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Definition of terms
In this section, I clarify the terms used in this thesis.
- ``A computer capable of communicating using the Internet protocols; includes `routers' '' .
- ``A single link-level
1.1 connection between two (or more) hosts; includes leased lines, ethernets, frame relay clouds, etc.'' .
- ``A host which facilitates network-level communication between hosts by forwarding IP packets'' .
- ``An electronic device to which multiple computers attach, usually using twisted pair wiring. A bub simulates a network that interconnects the attached computers. Hub technology is popular for Ethernets.'' 
- source host
- A host on which ping runs. Also referred to as source pinging host or pinging host.
- destination host
- A host to which ping sends request packets and from which it expects reply packets.
For a description of how ping works, see Section 3.2.1.
- A running copy of a computer program.
- A process that is capable of measuring network traffic on a single link.
A ping process and a tcpdump process are both examples of monitors, which are referred to as ping monitor and tcpdump monitor, respectively.
- monitoring machine
- A host on which a monitor runs. Also referred to as a measurement machine.
- A mark of the moment at which a packet is declared as first seen by a monitor. Also used as a verb referring to the action of recording a timestamp.
- wire time
- Either wire arrival time or wire exit time.
These two notions are defined in terms of an Internet host observing an Internet link at a particular location :
- ``For a given packet , the `wire arrival time' of at on is the first time at which any bit of has appeared at 's observational position on .''
- ``For a given packet , the `wire exit time' of at on is the first time at which all the bits of have appeared at 's observational position on .''
- monitor processing delay
- The sum of two time intervals and where
- spans from the moment at which a request packet is timestamped by a monitor ( which runs on host to observe link ) to the moment corresponding to 's wire exit time at on ;
- spans from the moment corresponding to the wire arrival time of 's reply packet at on to the moment at which is timestamped by .
For a ping monitor, it is also referred to as source processing delay.
- source host processing delay
- A special case of monitor processing delay where the monitor is a ping process.
- destination host processing delay
- The time interval from the wire arrival time of a request packet at a destination host on link to the wire exit time of 's reply packet at on link , where is the link from which receives and is the link to which sends . and can be identical.
Note that for a destination host that is a router, it is possible to receive a request packet from one link and transmit a reply packet to another link. This is the reason why two links, and , are distinguished. For a destination host that is not a router, and refer to the same link. Also note that, for a given request-reply packet pair, the destination host processing delay is a constant.
- Round-Trip Time (RTT)
- The time interval from the moment at which a request packet is timestamped by a monitor to the moment at which a reply packet for is timestamped by . Also referred to as round-trip delay.
- Wire Round-Trip Time (WRTT)
- A special case of RTT where the request packet 's wire exit time is timestamped by and the reply packet 's wire arrival time is timestamped by . Also referred to as wire round-trip delay.
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