NAT

NAT:-

       IT stands for network address translation.

            The current implementation of IPaddressing provides user with a very limited number of IP addresses that can be used for connectivity purpose. To solve this problem a number of organization have started implementing NAT addressing ,which allows them to use a single public IP address for a large number of internal system having unique private IP addresses.  All internal system in such a Nat network use a common public IP address to communicate with all external system on the Internet. 

                Let us Assume that there are a internal system ’ x’ (Many system connected with each other) having private IP address is unique. They all are connected with NAT, Which have a public IP address and NAT are Connected through the INTERNET.

      When any of private IP address of computer send data It send to only on NAT. Then NAT change the IP address of that packet then send to the Inertnet.(Change internal IP address to public IP) .The NAT use  Index table for Identifie  internal system because when reply comes from the Internet then it send the packet to internal system. IT works on two network junction.

Transmission Control Protocol / Internet Protocol

    The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite (IP), and is so common that the entire suite is often called TCP/IP. TCP provides reliable, ordered, error-checked delivery of a stream of octets between programs running on computers connected to a local area network,intranet or the public Internet. It resides at the transport layer.

        Web browsers use TCP when they connect to servers on the World Wide Web, and it is used to deliver email and transfer files from one location to another. HTTP, HTTPS, SMTP, POP3, IMAP, SSH, FTP, Telnet and a variety of other protocols are typically encapsulated in TCP.

         Applications that do not require the reliability of a TCP connection may instead use the connectionless User Datagram Protocol (UDP), which emphasizes low-overhead operation and reduced latency rather than error checking and delivery validation.

       Like OSI network model, TCP/IP also has a network model. TCP/IP was on the path of development when the OSI standard was published and there was interaction between the designers of OSI and TCP/IP standards. The TCP/IP model is not same as OSI model. OSI is a seven-layered standard, but TCP/IP is a four layered standard. The OSI model has been very influential in the growth and development of TCP/IP standard, and that is why much OSI terminology is applied to TCP/IP. The following figure compares the TCP/IP and OSI network models.

   

 * Difference between OSI and TCP/IP reference model

        

Unified Extensible Firmware Interface

The Unified Extensible Firmware Interface (UEFI)  (pronounced as an initialism U-E-F-I or like "unify" without the n) is a specification that defines a software interface between an operating system and platform firmware. UEFI is meant to replace the Basic Input/Output System (BIOS) firmware interface, present in all IBM PC-compatible personal computers. In practice, most UEFI images provide legacy support for BIOS services. UEFI can support remote diagnostics and repair of computers, even without another operating system.


           The original EFI (Extensible Firmware Interface) specification was developed by Intel. Some of its practices and data formats mirror ones from Windows. In 2005, UEFI deprecated EFI 1.10 (final release of EFI). The UEFI specification is managed by the Unified EFI Forum
        
              

UEFI booting:-

                             The UEFI specification defines a "boot 

manager", a firmware policy engine that is in charge of loading the operating system loader and all necessary drivers. The boot configuration is controlled by a set of global NVRAM variables, including boot variables that indicate the paths to the loaders.

Operating system loaders are a class of the UEFI applications. As such, they are stored as files on a file system that can be accessed by the firmware, called EFI  System partition (ESP). UEFI defines a specific version of FAT, which encompasses FAT32  file systems on ESPs, and FAT16 and FAT12 on removable media.Supported partition table schemes include MBRand GPT, as well as El Torito volumes on optical disks. UEFI does not rely on a boot  sector, although ESP provides space for it as part of the backwards compatibility.