Voice over Internet Protocol, Quality of Service - Essay Example

?QoS Voice over Internet Protocol (VoIP) has become a realistic substitute for public switched telephone network telephony services. To enhance mobile communication over a network, there has been development of infrastructure to include Video and Voice packet transfer over a wireless network. VoIP protocol, just like other data transmission protocol, is characterized by extreme bandwidth and delay sensitivity. This has been strengthened by the introduction of IEEE 802.11e quality of service enabled infrastructure on wireless LAN. Quality of service implementation is one among the mechanism of ensuring high quality voice and video transmission over the internet protocol. Key words IEEE 802.11e, Diffserv IEEE 802.11, WLAN, Quality-of-Service (QoS) Introduction As technology advances, communication over a wireless network is becoming preferable over other forms of communication. The modern networks are designed in such a way that they support more sophisticated traffic as compared to traditional networks. The advanced features of modern networks enables various traffic such as web traffic, file sharing traffic, and email traffic (Evans & Filsfils, 2010). In recent time, sensitive traffic such as video and voice have been introduced to share common transmission medium. The use of this sensitive medium demands regulated and guaranteed services. Considering the above stated sensitive nature of the data being transmitted, the traffic on transit is susceptible to many communication obstacles. Among the obstacles the sensitive traffic being transmitted meet include Lack of bandwidth, Delay, Jitter, and Data loss. For better, Quality of service tools have been developed (Alvarez, 2006). This Quality of Service tools have been specifically designed to provide applications which enable consistent and guaranteed experience to the user. In broadband technology, IEEE 802.11 has become prevalent. This technology is often referred to as the wireless Ethernet basing on Medium Access protocol and the ability to provide transmission rates of up to 54 Mbps. To make the IEEE 802.11 more efficient, the technology has evolved to support quality of service. Consequently, there has been the emergence of the IEEE 802.11e. This research paper is aimed at discussing limitations of IEEE 802.11 standards, Quality of Service methodologies, IEEE 802.11e standards, and to expose existing weaknesses in the Quality of Services architectures. Overview of 802.11 WLANs and its QoS limitations Point coordination functions and distributed coordination functions are the major access functions of the IEEE 802.11 definitions of the MAC sub – layer. Basically, the access function of IEEE 802.11 is the distributed coordination function (DCF). During packet transmission using the IEEE 802.11 standards, the data is exposed to various vulnerabilities as discussed below. Delay (Latency) This is one of the characteristics of a wireless network that can be measured quantitatively. This is the measure of the time packets that are transmitted across a network form end – to – end. The units for measuring latency are fractions of seconds. Measurement of latency can be done either to a single source from a single source ( One-way) or round – trip, which involves measurement from the single source to the destination and back to the original source (Cisco, 2012). In cases where there is fast communication between the devices, the time taken for packet transmission is automatically very low, this is referred to as low latency. On the contrary, when the transmission of the packets takes significant amount of time to be transmitted, between the destination and the source, there is an indication that there is high latency on the network. Generally, the occurrence of latency depends on the location of the communicating computers and the available network infrastructure. Occurrence of delay is not point specific. It occurs at any point along the network. Thus delay is also referred to as end – to – end – delay. Network Capacity and throughput Lack of Bandwidth on a wireless network is the description of insufficient throughput on a network. This severely paralyzes transfer of sensitive traffic which include video and audio on the affected network. To correct this, the immediate solution is increasing the amount of bandwidth on the network. Though is very effective, it is very time consuming and expensive (Vonage Forum, 2013). Like Ethernet network, bandwidth is offered at a fixed rate and like on frame – relay, it is offered at variable rates. To pseudo - increase a link capacity, there are various mechanisms, like compression, used. Jitter During packet transmission, there are various fragmentations which occurs as the traffic is transmitted and arrives either in wrong order or in irregular times. This occurrence is described as jitter. Therefore, a varying amount of delay can be described as jitter. Traffic which carries voice packets is the most susceptible to jitter. There are various ways is mitigating jitter, this is through two approaches. This are Designing an asynchronous network that has no jitter and using a protocol that has mechanisms of compensating for jitter. To allow proper communication without jitter, traditional telephone system are designed in an asynchronous network that has no jitter (Xiao, 2008). This type of network ensures that during packet transmission, the delay along all paths is similar. This is done by configuring the hardware so that all the paths have exactly the same delay (Cisco-Linksys, LLC, 2013). During the transmission of voice or video, over the internet, the network is designed such that it is able to compensate for jitter. This network design uses real – Time Protocol in transmitting the video or voice packets to compensate for jitter. This due to the fact that using real – time protocol in transmitting packets is much cheaper as compared to designing asynchronous networks. As packets are being transmitted on a given network, there is packet loss that occurs due to congestion on the link (Cisco, 2012). In some instances, a full queue on the network drops new arriving packets. This effect is referred to as tail drop. Jitter, packet loss, and data loss have an adverse effect on communication within an IEEE 802.11 network (Alwayn, 2001). Introduction of the IEEE 802.11e has been designed to remove the above stated drawbacks by implementing quality of service. Quality of Service (QoS) Support Mechanisms of 802.11e Methodologies for Implementing Quality of Service. The key methodologies used in implementing Quality of Service in Packet transmission include; differentiated services, and integrated services. Integrated service QoS (IntServ) This is also referred to as hard QoS or end – to – QoS. In the Implementation of Integrated Service methodology for QoS, an application is required. During the functioning of this application, if a specific level of service is required, the application sends a signal. To effect this, an Admission control protocol sends back its response by reserving resources or allocating resources for the application. In case of insufficient resources, the requested resources are not allowed i.e. the application is denied. Though integrated service is usually used, it does not provide a scalable solution for QoS implementation (Cisco-Linksys, LLC, 2013). This is due to finite number of bandwidth that can be reserved over the network and it adds overhead significantly on the network infrastructure since every amount of packet transmission must be maintained. Differentiated service QoS To provide a scalable solution during QoS implementation, Differentiated service QoS has been designed. In this method of QoS implementation, there is organization of traffic into specific classes. This traffic is then marked to facilitate the identification of its classification. In providing specific level of services, there is creation of policies and this predominantly depends on specific traffic classification. The Differentiated service QoS architecture is as indicated in fig. 1 below Fig. 1. Differentiated service QoS architecture (Cisco, 2012) IEEE 802.11e Standard This standards were designed specifically to define Quality of Service mechanisms for wireless Local Area Networks to support very sensitive packet transmission such as video and audio packet transmission. For IEEE 802.11e to support IntServ and Diffserv quality implementation, hybrid Coordination function (HCF) has been added. This coordination factor is mandatory to be used on all QSTA. The functionality of hybrid Coordination function is based on two access mechanisms. This access mechanisms are HCF Controlled channel access (HCCA) and EDCA (Enhanced Distributed Channel Access). Enhanced Distributed Channel Access In IEEE 802.11e, EDCA was designed specifically to facilitate performance improvement on DCF and also, to facilitate provision of Differentiated service QoS. In this access mechanism, different classes of traffic are assigned to any one of the four available ACs. Enhanced Distributed Channel Access in IEEE 802.11e has been designed in such a way that its use is based on contention prioritized Quality of Support mechanisms. To support service implementation in EDCA, there is the use of IFS values in different ACs and allocation of different CW sizes on distinct ACs. The main advancement in this transmission access in IEEE 802.11e is basic traffic priority introduction. This has facilitated support of four types of traffic on the network, the traffic include Video, Voice, background application and Best effort. Moreover, this access mechanism in IEEE 802.11e creates transmission opportunity for each traffic type. Conclusion Quality of Service functionality does not speed up the packet. It utilizes the available resources such as bandwidth, to ensure maximum functionality basing on the designed specifications of the network. Though implementation of Quality of Service is to facilitate optimum functioning of a given network, it does not fully eliminate all the network problems, but rather it improves the general network performance. Considering the shortcomings of the implementation of Quality of Service, there is an indication that quality of service, QoS, is an area that stimulates extensive research. To facilitate QoS network to have a reliable productivity platform, more effort needs to be done in QoS research to unveil new QoS implementation mechanisms that will ensure high productivity. Bibliography Alvarez, S., 2006. QoS for IP/MPLS Networks. s.l.:Cisco Press. Alwayn, V., 2001. Advanced MPLS Design and Implementation. s.l.:Cisco Press. Cisco, 2012. Quality of Service for Voice over IP. [Online] Available at: http://www.cisco.com/en/US/docs/ios/solutions_docs/qos_solutions/QoSVoIP/QoSVoIP.html [Accessed 25 August 2013]. Cisco-Linksys, LLC, 2013. Applications - QoS. [Online] Available at: http://support.linksys.com/en-mea/firmwarehelp/qos [Accessed 25 August 2013]. Evans, J. W. & Filsfils, C., 2010. Deploying IP and MPLS QoS for Multiservice Networks: Theory & Practice. s.l.:Morgan Kaufmann. Vonage Forum, 2013. Implementing QoS. [Online] Available at: http://vonage.nmhoy.net/qos.html [Accessed 25 August 2013]. Xiao, X., 2008. Technical, Commercial and Regulatory Challenges of QoS: An Internet Service Model Perspective. s.l.:Morgan Kaufmann. Read More