Supervisor : Cem Ersoy
Mehmet Yunus Dönmez
Sinan Işık
Netlab

 

Introduction:

         WIDE systems provide wireless information services to the clients in their isolated coverage areas. Clients with their wireless capable PDAs or Laptop computers receive the information, which are requested prior to or at the time of passing through the coverage area of an WIDE, without any user intervention. These data can be local maps or restaurant lists related to the local area of the WIDE, or information about courses or announcements in a campus of a university. It can also be information of general interest such as news articles, music or movie fragments. We define such type of information that can be requested by multiple clients at the same time as popular data. The aim is fast delivery of popular data to multiple recipients simultaneously while they are residing in the coverage area.

System Components:

         WIDE system is composed of four main elements:

  1. WIDE Cluster Controller (WICC)
  2. WIDE Server (WIS)
  3. WIDE Client (WIC)
  4. WIDE Access Point (WIAP)

         WICCs and WISs are desktop machines with powerful CPUs and high capacity RAMs, running Windows 2000 operating system.

         WICs are handheld PCs running Windows CE operating system or laptop computers running Windows 98,2000 or XP operating systems. WICs are made wireless capable with 802.11b PCMCIA cards or they have built-in capability.

         WIAPs are wireless access points (WAP), which supports IEEE 802.11b standard and they provide wireless networking services to mobile hosts in a limited coverage area with high bit rate (11,5,2,1 mbps), low cost and low power consumption.

         In NETLAB, with the aim of providing a wireless platform for experimental studies of MAST (Mobile ApplicationS Testbed), a WLAN is constructed by locating WAPs to appropriate places on Computer Engineering Department building to enable full wireless coverage. WIDE project uses this infrastructure.

         There are two network interface cards on each WIS, one is connected to WICC via LAN and the other is connected to WIAP(s). Multiple WIAPs can be connected to an WIS but an WIAP can be connected to only one WIS. Service Area (SA) of WIS is defined as the total coverage of WIAPs that are connected to that WIS.

Service Scenario:

         Since the duration of residing time of an WIC in a SA can be very short (1-5 seconds) the data must be on WIS and data transfer must be in electronic processing speed instead of user-computer interaction speed.

         Currently as an information service we only support file transfers. Our data items are files categorized with respect to their subjects. In a typical service scenario the client application on your PDA or laptop discovers that user is in the SA of an WIS by listening broadcast messages sent by WIS to a specified broadcast port.

         When WIS announces the authentication period WIC authenticates itself to the WIS by sending encrypted authentication information to authentication port of WIS. Authentication information includes user id and password. WIS transfer this authentication request to WICC and WICC decrypts this information and compares it with the records in UPD (User Profile Database). If user authentication information is correct, WICC controls UPD and learns the registered services by the user and informs WIS about the related data items to be prepared to send to the client. WIS schedules the transfer sequence of these data items. Data items of the services, which user has registered previously, are automatically downloaded to user device. New registration requests are also transmitted to WIS and related data items are downloaded automatically to user device.

         Users create their registration requests, in or out of SA by using the TOC GUI on client-side application. WIS transfers these registration requests to WICC and WICC updates UPD for that user.

Security:

         Security is provided by using MD5 and RC2 algorithms for key generation and ciphering method. Each user in the system has a unique user key. This key is known by the client application and WICC. This key is recorded in UPD. Client application sends authentication information encrypted using this key. WICC decrypts this information and if information is valid, the session key of the corresponding WIS is sent to client encrypted by user key. Following data transfers from WIS to client are encrypted using this session key and data transfers from clients to WISs are encrypted using user keys.

Reliable Data Transfer:

         Since aim in WIDE system is to deliver popular data to multiple recipients we used IP Multicast for data transfer. IP Multicast is supported by UDP transport protocol, which is unreliable. Reliability of UDP protocol is provided at the application layer. The packet loss and error rates are high in wireless environment so some error correction mechanisms must be used. In WIDE systems data packets are coded using FEC (Forward Error Correction) mechanism. In this mechanism files to be delivered in k packets, delivered as n (n>k) packets of the same size. If the recipient receives any k packets, it can construct the file using FEC encoding mechanism. We also use Data Carousel technique. Main idea of this technique is to deliver packets more than once. These mechanisms can be applied one by one and also together. A third mechanism involved in the system is the rerequest mechanism. If any data item cannot be constructed by these mechanisms then that data item is rerequested by the client to be able to capture the missing packets.

Application Areas:

         One of the application areas of WIDE System is campus environment. In a campus course notes, course web pages, problem solutions, exam results, announcements, and other services supplied by student clubs can be delivered to clients in the campus environment by placing access points to building entrances or to proper places that many recipients can be served.

         Another application area of WIDE system is traffic lights. By placing access points on the traffic lights in a city, we can deliver services to pedestrians and cars waiting for the green light, such as local information, road and traffic conditions, local maps (having information about shopping malls, cinemas, museums, etc. on it).

         Film festivals may also be considered as an application area for WIDE systems. By placing the access points to cinema entrances or the places where the number of festival visitors expected to be high, we can deliver movie intros and fragments, schedules and recent announcements to visitors.

Future Work:

         We want to give location based information services to clients. For this purpose we need to find the physical location of the client. Another project in NETLAB named "WLAN Tracker" implemented by Can Komar provides location information. As a future work we will integrate our project with Can Komar's project and give location based information services.

         We also want to vary our services. Currently we only give file delivery services. We plan to give services such as Music and Video Streaming, E-Mail transfer, web page transfer requiring special coding and security issues.

Documents :

         Technical report

         Presentation prepared for NETLAB weekly seminars