1. Network II.5 simulator .

2. 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

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

4. 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

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

6. 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

7. 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.

8. 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

9. 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

10. . 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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;

18. .
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

19. End .