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Conclusion: An efficient and robust algorithm for VQ-based
watermarking has been presented. It is efficient since it uses the
VQ indices to proceed with the embedding process, and to hide
the information into the secret key. Hence, watermarked image
quality would be guaranteed. In addition, in view of the simulation results under a variety of attacking techniques, we are able to
claim its robustness, effectiveness, and superiority over the existing
algorithm. Further work will concentrate on embedding multiple
watermarks into the same original source in the VQ domain to
protect the original source more effectively.
ter L y a c l c e t (long packet), which adapts DSCP of DiffServ to
RTPIUDPIIP packet format. Fig. 2 shows the L j u c k e t foimat,
which uses the ingress, intermediate, and egress routers. At the
ingress router, the L q a c k e t , which has the same destination and
DSCP, is classified and sent to the egress router through several
intermediate routers. At the intermediate router, it only transits
the L y a c k e t without any modification based on the DSCP value.
At the egress router, the L y a c k e t s that have arrived are separated
and processed according to the priority of the DSCP value.
destinatlon IP=routera DSCP_EFi I
0 IEE 2001
17 Aaril2001
Electronics Letters Online No: 20010567
DOI: 10.1049/el:20010567
Hsiang-Cheh Huang (Department of Electronics Engineering, National
Chiao Tung University, Hsinchu, Taiwnn, Republic of China)
Feng-Hsing Wang and Jeng-Shyang Pan (Department of Electronic
Engineering, National Kaohsiung University of Applied Sciences,
Kaohsiung, Tuiwan. Republic of China)
destination I P - r o ~ I e r aDSCP-BE,
HSU, c.T.,
and wu, J.L.: 'Hidden digital watermarks in images',
IEEE Traris. Image Process., 1999, IP-8, (I), pp, 58-68
LU, z.M., and SUN, s.H.: 'Digital image watermarking technique
based on vector quantisation', Elecrron. Lett., 2000, 36, (4), pp.
3 L I N D E , ~BUZO,A.,
and G R A Y , R . M . : 'An algorithm for vector
quantizer design', IEEE Trans. Cr,nn-"., 1980, COM-28, (l), pp.
Fig. 1 Overall architecture of proposed scheme
Voice traffic multiplexing scheme with
guaranteed 00s between VolP access
routers using DiffServ
IP UDP RTP, Payload, RTP Payload RTP3 Payload3
E.J. Ha and J.T. Park
A new efficient voice traffic multiplexing scheme with guaranteed
QoS between VoIP access routers using differentiated services
(Diffjerv) is presented. The performance of the proposed scheme
for traffic with various bit rate types is analysed. The proposed
scheme satisfactorilyguarantees the QoS requirements.
Introduction: There is a growing interest in building a VoIP system
because of the increase in use of the Internet. Low bit rate codes
such as G.723.1 and G.729 are applied to the baseline codec of
VoIP at present. Current VoIP transfer methods are still very inefficient due to their small payload in comparison with their large
overhead. Moreover, the traffic load on the access routers tends to
geometrically increase when the incoming traffic flow of short
packets increases. These factors cause problems such as intolerable
delay, jitter, and packet loss, which cause serious deterioration in
the voice quality. There have been some related investigations
dealing with these voice streams using a multiplexing technique
[l]. These solutions do not satisfy the true QoS requirements. In
this Letter, we propose a new QoS guaranteeing mechanism by
combining a RTPIUDPIIP packet multiplexing scheme with DiffServ QoS architecture.
V o I P system architecture using DiffServ:We present an overall
VoIP architecture and its multiplexing packet format using DiffServ. Fig. 1 shows the overall architecture. The number of access
networks, connected to one ingress router depends on the real
capacity of the ingress router. We use the RTPIUDPAP packet
multiplexing concept based on [2] to reduce the packet overhead.
However, the major problem of [2] is that it does not take into
account any QoS requirements. Thus, we expand the voice traffic
multiplexing scheme in [2] in order to support QoS requirements.
We propose a new multiplexing scheme using the diffserv code
point (DSCP) of DiffServ. The key idea is as follows: Add a voice
stream multiplexing scheme with identical destination IP address
and DSCP.
T o guarantee the QoS requirements, we propose a new RTPI
UDPIIP packet format at the ingress router. We define a parame-
EF-L-Packet 1
EF-L-Packet N
AF-L-Packet 1
AF-L-Packet N
BE-L-Packet 1
BE-L-Packet N
An ingress router contains a server, which is composed of
D S C P E F (DSCP expedited forwarding), D S C P A F (assured forwarding), and DSCP-BE (best effort) queues. When large
amounts of incoming voice traffic enter the ingress router simultaneously, packets are classified into different QoS guaranteed types
by classifiers. At the policer, the classified packets are checked if
they violate the bandwidth constraint requested in advance. Additionally, the qualified packets are queued in the DSCP-EF,
D S C P A F , and DSCP-BE server in turn. The process is executed
in a first come first serve (FCFS) manner and a non-pre-emptive
priority service discipline is employed.
Perjbrmannce evaluation: In the near future, it is expected that the
backbone network will be installed with a very high-speed WDM
network with more than 10GbitIs. In this very high-speed backbone network, the main problem of QoS deterioration may be
caused by poor bandwidth control. Thus, in Fig. I, we describe
the voice traffic blocking probability between VoIP access routers
21st June 2001
Vol. 37
No. 13
based on M/G/l with a HOL-NPR (head-of-line non-pre-emptive)
queueing model. We define a new concept of trunk as a group of
voice traffic with identical destination and DSCP. It is assumed
that at least one trunk should be established between the ingress
router and corresponding egress router. Each trunk has a different
voice traffic arrival rate and mean service timc. We assume that
there are P types of queues. In a queue of typc lc (k = I, 2, ..., P),
there are /nfcservers and no waiting room.
Packet loss occurs in two ways. I n one, a packet arrives when
its trunk is full; in the other, the trunk is empty but the reservation at the second step fails on arrival. We denote the blocking
probability of packets arriving in trunks of type /c in the former
and the latter cases by Pjr:,!s(IC) and PI:,!’,, respectively. P;(:,:T
( k ) . pfc
= h,hf, denotes the traffic intensity in a trunk of type k .
Conclusions: We have presented a voicc traffic iiiultiplexing
scheme with guaranteed QoS between VolP access routers using
differentiated services (DiftServ). At the ingress router, the newly
defined RTPIUDPIIP packets, namely, the Lgcrcltet (long packet),
are multiplexed for transmission efficiency by grouping the packets with identical destination egress routers and DSCP. To validate the proposed scheme, a network model has been developed to
analyse the blocking performance. Additionally, we havc analysed
the model using M/G/l with an HOL-NPR queueing system.
Finally, we have presented the numerical results of the analysis.
Through the results, the proposed scheme is shown to be very efficient at guaranteeing the QoS requirements over VoIP.
0 IEE 2001
24 Noveinher 2000
Llectronics Lettcw Onlitze No: 20010555
DOI: 10.1049/eI:20030555
where B(n2, p) denotes the blocking probability with traffic intensity p. It is well known that B(M,p) can bc computed by the rccursion [3];
p q n c . - I,p )
pB(nc.- 1,p )
= 1,2, ...
Next we consider the overall blocking probability Pfc,,,(/t).Since
the blocking probability is the fraction of lost customers to customers arriving in a unit time, we have
711 I
However, the above blocking probability is effective in the casc of
the total waiting time for customers from type k in which class N
cannot exceed the end-lo-end delay bounds. The total waiting time
q, in our queueing model is defined as follows:
E.J. Ha and J.T. Park (Depcrrfnierzf U/ Electronic Enginrering,
N(itiono1 University, 1370 SmKyirg-Dong, Bik-GLI.T ~ e g u ,
and OIE, Y. : ‘Dclay analysis for
traflic in static-priority scheduling: single-node and
homogeneous CBR traffic case’. IEEE SPIE’97, I997
2 HOSIII, T., ThNIWAQA, K., kllld T S U K A U A , K : ‘Voice Streall1
multiplexing bctwceii IP tclcphony gateways’, IEICE Trcrris. In/:
AsJ).St., 1999, E82-D, (4)
3 ROSS, I C . ~ . : ‘Multiservice
tcleconiniunication networks’ (Springcr, Berlin, 1995)
[IDA. IC., I’AKIUB,T , S U N A H A R A , 1 1 ,
Ion-exchanged waveguide add/drop filter
D.F. G e r a g h t y , D. Provenzano, M. Morrell,
S. H o n k a n e n , A. Y a r i v and N . Peyghambarian
Results; We havc evaluated the blocking probability using our
proposed schemc. We treat the heterogeneous trunk case and
assume two types of traffic, high and low. High traffic flows are
preferentially assigned to the DSCP-EF trunks. High trunks have
a larger capacity than low trunks, in order to meet their higher
demand. The low traffic flows are assigned to the DSCP-AF and
DSCP-BE trunks according to the trunk conditions. In our evaluation, thc total amount of traffic is fixed lo 12700 flows. Therefore, the mean utilisation becomes 84.7% if there is no blocking.
Table 1 shows the voicc traffic blocking probability according
to the varying capacity of each low class trunk. In this case, the
amount of D S C P E F is fixed at 1400 flows. From Table I , the
optimal value for minimising the voice traffic blocking probability
for DSCP-AF and DSCP-BE trunks exists in which DSCP-EF,
D S C P A F , and DSCP-BE trunk blocking probability become <
10 4. It shows that the QoS requirenieiits are well satisfied by
using our proposed scheme. Additionally, the same results are
obtained when the capacity of each of the high-class trunks varies
with time.
Extensive work has been done on thc development of add/drop filters due to their functionality in all-optical networks. Ionexchanged waveguides have demonstrated low propagation loss
[ 11, negligible birefringence [2] and photoscnsitivity [3]. Numerous
devices have been fabricated using this technology [I].
PI,, I, ( L )
An addidrop filter is fahricated using ion-exchanged waveguides
and photowritten Bragg gratings. The device exhibits 20 dB
extinction ratios and 3 dB bandwidths of 0.4nm (100GHz).
2 1st June 200 I
Vol. 37
Here we report the demonstration of an adddrop filter using
ion-exchanged waveguides and photowritten Bragg gratings. The
device design is similar to previously reported ones that used fibre
[4] and silica-on-silicon [5] waveguide technology. A schematic diagram is shown in Fig. l . Two singlemode wavcguides of different
widths are brought together into a two-mode section.. The twomode section is again later separated into the two singlemode
waveguides. lnput signals on the narrow waveguide are coupled to
the odd mode of the two-mode section. A tilted grating breaks the
orthogonality of the two modes and rellects one wavelength channel lo the backwards propagating even mode, and back out the
wide ‘drop’ port. The rest of the channels continue on to the output port. Additionally, a signal at thc dropped wavelength can be
added through the fourth port.
Surface waveguidcs were formed in borosilicate glass by silver
ion-exchange [I]. The waveguides were formed by first patterning
a lOOnm thick Ti mask layer on the glass substrate with the add/
drop design. The Ti mask was oxidised for I h in an N a N 0 3 salt
melt at 380°C. The sample was then placed into an AgN03 salt
No. 13
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