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(Jz IEEE
Transact.(oit_
on
Commu_ca_/_o_s.
N 9 2 - 2 3 4 '2°23o
A Robust
Coding
Scheme
Y.C. Chen, K. Sayood
for Packet
University
P
and D. J. Nelson
Deparmmnt of Electrical Engineering
for Commuvdcation
and Infom_ation
Center
Video
,",, (.t
I\ i _"'
Science
of Nebraska-Lincoln
Abstract
V,',: present
tansmissi_?n
a layered
scheme.
sigv, i*=.cant packet
packet
The
los_
video
coding
algo_-ifl_m providcs
wid_
graceful
goed
degradation
Si;,_v,!_.t[on rcsul{s for va;-i<)us coudi[ions
I.
algoritEm
based
on
compression
in the
a progressive
and
can
reconstruction
ha_:d!c
sequence.
are presented.
INTRODUCTION
D,cc :o _,e r:.pid cvolution
in the fields of image proccssing
will be an i,_:Feuant p'art of tomorrow's
telecommunication
and nctworkiug,
system.
vMco information
Up to now, video tr_smission
h:_s bccn main]y trausponcd over circuk-swkched
nctv,'crks. It is quite likely that packet-switched
networks ',till derail:ate t)_e communications
world in d_e near future. Asynchronous
transfer mode
(ATM) tecIm!quc._ in b_oadband-lSDN
envirop.mcr.t for video communication.
transmission ovcr such p.ctworks.
The classic
a continuous
circuit
approach
bandwidth
is therefore
bandwidth
in circuit
capacity
wasted.
can provide a tlcxible, independent m_d high pcrfonnance
Therefore, it is necessary to develop techniques for video
switching
in advance.
Rapidly
to be accommodated
is to provide
Any unused
varying
by a standard
signals,
a "dedicated
b_dwidth
like video
circuit-switching
path,"
capacity
signals,
channel.
thus reserving
on the aliocated
require
too much
With a certain
amount
of capacity assigned to a given source, if the output rate of that source is larger than the channel
capacity, quality will be. degraded.
If the generating
rate is less than the available capacity,
the excess channel
capacity
is wasted.
The
use of packet
of channel sharing protocols between independent
Another point that strongly favors packet-switched
of services in a network
the same format.
Some coding schemes
proposed
a DPCM-based
will be facilitated
which
system
networks
allows
sources and can improve
networks is the possibility
if all of the signals
support
packet video
which
is comprised
are separated
have been explored.
for the utilization
channel utilization.
that the integration
into packets
Verbiest
of an intrafield/interframe
and Pinnoo
predictor,
This work was supported by a grant from the NASA Goddard Space Flight Center (NAG 5-916)
/.
with
a
nonlinear
quantizer,
by switching
and a variabIe
between
replenishment.
layer bas_
contain
on hybrid
"add-on"
fidelity
is based
on
channel entropy.
transform coding,
presented
DCT-DPCM
"guaranteed
Darragh
by allowing
an algorithm
coder
with Progressive
This
layer
contain
DPCM,
using
and Baker
interfrmne
DPCM[2].
presented
DPCM
DPCM,
and no
coder
with a first
This scheme
generates
packets"
coder
which
tim sub-bm_ds
quantizer
attains
The codec's
to minimize
using discrete cosine
Karlsson and Vctterli
followed
by run-length
with run-length
coding for nonbascband[5].
In this paper, a
on a progressive
transmission
scheme called Mixture Block
(MBCPT)
[6,71 is invc_tigatcd.
use dcchna_ion
docsn't
However,
quality
rate to vary[3].
among
with a nonuniform
picture
and "enhancement
a sub-band
compression
distortion
stable
replenishment
vital information
that allocates
using
it does have
f_cqucnc;,, a:',.i h)w frequency
_,cc,.s_zc
intrafield
conditional
the encoder's
Transmission
above, MBCPT
in'.o sub-bands.
and second
codec obtains
Kishino ct al. describe a layered coding technique
which is suitable for packet loss compensation[4].
a sub-band
mcndo;_cd
Their
a two-layer
packets"
ceding for baseband and PCM
different coding scheme based
Coding
coder[I].
coding modes:
has simulated
information.
a user-prescribed
design
three different
Ghanbari
two type of packets:
length
and interpolation
the attraclive
information.
Unlike
prope_%, of dealing
This separa'ion
those
filtcrs to separate
is obtained
methods
the signals
separately
wkh high
by tl"e use of variable
;rap_q'om_ coding.
paFcr
*cqvircmcn:s
is organized
of: packet
video
as follows.
First,
are discussed.
sor_c
of the
In Section
importar_t
3, rise coding
characteristics
scheme
callcd
and
Nlixture
Block Codi;sg with Progressive
Transmission
(MBCtrI ") is prescmed.
In Section 4, a ne_work
simulator used in testing the scheme is introduced.
In Section 5, the simulation
resulLs are
discussed.
II.
Finally,
in Section
6 tt_c paper
CHARACTERISTICS
OF
The demand for various services,
communications,
is summarized.
and full-motion
PACKET
VIDEO
such as telemetry,
tfigh-resolution
terminal
and computer
connections,
voice
video, along with the wide range of bit rates and
holding times they represent, provides an impetus for building a Broadband Integrated
Digital Network (B-ISDN). B-ISDN is a projected worldwide public telecommunications
Service
network
that will service a wide range of user needs. The continuing advances in the technology of optical
fiber transmission and integrated circuit fabrication have been driving forces to realize B-ISDN.
The idea of B-ISDN
with broadband
has an access
is to build a complete
channels.
rate of about
Packet-switched
for transmission
acquire
requirement,
switching
bandwidth
it is attractive
the transmission
switched
defined
digital teIecommunication
by CCITT,
network
with fiber transmission,
H4
135 Mbps.
networks
and
and release
end-to-end
Still to be precisely
have the unique
resources,
as needed.
characteristics
and
the elimination
Because
to utilize a packet-switched
rate to vary, video
coding
of dynamic
the video
network
based on packet
bandwidth
of channel
signals
structure.
vary greatly
permits
They
in bandwidth
for video coded signals.
transmission
allocation
Allowing
the possibility
of keepingthe picturequalityconstant,by implementing"bandwidthon demand".There
threemainmeritswhentransmittingvideopacketsovera packet-switched
network:
arc
1. L'nprovcd and consistent image quality: if video signals are transmitted over fixed-rate
circuits, there is a need to keep the coded bit rate constant, resulting in image degradation
accomDanyh_g
2. Multimedia
provided
rapid motion.
integration:
using
3. Improved
sources,
efficiency:
video
using
sources,
at the same time,
video
above,
integrated
transmission
variable
bit-rate
are without
to tiae point
they have
tt_c ','aoi_qg rat..:. If the amount
to s,,vitch into a coding
In t)ackct-switched
efiicicntly
aL'.<oH)temporal
rate.
_d
control
variations
yields a better
varying
rate requirements
available
charnel
the interactions
into the requirements
1. Adaptability
infommtion
rendering
drawbacks:
from time _o time.
of constraha_
due to the Iluman
to tee wrong
and may seriously
damage
which
losses
of channel
coder
changes
the coder
These
threshold,
Division
receiver.
tl_e qua!ity
of
of individual
quality
sources
network
to avoid
by smoothing
capacity.
can
out the
buffers[8].
generates
resource
a high and greatly
varying
but use of a packet-switched
However,
it should be noted
on the traffic
that the
with the variations
in the network.
have to be considered
requirements
is
buffer
(ATDM)
a reM time sea-vice is a difficult
are inevitable,
depending
the encoder
Multiple×ing
may not be synchronized
and the network
for the coder.
a certain
rate but worse
Time
when the source
packet
of the video
exceeds
in the common
especially
utilization
capacity
between
of tl_e bit-rate
time and provide
ne_'orks,
network
Ix:cause
that has lower
Asbqachmnous
streams
in a limited
problem,
bandwidth
mode
networks,
independent
In packet-switched
where,
of data in the buffer
ovcrllo'<.
allocation
if othe.r
in the netv,'ork are nonstationzz_y and circuit-switching
is used
between the coder m_d the ct_anncl is needed to smooth out
it, strutted
packets
sharing
distortion
also has the following
because of errors and delivered
the acquirabIc
\Vi'_c_ _]'_csignals trans;nit_cd
v,,id_ ;imi:cd bazndwidth, a buffer
To deliver
,and channcl
without
that the de!a'.,,,qost effect can reach very high Icvels if t!",e combi_ed
'.>;c_s' rwq,airct',_.cat c×cccds
H',_ i_a ::g'e.
aggrcg, ate of sevcraI
can be
to be discarded.
3. llca_L_'_sof p:_.ckcts may be changed
lt I':_._"o i>_:emphasized
services
rapid motion.
over packet networks
2. P_,zt.cts may bc dclaTed
coding
_scenes can be transmitted
1. T]:c t]:'zc Iaken _o _ransmit a packet of dm,a may chan_c
',"i_Jal Sbstcm,
broadband
protocols.
transmission
an_ong multiple
tlov,cvcr
,as mentioned
unified
in
Therefore,
and be incorporated
include:
of the coding scheme: The video source we are dealing with has a varying
rate. So it is expected that the encoder should generate different bit rates by
the redund-ancy.
When the video is still, there is no need to transmit
anything.
2. Insensitivity
to error: The coding scheme has to be robust to the packet loss so that
tt_e quality of the image is never seriously damaged.
Remember
that retransmission
is
impossible
because
of the tight timing
requirement.
3. Resynchronizafion
of the video:Because
thevaryingpacket-generating
rateandthelack
of a commonclock betweenthe coderandthe decoder,we haveto find a way to
reconstruct
the receiveddatawhichis synchronous
to the displayterminal.
4. Ccrtrolof codingrate:Sensingthe heavytraffic in the network,thecodingschemeis
requiredto adjustthe codingrateby itself. In the caseof a congestednetwork,the
codercouldbe switchedto m_ott_er
modewhich generates
fewerbits with a minimal
degradation
of hnagequality.
5. Paralldarchitecture:
Thecodershouldpreferablybeimplen_ented
in parallel.Thatallows
thecodingprocedure
to be runat a lowerratein manyparallelstreams.
In tl",enextsection,we investigatea codingschemeto seehowwell it satisfiesthe above
rc({uirc_:Ic::[_.
III.
.",IIXTURIg
BI,OCK
CODING
WITtt
PROGP,
ESSIVE
TI,IANS>IISSION
.,",li:,:'_'.:icI-;1o.ck Ccding
(_t3C)
c,:_des t!.: i:p._:g,_ v,ith dill'trent
blocksizes
ko,,v-(>.:t':,:!cxit;,,' areas :':re. coded
_..'g[c)r_ :.:: coiled
is a variablc-blocksize
v,.ifl_ small blocksizc.
NIt3C !:____?:e ability to choose
parts <'/"tire same image.
Wt,.cn 'as{r,g MBC, the image
between
coding
complex
is divided
the reconstructed
coding-testing
procedure
continues
Mixture
combines
Block
Coding
approximations
information
coding.
block is dctennip.ed
"FEe advantage
Progressive
blocks.
(MBCPT)
converge
to the target
where the entire image is transformed
every pixel value, or the information
total bit rate may increase
image
approximations
image
is an approach
it. The process
the
processed
threshold.
is a coding
with the first approximation
enhancing
coding,
or the smallest
at a lower bit rate which can later be updated[9].
and the following
After
quality
coder.
The block being
until the reconstructed
coding
complex
with the same blocksize
is small enough
transmission
of using
That means
an image of higher
blocksize
by
of bits arc uscd _o
fails to meet the predetermined
is coded
with progressive
MBC and progressive
image to be transmitted
regions
until the distortion
is reached. In this scheme, every block
m_d then moves to ttm next block.
area.
to deal with different
block is calculated.
is suL':Uvided into smaller blocks if that distortion
of that block
wl'dle high-complexity
distol:ioa.
scheme
into maximum
and original
which
with tt_e same blocksize.
With the same rate, MBC is able to provide
than a cedi_qg scl_cme which codes different
distoi_ion
regions
a tiz_cr or coarser
algorithm
the same number
has higher
complex
coder
of [l_e specific
image when
image block
different
coding
the complexity
transform
The complexity
and original
cede c:_,ci_,kloc!<, eL more complex
i_ _}::::iv decs not process
upon
witll a large blocksize
'dnc di.,.'_o_-:ic:_,
bc:t,,vcen ;he coded
),iBC
depending
transform
The
blocksize
is satisfactory
scheme
that allows
which
an initial
In this way, successive
carrying
the "most"
is like focusing
a lens,
from low-quality into high-quality.
In progressive coding,
contained in it, is possibly coded more than once and the
due to different
coding scheme
and quality desired.
Because
only the
grossfeatures
of ml imagearebeingcodedandtransmittedin thefirst pass,theprocessing
time
is greatlyreduced
for the first passanda coarseversionof timimagecanbedisplayedwithout
significantdelay.It hasbednshownthatit is perceptually
usefulto get a crudeimagein a short
time,rafflerfilm1waitinga long time to get a clearcompleteimage.
-V',qth
differentstoppingcriterion,progressive
codingis suitablefor dynamicchmmelcapacity
allocation.
If a predetccmincd
refining action is needed.
the channel. Successive
threshold
priority,
(or iterations)
to the desired
image.
then a sudden decrease
image to suffer from quality degradation
MBCPT
is a multipass
fi_st pa_s ccdc:s d_e image
scheme
is met,
processing
value can be adjusted
approximations
coding and lead the receiver
with decreasing
distortion
The threshold
is stoppcd
according
are sent through
in
the chatmel in progressive
If these successive
in ch,_a-mel capacity
and no more
to the traffic condition
approximations
arc marked
may only cause the receiv'ed
rather than total loss of pa_..s of the images.
in which
with maximum
each pa';s
blocksize
bloc!:.,; ,,vi',ich fail to meet the. distot-tion threshold
deals with different
and transmits
go down
blocksizes.
it immediately.
to the. second
The
Only those
pass which
processes
lhc diffcrc=;ce image block, coming from the. original and coded image obtai_;cd in Hm first pass,
v:i!h sm:_]!cr _.>!_cks. The difference
image coding scheme continues until tee final pass which
deals ,.vi:il :.'qc miz_imum size block. At the receiving
ii_s_ pas.q {a a st',ort time. and the da{a from following
end, a cn'dc image is obtained from the
passes serve to enhance it. Fig. 1 shows
the st_-t:cterc cff pass c_,msisting of 16xi6 blocks for MBCt-q". Fig. 2 shows *I'veparallel structure
of ._[t;C_<. Codii_g algorithms using quad trees have also been proposed by Drcizen[10]
and
','aiscy
a::d Gc_h,,_[l 1]. In the quad uee coding structure
and the distortion
of the block
is calculated.
If the distortion
tJarcsh_?Id fcr 16"<i6 blocks,
the block is divided
codi_g-ci:cckir_g
is continued
procedure
arc those of size 2x2.
Fi_rc
storage
rcq_ircmenls,
but large enough
resull_s in t_gher compression,
larger than 16x16 because
scheme
to limit the inter-block
in the coded edge of spherical
match the zonal transform
four passes (16x16,
After applying
coding
in the first p_s
blocksize
the average
subsequent
real-time
of computations.
determines
blocksize
only four coefficients,
gray level
transform,
coefficients,
for that image
a laplacian
4-7 show images
are coded and others
with an 8-bit uniform
block
quantizer
is chosen
blocksize
the
In order to
and there are
from the 4 passes.
including
the dc and
are set to zero. The dc coefficient
due to the fact that it closely
and is hard
that is
to observe
the coding block is square.
used in this paper, 2x2 is the smallest
cosine
block size
So, 16x16
is too large, it is possible
objects because
and
for blocksizes
the finest visual quality
the discrete
passes follows
the thrcshold
Larger
hardware
Fig.
is coded
This
for e_e of processing
8x8, 4x4, 2x2) in this scheme.
three Iowest order frequency
coding.
not meeting
redundancy[12].
to build
in the number
minimum
act_.cvab!e in _,e busy area. If the minimum
blockiness
blocks
should b._ small enough
but it is re©, difficult
The
th_a the predetermined
the algoiit/un.
of the i_crease
to bc the largest blocksize.
is greater
into four 8x8 blocks for additionaI
umil the only image
3 shows
The blc<k size used in the coding
of ttlis paper, the 16x16 block is coded
to model.
model, and a 5-bit optimal
The dc coefficient
laplacian
nonuniform
reflects
in the
quantizer
is used to also follow a laplacian model with a variance greater than that of the dc coefficient
and can therefore also be coded using a laplacian quantizer.
As an alternative, an LBG vector
quantizer
with a 512 codebook
size is used to quantize
the vector which
comprises
the three ac
coefficients.
the
Tile
initial
operation
according
Because
only
side
if not,
channel
blocks
is needed
is needed
overhead;
of each
to the
partial
infommfion
of ovcrhcad
threshold
which
is selected
condition
and
fail
to instruct
for each
pass
the
block.
a 0 is assigmed.
to meet
quality
the
receiver
on
If a block
The
beforehand
cxm'nplc
and
during
required.
distortion
how
threshold
need
to reconstruct
is k) be divided,
shown
is readjustable
in Pig.
the
to be coded,
image.
One
a 1 is assigned
8 has
the
bit
to be its
following
overhead:
1,1001,1001,1001,1001,1001.
The
This
interfr,',,me
coder
frame
coder
processes
which
used
the
is locally
in this
paper
difference
decoded
image
from
codcn
Pig.
10 shows
a different
passes.
From
F!g.
11, it can
be seen
two
sci_cmcs
priorities
arc quite
_sigz:cd
c:_.sc, t]:c pcrformm:cc
Fig.
10.
m<!on
sourcc.
D,cE,'
ctmrac',cristlc,
u_cd
From
image
those
packc_s
the
frame
lost
IV.
when
from
pass
memory.
packet
belongs
to pass
SIMULATION
The network
de.ycleped
the
previous
algoritlml
with
in the nctwork,
to be discarded
9 is much
all four
perfonn_ccs
with
first
file one
in
In this
paper,
the
16
as
simulation
is used
0 to 255.
nor scenes
or motion
than
the
In this
in ot)r simulation.
frames
better
of
the
It is similar
chm_gcs.
compensation
to a
Due to this
have
_:ot txcn
in Table
I,
priority
possibility
loss
see
that
the. data
in it, creasing
in network.
the locally
error
image
into
4
cM1 this d_c
due to low
decoded
propagating
in pass
the sharpness
We therefore
of beir, g discarded
to reconstruct
packet
we can
is involved
priority,
and be storcd
following
frames
if
4.
NETWORK
simulator
by Nelson
the
the
the
video.
the lowest
be used
prevents
and
decoding
loss,
occurs
motion
par_ of the data
a substantial
4 won't
This
rapid
on MBCP'F.
9 shows
local
packet
r,n_,m_,
'_ _," ,, f;om
detection
is listed
This
with
With
wilh
broadcasting
that
data.
Iabclcd
pass(LSP).
has i_,eithcr
die
is based
frame
Fig.
cxpcctcd
in Fig.
graylcvcls
motion
does
9 is used
database
wiih
like
output
and is usually'
sigz:iKcant
in the
implemented
__040c; , of the entire,
least
USC
which
techniques
r_}:cd:_.t._.strea;n
rct.ucscms
el-the
bc
the
current
congestioa
scheme
which
data.
is no
4 arc
in Fig.
pixcls
tVFC
.
image
T
adv_mccd
but co'rid
from
is 256x256
which
pass
12) of the
scheme
the
pass
thcrc
But v,,hcn
from
scheme
from
three
scheme
sm'ne.
Fig.
coding
sequence
im.:gc
_.o_crv:,_._mg
""
e ....
:.
Vii!CO
the
first
fl_at when
packets
(from
7}:cJcfc_e
Krop.kite
the
to packets,
coming
the
of this
these
is a differential
used
et al.[13].
for figs
A brief
study
was
description
a modified
version
of the simulator
of an existing
is provided
simulator
here.
A. Introduction
As
mentioned
complicated
algorithms
system
in section
and dynamic
with
2,
structure.
communication
components.
The
tomormw's
scheme
integrated
Its efficiency
between
nodes
telecommunication
requires
reflecting
for communicating
6
sophisticated
the existing
information
network
monitoring
capacity
regarding
and
the
is a very
and
control
reliability
operating
of
status
is called the system protocol.
the ch_nel,
efficient
it reduces
the overall
system overall.
which,
capacity
Therefore,
in turn, depend
memory
Since the communication
upon
of the physical
system
the system
efficiency
topology,
and component
reliability.
Most network
in topological
structures
with. reasonably
reliability
In order to fit into the purpose
of system infom_ation
layers, but hopefully
depends
entirely
communication
protocols
provides
upon
these
charuml
a more
protocols,
properties,
have been developed
high channel
nodal
to provide
high
reliability.
were
made to the
simulator were in those modules concerning file network layer. Since the simulator
in modules which represent, to some degree, the ISO Model for packet switched
is structured
networks, a
more detailed description
B. The
Network
about
Layer
of this study,
must flow through
the network
and
most modifications
layer modules
Basic
which
follows.
Operation
The simulation of a layer at each node is rcprescnted
by a "proccssor"
m:d one or more
"packet queues." All events are scl',cdulcd through the. "Sim_Q"
which drives the simulator.
Ip,itially, the pa)cessors
are all idte, the packet
a:-c th,: ar:ival of messages
at ttne various
the next e.vcnt and pcrfomling
additional, events, generally
pIaccd
i._ sch.:dulcd
is removed
for completion.
_:_.t point in time),
completica
it removes
of the operation
in operation
for a givcn
The
occurs by examining
may result
times.
Whoa
layer, the processor
in the scheduling
a message
(as a result of the simulator
If the queue
or packet
must be pcrfomled.
to the ISO transport,
network
is empty,
from the queue
The la)'ers
,and datalink
is
is marked
by the processor
examines
the queue.
of
or packet
for that queue
and the task to be performed
the next message
which
t_k
operation
the task is completed
the. "processor"
is set idle; otherwise
indicated.
from the queue,
When
arc. all empty and the only tasks scheduled
The simulator
to as task completion
in ti:c input quet._e at anodc
as busy, fl,,¢ packet
dose
the t_k
referred
queues
nodes.
_d
reachir, g
the processor
schedules
in fl',e simulator
ttac
are quite
layers.
(1) The Session Layer
In die OS[ model, the session
remote s)stems.
In the simulator,
of the subscribers,
arriving
participates
and delivered.
"message"
At message
During initialization,
arrival
message
in flow-control,
with all of its randomly
are not in effect, submits
time.
layer (SL) allows users to establish "sessions"
on loc,'d or
as mentioned
above, it contains a relatively simple model
anributes
layer.
at that node.
collector
Q), the session layer
and if flow control
It then schedules
the task "SL_Rcv_Msg"
and placed
as a statistics
time (from Sire
selected
it to the transport
time of the first message
packet is generated
arrival
andacts
When
this task is executed
queue.
generates
or node
the
hold-down
the next message
for each node is queued
in the transport
for messages
in Sim_Q
arrival
for the
by the simulator,
a
The arrival of the next message
is then queued in SimQ
with the same task and with an arrival time determined by the random
number generator (Poisson Distributed).
The only other task performed by the session layer is
the "SL_Snd_Msg"
statistics
and "cleans
task that simulates
up" the queues
delivery
of messages
for messages
to the subscribers,
delivered.
develops
message
(2) The Transport
Layer
The basic function
session layer, place
of the transport
it in packets
and pass the packets
end, the packets are reassembled
the complex
task of assuring
the sending
and receiving
sending
into a message
reliable
nodes
node when all packets
used.
delivery,
entire message
is discarded.
at th_ network
level,
in the allotted
in this paper,
the transport
received.
At the sending
time period,
networks,
responsible
at L-_fl_
that is sent to the
in the specified
that in some
layer
mechanism
packet
the message
the retransmission
are not received
It is recognized
leaving
layer. At the receiving
time-out
have been satisfactorily
reported
end, if all packets
from the
to the session layer. To accomplish
acknowledgement
is not received
the message
on to the network
there is a transport
for the message
In tt',e simulations
At the receiving
end is to receive
for delivery
and a message
end, if a me.ssage acknowledgment
be rctransmiucd.
layer at the sending
feature
can
was not
period
of time, the
packetization
takes place
only for message-level
structures.
Re_sembly,
depending upon the protocol, can take place as low as the datali_9: level. These
tasks ware beth placed in the u'anspoJl: layer, but ,arc modular, and could be extracted a_:d
placed clsev,['_cre. Also, the simulator
the pac',e.ts do r,ot necessarily
ardvc
at Iiac data!ia_k lcvcI.
(3) The Network
was originally designed for datagram
in order, it is ul_likely tt_at assembly
I.myer
Ti_e. _:cr.vork layer is cop,cot-ned with controlling
isst:c is dc[cn-nining
how packets
avoid _t;c congestion
time.
caused
I_; _,: si_mdator,
aspects
aad tJ;e recovery protocols
new ct_anac!s whca
are routed
when
from source
layer
performs
which
some
require
layer is currently
to dcsdnatior_.
service
which
Anodmr
originating
tl_e most dynamic
issue is how to
related
at the same
to these two
t:d<es place at the session layer,
from the datalink
when packets
A key dcsigi-t
to tl'e nctwork
all of the functions
of flow control
and detem_ines
of the nctv,'ork.
are presented
of that _pect
needed
"Finenetwork
the operation
too mrmy packets
_i_e network
with the exception
discardS.
service, and sit:cc
would tr&e place
layer.
It also activates
at other nodes
are to be
with regard to the coding of modules.
Five modules currently comprise the network layer. These include relatively static modules; one
module for capturing lines or channels when more capacity is required and releasing them when
tt_ey are not needed; one module for the network processor and queue handling and one module
for the routines which are common to most routing algorithms. This leaves two modules for the
dynamic
parts of the routing
(4) The Datalink
and flow control
Layer
The main task of the datalink
into a line or channel
the sending
received,
that appears
of the message
the datalink
or by generating
algorithms.
layer
is to take a raw transmission
free of transmission
over the channel
actmowledgement
a datalink
and the delivery
is initiated
acknowledgement
errors
either
packet.
up",
health
packets
are used to establish
and transfom_
layer.
it
It simulates
at the other end. When a packet
by the piggy-back
As mentioned
level also simulates the physical layer on a statistical basis.
conjunction with a random number generator to determine
a line is "brought
facility
to the network
is
acknowledgement
previously,
the datalink
(Entered bit error rates are used in
if messages are corrupted.)
When
initial
connections.
Also, when
a
line "goesdown",anactivenodewill immediately
issuehealthcheckpacketsto ascertainwhen
the ch_mmel
is againavailable.
C. Modifications
A major problem
is that _L_b&ially
of using
designed
this system
the system
as a simu]aJon
did not actually
tool for the study of packet
transmit
messages
from node
video
to node.
While a "packet" carrying all the necess,ary describing
information
moved from node to node,
there no actu_ data in the packet. Therefore,
modifications
had to be made to the simulator
to accom_<odate
the video
real image
data is attached
the scs_ica
layer.
image
dam b:o
"b<_gc
In the sending
to the record
There
are three
chccks
s,'.;_.;eimage
node,
modules
message,
gcneratcd
"Receive
allocated
in this
generated
to see if d',ere is any image
data. Ttgrd,
a field called
"Packct_Ptr"
new
l_be imam,
go field of a message
Available"
that is mac, C.c. folJowing
contains
data.
First,
at a spccific
tI'o image
is on. Ira module
messages.
In module
for inmgc
including
the number
in
puts the
time and node.
Seceded,
data in the sessiou
Complete"
s:a,.istic:q arc calcdated
generated
"Get_Image"
If
node, is still _e image message
coIlccts
dift'c_ci'_t I.Iicritics
to different
contains
data that still needs to be transmitted.
of the icceivi:_g i_odc when the flag "Image
are assigned
which
to the message
layer.
at that specific
hnagc"
"Image"
"Session
"Session
of lost inaagc packets
and
layer
Msg_Anivc",
Msg_
Send",
and the transmission
son'e
delay
packets.
In th.z original deisgn, the transt'oIt layer simply duplicated J:c same. packet
a_ss:ig;:cd sc_lJcmial packet numbers
wilhout actually packctizing
the message.
with different
The module
"'Frans_:occ_Packe/izc"
resides
has been modil]cd
message _._cord queued
is called to reassemble
"Image
in "Transport
these image
Con_ent" defined
to really tmckctize
the. image data which
in the
Q" when it is called. The module "Transport_Reassemble"
packets according
to their packct number when the ftag
in "Packet_Ptr"
is true.
The
network
layer
is responsible
for routing
:rod _ox,,'-co;',trol. This module was already very well developed,
so the modifications
to be
performed i..cre were relatively minor. In the datalink layer, in order to simulate the dclivery of
packets
including
Lt=ough the channel,
a new packet is generated
_e inaage data from the transmitted
node) are copied into it. Using
existing
packet
at the receiving
(which
bit-error-rates,
and bit errors can be inserted in both the data and control
bits are simulated
occurs,
separately
the. transmission
the threshold
will still be resident
the transmission
number.
to fail and retransmission
In addition
success
bits in the packet.
as long as the error rates are consistent.
is assumed
of the timeout
node and the information
in the control
If an error in control bits
will occur,
to the modifications
Errors
at the sending
rate can be set
again depending
on
made to the layer modules,
we had to arrange some new memory elements allocated for image messages and packets. In
order to make sure the simulation
is run in the steady state, the image data is made available
to the network
after
some
simulation
time has passed.
V.
INTERACTION
When the video
These
OF THE
data is packed
are discussed
CODER
AND
THE
and sent into a nonideal
in the following
NETWORK
network,
some problems
emerge.
section.
A. Packetization
The task of the packetizer
if it exists, and synchronization
propagation
is to assemble video information,
coding mode information,
information
into traalsmission
cells. In order to prevent the
of the error resulting
from the packet
loss, packets
other and no data from the same block or sanae frame
segmentation
process
avoid the. bh stream
is separated
in the tr_msport layer has no information
being cut randomly,
e_c_>der, v.l-!ci_ is in the presentation
to kc ::ddcd i_-to the. datastrcam
desired
are made independent
the packetization
layer of the user's
to guide the transport
process
(>f a l:aC;:c_,video wifll
Otherwise,
to perfonu
n'an_:er. In order to limit the delay of packctization,
Ever)' i:ackct must contain
an absolute
address
address
of the following
blocks
with the
the packetization
has
in the
to stuff the Ia_st cell
full.
which indicates
the location
of the first block
r of bits in each pass, there is no
it carric.s. ?.ccau:¢e evcry block in NIBCPT has the .<area numl,
accd _o h'dicatc the relative
The
fore, at. 2"o
some overhead
it is necessary
bits if the cell is not completely
dumnty
packets.
the video
has to be intcgratcd
premise.
layer
into different
regarding
of each
contained
in the same packet.
There
alv.o.?s c:::i:_.; a tradcoff between packaging efficiency and error resiIicnce.
If e,'-ror resilience
is c<);l:<idcrab!c, one packet should contain a smalIer number of blocks. However, sit:co each
ch:n:c!
access by a station contains
ci'ficic_:c)'. Fixed length
overhead,
packetization
Because of the stcucturc
the packet length
is used in this paper
of the coding scheme,
for simplicity.
the packets
with the packets from the first pass classified as the highest
from th:: fou_ p_-Lss_ the lowest priority packets.
This
priori b,
assi_-m:ent
also
rcco;t_t_.action of the image sequence
the same amount of packets
B. Error
lass can be mainly
ability
created by higher
passes
became
that packets
attributed
astray
and packets
Table
of
the
and the packets
various
packets
to tt_e
1 shows the effect of approximately
error in tt_e received
to two problems.
are forced
get lost after being
First,
Second,
with zeros.
_e lost area is scattered
The distortion
spatially
bit errors
congestion
to be discarded
pass packet loss (like pass 4) in MBCPT
and replaced
effect is very
won't
in the network.
pass 1), though rare due to high priority,
the
importance
at the receiver.
into four priorities,
packets,
sequence.
Recovery
field, leading the packets
management
the
are cl_sified
priority
lost in each pass on the reconstructed
Them is no way to guarantee
Packet
reflects
should be large for transmission
is almost
and over time.
will create
objectionable.
10
sent into the network.
can occur
in the address
can exceed
the networks
due to buffer
overflow.
coding will be masked
invisible
However,
an erasure
when viewing
Effects
by the basic
at video
low pass packets
rates
loss (like
effect due to packetization
and
Considering
may
also
the
result
None.
In our
priority
and form
network
congestion
previous
when
complete
will
caused
block
is only
could
co,des
Sccc;_:d,
lost.
or
k_ss. TI,e
a::d
The
we. can
steady.
transpo_-t
It
by
the
to be performed
pass
are
4 are labeled
be discarded
and
won't
simply
in that
cause
This
too much
with
remedy
area.
Motion
for
replacement
area
lowest
whenever
covered
frame.
matched
video.
the
seems
detection
in the
see
that
timely
layer,
then
that
its output
change
rate.
in
the
output
rate
of
That
data
coding
loss
side
info1_nation
control
field
information
with
the latter
provide
depends
bit error
and
pros
of channel
circuit-switching
and
while
channel
amount
coding,
along
should
and
a certain
means
error
directions
in the
control
to rcscrve
First,
both
of such
be infom_cd
the
Im this
way,
can
rate.
1 and
capacity
be
used
for
different
decreasing
MBCFF
condition.
coding
rate
is overwhelming
with
fewer
quality
are some flow control
the encodcr
and the
steps
degradation
Depending
scheme,
the
or loosens
packetization
the
is obtainable.
on
if the buffer
rate
threshold
However,
to
fills
design.
congestion
and packets
there
between
t)_e network
In the
quantizer
smooth
congestion,
interaction
about
scheme.
bit generating
assigning
cause
severe nctv,'ork
If there is an
to a coarse
encoder
a severe
with
that
importance
and can
can
to use the
by
the
have
information
error
cotTelation
arrival.
its coding
switch
the
It is possible
encodcr
adjust
means
will
comFIicates
identifying
the
can
m_d ti_e. cncoder
disaster
applicd
is for bit error
feasible
So, this vital
for protection.
Coal:tel
is gctti_ G full,
quality
be
O_at the
loss,
It scorns
their
is very important.
s:<:a<tlr' data.
the encoder
decrease
can
distm_ce
In order to shield the viev,,cr from
schemes
which are considered
useful.
assigned
loss
in packet
can
previous
a best
scheme
fot_er
of packet
c>:_:yt::.v to cnsur.:
Flow
it can
pass
of motion
cm_ be used
codes,
minimum
probability
fr<>m Tal.>Ic. 2,
impo_:-;::
decoding
methods
convolutional
p:_ss 2 is quite
to the:re
Two
to th,: p:',ckctization.
en the ccv.,o;k's
also
packets
in the
to find
has
from
congestion
basic
amount
used
packets
These
area
small
be
in the MBCPT
to get
is f<>r packet
that,
by
feasible
recovery
the
the network
corresponding
there
error
data.
reduce
erasures
the
compensation
pcq_,cl",di:_l_r
C.
scheme,
_s not
fr'_e.
aik>ved
even
Thus,
MBCPT
of the
The
retransmission
congestion.
That
from
Sk!c infomlafion
like
part
occurs.
even
axed motion
is not
severe
a great
values
insufficient
constraint,
differential
in quality.
reconstructed
time
in more
decoder
degradation
tight
of 'each
a session
impact
from
on
pass
control
packet
shut
the
of the
priorities
down.
network
to packets
and
discarding
For
decoding
exampIe,
process.
1 are assigned
priority.
11
highest
protocols
different
packets
blindly
if the
In
to prevent
from
the
priority
side
MBCPT
and
the drastic
passes.
Without
sometimes
information
coding
higher
pass
brings
gets
scheme,
packets
lost
side
are
D.
Interaction
with
In tl:e ISO
model,
a network
node.
form
layers
and typically
the signet
physical,
The
reside
processing
capacity
m_d low
only deal
Protocols
datalink
higher
layers
and only
work
bit-error-rate
with link-management
transmission.
deleting
tim delay
ji_tcr
with input
assiging
mmsmission
video
coder.
lengttl
can h,: fixed
,a'hi!e
a va,fiable
supe1",'iscs
alv,'a)s
The
and
a tradco[t"
user
be obtained
\vhile
scheme.
The
256x256
pixels
The
compression
PSNR
Fig.
rate.
remains
the same.
4 is bunt),
of the image,
the
requires
about
adequate
The datalink
requesting
layer
rctransmission,
the network
care
can
is not
transmission
by
congestion
Fig.
the
it knows
with
session
video
all the
of the
format
application
session
layer
analog-digital
layer
There
is
can be dc'ennined
lx:twccn
most
packet
handling
quality.
trarumission.
tradcoff
the
The
for
does
The
and
of the
The
and packet
types
of a set-up
layer
here.
reassembly.
constant.
_vsignn:ent
13 shows
Becau._e
mid
different
quality
all the fimctions
seunentation
deIay
have
presematioq
high
image
quality
through
sequence
used
in this
shnulation
pixel,
simulation
which
the
is about
10 with
a mean
data
that
the
Of course,
PSNR
and video
signal
processing,
exactly,
works
signal
if an)'
on-or
as a boundary
conversion.
that
file use
data
PSNR
rates
of
16 frames,
15.3
of our
of 38.74
compression
of flxis differential
contains
in a bit rate
average
substantial
dB where
bIBCPT
each
Mbits/s,
system
given
of
size
a video
is 1.539
PSNR
cmr
Mbits/s.
is defined
as
a
rate
data
of the
rate
information
sequence
of pass
and data
highly.uncorrelated.
rate
profiles
channel
of some
sort
for passes
channel
for pass
4 data
which
show
results
2 shows,
Side
it performs
packetization
the p_%rity
As Table
the
and
layer
it can take
vidco
L/(_';-_,;)
It is clear
The
and
and deals
= 101ogle,,.-, _(25'5)2
14 shows
application
to do nothing
orderly
packct
8 bits per
rate
and
which
RESUUFS
in this
with
like
layers
ha.s to maintain
p:_ckctization
be perforated
maintaining
of 30 frarne_s.
pass
it \viii
monochrome
rate
physical
simplifies
which
cost.
The
and the network
obtained
tlm
the cost.
PERFORMANCE
Resul_
total
and
scheme
:rod comprcssio,m
bct,,:,ee;:
VI.
quality
thresholds.
is requircd,
he
kecp
the
length
for sessions
Ilk: higher
conceah::cnt
have
by technology.
s premises,
does
packet
Ici_gN_ can
t_:tv,'ccn
i_,cludip, g e.cparatien
Otherwise,
layer
Fixed
i_ the coding
d,e qu'ality,
The
only
layer
in the customer
tear-down
r<,.: by adiustiing
omput
layers
pipe".
the lower
presentation
lower
atl the mech,_a_ics,
buffering.
transport
p.'.cket
by the NrcshoId
d_c bc{tcr
reside
or variable.
set-up
session,
The
The network
comprise
priority.
As the h,;"eh_r
_" layers
packet
transport,
are detennined
because
video
layers
premises.
as a "packet
which
in packet
network
have
in a customer's
feasible
by
and
1-3
from
As
as shown
flames
pass
in Figure
and
comprises
the
morn
with
1 is constant
pass
2, even
4 data
side
pass
is not
14 and Table
side
than
12
information,
30%
infom_ation,
as long
of the
4 passes
as the quantization
3, is also.
The
essential
to the
1 suggest
the use
and
total
a perhaps
traffic.
and
mode
data
rate
of
reconstruction
of a reserved
more
Such
unreliable
a situation
can be accommodated
network
in a variety
of systems
with a packet-switched
such as a token
ring network
or a circuit
overlay.
Fig. 15 shows the PSNR for each frame in the sequence.
of the PSNR is only 0.2 dB, which
implies
a substantial
Notice that the standard
uniformity
of quality,
of objective performance
measures.
If constancy with regards to some
desired, it would be necessary to incorporate
this in the determination
the decision
mechmfism
throughout
for the quad tree.
tJ_e sequence.
tl_eshold
If further
In the simulation,
flexibility,
can be used for different
From the difference
9-13 contain substantial
switched
frames.
at least in terms
subjective criterion is
of the tt_esholds and
the same threshold
say for higher
deviation
has been used
visual quality is desired,
That may gcncrate
a more variable
a varying
bit rate.
images of this sequence, frmnes 1-8 seem quite motionless while frames
motion. ¥,re adjusted the traffic condition of the network to force some
of the packets to get lost and thus check d_c robusu_css of tee coding
w_ sct t:p in the motionlcss and motion period separately.
TI_o average
scheme.
Ilcavy traffic
packet loss percentage
was 3.3% _I_ich is considcrcd
images
high for most networks.
Fig.
16 shows
packet losses from pass 4. As can be seen, the cffcct of lost packets
tl_e Io._t packet rate is unrcalistically
pas._cs is rclatively
Fig.
high.
good and the packet
17 s]_o,,',s the case when packet
d_c n_otio:_ period.
What's
tl:e _cplcr_ist'dng scheme
worse,
used here
VII.
a_ea for replenishment
the pcrformm:cc
loss occurs
in pass 1. Clearly
is not sufficient
with a motion
for rcconstruction.
fl_crc arc ;'isiblc
to the iollo,,ving
in areas
compcnsater
a_:d error conccalmcat
suffcrcd
from the first thlcc
from the fourth pass is not csscntial
the C_TOrwill propagate
fl_is inco_lsisteI_cy can be eliminatcxt
appropriate
This is because
which
is not at all scvcre, evcn if
francs.
with motion.
a!gorittuu
de.fccts in
Apparcndy,
It is believed
that
which would find the
which limits the propagation
of error.
CONCLUSIONS
The network simulator
thne processor
was used only as a channel
is built, a Iot of statistics
upon the ceding scheme.
in this simulation.
can be collcctcd
These include transmission
In fact, before
from the network
delays
simulator
the real-
to improve
and losses from various passes
under
different network loads. For resynchronization,
the delay jitter between received packets can also
be estimated from the simulation.
The envirorm_ent for tomorrow's telecommunication
has been
described
and requires
the requirements
a flexibility
for applying
which
packet
is not possible
video
in mind,
in a circuit-switched
MBC'FT has been
network.
investigated.
With aH
It is found
that MBCFF has appealing properties, like high compression
rate with good visual performance,
robustness to packet lost, tractable integration with network mechanics and simplicity in parallel
implementation.
Some additional
system,
like designing
moving
scenes, the differential
concealment
useful
protocols,
or even attaching
tools to improve
considerations
have been proposed
packetizafion,
error recovery
MBCt_
scheme
function
commands
the performance
seems
insufficient.
into the coding
and will be the direction
13
for the entire packet
and resynchronizafion.
Motion
scheme
video
For fast
compensation,
error
are believed
to be
of future research.
VIII.
REFERENCES
[1] W. Vcrbiest and L. Pinnoo,
Networks,"
IEEE Y. Select.
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[2] M. Ghanbari,
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[3] J. Darragh and R. Baker, "Fixed Distortion Subband Coding of Images for Packet-Switched
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[,1] F. Kishina,
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[12] Y. S. Ho and A. Gersho,
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D. Vaise.y and A. Gersho,
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Adaptive
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47.8.1-10.
7?c:,':s. Col_:emm., vol.
[1i]
Using
Bit-Rate
vol. 7, pp.801-806,
Froc. 3lst ?,fidwcst S),mposi_em on Circlfits arzt S)'stet_ks', St.Lcuis,
[9] K. Slo_n, Jr. and S. T_limoto,
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"A Progressive
D. An:Lst_ssiou,
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CO,V:2',_t,
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912-915.
St;uistical Multiplexing
Nov.
"_qdco m_d Its Integration
Compression
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..\,.:g.19:{8.
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Comtnun.,
[7] ),L C. Rost and K. Sayood,
"Variable
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Nebraska-Lincoln,
Of
and H. Yasuda,
IEEEJ.
ICASSP,
D. Nelson,
K.
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Sayood,
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K-K535,
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2, pp.
Multi-Stage
1156-1159,
G. Ankenman
of Nebraska-Lincoln,
Vector Quantization
for Image Coding"
1988.
and
H. Chang,
Final Report
1986.
14
"Pnetsim
for ARMY
System
Programmer's
Contract
DAAB07-85-
Block
in
.....
to
• DCT
------_
i6x16
Q
1
Q-I
.........
overhead
/ /
buffer
_.__
--overhead
Figure
"
coding
j
goes
pass
data
Zonal
add
bur
0 to
fel:
e.dd i to
buffer
down
to
8 :,:8
1
Structure
of
for
I'IBCPT.
the
first
pass
consisting
of
16x16
blocks
IOverhead]
pass
16
x
-t _
16
Buffer_
l_
packetizer_
with
highest
priority
J
" pass
8
x
8
pa s s
4
with
pass
x
4
2
:< 2
with
decreasing
priority
lowest
priority
Figure
?!
2
Parallel
structure
for
r,_BCPT.
16
x
8
16
:< 8
4
2
:< 4
X
2
Figure
II
3
Example
"•
of
the
quad
tree
structure.
X
X
>£ x
16
overhead
Figure
8
:
Overhead
X
L6
l,!O01,!O0!,lOOl,lO01,1001
assignment
and zonal
coding.
LSP
Video
in
MBCPT
_
Q
CHAI_NEL
?
Coder
DCT-I
out
F
Decoder
Figure
;!
9.
Differential
I,IBCPI" coding
scheme
(I).
l,_
Video
video
in
MBCPT
_
Q
CHANNEL
I0-_I
coder
video
out
F
Decoder
Figure
If
I0
Differential
I',IBCPT coding
scheme
(2).
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Appendix
2-
Item
ll