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Reducing overall delay in MULTI-RADIO WOBAN with
least per node processing overhead on data packet
Asad Ali, Irfanullah, Savera Tanveer, Dr.S.M.H Zaidi,Fouzia Noureen
School of Electrical Engineering and Computer Science,
National University of Science Technology, Islamabad, Pakistan.
Email:{09msitaali,09msitirfanu,savera.tanveer,Drzaidi,08msitfnoureen}@seecs.edu.pk
bandwidth hungry applications, the need
Abstract-- Wireless-Optical Broadband
for such a network that support enormous
Access Network (WOBAN) is a hybrid network
technology. The back-End of the WOBAN being data and that has high capacity and
optical has very high performance both in bandwidth is apparent. Also optical
terms of speed and bandwidth. There has been network provides high data rate, low
lot of research and numbers of protocols were transmission loss, and low bit error rate,
designed and numerous algorithms have been Ultra-high bandwidth to meet the growing
proposed to bring the performance of the demand, improved performance, and
Front-End at par with that of the optical part. increased transmission rate. On the other
So in this paper too, we propose a technique hand, wireless network has also greatly
to upgrade the performance of the wireless influenced our lives. They provide number
part so that there may be lesser processing on
of advantages like mobility, flexibility, lesser
the actual data packet and may move
cost. So Wireless Optical Broadband Access
smoothly across the nodes in the wireless part
of WOBAN. Also when the data packet reaches network (WOBAN) combines the best
the Optical Network Unit (ONU), it may be feature of the wireless and optical
forwarded as soon as it reaches the ONU networks. WOBAN is the hybrid of the
without having to wait for the designated time Wireless and optical networks. WOBAN was
slot. In this way, there will be no time slot proposed so that there may be a flexible
synchronization delay at ONU . solution to the increased demand of access
network. Not only to overcome the demand
but also to have cost-effective deployment
of a WMN while having higher performance
Keywords: Protocol, Network Technology,
due to the optical network. Though the
Wireless-Optical Broadband Network, delay,
communication scenarios [1] of both are
ONU
totally different from each other. Optical
network are used for high bandwidth and
1. Introduction for long-haul communication and wireless
to provide flexible connectivity. So in
There has always been an increased in the WOBAN we combine both in an efficient
demand of the bandwidth. Also there is a and cost-effective manner in order to take
tremendous increase in the access network
the advantages of the best features of both.
traffic and particularly with the introduction Rest of the paper is organized as follows.
of services like high definition TV, Video
Section 2 highlights the Architecture of
Conferencing, telemedicine and other
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WOBAN, section 3 shows the a typical a Central office (CO) the Optical Line
scenario for data communication in Terminal (OLT) resides in CO. The CO and
WOBAN, section 4 is about the related work the wireless part is connected through a
on the problem, section 5 will be on our trunk fiber. At the wireless part, first of all
proposed scheme, section 6 consists of a there are gateway routers called ONUs. The
scenario for our proposed scheme and we’ll rest of the wireless nodes are connected to
draw conclusion in section 7. Section 8 will these ONUs. The distance between the
be about the future work and than ONU and the CO is almost 20Kms. However,
acknowledgement. this distance can be decreased or increased
depending upon the requirement and the
2. Architecture of WOBAN number of ONUs to be supported. End-
users whether stationary or mobile, are
WOBAN is an optimal combination of an
connected to the network through the
optical back-end and a wireless front-end
wireless nodes. There is an optical splitter
for an efficient access network [1][3].
between the OLT and the ONUs. The optical
Architecture of a WOBAN consists of
splitter, being passive device, so overall the
wireless part- The Front-End and the optical
architecture is more robust.
Part-The Back-End. At the back end, there is
Figure 1: Architecture of a WOBAN
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3. Data Communication in with the speed of the optical part, up to
some extent.
WOBAN
For communication in downward direction, 4. Related work
that is, from CO towards ONU, the packet is Number of routing algorithms has been
broadcast. The optical splitter split the proposed. Traditional routing approaches
signal equally among the entire ONUs. The like SPRA and MHRA are both based on the
entire ONUs rejects the packet except the shortest path. They don’t consider other
one for which the packet is aimed. In characteristics of the network like
upward direction, when end users want to congestion, available bandwidth, load on
send data packets, it does so by passing the the link etc. Most often the shortest path is
packet to the nearby nodes. That nearby not the best path. So both SPRA and MHRA
node passes the data packet to its other both do not overcome the delay problem in
neighboring node nearer to the ONU. In particular and also the load balancing and
This way, packet pass hop by hop to congestion problem. Another approach is
different nodes to reach the ONU and then PTRA, chooses the path with the highest
from ONU, through splitter, ultimately to throughput based on the Link State
the OLT. From OLT, the data packet is sent Advertisement (LSA). Again, the path with
in the similar fashion discussed above, that the highest throughput might not be the
is, the packet after reaching the OLT is sent shortest path. As we are interested in
back over the same fiber trunk. The optical choosing the shortest path having highest
splitter splits the signal equally among the throughput and least delay.
ONUs. The entire ONUs will reject the
packet except the ONU in which there is the There are some other routing algorithms
targeted user of the packet. If this packet is proposed to overcome the delay problem.
meant for a node out side this WOBAN, it is In DARA [3] and CaDAR [4] the authors have
routed by the CO outside the network. So in calculated the delay of each link and then
wireless part when the data packet is for forwarding the packet, overall delay of
passed hop by hop, doing various kinds of the end node from the ONU is calculated.
processing and making routing decision at The authors have identified four types of
each hop. There comes a significant delay. delay.
Since optical part has high speed, high
1. Transmission delay
bandwidth and high capacity, thus having
high performance. So the performance of
the wireless part must be brought at par 2. Slot synchronization delay
with that of the optical part. So first all this
delay must be reduced, in order to match
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3. Queuing delay Routing Dela y Good Load
algori thm handled? throughput? Balancing?
SPRA Upto some Not so much no
extent
4. Propagation delay—Nodes being MHRA Not No so much no
completel y
closer to each other. So negligible.
PTRA Not Yes Yes
Table 1: Compa rison of va rious algori thms DARA Yes* Yes Yes
Ca DAR Yes* Yes Yes
Table 1 shows the comparison of various Table 1: Comparison of Various Algorithm
algorithms. It is obtained by studying
various algorithms and their characteristics 5. Proposed scheme
about whether they solve the delay and
throughput problem or not. The above The link condition and the capacity required
table shows that the DARA and CaDAR are for a node is advertised in LSAs. LSAs are
almost same. However, CaDAR is better advertised periodically. So if after a LSA, link
then DARA in a sense that it also assigns condition are changed, say for instance,
capacities to all the links. In both the flow on the link is changed, then the link
proposed algorithm proposed, though they will be either under-utilized or over-utilized
very efficiently calculate the link delay, and and may lead to congestion, packet loss
selects the link with the least delay. depending upon the whether the demand
However, calculating these so many types of the node was increased or decreased
of delay for a link and for each packet and after that LSA.. Time-Slots for various nodes
then for the whole path, may itself be a and their data is adjusted also according to
delay. If a data packet has to undergo these the LSA. So all the algorithm discussed
so many processing and decision making, above, heavily depends upon the LSA, thus
the reduced delay may not be significant. So in the inter-LSA period, the network
in this paper we propose a mechanism in condition may change dramatically, thus
which there will be reduced processing and leading to the wrong estimation and
decision making on the actual data packet. calculations. Also the slot may be wrongly
Though the shortest path with the least synchronized. And due to lack of network
delay is calculated in similar fashion as in information the capacity may be wrongly
CaDAR and DARA but however, the assigned to the link thus leading to other
processing overhead will be much reduced offensive results like congestion, packet loss
on the actual data packet, so it will move and so on. One solution to all these is to
smoothly across the nodes. Thus there will send LSA quite often but in this case a
be significant reduction in the delay. major chunk of bandwidth will be used by
sending LSAs themselves. So In our
proposed scheme, we will send a control
packet ahead of the actual data packet.
Thus there will be no need of LSAs. In this
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method, we will embed the sequence will be forwarded as it reaches the node.
number and size of the data packet in the Similarly time slot will be reserved at the
control packet. The control packet is ONU, so as data reaches the ONU, it will be
actually the header of the data packet forwarded without waiting for the
separated from the data packet. So for designated time slot, as the designated time
synchronization and identification purpose slot will reach as soon as the data packet
we use the sequence number. The control will reach the ONU.
packet will contain fields for the sequence
number and the size of the data. One extra 6. Scenario
field will have to be added in the data
packet for the sequence number using the
bits of reserved field. The data packet will
travel ahead of the data packet, thus finding
the shortest path with the least delay for
the actual data packet. The data packet will
follow the same path which was followed
by the control packet. All the routing
decision will be made and the shortest path Figure 2: Back-End of WOBAN
with the least delay will be calculated for
Consider the Fig 2, above. Consider that
the control packet only. There will be no
End-User 2 generated data, suppose the
processing on the actual data. The
sequence number of the data be 500. Now
intermediate node, just looking at the
this sequence number and the size of the
sequence number of the packet will
data packet will be embedded in the control
forward it on the same path on which the
packet. The only thing which will be
control packet was forwarded. Also the
included in the data packet will be a field
control packet will tell each node exactly
for sequence number, so that the
how much data is coming from a particular
intermediate node recognizes this sequence
node. So in this way, capacities will also be
number. Now suppose the control packet
assigned to the link according to the
after reaching node A (since End-User is
information of the control packet as it
connected to the network via node A), finds
contains the size of the upcoming data
out the shortest path with the least delay
packet. Thus not only there will be no
link to node B, at B it find the shortest with
processing on the data packet and
least delay link to node C and then to ONU.
capacities will be assigned to the links, but
Based on the control packet, capacities will
also the control packet will so synchronize
also be assigned to the links {AB} and { BC}.
the time slot at each node, so that the
Also the intermediate node B and C will
when the data reach the node, it will not
adjust the time slot according to the arrival
have to wait for designated time slot and
of the data packet and then will not make
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any processing on the actual data packet, soon as its data packets reaches the node’s
the only things which the intermediate queue, its time slot will also come, so it will
node will do is to check the sequence be forwarded without having to wait for it
number. Thus recognizing the sequence designated time slot. Again, the only thing
number, they will forward the data packet which the intermediate node has to check is
on the path on which the control packet the sequence number of the data packet.
was followed. Another advantage of the The packet will be forwarded in similar
control packet is that, when the control fashion at ONU as well.
packet reaches the node B and C, it will also
so synchronize the time slots at the B and C,
that as soon as the data packet arrive these
nodes, its time slot also come. So the data
packet will be forwarded as soon as it
reaches the node without having to wait for
designated time slot and thus there will be
no queuing delay and time slot
synchronization delay as well. Similarly at
Figure 3: Queue of packets and their Time-Slots
ONU too, the control packet will reserve the
time slot for the data packet and will also
reserve the bandwidth for the data packet
to be forwarded on the fiber trunk. So 5. Conclusion
again as soon as the data packet reaches We have shown a fine technique to reduce
the ONU, its designated time slot will also the overall delay and efficiently use the
come, so it will be forwarded without network resources. With DARA and CaDAR,
having to wait for designated time slot. In delay will have to be calculated for all the
this way three types of delays namely, links and ultimately for the entire path, for
processing over head delay on the data each packet sent and then decision will
packet, queuing delay and time slot have to be made regarding the shortest
synchronization delay, significantly path with the least delay for every data
impacting the overall performance of the packet. Also both the algorithm depends
wireless part are reduced. upon the LSA, since network condition may
Figure 3 below shows data packet of various change even before next link state
End-Users and their time slots. Packet will advertisement. So in this paper, we have
be forwarded in the time slots one by one. shown an efficient mechanism in assigning
Since we know that time slots are capacities to the link and synchronizing the
synchronized on the basis of the LSAs. The time slots of the nodes and a mechanism in
control packet of a particular data packet which there will be no processing or routing
will so synchronize the time slot that as decision on the data packet. The only thing
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which the intermediate node has to check is the queue for its designated time slot. Thus
the sequence number of the data packet, there will be significant reduction in the
and it will be automatically forwarded on overall delay. Overall all the three types of
the path on which the control packet was delays will be eliminated, namely, queuing
forwarded. Since there is no other delay, time slot synchronization delay and
processing on the data packet and also the processing delay. The need for LSAs are also
control packet will also reserve the time for eliminated. So since there are no LSAs, thus
the data packet at intermediate nodes and there will be an efficient utilization of
ONU, so the packet does not have to wait in resources.
Table 2: Comparision of various algorithms with the proposed scheme
6. Future Work So that there may be equal load on the link
and a sort of load balance may prevail in
Some time it may happen that a single link the network. Also in the link, capacities are
is over loaded, the traffic of all the node sometime not properly assigned. So we also
flow on the same link or path, which may intend to work on equally assigning the
lead to failure of the link, packet loss, low capacities to links. Though there would
throughput or any sort of consequences. So have been worked carried out in this area,
in future we intend to work on equally but yet we will try to refine the existing
distributing the traffic load on all the links.
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