CNIT 34220 EXAM 2 REVIEW QUESTIONS
Uses of time in computers (name 3) - Answers - - Time stamping files
- Expiration on tickets
- Calendaring
- E-mail
- Logging
- Tracing
- Troubleshooting
What is the Julian Calendar? - Answers - - Created by Julius Caesar in 46 BC
- 365 days in year
- Error in leap year calculation
What is the Gregorian Calendar? - Answers - - Decreed by Pope Gregory XIII on Feb
24, 1582
- Still had 365 days in a year
- Fixed leap year calculation
What happened in September of 1752? - Answers - - Great Britain and colonies
changed from Julian to Gregorian calendar
- in order to adjust for leap year calculation, skipped last 11 days of the month (making it
a 19 day month)
How is time represented in UNIX systems? Windows? - Answers - UNIX: system clock
is UTC, 13:00 -5 DST, keeps time based on seconds since UNIX Epoch, 00:00:00
January 1, 1970 (overflows January 19, 2038 if not fixed)
Windows: system clock is local time zone, 9:00 AM -5 +1
What are the two types of computer clocks? Differences? - Answers - Real Time Clock -
keeps time in BIOS
System time - kept by process running in OS, depends on constant processor clock
speeds
How is time synchronized in Windows non-domain systems? Domain-based systems? -
Answers - Non-domain: no built in synchronization, default is to sync to
time.windows.com via SNTP
Domain: Primary Domain Controller is time server, all domain members synchronize to
PDC
What is SNTP? - Answers - Simple Network Time Protocol
, How many transactions can SNTP complete? What does this mean? - Answers - -
Single transactions
- Sets time once
- can be done repeatedly on a schedule - time can be off between syncs
What is NTP? - Answers - Network Time Protocol
How does NTP work? - Answers - - Uses UTC complete with leap seconds
- keeps clock constantly correct
- requires client to adjust internal clock to match reference time
What is Marzullo's algorithm? - Answers - used by NTP, takes into account transmission
duration for time data
How is a machine's stratum level determined? - Answers - A machine is one strata
higher than the time server to which it synchronizes
What are stratum 0 time sources? - Answers - Satellites, GPS receivers, Atomic clocks
What are stratum 1 time servers? - Answers - Machines directly connected to stratum 0
time sources, used only to service other time servers
What are stratum 2 servers? - Answers - Reference at least two stratum 1 servers,
typically only service stratum 3 servers
What are stratum 3 servers? - Answers - Get time from multiple stratum 2 servers,
typically serve clients within an organization, can serve higher level time servers (up to
16 levels)
What are NTP pools? - Answers - group of time servers available for public use
How many NTP pool servers are there? - Answers - 4147 as of January 2018
Explain NTP timestamps - Answers - 64 bit time representation
32 bits for seconds
32 bits for fractional seconds
How accurate are NTP timestamps? - Answers - Down to 0.233 nanosecond accuracy
What is SMTP? - Answers - Simple Mail Transfer Protocol
What does SMTP do? - Answers - - delivers mail between hosts
- hosts must always be available for connection
- uses TCP for reliable connection
- uses seven bit ASCII encoding
Uses of time in computers (name 3) - Answers - - Time stamping files
- Expiration on tickets
- Calendaring
- Logging
- Tracing
- Troubleshooting
What is the Julian Calendar? - Answers - - Created by Julius Caesar in 46 BC
- 365 days in year
- Error in leap year calculation
What is the Gregorian Calendar? - Answers - - Decreed by Pope Gregory XIII on Feb
24, 1582
- Still had 365 days in a year
- Fixed leap year calculation
What happened in September of 1752? - Answers - - Great Britain and colonies
changed from Julian to Gregorian calendar
- in order to adjust for leap year calculation, skipped last 11 days of the month (making it
a 19 day month)
How is time represented in UNIX systems? Windows? - Answers - UNIX: system clock
is UTC, 13:00 -5 DST, keeps time based on seconds since UNIX Epoch, 00:00:00
January 1, 1970 (overflows January 19, 2038 if not fixed)
Windows: system clock is local time zone, 9:00 AM -5 +1
What are the two types of computer clocks? Differences? - Answers - Real Time Clock -
keeps time in BIOS
System time - kept by process running in OS, depends on constant processor clock
speeds
How is time synchronized in Windows non-domain systems? Domain-based systems? -
Answers - Non-domain: no built in synchronization, default is to sync to
time.windows.com via SNTP
Domain: Primary Domain Controller is time server, all domain members synchronize to
PDC
What is SNTP? - Answers - Simple Network Time Protocol
, How many transactions can SNTP complete? What does this mean? - Answers - -
Single transactions
- Sets time once
- can be done repeatedly on a schedule - time can be off between syncs
What is NTP? - Answers - Network Time Protocol
How does NTP work? - Answers - - Uses UTC complete with leap seconds
- keeps clock constantly correct
- requires client to adjust internal clock to match reference time
What is Marzullo's algorithm? - Answers - used by NTP, takes into account transmission
duration for time data
How is a machine's stratum level determined? - Answers - A machine is one strata
higher than the time server to which it synchronizes
What are stratum 0 time sources? - Answers - Satellites, GPS receivers, Atomic clocks
What are stratum 1 time servers? - Answers - Machines directly connected to stratum 0
time sources, used only to service other time servers
What are stratum 2 servers? - Answers - Reference at least two stratum 1 servers,
typically only service stratum 3 servers
What are stratum 3 servers? - Answers - Get time from multiple stratum 2 servers,
typically serve clients within an organization, can serve higher level time servers (up to
16 levels)
What are NTP pools? - Answers - group of time servers available for public use
How many NTP pool servers are there? - Answers - 4147 as of January 2018
Explain NTP timestamps - Answers - 64 bit time representation
32 bits for seconds
32 bits for fractional seconds
How accurate are NTP timestamps? - Answers - Down to 0.233 nanosecond accuracy
What is SMTP? - Answers - Simple Mail Transfer Protocol
What does SMTP do? - Answers - - delivers mail between hosts
- hosts must always be available for connection
- uses TCP for reliable connection
- uses seven bit ASCII encoding
