Grade of Service

ITU-T Recommendation E.771 proposes network Grade of Service (GOS) parameters for current and evolving land mobile services. These parameters are defined, and their target values specified, assuming that the network and the network components are operating in their normal mode (i.e. are fully operational). Further, the parameters and their target values assume normal (as opposed to distress or emergency) traffic. 

In this Recommendation, the following traffic GOS parameters are specified for mobile circuit switched services: 

•Post Selection Delay: defined as the time interval from the instant the first bit of the initial SETUP message containing all the selection digits is passed by the calling terminal to the access Signaling system until the last bit of the first message indicating ccall disposition is received by the calling terminal (ALERTING message in case of successful call). 

•Answer signal delay: defined as the time interval from the instant that the called terminal passes the first bit of the CONNECT message to its access Signaling system until the last bit of the CONNECT message is received by the calling terminal. 

•Call release delay: defined as the time interval from the instant the DISCONNECT message is passed by the user terminal which terminated the call to the access Signaling system, until the RELEASE message is received by the same terminal (indicating that the terminals can initiate/receive a new call). 

•Probability of end-to-end blocking: defined as the probability that any call attempt will be unsuccessful due to a lack of network resources. 

•Probability of unsuccessful land cellular handover: defined as the probability that a handover attempt fails because of lack of radio resources in the target cell, or because of a lack of free resources for establishing the new network connection. The failure condition is based either on a specified time interval since the handover request was first issued or on a threshold on signal strength.