What is a SLA?
When a communication service provider (CSP) offers to sell an Ethernet service (e.g. E-Line or E-LAN), they usually include a Service Level Agreement (SLA) for the service. The SLA is a contract spelling out the agreed upon performance metrics used to measure what the end customer’s service experience will be.
The contract also provides details as to what occurs if the service does not line up to the expected performance level. A strong SLA is an important vehicle for attracting new and maintaining existing customers.
The following is an excerpt from an actual SLA, which shows some typical performance measures and billing credits given when the service is operating at various performance levels. As shown, the performance measures would include service availability (i.e. outage duration), packet delivery, network latency, and jitter statistics.
Tracking and reporting on these performance metrics is important as the CSP is contractually bound to deliver on the promise, and may incur monetary penalties for violations. But more importantly, not meeting the agreement could lead to customer retention issues.
SLA Monitoring Today
In today’s Ethernet service market, service providers deploy Network Interface Demarcation (NID) devices to provide a variety of functions.
In order to measure the service, NIDs are strategically placed at the User Network Interfaces (UNIs), and use protocols (e.g. SOAM) to periodically measure availability, packet loss, packet delay, and packet delay variation. The measurements are collected by Network Management Systems to produce SLA reports. These reports are shared with the end customer, and are used to determine if the service is meeting the SLA.
Customer Applications in the Cloud
As enterprise customers move applications from physical servers to virtual machines operating in the cloud, CSPs will be expected to provide virtual network connectivity with the same or similar SLAs as we have today. The end points (i.e. virtual port) of the virtual network are not exposed to the physical world. The cloud environment presents an interesting challenge in that today’s physical NIDs do not seamlessly fit into the virtual networks operating in the cloud. The CSP could measure data center to data center performance, but this does not provide the expected end-to-end view. A new solution is required.
Using the principles of NFV, the Service Assurance functions of a NID (e.g. vMon) could be virtualized and injected into the customer’s virtual network, acting as an SLA probe. The vMon would use the same SOAM protocols a NID would use to perform the measures, and provide the resultant statistics to north bound management systems. By using the same protocols, the vMon could interoperate with physical NIDs giving CSPs complete coverage between physical and virtual networks. Because the vMON is only handling the SOAM packets, it puts a very light incremental load on the servers and networks, providing a scalable solution. With the addition of the vMon, the CSP is now able to offer the end-to-end SLA customers have come to expect.
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