Telcom 2120 Network Performance Homework 6 Spring 2004
1. The International Telecommunication Union (ITU) T group has set benchmark
performance values for mobile phone database systems. For the Visitor Location Register
(VLR) database the benchmark values are
1) Mean Delay in response to a query - 1000msec (1 sec)
2) 95th percentile in query response time - 4000msec (4 sec)
3) Database can process up to 10 queries per active subscriber in the busy hour
Assuming a M/M/1 queue can be used to model the database system
and that the mean time to process a query is 50 msec determine the following
(a) Determine the maximum database utilization that can occur and still satisfy the
benchmark values above .Which condition is the most stringent?
(b) At the maximum database utilization that can occur, what is the average number in
the system and the mean interarrival time of queries?
(c) What is the maximum number of subscribers that can be supported by a single
database that satisfies the benchmark values?
2. From the Jain Textbook problem 31.5
3. A data concentrator has 40 terminals connected to it. During the busiest time of day each
terminal is occupied and produces packets which are exponentially distributed with a
mean of 1000 bits. The link connecting the concentrator to the campus network operate
at 1.552 Mbps. The arrival process of packets to the concentrator forms a Poisson
process with ten of the terminals producing on average 1 packet per 10 msec, twenty of
the terminals producing on average 1 packet per 50 msec, and ten of the terminals
producing on average 1 packet per .5 second.
(a) Determine the offered utilization of the concentrator.
(b) If the concentrator has a system capacity of 20 packets, determine the packet loss rate
(c) Determine the average delay in the system.
4. a local telephone service provider. Multiple T1 lines are used to interconnect PBXs to
central offices and to interconnect central offices. Note that links are only available in
modular quantities (T1 (which is 24 channels), 2T1, etc.). The service provider
dimensions its links by the following rules.
Normal load: grade of service is 1% call blocking.
Congestion load (10% overload): grade of service is 2% call blocking.
Determine the number of lines required to satisfy the rules above for the cases below.
(a) Link between a PBX and a central office where calls arrive according to a Poisson
process at rate 1481 per hour and have mean holding time of 175 sec.
