Network II.5 simulator .

Overview of network simulator Simulation package for modeling and simulating computer networks and communication systems Can model a system as simple as a single CPU connected to a single memory module Can model complex systems such as a local area network connected to a large number of workstations and servers Can model system hardware and as well as software components

Facilities provided by network ii.5 System description System simulation Simulation analysis

How large information network are taken care of ? Very large information network can be modeled by developing a number of sub models Created using geographical sub systems or logical sub systems Geographical subdivision: Divide a national network into a collection of state networks Logical subdivision: Divide a campus-wide network into a back bone network and departmental lans

Main three functions of network II.5 Provides facilities for three main functions 1.System description 2.System simulation 3.Simulation analysis

System description Done via the graphical user interface User defines the system connectivity and component details by entering data into forms Data structures used to describe the hardware and software logic of the system are processing elements ,transfer devices, storage devices, gateways and LANs modules and files User enters a system description using the NETGEN user interface This produces a *.NET file. NETWORK is the simulation engine that takes the system description from the *.NET file Runs the simulation based on the run-time parameters provided by the user Every simulation run produces a number of reports These reports show utilization, queue statistics ,execution time response time and confilcts By analyzing the reports user may draw conclusions about the system being modeled

Modeling hardware components Hardware components are modeled by three types of entities Processing elements- any device that has the ability to process information -Used to model low level system components such as a CPU and a bus controller -Also used to model high level system components like db server and a network controller Transfer device Used to model any channel that can carry bits from one device to another Any data transfer between PEs and SDs can take place over TDs only Ex: system bus Storage devices Any system for storing data can be modeled as a storage device -can be semiconductor memory, disk memory or the temporary buffer of a communication node.

Parameters of a processing element Parameters of the PE: Basic cycle time Instruction set I/O set up time Time slice Interrupt overheard Input controller

Processing Instruction Processing instructions are used to represent the ability of PE to perform logical and processing tasks An instruction executed on a PE in a network II.5 model like “COMPRESSIMAGE” will not take an uncompressed image as input and produce the compressed image as its output Simply will add upto the time for an image to be compressed Because the main concern of a discrete-event model is to keep track of simulate time Execution time of an instruction is made up of two parameters specified by the model builder : cycle time and number of cycles required for executing an instruction Statistical distribution functions may also be specified as the number of cycles for an instruction Consider performjoin instruction Can take different lengths of time depending upon the size of tables List of statstical distribution functions are quite extensive

. Read/write instructions Used to move files between storage devices and processing elements A TD is used to connect the PE to the SD Purpose of simulating such an instruction is to model the time taken by this instruction Total time is a function of the speed of the storage device as well as the speed of the transfer device

Message instructions Used to transfer data between PEs connected by a TD On execution of a message instruction ,the message text is sent to the destination processor’s receive message list This message stays like a token in the receive message list until consumed by a software module Semaphore instructions: A semaphore instruction has a name, a semaphore ,a set /Reset/Toggle flag ,an assignment type and a count value Semaphore status or count can be used by modules to schedule operations Binary semaphores are used for implementing synchronization primitives; counting semaphores are useful in modeling buffer management functions

Transfer Device Used to model any channel that can carry bits from one device to another Any data transfer between PEs and SDs can take place over TDs only The way in which PEs and SDs are connected determines the topology of the network Message instruction must be executed to perform the data transfer over a TD Message consists of a sequence of blocks Each block consists of a collection of words Each word contains one or more bits Blocks can be used to represent packets on an Ethernet framework and frames on a token ring network Timing calculation for data transfer over a TD is a function of the six parameters called cycle time, bits per cycle, cycles per word, word overheard time and block overheard time

Storage devices Any system used for storing data can be modeled as storage device Can be semiconductor memory, disk memory or the temporary buffer of a communication node A complete data set is broken into blocks Blocks can be used to model the sectors on a disk drive Blocks are further divided into words Every storage device has the following attributes: Bits per word,Read word access time,Read word overhead time, read block overhead time,Read access delay,capacity,words per block write word access time write word overhead time,write block overhead time,write access delay,number of ports

Routes Route is the destination of a message instruction It is a list of PEs and gateways defined at the level of the system When a message is sent to a route ,it visits all of the PEs and gateways listed in this route The final destination of a route must be a PE Gateways can automatically forward the messages ,but a PE must have a module that will explicitly forward the message

Software components Software is modeled using the module entity Extensions of the module and the instruction concepts are also used to model software These extensions are instruction mixes, macro instructions, and files

Modules A module is executed on a PE Represents the tasks to be performed by the PE There are four main components of a module’s description Scheduling conditions Host processing elements option List of instructions to execute List of modules to execute on its completion

Life cycle of a module Life-cycle of a module goes through four stages Every module is checking for its pre conditions all the time As soon as all the pre conditions are met The module request a host PE If the PE is not busy, access is granted to this module Instructions listed in the module are executed in the given sequence On completing the last instruction it chooses a successor ,based on the logic specified in the model In any model there must be at least one module that is executed as soon as the simulation begins; at time=0;

. Instructions mixes are pseudo instructions included in the instruction list of a module Macro instruction is a collection of instructions referenced by a single name A file represents an organised storage of information in a storage device Can be generated by NETGEN when the model is being built May be created dynamically with a PE executing a write instruction

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