A Comparative Analysis of Different Real Time Applications over Various Queuing Techniques of VOIP
INTRODUCTTION1.1 General Introduction
QoS is a network mechanism, which effectively controls traffic flood scenarios, generated by a wide range of advanced network applications. This is possible through the priorities allocation for each type of data stream. Quality of Service allows control of data transmission quality in networks, and at the same time improves the organization of data traffic flows, which go through many different network technologies. Such a group of network technologies includes ATM (asynchronous transfer mode), Ethernet and 802.1 technologies, IP based units, etc.; and even several of the abovementioned technologies can be used together.
The internet is expanding on a daily basis, and the number of network infrastructure components is rapidly increasing. Routers are most commonly used to interconnect different networks. One of their tasks is to keep the proper quality of service level. The leading network equipment manufacturers, such as Cisco Systems, provide on their routers mechanisms for reliable transfer of time-sensitive applications from one network segment to another. In case of VoIP the requirement is to deliver packets in less than 150ms. This limit is set to a level where a human ear cannot recognize variations in voice quality. This is one of the main reasons why leading network equipment manufacturers implement the QoS functionality into their solutions. QoS is a very complex and comprehensive system which belongs to the area of priority congestions management. It is implemented by using different queuing mechanisms, which take care of arranging traffic into waiting queues.
Time-sensitive traffic should have maximum possible priority provided. However, if a proper queuing mechanism (FIFO, CQ, WFQ, etc.) is not used, the priority loses its initial meaning.  It is also a well-known fact that all elements with memory capability involve additional delays during data transfer from one network segment to another, so a proper queuing mechanism and a proper buffer length should be used, or the VoIP quality will deteriorate.
QoS identification is intended for data flows recognition and recognition of their priority. To ensure the priority a single data stream must first be identified and then marked (if this is needed). These two functions together partly relate to the classifying process, which will be described in detail in the next section. Identification is executed with access control lists (ACL). ACL identifies the traffic for the purpose of the waiting queue mechanisms, for example PQ -Priority Queuing or CQ – Custom Queuing. These two mechanisms are implemented into the router, and present one of its most important subparts.
1.2 Goal of the research Work
QoS classification is designed for executing priority services for a specific type of traffic. The traffic must first be pre-identified and then marked (tagged).
Classification is defined by the mechanism for providing priority service, and the marking mechanism. At the point, when the packet is already identified, but it has not yet been marked, the classification mechanism decides which queuing mechanism will be used at a specific moment (for example, the principle of per-hop). Such an approach is typical in cases when the classification belongs to a particular device and is not transferred to the next router. Such a situation may arise in case of priority queuing (PQ) or custom queuing (CQ). The remainder of the paper is organized as follows
QOS (QUALITY OF SERVICE)
2.1 What is QOS?
Quality of Service allows control of data transmission quality in networks, and at the same time improves the organization of data traffic flows, which go through many different network technologies. Such a group of network technologies includes ATM (asynchronous transfer mode), Ethernet and 802.1 technologies, IP based units, etc.; and even several of the abovementioned technologies can be used together. An illustration of what can happen when excessive traffic appears during peak periods can be found in everyday life: an example of filling a bottle with a jet of water. The maximum flow of water into the bottle is limited with its narrowest part (throat). If the maximum possible amount of decantation (throughput) is exceeded, a spill occurs (loss of data). A funnel used for pouring water into a bottle, would in case of data transfer be in the waiting queues. They allow us to accelerate the flow, and at the same time prevent the loss of data. A problem remains in the worst-case scenario, where the waiting queues are overflowed, which again leads to loss of data (a too high water flow rate into the funnel would again result in water spills).Priorities are the basic mechanisms of the QoS operating regime, which also affects the bandwidth allocation. QoS has an ability to control and influence the delays which can appear during data transmission. Higher priority data flows have granted preferential treatment and a sufficient portion of bandwidth (if the desired amount of bandwidth is available). QoS has a direct impact on the time variation of the sampling signals which are transmitted across the network. Such sampling time variation is also called jitter (T. & S. Subash Indira Gandhi, 2006). Both mentioned properties have a crucial impact on the quality of the data and information flow throughput, because such a flow must reach the destination in the strict real-time. A typical example is the interactive media market. QoS reflects their distinctive properties in the area of improving data-transfer characteristics in terms of smaller data losses for higher-priority data streams. The fact that QoS can provide priorities to one or more data streams simultaneously, and also ensure the existence of all remaining (lower-priority) data streams, is very important. Today, network equipment companies integrate QoS mechanisms into routers and switches, both representing fundamental parts of Wide Area Networks (WAN), Service Provider Networks (SPN), and finally, Local Area Networks (LAN).
Based on the abovementioned points, the following conclusion can be given: QoS is a network mechanism, which successfully controls traffic flood scenarios, generated by a wide range of advanced network applications. This is possible through the priorities allocation for each type of data stream.
2.2 How QoS Works?
QoS mechanism, observed as a whole, roughly represents an intermediate supervising element placed between different networks, or between the network and workstations or servers that may be independent or grouped together in local networks. The position of the QoS system in the network is shown in (Figure 2.1) This mechanism ensures that the applications with the highest priorities (VoIP, Skype, etc.) have priority treatment. QoS architecture consists of the following main fundamental parts: QoS identification, QoS classification, QoS congestions management mechanism, and QoS management mechanism, which handle the queue.
Figure 2.1: Qos System’s Position in the network
2.2.1 QoS Identification
QoS identification is intended for data flows recognition and recognition of their priority. To ensure the priority a single data stream must first be identified and then marked (if this is needed). These two functions together partly relate to the classifying process, which will be described in detail in the next section. Identification is executed with access control lists (ACL). ACL identifies the traffic for the purpose of the waiting queue mechanisms, for example PQ – Priority Queuing or CQ – Custom Queuing. These two mechanisms are implemented into the router, and present one of its most important subparts. Their operation is based on the principle of “jump after a jump”, meaning that the QoS priority settings belong only to this router and they are not transferred to neighboring routers, which form a network as a whole. Packet identification is then used within each router with QoS support. An example where classification is intended for only one router can be found with the CBWFQ (Class Based Queuing Weighted Fair) queuing mechanism. There are also techniques which are based on extended control access-list identities. This method allows considerable flexibility of priorities allocation, including the allocation for applications, users, destinations, etc. Typically, such functionality is installed close to the edge of the network or administrative domain, because only in this case each network element provides the following services on the basis of a particular QoS policy.
2.2.2 QoS Classification
QoS classification is designed for executing priority services for a specific type of traffic. The traffic must first be pre-identified and then marked (tagged). Classification is defined by the mechanism for providing priority service, and the marking mechanism. At the point, when the packet is already identified, but it has not yet been marked, the classification mechanism decides which queuing mechanism will be used at a specific moment (for example, the principle of per-hop). Such an approach is typical in cases when the classification belongs to a particular device and is not transferred to the next router. Such a situation may arise in case of priority queuing (PQ) or custom queuing (CQ). When the packets are already marked for use in a wider network, the IP priorities can be set in the ToS field of the IP packet header. The main task of classification is identification of the data flow, allocation of priorities and marking of specific data flow packets.
2.3 QoS queuing management mechanism
When the queue is full, it cannot accept any new packets, meaning that a new packet will be rejected. The reason for rejection has been already discovered: the router simply cannot avoid discarding packets when the queue is full, regardless of which priority is applied in the ToS field of the packet. From this perspective the queue management mechanism must execute two very important tasks:
– Try to ensure a place in the round-robin queue or try to prevent the queue from
Becoming full. With this approach a queuing management mechanism provides the
Necessary space for high-priority frames;
– Enable the criterion for rejecting packets. The priority level applied in the packet must be checked at the beginning, after which the mechanism decides which packet will be Rejected and which not. Packets with lower priority are rejected earlier in comparison to those with a higher priority. This allows undisturbed movement of high-priority traffic flows, and if there is some additional space at the available bandwidth, other low priority traffic flows can also pass through the network. Both described methods are included in the Weighted Random Early Detect mechanism, which can be found in various sources under the acronym WRED.
2.4 QoS Overview
Quality of Service allows control of data transmission quality in networks, and at the same time improves the organization of data traffic flows, which go through many different network technologies. Such a group of network technologies includes ATM (asynchronous transfer mode), Ethernet and 802.1 technologies, IP based units, etc.; and even several of the abovementioned technologies can be used together. QoS is a network mechanism, which successfully controls traffic flood scenarios, generated by a wide range of advanced network applications. This is possible through the priorities allocation for each type of data stream. QoS mechanism, observed as a whole, roughly represents an intermediate supervising component placed between different networks, or between the network and workstations or servers that may be autonomous or grouped together in local networks. The position of the QoS system in the network is shown in (Figure 2.1) This This mechanism ensures that the applications with the highest priorities (VoIP, Skype,fring etc.) have priority treatment. QoS architecture consists of the following main elementary parts: QoS identification, QoS classification, QoS congestions management mechanism, and QoS management mechanism, which handle the queue.
TYPICAL QUEUING DISCIPLINE
3.1 Typical Queuing Discipline
As part of the resource allocation mechanisms, each router must implement some queuing discipline that governs how packets are buffered while waiting to be transmitted. Various queuing disciplines can be used to control which packets get transmitted (bandwidth allocation) and which packets get dropped (buffer space). The queuing discipline also affects the latency experienced by a packet, by determining how long a packet waits to be transmitted. Examples of the common queuing disciplines are first-in first- out (FIFO) queuing, priority queuing (PQ), and weighted-fair queuing (WFQ).
FIFO is an acronym for First In First Out .This expression describes the principle of a queue or first-come first serve behavior: what comes in first is handled first, what comes in next waits until the first is finished etc. Thus it is analogous to the behavior of persons” standing in a line” or “Queue” where the persons leave the queue in the order they arrive. First In First out (FIFO) is the most basic queuing discipline. In FIFO queuing all packets are treated equally by placing them into a single queue, then servicing them in the same order they were placed in the queue.
FIFO queuing is also referred to as First Come First Serve (FCFS) queuing. Generally, FIFO queuing is supported on an output port when no other queue scheduling discipline is configured. In some cases, router vendors implement two queues on an output port when no other queue scheduling discipline is configured: a high-priority queue that is dedicated to scheduling network control traffic and a FIFO queue that schedules all other types of traffic.
Figure 3.1: First In First out (FIFO)
PQ is a simple variation of the basic FIFO queuing. The idea is to mark each packet with a priority; the mark could be carried, for example, in the IP Type of Service (ToS) field. The routers then implement multiple FIFO queues, one for each priority class. Within each priority, packets are still managed in a FIFO manner. This queuing discipline allows high priority packets to cut to the front of the line. Priority queuing (PQ) is the basis for a class of queue scheduling algorithms that are designed to provide a relatively simple method of supporting differentiated service classes. In classic PQ, packets are first classified by the system and then placed into different priority queues. Packets are scheduled from the head of a given queue only if all queues of higher priority are empty. Within each of the priority queues, packets are scheduled in FIFO order.
Priority queuing mechanism provides a smooth transition of important traffic (packets), through the network, using management at all intermediate points. PQ works by giving priority to the most important traffic. Priority queuing can be flexible regarding the allocation of different traffic parameters such as: the network protocols (IP, IPX, AppleTalk, etc.), input interfaces, the size of packets, source/destination addresses, and so on. In the PQ case, each packet (according to the entered priority in the ToS field), is classified into one of the four queues that are distinguished by different levels (priorities). The lowest level is marked with a label “low”, and then the levels go up in the following subsequent order: “normal”, “medium” and “high”. Packets are individually sorted into appropriate queues according to the declared priority. Packets which are not classified or have not yet been classified (see the section on data flows classification) through the above described classification mechanism, automatically fall into the “normal” waiting queue as shown in (Figure 3.2) During the data transmission the algorithm first handles the high-priority queues and then the low-priority queues.
Figure 3.2: Priority queuing (PQ)
Weighted fair queuing (WFQ) was developed independently in 1989 by Lixia Zhang and by Alan Demers, Srinivasan Keshav, and Scott Shenke. WFQ is the basis for a class of queue scheduling disciplines that are designed to address limitations of the FQ model. The idea of the fair queuing (FQ) discipline is to maintain a separate queue for each flow currently being handled by the router. The router then services these queues in a round-robin manner. WFQ allows a weight to be assigned to each flow (queue). This weight effectively controls the percentage of the link’s bandwidth each flow will get. We could use ToS bits in the IP header to identify that weight.
Figure 3.3: Weighted fair queuing (WFQ) with round robin
(Figure 3.3) shows a weighted bit-by-bit round-robin scheduler servicing three queues. Assume that queue 1 is assigned 50 percent of the output port bandwidth and that queue 2 and queue 3 is each assigned 25 percent of the bandwidth. The scheduler transmits two bits from queue 1, one bit from queue 2, one bit from queue 3, and then returns to queue 1. As a result of the weighted scheduling discipline, the last bit of the 600-byte packet is transmitted before the last bit of the 350-byte packet, and the last bit of the 350-byte packet is transmitted before the last bit of the 450-byte packet. This causes the 600-byte packet to finish (complete reassembly) before the 350-byte packet, and the 350-byte packet to finish before the 450-byte packet.
Figure 3.4: Weighted Fair queuing (WFQ)
When each packet is classified and placed into its queue, the scheduler calculates and assigns a finish time for the packet. As the WFQ scheduler services its queues, it selects the packet with the earliest (smallest) finish time as the next packet for transmission on the output port. For example, if WFQ determines that packet A has a finish time of 30, packet B has a finish time of 70, and packet C has a finish time of 135, then packet A is transmitted before packet B or packet C. In (Figure 3.4). Observe that the appropriate weighting of queues allows a WFQ scheduler to transmit two or more consecutive packets from the same queue. Class-based weighted fair queuing (CBWFQ): CBWFQ represents the newest scheduling mechanism intended for handling congestions while providing greater flexibility. It is usable in situations where we want to provide a proper amount of the bandwidth to a specific application (in our case VoIP application). In these cases, the network administrator must provide classes with defined bandwidth amounts, where one of the classes is, for example, intended for a videoconferencing application, another for VoIP application, and so on. Instead of waiting-queue assurance for each individual traffic flow, CBWFQ determines different traffic flows. A minimal bandwidth is assured for each of such classes. One case where the majority of the lower- priority multiple-traffic flow can override the highest- priority traffic flow is video transmission which needs half of the T1- connection bandwidth. A sufficient link bandwidth would be assured using the WFQ mechanism, but only when two traffic data flows are present. In a case where more than two traffic flows appear, the video session suffers the regarding bandwidth, because the WFQ mechanism works on the fairness principle. For example, if nine additional traffic flows make demands of the same bandwidth, the video session will get only 1/10th of the whole bandwidth, and this is insufficient when using a WFQ mechanism. Even if we put an IP priority level of 5 into the ToS field of the IP packet header, the circumstances would not change. In this case, the video conference would only get 6/15 of the bandwidth, and this is not enough because the mechanism must provide half of all the available bandwidth on the T1 link. This can be provided by using the CBWFQ mechanism. The network administrator just defines, for example, the video-conferencing class and installs a video session into that class. The same principle can be used for all other applications which need specific amounts of the bandwidth. Such classes are served by a flow-based WFQ algorithm which allocates the remaining bandwidth to other active applications within the network.
Simulation testing network architecture is an imitation of a real network. The main aspiration of this simulation is to improve the network’s performances. The highest level in Figure represents the network server architecture designed by the internet service provider (ISP). Server_ subnet consists of five Intel servers where each of them has its own profile, such as; web profile (web server), VoIP, E-mail, FTP and video profile. These servers are connected through a 24 port switch and through a wired link to the private company’s router. Company’s network consists of four LAN segments including different kinds of users. In the lower left wing of the company are the VoIP users who symbolize technical support to the company’s Customers.
In the lower right wing of the company is a conference room where employees have meeting. Two places here are meant for two concurrent sessions. In the upper left wing there is a small office with only 10 employees who represent the expansion part of the company, and they use different applications needed for their work. For example, they are searching information on the web; calling their suppliers, exchanging files over FTP, and so on. The remaining upper right wing includes fifty disloyal employees who are surfing the net (web) during work time, downloading files, etc. (heavy browsing).
Each of the company’s wings is connected through a 100BaseT link to the Cisco 7505 router. This router is further connected to the ISP servers’ switch through a wired (VDSL2) 10Mbit/s ISPs’ link. Connections between servers and the switch are also type 100BaseT. The wired link in this case represents a bottleneck, where we have to involve a QoS system and apply different queuing disciplines.
4.1 Network Server Architecture Designed:
Figure 4.1: The Network Server Architecture Designed
4.2 Qos Attribute Config :
Figure 4.2 : Qos Attribute Config
From this simulation we have collected delay statistics from various typical queuing discipline scenarios (CQ, WFQ, PQ, FIFO ) for two different active applications (VoIP and HTTP) in the network and with different applied priorities by the ToS field of the IP packet header. It have been defined VoIP traffic flows between clients where such flows symbolize high-priority traffic; while HTTP traffic represents low-priority flow, based on a best effort type of service. In our scenarios, we have 82.09% users who use lower priority HTTP traffic and only 17.91% users who use the high-priority VoIP application. In (Figure 5.5), we can see that only 17.91% of users take up a majority part of bandwidth, so the lower priority HTTP traffic, which represents a majority of all traffic, must wait. This is the reason why delays rapidly increase as can be clearly seen in (Figure 5.4). Obviously VoIP traffic has lower delays in comparison with HTTP traffic. Best results are obtained with the typical queuing method, which ensures the requisite bandwidth at possible blockage points and serves all traffic fairly. Similar results are obtained also in case of HTTP. If the WFQ scheme is in use, high-priority traffic will be ensured with a fixed amount of available bandwidth defined by the network administrator. For example, the network administrator, using WFQ, defines 9Mbit/s for VoIP, in which case only 1Mbit/s remains for all other applications; so the majority of low-level traffic will be affected by rapid increasing of delays, as shown in (Figure 5.6).
5.2 ftp Download Response Time :
Figure 5.2 : ftp Download Response Time (sec)
Figure 5.2 shows ftp Download Response Time statistics, here as the traffic increased the performance graph lines are changing. WFQ and CQ.The performance graph line of PQ is better then FIFO, CQ.PQ is higher than WFQ. FIFO, WFQ and PQ are near bout each other.
5.3 ftp Upload Response Time (sec) :
Figure 5.3 : ftp Upload Response Time (sec)
Figure 5.3 shows ftp Upload Response Time statistics, where it can be observed that as the traffic increased the performance graph lines are changing. FIFO and CQ.The performance graph line of WFQ is better then FIFO, CQ. CQ is higher than FIFO and CQ. PQ is best then rest three.
5.4 User Object Response Time (sec) :
Figure 5.4 : User Object Response Time (sec)
Figure 5.4 shows User Object Response Time statistics for Http user, here when the traffic increased the performance graph lines are changing. FIFO and CQ.The performance graph line of PQ is only same in this case with WFQ, PQ. CQ, FIFO are higher than PQ And WFQ.WFQ is best then rest three.
5.5 User Page Response Time (sec) :
Figure 5.5 : User Page Response Time (sec)
Figure 5.5 shows User Page Response Time statistics for Http user, where it can be observed that as the traffic increased the performance graph lines are changing. FIFO and CQ.The performance graph line of PQ is only same in these case with WFQ, CQ are higher than PQ,FIFO.And WFQ.is best then rest three.
5.6 Video Conference Packet End to End Delay:
Figure 5.6 :Video Conference Packet End to End Delay
Here in Figure 5.6 showa that as the traffic increased the Video Conference Packet End to End Delay is decreasing for CQ, FIFO when Packet end to end delay time is increasing. Like VoIP, CQ, FIFO Packet end to end delay time is also always higher in Video conference.PQ,WFQ is near to zero.WFQ and PQ is Better among them.
5.7 Video Conference Packet Delay Variation:
Figure 5.7 :Video Conference Packet Delay variation
Figures 5.7 shows Packet delay variation time for Video conference, where it can be observed that as the traffic increased the Packet delay variation time decreased for WFQ ,FIFO ,PQ . but as Packet delay variation time is increased for PQ Packet delay variation time is Lower in Video conference. and its goes near to zero.CQ is so higher here.
5.8 Voip Packet End to End Delay (sec) :
Figure 5.8 :Voip Packet End to End Delay(sec)
Figures 5.8 shows Packet end to end delay time for Voip. For both the cases such as time increase or traffic increase FIFO and WFQ packet end to end delay line always higher. But here PQ and CQ packet end to end delay I near about zero.
5.9 Voip Packet Delay variation:
Figure 5.9 :Voip Packet Delay variation
Figure 5.9 shows Packet delay variation time for VoIP, for all the cases such as time increase or traffic increase FIFO and WFQ groups packet delay time shows higher then PQ and CQ.here PQ and CQ shows near about zero.
5.10 Ftp Traffic Sent (byte/sec) :
Figure 5.10 : Ftp Traffic Sent (byte/sec)
Figure 5.10 shows Ftp Traffic Sent statistics, where it can be observed that as the traffic increased the performance graph lines are changing.FIFO and CQ. The performance graph line of PQ is better then FIFO, WFQ are higher than FIFO and CQ. PQ is best then rest three.
5.11 User Traffic Sent (byte/sec) :
Figure 5.11 : User Traffic Sent (byte/sec)
Figure 5.11 shows User Traffic Sent statistics for Http user, where it can be observed that as the traffic increased the performance graph lines are changing.FIFO and WFQ. The performance graph line of PQ is only same in case of FIFO, PQ are higher than FIFO. And WFQ.is best then rest three.
5.12 Video Traffic Sent (byte/sec) :
Figure 5.12 : Video Traffic Sent(byte/sec)
Figures 5.12 shows Video Traffic Sent(byte/sec), here in this cases FIFO, WFQ is higher than the performance graph of CQ and PQ and both they are near to zero.
5.13 Voip Traffic Sent (byte/sec) :
Figure 5.13 : Voip Traffic Sent(byte/sec)
Figures 5.13 shows Voip Traffic Sent , here in these cases of all FIFO, WFQ is higher than the performance graph of CQ and PQ. they are here near to zero.
5.14 Ftp Traffic Receive (byte/sec) :
Figure 5.14 : Ftp Traffic Receive (byte/sec)
Figure 5.14 shows traffic Receive statistics for FTP, where it can be observed that as the traffic increased the file receiving performance graph line is same in both FIFO and WFQ. The performance graph line of PQ is only same in case of FIFO, PQ, and WFQ.but CQ is higher then rest three.
5.15 User Traffic Received (byte/sec) :
Figure 5.15 :User Traffic Received (byte/sec)
Figures 5.15 shows User Traffic Received, here in these cases CQ, FIFO is higher than the performance graph of WFQ and PQ.
5.16 Video Traffic Received (byte/sec) :
Figure 5.16 :Video Traffic Received (byte/sec)
Figures 5.16 shows traffic Received statistics for Video conferencing, here in these cases of FIFO, WFQ video receiving rate graph is higher than the performance graph of CQ and PQ. the performance graph of PQ and CQ is near zero.
5.17 Voip Traffic Received (byte/sec) :
Figure 5.17 : Voip Traffic Received (byte/sec)
Figures 5.17 shows traffic Received statistics for VoIP, where it can be observed that as the traffic increased the performance graph line increased in both FIFO and WFQ. The performance graph line of FIFO is always higher compared to the PQ and CQ.
In this simulation, we have observed the effect of typical queuing mechanism regarding real time application such as FTP, VoIP, User (HTTP or Web). We have compared the results with each other and among all the techniques it is found that except HTTP application all other application has great impact on PQ queuing technique on the real time network. After the comparison of the results it is clear
that in case of PQ performance always depends on traffic’s number and shows better output even when the number of clients increases and it’s performance is better than FIFO in some cases. FIFO performance is also better in some cases compared with PQ cording to the dropped packet graph it is also found that the packet delay among all the queuing method PQ and WFQ has optimum. if we compare WFQ with FIFO and PQ in case of traffic drop, File receiving, voice data receive and video conferencing; WFQ always shows the best performance among them. Some problems with the integration between VOIP architecture and Internet. For any meaningful exchange, voice data communication must be a real time stream. This is in contrast with the Internet architecture that is made of many routers, which can have a very high roundtrip time (RTT), this can delay the voice data in reaching the proper address at a continuous rate . But according to the simulation it is already proven that a modernized format of fair queuing WFQ can perform better. So ,it can be said with confidence that user traffic stream like voice, video, data can be easily transferred with it’s efficient level performance by using Weighted Fair Queue algorithm in routers where the voice, video and data streams are routed to go to their desired destination.
In future, hybrid queuing method can be implemented in the network and observe the overall impact.
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