provides a single point of access that allows users to centrally search for information across a distributed network.
In other words, it indexes databases, files and information across large network and allows keywords, Boolean and other searches.
3.) Communications servers:
Communications servers are open, standards-based computing systems that operate as a carrier-grade common platform for a wide range of communications applications and allow equipment providers to add value at many levels of the system architecture.
4.) Database servers:
A database server is a computer program that provides database services to other computer programs or computers, as defined by the client–server model . The term may also refer to a computer dedicated to running such a program. Database management systems frequently provide database server functionality.
Such a server is accessed either through a "front end" running on the user’s computer which displays requested data or the "back end" which runs on the server and handles tasks such as data analysis and storage.
5.) Fax Server:
A fax server is a system installed in a local area network (LAN) server that allows computer users whose computers are attached to the LAN to send and receive fax messages.
Alternatively the term fax server is sometimes used to describe a program that enables a computer to send and receive fax messages, set of software running on a server computer which is equipped with one or more fax-capable modems (or dedicated fax boards) attached to telephone lines or, more recently, software modem emulators which use T.38 ("Fax over IP") technology to transmit the signal over an IP network. Its function is to accept documents from users, convert them into faxes, and transmit them, as well as to receive fax calls and either store the incoming documents or pass them on to users. Users may communicate with the server in several ways, through either a local network or the Internet. In a big organization with heavy fax traffic, the computer hosting the fax server may be dedicated to that function, in which case the computer itself may also be known as a fax server.
6.) File Server:
In computing, a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files (such as documents, sound files, photographs, movies, images, databases, etc.) that can be accessed by the workstations that are attached to the same computer network. The term server highlights the role of the machine in the client–server scheme, where the clients are the workstations using the storage. A file server is not intended to perform computational tasks, and does not run programs on behalf of its clients.
It is designed primarily to enable the storage and retrieval of data while the computation is carried out by the workstations.
File servers are commonly found in schools and offices, where users use a LAN to connect their client computers.
7.) Game Server:
A game server (sometimes host or shard) is a server which is the authoritative source of events in a multiplayer video game. The server transmits enough data about its internal state to allow its connected clients to maintain their own accurate version of the game world for display to players. They also receive and process each player's input.
8.) Home Server:
A home server is a server located in a private residence providing services to other devices inside and/or outside the household through a home network and/or the Internet.
Such services may include file and/or printer serving, media center serving, web serving (on the network or internet), web caching, account authentication and backup services.
Because of the relatively low number of computers on a typical home network, a home server commonly does not require significant computing power.
9. Print server:
A print server, or printer server, is a device that connects printers to client computers over a network. It accepts print jobs from the computers and sends the jobs to the appropriate printers.
Print servers may support a variety of industry-standard or proprietary printing protocols including Internet Printing Protocol, Line Printer Daemon protocol, Microsoft Network Printing protocol, NetWare, NetBIOS/NetBEUI, or Jet Direct.
A print server may be a networked computer with one or more shared printers. Alternatively a print server may be a dedicated device on the network, with connections to the LAN and one or more printers. Dedicated server appliances tend to be fairly simple in both configuration and features. Print server functionality may be integrated with other devices such as a wireless router, a firewall, or both. A printer may have a built-in print server.
A wireless print server
10.) Proxy Server:
A proxy server is a server (a computer system or an application) that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource available from a different server and the proxy server evaluates the request as a way to simplify and control their complexity. Today, most proxies are web proxies, facilitating access to content on the World Wide Web.
Communication between two computers (shown in grey) connected through a third computer (shown in red) acting as a proxy.
TYPES OF NETWORKS:
A computer network, or simply a network, is a collection of computers and other hardware components interconnected by communication channels that allow sharing of resources and information.[1] Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network. Simply, more than one computer interconnected through a communication medium for information interchange is called a computer network.
Networks may be classified according to a wide variety of characteristics, such as the medium used to transport the data, communications protocol used, scale, topology, and organizational scope.
A local area network (LAN) is a network that connects computers and devices
in a limited geographical area such as home, school, computer laboratory,
office building, or closely positioned group of buildings. Each computer or
device on the network is a node. Current wired LANs are most likely to be
based on Ethernet technology, although new standards like ITU-T G.hn also
provide a way to create a wired LAN using existing home wires (coaxial
cables, phone lines and power lines).
Typical library network, in a branching tree topology and controlled access to resources
A sample LAN is depicted in the accompanying diagram. All interconnected
devices must understand the network layer (layer 3), because they are
handling multiple subnets (the different colors). Those inside the library,
which have only 10/100 Mbit/s Ethernet connections to the user device and a
Gigabit Ethernet connection to the central router, could be called "layer 3
switches" because they only have Ethernet interfaces and must
understand IP. It would be more correct to call them access routers, where
the router at the top is a distribution router that connects to the Internet and
academic networks' customer access routers.
The defining characteristics of LANs, in contrast to WANs (Wide Area
Networks), include their higher data transfer rates, smaller geographic
range, and no need for leased telecommunication lines. Current Ethernet or
other IEEE 802.3 LAN technologies operate at data transfer rates up to 10
Gbit/s. IEEE has projects investigating the standardization of 40 and 100
Gbit/s.[14] LANs can be connected to Wide area network by using routers.
A LAN is a computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings, however, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN).Most LANs connect workstations and personal computers. Each node(individual computer ) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.
A local area network (LAN) supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN.
Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist.
FEATURES OF LAN
A LAN is designed for a small area. Generally it spans a single office, work group floor in a building, or in a campus etc. LAN uses different protocols or rules lor information transmission.
Limited No. of Users: - Most LAN supports I number of users usually around five or ten. More users can be supported by connecting different LANs together, which gives better results than making one; by network of the nature of MAN.
Reliability & Stability: - LANS tend to be very reliable failures on a LAN are mostly due to wrong or improper installation and monitoring. Software that comes along with a LAN provides a number of useful programs like error-detection, prevention of transmission loss and excellent security features.
Flexibility: - Major development in LANs today is flexibility they offer. Earlier versions would support only one type of desktop computers. Today's advanced LANs however can support different types of computers. The flexibility also extends to operating systems & storage media.
(a)Advantages of LANs
1. expensive hardware can be shared e.g. laser printer2. network software is cheaper than buying individual packages3. users can access the same files4. messages can be sent between users5. a single Internet connection can be shared among many users
(b) Disadvantages of LANs
1. quite expensive to set up and maintain2. a virus can spread to all the computers on the network3. more prone to hacking because of multiple points of access4. if the file server goes down, the entire network may go down (star network)
MAN :
A metropolitan area network (MAN) is a computer network that usually spans a city or a large campus. A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks (or WAN) and the Internet.
The IEEE 802-2002 standard describes a MAN as being:[1]
“ A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks.
Characteristics of MAN’S :
The network size falls intermediate between LANs and WANs. A MAN typically covers an area of between 5 and 50 km diameter. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings or as large as the North of Scotland.
A MAN (like a WAN) is not generally owned by a single organisation. The MAN, its communications links and equipment are generally owned by either a consortium of users or by a single network provider who sells the service to the users. This level of service provided to each user must therefore be negotiated with the MAN operator, and some performance guarantees are normally specified.
A MAN often acts as a high speed network to allow sharing of regional resources (similar to a large LAN). It is also frequently used to provide a shared connection to other networks using a link to a WAN.
Advantages of MANs
The biggest advantage of MANs is the bandwidth (potential speed) of the connecting links.
This means that resources (such as databases and files) shared on the network can be accessed extremely quickly.
Some installations allow multiple users to share the same high-speed Internet connection, thereby sharing the cost of the service and securing a better quality of service through collective bargaining and economies of scale.
Disadvantages of MANs
The key disadvantage of MANs is the cost of the cutting-edge technology employed. Also, this equipment generally has to be installed for the first time, as the copper traditionally used for the phone network is generally considered to be too slow to be annexed for this purpose.
The cost is what inhibits the geographical reach of MANs, which is also another drawback.
WAN:
A Wide Area Network (WAN) is a network that covers a broad area (i.e., any network that links across metropolitan, regional, or national boundaries). The Internet is the most popular WAN, and is used by businesses, governments, non-profit organizations, individual consumers, artists, entertainers, and numerous others for almost any purpose imaginable.[1]
Related terms for other types of networks are personal area networks (PANs), local area networks (LANs), campus area networks (CANs),
or metropolitan area networks (MANs) which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively.
A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs).Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is theInternet.
Characteristics of WAN:
Followings are the major characteristics of WAN.
1.Communication Facility: For a big company spanning over different parts of the country the employees can save long distance phone calls and it overcomes the time lag in overseas communications. Computer conferencing is another use of WAN where users communicate with each other through their computer system.
2.Remote Data Entry: Remote data entry is possible in WAN. It means sitting at any location you can enter data, update data and query other information of any computer attached to the WAN but located in other cities. For example, suppose you are sitting at Madras and want to see some data of a computer located at Delhi, you can do it through WAN.
3.Centralised Information: In modern computerised environment you will find that big organisations go for centralised data storage. This means if the organisation is spread over many cities, they keep their important business data in a single place. As the data are generated at different sites, WAN permits collection of this data from different sites and save at a single site.
Examples of WAN1.Ethernet: Ethernet developed by Xerox Corporation is a famous example of WAN. This network uses coaxial cables for data transmission. Special integrated circuit chips called controllers are used to connect equipment to the cable.
2.Aparnet: The Aparnet is another example of WAN. It was developed at Advanced Research Projects Agency of U. S. Department. This Network connects more than 40 universities and institutions throughout USA and Europe.
Advantages Of WAN
-Messages can be sent very quickly to anyone else on the network. These messages can have pictures, sounds, or data included with them (called attachments).
-Expensive things (such as printers or phone lines to the internet) can be shared by all the computers on the network without having to buy a different peripheral for each computer.
-Everyone on the network can use the same data. This avoids problems where some users may have older information than others.
-Share information/files over a larger area
Disadvantages Of WAN
-Setting up a network can be an expensive and complicated experience. The bigger the network the more expensive it is.
-Security is a real issue when many different people have the ability to use information from other computers. Protection against hackers and viruses adds more complexity and expense.
-Once set up, maintaining a network is a full-time job which requires network supervisors and technicians to be employed.
-Information may not meet local needs or interests
What is networking?
Networking is the word basically relating to computers and their connectivity. It is very often used in the world of computers and their use in different connections. The term networking implies the link between two or more computers and their devices, with the soul purpose of sharing the data stored in the computers, with each other. The networks between the computing devices are very common these days due to the launch of various hardware and computer software which aid in making the activity much more convenient to build and use. Networking is the word basically relating to computers and their connectivity. It is very often used in the world of computers and their use in different connections. The term networking implies the link between two or more computers and their devices, with the soul purpose of sharing the data stored in the computers, with each other. The networks between the computing devices are very common these days due to the launch of various hardware and computer software which aid in making the activity much more convenient to build and use.
Computer networking is then categorized into several different areas and uses, such as the most common ones like LAN and WAN.
Computer networking is also based on different network designs. The two basic classification categories of the network design are the client-server and peer-to-peer. The client-server networking refers to the computer servers
that are centralized, which are mainly used in storing emails, web pages, files and applications. The peer-to-peer network is the most commonly used and all the computers mainly support its functions. The Client server is used extensively in the business functions, whereas the peer-to-peer server is for home use.
Every network requires a topology to work through which the data flows and the computers can communicate with each other. The most common types of topologies are bus, star, ring, and mesh.
Networking also involves a special communication language used by the computer devices. These languages are called network protocols, and most of the computers use a range of protocols which they support. The most common network in the Internet and home networks is the TCP/IP.
Networking can be either wired or wireless. The most common wired networks like Ethernet cables were extensively used but now wireless networking have emerged and the new computer networks mainly support this feature.
With the increasing use of the computers and the networking the local area network of the LAN is one such network type which links the two computers in a connection.
For this connection a Local area network card or the LAN card is required which enables the connection of the computers in a network. It is a piece of hardware which is connected inside the PC linking the computer network.
The LAN Card is of both the common types which are the OSI layer 1 and 2, dealing with the physical as well as the data link layer respectively. It uses the correctly entered MAC addresses for the network to work. This then allows the computers to connect using cables or even wirelessly which then requires a special type of LAN card called the WLAN card.
What is LAN CARD?
With the increase in the development and technology, the local area network of the wireless type is now mostly preferred. Therefore a Wireless LAN Card is required for this purpose. The computers with the wireless LAN Card can transmit and receive data via radio waves using the special technology of SST or the Spread-Spectrum technology.
The wireless LANs are available in four basic types which include the 802.11, followed by type a, b and also g.
Any sort of LAN card you use will have some of the typical features of a network card which includes the twisted pair, the AUI socket and also the BNC. It is at the AUI socket that the network cable has to be connected. The LAN cards usually are designed to support the rate transfer to be ranging from 10 to 1000 megabits per second.
HUBA 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.A passive hub serves simply as a conduit for the data, enabling it to go from one device (or segment) to another. So-called intelligent hubs include additional features that enables an administrator to monitor the traffic passing through the hub and to configure each port in the hub. Intelligent hubs are also called manageable hubs.A third type of hub, called a switching hub, actually reads the destination address of each packet and then forwards the packet to the correct port.
Network switch
A network switch or switching hub is a computer networking device that
connects network segments or network devices. The term commonly refers
to a multi-port network bridge that processes and routes data at the data
link layer (layer 2) of the OSI model. Switches that additionally process data
at the network layer (layer 3) and above are often referred to as layer-3
switches or multilayer switches.
The first Ethernet switch was introduced by Kalpana in 1990
Definition: A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). Technically, network switches operate at layer two (Data Link Layer) of the OSI model.Network switches appear nearly identical to network hubs, but a switch generally contains more intelligence (and a slightly higher price tag) than a hub. Unlike hubs, network switches are capable of inspecting data packets as
they are received, determining the source and destination device of each packet, and forwarding them appropriately. By delivering messages only to the connected device intended, a network switch conserves network bandwidth and offers generally better performance than a hub.As with hubs, Ethernet implementations of network switches are the most common. Mainstream Ethernet network switches support either 10/100Mbps Fast Ethernet or Gigabit Ethernet(10/100/1000) standards.
Different models of network switches support differing numbers of connected devices. Most consumer-grade network switches provide either four or eight connections for Ethernet devices. Switches can be connected to each other, a so-called daisy chaining method to add progressively
Function
A switch is a telecommunication device which receives a message from any device connected to it and then transmits the message only to the device for which the message was meant. This makes the switch a more intelligent device than a hub (which receives a message and then transmits it to all the other devices on its network). The network switch plays an integral part in most modern Ethernet local area networks (LANs). Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office (SOHO) applications typically use a single switch, or an all-purpose converged device such as a residential gateway to access small office/home broadband services such asDSL or cable Internet. In most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may also include a telephone interface for VoIP.
An Ethernet switch operates at the data link layer of the OSI model to create a separate collision domain for each switch port. With 4 computers (e.g., A, B, C, and D) on 4 switch ports, any pair (e.g. A and B) can transfer data back and forth while the other pair (e.g. C and D) also do so simultaneously, and the two conversations will not interfere with one another. In full duplex mode, these pairs can also overlap (e.g. A transmits to B, simultaneously B to C, and so on). In the case of a repeater hub, they would all share the bandwidth and run in half duplex, resulting in collisions, which would then necessitate retransmissions.
Role of switches in a network
Switches may operate at one or more layers of the OSI model, including data link and network. A device that operates simultaneously at more than one of these layers is known as a multilayer switch.
In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, ATM, ITU-T G.hn and 802.11. This connectivity can be at any of the layers mentioned. While layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring is easier at layer 3.
Devices that interconnect at layer 3 are traditionally called routers, so layer-3 switches can also be regarded as (relatively primitive) routers.
Where there is a need for a great deal of analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors provide firewall,[2][3] network intrusion detection,[4]and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules.[5]
In other cases, the switch is used to create a mirror image of data that can go to an external device. Since most switch port mirroring provides only one mirrored stream, network hubs can be useful for fanning out data to several read-only analyzers, such as intrusion detection systems and packet sniffers.
Hubs, Bridges, Switches and Routers are used to build networks. If you are trying to design your own LAN (Local Area Network) at home, then you probably need to know what they do and the main differences between them. I will try to cover all that in addition to some networking details to cultivate the article and provide better understanding of how the internet works. After all, always remember that the internet as you know it is nothing more than a network of networks!
Hubs are used to build a LAN by connecting different computers in a star/hierarchal network topology, the most common type on LANs now a day. A hub is a very simple (or dumb) device, once it gets bits of data sent from computer A to B, it does not check the destination, instead, it forwards that
signal to all other computers (B, C, D…) within the network. B will then pick it up while other nodes discard it. This amplifies that the traffic is shared.
There are mainly two types of hubs:
1. Passive: The signal is forwarded as it is (so it doesn’t need power supply).2. Active: The signal is amplified, so they work as repeaters. In fact they have been called multiport repeaters. (use power supply)
Hubs can be connected to other hubs using an uplink port to extend the network.
OSI Model: Hubs work on the physical layer (lowest layer). That’s the reason they can’t deal with addressing or data filtering.
Switches on the other hand are more advanced. Instead of broadcasting the frames everywhere, a switch actually checks for the destination MAC address and forward it to the relevant port to reach that computer only. This way, switches reduce traffic and divide the collision domain into segments, this is very sufficient for busy LANs and it also protects frames from being sniffed by other computers sharing the same segment.
They build a table of which MAC address belongs to which segment. If a destination MAC address is not in the table it forwards to all segments except the source segment. If the destination is same as the source, frame is discarded.
Switches have built-in hardware chips solely designed to perform switching capabilities, therefore they are fast and come with many ports. Sometimes they are referred to as intelligent bridges or multiport bridges.Different speed levels are supported. They can be 10 Mb/s, 100 Mb/s, 1 Gb/s or more.
Most common switching methods are:
1. Cut-through: Directly forward what the switch gets.2. Store and forward: receive the full frame before retransmitting it.
OSI: Switches are on the data link layer (just above physical layer) that’s why they deal with frames instead of bits and filter them based on MAC addresses. Switches are known to be used for their filtering capabilities.
VLANs (Virtual LANs) and broadcast domains: Switches do not control broadcast domains by default, however, if a VLAN is configured in a switch it will has its own broadcast domain.
*VLAN is a logical group of network devices located on different LAN physical segments. However they are logically treated as if they were located on a single segment.
Bridges are used to extend networks by maintaining signals and traffic.OSI: Bridges are on the data link layer so in principle they are capable to do what switches do like data filtering and separating the collision domain, but they are less advanced. They are known to be used to extend distance capabilities of networks.
In a comparison with switches, they are slower because they use software to perform switching. They do not control broadcast domains and usually come with less number of ports.
Routers are used to connect different LANs or a LAN with a WAN (e.g. the internet). Routers control both collision domains and broadcast domains. If the packet’s destination is on a different network, a router is used to pass it the right way, so without routers the internet could not functions.
Routers use NAT (Network Address Translation) in conjunction with IP Masquerading to provide the internet to multiple nodes in the LAN under a single IP address.
Now a day, routers come with hub or switch technology to connect computers directly.
OSI: Routers work on the network layer so they can filter data based on IP addresses. They have route tables to store network addresses and forward packets to the right port.
Gateways are very intelligent devices or else can be a computer running the appropriate software to connect and translate data between networks with different protocols or architecture, so their work is much more complex than a normal router. For instance, allowing communication between TCP/IP clients and IPX/SPX or AppleTalk.
OSI: Gateways operate at the network layer and above, but most of them at the application layer.
P.S. The term Gateway is used to refer to routers in some articles so beware. In this case, the router has gateway software. And Default Gateway is used to refer to the node (e.g. router) connecting the LAN to the outside (e.g. internet).
Repeaters are simple devices that work at the physical layer of the OSI. They regenerate signals (active hubs does that too).
There is an important rule to obey while using repeaters/hubs to extend a local network and is called the 5-4-3 rule or the IEEE way. The rule forces that in a single collision domain there shouldn’t be more than 5 segments, 4 repeaters between any two hosts in the network and only 3 of the segments can be populated (contain user connections).This rule ensures that a signal sent over the network will reach every part of it within an acceptable length of time. If the network is bigger, the collision domain can be divided into two parts or more using a switch or a bridge.
Conclusion
What have been introduced so far are the main traditional devices used to build networks, understanding how they work helps to understand the logic behind networks designing, however, now that technology advance quickly, it is possible to find new products in the market combining two or more of these devices into one.
Examples are:
- Brouter: Works as a Bridge and as a Router.- IP Switch or MultiLayer Switch (MLS): New switches with routing capabilities, they forward data based on IP addresses, work at the network layer too.
Router (computing)
A Cisco ASM/2-32EM router deployed atCERN in 1987
A router is a device that forwards data packets between computer
networks, creating an overlay internetwork. A router is connected to two or
more data lines from different networks. When a data packet comes in one of
the lines, the router reads the address information in the packet to
determine its ultimate destination. Then, using information in its routing
table or routing policy, it directs the packet to the next network on its
journey. Routers perform the "traffic directing" functions on the Internet. A
data packet is typically forwarded from one router to another through the
networks that constitute the internetwork until it gets to its destination node.[1]
The most familiar type of routers are home and small office routers that
simply pass data, such as web pages and email, between the home
computers and the owner's cable or DSL modem, which connects to the
Internet through an ISP. More sophisticated routers, such as enterprise
routers, connect large business or ISP networks up to the powerful core
routers that forward data at high speed along the optical fiber lines of
the Internet backbone.
Types of routers
The earliest types of EDA routers were "manual routers" -- the drafter clicked
a mouse on the endpoint of each line segment of each net. Modern PCB
design software typically provides "interactive routers" -- the drafter selects
a pad and clicks a few places to give the EDA tool an idea of where to go,
and the EDA tool tries to place wires as close to that path as possible without
violating DRC. Some more advanced interactive routers have "push and
shove" features in an interactive router; the EDA tool pushes other nets out
of the way, if possible, in order to place a new wire where the drafter wants it
and still avoid violating DRC. Modern PCB design software also typically
provides "autorouters" that route all remaining unrouted connections without
human intervention.
The five main types of autorouters are:
Maze router[1]
Line probe router[2]
Channel router[3]
Area routers
Switchbox routing
Bridge - network bridgesDefinition: A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments.
Bridges operate at the data link layer (Layer 2) of the OSI model. Bridges inspect incoming traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects each incoming Ethernet frame - including the source and destination MAC addresses, and sometimes the frame size - in making individual forwarding decisions.
Bridges serve a similar function as switches, that also operate at Layer 2. Traditional bridges, though, support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.
Modem
A modem (modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such 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. Modems can be used over any means of transmitting analog signals, from light emitting diodes to radio. The most familiar example is a voice band modem that turns the digital data of a personal computer into modulated electrical signals in the voice frequency range of a telephone channel. These signals can be transmitted over telephone lines and demodulated by another modem at the receiver side to recover the digital data.
Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second (bit/s, or bps), or bytes per second (B/s). Modems can alternatively be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. For example, the ITU V.21 standard used audio frequency-shift keying, that is to say, tones of different frequencies, with two possible frequencies corresponding to two distinct symbols (or one bit per symbol), to carry 300 bits per second using 300 baud. By contrast, the original ITU V.22 standard, which was able to transmit and receive four distinct symbols (two bits per symbol), handled 1,200 bit/s by sending 600 symbols per second (600 baud) using phase shift keying.
What is Modem and its benefits?
Modem is actually one of the most important hardware devices used in the computer especially for the purpose of networking of the internet. Modems are used to modulate signals of analog types so as to be able to encode the digital information from it. Modems are also used for demodulation of the signals so as to decode the information transmitted.
Therefore it is for the soul purpose of transmission of the signal easily so that it can be decoded to reproduce the digital information.
The classification of modems is done on the basis of the information that can transferred in a given time period by them which is usually measured in bps, or bits per second. Modems are now used by the internet users, which preferably run faster than such as the cable and the ADSL modems.
These days the modems area great benefit to be used in the telecommunication systems with the launch of the radio modems. These modems are the microwave modems and can transmit even more than a
hundred million bits per second, which is a very high speed for any modem to work on. The launch of the optical fibers has given rise to the optical modems which are now used for the purpose of transmission of data over undersea optical fibers. These modems have unbelievably high rate of transmission, which can reach up to about a billion bits per second.
Although modem internet connection has been replaced over the recent years with broadband, modems still hold a vital position is certain other aspects of the modern world such as the space telecommunications and of course in the telephone communications.
OSI MODEL
Virtually all networks in use today are based in some fashion on the Open Systems Interconnection (OSI) standard. OSI was developed in 1984 by theInternational Organization for Standardization (ISO), a global federation of national standards organizations representing approximately 130 countries.
The core of this standard is the OSI Reference Model, a set of seven layers that define the different stages that data must go through to travel from one device to another over a network. In this article, you'll find out all about the OSI standard.
Description of OSI layers
At each layer, certain things happen to the data that prepare it for the next layer. The seven layers, which separate into two sets, are:
Application Set
Layer 7: Application - This is the layer that actually interacts with the operating system or application whenever the user chooses to transfer files, read messages or perform other network-related activities.
Layer 6: Presentation - Layer 6 takes the data provided by the Application layer and converts it into a standard format that the other layers can understand.
Layer 5: Session - Layer 5 establishes, maintains and ends communication with the receiving device.
Transport Set
Layer 4: Transport - This layer maintains flow control of data and provides for error checking and recovery of data between the devices. Flow control means that the Transport layer looks to see if data is coming from more than one application and integrates each application's data into a single stream for the physical network.
Layer 3: Network - The way that the data will be sent to the recipient device is determined in this layer. Logical protocols, routing and addressing are handled here.
Layer 2: Data - In this layer, the appropriate physical protocol is assigned to the data. Also, the type of network and the packet sequencing is defined.
Layer 1: Physical - This is the level of the actual hardware. It defines the physical characteristics of the network such as connections, voltage levels and timing.
The OSI Reference Model is really just a guideline. Actual protocol stacks often combine one or more of the OSI layers into a single layer.
According to recommendation X.200, there are seven layers, labeled 1 to 7, with layer 1 at the bottom. Each layer is generically known as an N layer. An "N+1 entity" (at layer N+1) requests services from an "N entity" (at layer N).
At each level, two entities (N-entity peers) interact by means of the N protocol by transmitting protocol data units (PDU).
A Service Data Unit (SDU) is a specific unit of data that has been passed down from an OSI layer to a lower layer, and which the lower layer has not yet encapsulated into a protocol data unit (PDU). An SDU is a set of data that is sent by a user of the services of a given layer, and is transmitted semantically unchanged to a peer service user.
The PDU at a layer N is the SDU of layer N-1. In effect the SDU is the 'payload' of a given PDU. That is, the process of changing an SDU to a PDU, consists of an encapsulation process, performed by the lower layer. All the data contained in the SDU becomes encapsulated within the PDU. The layer N-1 adds headers or footers, or both, to the SDU, transforming it into a PDU of layer N. The added headers or footers are part of the process used to make it possible to get data from a source to a destination.
OSI Model
Data unit Layer Function
Hostlayer
s
Data
7. Application Network process to application
6. Presentation
Data representation, encryption and decryption, convert machine dependent data to machine independent data
5. SessionInterhost communication, managing sessions between applications
Segments 4. TransportEnd-to-end connections, reliability and flow control
Media
Packet/Datagram
3. Network Path determination and logical addressing
layers
Frame 2. Data link Physical addressing
Bit 1. PhysicalMedia, signal and binary transmission
Some orthogonal aspects, such as management and security, involve every layer.
Security services are not related to a specific layer: they can be related by a number of layers, as defined by ITU-TX.800 Recommendation.[3]
These services are aimed to improve theCIA triad (confidentiality, integrity, andavailability) of transmitted data. Actually the availability of communication service is determined by network design and/ornetwork management protocols. Appropriate choices for these are needed to protect against denial of service.
Layer 1: physical layer
The physical layer defines electrical and physical specifications for devices. In particular, it defines the relationship between a device and a transmission medium, such as a copper or fiber optical cable. This includes the layout of pins, voltages, line impedance, cable specifications, signal timing, hubs, repeaters, network adapters, host bus adapters (HBA used in storage area networks) and more.
The major functions and services performed by the physical layer are:
Establishment and termination of a connection to a communications medium.
Participation in the process whereby the communication resources are effectively shared among multiple users. For example, contention resolution and flow control.
Modulation or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. These are signals operating over the physical cabling (such as copper and optical fiber) or over a radio link.
Parallel SCSI buses operate in this layer, although it must be remembered that the logical SCSI protocol is a transport layer protocol that runs over this bus. Various physical-layer Ethernet standards are also in this layer; Ethernet incorporates both this layer and the data link layer. The same applies to other local-area networks, such as token ring, FDDI, ITU-T G.hn and IEEE 802.11, as well as personal area networks such as Bluetooth and IEEE 802.15.4.
Layer 2: data link layer
The data link layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the physical layer. Originally, this layer was intended for point-to-point and point-to-multipoint media, characteristic of wide area media in the telephone system. Local area network architecture, which included broadcast-capable multi-access media, was developed independently of the ISO work in IEEE Project 802. IEEE work assumed sublayer-ing and management functions not required for WAN use. In modern practice, only error detection, not flow control using sliding window, is present in data link protocols such as Point-to-Point Protocol(PPP), and, on local area networks, the IEEE 802.2 LLC layer is not used for most protocols on the Ethernet, and on other local area networks, its flow control and acknowledgment mechanisms are rarely used. Sliding window flow control and acknowledgment is used at the transport layer by protocols such as TCP, but is still used in niches where X.25 offers performance advantages.
The ITU-T G.hn standard, which provides high-speed local area networking over existing wires (power lines, phone lines and coaxial cables), includes a complete data link layerwhich provides both error correction and flow control by means of a selective repeat Sliding Window Protocol.
Both WAN and LAN service arrange bits, from the physical layer, into logical sequences called frames. Not all physical layer bits necessarily go into frames, as some of these bits are purely intended for physical layer functions. For example, every fifth bit of the FDDI bit stream is not used by the layer.
Layer 3: network layer
The network layer provides the functional and procedural means of transferring variable length data sequences from a source host on one network to a destination host on a different network (in contrast to the data link layer which connects hosts within the same network), while maintaining the quality of service requested by the transport layer. The network layer performs network routing functions, and might also perform fragmentation and reassembly, and report delivery errors. Routers operate at this layer, sending data throughout the extended network and making the Internet possible. This is a logical addressing scheme – values are chosen by the network engineer. The addressing scheme is not hierarchical.
The network layer may be divided into three sublayers:
1. Subnetwork access – that considers protocols that deal with the interface to networks, such as X.25;
2. Subnetwork-dependent convergence – when it is necessary to bring the level of a transit network up to the level of networks on either side
3. Subnetwork-independent convergence – handles transfer across multiple networks.
An example of this latter case is CLNP, or IPv6 ISO 8473. It manages the connectionless transfer of data one hop at a time, from end system to ingress router, router to router, and from egress router to destination end system. It is not responsible for reliable delivery to a next hop, but only for the detection of erroneous packets so they may be discarded. In this scheme, IPv4 and IPv6 would have to be classed with X.25 as subnet access protocols because they carry interface addresses rather than node addresses.
A number of layer-management protocols, a function defined in the Management Annex, ISO 7498/4, belong to the network layer. These include routing protocols, multicast group management, network-layer information and error, and network-layer address assignment. It is the function of the payload that makes these belong to the network layer, not the protocol that carries them.
Layer 4: transport layer
The transport layer provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers. The transport layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control. Some protocols are state- and connection-oriented. This means that the transport layer can keep track of the segments and retransmit those thafail. The transport layer also provides the acknowledgement of the successful data transmission and sends the next data if no errors occurred.
OSI defines five classes of connection-mode transport protocols ranging from class 0 (which is also known as TP0 and provides the least features) to class 4 (TP4, designed for less reliable networks, similar to the Internet). Class 0 contains no error recovery, and was designed for use on network layers that provide error-free connections. Class 4 is closest to TCP, although TCP contains functions, such as the graceful close, which OSI assigns to the session layer. Also, all OSI TP connection-mode protocol classes provide expedited data and preservation of record boundaries. Detailed characteristics of TP0-4 classes are shown in the following table
Feature NameTP0
TP1
TP2
TP3
TP4
Connection oriented network Yes Yes Yes Yes Yes
Connectionless network No No No No Yes
Concatenation and separation No Yes Yes Yes Yes
Segmentation and reassembly Yes Yes Yes Yes Yes
Error Recovery No Yes Yes Yes Yes
Reinitiate connection (if an excessive number of PDUs are unacknowledged)
No Yes No Yes No
Multiplexing and demultiplexing over a single virtual circuit
No No Yes Yes Yes
Explicit flow control No No Yes Yes Yes
Retransmission on timeout No No No No Yes
Reliable Transport Service No Yes No Yes Yes
An easy way to visualize the transport layer is to compare it with a Post Office, which deals with the dispatch and classification of mail and parcels sent. Do remember, however, that a post office manages the outer envelope of mail. Higher layers may have the equivalent of double envelopes, such as cryptographic presentation services that can be read by the addressee only. Roughly speaking, tunneling protocols operate at the transport layer, such as carrying non-IP protocols such as IBM's SNA or Novell's IPX over an IP network, or end-to-end encryption with IPsec. While Generic Routing Encapsulation (GRE) might seem to be a network-layer protocol, if the encapsulation of the payload takes place only at endpoint, GRE becomes closer to a transport protocol that uses IP headers but contains complete
frames or packets to deliver to an endpoint. L2TP carries PPP frames inside transport packet.
Although not developed under the OSI Reference Model and not strictly conforming to the OSI definition of the transport layer, the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the Internet Protocol Suite are commonly categorized as layer-4 protocols within OSI.
Layer 5: session layer
The session layer controls the dialogues (connections) between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for full-duplex, half-duplex, or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures. The OSI model made this layer responsible for graceful close of sessions, which is a property of the Transmission Control Protocol, and also for session checkpointing and recovery, which is not usually used in the Internet Protocol Suite. The session layer is commonly implemented explicitly in application environments that use remote procedure calls. On this level, Inter-Processcommunication happen (SIGHUP, SIGKILL, End Process, etc.).
Layer 6: presentation layer
The presentation layer establishes context between application-layer entities, in which the higher-layer entities may use different syntax and semantics if the presentation service provides a mapping between them. If a mapping is available, presentation service data units are encapsulated into session protocol data units, and passed down the stack.
This layer provides independence from data representation (e.g., encryption) by translating between application and network formats. The presentation layer transforms data into the form that the application accepts. This layer formats and encrypts data to be sent across a network. It is sometimes called the syntax layer.[5]
The original presentation structure used the basic encoding rules of Abstract Syntax Notation One (ASN.1), with capabilities such as converting an EBCDIC-coded text file to anASCII-coded file, or serialization of objects and other data structures from a
Layer 7: application layer
The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application. This layer interacts with software applications that implement a communicating component. Such application programs fall outside the scope of the OSI model. Application-layer functions typically include identifying communication partners, determining resource availability, and synchronizing communication. When identifying
communication partners, the application layer determines the identity and availability of communication partners for an application with data to transmit. When determining resource availability, the application layer must decide whether sufficient network or the requested communication exists. In synchronizing communication, all communication between applications requires cooperation that is managed by the application layer.
BIBLIOGRAPHY
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