Here you will learn OSI Model Layer Introduction, overview of the 7 OSI reference model, applicaion, session, transport, network and physical layers. If you want to remember the sequence of the OSI layers model name then the following two sentences can help you a lot for this purpose.“All People Seems To Need Data Processing”. Open Systems Interconnection (OSI) model is developed by ISO (International organization for standardization) in 1984. OSI reference model is a logical framework for standards for the network communication.
OSI reference model is now considered as a primary standard for internetworking and inter computing. Today many network communication protocols are based on the standards of OSI model. In the OSI model the network/data communication is defined into seven layers.
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, SMTP, FINGER, TELNET, TFTP, 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.
OSI 7 Layers Reference Model
Introduction to TCP/IP
Here you will learn about Tcp ip network overview, data communication, ip addressing introduction, basic protocols, routing in the internet. TCP/IP short for Transmission Control Protocol is a suite of the communication protocols used to connect the hosts on the internet. TCP and IP were developed by a department of defense (DOD) in a research project to connect the number of networks by different vendors to form a big network of networks (the Internet).
It was originally successfully because of the services it gave, which everyone wanted to use such as file transfer, electronic mail, remote logon across a very large number of clients and server system. Several computers in a small network can use TCP/IP to communicate with each other. The IP component of the TCP/IP suites provides the routing between the two locally or remote computers.
IP forwards each packet based on a four byte, 32 bits address. TCP is responsible for verifying the correct delivery of data from the client to server. TCP also supports to detect the errors in the transmission and also triggers the data to retransmit correctly.
TCP/IP is a de facto standard of transferring the data on the network and on the internet. Each network operating systems that have their own protocols must support TCP/IP too. All the computers in a network must follow the rules to communication with each other.
TCP/IP stands for Transmission Control Protocol and Internet Protocol and it is a communication standard that defines how data travels on the internet and how network/communication devices communication with each other.
Inside the TCP/IP
TCP/IP is a not a single protocol but it is a suite of the protocols. There are the numerous protocols in the TCP/IP suite such as TCP, UDP, ICMP, DHCP, IMAP, HTTP, HTTPS, SSL, SMTP and many others.
Internet Protocol is a connectionless protocol that is used to communicate between the two computers. IP does not occupy the communication line between the two computers. With the IP communication, data is broken into the smaller pieces called packets, and these packets communicate between the two locally or remotely connected devices in a computer network or via internet. IP is also responsible for routing the packets to its destination. Routers are responsible for routing the packets towards its destination when a computer sends packets to an IP router. Data is routed towards its destination is all by a router. Router works as a post office.
TCP/IP
The TCP/IP (transmission control protocol/Internet protocol) work together in which TCP takes care communication between the application software i.e browsers whereas IP takes care of the communication between the computers. TCP breaks the data into smaller packets before they can be sent and IP sends the packets to the receivers.
IP Addresses
Each computer in a network or on internet must have a unique IP address before it can communicate with the other computer. The packets must have the address of the destination computers or devices. Each IP address is composed of 32 bits and 4 octets each packet must have an address before it can be sent to another computer.
This is an IP address 100.100.100.10 and this website http://www.example.com might have mapped with the same IP address. Without a unique IP address the communication on the internet is impossible. The numbers in the address must range between 0 and 255 in four period separated portions. Each IP address consists of 32 bits and 32 bits are consisting of 4 bytes. A computer byte can contain 256 different values e.g 00000000, 00100010, 00000111, 11111000, 01010101, 001100110 and up to 11111111.
Domain Names
Domain names are the unique identifier of a website because 12 digits numbers are difficult to remember. The name used for the web address is called a domain name e.g www.google.com, www.msn.com, www.yahoo.com all are domain names and comparatively are easy to remember instead of 12 digits numbers like, 123.220.44.240, 100.100.100.101 and 202.202.56.110. When you type a domain name in your web browser the domain name is translated into IP address by the DNS server, which is managed by your local ISPs or your corporate DNS servers.
All over the world a larger number of the DNS servers are connected with each other some are primary DNS servers, secondary DNS servers, Master DNS servers and Root DNS servers. When a new domain is registered by a domain registrar with associated TCP/IP address then DNS servers from all over the world are updated.
TCP/IP is a large collection of the different communication protocols.
TCP/IP is a large collection of different communication protocols.
A Family of Protocols
TCP/IP is a large collection of different communication protocols based upon the two original protocols TCP and IP. Each protocol in the TCP/IP suite is responsible for the different communication tasks. HTTP is responsible for the communication between the web server and the web browser. It sends requests from the client (browser) to web server and returning the web pages to the client.
HTTPS is responsible for the secure communication between the web browser and the web server. HTTPS usually handles the credit card transactions and other sensitive and secure data. SSL is responsible for the encryption of the data for the secure communication. SMTP (Simple mail transfer protocol) is responsible for sending the emails. MIME (Multi purpose Internet mail extension) is responsible for communicating the multimedia data such as, voice, video, graphics etc. IMAP (Internet Message Access Protocol) is responsible for storing and retrieving the emails.
POP (post office protocol) is used for downloading the emails from the email server to the personal computer. FTP (File transfer protocol) it takes cares of transferring the files between the computers. NTP (Network time protocol) is used to synchronize the time between the networks. DHCP (Dynamic host configuration protocol) is responsible for assigning the IP address dynamically to the network computers. SNMP (Simple Network Management Protocol) is used for administration of a computer network.
LDAP (Light weight directory access protocol) is used for storing the names and email addresses on the internet and also communicating with the Active directory in computer network. ARP (Address resolution protocol) is used to find the hardware address of a computer based on the IP address. Boot P protocol is used for starting computers in a network. PPTP (Point to point tunneling protocol) is used to make a secure tunnel in the private networks such as VPN.
TCP/IP is the Internet Communication Protocol.
A protocol is a set of rules, agreed upon methods or a communication language, which both computers understand and agree upon. TCP/IP defines the rules to communicate over the internet. Internet browsers and Internet servers uses TCP/IP to communicate on the internet
Web browsers, Web servers, Email programs and internet address all follow TCP/IP. An IP address is a part of the TCP/IP protocols.
Computer Network Protocols
The word protocol is derived from the Greek word “protocollon” which means a leaf of paper glued to manuscript volume. In computer protocols means a set of rules, a communication language or set of standards between two or more computing devices. Protocols exist at the several levels of the OSI (open system interconnectivity) layers model. In the telecommunication system, there are one more protocols at each layer of the telephone exchange. On the internet, there is a suite of the protocols known as TCP/IP protocols that are consisting of transmission control protocol, internet protocol, file transfer protocol, dynamic host configuration protocol, Border gateway protocol and a number of other protocols.
In the telecommunication, a protocol is set of rules for data representation, authentication, and error detection. The communication protocols in the computer networking are intended for the secure, fast and error free data delivery between two communication devices. Communication protocols follow certain rules for the transmission of the data.
Protocols Properties
Different protocols perform different functions so it is difficult to generalize the properties of the protocols. There are some basic properties of most of the protocols.
• Detection of the physical (wired or wireless connection)
• Handshaking
• How to format a message.
• How to send and receive a message.
• Negotiation of the various connections
• Correction of the corrupted or improperly formatted messages.
• Termination of the session.
The widespread use of the communication protocols is a prerequisite to the internet. The term TCP/IP refers to the protocols suite and a pair of the TCP and IP protocols are the most important internet communication protocols. Most protocols in communication are layered together where the various tasks listed above are divided. Protocols stacks refer to the combination of the different protocols. The OSI reference model is the conceptual model that is used to represent the protocols stacks. There are different network protocols that perform different functions. Following is the description of the some of the most commonly used protocols.
HTTP (Hyper Text Transfer Protocol)
Hypertext transfer protocol is a method of transmitting the information on the web. HTTP basically publishes and retrieves the HTTP pages on the World Wide Web. HTTP is a language that is used to communicate between the browser and web server. The information that is transferred using HTTP can be plain text, audio, video, images, and hypertext. HTTP is a request/response protocol between the client and server. Many proxies, tunnels, and gateways can be existing between the web browser (client) and server (web server). An HTTP client initializes a request by establishing a TCP connection to a particular port on the remote host (typically 80 or 8080). An HTTP server listens to that port and receives a request message from the client. Upon receiving the request, server sends back 200 OK messages, its own message, an error message or other message.
POP3 (Post Office Protocol)
In computing, e-mail clients such as (MS outlook, outlook express and thunderbird) use Post office Protocol to retreive emails from the remote server over the TCP/IP connection. Nearly all the users of the Internet service providers use POP 3 in the email clients to retrieve the emails from the email servers. Most email applications use POP protocol.
SMTP (Simple Mail Transfer Protocol)
Simple Mail Transfer Protocol is a protocol that is used to send the email messages between the servers. Most email systems and email clients use the SMTP protocol to send messages to one server to another. In configuring an email application, you need to configure POP, SMTP and IMAP protocols in your email software. SMTP is a simple, text based protocol and one or more recipient of the message is specified and then the message is transferred. SMTP connection is easily tested by the Telnet utility. SMTP uses the by default TCP port number 25
FTP (File Transfer Protocol)
FTP or file transfer protocol is used to transfer (upload/download) data from one computer to another over the internet or through or computer network. FTP is a most commonly communication protocol for transferring the files over the internet. Typically, there are two computers are involved in the transferring the files a server and a client. The client computer that is running FTP client software such as Cuteftp and AceFTP etc initiates a connection with the remote computer (server). After successfully connected with the server, the client computer can perform a number of the operations like downloading the files, uploading, renaming and deleting the files, creating the new folders etc. Virtually operating system supports FTP protocols.
IP (Internet Protocol)
An Internet protocol (IP) is a unique address or identifier of each computer or communication devices on the network and internet. Any participating computer networking device such as routers, computers, printers, internet fax machines and switches may have their own unique IP address. Personal information about someone can be found by the IP address. Every domain on the internet must have a unique or shared IP address.
DHCP (Dynamic Host Configuration Protocol)
The DHCP or Dynamic Host Configuration Protocol is a set of rules used by a communication device such as router, computer or network adapter to allow the device to request and obtain and IP address from a server which has a list of the larger number of addresses. DHCP is a protocol that is used by the network computers to obtain the IP addresses and other settings such as gateway, DNS, subnet mask from the DHCP server. DHCP ensures that all the IP addresses are unique and the IP address management is done by the server and not by the human. The assignment of the IP addresses is expires after the predetermined period of time. DHCP works in four phases known as DORA such as Discover, Observe, Request and Authorize
IMAP (Internet Message Access Protocol)
The Internet Message Access Protocol known as IMAP is an application layer protocol that is used to access to access the emails on the remote servers. POP3 and IMAP are the two most commonly used email retrieval protocols. Most of the email clients such as outlook express, thunderbird and MS outlooks support POP3 and IMAP. The email messages are generally stored on the email server and the users generally retreive these messages whether by the web browser or email clients. IMAP is generally used in the large networks. IMAP allows users to access their messages instantly on their systems.
ARCNET
ARCNET is a local area network technology that uses token bus scheme for managing line sharing among the workstations. When a device on a network wants to send a message, it inserts a token that is set to 1 and when a destination device reads the message it resets the token to 0 so that the frame can be used by another device.
FDDI
Fiber distributed data interface (FDDI) provides a standard for data transmission in a local area network that can extend a range of 200 kilometers. The FDDI uses token ring protocol as its basis. FDDI local area network can support a large number of users and can cover a large geographical area. FDDI uses fiber optic as a standard communication medium. FDDI uses dual attached token ring topology. A FDDI network contains two token rings and the primary ring offers the capacity of 100 Mbits/s. FDDI is an ANSI standard network and it can support 500 stations in 2 kilometers.
UDP
The user datagram protocol is a most important protocol of the TCP/IP suite and is used to send the short messages known as datagram. Common network applications that uses UDP are DNS, online games, IPTV, TFTP and VOIP. UDP is very fast and light weight. UDP is an unreliable connectionless protocol that operates on the transport layer and it is sometimes called Universal Datagram Protocol.
X.25
X.25 is a standard protocol suite for wide area networks using a phone line or ISDN system. The X.25 standard was approved by CCITT now ITU in 1976.
TFTP
Trivial File Transfer Protocol (TFTP) is a very simple file transfer protocol with the very basic features of the FTP. TFTP can be implemented in a very small amount of memory. TFTP is useful for booting computers such as routers. TFTP is also used to transfer the files over the network. TFPT uses UDP and provides no security features.
SNMP
The simple network management protocol (SNMP) forms the TCP/IP suite. SNMP is used to manage the network attached devices of the complex network.
PPTP
The point to point tunneling protocol is used in the virtual private networks. PPP works by sending regular PPP session. PPTP is a method of implementing VPN networks.
OTHER PROTOCOLS
VTP, ARP, IPX, OSPF, RARP, NFS, BOOTP, NNTP, IRC, RADIUS, Soap, Telnet, RIP, SSH.
Subnetting
Here you will find subnet network overview, ip addressing, address translation, network overview, subnet masking and subnetting overview. A subnet or a subnetwork is a separate part of an organization’s network. In a subnet all the machines are typically in one room, building or at one geographical location.
By dividing an organization’s network into the subnets allows it to connect to the internet by using the same shared network address. Without subnet’s an organization may get different connections to access the internet. Subnetting is the modification of a single IP network to create two or more logically different networks.
A subnet allows the flow of network traffic between hosts to be segregated based on the configuration of a network. Subnetting can improve the network security and performance by arranging the hosts into the different logical groups. Subnetting is required when one network address needs to be distributed across multiple network segments. Subnetting is required when a company uses two or more types of the network technologies like Ethernet and Token Ring.
Two network segments are restricted by distance limitations. Submetting or dividing the network into the segments is also required when localized network management is required for example accounting, sales, customer service departments. There is another reason for the subnetting, which is that the computers on the network, which use more bandwidth, needs to be separated from the rest of the computers. There are certain advantages and disadvantages of the subnetting. Before you start dividing your network into the different segments, you should assign the IP address to each computer in your network segment.
Subnetting makes the network management easier and it is also very helpful for the troubleshooting of a network segment. The internet is a collection of networks where users communication with each other. Each communication on the internet carries the source and the destination address of the computer. This address is called IP address. This 32 bit address has two parts: one part represents the network portion and the other part represents the host portion of the IP address. A company can use some of the bits in the machine or host portion of the address to identify a subnet. In this scenario, the IP address contains three parts: the network address, the subnet address and the machine address.
Subnet Mask Basics
The most recognizable part aspect of subnetting is the Subnet mask. A subnet mask contains 4 bytes, 32 bits and is divided into 4 period separated octets. Typically, a very common subnet mask in binary looks like this.
11111111 11111111 00000000 00000000
255 255 0 0
How to Apply a Subnet Mask
A subnet mask does not work like an IP address and it cannot exist separately without an IP address. An IP address and subnet mask work together to form a network. An IP address splits into two main parts when applying the subnet mask. The leftmost bits of a subnet mask must be set to 1. For example
11111111.00000000.00000000.00000000
11111111.11111111.00000000.00000000
11111111.11111111.11111111.00000000
The above example shows the valid representation of a subnet mask into the binary numbers.
00000000.00000000.00000000.00000000 is an invalid subnet mask.
11111111.11111111.11111111.11111111 is also invalid subnet mask.
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.
Subnetting an IP network can be performed for a variety of reasons such as using the different physical media in an organization, such as FDDI, WAN and Ethernet, preservation of the addresses and for the purpose of security, management and ease of troubleshooting. The most
common reason of the subnetting is to control the network traffic. In an Ethernet network, all computers in a segment see all the packets that are transmitted by all the other computers on the same segment.
In this situation, the network performance can be badly affected due to the heavy traffic loads, collisions and the retransmission of the packets. A router is used to connect the IP networks and it also helps to minimize the load of the traffic.
Subnet Masking
By applying the subnet mask to the IP address you can identify the network and host portion of the IP address. The decimal number 1 represents the network portion in the subnet mask and the node is represented the 0s. Performing a logical AND operation between the IP address and the subnet mask resulting in the network address.
For example, using our test IP address and the default Class B subnet mask, we get:
10001100.10110011.11110000.11001000 140.179.240.200 IP address of the class B
11111111.11111111.00000000.00000000 255.255.000.000 Default subnet mask of class B
--------------------------------------------------------
10001100.10110011.00000000.00000000 140.179.000.000 Network Address value
The following example shows the default subnet masks.
• Class A Subnet Mask- 255.0.0.0 - 11111111.00000000.00000000.00000000
• Class B Subnet Mask- 255.255.0.0 - 11111111.11111111.00000000.00000000
• Class C Subnet Mask- 255.255.255.0 - 11111111.11111111.11111111.00000000
Subnetting Review
Subnetting allows network and system administrators some flexibility in defining relationship among the hosts of a network. Hosts on the logically and physically different subnets can talk to each other through specialized devices called gateway or router. The ability to filter the traffic between
subnets can make the more bandwidth availability. Subnetting referred to as subdivision of a class based networks into subnetworks.
A router can exchange subnet routes with the other routers in the network. A subnetted network can’t be split into the isolated portion. All the subnets must be contiguous because the routing information cannot be passed to a non-network member. Router can exchange subnet routes with other routers within the network. Since the subnet masks are identical across the network, the routers will interpret these routes in the same manner. However, routers not attached to the subnetted network can't interpret these subnet routes, since they lack the subnet mask.
Therefore, subnet routes are not relayed to routers on other networks. This leads to our second
restriction. Subnetting allows you to create multiple logically different networks within the same class A, B or C. If you break a major network into smaller networks, it allows you to create a network of interconnecting subnetworks. Any device or gateway that is responsible for connecting the different subnetworks must have the distinct IP address one for each subnetwork.
To subnet a network use and extend the natural subnet mask using some of the bits from the host ID portion to create a subnetwork ID. In this example, given a Class C network of the IP address 4.15.5.0 which has a natural subnet mask of 255.255.255.0, you can create subnets in this manner:
11001100.00001111.00000101.00000000 204.15.5.0
11111111.11111111.11111111.11100000 255.255.255.224
---------------------------------|subnet|----
By extending the natural subnet mask to be 255.255.255.224, you have used three bits from the host portion of the mask and used them to make subnets. By using these 3 bits, it is possible to create 8 subnets. The remaining five ID bits of the host portion, each subnet can make 32 host addresses and the 30 addresses out of 32 are assigned to the devices or computers. The host IDs
of all zeros and all ones are not allowed.
204.15.5.0 255.255.255.224 host address range 1 to 30
204.15.5.32 255.255.255.224 host address range 33 to 62
204.15.5.64 255.255.255.224 host address range 65 to 94
204.15.5.96 255.255.255.224 host address range 97 to 126
204.15.5.128 255.255.255.224 host address range 129 to 158
204.15.5.160 255.255.255.224 host address range 161 to 190
204.15.5.192 255.255.255.224 host address range 193 to 222
204.15.5.224 255.255.255.224 host address range 225 to 254
GATEWAY
Here you will get the software and hardware network gateway overview and general introduction, basic configurations, software configuration, bandwidth, firewall overview and routing methods. Gateway is a network point that acts as the entrance point to another network. A gateway can be a hardware or software. On the Internet, a node or a stopping point can be a gateway or a host. A router also acts as a gateway. The computers that control and manage traffic and bandwidth within your company’s network or at the ISP are the gateway nodes. In the enterprise network the gateway node acts as a proxy server and a firewall. The gateway is also associated with a router and a switch.
A network gateway is an internetworking system that joins two networks together and it can be configured in software, hardware or both. Network gateway can operate at any level of OSI layers model.
CONFIGURING THE GATEWAY
The gateway has two sides: The WAN side connects to your cable DSL modem and LAN side connects to your private network via a hub or switch. The main function of it is to route the traffic from computer to the Internet and back to the computer. A computer with the two NIC cards can act as a gateway. It routes the network traffic between two logically and physically different networks.
In its configurations, you first configure the public side of the gateway and the IP address, which is assigned to you by your ISP. The public side configurations generally includes, assigning the IP address, DNS server, subnet mask, ISP gateway IP address and host name. Additionally, if your ISP uses PPPoE, you simply have to enable PPPoE in your gateway.
On the other hand to configure the private side , you have to enable DHCP. By enabling this feature each computer in your network, will automatically pick the settings from the DHCP server that are required for a computer to be a part of the network and communicate.
SOFTWARE CONFIGURATION
The last step in the configurations, is to configure each PC in such a way that it automatically gets the all the settings from the DHCP server. Make sure that TCP/IP protocol is properly installed in each computer of your network. After configuring each PC in your network perform a reboot.
After rebooting the each PC in your network, you will see a blinking underneath network icon on the right side of the task bar. If everything is done then you can access the internet, share the printer and data in your network.
The firewall can also be configured with it to put a check on the unauthorized network traffic from the internet to your computer or network.
Network Routing
You will be able to find the basic network routing overview, router configuration, router working, simulations static routes and routing table. Routing is the process of defining routes for the packets to its destination through an internetwork and this is performed by the router.
Routing is consist of two separate tasks.
1. Defining paths for the packets through and internetwork.
2. Forwarding data packets based on their predefined paths.
Generally, there are two types of routing.
STATIC AND DYNAMIC ROUTING
Routing can be performed by manually defining the routes or paths for packets to reach its destination. This is called static routing.
Stating routing works well for the small networks and when using the static routing, the routing table of the each router should be updated each time there is any change in the network configuration or topology. A router, whose routing table is not regularly updated, cannot communicate with the other routers.
While on the other end in most of the networks, routing is accomplished through the use of the dynamic routing. In the dynamic routing, routing protocols, such as RIP, OSPF etc create and maintain the routing tables of each router. Practically, dynamic routing functions very well than the static routing
ROUTING TABLE
A routing table is a set or rules, viewed in a tabular format and this used to define the routes of the data packets. All the network devices, which have IP, enabled functionality such as routers and switches use the routing tables. Routing table stores the information and configurations of every router in the IP enabled network. A routing table contains the information necessary to transmit the packets toward its destination.
When a packet is received, the network devices matches the information contained in the packets and the information in the routing tables and then it defines the shortest possible route for the transmission of the packets towards its destination.
Each packet contains the information of its origin and destination and the routing table contains the following information.
• Destination: The IP address of the packet’s final destination (next hop). Next hop: The IP address to which the packet is forwarded
• Metric: It assigns the cost to each route so that most-effective paths can be picked up.
• Routes: It includes directly attached direct subnets, indirect subnets, that are not directly connected to the device but it can be accesses through one ore more hops
• Interface: The outgoing network interface the device should use when forwarding the packet to its final destination.
Routing tables can be maintained manually by the network administrator or by dynamically (automatically). The static network tables do not change unless the network administrator changes them. Routing tables can be maintained manually or dynamically. Tables for static network devices do not change unless a network administrator manually changes them. In the dynamic routing, the network devices such as routers and switches maintain the routing tables dynamically by using the routing protocols, such as RIP, OSPF etc. In the dynamic routing, the network devices listen and detect any network or devices failure and packet congestions.
Routing in the Internet
Routing is the method in which data finds its destination from one computer to the next. In the Internet there are 3 major aspects of routing.
1. Physical Address Finding
2. Determination of inter-network gateways
3. Numeric and symbolic Addresses
Physical address finding is the method of the Internet Routing and is used when datagram is transmitted from a computer. It is necessary to encapsulate the IP datagram. This encapsulation requires the local network or physical address.
If a computer wishes to transmit IP datagram it needs to encapsulate the physical address of the destination network device in the frame. This address can be achieved by using the table that will map the IP address with the physical address. Such table can be configured into a file that can be read into the memory at the boot up time. Computer normally uses the Address Resolution Protocol (ARP), which operates dynamically to maintain the translation table.
The second method is necessary because the Internet consists of a large number of local networks, which are interconnected with each other by gateways. Such gateways are known as routers, which has physical as well as logical connectivity with many networks.
The determination of the best suitable gateway and port for a particular IP address is called routing.
The third method generally involves the translation of the human friendly form (names) to the number address (IP Address). IP address can’t be remembered due to its numeric form but the simplest names (domain names) are easy to remember e.g www.yahoo.com, www.google.com, www.msn.com are easiest to remember as compared to the IP addresses 122.11.22.34, 223.45.66.76, 155.44.55.120. DNS translates the domain names into the IP address and IP address into the domain name. This domain to IP translation is a must for communicating on the Internet because communication on the Internet is performed by the IP addresses.
Communication between routers
The Internet is a network of networks. The Internet consists of large number of autonomous systems, each of which further consists of routing domains. Such autonomous systems are usually run by the larger companies or universities. Within the Autonomous system, a router communicates with the other router using the best intra domain routing protocols, which are known as interior gateway protocols. Autonomous system are connected via gateways, these exchange information using inter domain routing protocol, which are also called exterior gateway protocols.
The RIP or (Routing Information Protocol) is the commonest interior gateway protocol and the recent protocol such as open shortest path first (OSPF). The purpose of these protocols is to enable routers to exchange locally so that all the routers in the autonomous system must a have coherent and up to date information.
When a host receives the new routing information, it is likely to update not only to it but also sends this new updated information to all the connected hosts so that they can updated themselves. Hence these changes propagate across the entire network.
Internet Fax Services
Here you will learn internet fax server overview and general introduction to the online faxing methods, how to send a fax and online services. A fax server consists of these things a PC, which is connected to the LAN, Fax server software installed on the PC and a Fax modem or a Fax board. Fax messages can be stored as printable documents, spread sheet, database or graphics. When someone wants to fax the documents, they can print the document to the fax printer then put the recipient information such as name and fax number, select the cover letter, type your message and then send the fax through the faxing software installed on your PC.
Alternatively, you can send the fax to the email messages and can take the fax number from the outlook express contact’s list. Sending fax through PC typically takes less than 30 seconds.
Alternatively, fax server can also be setup to receive the faxes and after receiving the faxes, these can be sent to the printer machine or can be sent to the specific recipient’s email address to notify them that he/she has received a fax.
There are certain advantages of the PC fax server, which I have discussed as follows.
1. The main feature of the Fax server is that it saves your time and cost and you can send the fax in the same way as you send emails and attached the fax to send to the recipients.
2. Invoicing, purchase orders and requested information can be scheduled to be faxed to the intended recipients.
3.Fax server will also retry if the recipient number is busy or if there is any error in the number.
4. You can also save the fax numbers of the frequent users.
5. Fax books also make it easy to send the faxes to the groups of people and at the scheduled times.
6. The faxes that are sent directly through the PC are looks better in terms of the resolution.
7. You can also manage the fax server to redirect the receiving faxes to the appropriate recipient so ensuring the security and timely receiving of the faxes.
8. The administrators can automate many functions of the fax server. A fax server can be configured to automatically send the invoices, purchase orders and the promotional newsletters. Additionally, a fax server can work without papers and reduces the overhead of putting and checking the papers again and again. Fax messages can be stored in your PC.
What is a Internet Fax
Internet fax is a device that uses IP networks to transmit the faxes instead of the PSTN. Internet fax uses e-mails as the medium for sending the faxes. Internet fax services include email to fax, fax to email and PC to fax (sending faxes from your computer). Internet fax is type of service, which enables you to send and receive the faxes in a timely manner without a fax machine. Only an email accounts is required to setup your Internet fax account.
Subscribers have to monthly fees to the internet fax service providers. Internet fax service providers usually works in a way that when a fax is sent to the subscriber’s number, the fax service receives the fax and send it to the recipient’s email address as an attachment.
All you need is to have the registered email address with the internet fax service providers. You have to write the fax content in the body of the email and type the fax number in the “To” field with a @ sign and a internet fax service name e.g 14545668999@efax.com. In the subject field sender can write the name of the recipient.
There is a small tool bar in the system tray for sending and receiving the faxes and it comes after installing the fax software. Upon receiving the email to the Internet fax service providers the automated programs convert the email messages to the fax format and send the fax to the recipient fax number. On the other, hand the recipient receives the fax on their fax machine normally.
The Internet fax services provide very ease and you assigned a fax number, which has to be active 24 hours so that you account can accept the faxes. On the other hand, the working of the regular fax machine is typically depends on your telephone line, which should be free while sending and receiving the fax. Internet fax service also saves your papers and the need of the fax machine.
Internet fax service is very familiar to the sending and receiving the email messages and it also saves the cost and time so many people are likely to use this service.
Another big advantage is given by the Internet service providers is that it offers the toll free numbers to its subscribers in USA and Canada. So the people from USA and Canada can send faxes for free. Most internet fax services costs $10-20 per month. The communication charges are greatly reduced as opposed to the conventional fax machines, which costs a user per page.
