Quality of service of a network

Quality of portion of a lucre congestion MANAGMENTNe cardinalrks which ar programmeed to confirm near(prenominal) diametrical calling figures which grapple a single selective information highway in the midst of r byers. congestion cargon techniques should be considered in such cases to ensure the bore and treatment for the assorted vocation types.Traffic prioritization especiall(a)y important for condition-sensitive, interactive transaction base coat for instance, for example takes television receiver conferencing that requires higher precession than the file air applications. However work of WFQ (weighted fair queuing) ensures that all traffic is treated fairly.Prioritization is just about effective in WAN links where the combination of bursty traffic and comparatively lower selective information regularizes gutter acquire temporary congestion if there is no congestion on the WAN link, there is no reason to implement traffic prioritization.APPLICATION Q UALITYBy several(a) parameters employ for engagement timbre of portion which allows the unique(predicate)ation of quality metrics. much(prenominal) quality of work metrics are monitored and analysed using network quality parameters and important aspect of quality which is always ignored in some cases and overlooked is the behaviour of each and every individual applications in the meshing recognised . nigh applications try to possess a majority part of network re artificial lakes possible, immediately it may non or influence the quality of an application. mesh topology QUALITY OF SERVICEThe Ability to provide erupt service to a selected traffic.Quality of service refers to the ability of a network to provide highest quality service to any(prenominal) selected network traffic using various technologies in the in vogue(p) networks apply with a combination of traffic Qos ensures the exact application to be accessed to the re lineages of the network first, it is a combina tion of various technologies which allows application to recive request most acceptable and predicted service levels in terms of data and its Bandwidth (through and throughput capacity) latent period variety in jitter, computer software loss and delays.Qos provide the best take ins and more predictable network service by copying methods(cisco 2009) Dedicated ringwidth and support waiver characteristics Congestion scheme and mangment of network Network traffic cause surgical process OF QOS Qos distinguishes the traffic and splits it with very exact timing requirements It improves resources in the network so that all the traffic reaches the qualify finiss reliably and faster It doesnt create any bandwidth it alone manages it effectively to meet the application requirements (OPNET 2008)Here the working of qos follow a serial publication ladder of simple rules in order to hightail it the file or a big bucks and at first the tract is pass through the classification which actor that the following packet moldiness be in which group does it fit then the packet is go on to the next level which is the pre-queuing which core that the following packet is tick up in a order according to the source and the destination poesy and then it is again moved on to the next level which is the queuing and scheduling its main work is to caste the stream to the destination point so that it automatically enforces the bandwidth allocations then moves on to the last level which is the post queuing which increases throughput on the lower speed links so that it reaches the destination point inside the time it has decided and thus the working of the qos is comed.ADVANTAGES OF QOS Dedicated bandwidth conquerled network response time and jitter Improved loss characterstics Control and predictability beyond best effort sentiment (OPNET NETWORK 2008)NEED OF QOS IN A NETWORKAll packets in a network are letn equal access to all the resources , the priorty acn only be precondition when we can distinguish data packet from a voice packet. For a company network to effectively use the network and its resources it mustiness identify which network traffic is the appropriate and which is not to allocate the right recourses to effectively support the traffic streams . The anteriority should be given to all the data streams to failing to do so can create low quality of voice and data, because most of the audio and optic application is delay and jitter sensitive. Only a good Qos can give the audio and video packets the best antecedence access. Qos evolution The networks which are use with Qos enabled are called the Best -effort network. Where each and every packet is treated in the equivalent way which is strongly important in the network design for preferable results, when compensate space in the cpu is available these type of networks work prominently. There are two major computer architectures of qos, both the architecture have different approac h and different ways of quality of service in their own preferable ways. The main architecture of Qos is integrated go and differentiated services.Traffic characteristics that Qos tools can effect1) Bandwidth 2) latency3) jitter4) compression5) queuingBANDWIDTH Bandwidth refers to fig of bits per second that can reasonably be expect to be successfully expected across same medium. firstly bandwidth techniques are mainly used to attain or define network traffic and to do this we can set some special type of techniques which are mainly used by the network devices such as blue coat for instance and by using this we can setup a type of service (TOS) in the packet of the internet protocol header and by using the un barable information of the type of service we can set the device in action and allow the traffic to blend in different bursting charge and for an different instance we can choose some factors to involve this slew such as audio clarity, if the sound is audible in two di fferent direction then it is said to be working in perfect condition and this can be measured by the MOS (which means the mean opinion score) , so by this we can rate from 1-5 which means that 1 scores the worst and 5 scores the best and the comely typical analogue call which rates from 4.1 to 4.7 and a avg cell telephony ranges from 3.5 to 3.9 and if we considered the VOIP CALLS ranges from the 4.0 to 4.4 so which means that the VoIP also has the best average rating in audio clarity and if we comes to reliability comes to 99.999 so which is more reliability to the customers and the consumption of them is also more and the techniques used in this kind of symphony which is advanced(a) and the consistency is also more which is mixed out with the qos so this is in short all about bandwidth in qosLATENCY It is mainly specified as some serious problem to qos which is also known as the delay and if we speak in technical words its the same gist of time taken by a packet from source to destination and if the latency and the bandwidth are defined they are for speeding the network so for instance we can say that a conventionalism average person can hear a call upto 250 ms approx and 200 ms in sensitive person ear so if the call doesnt return in that range the caller is going to be disappointed.JITTER It also refers to the same problem but for connection slight or wireless so which is also called as a delay which must be a serious and most inappropriate but business customers such as for company which is traffic with important calls so in this here if we see the database emcee is connected to some system and the employees are storing some information to the database systems and in between there are calls to handled and the calls doesnt seems to go through the cloud of the similar database server so we can find the disturbance which are caused by the latency and jitter so in order to watch and control the traffic we must maintain the jitter in control and the s pecification for this is it must be less than 100 ms for the communication less than 100 ms for normal database because if the jitter took place a bit slow in voice band it doesnt have a problem but if it takes downstairs the packet series then it might be some kind of serious expose so in order to reduce this we must all sustentation the jitter in control. bandwidth refers to topic of bits per second that can reasonably be expected to be successfully delivered across same medium Compression all the pay excites or the headers compressed by reducing the total count of bits ask to transmit the data.Call entree control reduces all the boilers suit load of the network by denying any new incoming voice and video calls.QueuingQos refers to a broad collection networking technologies and techniques. The goal of Qos is to provide guarantee on the ability of a network to deliver predictable results.Qos involves prioritization of a network, Qos is a method to guarantee the bandwidth r elationship between individual or application or protocols. Qos refers to the capability of a network to provide a better service to selected network traffic over various underlying technologies including physique relay,(Cisco systems Inc. 1999). There are seven Qos mechanisms and tools that are used to implement Qos in a computer network. Congestion management Congestion avoidance Control admission control Shaping and policing Bandwidth reservation Link efficiency compartmentalization and marking1.1.3 Aim of Qos is to provide a dedicated bandwidth sufficient to deliver for the service of the applications by controlling latency and jitter, and by reducing data loss.Network characteristics managed by quality of service. Category of quality of service mechanisms1) Admission control2) Traffic control 1.2.1 Admission controlGives the information of number of users and the applications used to network resources it allows only specific users and resources which can be used in a networ k segment (subnet).1.2.2 Traffic controlIt controls and regulates the data flow by classifying and marking the packets establish on priority and by stopping traffic, service class assigned to a traffic flow which evaluates the quality of service treatment, the traffic receives.1.2.3 Call admission controlIt provides the overall quality for all the networks, it controls the voice disturbance from the voice traffic, and video from the other video traffic1.3.2 Classification and markingFor defining a quality of service identifying the traffic is the first case involved in the effect which is treated either differently or preferentially which is done by classification and marking. 1.3.3 Bandwidth reservationBandwidth reservation provides guarantee to the bandwidth, i.e., bandwidth is provided whenever engageed without reserving it for a specific application or flow in a network.1.3.4 Shaping and policingThe significant issues related to quality of service in a network are solved by tr affic shaping , the delay and loss in a network are solved by traffic shaping which is called as(egress blocking)The data which is sent or received are measured by traffic shaping and traffic policing . traffic policing in a network is used to remove all the excess packets which helps to overcome the policed rate. The excess packets are again en- waiting lined by shaping. Both shaping and policing prevent the traffic from particular(a) the bit rate defined.Link efficiency Link efficiency is used increase the quality of service of a network,particularly if the given note constantly increase the bandwidth rate on a network which causes the sudden tack in behaviour of the network. Which slows down data applications significantly.if the load exceeds the given bandwidth for a period of time the application slows down completely or even stops down ata particular point because of the continuous queues which can be avoided by using the link efficiency.1.3.6 Congestion managementWhenever queuing occurs in a network congestion management gives the ability to rearrange the packets.1.3.7 Congestion avoidance Congestion avoidance tools are used to avoid congestion. It enables queue to avoid congestion. Whenever the rate of transmission load and offer load exceeds the line rate send by various senders.Queues are formed which may cause congestion. The queue are managed by congestion avoidance tool by dropping the packets randomly which are selective which reduces the congestion level.WHY DO WE NEED QOSEach and every packet will be given equal access to resources when we not consider the QoS policies. We cannot give voice priority if we cannot tell a voice packet from a data packet. In order to utilize its network resources efficiently for a company, so to support those traffic streams it must identify which network traffic is critical traffic and allocate appropriate resources to support those traffic streams. Otherwise, the result could be sporadic with voice quality co mplaints. Applications like voice and video are delay and jitter sensitive. Voice packet will be given first priority access to the interface queue, when we use a good QoS policy. For example, both file transfer protocol and an voice packet arrive at the same time at an outbound router interface. When we not consider the QoS policies the voice packet may need to wait in the queue until the FTP packet has been processed out the interface. This may results delay of unacceptable amount of delay into the voice path which will depends upon the interface speed. Traffic flow with out qos (global knowledge,whitepapers,2,authorgardiner2008)The voice packet could be given priority first over the FTP packet when we use QoS configuration. The FTP packet may be fragmented to book sure that the voice packet does not show any excessive delay, if the interface speed is less than T.QoS EvolutionThe main reason for the broad(a) transformation of best-effort models to more complex differentiated ser vices models is by in camera owned enterprise and service providers networks, the meaning that the network gives different applications differing levels of service.2.6.1 Congestion Management (Queuing) QoS queuing tools provide you with a variety of queuing methods. Queuing tools define a number of queues. The queuing tools are as followsa. precession Queuing(PQ)b. impost Queuing(CQ)c. plodding fair(a) Queuing(WFQ)d. Class-Based Weighted Fair Queing(CBWFQ)e. Low Latency Queuing(LLQ)f. Modified Deficit Round-Robin(MDRR)a. Priority Queuing Priority Queuings most distinctive feature is its scheduler. PQ schedules traffic such that the higher-priority queues always make out serviced, with the side affect of starving the lower-priority queues. With a level best of four queues, called High, Normal, and Low, the complete logic of the scheduler can be easily represented, as shown in figure. (Cisco systems, 1999)b. Custom Queuing As with most queuing tools, the most interesting part of the tool is the scheduler. The CQ scheduler militia an approximate percentage of overall link bandwidth to each queue. CQ approximates the bandwidth percentages, as foreign to meeting an exact percentage, due to the simple operation of the CQ scheduler. The CQ scheduler performs round-robin service on each queue, beginning with queue 1. CQ takes packets from the queue, until the total byte count specified for the queue has been met or exceeded. After the queue has been serviced for that many bytes, or the queue does not have any more packets, CQ moves on to the next queue, and repeats the process. (Morgan, 1991)c. Weighted Fair Queuing Weighted Fair Queuing differs from PQ and CQ in several significant ways. The first and most obvious difference is that WFQ does not allow classification options to be configured. WFQ classifies packets based on flows. A flow consists of all packets that have the same source and destination IP address, and the same source and destination port numbe rs. So, no explicit matching is configured. The other large difference between WFQ versus PQ and CQ is the scheduler, which simply favors low-volume, higher- antecedence flows over large-volume, lower-precedence flows. Also because WFQ is flow based, and each flow uses a different queue, the number of queues become rather large up to a maximum of 4096 queues per interface. And although WFQ uses tail drop, it really uses a slightly modified tail-drop scheme- yet another(prenominal) difference. (Cisco systems Inc, 1999)d. Class-Based WFQ CBWFQ is most like CQ, in that it can be used to agree minimum bandwidth for each queue. It does differ from CQ in that you can configure the actual percentage of traffic, rather than a byte count. CBWFQ is like WFQ in that CBWFQ can really use WFQ inside one particular queue, but it differs from WFQ in that it does not keep up with flows for all the traffic.e. Low Latency Queuing (LLQ) LLQ combines the bandwidth reservation feature of CBWFQ with a PQ-like high priority queue, called as Low Latency Queue, which allows delay-sensitive traffic to spend little time in the queue. But first, this section begins with WFQ, which uses a completely different scheduler.Table 2 Comparison of Queuing Tools. (Odom W, et al, 2005)Tool supremeNumber ofQueuesClassificationCapabilitiesQueue Service Algorithm/ End turn up of AlgorithmPriorityQueuing (PQ)4IP ACLInput interfaceFragmentsStrict service always serves higher-priority queue over lower queue.Custom Queuing (CQ)16IP ACLInput interfaceFragmentsServes a configured number of bytes per queue, per round-robin pass through the queues. Result Rough percentage of the bandwidth given to each queue under load.Weighted Fair Queuing (WFQ)4096Automatic, based on flows, (Flow identified by source/destination address and port numbers, plus protocol type.)Each flow uses a different queue, Queues with lower volume and higher IP precedence perk up more service high volume, low precedence flows get le ss service.Class-Based Weighted Fair Queuing (CBWFQ)64IP ACLNBARSame as CB markingService algorithm not published results in set percentage bandwidth for each queue under load.Low Latency Queuing (LLQ) N/ASame as CBWFQLLQ is a variant of CBWFQ, which makes some queues priority queues, always getting served next if a packet is waiting in that queue. It also polices traffic.Modified Deficit Round-Robin (MDRR)8IP precedence resembling to CQ, but each queue gets an exact percentage of bandwidth. Supports LLQ mechanism as well.