(KPI) for real-time services such as VoIP and Internet Protocol television (IPTV) and is not measured by the RFC 2544 methodology. Network operators that performed service testing with RFC 2544 typically must execute external packet jitter testing outside of RFC 2544 as this KPI was not defined or measured by the RFC. Testing is performed sequentially on one KPI after another. In today's multiservice environments, traffic is going to experience all KPIs at the same time, although throughput might be good, it can also be accompanied by very high latency due to buffering. Designed as a performance assessment tool, RFC 2544 measures each KPI individually through its subtest and therefore cannot immediately associate a very high latency with a good throughput, which should be cause for concern. Service definitions The ITU-T Y.1564 defines test streams (individually called a "Test Flow") with service attributes linked to the Metro Ethernet Forum (MEF) 10.2 definitions. Test Flows are traffic streams with specific attributes identified by different classifiers such as 802.1q VLAN, 802.1ad, DSCP and class of service (CoS) profiles. These services are defined at the user–network interface (UNI) level with different frame and bandwidth profile such as the service's maximum transmission unit (MTU) or frame size, committed information rate (CIR), and excess information rate (EIR). A single Test Flow is also able to consist of up to 5 different frame sizes called an EMIX (Ethernet Mix). This flexibility allows the engineer to configure a Test Flow very close to real-world traffic. Test rates The ITU Y.1564 defines three key test rates based on the MEF service attributes for Ethernet virtual connection (EVC) and user-to-network interface (UNI) bandwidth profiles. CIR defines the maximum transmission rate for a service where the service is guaranteed certain performance objectives. These objectives are typically defined and enforced via SLAs. EIR defines the maximum transmission rate above the committed information rate considered as excess traffic. This excess traffic is forwarded as capacity allows and is not subject to meeting any guaranteed performance objectives (best effort forwarding). Overshoot rate defines a testing transmission rate above CIR or EIR and is used to ensure that the DUT or network under test does not forward more traffic than specified by the CIR or EIR of the service. Service configuration test Forwarding devices such as switches, routers, bridges and network interface units are the basis of any network as they interconnect segments. If