Boston University 2020 Call monitoring • Service monitoring, e.g. source and destination phone numbers, their first and last cell towers Examples: • Location-based services • Monitor cell tower and computes: 29 1. the maximum number seen so far 2. the average of all numbers seen so far 3. the median of all numbers seen so far Vasiliki Kalavri | Boston University 2020 [1, 4, 5, 23, 8, 0,

solution: maintain a hash table Convert the stream into a multi-set of uniformly distributed random numbers using a hash function. ??? Vasiliki Kalavri | Boston University 2020 How can we count the number hash values we shall see. Convert the stream into a multi-set of uniformly distributed random numbers using a hash function. ??? Vasiliki Kalavri | Boston University 2020 Let h be a hash function that

2020 40 • A source of increasing numbers partitioned into a stream of even and odd numbers • Two sum operators maintaining the running sums of even and odd numbers • The snapshot contains the source