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Poster Paper Proc. of Int. Colloquiums on Computer Electronics Electrical Mechanical and Civil 2011

On the Accuracy of Prioritizing Packets in Routers Julie Varghese1, Basil Baby2 1

Viswajyothi College of Engineering and Technology,Dept of Computer Science,Kerala,India Email: julievarghese2008@gmail.com 2 Viswajyothi College of Engineering and Technology,Dept of Computer Science,Kerala,India Email:basilbaby@gmail.com Abstract— The recent success of the Internet arguably stems from the philosophy that complexity should be relegated to the endpoints of the network. As the Internet grows larger, measuring and characterizing its dynamics grows harder. Packet forwarding prioritization (PFP) in routers is one of the mechanisms commonly available to network operators. Many such techniques rely on several network metrics like delay, loss rate, bandwidth, jitter etc. However these methods will not be much accurate in the real world scenario. Here a new technique is proposed that takes into account both loss rates and importance of packet content in order to rank and prioritize the packets. Further, confidentiality can be provided by encrypting the packets.

considering both loss rates as well as the intensiveness of the data conveyed through the packets. The rest of the section is organized as follows. Section II makes an insight into the previous related works. Section III gives a description about packet prioritization techniques. The next section describes the problem statement and then the proposed method is described which tries to eliminate the disadvantage of previous methods. Finally the paper is concluded. II. RELATED WORKS As the Internet grows larger, measuring and characterizing its dynamics grows harder .Inference and prediction of network conditions is of fundamental importance to a range of network-aware applications. The two main approaches used for the statistical inference of network internal characteristics based on end to end measurements of point to point traffic [4]-[5] are active approaches and passive approaches. Active approaches introduce additional probe traffic into the network. Passive approaches do not induce additional traffic into the network. They make inferences based only on the existing network traffic. The former approach is flexible because one can make measurements at those locations and times which are most valuable. The benefit of the latter approach is that no additional bandwidth and network resources are consumed solely for the purpose of data collection [6]. The other classifying approaches include receiver–oriented and sender oriented (based on where the inferences are made) or multicast driven and unicast driven (based on the model used to transmit the probe traffic). Mark Coates and Alfred Hero in their paper titled Internet Tomography [1], deals with the problem of identifying topology and inferring link-level performance parameters such as packet drop rate or delay variance using only endto-end measurements. This inference is commonly referred to as network tomography [8]. The presence of parallel paths between the source and destination results in out of order delivery and delay [10], [7]. In [3], it presents an end-to-end approach for packet forwarding priority inference by measuring the loss rate difference of different packet types and its associated tool, POPI. This tool can be used by the enterprises or end-users to discover whether their traffic are treated differently by the ISPs, and whether the ISPs has fulfilled the contracts between them and the users. This paper tries to identify the disadvantages associated with the above stated approach and proposes a better solution.

Index Terms— Packet forwarding priority, loss rate, inference, encryption

I. INTRODUCTION Today’s Internet is a massive, distributed network which continues to explode in size as e-commerce and related activities grow. The heterogeneous and largely unregulated structure of the Internet renders tasks such as dynamic routing, optimized service provision, service-level verification, and detection of anomalous or malicious behaviour increasingly challenging tasks. The problem is compounded by the fact that one cannot rely on the cooperation of individual servers and routers to aid in the collection of network traffic measurements vital for these tasks [1]. As the Internet grows in size and diversity, its internal behaviour becomes ever more difficult to characterize. Any one organization has administrative access to only a small fraction of the network’s internal nodes, whereas commercial factors often prevent organizations from sharing internal performance data. Thus it is important to characterize internal performance from end-to-end measurements [2], [9]. Several methods are present to characterize the packet forwarding mechanisms in routers. Most of such mechanisms rely on network metrics like bandwidth, delay, jitter, loss etc. Commercial routers such as Cisco and Juniper Networks provide support for packet forwarding prioritization. The most recent work in this field is that of Packet forwarding Priority Inference tool which is based on loss based rank metric [3], which can be used by the end users to determine whether their traffic are treated differently by the Internet Service Providers. However, each of these techniques has their own pros and cons. Moreover these techniques are focused on selectively filtering the data .But they do not provide any means to secure the prioritized data. There are also other techniques that concentrate on ensuring the security of the packets in transit by providing them confidentiality, authentication and integrity. The proposed technique tries to assign ranks to the packets © 2011 ACEEE DOI: 02.CEMC.2011.01. 564

Poster Paper Proc. of Int. Colloquiums on Computer Electronics Electrical Mechanical and Civil 2011 and all segments of a packet need not be of equal sizes. So this approach may not succeed in such situations. 2. The accuracy solely depends on the performance of clustering method employed. There are several better clustering methods that can yield better accuracy to the measurements taken. 3. As the number of group partitions increases, the overall performance decreases. 4. Moreover it can happen that the most insignificant packet may be rated as rank 1 in this approach which will cause a block to the transfer of other significant packets. This happens because the method considers only loss rates and hence the priority is given to the packet type with highest loss rate.

III. PACKET PRIORITISATION Prioritization of network traffic is simple in concept: give important network traffic precedence over unimportant network traffic. The problem with network priority schemes is that lower-priority traffic may be held up indefinitely when traffic is heavy unless there is sufficient bandwidth to handle the highest load levels. As traffic load increases, router buffers begin to fill, which increases the delay. If the buffers overflow, packets are dropped. Prioritization schemes can help by forwarding high-priority and delay-sensitive traffic before other traffic as soon as the buffer is being occupied. Packet forwarding prioritization (PFP) in routers is one of the mechanisms commonly available to network operators. PFP can have a significant impact on the accuracy of network measurements, the performance of applications and the effectiveness of network troubleshooting procedures.

V. PROPOSED SYSTEM The proposed method tries to eliminate some of the pitfalls that were identified above. This requires some method to identify the packet content which can be considered together with the loss rate for estimation of ranks. This requires the need for a buffer at the sender, receiver and at the router. The end host which gathers the information into packets and sends is the owner of the data packet and knows the content, its purpose and its importance. So when it sends the packet it must note this in the buffer and also attaches this information along with the packet by using an additional tag or label. Assume that the routers in the local network of the sender have the capability to assess this tag and assess the overall network traffic. If it discovers high traffic, it compresses the packet to reduce size and determine whether to encrypt or not based on the importance of the content. This packet now enters into the internet and goes through several routes. And if the router drops the packet, then its loss rates are calculated as in [3]. But in this proposed method the router also look into the tag field to understand the significance of the packet. If it cannot prioritize based on this tag, it checks whether the packet is encrypted or not. If so, the router can make sure that the packet need to be given rank 1, despite other packets which may have higher loss rates (but insignificant content) than this one. If the method had used the approach in [3], it may not be able to transmit this packet as it may get lower ranks when considering other high loss rate packets. So the proposed scheme provides a better insight into the prioritization techniques employed and securely transmits the high priority packets by encrypting the high priority packets.

A. PFP in POPI It uses packet loss as the inference metric because it is the most direct consequence of a priority configuration. PFP in routers are set in a per-interface basis. This observation defines the basis of the approach used in POPI: In order to reveal packet-forwarding priorities, one needs to saturate the path available bandwidth for a given class to produce loss rates difference among different classes. Assuming the existence of a PFP mechanism in routers such an approach will succeed at uncovering priority settings in routers along a path if the available bandwidth for the controlled class is lower than the bottleneck available bandwidth of the path. For every burst in Fig. 1, loss rate ranks are computed by first sorting packet types in ascending order according to their packet loss rates in that burst and then assigning ranks in order. First, identify whether there is consistent difference among k ranks over n observations and then the average normalized rank for each packet type is calculated over n bursts using the equation given below.

Here NRim represents the normalized rank for packet i in mth burst. There are a total of nb bursts. Based on ranks packets are grouped using hierarchical divisive clustering. Grouped packets are assigned priority on loss basis and priority is inferred at user level.

DISCUSSION Packet forwarding prioritization techniques are widely used by the enterprises and end users to monitor and determine how their traffic is treated by various Internet Service Providers. This paper shows the design of such packet forwarding prioritization techniques which is supposed to be better than the previous approaches. It is a non parametric approach as it is not based purely on any network QoS parameters. This approach takes into account the content type of the packet along with average normalized ranks in order to identify the priorities of the packets.

Figure.1 A burst consists of nr x k packets

IV. PROBLEM STATEMENT There are several potential pitfalls associated with the above approach in [3]. 1. It assumes that all packets are equally sized. But in reality the way that a packet is segmented depends on several factors ÂŠ 2011 ACEEE DOI: 02.CEMC.2011.01. 564

Poster Paper Proc. of Int. Colloquiums on Computer Electronics Electrical Mechanical and Civil 2011 REFERENCES

Thus the proposed new method makes use of a combination of measures to infer the packet priority. Hence this scheme will be more accurate. Moreover the approach provides added security by encrypting the packet that has more priority than the other packets. But the method may be little time consuming due to the additional overhead of encryption involved in the process.

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CONCLUSIONS Most of the networks make use of PFP techniques for monitoring the traffic. These PFP settings have a great impact on several aspects of a network. It is crucial for a network operator to mark the packets according to the priority. Most of the approaches are either passive approach or active approach. The method described in this paper is an active approach that tries to infer the packet forwarding priority more accurately. The method prioritizes packets at the routers by calculating the ranks not only based on loss rates, but also considering the importance of the content within the packet. Thus it is hoped that this will give a more accurate inferring of the packets forwarding priority than most of the current techniques.