A VIDEO DELIVERY METHOD USING AVAILABLE BANDWIDTH

OF LINKS WITH BUFFERS AND DISKS

Hideaki ITO

Graduate School of Computer and Cognitive Sciences, Chukyo University

101 Tokodachi, Kaizu-cho, Toyota, 470-0393, Japan.

Teruo FUKUMURA

Graduate School of Computer and Cognitive Sciences, Chukyo University

101 Tokodachi, Kaizu-cho, Toyota, 470-0393, Japan.

Keywords:

Video delivery, resource allocation, link bandwidth, available bandwidth, delivery scheduling.

Abstract:

Scheduling policies and methods are required to deliver videos through network structure since the videos

are key contents, and they are continuous media, in order to design the networked multimedia systems. These

systems allocate resources before video clips leave their servers for guaranteeing continuous play of the videos.

The policies for achieving video delivery play an important role in sense of effective delivery. The method

for utilizing the links is a momentous problem, since their capabilities are restricted, and extensions of their

capabilities are a difﬁcult issue. The policy shown in this paper is that available network bandwidth is used for

delivering one video clip at once. The bandwidth of a link is exclusively used to deliver only one video clip.

On the other hand, buffers and disks are established easier than the links. Moreover, some simulating results

are shown. Then, the amount of buffer space is restricted, and disks are used for storing the video in temporal.

1 INTRODUCTION

In recent, videos have been dealt with as primary con-

tents in networked multimedia systems(Dashti, 2000;

Hua, 2000). Such systems deliver videos through net-

work structure. Then several kinds of resources are

used to achieve this, scheduling of link utilization is

one of vital problems for designing the systems.

From the viewpoint of the utilization of restricted

link bandwidth, there are two types of methods(Ito,

2004). One is that a video clip is transmitted by using

link bandwidth as much as possible; the other is that

a video clip is transmitted as little as possible. The

former is the method that an entire link bandwidth is

used for delivering only one video clip, the latter is

that a minimum bandwidth is used. These two de-

livery methods are called the available bandwidth de-

livery method and the minimum bandwidth delivery

method, respectively.

In the available bandwidth delivery method, an en-

tire link bandwidth is used for transmitting only one

video clip. While the video clip is transmitted through

a link, this link is exclusively used to achieve this

transmission. Also, there is the case that there is dif-

ference between bandwidths of two links which are

connected to intermediate servers. At an intermediate

server, if the link bandwidth of the link used for re-

ceiving the video is broader than the link bandwidth

for sending it to another server, buffer space is re-

quired to store overﬂowed video.

An algorithm for delivering videos is proposed by

(Zhang, 2000). This algorithm treats scheduling of re-

sources which are disk bandwidths and network band-

widths in sense of physical structure. Routing al-

gorithms are proposed by (Vogel, 1996), which sat-

isfy Quality of Services constraints. The method de-

scribed in (Won, 1999) treats the video placement,

and transmission costs of video clips. The method

shown in (Shahabi, 2000) deals with transmitting

videos and buffering in servers. An entire bandwidth

of a link is used for transmitting a video.

This paper is organized as follows. Section 2

presents an overview of a networked video delivery

system. An overview of scheduling with buffer re-

striction and with disks in Section 3. Some simulating

results are presented in Section 4. Finally, Section 5

presents some concluding remarks.

2 AN OVERVIEW OF A

DELIVERY MODEL

A structural overview of a model for delivering videos

is shown in Figure 1 from the viewpoint that a video

453

ITO H. and FUKUMURA T. (2005).

A VIDEO DELIVERY METHOD USING AVAILABLE BANDWIDTH OF LINKS WITH BUFFERS AND DISKS.

In Proceedings of the Seventh International Conference on Enterprise Information Systems, pages 453-456

DOI: 10.5220/0002548904530456

 SciTePress

video server

intermediate server intermediate server client

...

link link link

video

a set of video clips

buffer

disk

buffer

disk

Figure 1: An overview of a networked video delivering sys-

tem.

is delivered from a video server to a client site. A

video server and a client are connected by some links.

When a client requests to watch a certain video, the

requested video is delivered from the video server to

the client site through several intermediate servers.

The sequence which consists of a video server, some

intermediate servers and a client site, is called a de-

livery path which is used for delivering a requested

video clip. The intermediate server consists of links,

a disk and a buffer. The disk is used for storing re-

ceived video. Stored videos are kept in an intermedi-

ate server since the video is removed from the disk.

Stored video in the buffers is sent automatically and

implicitly, while stored video in disks are arrived and

are left explicitly in sense that they are scheduled.

For delivering video, costs are computed. The costs

are deﬁned from two viewpoints. One is related to

quality of the delivery path in sense of Quality of Ser-

vices(QoS), another is related to usage costs of re-

sources. These costs are called a quality cost and a

charge cost, respectively. The quality cost is speci-

ﬁed in failure rate, packet loss ratio, and delay time

of intermediate servers and links. The quality costs of

paths are computed as the follow expression;

cost

quality

(path) = W

F R

× FailureRate

+ W

P L

× PacketLoss

+ W

× DelayTime

FailureRate, PacketLoss and DelayTime are QoS pa-

rameters. While, W

F R

, W

P L

and W

are their

weights.

A charge cost of a delivery schedule is computed

as the follow way;

cost

charge

(s) =

link

× LinkUsageTime

disk

× DiskUsageTime

buffer

× BufferUsageSpace

s is a schedule. C

link

, C

disk

and C

buffer

are unit costs

for using each link i, disk j and buffer k of a schedule,

respectively. Costs of links and disks are charged for

their usage times. A unit cost for a buffer is charged

to the amount of utilized buffer space.

3 A SCHEDULING METHOD

WITH BUFFERS AND DISKS

The policies to construct schedules are as follows;

• An entire link bandwidth is used for delivering one

video clip. During this delivery the link is utilized

exclusively.

• The ﬁrst video clip of a certain video leaves from

its video server, as soon as possible, if the quality

costs of paths are the same.

• The usage of buffers takes precedence over the us-

ages of disks.

• When the disk is used for storing a video tempo-

rally, the video is stored into the intermediate server

nearby a client than a video server.

Schedules are constructed in the following way. At

ﬁrst, when a request occurs at client site, paths from

video servers to the client are obtained for each video

clip of a requested video. These paths are called can-

didate paths for delivering video clips.

Next, a delivery path is selected among candidate

paths by using a certain strategy to decide the delivery

path. There are three strategies. They are;

• Departure time effective strategy. The ﬁrst video

clip departures from a video server as soon as pos-

sible.

• Quality cost effective strategy. The path whose cost

is the lowest among a collection of candidate paths

is selected preferentially than others. The quality

cost is measured in cost

quality

(path).

• Score effective strategy. The collection of candi-

date paths is ordered based on their scores. Scores

of the paths are calculated in terms of their quality

costs and their initial latency times when candidate

paths are used to deliver clips.

Finally, departure times of the consequent video

clips of the requested video are computed conse-

quently.

Figure 2 (a) shows a simple network structure, in

which there are one intermediate servers IS, and four

links, I1, I2, O1 and O2. Let the bandwidth of I1 and

O1 are a [Mbps] and b [Mbps], a > b, respectively,

and a video clip be delivered from I1 to O1, whose

size is M [Mbyte]. In (b), the short dotted line shows

the required buffer size of the intermediate server.

The maximum required buffer size is computed as:

the maximum required buffer size = (a − b) ∗ M/a.

On the other hand, there is the case that an interme-

diate server is connected to some servers and client

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454

I2 O2

(a) An example of an intermediate server.

required buffer space

time

required buffer space

time

(b) Required buffer space in an intermediate server.

and restricted buffer space.

limit

Figure 2: Required buffer space in an intermediate server

and restricted buffer space in the intermediate server.

sites. For example, input streams of the intermedi-

ate server are I1 and I2, and output streams are O1

and O2, as shown in Figure 2 (a). In (b), a short dot-

ted line and a long dotted line show required buffer

size to transmit I1 to O1, and I2 to O2, respectively.

Required buffer space for delivering these two video

clips is shown in a solid line. If the buffer of the inter-

mediate server is unlimited, these two video clips are

able to be delivered. However, if the buffer space is

restricted, the arrival time of the clip using I2 and O2

is shifted to t2 from t1 as (c).

The scheduler tries to make a schedule which uses

disks, when it is impossible to deliver video clips due

to buffer overﬂow. Figure 3 shows an example of time

schedule using disks. A delivery path is shown in

Figure 3 (a). This path consists of the video server

(VS), three intermediate servers (IS1, IS2, IS3) and

the client site (Client). The client requests the video

which consists of two video clips. The time schedule

which is shown in (b) is constructed in the simplest

way. The time schedule for delivering the ﬁrst video

clip is shown in the white squares, the time schedule

for the second clip the gray squares, respectively.

Figure 3 (c) shows the time schedule using a disk.

Black squares show the region which is allocated

for delivering some other videos than the requested

VS IS1 IS2 IS3 Client

time

(a) An example of a delivery path.

(b) An example of time schedule.

t10

t11

t12

t13

t14

t15

t16

t17

t10

t11

t12

t13

t14

t15

t16

t17

Figure 3: An example of time schedule using disks.

video. The ﬁrst video clip is delivered by the same

time schedule shown in (b). However, the second clip

is not able to be delivered in the same way shown

in (b). Because, the region which is required to de-

liver the second video clip had been allocated to de-

liver other clips. In this case, the second video clip

is able to be delivered without skew time and without

increasing the initial latency time by using the disk

which is provided in intermediate server IS2. Also,

the scheduler tries to use the disk of IS3, however to

use this disk is difﬁcult since the time interval that

is required to deliver the clip by the link between

IS2 and IS3 is not sufﬁcient for delivering the second

video clip.

To prevent the occurrence of skew time, the sec-

ond video clip has to arrive to the client site by t8.

The link between IS2 and IS3 is able to be used for

delivering the second video clip. However, the links

between VS and IS2 are not used for its delivery. On

the other hand, the links between VS and IS2 is able

to deliver the clip for [t2, t4]. The video clip which is

transmitted using the interval [t2, t4] is stored into the

disk of IS2. At t8 this stored video in IS2 is delivered.

The client receives the second video clip without the

skew time. The striped region of this ﬁgure (c) depicts

the usage time of the disk in IS2.

A VIDEO DELIVERY METHOD USING AVAILABLE BANDWIDTH OF LINKS WITH BUFFERS AND DISKS

455

with buffer restriction

without buffer restriction

Figure 4: Initial latency time of schedules with buffer re-

striction.

without usage of disks

usage of disks

Figure 5: Initial latency time of schedules with disks.

4 SOME SIMULATION RESULTS

Some simulating results are shown by making some

assumptions. At ﬁst, the network structure is as-

sumed. There are three video servers, nine intermedi-

ate servers, and links connecting servers. Each video

server is connected to one intermediate server. Ca-

pabilities of links are several tens and/or several hun-

dreds bandwidth [MByte]. The bandwidth of the links

between a video server and an intermediate server are

several hundreds. The client sites are connected to in-

termediate servers. Moreover, the size of each video

is 40 [MByte]. All videos consist of two video clips

whose size is 20 [MByte], and their consuming ratios

are 1 [MBps]. These two video clips are stored in the

same server. Furthermore, the requests occur during

100 seconds. The request times are generated as uni-

form random variables.

The initial latency times of some schedules which

are made using the departure time effective strategy

are shown. Figure 4 shows the initial latency times, in

which two lines are shown. They are corresponding

to the initial latency times when the buffer space is

restricted, and when the buffer space is not restricted.

On the other hand, Figure 5 shows the initial latency

times whether the scheduler uses disks or not. The

initial latency times are reduced by introducing disks.

The efﬁciency for introducing the disks appears al-

though the number of clients is small.

5 CONCLUDING REMARKS

An overview of the method that the full bandwidth

of a link is used for delivering one video clip is de-

scribed. Then, the utilization of buffers and disks are

introduced. Now, we plan to extend the capacity of

the scheduler from the following viewpoint. Utiliza-

tion of bandwidths of links makes be more effective.

When the bandwidth of an output stream is larger than

a bandwidth of an input stream, the link of the output

stream is used in partial.

ACKNOWLEDGEMENTS

We would like to thank Ikoma, Y. and Naito, T. for

their cooperation to implement schedulers.

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