Information Technology Reference
In-Depth Information
Since the transmission rate must be positive and less than infinity, we have the condition
that
Q
R
V
=
τ<
T
F
(12.11)
In other words, the server clock jitter must be smaller than a micro-round. Note that under this
condition, traffic overlapping involves at most two servers and the data rate is doubled to 2
R
V
in
the overlapping region. As
R
ORT
in equation (12.10) can become very large when the denomina-
tor becomes small, the useful operating range for over-rate transmission is actually limited by:
R
ORT
<
2
R
V
(12.12)
Substituting equation (12.10) into equation (12.12) and rearranging we can then determine
the maximum clock jitter for which ORT is applicable:
Q
2
R
V
=
τ<
0
.
5
T
F
(12.13)
Therefore, ORT can prevent traffic overlapping if clock jitter is less than half of a micro-round.
With ORT, the maximum network bandwidth needed at each server will be increased to
QR
V
C
ORT
=
R
ORT
=
(12.14)
Q
−
R
V
τ
12.5 Buffer Management
In this section, we present buffer management algorithms for the server and the client, and
derive the respective buffer requirements. For simplicity, we ignore network delay and delay
jitter. However, the effect of network delay and delay jitter can be incorporated in the same
way as clock jitter and the same derivations are still valid.
12.5.1 Server Buffer Requirement
There are
N
S
micro-rounds in a macro-round, therefore the duration of a macro-round, denoted
by
T
R
,isgivenby
N
S
Q
R
V
T
R
=
(12.15)
Q
buffers for
each server, regardless of the number of servers and clients in the system. Therefore, existing
servers do not need any upgrade when one scales up a system by adding more servers.
As buffers are released after each micro-round, this scheduler requires only 2
12.5.2 Client Buffer Requirement
Many studies on VoD system have assumed that video data are consumed periodically by the
video decoder. However, as previously discussed in Section 10.3.2, hardware and software
Search WWH ::
Custom Search