NETWORK COMMUNICATION

Computer Networks

    System of interconnected computers and its peripherals like printers is called a computer network. This interconnection help the computers to share the information between them. The connection between computers in a network either wired or wireless.

Classification of Computer Network

Computer networks are classified based on various factors.

• Geographical span
• Inter-connectivity
• Administration
• Architecture

Geographical Span :-

     Geographically a network may be spanned across your table, ie, Bluetooth enabled devices, ranging not more than few meters. It may be spanned across a whole building, including intermediate devices to connect all floors. It may be spanned over a whole city. It may be spanned across multiple cities or provinces. It may be one network covering whole world. 

Inter-Connectivity:-

      Components of a network can be connected to each other either logically, physically or both ways. Every single device can be connected to every other device on network by making network mesh. By creating bus-like structure, all devices can be connected to a single medium but geographically disconnected. By creating linear structure, each device is connected to its left and right peers only. By creating star-like structure, all devices connected together with a single device.

Administration :-

         From an administrator's point of view, a network can be private network, which belongs to a single autonomous system and cannot be accessed from outside to its physical or logical domain. A network can be public, which is accessed by all.

Architecture :-

           Computer networks can be discriminated into various types such as client-server, peer-to-peer or hybrid, depending upon its architecture. There can be one or more systems acting as server. The client requests the server to serve requests. Server takes and processes request on behalf of clients. Two systems can be connected point-to-point or in back-to-back fashion. They both reside at the same level and called peers. They can be hybrid network which involves network architecture of both the above types.

Network Applications

Computer systems and peripherals are connected to form a network. They provide numerous advantages :-

• Resource sharing such as printers and storage devices
• Exchange of information by means of e-mails and FTP
• Information sharing by using web or internet
• Interaction with other users using dynamic web pages
• IP phones
• Video conferences
• Parallel computing
• Instant messaging

Cisco Certified Network Associate (CCNA) Routing and Switching is a certification program for entry-level network engineers that helps maximize your investment in foundational networking knowledge and increase the value of your employer's network.

CCNA includes the following,

1. Introduction to Networks
2. OSI
3. IPv4
4. IOS
5. Routing
6. Security
7. NAT
8. Switching
9. VLAN
10. IPv6
11. WLAN
12. WAN

NETWORK

   Interconnection of autonomous system is called a Network. They must able to exchange data or share resources. By creating a network we got some advantages like time saving, money saving, network avoids travelling and a network have available full time connectivity. The networks have mainly two types of components, hardware and software. The main hardware components are computer, router, switches, hub, access point, MSAU( Multi Station Access Unit), etc. The main software components are protocols, network operating system, drivers etc. The firewalls in the network filters the data traffic. The amplification or strengthening the data is done by the repeaters. FDDI(Fiber Distributed Data Interface) is used for medium. For creating a network we need a NIC(Network Interface Card). The main components of NIC are transmitter, receiver, controller, serial to parallel converter, ROM section. The ROM section of NIC contains MAC address. MAC address means Media  Access Control. MAC address is unique. It is 48 bit binary or 12 digit hexadecimal. In 12 digit hexadecimal 6 digits for vendor and the remaining 6 digits for vendor assigned part.

Types of Networks

     There are mainly five types of networks. They are,

1. PAN - Personal Area Network

2. LAN - Local Area Network

3. CAN - Campus Area Network

4. MAN - Metropolitan Area Network

5. WAN - Wide Area Network

1. PAN

   Personal Area Network is in limited in location, that is similar to Bluetooth sharing network. A PAN is a network that is used for communicating among computers and computer devices (including telephone) in close proximity of around a few meters within a room. PAN can be used for communicating between devices themselves, or for connecting to a large network such as internet. PANs can be used wired or wireless. PAN is a computer network used for communication among computer devices including telephones and personal digital devices, which are close to the person's body. The range of a PAN is few meters. PAN is smallest network which is very personal to a user. This may include Bluetooth enabled devices or infra-red enabled devices. PAN connectivity range up to 10 meters. PAN may include wireless computer keyboard and mouse, Bluetooth enabled headphones, wireless printers and TV remotes.

2. LAN

   In Local Area Network computers interconnected in the same geographical location, all are using the same LAN protocol for communication, all are using the same range of IP address. A LAN is a network that used for communicating between computer devices within an office or a home. LANs enable the sharing of resources such as files or hardware devices that may needed by multiple users. LAN is limited in size, typically spanning a few hundred meters, not more than a mile. LAN is fast with speed from 10 Mbps to 10 Gbps. LAN requires little wiring, typically a single cable connecting to each device. LAN has lower cost compared to MANs or WANs. LANs can be either wired or wireless. Twisted pair, coaxial or fiber optic cables can be used in wired LAN. Every LAN uses a protocol. Protocol means a set of rules that governs how packets are configured and transmitted. Nodes in a LAN are linked together with a certain topology like, bus topology, ring topology, star topology. LANs are capable of very high transmission rates. Usually LAN covers an organization offices, schools, colleges or universities. Number of systems connected in LAN may vary from at least two to 16 million. LAN provides a useful way of sharing the resources between end users. The resources such as printers, file servers, scanners and internet are easily sharable among computers. LANs are composed of inexpensive networking and routing equipment. It may contains local servers serving file storage and other locally shared applications. It mostly operates on private IP addresses and does not involve heavy routing. LAN works under its own local domain and controlled centrally. LANs have some advantages like, speed,cost,security,resource sharing etc. Also have disadvantages like, expense to install,requires administrative time,file server may fail,cables may break etc.

3. CAN

    In Campus Area Network two or more LANs in a campus are interconnected without the help of a service provider. CAN is larger than LAN and it spans a campus.

4. MAN

   In Metropolitan Area Network interconnection of two or more LANs in a city with the help of a service provider. A MAN is a large computer network that usually spans a city. A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of a building to entire cities. MAN might be owned and operate by a single organization, but it usually will be used by many individuals and organization. MAN often acts as a high speed network to allow sharing of regional resources. MAN typically covers an area between 5 and 50 km diameter. MAN can be in the form of Ethernet, Token-ring, ATM or Fiber Distributed Data Interface (FDDI). Metro Ethernet is a service which is provided by ISPs. This service enables its users to expand their LANs. For example, MAN can help an organization to connect all of its officers in a city. Backbone of MAN is high-capaciy and high-speed fiber optics. MAN works in between LAN and WAN. MAN provides uplink for LANs to WANs or internet. The main examples are telephone network that provides a high speed DSL to customers and cable TV network.

5. WAN

   A Wide Area Network is a computer network covering a large geographical area. Typically, a WAN is formed by interconnecting two or more local area networks at different geographical locations. WANs help in transmission of voice, data and video information across greater geographical distances.

Internetwork

A network of network is called an internetwork, or simply the internet. It is the largest network in existence on this planet. The internet hugely connects all WANs and it can have connection to LANs and Home networks. Internet uses TCP/IP protocol suite and uses IP as its addressing protocol. Present day, Internet is widely implemented using IPv4. Because of shortage of address spaces, it is gradually migrating from IPv4 to IPv6. Internet enables its users to share and access large amount of information worldwide. It uses WWW, FTP, email services, audio and video streaming etc. At huge level, internet works on Client-Server model. Internet uses very high speed backbone of fiber optics. To inter-connect various continents, fibers are laid under sea known to us submarine communication cable. Internet is widely deployed on World Wide Web services using HTML linked pages and is accessible by client software known as Web Browsers. When a user requests a page using some web browser located on some Web Server anywhere in the world the Web Server responds with the proper HTML page. The communication delay is very low. Internet is serving many proposes and is involved in many aspects of life. Some of them are,

• Web sites
• E-mail
• Instant Messaging
• Blogging
• Social Media
• Marketing
• Networking
• Resource Sharing
• Audio Streaming
• Video Streaming

Types of Communication

1. UNICAST

2. MULTICAST

3. BROADCAST

1. UNICAST

    It is one to one communication and the traffic is forwarded to an address which represents a single host. Unicast is a term used in communication to describe a piece of information to send from one point to another. There are only sender and receiver. All LANs support unicast transfer mode and most applications that employ TCP transport protocol uses unicast messaging.

2. MULTICAST

   It is one to many communication and the data is send to an address which represents a particular group of hosts. Multicast is a term described in communicating a piece of information sent from one or more points to a set of other points. The senders and receivers are one or more. 

3.BROADCAST

  It is one to all communication and the data is send to an address which represents all the hosts. Broadcast is a term used for describing communication that is sent a piece of information from one point to all other points. There is one sender and multiple receivers. All LANs support broadcast transmission. 

Modes of Communication

1. Simplex

2. Half Duplex

3. Full Duplex

Simplex

It is one way communication. It is not used in network communication.

Half Duplex

It has communication in one direction at a time. That is its a two way communication.

Full Duplex

It is simultaneous two way communication.

OSI (Open System Interconnection)

  Network Engineering is a complicated task, which involves software, firmware, chip level engineering, hardware and electric pulses. To ease network engineering, the whole networking concept is divided into multiple layers. Each layer is involved in some particular task and each layer is independent of all other layers. But almost all networking tasks depend on all of these layers. Layers share data between them and they depend on each other only to take input and send output.

Layered Tasks: In layered architecture of Network model, one whole network process is divided into small tasks. Each small task is then assigned to a particular layer which works dedicatedly to process the task only. Every layer does only specific work.

Importance of OSI Layer concept.

 It is easy to identify network communication. Allows standardization of network components and protocols. It reduces the complexity of network communication. In this layer concept problems in one layer will not affect the other.

Seven Layers of OSI

 7. Application layer

 6. Presentation layer

 5. Session layer

 4. Transport layer

 3. Network layer

 2. Data link layer

 1. Physical layer

*Order is for sending information, for receiving the order just reversed.

Application Layer

  It creates user interface based upon the application layer protocols. This layer encompasses protocols which directly interact with the user.

eg: http, fttp, DNS, SMTP, POP3, .......

Presentation Layer

  This layer defines how data in the native format of remote host should be presented in the native format of host. It presents the data to application layer. Code formatting, translation services, compression & decompression, encryption & decryption, multimedia operations are also the applications of presentation layer.

Session Layer

   This layer maintains sessions between remote hosts. For example, once user/password authentication is done, the remote host maintain this session for a while and does not ask for authentication again in that time span. End to end session (conversation) establishment, maintenance and termination, choosing the mode of communication, dialogue control (to keep different application data separate from each other) are the functions of Session layer.

Transport Layer

  Segmentation of data, end to end connection establishment (choose protocols like TCP/UDP), flow control, error recovery, sequencing, multiplexing are the functions of Transport layer.

Flow control includes buffering, conjunction avoidance and windowing. Buffer is one of the memory locations of destination. Conjunction avoidance is a notification given to the source device that there is a chance of conjunction in the network, so stop transmitting for some time. This notification is called source quench. When the buffer is free destination send a notification called resume transmit to continue transmitting. The window size means the number of data to be transmitted before getting an acknowledgement.Error Recovery : For recovering error data, it uses negative acknowledgement, that means re-transmitting the data.

Sequencing is the method of arranging the received data in proper order based upon sequence number. Multiplexing is the method of converging number of requests into a single format. 

Network Layer

  Network layer provides logical address, path selection, inter network communication. Packets are of two types, Data packets and Route update packets. Packets which are used for sending user data are called data packets. Packets which are used for sending routing information between routers are called route update packets.

Data Link Layer

   Data link layer provides physical addressing (MAC address), error detection, data arbitration standards, identifying the upper layer protocol. Data arbitration standards means when and how to access the media for communication.

Physical Layer

  Physical layer provides physical interconnection of devices, voltage regulations, controls wire speed, controls physical topology.

IPv4

  It is a logical network layer address used for identifying a network, host in a network, a group of host or all the host in a network. It is a 32 bit address. It is a 32 bit address. It is divided into 4 octet. Each octet is represented in decimal format. Each octet is separated with dots.

eg : 192.168.0.254

IOS

   It is the OS which creates a user interface with the hardware device.

Router

     Router is a layer three device, used for interconnecting different networks. It works based upon the logical address ( ip address) to forward data to other network sections. It uses access control list for filtering packets. Router won't forward broadcast from one network to another, it creates multiple broadcast domains. Router can provide interconnection between different VLANs (Virtual LAN). Each interface of a router will be in different networks. RSP (Route Switch Processor), RAM (Random Access Memory),ROM (Read Only Memory), NV RAM (Non Volatile RAM), Flash memory are the internal components of a router. We can access a router through GUI (Graphic User Interface) or CLI (Command Line Interface).

Routing

   Process of transferring packet from one network to another network. For forwarding packets through routers, the router must have entries in the routing table about all the networks and paths to reach each network. By default routers will enter the information about connected networks in the routing table automatically. Based upon the IP address and mask given to each interface.
Static Routing
  Method of configuring information about unknown remote networks into the routing table (list of all the networks and path information known to the router) manually by the administrator specifying the network address, mask and path.

Dynamic Routing

   Method of configuring routing table with the help of routing protocol. Routing protocols are mainly divided into two, IGP (Interior Gateway Protocol) & EGP (Exterior Gateway Protocol). IGPs are protocols used for communication between routers with an autonomous system. EGPs are used for enabling communication between different autonomous systems. An autonomous system means a group of networks or routers which comes under a common administration.

Security

    Access control lists are security statements configured in router and placed on any router interface. When an access list placed on an interface, it will check each and every packet passing through that interface in the specific direction. The checking is done in sequential order of the access list statements. When a match is found, the packet is acted upon and no further checking is done with the remaining statements. When a packet does not match with any of the conditions in the access list, the packet is denied, because there is an implicit deny at the end of every access list.

NAT [Network Address Translation]

   It is the method of translating a public IP to private IP and vice versa.
Static NAT
  It is one to one translation. In this method the administrator manually configured the translation table specifying the exact private IP and public IP. Only that specified private machines will be allowed to communicate through public networks.
Dynamic NAT
   It is also one to one translation, but here the administrator will specify multiple private IPs using access list and public IP using pool statement. The translation is based upon first come basis.

Switching

     Address learning, forward or filter decision, loop avoidance are the main functions of a switch.

Address Learning : Switches have the capability to learn MAC address of devices connected to it. When a frame is received, switch will learn the source MAC address of the frame & stores it in a database called MAC address table/CAM (Control Access Memory) table, corresponding to the port through which the frame is received.

Forward / Filter Decision : When a frame is received through one port, after learning MAC address, it will verify the destination MAC address of the frame & matches it with the entries in the MAC address table. If it finds any match, the frame is forwarded only through that port. If it does not find any match, the frame is forwarded (flooded) through all ports except the source port.

Loop Avoidance : When we interconnect multiple switches with redundant links, there is a chance of layer 2 switching loops in the network. Switches & bridges uses a protocol called STP (Spanning Tree Protocol), for avoiding the loops. STP will make only one path in forwarding state & blocks all other redundant links.

VLAN (Virtual LAN)

        VLAN configuration is a switched network which divides the single large broadcast domain into multiple smaller broadcast domain at layer 2. A VLAN is a logical group of users in a LAN. It is a switched network that is logically grouped based on functions, or project teams without regard to the physical location of users. The idea becomes simple if we consider the local area network of a college, the group of computer in each department of college constitute a VLAN. Thus if there are four departments we may configure four VLANs.

IPv6

    The exhaustion of IPv4 address gave birth to a next generation Internet Protocol. IPv6 address is nodes with 128 bit wide address, providing plenty of address space for future to be used on entire planet. IPv6 has introduced Anycast addressing but has removed the concept of broadcasting. IPv6 enables devices to self-acquire an IPv6 address and communicate within that subnet. This auto configuration removes the dependability of Dynamic Host Configuration Protocol (DHCP) servers. This way even if the DHCP server on that subnet is down, the hosts can communicate with each other. IPv6 provides new feature of IPv6 mobility. Mobile IPv6 equipped machines can roam around without the need of changing their IP addresses. IPv6 is still in transition phase and is expected to replace IPv4 completely in coming years. At present, there are few networks which are running on IPv6. There are some transition mechanisms available for IPv6 enabled networks to speak and roam around different networks easily on IPv4. They are :

• Dual stack implementation
• Tunneling
• NAT-PT

Wireless LAN

  Wireless networking is a rapidly evolving technology for connecting computers. A WLAN connects network components through a wireless medium over a relatively short distance. The wireless medium typically used includes radio waves and infrared waves. Currently there are a number of standards and technologies for wireless LANs. But the standard most used is the IEEE 802.11b standard (wireless Ethernet and Wi-Fi).

WAN(Wide Area Network)

   In Wide Area Network interconnection of two or more LANs with the help of service provider globally anywhere. WAN covers a large geographic area such as a country, continent or even whole of the world. WAN is two or more LANs connected together. The LANs can be many miles apart. To cover greater distances, WANs may transmitted data over leased high speed communication lines or wireless links such as satellites. Multiple LANs can be connected together using devices such as bridges, routers or gateways which enable them to share data. The world's most popular WAN is the internet. S the name suggests, the Wide area Network (WAN) covers a wide area which may span across provinces and even a whole country. Generally, telecommunication networks are Wide Area Network. These networks provide connectivity to MANs and LANs. Since they are equipped with very high speed backbone, WANs use very expensive network equipment. WAN may use advanced technologies such as Asynchronous Transfer Mode (ATM), Frame Relay, and Synchronous Optical Network (SONET). WAN may be managed by multiple administration.