Background Of Wimax Network 802.16


Advancement of the technologies has exponentially growing. The backbone of all the advancement is communicational advancement. Since Development of IEEE 802.3 Ethernet the revolution has been stared. Now the most speeding and reliable networking technology has been released to fulfill the end users requirements with the ease of mobility and high quality of the services integrating with best effort and connection oriented paradigm. WIMax IEE802.16 has been developing for achieving the same; it also called 3G communication [1]. The aim of these networks would be to provide multimedia services, such as voice, video and continuous data streams at high data-rates to mobile users in large coverage areas at all times. The architecture for the next generation of wireless networks aims to integrate multiple networks and benefit from the resulting synergy. There are various standardization bodies working towards this vision. Examples include the 3GPP (3rd Generation Partnership Project), 3GPP2, IEEE 802.21 Media Independent Handover Working Group and Network Working Group (NWG). However, to achieve a seamless integration there are several technical challenges that have to be addressed such as mobility management, resource allocation, admission control, protocol adaptation, security, and pricing. On the brighter side, the advances in integrated circuit design and software radio make it possible to implement multiple network interfaces in a single mobile terminal. Such terminals can access different types of wireless and mobile networks, which provide more versatile and flexible access options, making the integration feasible.
1.2 Background of WIMax Network 802.16
The IEEE 802.16 Working Group is the IEEE group for Wireless Metropolitan Area Networks (WMANs) air interface for Fixed Broadband Wireless Access Systems. IEEE 802.16 group was formed in 1998 to develop standards and recommended practices to support the development and deployment of fixed broadband wireless access systems or air-interface standards. The first 802.16 standard was approved in December 2001. it is designed as to use the single carrier physical layer with time division multiplexing.

IEEE-802.16a was an amendment to 802.16. 802.16a was ratified in January 2003 and was intended to provide last mile fixed broadband access 802.16c. In September 2003, a revision project called 802.16d commenced IEEE 802.16d which is for fixed subscriber stations. This project concluded in 2004 with the release of 802.16-2004 which replaced all prior versions including the a/b/c amendments and formed the basis for the first WIMax solution. These early WIMax solutions based on IEEE 802.16-2004 targeted fixed applications, and are referred to as Fixed WIMax. IEEE 802.16e which supports mobility. WIMax devices are created to operate the three different bands 2.5, 3.5 and 5.7 GHz. The physical layer In WIMax uses orthogonal frequency division multiplexing (OFDM) technology and the maximum data rate in WIMax is 70 Mbps. Wi-max is intended to give a higher coverage area of 20 miles. WIMax standard eliminate the problem of last mile and act as an alternative to cable and DSL technologies. Since it support mobile application thats why it is called as mobile WIMax. As shown in Table 1.1 data for WIMax standards.

Parameters 802.16 802.16-2004 802.16e-2005
Status Completed December 2001 Completed June 2004 Completed December 2005
Frequency band 10GHz'66GHz 2GHz'11GHz 2GHz'11GHz for fixed; 2GHz'6GHz for mobile applications
Application Fixed LOS Fixed NLOS Fixed and mobile NLOS

MAC architecture Point-to-multipoint, mesh Point-to-multipoint, mesh Point-to-multipoint, mesh
Transmission scheme Single carrier only Single carrier, 256 OFDM or 2,048 OFDM Single carrier, 256 OFDM or scalable OFDM with 128, 512, 1,024, or 2,048 subcarriers
Modulation QPSK, 16 QAM, 64 QAM QPSK, 16 QAM, 64 QAM QPSK, 16 QAM, 64 QAM
Gross date ratio 32Mbps-134.4Mbps 1Mbs-75Mbps 1Mbps -75 Mbps
Multiplexing Burst TDM/ TDMA Burst TDM/ TDMA/OFDMA Burst TDM/ TDMA/OFDMA
Duplexing TDD and FDD TDD and FDD TDD and FDD

Channel Bandwidth 20 MHz, 25MHz, 28MHz 1.75MHz to 8.75MHz 1.75MHz to 8.75MHz
Wimax implementation None OFDMA as fixed Wimax OFDMA as mobile Wimax
Table 1.1 Basic Data on IEEE 802.16 Standards

1.3 WIMax Architectural Issues
Figure 1.1 shows a Wimax Network Management Reference Model. Wimax uses MIB, which stands for Management Information Base, to store information pertinent to network management.Wimax is used as metropolitan area network wireless connectivity. Wimax provides broadband data access for urban and rural areas. It provides point-to-point links, residential broadband and high-speed business connections. Wimax systems also support mesh networks, allowing Wimax system to forward packets between base stations and subscribers without having to install communication lines between base stations.

Figure 1.1: WIMax Network Management Reference Model
Various architectural issues involved with Wimax like point to point Vs point to multipoint, Los Vs NLOS are discussed in following :
1.3.1. P2PVs PMP
There are two scenarios for wireless deployment: point-to-point and point-to-multipoint.
13.1.1. Point-to-Point (P2P) - Point to point is used where there are two points of interest: one sender and one receiver. This is also a scenario for backhaul or the transport from the data source (data center, fiber, Central Office, etc) to the subscriber or for a point for distribution using point to multipoint architecture. Backhaul radios comprise an industry of their own within the wireless industry. As the architecture calls for a highly focused beam between two points range and throughput of point-to point radios will be higher than that of point-to-multipoint products.
13.1.2. Point-to-Multipoint (PMP) - As shown in the figure 1.1, point-to-multipoint is synonymous with distribution. One base station can service hundreds of dissimilar subscribers in terms of bandwidth and services offered.

1.3.2. LOSVs NLOS
Earlier wireless technologies were unsuccessful in the mass market as they could not deliver services in non-line-of-sight scenarios. This limited the number of subscribers they could reach. WIMax functions best in line of sight situations and, unlike those earlier technologies, offers acceptable range and throughput to subscribers who are not line of sight to the base station. LoS and non-LoS configuration shown in fig. 13.Wimax's ability to deliver services non-line-of-sight, the WIMax service provider can reach many customers in high-rise office buildings to achieve a low cost per subscriber because so many subscribers can be reached from one base station.

Various WIMax types like Fixed WIMax and Mobile WIMax are discussed in following subtopics [2]:
1.4.1. Fixed-WIMax
WIMax provides fixed, portable or mobile non-line-of sight service from a base station to a subscriber station, also known as customer premise equipment (CPE). Some goals for WIMax include a radius of service coverage of 6 miles from a WIMax base station for point-to-multipoint, non-line-of-sight service. This service should deliver approximately 40 megabytes per second (Mbps) for fixed and portable access applications. The WIMax cell site should offer enough bandwidth to support hundreds of businesses with T1 speeds and thousands of residential customers with the equivalent of DSL services from one base station [3].
1.4.2. Mobile WIMax
Mobile WIMax takes the fixed wireless application a step further and enables cell phone-like applications on a much larger scale. For example, mobile WIMax enables streaming video to be broadcast from a speeding police or other emergency vehicle at over 70 MPH. In addition to being the final leg in a quadruple play, it offers superior building penetration and improved security measures over fixed WIMax. Mobile WIMax will be very valuable for emerging services such as mobile TV and gaming [4].


1.5 Challenges in WIMax network
In WIMax there are few important technical areas. They are listed in the followings [5].
Wireless radio channel-wireless radio plays a very important role in Wimax. As compared to other communication channels the signals are protected by the physical medium which is comparably stable and robust. There are certain more factors like obstructions, terrain undulations, relative motion between the transmitter and the receiver, interference, noise created by some other source can affect the radio channel and these factors are more unpredictable. These are the same factors which need to be taken care in WIMax, for example shadowing, multipath fading, inter symbol interference, Doppler spread, Additive white Gaussian noise (AWGN) [5].

1.5.1. Spectrum scarcity:-In WIMax the range of spectrum allocation has a very less as compared to other wireless network. WIMax is designed especially for the need of providing service for increasing number of users and providing flexible applications user services that's why the designers need to use the spectrum more efficiently [6].
1.5.2. Quality of service:-WIMax designed to provide a high range of application. An application can be of different type such as voice, data, video and multimedia. Every application is depend upon the terms like data rate, traffic flow, packet loss, delay and so on. So it is a challenge to rightly balance the resource allocation with various applications and users and another factor the QoS requirement across the wireless link, Quality of service has to be defined for end-to-end users in the network that includes switching a variety of aggregation, switching and routing elements between the end to end users [5].
1.5.3. Latency - Latency is the end-to-end delay of the voice signal from the person on one side of the conversation to the person on the other end of the conversation.
1.5.4. Packet Loss - Packet loss occurs when one or more of these packets are lost during transmission. Packet loss can occur due to network congestion or connectivity errors between end- points. To decrease packet loss in VoIP , the Service Provider should ensure that sufficient bandwidth is available for the given VoIP session regardless of whether it is over a wired or wireless medium [7].
1.5.5. Jitters - Jitter is variation in the order and time in which packets are sent and received. In an attempt to smooth the incoming voice packets, a jitter buffer has been implemented in all modern VoIP deployments.
1.5.6. Mobility:-The challenge for mobility is comes from the fact of handling roaming and handoff process. It is very important thing to find the right way of handling the resource consumption and the performance. The future of WIMax network consist of IP based network so it is also important to define the IP-based mobility management [5].
1.5.7. Power consumption:-Power consumption is another very important issue in the WIMax network. Portability and mobility are key points in power management. The need of low power saving protocols, better signal-processing algorithms, circuit-design with low power and fabrication, and battery technologies with long life are key issues in the field of power consumption. In WIMax there is need to search for power efficient transmission schemes and power saving protocols.
1.5.8. Security:- Security is important feature for any network and it is also play important role in the WIMax. From the user perspective the privacy and data integrity are the essential parameters in security and from service providers perspective they want to prevent unauthorized use of the network resources and provide service per user demand.
1.5.9. Support IP in wireless:-IP-based networking has the advantages of cost and flexibility for supporting more applications and their popularity in the modern communication protocol However challenges are following like efficient bandwidth, more reliability and quality of service. These points should be more precise and more flexible and it should be changes according to the changes in the network.

1.6 Features of WIMax
WIMax is a wireless broadband solution that offers a rich set of features with a lot of flexibility in terms of deployment options and potential service are offerings. Some of the more salient features that deserve highlighting are as follows [5]:
1.6.1. Very high peak data rates: WIMax is capable of supporting very high peak data rates. In fact, the peak PHY data rate can be as high as 74Mbps when operating using a 20MHz wide spectrum. More typically, using a 10MHz spectrum operating using TDD scheme with a 3:1 downlink-to-uplink ratio, the peak PHY data rate is about 25Mbps and 6.7Mbps for the downlink and the uplink, respectively[.
1.6.2. OFDM-based physical layer: The WIMax physical layer (PHY) is based on orthogonal frequency division multiplexing, a scheme that offers good resistance to multipath, and allows WIMax to operate in NLOS conditions. OFDM is now widely recognized as the method of choice for mitigating multipath for broadband wireless.
1.6.3. Adaptive modulation and coding (AMC):WIMax supports a number of modulation and forward error correction (FEC) coding schemes and allows the scheme to be changed on a per user and per frame basis, based on channel conditions. The adaptation algorithm typically calls for the use of the highest modulation and coding scheme that can be supported by the signal-to-noise and interference ratio at the receiver such that each user is provided with the highest possible data rate.
1.6.4. 1.6.4 Support for advanced antenna techniques: The WIMax solution has a number of hooks built into the physical-layer design, which allows for the use of multiple-antenna techniques, such as beam forming, space-time coding, and spatial multiplexing. These schemes can be used to improve the overall system capacity and spectral efficiency by deploying multiple antennas at the transmitter and/or the receiver.
1.6.5. Quality-of-service support: The WIMax MAC layer has a connection-oriented architecture that is designed to support a variety of applications, including voice and multimedia services. The system offers support for QoS parameters such as constant bit rate, variable bit rate, real-time, and non-real-time traffic flows, in addition to best-effort data traffic. WIMax MAC is designed to support a large number of users, with multiple connections per terminal, each with its own QoS requirement.
1.6.6. Link-layer retransmissions: For connections that require enhanced reliability, WIMax supports automatic retransmission requests (ARQ) at the link layer. ARQ-enabled connections require each transmitted packet to be acknowledged by the receiver; unacknowledged packets are assumed to be lost and are retransmitted. WIMax also optionally supports hybrid-ARQ, which is an effective hybrid between FEC and ARQ.
1.6.7. IP-based architecture: The WIMax Forum has defined a reference network architecture that is based on an all-IP platform [12]. All end-to-end services are delivered over an IP architecture relying on IP-based protocols for end-to-end transport, QoS, session management, security, and mobility. Reliance on IP allows WIMax to ride the declining cost curves of IP processing, facilitate easy convergence with other networks, and exploit the rich ecosystem for application development that exists for IP.
1.6.8. Robust security: WIMax supports strong encryption, using Advanced Encryption Standard (AES), and has a robust privacy and key-management protocol. The system also offers a very flexible authentication architecture based on Extensible Authentication Protocol (EAP), which allows for a variety of user credentials, including username/password, digital certificates, and smart cards.
1.7 Applications of WIMax
WIMax has the potential to replace a number of existing telecommunications infrastructures. In a fixed wireless configuration, it can replace the telephone company's copper wire networks, the cable TV's coaxial cable infrastructure while offering Internet Service Provider (ISP) services. In its mobile variant, WIMax has the potential to replace cellular networks. This Broadband technology, which put forward Point-to-Multi Point (PMP) broadband wireless access. It offers both fixed and mobile broadband wireless Internet access with a high range equal to 30 miles, and can transport broadband at around 1 gigabits/sec. WIMax covers large regions such as metro cities, suburban, or rural, supporting mobile broadband Internet access at speeds similar to existing broadband. It also provides the mobility features, i.e., connection to Internet will be always be there even when moving. It permits right to use broadband Internet in high 77.5 miles per hour vehicular speed [8].
Apart from the sheer number of mobile endpoints, a huge number of additional factors also there to pony up wireless and 3G networks more susceptible to attack. Some of them are listed below-
1. Limited wireless link bandwidth: As opposed to most wire line links, 3G wireless links tend to have much lower capacity thus it takes significantly less traffic to overload the link.
2. Signaling overhead: For transferring uniform size (amount) of information or data more controlling messages (signaling/handshakes) are required using existing wireless 3G networks as compared to wired network. For example to the extent to improve the utilization of limited radio resources, a radio channel is allocating policy is dynamic (grant when required) to a mobile or mobile subscriber and it will be revoked after an idleness action (or after a threshold amount of time). Such dynamic channel allocation and revocation (provisioning) procedures precedes lots of signaling operations.
3. Heavy control processing: The hierarchical nature of current 3G (CDMA2000 or UMTS) networks places certain critical system functions such as power control, resource allocation, paging, etc. on a few infrastructure elements. The radio network controller (RNC) and the base stations (BS) are involved in these activities for each mobile. By necessity, the engineering of these network elements is typically based on a certain load profile that is derived from the projected traffic patterns and behaviors of mobiles. Any serviceable discrepancy from design hypothesis may lead to serious pile condition, and probably awkward perversion.
In a nutshell, 3G wireless networks are significantly more fragile than wire line networks. To begin, most of the wire line DoS attacks would still apply to a wireless network. In addition, the above unique vulnerabilities of 3G networks can be exploited by new forms of wireless-specific DoS attacks.
In the article author has dogged about a novel DoS types attack phrase signaling attack, which seeks to overload the control plane of a 3G wireless network using low-rate, low-volume attack traffic, based on some of the aforementioned 3G-specific vulnerabilities. Unlike conventional DoS attacks that focus on the data plane, the signaling attack creates havoc in the signaling plane of a 3G network by repeatedly triggering radio channel allocations and revocations. To accomplish this, an attacker first sends a low-volume pack-et burst to a mobile. If the mobile does not currently have a radio channel, the network will allocate a new one to complete the data transfer. After an inactivity timeout, the radio channel is torn down to recycle it back for others' use and help preserve the mobile energy that will other-wise be wasted on maintaining the channel. Immediately after the channel release, the attacker sends another low-volume packet burst to the mobile so as to trigger another radio channel establishment. By repeatedly doing so at appropriately timed periods, this can generate a consider-able number of signaling operations. As detailed in Section 2, each channel establishment/release requires the RNC and BS to process more than 20 signaling messages. Launching this against large number of mobiles can easily introduce an excessive amount of signaling messages. The potential damage includes (1) overloading of RNC and BS, leading to reduced system performance, (2) denial of ser-vice to legitimate signaling messages due to congestion in the signaling paths, and (3) shortening of the mobile battery life.
Modern Denial of Service attacks produce intrusive traffic (high volume) while in signaling attack can be exploit producing with generating less volume of traffic at slower rate as compared to DoS. Hence, signaling attack can efficiently dodge by applying modern intrusion detection/prevention approach especially via the mechanism of flooding-based DoS attacks detection. To understand the damage caused by the signaling at-tack, suppose that a 3G wireless network has inactivity timeout set to 5 s 1 and that an attacker generates a 40-byte packet burst (e.g., a TCP/IP packet with zero payloads).
Experiments shows that if an attacker sends packet bursts in interval of 5 seconds or large than only 64 bits per second traffic volume has been produced by the attacker, which is undetectable by volume-based recognition systems. In other experiments, suppose if attacker is use a cable modem having 1.5 Mbps uplink bandwidth capacity then it can concurrently attack approximately 24 K mobiles, a number that is sufficient to bring down a wireless network infrastructure.
Note that this signaling attack can also be mounted to other emerging wide-area networks such as 802.16/WIMax that shares the same vulnerability.
The main goal of the proposed system is to detect the Denial of Service (DoS) attack in WIMax Network.
DoS attacks based on Ranging Request/Response (RNG- REQ/RNG-RSP) messages
1. The RNG-REQ message is the first message sent by a SS to BS requesting transmission time, power, and frequency and burst profile information before joining the network.
2. Propose system is providing the solution against DoS (flooding) attack in WiMax network. Proposed algorithm has been divided into 2 segments-
a. Exploiting DoS attack in WIMax for effective evaluation of the DoS- To achieve this two scenario has been consider '
i. MAC layer DoS attack by modifying RNG-RS function design initialization of the SS onto BS.
ii. Transport Layer- Excessive number of small packets has fired towards BS continuously
In summary, the main goal of the thesis is to secure WIMax network against flooding exploitation by unauthorized harmful users.
1.10 Dissertation Outline
This dissertation is organized in six chapters namely including this chapter that introduce the topic and state the problem. The rest of the dissertation is organized as follows.
Chapter 2 gives the description of literature survey.
Chapter 3 gives overview of the WiMax Network and their Countermeasures
Chapter 4 gives the solution of the problem identified during analysis.
Chapter 5 gives the simulation and result analysis comparison.
Chapter 6 concludes the work and gives the direction for future work.

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