A PRESENTATION

ONSIMNET

Presented By:

DEEPAK KUMAR BAIRWA

2011PMM5060I SemesterMSE, M. Tech.MNIT Jaipur

Introduction to SIMNET II

• SIMNET II is a network-based discrete simulation language that utilizes only four nodes: a source - from which transactions (customers) arrive a Queue - where waiting takes place if necessary a facility - where service is performed. an auxiliary - which is added to enhance the modelling capabilities of SIMNET II.

Introduction to SIMNET II

The nodes in simnet ii are connected by branches. As transactions traverse the branches, they perform important functions that include:

(i) Controlling transaction flow anywhere in the network.

(ii) Collecting pertinent statistics.(iii) Performing arithmetic calculations.

Continued

• During the simulation execution, SIMNET II keeps track of transactions by placing them in files.

A file can be thought of as a two- dimensional array in which each row stores information about a single transaction.

The columns of the array represent the attributes that allow the modeler to keep track of unique characteristics of each transaction.

Continued

•SIMNET II uses three types of files: (i) Event calendar (E.FILE). (ii) Queue. (iii) Facility. The event calendar (or E. FILE) is the principal file that drives the simulation. It keeps track of an updated list of the model’s events in their proper chronological order.

Statement Representation• The general format of the SIMNET II statement isidentifier; field 1 ; field 2 ;……..; field m: A node identifier consists of an arbitrary user-defined name followed by one of the codes *S,*Q,*F or *A that identifies the name as a source, a queue, a facility, or an auxiliary. A branch identifier consists of the code *B only. The fields are separated by semicolons, & statement must be terminated with a colon .

For Example• Consider, ARIV *S ; EX(5) ; ; ; ; ; LIM=100 : Source ARIV creates a maximum of 100 entities with the interarrival time determined from an exponential distribution with a mean of 5 time units. If field is not used or defaulted, its order is preserved by successive semicolons.

Continued The coding in SIMNET II is free formatted as well as uppercase/lowercase insensitive. A statement may be segmented among any number of successive lines by terminating each line with an ampersand (&).For Example: ARIV *S ; EX(5) ; ; ; ; LI& ! Line 1 of ARIV M=100 : ! Line 2 of ARIV A SIMNET II line may include a comment, which is prefixed by exclamation mark (!).

Basic Rules for the Operation of Nodes1. A source may not be entered from any node,

including another source.2. A queue may not feed directly into another

queue, nor can it feed back into itself.3. Facilities may follow one another without

intervening queues. However, a facility may not feed directly into itself.

4. An auxiliary is only node that can feed directly into itself

5. A transactions will skip a queue if the queue is not full to its capacity

6. If a facility is preceded by a queue the facility automatically will attempt to draw a waiting transaction immediately when a service is completed.7. The movement of transaction in and out of the queue must be initiated by another node.

Source Node The source node is used to create the arrival of entities into the network. SNAME: *S;F1;F2;F3:MULT = F4;LIM = F5;F6;F7;*T:

Field Identifier Default

F1 Interarrival time 0 F2 Occurrence time of first creation 0 F3 Mark attribute number with the None attribute automatically carrying creation time if F3>0 or serial number if F3<0. F4 /m/ Simultaneous transaction per signal 1 creation. F5 /L/ Limit on number of creation if F5>0 ∞ or limit on time of creation if F5<0. F6 /s/ Output select rule None F7 /r/ Resources returned by source None *T List of nodes reached from source by None direct transfer.

EXAMPLE

TV unit arriving on a conveyor belt every 5 minutes are send to packaging.

Sol:TVS *S; 5 ; goto - PAKAGE :

The “goto” field represents the T field, *T is a floating field, in the sense that it always occupies the last field of the node regardless of any default field that may precede it.

QUEUE Node

• The purpose of a queue (buffer) is to house waiting transactions

• An arriving transaction that cannot be serviced immediately must wait in a queue until the facility becomes available.

• A queue size may be finite or infinite• The initial number waiting at start of the

simulation may be zero or greater than zero.

QUEUE Node

SNAME: *S;F1;F2;F3:MULT = F4;LIM = F5;F6;F7;*T:

Field Identifier Default

QNAME: *Q;F1(SUBF1);F2(SUBF2);F3;F4;F5;*T:

Field Identifier Default

F1 Max queue size ∞ SUBF1 Initial number in queue 0 F2 no. of waiting transection required to create one leaving transection 1 SUBF2 the rule for computing the attribute of the leaving transection when F2>1: LAST SUM,PROD,FIRST,LAST, HI(#),LO(#), where # is an attribute number. F3 /d/ Queue discipline: FIFO,LIFO,RAN,HI(#),LO(#). FIFO F4 /s/ Output select rule. None F5 /r/ Resources returned by queue. None *T List of nodes reached from source by None direct transfer.

F4

Queue Discipline Codes

Discipline Leaving Transaction• FIFO First in, first out• LIFO Last in, first out• RAN RANdom selection• HI(#) Transaction having the Highest attribute A(#), where # is an integer constant

LO(#) Transaction having the Lowest Attribute (#).

Example Unit of product are packaged four to a carton. The buffer area

can hold a maximum of 75 units. Initially the buffer is holding 30 units.

Sol:- QUNIT *Q;75(30) ;4: Field 1 sets the maximum queue capacity (=75) and the initial number in the system(=30).Field 2 Indicates that four product units will be converted to a single

carton. By default, the attributes of the “carton” transaction will equal those of LAST of the four transaction forming the carton. The queue discipline is FIFO because field 3 is defaulted.

Facility node •A facility node consists of one or more parallel service. •When all the service are busy ,new transaction cannot enter the facility.• When a server completes a service ,the facility automatically attempt to pull a new transaction from a predecessor queue, if one exits

Continued

FNAME: *F;F1;F2;F3(SUB F3);F4;F5;*T:

Field Identifier Default

F1 rule for selecting an input queue none F2 service time 0

F3 number of parallel server 1

SUB F3 initial number of bussy server 0

F4 /s/ Output select rule. None

F5 /r/ Resources returned by facility. None

*T List of nodes reached from facility by None direct transfer

F1 F4

F2

F3(SUB F3

Example A small shop has on machine and 10 waiting job, in addition to the job that is currently being processed.The processing time per job is uniform between 20 and 30 minutes. sol: QJOB *Q;(10) : FJOB *F; ; UN(20,30); (1); goto-TERM:Because FJOB is initially busy, as indicated by the entry(1) in field3,the facility will process its resident job in UN(20,30) minutes. After the job leaves FJOB to be TERMinated, the facility will automatically “look back” and pull a new job from QJOB. The process is repeated until of 10 JOB are processed.

Auxiliary node The auxiliary is an infinite capacity node that accepts all incoming transactions. The node is mostly suited for representing delays.The auxiliary is the only node that can enter itself, a characteristic that is particularly useful in simulation loops.

Continued

ANAME: *A; F1 ; F2; F3; *T:

Field Identifier Default

F1 Delay time 0 F2 /s/ Output select rule. None

F3 /r/ Resources returned by auxiliary. None

*T List of nodes reached from auxiliary by None direct transfer

FFF1F2

Example of Auxiliary Node

• Job applicants arrive at an employment office every EX(25) minutes. Each applicant must fill out a form and then wait to be interviewed. It takes approximately 15 minutes to complete the form.

ARIV *S;EX(25):FORM *A;15;WAIT *Q:

Layout of SIMNET II Language

Layout of SIMNET II Language

Example (Multiserver Queuing Model)

• Customers arrive randomly at a three-clerk post office. The interval time is exponential with mean 5 minutes. The service time is also exponential with mean 10 mins. All arriving customers form one waiting line and are served by free clerks on a FIFO basis

Input (Multiserver Queuing Model)

• $PROJECT; Post Office; 20 January, 2009, M. C. Okoronkwo:

• $DIMENSION; ENTITY(30):• $BEGIN:• ARVL *S; EX(5): !Arrivals• LINE *Q: !Wait in line• $CLKS *F;;EX(10);3;goto-TERM: !Served by one of 3

clerks• $END:

Example (Multiserver Queuing Model)

• $RUN-LENGTH = 480 !Run model for 480 minutes• $STOP:

Output of the Model

• SIMNET OUTPUT REPORT

Summary •Simnet II is based on the use of only for nodes, which makes it particularly easy to learn and use despite it simple structure ,the language is sufficiently powerful to tackle complex situations•The use of special assignment within the conditional IF ENDIF provides powerful modelling capabilities .•The full SIMNET II system is totally interactive both for debugging and obtaining the global statistical result

Reference

• http://en.wikipedia.org/wiki/Simulation_language

• http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=185606

• Hamdy A. Taha (1990) SIMNET simulation language in:Simulation Conference, 1990. Proceedings., Winter Issue Date: 9-12 Dec 1990 On page(s): 99 - 105

• Computers & Industrial Engineering Volume 14, Issue 3, 1988, Pages 281-295