Carrier Ethernet – The CIO PerspectivePart II: Service Levels and SLAs RAD Data CommunicationsJune 2011
What’s in an SLA? A business-grade SLA for Carrier Ethernet services will typically include the following: Connection rates Class of Service (CoS) levels definition and traffic priority settings Bandwidth commitments per CoS Quality of Service (QoS) KPI (Key Performance Indicators) guarantees Monitoring and reporting Service and support hours, response and repair times Restrictions Credits/SLA violation remedies Etc…
Carrier Ethernet SLAs Throughput Guarantees CIR: Committed Information Rate. Bandwidth with guaranteed delivery, regardless of network conditions EIR: Excess Information Rate. The bandwidth allowance depending on network resource availability PIR: Peak Information Rate; CIR+EIR – defines the maximum bandwidth allowed
Carrier Ethernet SLAs – CoS, QoS and KPIs Each level requires differentiated SLAwith appropriate QoS parameters to ensure user QoE (Quality of Experience) “Bursting” is the ability to exceed the designated bandwidth for a short period to avoid traffic dropping
Key service elements that directly effect QoE Availability: Network uptime on a monthly basis, after measuring the number of minutes and seconds that the service was unavailable to the enterprise Business-grade SLA: 3-5 Nines (99.9% -99.999%), depending on CoS Latency: The time for transmitting a packet/frame of data from a source to its destination Effect on voice traffic: Delays, overlapping speech, echo Effect on video traffic: From blanks to session termination Jitter: The difference in delay between two consecutive frames/packets Effect on Voice: Static, distorted speech Effect on video: Momentary signal loss, shaky image Loss: Percentage of undelivered frames out of all sent frames Effect on data: requires re-transmissions which lower throughput Effect on video: Momentary signal loss, graininess, session termination MTTR: Mean Time to Repair
KPI Performance Parameters An SLA should specify how parameter values are measured: The percentage of traffic to which the guarantee is applicable, over what time interval, etc (MEF 23.1 Draft):
Monitoring and Reporting: Are You Getting the SLA You’re Paying For?
Monitoring and Reporting: What You Should Look for? Choose a service provider that can provide performance reports: Monitor the service Compare actual performance to the SLA you buy Get service credits when the service provider fails to deliver Change service provider if failures are repeated Different reporting options: Periodical (weekly/monthly) Self-managed 24x7 portals: View KPI data in real-time
Service Provider Tools to Guarantee Carrier Ethernet SLAs Service providers can now implement the following capabilities in their networks: Traffic and bandwidth management for multilevel QoS Performance monitoring and reporting Fault detectionand repair Resiliency and protection In order for these attributes to be effective, they need to be implemented at the service hand-off point, i.e., in the service provider’s CPE (also called Ethernet demarcation) installed at customer premises
Multi-CoS Traffic Management Tools Traffic classification according to enterprise preference and equipment (e.g., IP Precedence, address, VLAN Priority bit, etc) Advanced traffic mapping to ensure QoS adherence and transparency of user classification over the WAN Rate metering and policing per CIR/EIR profiles for multi-flow Ethernet connections (i.e., different profiles over the same link) Hierarchical scheduling for multi priority traffic Traffic shaping and queue management to avoid packet dropping and congestion CoS 7 = Management CoS 6 = VoIP CoS 5 = Video CoS 4 = Interactive CoS 3 = Priority Data CoS 2 = Other Data CoS 1 = Best Effort CoS 0 = Best Effort An 8-CoS Traffic Queue
Service Lifecycle Management Tools An elaborate set of tools to provision, monitor and control Ethernet services at turn-up, as well as for on-going monitoring and fault management Specific standardized tests to continuously evaluate SLA performance metrics and report results/statistics to network management system (OSS/BSS) Shorten lead-times for fault identification and resolution to avoid service disruptions Identify trends and take preventive measures before service and users are affected
Resiliency and Protection Tools Ensure High Availability and speedy restoration by protecting the links, as well as the entire service path Standardized redundancy schemes: Link Aggregation: Parallel connections are bundled to a single virtual link Ethernet Linear Protection Switching: Redundancy at the service path level with an EVC (Ethernet Virtual Connection) backup Ethernet Ring Protection Switching: Ring protection with fast failover Without proper protection mechanisms QoE is compromised due to retransmissions or even loss of service
Additional Questions to the Service Provider Is the Ethernet service certified by the MEF (Metro Ethernet Forum)? Can the service provider guarantee service consistency even when some locations are not fiber-fed? Can the service provider guarantee service consistency even for out of footprint locations (e.g., on a national and global scale)? How accurate are the link quality and service performance measurements? How many provider boxes need to be installed at the premises (e.g., CPE/demarcation and test probes)?
In Conclusion Carrier Ethernet SLAs should include specific definitions of service levels and guarantees for key performance indicators Service KPIs directly effect how users experience application performance. KPI metrics differ by provider, but industry standardization efforts are under way Getting SLA reports ensures you get what you paid for Business-grade services require smart Ethernet demarcation devices to be installed at customer premises Check out other installments in the series: Part I: Why Choose Carrier Ethernet WAN Services? Part III: Ethernet and IP VPNs, When to Use Which?
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