99 lines
7.4 KiB
HTML
99 lines
7.4 KiB
HTML
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<meta name="DC.Title" content="Service-level agreement" />
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<meta name="abstract" content="This topic points out some of the important aspects of a service-level agreement (SLA) that might affect your quality of service (QoS) implementation." />
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<title>Service-level agreement</title>
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</head>
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<body id="rzak8sla"><a name="rzak8sla"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Service-level agreement</h1>
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<div><p>This topic points out some of the important aspects of a service-level
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agreement (SLA) that might affect your quality of service (QoS) implementation.</p>
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<p>QoS is a network solution. To receive network priority outside your private
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network, you might need to have an SLA with your ISP.</p>
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<div class="section"><h4 class="sectiontitle">When is an SLA required</h4><p>You only need a SLA if your
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policies require priority outside your private network. If you are using outbound
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policies to throttle traffic leaving your server, then no service guarantee
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is required. For example, on the server, you can create a policy that gives
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one application higher priority than another application. Your server recognizes
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this priority, but anything outside the server might not recognize the priority.
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If you have a private network and configure your routers to recognize codepoint
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markings (used to give outbound policies a service-level), then the routers
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will give priority through your private network. However, if the traffic leaves
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your private network, there are no guarantees. Without an SLA, you do not
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control how network hardware will handle traffic. Outside your private network,
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you will need a SLA to guarantee priority for a class of service or resource
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reservation.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Why is an SLA required</h4><p>Your policies and reservations
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are only as good as the weakest link. This means, that QoS policies enable
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applications to receive priority through the network. However, if one node
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anywhere between the client and the server is unable to perform any of the
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traffic-handling characteristics discussed in the differentiated service or
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integrated service topics, your policies will not be handled as you intended.
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If your SLA does not allow you enough resources, even the best policies will
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not help your network's congestion problem.</p>
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<p>This also involves agreements
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across ISPs. Across domains, every ISP must agree to support QoS requests.
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Interoperability might cause some challenges.</p>
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<p>Make sure that you understand
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the service-level that you are actually receiving. Traffic conditioning agreements
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specifically address how traffic is handled, what is dropped, marked, shaped,
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or retransmitted. The key reasons to provide QoS involve controlling latency,
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jitter, bandwidth, packet loss, availability, and throughput. Your service
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agreements must be able to give your policies what they request. Verify that
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you are receiving the amount of service you need. If not, you might waste
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your resources. For example, if you ask to reserve 500 Kbps for IP telephony
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but your application only needs 20 Kbps, you might pay extra without receiving
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any notice from your ISP.</p>
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<div class="note"><span class="notetitle">Note:</span> QoS policies allow you to negotiate service-levels
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with your ISP which might decrease network service costs. For example, your
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ISP might be able to guarantee you a certain monetary rate if you do not exceed
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an agreed upon bandwidth level. Or you might state that using QoS policies,
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you will only use "x" amount of bandwidth during daytime hours, "y" amount
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of bandwidth at night, and agree to a rate for each time frame. Again, if
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the bandwidth is exceeded, the ISP might charge more. The ISP will need to
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agree to a certain service-level and have the ability to track the bandwidth
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you use.</div>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzak8planning.htm" title="The most important step to accomplishing quality of service (QoS) is planning. To receive expected results, you must review your network equipment and monitor network traffic.">Plan for QoS</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rzak8what_is.htm" title="If you are new to quality of service (QoS), you can read some basic QoS concepts. This will give you an overview of how QoS works and how QoS functions work together.">Concepts</a></div>
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<div><a href="rzak8example_1.htm" title="You can use quality of service (QoS) to control traffic performance. Use a differentiated service policy to either limit or extend an application's performance within your network.">Scenario: Limit browser traffic</a></div>
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<div><a href="rzak8example_4.htm" title="If you are using a virtual private network (VPN), you can still create quality of service (QoS) policies. This example shows the two being used together.">Scenario: Secure and predictable results (VPN and QoS)</a></div>
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<div><a href="rzak8example_3.htm" title="If you need predictable delivery and still need to request a reservation, you also use an integrated service policy. This example uses a controlled load service.">Scenario: Predictable B2B traffic</a></div>
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<div><a href="rzak8example_2.htm" title="If you need dedicated delivery and want to request a reservation, you use an integrated service policy. There are two types of integrated service policies to create: Guaranteed and controlled load. In this example, guaranteed service is used.">Scenario: Dedicated delivery (IP telephony)</a></div>
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</div>
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</div>
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</body>
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