IMPLEMENTATION OF A PACKET PRIORITY AND FIFO QUEUING MODEL IN PACKET RADIO SYSTEM

Transcription

1 IMPLEMENTATION OF A PACKET PRIORITY AND FIFO QUEUING MODEL IN PACKET RADIO SYSTEM H. Lami 1, A. Affandi 2 1, 2 Department of Electrical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember s: hendrolami@yahoo.com 1, affandi@ee.its.ac.id 2 ABSTRACT Packet radio is a method that will encode text as binary data and transmit over radio channel. The successful transmission depends on several conditions such as the technical standards of the hardware, the protocol access, and software of the packet interface. The focus of this paper is to achieve a new solution to manage multi user activity of the amateur packet radio gateway. In this works, all terminal are assumed to share a common radio channel and to be within range of VHF mode and in line of sight of a receiver station. KISS mode is used to implement p-persistent CSMA. This work uses a mysql database with delphi to design GUI for data transmission beetwen node and gateway. Web services with Mysql and PHP are being adopted in this works to solve the problem when a node needs to get data from another gateway. By using mysql as a database server in the gateway, message from multi user can be replied or forwarded to another destination, ordered by Priority packet or FIFO model. Keywords: FIFO, Packet, Protocol access, KISS mode, VHF mode, p-persistent. 1 INTRODUCTION Packet radio system has benefits to amateur packet radio communities. However, it has long been problem in management of multi user data traffics in such a system. In this system, TNC (Terminal node controller) allow computer user to send information to another computer based on AX.25 mode in local area. The AX.25 TNC mode with 1-persistent carrier sense multiple access (CSMA) protocol cannot give a solution for multi terminal access related to packet collision and capacity of the system. In a term to solve the problems, p-persistent protocol is added to the kiss TNC. In this new protocol, all stations use P- Persistence method to decide when to send their data resulting in lower probability of data collision in the system. P-persistent CSMA is also proved for giving a better maximum capacity than 1-persistent method does [1]. Another alternative is to set a fixed transmission time slot for each node. Thus, for example, station A could transmit during the first time slot, Station B during the second time slot, and so on. In the technique a minimal interference will occur but the throughput will go down when some nodes do not have a packet to send but then time slots are still given to them [2]. In this paper, we suggest another solution to packet radio problem ( how to manage data from node and sending to another destination ) by combining KISS TNC as a simple Host to TNC and software approach. We use Delphi, PHP, and Mysql database to design GUI data transmission and web services. 2 MODEL AND IMPLEMENTATION In this section, we describe the theory, design model, analysis, and implementation of our system. 2.1 p-persistent CSMA In a random protocol multiple access, all terminals shared a single channel to transmit and receive packet data from each other. P-Persistent CSMA is a random access protocol [3]. By using this access technique, each terminal has capability to sense channel with random value p between (0, 1). This algorithm works as follows: 1. If channel is sensed idle, node transmits packet data with probability p, 2. With probability (1-p), node delays to transmit packet by τ seconds. If at this time, the channel is detected idle, the process is repeated to first step. Otherwise, node must wait and reschedule the transmission packet according to retransmission delay distribution. 15

2 16 The 5 th International Conference on Information & Communication Technology and Systems For given offered traffic G and given value of the parameter p, the throughput S can be determined as [3] [4] (1) In Table 1, Kleinrock and Tobagi summarize that the maximum achievable throughput of p-persistent CSMA will increase when value of p is small. Table 1 describes that p-persistent CSMA value has maximum capacity for p = Table 1. Maximum Capacity of random access protocol Protocol Capacity Pure Aloha S-Aloha Persistent CSMA Slotted 1-persistent CSMA Persistent CSMA Non-Persistent CSMA Persistent CSMA Slotted Non-persistent CSMA Perfect Scheduling Priority In this method, Gateway gives priority for a packet data based on its port, IP address, arrival time, or sub-net. If the traffic on the gateway is high, high priority messages will be processed, while the other will be put into the queue or discarded. Priority packet method is applied to the most suitable internet connection that has a narrow bandwidth. 2.3 System Model The goal of our research is to manage multi user traffic activity on the gateway. In our design, the gateway will handle messages from nodes and store messages into buffer queue. We apply FCFS technique and priority packet in our system. We describe our system model in Figure Traffic Model In the previous section, we identified the system protocol p-persistent CSMA. Here we characterize the traffic source and its assumptions to handle congestion of multi user traffic FCFS First Come First Served (FCFS) is a method for handling multi user traffic activity. When users need gateway forwarding their messages to another user, gateway will store message in its buffer (data stored). The first data in the buffer will be the first data to be sent. Service time and inter arrival time in FCFS are exponentially distributed. FIFO method is become to the appropriate internet connection with medium bandwidth, to avoid the bottleneck on the network LAN. This method is applied to our queue system model to send message from gateway to node in coverage area, or vice versa [5]. Figure 1. Packet Radio System Model Mesh topology is used in our system. We assumed, this topology is the best communication network in our case and a good way of getting the traffic to its destination. Under the concept of KISS (keep it simple stupid), there is no central computer and all computer will display status of any single item in the database. Packet data will be transmitted and received in mode error free but without acknowledgment. Implementation of p-persistent CSMA to TNC allows users to request channel communication in mini slots time. Persistence method in KISS mode works as follows [6]:

3 A03 - Implementation Of A Packet Priority And Fifo Queuing Model 17 In Packet Radio System - H. Lami 1. TNC begins monitoring the carrier and detecting signal from modem. It waits indefinitely for this signal to go idle and ready to use. 2. When the channel is idle, the TNC generates a random number between 0 and 1. IF the number is less than or equal to parameter p, wait 0.01 * TXdelay second. Moreover, transmits all queued frames. If all packet is sent, channel goes back to idle state 3. If the random number is greater than p, The TNC delays 0.01 * slot time second and repeat the procedure beginning with the sampling of the carrier detect signal. To guarantee communication between node and gateway, each host computer has a buffer to store message before being sent. 2.4 Design and Implementation Design and implementation are the most important in our works. We split our work in five steps as describe in Figure 2. Message Frame structure design Installation and configuration (4 byte), Flag (1 byte), Data ( byte), Check Sequence (1 byte), and End of frame (1 byte). Table 2. Message Frame structure ID User/ group SRC DST GW Flag Data Check Sequence Endof frame The next step is to implement Request to Send (RTS) and CTS (Clear to Send) between Modem and host computer. The algorithm of this method is shown in Figure 3. connect To Server Server Listening Server Connect to Sending Message GUI DESIGN For transmitting and receiving message P-Persistent CSMA Implementation (KISS Mode) Connect to Server Disconncet Figure 3. RTS/CTS between modem and Host Simulation transmit and receive message Start Figure 2. Design and Implementation Init serial port Message frame structure is depending on mode of TNC. For all modem in 1200 bps (VHF mode), we start with the combination that produces about maximum 128 character outstanding at one time [7]. By using KISS mode we can transmit message. We modified frame structure consist of ID USER/Group (3 byte), Source (3 byte), Destination Rx. timer start Stop Figure 4. Main program

4 18 The 5 th International Conference on Information & Communication Technology and Systems We solve the RTS/CTS problem by designing GUI transmit/receive message using Borland Delphi programming language. T-serial component on Borland Delphi can connect host computer and serial interface (RS-232). The flowcharts of designing GUI for transmit receive packet are described in figure 4, Figure 5, and Figure 6. Figure 7 and Figure 8 show the screenshots of the designed GUI. The database is useful for managing the traffic in multiuser activity Start Have data Figure 7. Receive message GUI Read serial Save data with procedure FIFO T End of frame Y Get frame from FIFO buffer define frame as data (source, destination, via, flag, data) Show data Stop Figure 5. Receive message Start Get data from gui Data Format Sent to modem Figure 8. Send message GUI For storing message on mode transmit and receive, we create a data base mysql structure to our GUI design. Gateway use database for serving when nodes need information. The database structure is shown on table 2. Table 2. Database structure ID Src Dst Lon Lat Prior message Rxt This database is useful for us managing traffic in multi user activity. We can order database by priority and Rxt (FIFO). Stop Figure 6. Transmit message 3 RESULT Based on the previous section, our system can transmit and receive packet by using designed GUI. Figure 9 shows the result of transmitting

5 A03 - Implementation Of A Packet Priority And Fifo Queuing Model 19 In Packet Radio System - H. Lami packet between two nodes and gateway in a local area network. Figure 11. Priority and FIFO implementation Figure 9. Communication between node and gateway in Local area The maximum delay transmission in the local area network is 1.95 seconds for the packet length of 128 bytes. The result of delay in our simulation is shown on Figure 10. Figure 10. Time utilization For internetworking, we define a packet priority in three tree condition, Low priority, High priority, and Emergency. All conditions can be ordered from database. If a gateway wants to serve nodes, it can access and use the databases. The Gateway can serve nodes by priority or FIFO condition. Figure 11 shows the implementation of priority packet and FIFO to connect all gateways. We design web server with Mysql and PHP. 4 CONCLUSION AND DISCUSSION. Packet radio systems have benefits to amateur packet radio communities. The software approach can give a new solution to manage multi user traffic. By implementing MySQL database on GUI under Delphi and web server with PHP, we can handle the data traffic ordered by packet priority and FIFO. The result of our simulation in local area network shows that the maximum delay maximum is 1.95 seconds for the packet length of 128 bytes. REFERENCES [1] Tanenbaun, Andrew S, (1981) Computer Networks. Prentice-Hall, pp [2] Tobagi, F. A. (1974) Random Access Techniques for Data Transmission over Packet Switched Radio Networks. Phd Thesis, Computer Science Department, UCLA. pp

6 20 The 5 th International Conference on Information & Communication Technology and Systems [3] Kleirock, Tobagi (1975) Packet Switching in radio channels: part 1-carrier senses multiple access modes and their throughput-delay Characteristics 23: [4] Lam S, Kleinrock (1975) Packet Switching in a Multi access Broadcast Channel: Dynamic Control Procedures, IEEE Trans 23: [5] Tobagi, (1980) Multi Access Protocols in Packet Communications Systems, IEEE Trans. Com, 28: [6] Chepponis M (1997), the KISS TNC: A Simple Host-to-TNC Communications Protocol. ARRL 6 th Computer Networking Conference, Redondo Beach CA [7] MFJ Enterprises, INC (1994), MFJ TNC2 Data Controller, System Manual. MFJ Enterprises, INC.