Definition of terms

In this section, I clarify the terms used in this thesis.

host

``A computer capable of communicating using the Internet protocols; includes `routers' '' [33].

link

``A single link-level ^1.1 connection between two (or more) hosts; includes leased lines, ethernets, frame relay clouds, etc.'' [33].

router

``A host which facilitates network-level communication between hosts by forwarding IP packets'' [33].

hub

``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.'' [20]

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.

process

A running copy of a computer program.

monitor

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.

timestamp

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 $H$ observing an Internet link $L$ at a particular location [33]:

• ``For a given packet $P$, the `wire arrival time' of $P$ at $H$ on $L$ is the first time $T$ at which any bit of $P$ has appeared at $H$'s observational position on $L$.''
• ``For a given packet $P$, the `wire exit time' of $P$ at $H$ on $L$ is the first time $T$ at which all the bits of $P$ have appeared at $H$'s observational position on $L$.''

monitor processing delay

The sum of two time intervals $\vert\Delta T_1\vert$ and $\vert\Delta T_2\vert$ where

• $\Delta T_1$ spans from the moment at which a request packet $P_{request}$ is timestamped by a monitor $m$ ( which runs on host $H$ to observe link $L$ ) to the moment corresponding to $P_{request}$'s wire exit time at $H$ on $L$;
• $\Delta T_2$ spans from the moment corresponding to the wire arrival time of $P_{request}$'s reply packet $P_{reply}$ at $H$ on $L$ to the moment at which $P_{reply}$ is timestamped by $m$.

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 $P_{request}$ at a destination host $H_{dst}$ on link $L_{dst}^{in}$ to the wire exit time of $P_{request}$'s reply packet $P_{reply}$ at $H_{dst}$ on link $L_{dst}^{out}$, where $L_{dst}^{in}$ is the link from which $H_{dst}$ receives $P_{request}$ and $L_{dst}^{out}$ is the link to which $H_{dst}$ sends $P_{reply}$. $L_{dst}^{in}$ and $L_{dst}^{out}$ 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, $L_{dst}^{in}$ and $L_{dst}^{out}$, are distinguished. For a destination host that is not a router, $L_{dst}^{in}$ and $L_{dst}^{out}$ 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 $P_{request}$ is timestamped by a monitor $m$ to the moment at which a reply packet $P_{reply}$ for $P_{request}$ is timestamped by $m$. Also referred to as round-trip delay.

Wire Round-Trip Time (WRTT)

A special case of RTT where the request packet $P_{request}$'s wire exit time is timestamped by $m$ and the reply packet $P_{reply}$'s wire arrival time is timestamped by $m$. Also referred to as wire round-trip delay.