Over the last few years the demand for wireless broadband services, high data rates and wireless access network has been rapidly increased. The demand for wireless access network have emerged over the last few years.WiMAX(Worldwide Interoperability for Microwave Access) is an IEEE standard 802.16 defines the Medium Access Control and Physical layer specifications for the wide broadband wireless access networks.
An alternative for the wired networks such as fiber optics ,DSL lines and coaxial systems using cable modems is given by WiMAX.A very high speed data access is offered by the WiMAX covering an area up to 50 km, supporting data rates up to 100Mbps.The speed of the data depends up on the distance from the base station and the underneath Physical layer.With the capability of covering larger areas with high data rates WiMAX standard can deliver backhaul connections for business units, enterprise campuses and cellular networks.
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The Point- to- Multipoint and Mesh topologies are supported by the MAC layer of WiMAX.The duplexing techiniques Frequency Division Duplex(FDD) and Time Division Multiple Access (TDD) are used by the wireless medium access.It is based on the Time Division Multiple Access(TDMA) or Frequency Division Multiple Accesss.
For a frequency band of 10-66 GHz and 2-11GHz multiple Physical layer specifications are supported for Line of sight(LOS) and Non Line of Sight(NLOS) operational environments.The mobility support is added to the WiMAX network by the IEEE 802.16e amendment.
NS-3 is a new simulator that has been implemented from the scratch and it is a replacement for the ns-2 network simulator. The ns-2 network simulator is one of the widely used simulators in both industrial and academic community in the past years. The new network simulator ns-3 has major enhancements over ns-2 with all new capabilities of becoming a leading network simulator in the future.
Except a few features many of the new features of ns-3 are completely re-written soft-core with documented API, giving support for simulating virtual networks, support for test beds, memory management automation, configurable tracing system and easier software integration .
The early version or the first version of ns-3 release was made around June 2008 with an extensive support for a numerous modules including CSMA, TCP,UDP, IPv4, 802.11 WiFi and peer to peer network.The progress on the many modules is still under development.For ns-2,there are many modules available though WiMAX based on PMP topology with TDD as a duplexing technique.The module proposed by the Networks and Distributed Systems Laboratory , probably one of the first WiMAX modules available for scheduling services and bandwidth management.
The proposed module is highly simplified and it ignores many implementation details and it is not compliant to the standard. . The module proposed by National Institute of Standards and Technology (NIST) includes a number of features such as OFDM Physical layer and fragmentation and de-fragmentation.The QoS scheduling service is lacking in it.Finally a collaborative effort between WiMAX Forum,Rensselaer Polytechnic Institute (RPI) andWashington University St. Louis (WUSTL) provides support for QoS scheduling services,OFDMA Physical layer and ARQ mechanism to this module.
The newly developed and updated module is now officially accepted by the WiMAX forum and is available for download . A plug in has been proposed by the Telecom Bretagne also provides support for the NIST module along with QoS scheduling services feature. Finally an updated and recent module is proposed by the Computer Networks Laboratory (CNL).This is based on DOCSIS module.This supports the scheduling services and the bandwidth management,but this lacks the implementation of a WiMAX compliant Physical layer.The modules that are proposed by the NDSL and CNL makes them selves as less attractive for the developers who intended to implement new features and plug-ins.
The module which we are using is based on IEEE 802.16 , a 2004 standard and ns-3 version of 3.2. The code is available under the GNU public license. This implements the PMP topology with Time division duplexing mode and aims to facilitate the detailed and standard compliant implementation of the standard,which supports many of the important features which includes QoS scheduling service, bandwidth management ,the uplink and downlink services, and OFDM Physical layer.This module is developed completely in C++ with 36 classes and almost 17000 lines of code.
Always on Time
Marked to Standard
Though it is the first WiMAX module that is designed for the ns-3 simulator , this is quiet different from the above mentioned modules in the places of facilitating modularity ,reusability, maintenance, scalability and this is fully object oriented . For the design and the analysis phase Unified Modeling Language is used.
This is a significant work that has done which allows simulations of WiMAX network with a more close to the real implementation of the standard.This also provides the add-on flexibility of adding any new modules to the various components.Along with the benefits of the ns-3 network simulator this modules enables features like tracing functionality ,flexiblility and simulation of real networks. The other benefits that are provided by this module includes TCP/IP-stack, emulation and the helper API will give scope of defining any new simulation scenarios.
The above concepts are given in a brief description starting with introduction to the overview of IEEE 802.16 , detailed description of the proposed modules by the various institutions including its software design, defining the MAC and PHY layers with a detailed operation of each component and finally the development and the enhancements of the above discussed topics.
chapter2. Literature Survey
The network simulator ns-3 has primarily concentrated on research and educational use.It is a discrete event network. The ns-3 is an open source project.The ns-3 documentation can be available in four different ways
- ns-3 wiki
- This documented tutorial
- Reference manual
- ns-3 Doxygen
This tutorial is particularly concentrated on the new users of ns-3.this will introduce the new users to the system in a collaborated fashion.to convert the information that is absorbed from the manuals into working simulations is a bit difficult task for the new users.this tutorial will completely help them with a build of several example simulations,analyzing key concepts and different features as we go further.for the users who are highly interested in delving deeper concepts this tutorial will provide a complete documentations from pointers to source code.
The important points are given as.
- 1.a new simulator has introduced and it is called ns-3 which is not an extension of ns-2.
- both of the simulators are written in c++ but the new simulator ns-3 does not provide any support for ns-2 api's.some important models has been merged in ns-3 and this project will be maintained while ns-3 is being newly built.the transition and the integration mechanisms will be studied.
- as the this ns-3 is an open source project this will allow the researchers and the developers to contribute and distribute their software.
For ns-2 users:
The flexibility involved in ns-3 is that choice of a scripting language.this makes most of the ns-2 users to migrate to ns-3.the scripting language offered in ns-2 is otcl and the results of simulations can be viewed using a network animator called nam.without using otcl scripting it is not possible to run a simulation purely as a c++(main() program) in ns-2.some of the modules in ns-2 are written in otcl and the others in c++
The simulator in ns-3 are completely written in c++ providing an optional python bindings.so there will be an option for simulation scripts .they can be written in c++ or in python.only some simulation results can be visualized by nam and new animators were under development.the trace files that can be generated in ns-3 is pcap and there are many other utilities that can be used to analyze traces as well.this tutorial is mainly concentrated on scripting in c++ and interpreting results through trace files.
There are many similarities in between ns-2 and ns-3 and this can be listed out in this tutorial as we move forward.most of the users have a similar question”wheater they can be moved to ns-3 or they can use ns-2”.this is purely depends on the users.
Ns-3 does not contain all the models that are currently existing in ns-2 but there are many new features and capabilities in ns-3.
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The models that are existed in ns-2 can be ported to ns-3.many active developments are taking place in the fronts for ns-3.the developers of ns-3 belive that ns-3 is ready for use and this can be an alternative for the users who are looking to start a new simulation projects.
To manage and organize the underneath code and documentation there should be a way for the complex software systems.a numerous ways are currently in existence to do this task and the concurrent vercion system (cvs) is the well known.
To maintain and organize source code both ns-2 and ns-3 use a different ways.ns-3 uses mercurial to manage and organize its source code system.there is no necessary to become an expert in mercurial but this tutorial recommends the users to get familiar with mercurial so as to access the source code.
A website is designed for mercurial and is given as www.selenic.com/mercurial, from where users can get the binary or any source related releases of the software configuration management system.a lot of information can be found in the above mentioned web site relating to ns-3 and mercurial and any information can be downloaded.
The downloaded source code in your local system should be compiled to produce an appropriate usable programs.a lot of tools are available to manage the source code.make is the most popular tool among the available tools.make is the most complex tool that can be used in a large and highly configurable system despite being a most well known tool.alternatives are being developed because of its complexity.in recent times python language is used largely to develop to develop these systems.ns-3 project uses the build system waf.this is new generation in python based build systems.it is not highly recommended to expertise python language to build the existing ns-3 system and a little language is required to use the subset of python to expand the system.
The scripting languages used in ns-3 is c++ and python.ns-3 api's are widely available in c++.a review will be taken to understand the language features and design patterns in this tutorial.
This tutorial is not completely concentrated on c++ but a basic knowledge on the subject is required. Users can find a lot of materials ,tutorials, cookbooks, logs or websites on the internet and a minimum basic knowledge is essential before further proceedings.
A numerous component of gnu tool chain are used for the development of a ns -3 system.a group of programming tools are available as a tool chain. A quick reference of the tools that are included in the gnu tool chain can be found at wikipedia .ns-3 user gcc compiler gnu binary utilities(gnu binutils) and gdb.the build system tools make or autotools fo gnu are not used.waf is user for this type of functions.the users of ns-3 mostly work in linux or linux like environment.
A linux like environment can be simulated in windows for the users who are working on windows.cygwin provides the required linux like enviromnet and users cab directly access the website www.cygwin.com for any downloads.cygwin supports most of the linux system commands.
Sometimes problems can encounter by using cygwin .the interactions with other windows software may encounter problems.using logitech products can save a bit of work done.users can compile their source code and the logitech process monitor can introduce itself to create a dll in the machine while it is running.in a critical environment this will kill your cygwin and stops the debugger from running.necessary precations should be taken while using logitech software when cygwin is in use.the alternative option to use cygwin is in a virtual machine environment.
A lot of discussions are underwent in the past to invest on the wifi hot spots.the 802.16 is a wman(wireless metropolitan area network) which is developed and introduced by wimax industry group in which intel and nokia are crucial and powerful members.
The wimax name is being accepted as a standard for itself.a large capacity of the service is offered at a low cost when compared to dsl or cable lines.the fast internet access can be implemented in a business environment or at home.when wimax is standardized through the ieee 80.2.16 the potential of the network is widely increased.
- It can emerge as an alternative for 3g networks
- The range of the network is widely increased
- Wireless the essential part of the network
Background and 80.2.16
The project of wimax has been started earlier in 1998 but the implementation and the introduction of these networks are done around 2003 .the main concept of the network is to make a wireless network as widely accepted under cheaper conditions in a metropolitan area netowork.the concept involved in 802.16 is that a base station is set for carrier signal to a public network.a single base station will have a capacity to support a few hundreds of subscriber stations merely that are mounted on rooftops.
The mac layer is used by the base station,which is a common interface.this makes the network highly interoperable and can instantly assign an uplink and downlink bandwidth to the subscribers as per their needs.
Users with mobile handsets can use the wimax network within the range of 50 mile while moving.this extends the flexibility and feasibility of wimax network.the first published papers on the wimax network is done around 2002 which briefs a fixed line of sight connection for a first mile to last mile link. This has particularly concentrated on all the licensed frequencies available between 10-66ghz bandwidths
Wimax offers a very reliable performance .this provides the highest performance broadband and a widely accepted technology.ieee 802.16 has not taken a least approach. Wimax is not a wide network as 2g or 3g.this could deliver higher rates with an enough widespread deployment and this can be cut into a cellular network in many areas.
The wimax can be operated upto 124mbps in a 28mhz channel and 802.16a at 70mbps in lower frequencies of 2-11ghz spectrum.
Ofdm is orthogonal frequency division multiplexing .ofdm is highly established and this is integrated into new generation carrier services.this is a fundamental to digital tv .a huge number of mixed signals can be transmitted simultaneously along one cable path with different frequencies by the ofdm with an orthogonal element spacing of these frequencies to prevent interference.this is also supported in 802.11a wlan
Fdd and tdd:
Time division duplexing and frequency division duplexing are also supported by this standard.this will enable interoperability with mobile and other wireless network systems.fdd is widely deployed in cellular network telephony.fdd is a legacy duplexing method.it requires dual channel pais in which one is for transmission and the other is for reception .some part of the frequency is used to separated them from self -interference.in the other side tdd uses a single channel for both transmitting and receiving and dynamically allotting a bandwidth depending on the traffic requirements.in regular environment structured channel pairs does not exist .
The wimax takes necessary precautions for encryption and privacy.data encryption can be done using des in cipher block chaining mode along with hooks defining for stronger algorithms such as aes.authentication can be done with x.509 certificates.
Upon the important and most powerful wireless standard hosts wimax is emerging as a prominent one from the ieee bodies.wimax can be the leading technology in the field of wireless networking in the coming years. This has attracted many companies to involve in this sector .it has gained a lot of market acceptance in the field of networking .
Wimax acts a crucial element in near future as most of the cellular operators move to ip based fourth generation systems.wimax will be the dominant solution in countries like china which is the worlds largest potential market for broadband users.this technology has already been implemented by the government and will fill the gaps in the 3g coverage.the use of wi-fi network will come down and this can be a local area network with limited access when wimax emerged as a dominant technology .the next generation centrino will support for wimax and will have a huge startup in the markets including rural areas of many countries.
Mobile handset are also modeled to support for wimax in near future nokia will be profited with a raise of 802.16 by adding a new base station business to its ailing equipment unit .wimax is emerging as a significant technology in the market giving room for more free spectrum.
Methodology and Terminolgy
3.1 Hardware Configuration
Pentium IV,2 Ghz(minimum)
512 MB (recommended 1 GB)
10 GB minimum
3.2. Software Configuration
- Operating System:- Ubuntu 8.10 intrepid
- Ns-3.2 all in one
- IT++ 4.0.4
IT++ is a C++ library of mathematical, signal processing and communication classes and functions. Its main use is in simulation of communication systems and for performing research in the area of communications. The kernel of the library consists of generic vector and matrix classes, and a set of accompanying routines. Such a kernel makes IT++ similar to MATLAB or GNU Octave
The IT++ library originates from the former department of Information Theory at the Gothenburg, Sweden. Because the library is coded in C++, the name IT++ seemed like a good idea at the time.
IT++ makes an extensive use of existing open-source or commercial libraries for increased functionality, speed and accuracy. In particular BLAS, LAPACK and FFTW libraries can be used. Instead of the reference BLAS and LAPACK implementations, some optimized platform-specific libraries can be used as well, i.e.:
- ATLAS(Automatically Tuned Linear Algebra Software) - includes optimised BLAS and a limited set of LAPACK routines
- MKL(Intel Math Kernel Library) - includes all required BLAS, LAPACK and FFT routines (FFTW not required)
- ACML(AMD Core Math Library) - includes BLAS, LAPACK and FFT routines (FFTW not required)
It is possible to compile and use IT++ without any of the above listed libraries, but the functionality will be reduced.
IT++ should work onGNU/LINUX, SUNSOLARIS , Microsoft Windows (withCygwin,Microsoft Visual c++) and Mac Os operating systems.
Overview of ieee 802.16
Worldwide interoperability for microwave access is shortly termed as wimax forum is formed around june 2001 to promote and distribute the conformance and interoperability of the IEEE standard 802.16 which is officially known as Wireless MAN . wimax is termed as a standard based technology that enables and delivers to the last mile wireless broadband access .This can be an alternative to the generally used DSL broadband access. Many of the companies are highly interested in the wimax as it delivers it high data rates up to the last mile.so this can reduce the lower pricing for both business field customers and home based customers .This network can go to the deeper rural areas where there is no pre existence of any cable or telephone lines.This network can be alternative with high data rate.Prior to this network most of the operators and customers are using the generally available fixed wireless technologies for broadband services.
WiMAX is available for the customers as an indoor and outdoor units from several manufacturers.Users can have their self installed units but they should be close to the base station.The indoor units that are installed requires higher infrastructure investment along with operational cost because of high number of base stations required to cover a given area.The indoor installed units are comparable to the size of a cable modem or to a DSL modem where as the outdoor units allow the subscribers to be much far away from the wimax base station and this requires a professional installation.The outdoor units are just like a residential stallite dish. A misconception is that wimax will deliver data at a rate of 70mbsps over 70 miles, but these are true when individually held under ideal circumstances.when coming to the practice this means that when in line of sight environment this could deliver data at a rate of 10mbps over 10km .when coming to urban environment it is more likely that most of the installations are in non line of sight and therefore the users may receive the signal only at a data rate of 10mbps over 2km.
Though wimax is different from dsl cable connection still there are some comparable similarities which means that either a high data rate or a long range.wimax is shared between the users around the given radio sector.when the users are increased in this radius sector the bandwidth is automatically decreases.wimax is termed as an eroperable implementation of IEEE 802.16 standard.This is similar to the ineroperable implementation of wifi which is 802.11 wireless lan standard .But when coming to the work wimax and wifi differs each other in both performance and reliability
The use of mac layer is different when compared to wifi and wimax.In wifi the mac layer uses contention access which means all the subscribers stations should pass the data through a wireless access point .This can cause the subscriber stations distant from the access point to be continuously interrupted by the closer station which will simultaneously reduce the throughput.This reduces the quality of service , and maily effect the VoIP and IPTV which are highly dependent on the available bandwidth.
When coming to the wimax (802.16) mac uses a scheduling algorithm in which the subscriber stations need to compete once only for the intial entry into the network.There after an access slot is allocated to it by the base station. The time slot is allocated to it by the base station which means this can be enlarged or contracted but it remains assigned to the subscriber station .so the other stations cannot access the already allocated slots.the scheduling algorithm is stable under over load.This can also be the more bandwidth efficient.This algorithm will allow the base station to control the parametes of qos by balancing the time slot assignments among the different appliacation needs of the subscriber stations.
The standard has been specified for the wimax is upto the frequency range of 10 to 66ghz
The standard 802.16d is updated to 802.16e and it uses scalable orthogonal frequency division multiplexing version with a 256 sub carriers.This will bring a potential benefits in the areas of self installation , power consumption ,coverage,bandwidth ,frequency reuse.This updated version also supports the capability for full mobility support.
This will allow the interoperability with other certified products as along as they are in the same profile.
The main concentration is on the 802.16d and on 802.16e as this lower frequencies suffer the less inherent signal attenuation and will give enhanced range and inbulding penetration.
Spectrum allocation issues:
The 802.16 wimax specifications will also applies to the rf spectrum.But the specification is not the same as permission to use.There is no exact global licensed spectrum for the wimax.considering in the countries like us the biggest spectrum that is allocated is around 2.5ghz and is already assigned .This is primarily assigned to companies likes sprint Nextel and clearwire.
Most of the companies planning to utlize the wimax standard in the range of 1.7 to 2.1 ghz spectrum band recently auctioned by the fcc
Chapter 4Problem specification
The Wi-Max standards given as IEEE (802.16) delineate the physical layer and medium access layer specifications for a broad band wireless network. The physical medium is bifurcated into frames of constant length. Each frame is segmented into downlink and uplink sub frames to link up in network traffic.
The construction of the frame underlie in the physical layer. A numerous physical layers defined for various operational environments by the standards. Depending on the various carrier modulations different physical layers are defined.
- Wireless MAN-SC for a frequency 10-66 GHz band depending on single carrier modulation.
For the frequencies less than 11 GHz three alternative physical layers are defined
- Wireless MAN-SCa with a single carrier modulation
- Wireless MAN-OFDM with a orthogonal frequency division multiplexing
- Wireless MAN-OFDM with a orthogonal frequency division multiple access
The IEEE(802.16) standard endorse two duplexing techniques.
- FDD in which downlink and uplink sub frames with distinct frequencies takes place at same time.
- TDD in which downlink and uplink sub frames takes place at distinct time and with a similar frequency.
The medium access layer is divided into three sub layers, they are
- Convergence sub layer
- MAC common part sub layer
- Security sub layer
The convergence sub layer is amenable for receiving Protocol data units from a higher layer and assigning them to a reserved connection, processing and distributing to appropriate MAC Service access point.
The basic MAC functionalities provided by common part sub layer includes establishment of connection, management, generation of MAC management messages, ranging, registration, service flow management scheduling services and registration.
The wireless medium is distributed along dual modes are defines as
- PMP mode in which subscriber stations convey to each other by a Base station
- Mesh mode in which stations are configured in an ad-hoc fashion and convey each other directly.
In connection oriented communication the network packets are distributed in the ways of connection and the MAC protocol is defined as a connection oriented communication.
The connections are defined in two different ways.
- Transport connections for data transmission
- Management connections for transmitting control messages
An initial ranging phase is included in the registration phase in which management messages RNG-REQ and RNG-RSP are switch between SS and BS.On receiving RNG-REQ the BS verifies parameters such as power level.
To transmit and receive control messages these connections are then used.
A set of control messages are defined by MAC which are called as management messages and the important messages are DL-MAP, UL-MAP, DCD and UCD.
When a Base station broadcasts messages then downlink MAP and uplink MAP defines the access to the sub frames of Downlink and Uplink of current frame.
These message headers contain a set of information in which each specifying an SS of the DL or UL grant assigned to it. These are preceded by a set of DCD and UCD messages which include a set of general information about the channel and a pack of burst profiles, Each burst profile determines a set of parameters that are used to send and receive data in a given profile of down link and uplink grant. A complete set of data is carried under transport connections. There is a peer to peer relationship between a service flow and a transport connection. A service flow determines a unidirectional flow of data traffic and binds it with a set of QoS parameters.
The standard supports a huge set of QoS parameters. A service flow is created by set of special MAC management messages DSA-REQ and DSA-RSP which are exchanged between SS and BS. The standard classified a set of four scheduling services and are given as UGS (Unsolicited Grant Service), rtPS (Real-Time Polling Service), nrtPS (Non-Real-Time Polling Service) and BE (Best Effort).
Unsolicited grant service is created for a real time application with a constant size of packets. Real time polling service is created with a variable size packet on interval basis for real time applications. Real time polling service is different from UGS and is polled by the base station on interval basis allowing to send bandwidth requests. The request is accomplished based on the available bandwidth. For delay tolerat applications non real time polling service is created. Even in heavy network congestion conditions the non real time polling services is ensured with a minimum bandwidth by polling it on a regular basis. For HTTP and Email services best effort is designed and it does not guarantee a minimum bandwidth. An additional class of ertPS(extended real time polling service has introduced by the IEEE 8.2.16e amendment cascade the features of UGS and rtPS allowing unsolicited grants for variable packet size applications. A bandwidth request is accomplished by sending a bandwidth request packet.
A bandwidth request packet is sent by a special transmission which is allocated in uplink sub frame .A response is given by the BS with a grant allocated in subsequent frames. A bandwidth is requested on per connection basis but assigned on per SS basis. Then the responsibility is taken by SS to decide which connection will transmit in a defined grant. In the similar fashion BS scheduler selects packets which will be transmitted in DL sub frame. A manufacturer defines all the scheduling algorithms and this standard does not interfere in defining scheduling algorithms.
DESIGN AND IMPLEMENTATION
5.1 THE PROPOSED IEEE 802.16 MODULE
The present chapter giving requirements of the proposed section is generally composed the 3 layers:The Convergence Sublayer, the (Common-Part Sublayer) MAC CPS and the PHY layer. Near to the PHY layer there two distinct PHY implementation will be supported. By showing a few of its key mechanism and also their interface. following sections is providing the detailed explanation of three(3) layers .
5.2. Software Design
The designing of module carefully follows the objective-oriented study and also the design pattern in order to achieve through the classic uniqueness of the objective-oriented software structure include modularity, encapsulation, polymorphism and also the inheritance, and to match to totally objective-oriented designing pattern of the ns-3. Unified Modeling Language(UML) has adopted particularly for Designing.
More distinctively, the software constructed techniques given in have commonly followed. In the following module class diagram is given . The important issue here shows only the important data members in the diagram and also functionalities and due to the less space the multiplicity is being removed . As given in the following figure, the design module is poised of many C++ classes with each represents the core module of system and also taking the care of a exact functions. All the responsibilities which have been with awareness delegated to distinct components or classes to make sure more cohesion and also low combination.The more concentration has to put to the design an API which ensures the scalability,reusability as well as the maintainability to software design.
In the feature the module design facilitate the expension of software . Adding of fresh components and the plug-ins, such as the new PHY or the scheduler implementation, could be easily done.
5.2 The Convergence Sublayer(cs)
The MAC 802.16 layer is categorised in to two different sublayers.The one is CS(Convergence Sublayer) and the other is core of the MAC layer is called the MAC (Common-Part Sublayer).Convergence Sublayer(cs) is additionally sub- categorised into two different types. The one is Packet CS(Convergence Sublayer) and the other one is ATM Convergence Sublayer(CS).The present module is going to implement the Packet Convergence Sublayer,which is implemented to work with packet based protocol at upper layers.At the upper layers the CS will be responsible for receiving packets from the upper layer and also from the peer locations, classification of the packets to suitable connections or for the servicing flow and processing of the packets. It also manages a mapping of the transportation of the connections to the servicing flow. This is going to enable the MAC(CPS) by the identification of the Quality Of Service(QoS) parameters which is linked to a transport the connection and ensure the (QoS)Quality Of Service requirements. The Convergence Sublayer(CS). presently employs a easy classiffer which is dependent on the destination of address of the MAC. In the feature ,Supporting for another standard submissive classification is to be aimed. The important thing is that the possible feature of Payload Header Suppression(PHS), that allow the suppression of repetitive segment to the payload of the headers,by the module it has not been implemented .
5.3 The MAC_Sublayer
The major sublayer is MAC(CPS) in the IEEE 802.16(MAC) and it perform the basic functionalities of MAC. The module then implements PMP mode. Among all of several SSs In the PMP mode(BS) will be responsible for the supervising the communication. The important functionalities of MAC(CPS) which include addressing and framing, registration and initialization of SS,generating the MAC managing messages,flow for the service management,managing of bandwidth and services like scheduling.The Figure 2 represents WiMAX networking device(WimaxNetDevice) which shows MAC layer. This class is going to expand NetDevice group of the API ns-3. It facilitates abstraction to the networking device.
The Wimax Network Device is further expanded by (BS)BaseStationNetworkDevice and (SS)SubscriberStationNetDevice classes,by defining the MAC layers of BaseSstation and SubscriberStation, respectively. in addition of these these major classes, the important functions of MAC is being distributed to a number of other categories to achieve the software uniqueness discussed as in the Section 3.1. As it is shown in the Figure, a few of the important classes that will implement the functions of the MAC which includes Service Flow Management ,Link Management for both of the (SS and BS), Uplink Scheduler,manager for Burst Profile ,Connection Manager and Bandwidth Manager, Scheduler for both (SS and BS),
5.3.1 Framing and Management Messages
To manage the bandwidth more effectively and economically, the frame has been divided into the integer numbers of the symbols and also (PS)Physical Slots which is highly helpful in it.
The set of symbols for each frame will depends on the original implementation of PHY layer. The content of a UL or DL burst has been specified in the symbolic units.As shown in the Figure 3 the system of MAC implemented frame and also the key managing messages are UCD, DCD,UL-MAP and DL-MAP.The MAC managing messages are being played fundamentally as role in the MAC IEEE 802.16.
A amount of managing messages have been defined. These messages only carry control information and are transmitted on management connections (including predefined broadcast and multicast connections). The most important of these messages are DL-MAP, UL-MAP and DCD and UCD. DL-MAP and UL-MAP are called DL and UL bandwidth allocation maps and define access to the downlink and uplink, respectively. DCD and UCD are called channel descriptors and contain information about the chan nel and how data shall be transmitted/received on it.
Next part is going to describe all these messages with additional detail. In the case of these following these messages, the usual defines the different pairs of managing messages to transmit particular tasks like service flow management, registration,ranging,burst profile management and so on. The present module now implementing the following managing messages like: UL-MAP,DCD, UCD,DSA-RSP RNG-RSP, DL-MAP, DSA-REQ, RNG-REQ and DSA-ACK. The section implementing these type of messages,and the regular packets as well and also the Grant Management Subheader,Bandwidth Request Header, Generic MAC Header and 802.16 MAC headers Grant Management Subheader, utilizing the ns-3's header/ Packet API, that, between other characters,which allows the bit-by-bit de-serialization and also serialization of the packet bytes by using the help of the fundamental bytes of buffering.To assist the characterstics like emulation ,the serialized version the data in packet is to be done to equal original networking packets.
DCD/UCD Messages and DL-MAP/UL-MAP Messages
As shown in the figure the format of UL-MAP,DL-MAP, DCD, and also UCD messages. UL-MAP and DL-MAP messages will define the way in to the UL and DL sub-frames to the frame in MAC.The beginning time of the UL frames sub-frames will be indicated by the portion Starting of Time field of the UL-MAP. Which is relative to the starting of the DL of subframe. As shown in figure, UL-MAP and DL-MAP which have a place of specialised data structures,which is called Information elements IE .Each IE Information elements which notify an (set of SSs) SS of an future UL or DL burst or grant. The in depth contents of UL-MAP and DL-MAP IE are given below.
Every DL-MAP IE Information elements which includes, along with others, a CID field identify an set of SSs in case of multicast or broadcast( SS ) that is going to receive the equivalent DL burst, and a Downlink Interval Usage Code DIUC which is indicating the burst profile has to be use to receive the burst. A burst profile defines a set of PHY parameters that the SS must use to recieve or send the packets. UL and DL burst profile are defined in the UCD and DCD, respectively. DL-MAP Information elements IE also including a Start Time to field that which allows SSs which goes into the sleep.
BLOCK DIAGRAM OF PROPOSED WIMAX MODULE
UCD and DCD messages take account of information to the channel as well and pair of the burst profiles. For creating this messages and burst definition the Burst Profile Manager component is accountable.
UCD message which contains the most essential parameters together with the backoff limiting for the strife ranging and the bandwidth requesting process, and amount of the range and the bandwidth apply for transmitting opportunities. DCD message include information which will have the size of the TTG recieve/transmit RTG transmit/recieve Transition Gap, (TTG)Transition Gap and (Receive/transmit Transition Gap) RTG, a no of classified the present frame, and the phase of the framework. The data structure burst profile includes a group of modulation and DIUC/UIUC and a FEC code individually observe the burst profile. In the Wireless PHY MAN-OFDM layer, FEC codes and 7 combinations of modulations are supported .
In the above the four managing messages are explained in the above are all the time sent to the first and fore most burst in the DL of subframe, which have broadcasting messages. In present implementation, In every frame UL-MAP and DL-MAP are being sent in the each and every frame UCD and DCD are being sent on change basis by the simulation of the genuine network where it may up date with time the definitions of burst profiles.. The remaining of the bursts with in the subframe are usual data bursts intended for straight to the self set of SSs( SSs). When an SS(service sublayer) gets a MAP-DL message, it repeats over the DL-MAP Information elements (IEs )to decide whether a DL burst has diverted towards in the particular direction it follows the present broadcasting burst. If so, it gets the burst when the decoding has been done it uses the attributes in the relevant to burst profile. in the same way, like SS gets a UL-MAP representing an UL contribution for it, the SS will begins bye sending its awaiting data like the start beginning of the contribution elapses.
5.3.2 Uplink and Outbound Schedulers
The above standard which defines two different kinds of schedulers. To send from outbound queeues the outbound of the scheduler which chooses packets,and the BS(base station) uplink scheduler that will allocates the bandwidth to the (service sublayer) SSs in the following UL, to permit them to distribute their packets. Classes BSScheduler and SSScheduler implementing the outbound of the schedulers of BS and SS, and the class UplinkScheduler which will implements the (Base Station)BS uplink scheduler. The Base station( BS) Scheduler also called to as Downlink Scheduler that schedules, out of the different connections packets, queues to sent in to the DLÂ_subframe.
Format of the MAC frame and key managements messages
The subscribe station(SS) Scheduler that schedules, outside of the associates packets, queues for sending in an UL contribution which is allocated to it. The UL bandwidth,Uplink Scheduler manages, by using the assistance of Bandwidth Manager, and that schedule the work plan SSs whwre it would be allocated to the UL permits depends on the quality of service(QoS) necessities to their bandwidth requests and service flow(s). Note that the standard is going not define any exact scheduling algorithm for the following schedulers and left it for the decision of the manufacturers.
The Uplink Scheduler and Downlink Scheduler contents of base station(BS) are call up at the entrence of each and every frame of the MAC .These present two schedulers are going to dependable of making the UL and DL of the subframes or the UL-MAP and DL-MAP messages respectively. The Downlink Scheduler which creates the bursts for sending in to the subframe of DL by chosing packets, to queues of all the SSs(subscriber station) registered to the BS(base station). A burst might be having different number of packets for the identical SS (subscriber station) as the burst is being directed in particular direction.
As shown in the given Figure , the BS(base station) enables work plan on queue as per link per SS(subscriber station) basement in its place of maintaining only one queue per SS(subscriber station) or per arranging service model. Due to more expensive computations where it involves the following designing has been preferred more than the later .
later than creation of the bursts, it is going to made a listing of DL- MAP Information elements (IEs), for each and every Information elements( IE) pointing towards to the burst. This advanced creation of DL-MAP Information elements (IEs) are then being used to setup the DL-MAP in the initial burst of subframe of the Information elements DL. The advanced bursts are being sent to the following initial burst. in the same way, the Uplink Scheduler is going to made a listing of UL-MAP Information elements IEs and on the basis of that IE the UL-MAP will be created. The SS Scheduler will invoke each and every point of time then,a UL grant is being allocated to the(s ubscriber station)SS.
5.3.3 Initialization and Network Entry
The initialization phase and the network entry is mainly divided into two different sub-phases, first one is synchronization and scanning and the second is basic ranging. The total phase will be performed by the Link Manager contents of BS and SS.
Scanning and Synchronization
When Once the SS is willing to connect the network, there firstly scanning process will be done then for the suitable channel will be searched by the downlink frequencies.Once The search have been completed immidiately it will be detected by a PHY frame. The next following way is to make synchronization with the Base station( BS). The synchronization phase will be completed when Once SS receives a DL-MAP message and it leftovers synchronized untill it keeps getting DCD and DL-MAP message messages. soon the synchronization is being established, ( subscriber station)SS will be waiting for a UCD message which is to hold uplink parameter of the channel. Once the parameters is acquired, the beginning of the sub-phase of the initialization and networking entry will be completed.
Registration and Initial Ranging
When the synchronization has achieved, the subscriber station(SS) will waits for the UL-MAP messaging which is to trace a unique grant, which is called initial ranging interval, in the subframe of UL. The following grant is being allocated by the base station(BS)Uplink Scheduler at usual intervals of the time, and it becomes always the initial grant if it present. It always the broadcast CID and uses of predefined most robust burst which will be broadcasted , with bit pahese shift keying (BPSK) 1/2 modulation/FEC.At present the interval is setup to the 0.5 ms, however the user will be initiated to alter its value over the simulation of the script.
Starting range of interval is made of more or one transmission attempts. Opportunity is fixed in the case if size, it is being determined by the base station(BS)and that will allows enough of time to throw a RNG-REQ message which has the transparency ,SS learns its size from UCD message. Once it is identified, the subscriber station(SS) will sends a RNG-REQ message following by performing the backÂ-off based strife resoluting process.
The base station(BS) upon receiving a RNG-REQ to represent whether the ranging is going to by indicating with a RNG- RSP message, or signifying the SS to regulate its the timing power/offset parameters. At the similar time the SS Manager attributes adds the subscriber service(SS) in the same database of subscriber service(SSs). The SS Manager parameters is widely used by the base station(BS) for managing subscriber service(SSs) in different of to that operations.
The switch over of RNG-RSP and RNG-RGQ messages will continues up to the ranging is going to reject or accept. Figure shows a very basic set-up of initial ranging phase. Note that original ranging is going to initially accomplished on the advanced definition of initial range of connectivity up to base station (BS) allocates the initial and Primary managing set up to the subscriber service(SS)over the RSP-RNG message. From the beginning of this point subscriber service(SS) will allocates a new (or unicast) range of (basically a UL grant) opportunity , to carry on range of processing.
5.3.4 Connections and Addressing
The whole communication at the point of MAC layer has been carried out in provisions of connections. The standard is going to defines a suitable connection as a single directional mapping among the subscriber service(SS) and base station (BS's) MAC objectives are for the transmission of the traffc. As explained in the standard which defines two different kinds of connections: for transmitting controlled messages management connections to be done and transport
The connections for the transmission of data. A connection will be recognized by a 16-bit Connection Identifier(CID). Classes ConnectionIdentifier and Wimax-Connection in the given Figure that implements the CID and connection, respectively. Note that each and every connection will maintains their own transmitting queue where as packets for transmission on that total connections are being queued. The Connection Manager factors of the base station(BS) is responsible managing and creating connections for total subscriber service(SSs).
There are two management key connections are there which are defined by the standard module, namely the Primary and Basic management connections, where they are allocated and created during the ranging of process to the subscriber service(SS).the whole operating of (SS) the Basic connection is going play an very important role over the connection and also due to all (unicast) DLand grants of UL are steamlined over CID of the basic SSs.In count of managing connections, an subscriber service(SS)might have more or one transporting connections for the sending of data packets as shown Section 3.3.5.
The connections which are associated to the subscriber service(SS) will be managed by the Connection Manager components.As it has defined by the module standard, a connection management is going to be bidirectional,that is a set of uplink and downlink connections is being represented by the identical CID. This unique feature has implemented in a method that one of the connection in DL direction is being created by thebase station(BS) and over the departure of the CID the subscriber service(SS) then with the identical CID identical connection is being created (in UL direction).
Table 1: CID value ranges.
0x000 - m
m+1 - 2m
Transport & Secondary
2m+1 - 0xFE9F
0xFEA0 - 0xFEFE
0xFF00 - 0xFFF9
Note that because MAC is totally connection oriented implementation,before the managing CID are being allocated the address of MACs subscriber service(SS) will be used throughout the initial ranging of the phase.Once it has allocated, transport CIDs and management will be used to address the subscriber service(SS) and also the connections which are individual that are associated to subscriber service(SS). To indicate the connection a packet will be sent on to the CID which is included in the header of MAC. The component of CID Factory (class CidFactory as shown in the Figure 2) at the base station(BS) that will generates distinct CIDs for the all kind of connections. Table 1is listing set of ranges of values for CID for every kind of connection as it has defined by the module standard.
5.3.5 Service Flow Creation
The standard is going to defines a service of flow as an unidirectional stream of MAC- PDUs on the transport of connection that will results in particular quality of service(QoS)requirements. A flow of service is being identified by a Service Flow 32-bit (SFID) ID and which is linked to accurately one connecting transport and parameter set of the quality of service. Classes QoSParameterSet and ServiceFlow as shown in the Figure 2 that is going implement the flow of service and QoS (quality of service)parameter set, correspondingly. For managing and creating the component Service Flow Manager at the base station(BS) is responsible.
The standard is defining that thare are two types of creation of service flow : as the subscriber service (SS)-initiated mechanism here subscriber service SS that requests the base station(BS) to make the flow of service , and as the base station(BS)-initiated mechanism here the base station (BS) robotically makes service flow to the subscriber service of SS. This module is going to implements the basic of the one of the above all the mechanisms. From the following mechanism the user is being permitted to set of connections, for each and every application that she/he will be intended to simulate, a (QoS) quality of service parameter set that will matche to the quality of service(QoS) necessities of the function. When the subscriber service has been SS is being registered, it will send the request (a DSA-REQ message) to the base station(BS), over the predefined quality of service(QoS) set of parameter ,for the creation service flow. The base station BS will examines the functionalities and by assuming to that each type of parameters are being supported,which creates the service flow and transport connection and also that will reacts with the DSA-RSP message.Here the subscriber service(SS) might be starting by using the flow of service receive/sending data.
SERVICE FLOW CREATION PROCESS
This section shows the major steps for the creation process of service flow. To the all DSA messages that are directly sent on the connection called Primary management connection. The Service Flow Manager components of BS and SS have performed entirely for service flow creation process. Multiple flow of service per subscriber service (SS) are being allowed and also for each service flow the above message trade is being invoked for the each of service flow. The each set of service flows should be formed with the identical QoS quality of service parameters for the both receiver and also sender. Here to note that a subscriber service SS couldn't begin data transmission until and unless it has hold minimum one service flow.
5.3.6 Scheduling Services
According to the standard 802.16-2004 defines that the module is going to supports the four types of scheduling services BE ,UGS,nrtPS, rtPS BE. The following scheduling services will perform in the different manner in the connection of how they are going to request bandwidth as well as how that it is granted.Every service flow is being related to accurately one the scheduling of the service, and the quality of service QoS parameter set will connected to the flow of service in fact that defines the following scheduling of the service which is belongs to. Table 2 listing the compulsory (QoS) quality of service parameters that is going defined with the standard that should be accompined by the service of scheduling.
The Uplink Scheduler will calculates the required parameters when a service flow is being created such as the grant interval and grant size which depends on QoS quality of service parameters linked to it.Depending up on the counted interval For the(UGS and rtPS) real-time services the base station(BS) then then it assigned to polls/ grants on standard basis.In the case of non-real-time for the services only (nrtPS and BE) minimum occupied bandwidth is being guaranteed,even after possiable servicing real-time-flows.It is important to know that by the sheduler all of the listed parameters are not being utilized currently. Also one more thing is to note,at present only the flow of service with standered packet size are being supported. As shown in Section 4.3.2, the module standard does not propose any arrangement algorithm to the schedulers.With simple priority based the implemented schedulers is going to work.
Table 2: Scheduling services and suggested parameters.
Minimum Reserved Traffic Rate
Unsolicited Grant Interval
Minimum Reserved Traffic Rate
Maximum Sustained Traffic Rate
Minimum Reserved Traffic Rate
Maximum Sustained Traffic Rate
Maximum Sustained TraÂ±c Rate
First Come First Served(FCFS) algorithm. To get the uplinked scheduling, From highest of the priority scheduling model to the very lowest of the priority one for that priority will be given at the(UGS > rtPS > nrtPS > BE) starting.Based on first Come First Served the priority is given among the flowing of identical scheduling type. For the base station(BS) and subscriber service(SS),the highest of the priority has been given to the management connections and initial ranging,that is broadcast > initial ranging > basic > primary > UGS > rtPS > nrtPS > BE. The below explanation is about brief outline of the implemented scheduling.
unwanted Grant tune-up UGS is has been designed for the sake of real-time functions with standard packet size. It assures the bandwidth on the based of real-time task, by assigning the flow for UL grants based on the regularization. The importamt parameters of this check minimum reserved traffic rate, maximum latency and are tolerated jitter. The highest tolerable delay variation has been specified by tolerated jitter parameter and the forwarding fo packet and maximum delay has been specified by maximum latency . The lowest bandwidth (in bps) that has been specified by the Minimum reserved traffic rate parameter that should be in the reserved for the sake of flow.While arranging up the service flow,these parameters are being supplied by the user.Depending up on the on this parameters, the base station(BS) that counts the interval,which is called as unsolicited grant interval, when the grant has assigned by the service flow.The flow are met by the latency requirement must ensure the status of the traffic by the Downlink Scheduler, whereas scheduling the traffic of UGS.Each and every time the scheduler will be asked for the status, Packets where the latency of the end will be over and being done by the dropped,the queues will be refreshed.
Real-Time Polling Service(rtPS) is being made with change of packet size for the real-time attempt, and is being assured UL grants based on the periodic interval. For the flow of rtPS,the subscriber service will be polled by the base station BS with the help of specially made grant, which is called as the request opportunity,by sending it a bandwidth request has to be sent. The base station(BS) in the given result that assigns required bandwidth in the sufficient frames. Then the size of the grant is enbled by this mechanism, to gather flow's changeable range traffic needs. nevertheless, balanced to rtPS, UGS incurs new transparency because of bandwidth on the request of packets. The important parameters for the rtPS service are minimum reserved traffic rate and maximum latency. The base station(BS), which depends of this parameters, by calculating the unsolicited polling interval(polling interval) and. The Scheduler of Uplink that tells the lowest bandwidth of flow. Same as UGS, the Downlink of the Scheduler ensures that the the flow are met by the latency requirements.
The main dissimilarity between nrtPS and rtPS Non-Real Time Polling Service, latter that has been designed for the non real time applications. Only when bandwidth is available sufficiently on the periodic basis the nrtPS flows will not be polled. The subscriber service(SS) then it point outs the size of the grant through the bandwidth request packet and base station(BS) will responds by allocating sufficient bandwidth only when available. Whatever it may be the base station(BS) that predicts the flow of the lowest bandwidth based on minimum reserved traffic rate parameter through periodically which is the base station (Best Effort)BE service,it has been designed for the least priority the best application as its name suggests.When servicing to the highest flows, the scheduler is going assign the bandwidth only when the more enough of bandwidth is obtainable when servicing to the higher priority flows.For this service no lowest bandwidth is being guaranteed.
5.3.7 Bandwidth Request and Grant Mechanism
For the WiMAX MAC grant mechanism and Bandwidth request are the very important feature while all the three of non-UGS scheduling models clearly ask for for bandwidth by distrubuting a band width requesting of the packet. The grant mechanism and bandwidth request is being implemented over the the Bandwidth Manager components of subscriber service(SS) and (BS). The system works as the following.With the help of BS the subscriber service(SS) with nrtPS,rtPS or base station(BE) flow is being polled by the base station BS, by assigning it to the request opportunity, based on the period.
Directed over subscriber service(SSs) basis of CID that is request chance is generally by the grant of UL.To sending the data packets that couldn't be used however. It has been distinguished from regular UL grants for data to send the bandwidth requests the predefined a large amount robust burst profile is used. The grants size is standard, to send a bandwidth request packet by allowing sufficient bandwidth. A special Bandwidth Request Header request packet is included. To report the base stationBS the requested bandwidth which is in units of bytes, the BR field of this header will be used.
As the subscriber service(SS) which is received by poll, the subsceiber service(SS) Scheduler is going to repeat over the subscriber service(SS's)for the non-UGS flows and also the awaiting packets of the flow, in border of the queue it is going to sets the size of the packet is being set by the BR field. The flow CID has been set by the header. Then the bandwidth requesting packet is to be sent and in subsequent frames the base station(BS) is going to responds by the sufficient allocation.The given figure resolves that the major steps of bandwidth grant/request of the process. With Generic MAC Header that includes the Bandwidth Request Header is equally exclusive. The module standard is going defines a possible piggyback request that is going to permit sending the band-width of requesting with data by the piggybacked.
In our implementation the above feature has not been supported. As discussed above, the bandwidth is at all times requested as per the flow of basis but the granted is based on the subscriber service(SS).In the given grant the SS Scheduler then decides what type of flow has to be send its data.nt. For the rtPS flows and UGS, the scheduler is going utilizes the unsolicited polling interval paramete