- Purpose:
The purpose of this SRS is to help protocol developers understand and use the PSANS tool.
- Scope:
The PSANS tool is being developed as a testing platform for protocol developers. It is meant for CIS725 students and anyone who wants to learn how to develop protocols as well as study existing protocols. The developer, having implemented their own protocol, can attach their stack to the NCARD module.
- Definitions:
- PSANS - Protocol Attachable Network Simulator
- NCARD - The Network Card Simulator for the PSANS tool
- NCILIB - The Network Card Simulator Interface Library
- Bus/Broadcast
Network - A network environment where
a single channel is shared by multiple
machines.
- Computer Networks - One or more computers which are connected together to allow for sharing of data and/or resources.
- Physical Layer - A layer of the protocol stack, which deals with the transmission of raw data bits over a network connection.
- Physical Medium - The actual fiber and hardware which connects nodes of the network.
- Point-to-Point
Network - A network environment made
up of many cables, where each wire
connects two machines.
- References:
- Comer, Douglas E, Internetworking with TCP/IP. Vol. 1. 3d ed. New Jersey: Prentice Hall, 1997.
- Fitzgerald, Jerry, and Alan Dennis, Business Data Communications and Networking. 5th ed. New York: John Wiley & Sons, Inc., 1996
- Holzman, Gerard J, Design and Validation of Computer Protocols. New Jersey: Prentice Hall, 1991.
- Hughes, Larry, Introduction to Data Communications: A Practical Approach. Maine: Jones and Bartlett, 1997.
- Tanenbaum,
Andrew S, Computer Networks. 2d ed.
New Jersey: Prentice Hall, 1988.
- Overview:
The remainder of this document will explain the use and requirements of the PSANS tool.
- Project
Perspective:
PSANS is a non-graphical tool consisting of 2 parts: the NCARD module, and the protocol stack of the user, including calls from the NCILIB.
- Project Functions:
The main function of the PSANS tool is to provide an educational tool, which allows protocol developers to test their stack out on a simulated physical layer of a network environment.- The developer launches the NCARD module.
- The developer then launches their protocol stack module (one copy for each node on the network).
- The developers protocol stack "attaches" to the NCARD module using the NCILIB's attach command.
- The
developers protocol stack can then send
or receive data through the NCARD module
utilizing the NCILIB's send or receive
commands.
- User
Characteristics:
The initial target user of the PSANS tool is a student in CIS725, though the use of the tool is not limited to this group. Users of the tool are expected to be programmers with a firm understanding of network protocols.
- Constraints:
The PSANS tool is being developed purely for educational use. It is meant as a tool for understanding and exercising the theories of protocol development. The system is not meant for commercial use of any kind.
- Assumptions and
Dependencies:
The PSANS tool is being developed for the Unix operating system. The system will require the use of multiple nodes to create the network environment. The user, therefore, will need access to multiple terminals in one location. Alternatively, if a workstation is available, the user may have multiple windows open to achieve the same results.
There will be two differnet versions of the PSANS tool. The first is a compiled version written in C++. This must be run on the Unix platform. The second version will be a JAVA version. This version will be able to run on any machine which is capable of running a JAVA program.
At the current time, there is a prototype, PStack, which has been written for PSANS. It is currently in use by the 725 students. Based on their results, the direction of this project may change.
- Apportioning of
Requirements:
Future Releases of the PSANS tool will include a C++ version of the NCARD module, as well as the NCILIB, which is written using Winsock. This will allow developers the choice of developing their stack on a UNIX system, PC system, or a combination of the two.
- Topology File:
The topology file is a text file, which maps out the network architecture. This file should list all the nodes on the network. It should also list all of the lines connecting the nodes and their capacity. It also should tell what kind of connection the line is. The file also will contain the loss and reorder probabilities for the network. Appendix 1 shows a sample topology file.
- NCILIB:
NCILIB is a library of method calls, which allows the developers protocol stack to communicate with the NCARD module. This library will consist of 3 main calls. These calls are send, receive, sense, and attach.
The attach method will take care of connecting the developers protocol stack to the NCARD module. It will open a TCP socket connection to allow for packets to be exchanged between the two modules. The use of this method allows the system to handle the network connection, so the developer does not hat to worry about setting up these connections. This also allows the system to "hide" the connection, which gives a more realistic feel to the developer. The attach method will also setup the receive and command buffers to store the incoming messages. The final thing the method does is to start the receive thread.
The sense method will be used by protocol stacks which are connected to a bus. This method will allow the stack to check the line to see if there is a message on the line or not. It will return a Boolean value which reflect the status of the line.
The other two methods are the send and receive methods. These are the methods that are used by the developer to place packets on, and to get packets off of the network.
- NCARD Module:
The NCARD module is the heart of the PSANS tool. This module represents the network card and the actual fibers, which carry data in an actual network environment.
The PSANS tool will allow for both Bus and Point-To-Point architectures. The module reads the topology file. It will make a decision as to what mode it is acting in. If all the connections, listed in the topology file, are Bus connections, then NCARD will be in the BUS mode. If all connections are Point-To-Point, then it will be in the PTP mode. In the case where the topology file contains a combination of both types of connections, the NCARD module will be in the BOTH mode.
NCARD will now create a series of buffers based on the information read from the topology file, and the mode it is in. If the module is in the BUS mode, there will be a receive class for each bus. This class will house information which shows the current status of the line. If there is a message waiting to be sent, it will show who sent that message. It will also show if a collision has occurred on the line. If the module is in the PTP mode, it will create 1 receive buffer for each node. In all modes, a final buffer is created to store commands which are sent by the protocol stack.
When the attach method is executed by the developers protocol stack, it sends a request to a central socket which the NCARD module is listening to. The module then binds this request to a unique socket for the node. This new socket creates a channel between the protocol stack and the module. This channel is what is used to exchange packets between the two modules.
- Protocol Stack:
The protocol stack is the developers part of the PSANS tool. The developer builds the stack in whatever manner they choose. The only requirements is that they use the NCILIB methods to connect to the NCARD module, as well as to exchange data.