Abstract

With the exponential growth of the Internet, networks are increasingly faced with QoS problems. In the specific case of traffic jam or congestion collapse, where we have undelivered packets, due to the fact that the bandwidth available at the router links is no longer sufficient. In other words, the router receives more packets than it can handle. And then, the buffer size of a router become overflowed by packets. That is why avoidance or prevention mechanisms have been put in place. The main objective of this research will be to design and implement a technique (or protocol) of congestion control avoidance called a Network Border Patrol. This concerns routers (ingress, egress, core-stateless) which will have to regulate the traffic in such a way that there is never a case of undelivered packets or packet loss. The use of certain network simulators will be necessary in order to visualize exactly how we can prevent congested link collapse (using some algorithms) and therefore congestion collapse.

Keywords: QoS, congestion collapse, bandwidth, network border patrol, ingress router, egress router, core-stateless router, congested link.

CHAPTER

GENERAL INTRODUCTION

The design, deployment and evolution of a new network nowadays requires consideration of the ever-increasing demand for bandwidth by users. And the appearance of multimedia applications (Online games, Video calls, …) did not help anything because they demand a lot of resources (bandwidth, delay, latency, jitters …) for an excellent user experience by users who use this network. And if these parameters are neglected when setting up the network, the probability that this network is the victim of congestion is rather high.

1.1 Background and Context of Study

Understanding this project requires a small example. We have all already found ourselves in a situation where while browsing on the Internet, we try to gain access to a page and the returned result is an incomplete page with files that could not be displayed or loaded. This is a classic case of traffic congestion (congestion collapse) where it is obvious that either all the packets constituting our request (or constituting the response to the said request) have not all reached their destination. This is a very common example and the thesis that there are certainly many of you who want to access this page through the same ISP (Internet Service Provider) who has allocated you limited bandwidth, explains this dysfunction. And so I will approach this section as follows:

• Illustration of traffic jam or network congestion
• Ways for solving congestion collapse
• Use of Network Border Patrol

1.1.1    Illustration of traffic jam or network congestion

The traffic jam occurs when a router receives more packets than it can handle; therefore, the router drops some packets when its buffer is full.

On a figure 1 and 2 above we can see, how different types of IP packets are arriving to the LAN interfaces (virtual or physical) of the router and also, we see how these packets exit the router through the WAN interface. It’s not hard to guess, that capacity of WAN interface is limited and not enough to treat all incoming packets. So, the situation, when the network device interface doesn’t have enough link capacitance called congestion (interface or link congestion). A simple analogy with congestion on a communication channel would be pouring water from one bottle to another. If we pour water into the second container faster than the neck can accommodate, the water will overflow and run down the side of the bottle. We can temporarily solve the problem by pouring water into a funnel, which would hold the extra water, but eventually, if we pour the syrup quickly, the funnel will fill up and overflow as well.

1.1.2    Ways for solving congestion collapse

The first method is the easiest and doesn’t need any effort to analyze and investigate what was the reason of connection link overflow. Actually, it is rather good and logical method, but doesn’t guarantee that after some period of time traffic congestion appears again. Although this type of solution sounds simple, increasing bandwidth could be expensive and could take a time for implementation. Sometimes some geographical or technological limitations can be obstacle on a way to channel being upgraded. For these situations QoS methods could seems very attractive as a one of the solutions, which can help partly eliminate congestion.

The second method, as I already told above, allow network administrator to clarify the reasons of congestion and using different types of congestion control methods to solve existing problems. Here are the examples of some basic QoS mechanism, which could be used for congestion problem elimination or minimization:

• Queuing mechanism (priority queuing, custom queuing and etc.)
• Congestion avoidances (Random Early Detection, Network Border Patrol,)
• Link Efficiency mechanism (payload compression, header compression)

1.1.3 Use of Network Border Patrol

As we define earlier, when packets are buffered in the routers presents in the network which causes congestion collapse from undelivered packets arises when bandwidth is continuously consumed by packets that are not dropped before reaching their ultimate destinations. For solving this problem, a new congestion avoidance mechanism have been put in place called a Network Border Patrol (NBP); which is able to prevent congestion collapse by ensuring at the border of the network that each flows packets do not enter the network faster than they can leave.

1.2 Problem Statement

Congestion collapse, a dreaded-down condition which results from a network congestion, has been a serious challenge facing network administrators in the management of organization network especially since the upsurge of internet multimedia traffic demands. There is a need to provide an efficient and reliable system that will combat this menace to ensure continual quality of service. Most congestion control mechanism which try to prevent network congestion are basically host-based and haven’t been able to avert traffic congestion resulting from dropped packets. To solve this problem, an improved system of congestion control needs to be designed to detect and prevent congestion at the edges of a network before they can occur in a time efficient manner; it is called a Network Border Patrol.

1.3 Objectives of the Study

To decrease the probability of packets drops and make IT packets transit through the network more reliable many of different methods and algorithms were developed (Muhhin, 2010).

1.3.1 General objective

The main aim of this study is to design and implement a system that can detect and prevent congestion collapse using a Network Border Patrol or using a combination of leaky bucket, rate control and feedback control algorithms for improved QoS. So, we can clearly deduce that the NBP is mostly an admission control mechanism as the figure 4 above is showing.

1.3.2    Specific objectives

The following objectives all flow from the main one above:

1. Design and simulate congestion control mechanism (Network Border Patrol)
2. Implement the different algorithms required by NBP
3. Make sure that undelivered packets or packet loss case occurs

At the end, we would develop a system that can detect and prevent congestion collapse in a network using a combination of the leaky bucket, rate control, feedback control algorithms for improved QoS.