International Journal of Research in Advent Technology, Vol.2, No.7, July 2014 E-ISSN: 2321-9637
Vertical Handoff Performance in WLAN Wireless Networks Renu1, Anil Dudy2 Electronics and communication1, 2,Shri Baba Mastnath Engg. college1, 2 Email:renudalal89@gmail.com1, anildudy10@gmail.com2
Abstract- The WiFi handoff setup compares the data traffic received by different APs in the network. Since the initial stations of AP_0 are mobile ones, AP_0 receives data traffic only at the beginning and then at end of simulation when its stations start their tour and come back. Additionally, it receives data traffic when the stations started from south visit its section and get connected to it. In contrast to AP_0, AP_2 has stable stations, so the data traffic received by it does not drop to 0 like AP_0's traffic. As expected, its received data traffic doubles when the moving stations from west and south cross its section. AP_3 is visited by all moving stations at the same time. Hence, its received data traffic is tripled when this happens during simulation. Hence the throughput and delay for the wlan MS is obtained. The vertical handover setup consists of a gateway, application server providing voice service to the wimax BS and to the wlan router. Index Terms- AP, DCF, PCF, LAN, WLAN 1. INTRODUCTION
2. WIRELESS LAN SYSTEM
Communication is always necessary in building relations to mankind, when two persons meet they need some medium to interchange their views but due to distance barriers some tools are required to communicate each other. At the end of 19th century, renowned scientist Graham Bell laid the first stone in the field of communication using different tools regardless of distance. He invented first wired base telephony equipment. It was the solution for the voice communication for the people how far apart they are. After this radio based communication systems Era started. It was an extension of wired based networks.
The Wireless Local Area Network (WLAN) is an unlicensed band of 802.11 ISM frequency band. 802.11 is one of the recent communication technologies of IEEE standard. It specifies medium access control (MAC) and physical layer that is why it is called Wireless LAN. It has three widely used types which operates on different frequency bands. These three types are 802.11a, 802.11b and 802.11g. 802.11a operates on 5 GHz frequency band and it gives the maximum data rate speed of 54 Mbps, which is higher than 802.11b because 802.11b operates on 2.4 GHz frequency band and give the maximum data rate speed of 11Mbps. 802.11b operates. 802.11g is recently developed standards of Wireless LAN. It also operates on 2.4 GHz frequency band and give the maximum data rate speed of 54 Mbps. In 802.11 Wireless LAN standards, the two types of MAC protocols Distributed Coordination Function (DCF) and Point Coordination Function (PCF) are used. Nowadays the most applications available in the markets are uses DCF because it is simple, robust and easy to implement.
In the beginning it was developed for some special purposes like military and police usage. With the passage of time these systems emerged to allow common peoples to communicate with each other, rather than using wired based network. After this the age of faster communication and capabilities of voice get started and evolved into new telecommunication system. The capability to achieve wireless access anywhere, anytime, and anyplace has become common expectation as it provides significant flexibility and freedom in mobility. But to achieve global mobility in heterogeneous networks for any mobile device requires seamless connectivity using vertical handoff. Since none of the existing wireless frameworks provide practical solutions for vertical handoff. End-to-End Vertical Handoff (E2EVH) proposed in this paper offers a new concept to perform vertical handoff between heterogeneous wireless networks. To deliver network services without interruption, E2EVH present a novel design to monitor the network availability, it then picks the best accessible network for application layer [1].
DCF is the basic MAC layer function in Wireless LANs, Which used Carrier Sense Multiple Access technique (CSMA) also with an addition of Collision Avoidance of (CA). It resolves the CA problems of the packets transmitted at the same time. Architecture of Wireless LAN Wireless Local Area Network instigate as an overlay to the Wired Local Area Network. Lightweight and Autonomous are two discrete architectures used in WLAN environment.
7
International Journal of Research in Advent Technology, Vol.2, No.7, July 2014 E-ISSN: 2321-9637 Each of the architectures has wide impact on wired LAN architecture. The selection of WLAN architecture is based on the consideration of building, future proof, integrated wired and Wireless LAN to accomplish high return on investment. Both architectures are popular but Lightweight architecture has plus advantages over the WLAN market. 2.1 Lightweight Model Lightweight is the part of WLAN architecture. With most of wireless intelligence which residing at central controlling device, lightweight Wireless Access Point architecture have narrow functionality.
controller commands the neighbouring WAP to regulate their power level, where as in autonomous there is no concept of the visibility of its WAP neighbouring and in this case to perform self healing it cannot adjust the power level. If single WAP is busy or overloaded then in this situation wireless controller can relieve the wireless client to neighbouring WAP. In critical applications such as VoIP, self-healing and load balancing are important issues. 2.2 Autonomous Model In Autonomous Model WAP is not mandatory as shown in Fig. 2.
Fig 2: Autonomous Architecture Model Fig 1: Lightweight Architecture Model Lightweight model is simple. The devices that provide the communication to the end user as Access Layer are identified by lightweight. Distribution layer provide the inter communication and the top layer (Core Layer) of Lightweight model is responsible fast and consistent data between networks. Wireless Access Point (WAP) resides at the interface of access layer and provides the communication interface to end user. In lightweight architecture model, the management of operation is easy because it give the permission to WAP from single device, because the lightweight WAP have the knowledge of visibility and attentiveness of the neighbours WAPs. They can observe and if any one of their neighbours becomes the victim of fault it notifies the wireless controller. Lightweight WAP may be Self-healing because to pay compensation for unsuccessful counterpart,
Autonomous Wireless Access Point sustains the switching and strong security as well as networking function that are indispensable to route the wireless traffic. As in autonomous system there is no concept of the visibility of WAP so it cannot make the load balancing. Autonomous model cannot differentiate whether nearest WAP is part of WLAN infrastructure or illegal rouge WAP. The difference between the autonomous and lightweight is negligible. The difference is only this that lightweight have one extra component (WLAN controller). VERTICAL HANDOVER Between the heterogeneous wireless networks the handover process can be set apart in to handover execution and handover decision process. In handover decision process both the mobile node and network decides that when the handover process will be occur. After taken handover decision, the handover execution process continues. The handover decision process involves supplementary network information such
8
International Journal of Research in Advent Technology, Vol.2, No.7, July 2014 E-ISSN: 2321-9637 as replica address detection time in Mobile IPv6, when handover decision and detection process overlaps. The handover delay can be alienated in to three main mechanisms. Discovery Time (td) In this process via link layer beacon, the mobile terminal perceive that it is in the under the range of new wireless network from where it get the Router Advertisement (RA) of new access router. Through the RA and triggered-based router solicitation from access router in the visited network, the MT detects the coverage on new network. Address Configuration Period (tc) In this period the MT receive the Router Advertisement (RA) and updates its routing table and assign the new Care of Address (CoA) to all its interfaces. This new CoA based on new access router accessible form RA. Network Registration Period (tr) In this period the binding updates are transmit to Home Agent (HA) as well as correspondent node and collect the acknowledgement from correspondent node. As binding acknowledgement from correspondent node is elective, so we consider the situation when mobile node accept packet from correspondent. Thus an IP level handover consist of td, tc and tr. This recommended that by optimizing IP-level vertical handover delay would really involve minimizing the discovery time and network registration period, where as address configuration period based on mobile device computing potential.
3. Simulation results Horizontal handoff in WiFi network This scenario shows the mobile station performance during horizontal handoff (roaming) between eight APs while the MS is moving in clock wise direction. This scenario shows WiFi wireless technology. This scenario also comprise one video conferencing server, one client connected to the server via L3 switch and wlan stations surrounding the access points. STA_0, STA_1, STA_2, STA_18, STA_19, STA_20 are roaming at a speed of 30 m/s around the access points and rest all stations are stationary. All the links used here are 100 BASE T links. The MS is roaming from AP0 to AP7 at the speed of 1 m/sec. The throughput of the MS that is stable between 10k – 20k bit/sec. But the throughput drops down during the handoff. The maxim delay points are 0.040 sec., which is considered to be tolerable for most applications.
Fig. 3 : Set–up of WiFi Handoff Table 1 : Wireless LAN Parameters (for mobile node) BSS Identifier
0
Access Point Functionality
Disabled
Physical Characteristics
Direct Sequence
Data Rate (bps)
11 Mbps
Transmit Power (W)
0.002
Packet ReceptionPower Threshold (dbm)
-95
CTS-to-self Option
Enabled
Short Retry Limit
7
Long Retry Limit
4
AP Beacon Interval (secs)
0.02
Max Receive Lifetime (secs)
0.5
Buffer Size (bits)
256000
Roaming Capability
Enabled
Large Packet Processing
Drop
Initially due to set up time, the delay is more. Then the mobile node and the stations start roaming around the access points and hence the delay is almost constant. Then after 9 minutes there is small increase in the delay which is again due to the non
9
International Journal of Research in Advent Technology, Vol.2, No.7, July 2014 E-ISSN: 2321-9637 availability of stations. (bits/sec). The simulation time is 10 min. The throughput drops during handoff.
Fig 4 : Throughput and delay for MS in the WiFi set-up Wlan Backbone OPNET WLAN models support wireless-LAN backbones that consist of routers with WLAN interfaces belonging to the same BSS. These backbones can serve to WLAN EBSSs as well, where they are connected to the wireless backbone via their access points like they would be connected to a wired backbone. This scenario is built to provide an example on configuring such networks.
Fig 5 : Wlan network with wireless sever, router, wireless clients The network contains wireless FTP clients and a wireless FTP servers. The clients and server belong to different wireless- LANs, BSS 0 and BSS 1, respectively. These two LANs connected to each other with two routers. These routers, which have two WLAN interfaces, serve as the access points for
BSS 0 and BSS 1 and also compose the WLANbackbone, which is the BSS 2. To achieve this, among the two WLAN interfaces of Wireless Router 0, the first interface, IF0, was configured as an access point and its BSS ID was set to 0. The access point fuctionality of the other interface, IF1, was disabled and its BSS ID was set to 2. The second router was also configured similarly. Hence, IF0s on the routers became the access points, and IF1s were connected to the backbone. The backbone-LAN, BSS 2, does not have an access point and doesn't need to have one, though it is possible to configure one of the backbone interfaces as an access point. Additionally the physical layer technology used by IF1s on the routers are set to "OFDM (802.11a)" to enable 802.11a data rates and their data rates are set to 54 Mbps. In other words, BSS 2 deploys the 802.11a PHY, while BSS 0 and BSS 1 use 802.11/11b PHYs. FTP client 5 is moving at a speed of 1 m/s in the defined trajectory path. While all other clients are stationary. Two routers form a wireless backbone network. FTP server, wireless router 1 is in one BSS, wireless router 0 and wireless router 1 are in other BSS, the FTP clients and wireless router 0 are in another BSS. Table 2 : Wireless LAN Parameters (for Wireless FTP clients) BSS Identifier
0
Access Point Functionality
Disabled
Physical Characteristics
Direct Sequence
Data Rate (bps)
2 Mbps
Transmit Power (W)
0.005
Packet ReceptionPower Threshold (dbm)
-95
CTS-to-self Option
Enabled
Short Retry Limit
7
Long Retry Limit
4
AP Beacon Interval (secs)
0.02
Max Receive Lifetime (secs)
0.5
Buffer Size (bits)
256000
Roaming Capability
Enabled
Large Packet Processing
Drop
10
International Journal of Research in Advent Technology, Vol.2, No.7, July 2014 E-ISSN: 2321-9637 The performance of all the wireless FTP clients is observed and graphs obtained for delay, throughput and traffic received, traffic sent for the FTP clients. Since the FTP data is sent and received in the form of packets, hence the graphs show various sharp peaks. Simulation time is taken as 4 Minutes.
Fig. 8 : Delay and throughput for FTP client 2
Fig 6: Traffic received and traffic sent (packets/sec) for FTP client 5
Fig 7 : delay and throughput for FTP client 5
Fig. 9 : Traffic received and traffic sent (packets/sec) for FTP client 2
The differences in the delay, throughput of FTP client 5 and FTP client 2 can be easily seen from the above graphs. As we know that FTP client 5 is roaming in BSS 0 following some defined trajectory, while FTP client 2 is stationary as all others are. And hence the traffic received (bits/sec),
11
International Journal of Research in Advent Technology, Vol.2, No.7, July 2014 E-ISSN: 2321-9637 traffic sent (bits/sec), delay (sec), throughput (bits/sec) is different for them.
[3] Carlos de Morais Cordeiro, Dharma Prakash Agrawal ,Ad-hoc and sensor networks theory and application, World Scientific publication,2006. [4] L. Pomante: Wireless Sensor Networks, Seminar in Wireless Communications -University of L’Aquila, March 2007. [5] Shah, T. ; Javaid, N. ; Qureshi, T.N., "Energy Efficient Sleep Awake Aware (EESAA)intelligent Sensor Network routing proto col”, International Multitopic Conference (INMIC), , Page(s): 317 – 322, 2012. [6] W. Heinzelman, A. Chandrakasan, and H. Balakrishnan, “Energy-efficient routing protocols for wireless micro sensor networks,” in Proc. 33rdHawaii Int. Conf. System Sciences(HICSS), Maui, HI,Jan. 2000
Figure 10: Delay and throughput for the Wireless FTP Server
From the above graph it is clear that the set up time is more than 1 minute, after which the FTP data packets transmission starts. Results saved with the scenario indicate the FTP traffic successfully flowing over the WLAN backbone between the wireless clients and server. 4. CONCLUSION The vertical handover setup consists of a gateway, application server providing voice service to the wimax BS and to the wlan router. Initially both the mobile nodes are placed near the wimax BS from where they start roaming towards the wlan router. As they reach near the router, the wimax throughput is reduced and the WLAN throughput starts increasing which depicts vertical handoff triggering properties. The graphs for throughput and delay are obtained as expected. REFERENCES [1] Di Tian ; Georganas, Nicolas D., et.al. "Energy efficient routing with delivery in wireless sensor networks”, IEEE Wireless Communications and Networking, Vol: 3, Pag: 1923 – 1929, 2003. [2] El-Hoiydi: On the Lifetime of Wireless Sensor Networks, IEEE Com- munications Letters, Vol. 9, No. 11, November 2005.
12