Exploration and Reform on TCP/IP Protocol Analysis Experiment Under Simulation System

Abstract

TCP/IP protocol architecture is complex and difficult to understand. In addition to classroom teaching, practical teaching is also very important.The paper introduces protocol simulation system into practical teaching,illustrates analysis examples of ICMP,IP and ARP packets run under the system and stresses the important roles the system plays on theoretical teaching. Importance of TCP/IP Protocol Experiment Course TCP/IP protocol is the suite of communications protocols used to connect hosts on the Internet and provides the most basic mechanism for computer network to achieve its functions. A large number of abstract and complex protocols run at all levels in the computer network architecture,so it is very difficult for students to understand and master the contents only through theoretical teaching.How to improve experimental teaching of TCP/IP protocol by building a simulation platform for network protocol experimental teaching,which enables students to better understand, validate and consolidate classroom teaching contents and enhances their perceptual knowledge on network protocol and thereby cultivates their ability to integrate theory with practice is a problem to be solved. To experiments of the TCP/IP course is Computer Protocol Simulation System from JLCSS applied.Through the system,students can visually observe not only transmission of data streams across the network and protocol conversations,but roles protocols from different levels play in one communication,which enhances students ' understanding of protocols and improves their ability to analyze and solve problems. Simulation Platform Introduction Components. The simulation platform is composed of two functional softwares:Simulation Editor and Protocol Analyzer.  Simulation Editor Simulation Editor is used to visually edit some protocol packets of TCP/IP,and after that send them to network.  Protocol Analyzer Protocol Analyzer is responsible for capturing frames in the network and analyzing protocols contained in the different layers.It includes two functional modules: Conversation Analysis and Protocol Analysis.  Conversation Analysis can add captured data frames of commonly used protocols to the list of sessions and shows session sequences and data transmission directions,which enables students to observe and analyze a full session visually and understand in-depth protocol principles and working process.  Protocol Analysis incoudes the display of outline codes, detailed decoding and initial data,which provides detailed explanation and description of protocols and dynamic tracking display depending on choices so as to analyze data easily. Experiment Form. Experiment form is to divide hosts into groups.Each group consists of six hosts 3rd International Conference on Science and Social Research (ICSSR 2014) © 2014. The authors Published by Atlantis Press 188 marked A,B,C,D,E,F respectively.There are three topology available for experiment environment.In each topology,six hosts can edit and capture packets acting as different roles to show working process of TCP/IP protocols. Protocol Analysis Teaching Examples Applying Simulation System ARP is an auxiliary protocol of IP.When a packet reaches a node,IP will select the path for the being transmitted packet based on its destination IP address to get IP address of the next node.At this point,ARP is responsible for resolving the IP address of the next node into MAC address provided for the frame formed on the layer of data link. It can be seen from this process that ARP acts as a connecting bridge between network layer and data link layer.Studying ARP,students are able to understand the roles played by MAC address and data link layer in the network communication. This section should be taught by associating it with routing table that describes how IP packets are passed from the perspective of network layer,whereas ARP reflects at a certain extent how data frames are passed at the data link layer.The combination helps students have a relatively complete understanding of the roles IP address and MAC address play during the network transferring and thereby understand the meanings of network layer and data link layer.In addition, specific experiment can be used to verify this combination of two points. With regards to this, a verification experiment is designed with the second topology simulation platform gives,which is shown in Fig 1. In the topology,Host A,C and D are in the same subnet (172.16.1.0/24),and Host E and F are in the same subnet(172.16.0.0/24).Host B with two network interface cards functions as a router connected to two subnets after routing configuration. Now Host A(172.16.1.2) Ping Host E (172.16.0.2).Since Ping is the application of ICMP,the Ping packet is first encapsulated as ICMP packet and in turn encapsulated as IP packet (shown in Fig.2),and then makes routing according to the routing table of Host A(as shown in Fig.3).Due to A and E in the different subnets,A is not able to directly transfer the IP packet to E.After referring to the routing table, A learns that the packet should be transmitted to the router's interfaces b1 (172.16.1.1). As for specific transmission,the IP packet requires encapsulating in the frame with the corresponding MAC address of 172.16.1.1 as its destination MAC address.Next, ARP is needed to play the role as a bridge.Given that there is no mapping of MAC address to 172.16.1.1,ARP needs to send a request packet(shown in Fig.4) in which MAC address(008899-000495),IP address(172.16.1.2)of Sender A,and Destination MAC address(000000-000000),IP address(172.16.1.1)are specified respectively. Fig. 1 topology structure