Service Delay

This is referred to as the overall time required to execute a service. For the purpose of this study, the following components of the delay are defined.

Waiting time: is the time interval between the arrival of a request at the destination and the beginning of execution.

Activation time: is defined as the time taken to activate the mobile agent platform.

Activation of mobile agent platform is defined as the process by which the mobile agent platform on the destination hosts senses and is triggered to receive agents for execution.

Transfer delay: is the time interval between the generation of the last bit of packet at the information source and the transfer of agent.

Service time: is the time taken to complete agent‟s requests i.e. time interval between the beginning and end of execution of a particular service (st).

Transfer delay is suffered twice, when the agent leaves its source on request operation and when it leaves the destination on response operation. In this simulation, the transfer delay consists of two components

(i) Time to save agents internal state (ts) (ii) Time to sign off from agent platform (ti)

Activation time is the total time it takes the agent to be triggered i.e. the time interval between when the agent arrives on a host and the beginning of its operation. The activation time is broken down into the following components

(i) Time to accept and authenticate incoming agent (ta) (ii) Time to provide a hierarchical name space for agent (tp)

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127 (iii) Time to allow agent migration and communication (tc)

(iv) Time to restore agent‟s internal state (tr)

Waiting time: the time interval between the arrival of a request at its destination and the beginning of execution (tw).

Assumptions

Both systems operate on the same principle for transmission, both are java based agents, therefore, the processing delays due to packet transmission through the network is the same, and thus not considered.

For the first request tw = 0 since there are no previous requests For the second request tw is the service time of the first request i.e.

( ) ( ) (3.1)

and for the third request tw is the sum of the service times for the first and second requests

( ) ( ) ( ) (3.2)

Assume the service times for all requests are equal and it is st, the total waiting time for n requests follows an arithmetic progression with a common difference st.

Arithmetic progression

( ( ) ) (3.3)

Where a is the first term corresponding to tw1 and d is the common difference corresponding to st.

Therefore

) ) 1 (

* 2 ( 2

/ tw₁ n st

n

tw_t   

(3.4)

but tw(1) = 0, then st n n

tw_t  /2( 1) (3.5)

Service time is the time taken to complete a request i.e time interval between the beginning and end of execution of a particular request in a service, st. Assume each request takes equal time to execute, then,

st st st

st

st₁  ₂  ₃  _n  total service time will be

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128





 ⁿ

i i

t st

st

1 (3.6)

Therefore,

nst st n

st_t  *  (3.7)

JADE operates only on hosts with the Mobile Agent System (MAS) previously installed; therefore it suffers a transfer delay equivalent to (time to save state + time to sign off the platform)

ti ts

TD  (3.8)

The JADE needs to be activated on getting to its destination by the agent platform.

The agent is authenticated and accepted, a hierarchical name space is provided for the agent before the agent is allowed to communicate and migrate and its internal state is restored.

Activation time of the JADE is equivalent to tr

tc tp ta

AT     (3.9)

The service time for n requests

nst st_t  waiting time

st n n

tw_t  /2( 1) (3.10)

JADE suffers another transfer delay on the response operation ti

ts

TD₂   (3.11)

The total delay

TD2

st tw AT TD

D_TA    _t  _t  (3.12)

If we assume that equal delay is suffered during request and response operations, then TD2

TD Therefore

t t

TA TD AT tw st

D 2    (3.13)

nst st n n tr tc tp ta ti

ts       

2( ) /2( 1)

st n n tr tc tp ta ti

ts ) /2( 1)

(

2       



(3.14)

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129 Proposed Embedded Mobile Agent (EMA)

The proposed agent connects directly with the operating system and needs no MAS. It suffers a transfer delay that is equivalent to the time it it takes to save its internal state.

ts TD Activation time

Since there is no agent platform, the mobile agent interacts directly with the operating system on the destination host. Its activation time is limited to the time taken to authenticate and accept agent and the time to restore the agent internal state.

tr ta

AT   (3.15)

Service time for n requests remains the same as for JADE.

nst

st_t  ` (3.16)

Waiting time also remains the same st

n n

tw /2( 1) (3.17)

Transfer delay on response operation is ts

TD

The total delay for the proposed EMA agent is equivalent to TD

st tw AT TD

D_TB    _t  _t 

t

t st

tw AT

TD  

2

nst st n n tr ta

ts     

2( ) /2( 1) st n n tr ta

ts) /2( 1) (

2    

 (3.18)

Assuming X number of hosts are visited, the delay on X host will be X*D_TA and X*D_TB.

) ) 1 ( 2 / )

( 2

( ts ti ta tp tc tr n n st

X

D_TA        

) ) 1 ( 2 / 2

( ts ta tr n n st

X

D_TB     

For simplicity, lets assume that it takes equal amount of time to save agents‟ internal state and sign off from agent platform i.e

th

ti ts  also, lets assume

td

tr tc tp

ta    

then

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130 )

) 1 ( 2 / 4 4

( t t n n st

X

D_TA  _h _d    X(4(t_h t_d)n/2(n1)st) (3.19) )

) 1 ( 2 / 2 2

( t t n n st

X

D_TB  _h _d    X(2(t_ht_d)n/2(n1)st) (3.20)

In document A FRAMEWORK FOR DEPLOYMENT OF MOBILE AGENTS AS WINDOWS OPERATING SYSTEM SERVICE FOR INFORMATION RETRIEVAL IN DISTRIBUTED ENVIRONMENTS (página 141-145)