As articulation and abstracts networks assemble into a distinct communications network, Affection of Account (QoS) is of growing importance. QoS allows a arrangement to accommodate bigger account to alleged cartage and enables the arrangement to handle both mission-critical and best-effort cartage on the aforementioned infrastructure. But what happens back there are problems with articulation affection on this new converged network?
Today, back an end user complains of articulation affection problems, an ambassador has to analysis a cardinal of areas like QoS configurations, interface errors and arrangement appliance to acquisition the cause. For calls aloft a Wide Area Arrangement (WAN) affiliation amid sites, there is no way to apperceive if the botheration is on the alien Bounded Area Arrangement (LAN), the bounded LAN, or the WAN in between.
The band-aid lies in the adeptness to added carefully appraise the botheration and actuate area in the abstracts beck the botheration is occurring, why it is occurring and what can be done to actual it. QoS abandoned is not the answer. The acknowledgment lies in Articulation Affection Monitoring (VQM).
VQM moves aloft QoS and can save time in the troubleshooting action for arrangement administrators, value-added resellers (VARs), managed account providers and carriers. With VQM, the time complex in troubleshooting the problem, free the account and alive against a resolution is decidedly reduced. The aftereffect is a accelerated acknowledgment to a high-quality account acquaintance for the VoIP user.
In essence, VQM allows the arrangement ambassador to appraise the abounding abstracts beck and analyze botheration areas bottomward to the packet akin in an easy-to-use graphical interface. To bigger accept how VQM works and the allowances it provides, let’s appraise some accepted problems encountered on a VoIP network.
The aboriginal constant about advised back there is beneath than adorable achievement on a VoIP arrangement is the Beggarly Opinion Score or MOS. The MOS provides a after admeasurement of the affection of animal accent at the destination end of the circuit. The arrangement uses abstract tests (opinionated scores) that are mathematically averaged to access a quantitative indicator of the arrangement performance. To actuate MOS, a cardinal of admirers bulk the affection of analysis sentences apprehend aloud over the communications ambit by macho and changeable speakers. A adviser gives anniversary book a appraisement as follows: (1) bad; (2) poor; (3) fair; (4) good; (5) excellent. The MOS is the accession beggarly of all the alone array and can ambit from one to five. Acceptable MOS array are four and above. Back an unacceptable MOS is noted, the account charge be bent because the alarm affection is illegible.
In accession to MOS, there are three primary areas that charge to be advised to appropriately actuate the account of the unacceptable articulation quality. These are delay, jitter, and packet loss.
Delay, or artlessly stated, the bulk of time amid accession of packets, is analytical to articulation quality. So abundant so that the ITU G.114 blueprint outlines a one-way adjournment of no added than 150 milliseconds, in adjustment to accommodated the admeasurement of a “high-quality” articulation experience. It is this bulk that the packet arrangement charge be engineered to meet, at worst, and finer exhausted it by a acceptable margin.
Next is jitter. A VoIP chat is fabricated up of abounding bags of packets. IP networks with all the added applications abounding over it will inherently affect alone packets of a chat differently, consistent in variations in the absolute adjournment for a distinct packet. That aberration is alleged jitter. Too abundant jitter is a bad thing. There are some mechanisms on VoIP accessories to atone for a baby bulk of jitter, alleged jitter buffers, but if the variations are too extreme, alike the best jitter buffers will not be able to afflicted the variation.
Packet accident can be a above affair in VoIP networks. The bulk of accident accomplished by a packet breeze is afflicted by absorber burnout and advised packet drops.
Absorber burnout is a aftereffect of bottleneck acquired by oversubscription or bulk decoupling. For archetype if there are too abounding Gigabit agriculturalist access to a distinct Gigabit uplink the aftereffect is oversubscription. The about-face accessory alone has a bound bulk of absorber amplitude to authority balance packets while it tries to address on the distinct uplink. Under nominal operating conditions, these links are about not a problem. But, in a aerial cartage situation, it is attainable to see area some cartage charge be dropped.
Rate-decoupling is a accepted occurrence. In this instance, accelerated LAN meets a abundant lower acceleration WAN connection. For instance, the Gigabit articulation from a router is agriculture cartage to a router that has alone a 45 megabit affiliation to the WAN, which is beneath than one-third of the LAN’s bandwidth. It is attainable to see how the router would run out of absorber space.
Another constant that is sometimes advised is out-of-order packets. Packets actuality beatific out of adjustment are not a problem. However, problems appear back there are issues on the accepting end of the beck and packets are not reassembled in the actual order.
The assay of these ambit is not new. In fact, there are standalone accouterments and software bales that can be acclimated to acquire this data. However, this is about presented in a abecedarian spreadsheet table acute a abundant accord of assignment to accomplish it calmly understandable. Historically, standalone systems that accommodate the abstracts in a address that is easier to use accept agitated a ample amount tag. Recently, some accessories manufacturers accept amorphous alms VQM as a affection of their operating systems. While this is a almost new development, it has accustomed a balmy acceptable from arrangement administrators. The VQM technology in these systems accommodate a user-friendly, easy-to-understand graphical interface that allows administrators to bound analyze problems upstream, after and alike aural an alone unit.
At view, VQM provides a attending at all IP interfaces and capacity in a blueprint architecture the cardinal of calls that were rated good, fair or poor quality. It additionally provides the adeptness to attending at both accomplished and alive calls. Best users don’t apperceive what affectionate of affection botheration they’re experiencing during a bad alarm — they aloof apperceive it sounds bad. VQM allows arrangement administrators to bound see the blazon of botheration and investigate the best acceptable sources of agitation accordingly.
Aboriginal accede a book area all users at a armpit accuse about poor audio on all calls. Using VQM, the arrangement ambassador determines that there is a aerial akin of packet accident in the network. Packet accident is about accompanied by interface errors — these errors will explain what is wrong. In our example, the arrangement ambassador sees that all of the about-face ports affiliated to phones accept detected alignment and CRC errors. These errors about aftereffect from bifold mismatches. Looking deeper, the arrangement ambassador sees that the about-face ports are statically configured for 100Mbps / Abounding Bifold operation. The phones, however, accept been configured for auto-negotiation. Because the about-face is statically configured, and the phones are auto-negotiating, there is a bifold mismatch, arch to interface errors. These errors account packet loss; and absent packets account poor audio.
In Figure 1, the arrangement ambassador watches an alive alarm and sees that there are abbreviate cycles of packet accident on the audio beck advancing from addendum 3015.This acceptable agency there are errors on a arrangement interface about amid the buzz and the router.
Looking at added accomplished calls, the ambassador sees that this is not the aboriginal alarm to acquaintance packet loss. The botheration exists about off of Ethernet 0/2. (See Figure 2.)
Back the arrangement ambassador looks at the about-face anchorage affiliated to the addendum 3015, he notices some errors. The key errors are alignment errors and CRC errors. (See Figure 3.) These problems advance a bifold conflict — in particular, they advance that the bounded articulation is configured for abounding bifold operation (as additionally adumbrated in the stats), but the added ancillary is alive bisected duplex. The botheration is that the about-face has been configured for changeless acceleration and bifold settings, admitting the buzz is auto-negotiating acceleration and duplex.
Back analytical actual calls, VQM displays the cardinal of Real-time Transport Protocol (RTP) flows per interface and provides statistics such as MOS, jitter, adjournment and loss. It allows the arrangement ambassador to chase by a cardinal of altered belief including extension, user and time of day. Anniversary alarm is reflected as a abstracts point. Both entering and outbound calls can be viewed. Once any abstracts point is selected, a abundance of abstracts is displayed in an easy-to-ready graphical manner. Abundant of this abstracts is the aforementioned as that you would acquire from the Command Line Interface (CLI), but it is calmly attainable and presented in a abundant added convenient manner.
Alive calls are polled every seven abnormal accouterment a real-time abstracts back actively troubleshooting calls. The ambassador can absolutely watch calls as they occur. The aforementioned blazon of abstracts is accessible on alive calls as accomplished calls.
Articulation Affection Monitoring provides the adeptness to attending at anniversary antecedent IP and appearance a ambit of MOS scores, RTP flows, jitter, accident and out of adjustment packets. Thus, VQM allows the arrangement ambassador to accept a abounding appearance of cartage as it transverses the network. This is a abundant benefit, abnormally back there are assorted accessories in the arrangement that could be the agent of the problem. VQM can abundantly abate the time bare to troubleshoot and adjust the problem.
For our added scenario, accede a aggregation that has two offices, affiliated via a point-to-point T1. There is an IP PBX at the beyond of the two offices (Office A), which facilitates alarm bureaucracy and tear-down for all VoIP calls, but audio amid IP phones goes anon amid phones. The IP PBX additionally has trunks for all calls to and from the PSTN, so it terminates the audio for alien calls. Users at the abate appointment (Office B) accuse about alternate articulation affection problems for alien calls. Despite the actuality that entering audio sounds bad, users say that the bodies at the added end of their calls never accuse about the affection of the audio they hear. Users at Appointment A do not acquaintance poor audio on any calls. Furthermore, calls amid the two offices never accept poor audio.
Using VQM, the arrangement ambassador begins investigating audio streams from the IP PBX at Appointment A to phones at Appointment B. The arrangement ambassador finds no problems on the router at Appointment A, but notices that there is ample jitter and a baby akin of packet accident on the router at Appointment B. Because these affection advance a accessible botheration with QoS, the arrangement ambassador confirms the QoS agreement on the router at Appointment A. It is (correctly) configured to accord antecedence to cartage with a DSCP bulk of 46, which is the aforementioned bulk acclimated by phones in the company. However, added VQM capacity appearance the ambassador that alarm streams advancing from the PBX are tagged with IP Precedence of 5 (DSCP 40), instead of 46. So, this cartage is not accustomed the adapted bandwidth guarantees. By afterlight the QoS agreement at Appointment A to bout either DSCP or IP Precedence 5, the arrangement ambassador is able to dness the alien alarm affection problems.
From these examples, you can see the complication in troubleshooting VoIP issues and how an easy-to-use graphical accomplishing of VQM reduces blow and supercharges QoS. A graphical VQM not alone reduces both the time and affliction associated with troubleshooting arrangement issues, but additionally provides a abundance of advice acceptance arrangement administrators to fine-tune their networks to actualize an alike higher-quality end-user experience.
Todd Lattanzi is a Senior Product Manager for the Enterprise Networks Division of ADTRAN, Inc. For added information, appointment the aggregation online at http://www.adtran.com.
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