16
1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University [email protected] [email protected] * Supported by Polytechnic University Acknowledgement: David Rouse, Lucent Technologies

1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University [email protected]

Embed Size (px)

Citation preview

Page 1: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

1

Scheduling calls with known holding times

Reinette Grobler* Prof. M. Veeraraghavan

University of Pretoria Polytechnic University

[email protected] [email protected]

*Supported by Polytechnic University

Acknowledgement: David Rouse, Lucent Technologies

Page 2: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

2

Outline

• Problem statement

• Motivation for solving this problem

• Proposed algorithms: F and timeslots

• Simulation comparison

• Conclusions and future work

Page 3: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

3

Problem statement and motivation

• Problem statement– Define call scheduling algorithms for calls with

known holding times

• Motivation– There are applications that could generate calls

with known holding times– Improves network utilization and call blocking

probabilities by allowing for call queueing

Page 4: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

4

Applications vs. data transfers

• “Communications applications” consist of data transfers

• Data transfers can be classified as shown below

• Define a call as a “data transfer” rather than an “application session”

Interactive/Live streaming

Recording

Stored streaming File transfers

Consuming endLive Stored

Live

Stored

Sending end

Page 5: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

5

Data transfers (“calls”) with known holding times

• For calls to have known holding times, two characteristics must be met:– Sending end of the data transfer is stored– Network uses preventive congestion control

• Examples:– Transferring a file on a circuit or CBR ATM connection

• Can compute holding time using knowledge of file size, data rate of circuit, and propagation delay

• Demonstrates need for the “preventive congestion control clause”– File transfer on a TCP/IP network does not have a known holding time

– Video-on-demand transfer on an VBR ATM connection

Page 6: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

6

Loss, delay, utilization

• Learning from the “packet world”– Packet switches use buffers to achieve high line

utilization and tradeoff packet delays with packet loss

– Apply this concept to calls • appears to be only possible if calls have known

holding times

Page 7: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

7

Call blocking vs. call queueing

• Telephone networks, ATM networks and MPLS networks only allow call blocking

– If only call blocking is allowed (i.e., no delayed starts), then need to overprovision to keep call loss low

• Why not allow for delayed starts?– If call holding times are unknown and calls are queued at each switch in sequence, then

utilization could really suffer and call blocking could even increase with finite buffers

SETUP

The call waits (queues) until resources becomeavailable on link 1, reserves and holds bandwidth forthis call until the call is setup all through

SETUP

While call is being queued for link 2 resources, link 1resources are idle

Host Switch Switch Hostlink 1 link 2

referred to as kTwait scheme

Page 8: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

8

Knowledge of holding times

• Allows switches to immediately determine an agreed upon delayed start time for a call c

• Allow other calls sharing segments of the end-to-end path of c to use the network resources before c starts

• Results in high utilization and lower call loss

Page 9: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

9

Call scheduling schemes• Each switch maintains a time variant available capacity

function ai(t) for each outgoing interface I reflecting the scheduled start times of all admitted connections

Page 10: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

10

Call scheduling schemes (cont.)

• F scheme:– Ingress switch selects an earliest possible start time (epst) and reserves

resources for a time period F (from epst), where F is much larger than the holding time, and sends this time period in the SETUP message

– Intermediate switches search for largest time period inside the received period during which it can accommodate the connection

• timeslots scheme:– The ingress switch selects a set of time ranges during which it has the

resources available for the new call, and sends these in SETUP message

– An intermediate switch attempts to admit the call during each of the time ranges or any part of each range greater than or equal to the holding time, the new time ranges are passed in a SETUP message

Page 11: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

11

Example: F and timeslots schemes

– F scheme (large time period: F=4): Swith1 - (10pm,2am), Switch2 – (10pm,12am)

SETUP SETUP

Switch1 Switch2

• Connection request for a call starting immediately with holding time of 1 hour

– timeslots scheme (number of time ranges = 3): Switch1 - ([3pm,5pm],[8pm,9pm],[10pm,], Swicth3 - ([4pm,5pm], [10pm,12am], [1am,2am])

Switch1 Switch2Host Host

SETUP

Page 12: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

12

Simulation

Switch1 Switch2 Switch4Source DestSwitch3

dest3dest2dest1

src1 src2 src3

Parameter (scheme) Values

F (Large period) 20, 50 and 100 seconds

n ( number of timeslots)

2, 3 and 4

•kTwait has no parameters.

Page 13: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

13

Results: Blocked calls

Page 14: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

14

Results: Start time delay

• Indicates time from connection request to start of data transmission of study traffic

• High F values increase delay

• Large queueing delays cause kTwait to provide later start times

• timeslots scheme performs best

Page 15: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

15

Results: Utilization

• timeslots scheme allows for close to optimal utilization

• kTwait unable to handle load of more than 70%

• Increasing F decreases utilization

Page 16: 1 Scheduling calls with known holding times Reinette Grobler * Prof. M. Veeraraghavan University of Pretoria Polytechnic University rgrobler@cs.up.ac.za

16

Conclusions and future work

• Use known holding times to schedule connections to improve network resource utilization and call queueing delays

• Required extensions:– Switch programming time– Propagation delay– Time synchronization