This is from (Queuing Theory Basics, n.d) stated that there is 3 process of a queueing system. They are arrival process, service process and lastly number of server.
During the arrival process which indicate that the customer arrivals in the system. Second is service process that determines the customer service times in the system. Since message transmission is directly proportional to the length of the message, this parameter indirectly refers to the message length distribution.
Number of servers available to service the customers. In a messaging system, this refers to the number of links between the source and destination nodes. Unfortunately this system are only use for business that have a lot of customer like bank.