16-04-2012, 01:13 PM
INTERNET WORK
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INTRODUCTION
INTERNET WORK
An internet work is a collection of individual networks, connected by intermediate networking devices that function as a single large network. Internetworking refers to the industry, products, and procedures that meet the challenge of creating and administering internet works.
HISTORY OF INTERNETWORKING
The first networks were time-sharing networks that used mainframes and attached terminals. Both IBM’s Systems Network Architecture (SNA) and Digital’s network architecture implemented such environments.
• Local-area networks (LANs) evolved around the PC revolution. LANs enabled multiple users in a relatively small geographical area to exchange files and messages, as well as access shared resources such as file servers and printers.
• Wide-area networks (WANs) interconnect LANs with geographically dispersed users to create connectivity. Some of the technologies used for connecting LANs include T1, T3, ATM, ISDN, ADSL, Frame Relay, radio links, and others. New methods of connecting dispersed LANs are appearing everyday.
AIM OF THE PROJECT
The main aim of this project is to generate fragmented data frames in MAC layer and to transmit it using WiFi technology. To simulate this program we are using ModelSim software. To design WiFi MAC Transmitter effectively VHDL programming is used. This project overcomes the occurrence of collisions during transmission as it uses CSMA/CA protocol.
MOTIVATION FOR THE PROJECT
Needless to say WiFi MAC Transmitter is a pivotal component in any modem and in the internet access it has found its wide range of applications. Starting from the modest design aim, with lot of motivation the WiFi MAC Transmitter has been developed. This project will be helpful in generating MAC address and fragmenting the data packets that is being transmitted.
ORGANIZATION OF THE PROJECT
This project consists of ten chapters including introduction and conclusions. The main aim, history and technical approach are presented in Chapter 1. Chapter 2 describes the WIFI technology and discusses its varied features and security protocols. Chapter 3 presents the detailed description of ISO-OSI Reference model. Chapter 4 describes the features of IEEE802.1. . Chapter 5 explains the frame format of MAC transmitter, frame structure and address generation. Chapter 6 provides detailed description of MAC Transmitter. Chapter 7 mainly concentrates on VHDL language and ModelSim software.
WiFi TECHNOLOGY
"WiFi", also known as Wireless Fidelity, is the way to connect devices together without wires. It can be done in homes, businesses, between businesses, etc. WiFi offers a lot of advantages over LANS (Local Area Networks). Wireless Internet Access has four components that form its structure: high-speed access, a networking gateway, a wireless network, and a wireless customer.
WIRELESS MEDIA ACCESS
Sharing media access among many transmitting stations in a wireless network is more complex to achieve than in a wired network. This is because a wireless network station is not able to detect a collision between its transmission and the transmission from another station, since a radio transceiver is unable both to transmit and to listen for other stations transmitting at the same time.
USE OF RTS AND CTS
Hidden Nodes are solved by the use of a RTS (request to send) and CTS (clear to send) protocol prior to packet transmission as shown in fig 4.4. In our three node network above Node A sends a small RTS packet which is heard by Node B which send a small CTS packet which is heard by both Nodes A and Node C. Node C will not transmit in this case.
NODE IDENTIFICATION
Each node in 802.11 networks is identified by its MAC address which is 48 bit value. Receiving nodes recognize their MAC address. In general, the MAC Layer manages and maintains communications between 802.11 stations radio network cards and access points by coordinating access to a shared radio channel and utilizing protocols that enhance communications over a wireless medium. Often viewed as the brains of the network, the 802.11 MAC Layer uses an 802.11 Physical (PHY) Layer, such as 802.11b or 802.11a, to perform the tasks of carrier sensing, transmission, and receiving of 802.11 frames.
MEDIUM ACCESS BASICS
Before transmitting frames, a station must first gain access to the medium, which is a radio channel that stations share. The 802.11 standard defines two forms of medium access, distributed coordination function (DCF) and point coordination function (PCF). DCF is mandatory and based on the CSMA/CA protocol. With DCF, 802.11 stations contend for access and attempt to send frames when there is no other station transmitting. If another station is sending a frame, stations wait until the channel is free.
CONCLUSIONS
In our project “DESIGN OF WIFI MAC TRANSMITTER USING VHDL” we have successfully designed the transmitter section of WiFi in MAC layer using VHDL Language and ModelSim software. The data packets are fragmented and MAC address is generated for each frame describing its type and subtype. The entire data that arrives at data link layer is stored in ROM and required bytes of data which has to be fragmented is made available at RAM.
Further the working of five blocks of WiFi MAC Transmitter is shown in detail. The memory block contains the data which is sent to controller block where the MAC address is added. The MAC address is generated in MAC Header Register Block, the data unit interface block multiplexes the data frames and finally the data processing block processes the data using serializer.