APPENDIX A – GLOSSARY OF THE TERMS USED IN PINGER LINKED OPEN DATA PROJECT
App User – It is the node information used by PingER that refers to the Windows user name of the last user to edit the node's record through the User Interface.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Average Round Trip Delay – It is the arithmetic mean of a sample of RTT values measured in a given time period, say 1 hour.
Beacon Node – A node that is meant to be monitored by all PingER monitoring hosts.
Conditional Loss Probability (CLP) – It is the probability that if one packet is lost, the following packet is also lost. More formally, Conditional_loss_probability = Probability(loss(packet n+1)=true | loss(packet n) = true) (http://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#loss).
Contact Information – It is the node information used by PingER that keeps the name and email address(es) of the node's maintainer(s).https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Continent – The continent where the node is located. Europe, Africa, Asia, North America, South America, Oceania, Antarctica. It can be also a subclass of the entity L.CONT defined by Geonameshttp://www.geonames.org/export/codes.html.
Country – The country where the node is located.
County – A second-order administrative division. A subdivision of a first-order administrative division. It is commonly applicable for nodes in the United States.
Data Server – It is the node information used by PingER that refers to the URL for retrieving PingER data from the described node.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Directivity - This is a metric to identify the directness of the connection between 2 nodes at known locations. Directness is represented by Alpha. Alpha close to 1 means that the path between the hosts follows a roughly great circle route. Values much smaller than 1 mean that the path is very indirect. The derivation of directness coefficient is givenhere.http://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#directness
Duplicate Packets – Measures the amount of duplicate ping response. See [refhttp://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#duplicates] for details about how this event may occur.
Endowment - The total value of an institution's investments is often referred to as the institution's endowment and is typically organized as a public charity, private foundation, or trust. In PingER LOD, the values of schools’ endowment are currently being retrieved from DBPedia. http://en.wikipedia.org/wiki/Financial_endowment
Faculty Size – Usually, it refers to the number of teaching staff of a school. In PingER LOD, the values of schools` faculty size are currently being retrieved from DBPedia.
IEPM-BW - It was the Internet End-to-end Performance Monitoring (IEPM) project's Bandwidth Monitoring. It was the predecessor of the perfSONAR monitoring and was terminated in 2007.
Inter Packet Delay Variation (IPDV) – Also known as short term variability or "jitter" of the response time. Jitter is a symptom that there is congestion, or not enough bandwidth to handle the traffic. The jitter specifies the length of the VoIPcodec de-jitter buffer to prevent over- or under-flow. It is very important for real-time applications such as telephony. Web browsing and mail are fairly resistant to jitter, but any kind of streaming media (voice, video, music) is quite susceptible to jitter. An objective could be to specify that say 95% of packet delay variations should be within the interval [-30msec, +30msec] (http://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#variable).
Mean Opinion Score (MOS) – It is a voice quality metric used by the telecommunications industry. The values of the MOS are: 1= bad; 2=poor; 3=fair; 4=good; 5=excellent. See alsohttp://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#mos
Measurement – A system used to determine factors of an object such as height, length, width, etc. In PingER, the main factors measured are Round Trip Time (RTT), and loss. The system used to make the measurements is ping.
Measurement Data – Any data concerning a measurement. It can be the value of a measurement, the definition of the metric being measured, or the information about the nodes being measured.
Metric – For the network measurement, a metric is the concept that defines which measurement is being made and how it is made. TCP Throughput and Packet Loss are examples of metrics
Maximum Round Trip Delay – It is the maximum value of a sample of RTT values measured in a given time period, say 1 hour.
Minimum Round Trip Delay – It is the minimum value of a sample of RTT values measured in a given time period, say 1 hour.
Monitor Node – Also known as PingER site and Monitoring Node. A PingER monitoring node is one that has installed the PingER monitoring software and is actively using PingER to monitor other nodes. In the metric (pair source and destination nodes), it is the source node.
Monitored Node – Also known as remote node. In the metric (pair source and destination nodes), it is the destination node. In other words, it is any node that is monitored by a monitor node.
Nearest City – The nearest town or city from where the node is located with population greater than 15000 habitants, according to Geonames data.
Node – A point at which network links intersect or branch a connecting point. This typically refers to a router, switch or end point. It can also be referred as “site”. Note: an end-point is usually a host (i.e. a server, desktop, laptop, smartphone, notepad etc.).
Node Comments – Comments and notes on when and how the node's record was last updated.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Node GMT – PingER information about the node's time offset from GMT.
Node Information – Also known as Node Details. It is the generic term used to any information that describes a node.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Node Name – It is the generic term that refers to any type of name of a node. In addition to the DNS host name, a node can have a full name, a nick name, and a site name.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Node URL – It is the URL for the home page for the institution running the node. For the PingER Node example, “http://www.slac.stanford.edu” is the Node URL.
Out of Order Packets - For each sample of 10 packets, it looks to see if the sequence numbers of the responses are received in the same order as the requests were sent. If not, then that sample is marked as having one or more out of order responses. For a given interval (say a month) the value reported for out of order is the fraction of samples that were marked with out of order ping responses. Since the ping packets are sent at one second intervals it is expected that the fraction of out of order samples will be very small, and may be worth investigating whenever it is not.
Packet Loss - The loss is a good measure of the quality of the link (in terms of its packet loss rates) for many TCP based applications. Loss is typically caused by congestion which in turn causes queues (e.g. in routers) to fill and packets to be dropped. Loss may also be caused by the network delivering an imperfect copy of the packet. This is usually caused by bit errors in the links or in network devices. (http://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#loss-measure).
Physical Location – It contains information about where the node is located. It records location information provided by PingER. Note: It is commonly used just to keep track of PingER information about a node.
Ping – The name of a standard software utility (tool) used to test network connections. Ping tools send request messages to a target network address at periodic intervals and measure the time it takes for a response message to arrive.
Ping Server – It is the node information used by PingER that refers to the URL for requesting a ping from the described node to another.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Ping Size – It is the node information used by PingER that refers to the size of pings to be sent to the described node - only controls SLAC's PingER install.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
PingER Node Information - It is the generic term that refers to additional information that PingER needs to use about a node.
Project Type – It is the node information used by PingER that refers to flags that describe how the node is used. Flag “NOT-SET” is the default, meaning that it is a regular monitored node; Flag “B” means a beacon node; Flag “D” refers to a disabled node, i.e., no longer monitored, monitors or checked; Flag “I” means IEPM-BW; Flag “M” refers to a monitor node.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Round Trip Delay - also known as response time or Round Trip Time (RTT). The RTT is related to the distance between the sites plus the delay at each hop along the path between the sites. The distance effect can be roughly characterized by the speed of light in fiber, and is roughly given by distance / (0.6 * c) where c is the velocity of light (the ITU in document G.144, table A.1 recommends a multiplier of 0.005 ms/km, or 0.66c). Putting this together with the hop delays, the RTT R is roughly given by: R = 2 * (distance / (0.6 * c) + hops * delay) where the factor of 2 is since we are measuring the out and back times for the round-trip (http://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#rtt-measure)
Sample – A set of n pings.
School – Any educational establishment that is a node monitored by PingER or that is a PingER monitor e.g. Stanford University.
Simple Measurement – All measurements made by PingER that include a metric (such as Packet Loss or TCP Throughput). Information about a simple measurement typically include the name of the metric being measured, the default unit, and the default packet size.
Site Name – It is the domain name of a node. For the PingER node example, “slac.stanford.edu” is the site name.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Source Full Name – It is a human-friendly description of a node. For the PingER node example, “Stanford Linear Accelerator Center” is the full node name. See also Source Name.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Source IP – It is the IPv4 address of the node. See also Source Name.
Source Name – It is the DNS node name. It is commonly used to identify a node. For the PingER node example, “pinger.slac.stanford.edu” is the name. Note: The term “source” in a node name means that the name refers to the node being specified. In a metric (pair source and destination nodes), a source name is used for the description of the DNS of both the source node and the destination nodes. In other words, a destination node also has a source name.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Source Nick Name – It is an abstraction of the node name with the TLD first. For the PingER node example, “EDU.SLAC.STANFORD.N3” is the nick name. See also Source Name.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
State – The state where the node is located when the node is located in a country that can be divided into states or a first order division equivalent. It can be also a subclass of the entity A.ADM1 defined by Geonames.http://www.geonames.org/export/codes.html
Statistical Analysis – It is the definition of a specific measurement. It combines all parameters needed for a simple measurement and has the value of the measurement. It is defined by a combination of the name of the network metric (e.g. Packet Loss), the metric (pair source and destination nodes involved), and information about when the measurement was made.
TCP Throughput – Measures the transfer rate or throughput using TCP as transport protocol. The standard unit used by PingER is kbit/s. See alsohttp://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#derive andhttp://www.slac.stanford.edu/comp/net/wan-mon/thru-vs-loss.html for more information about how TCP Throughput is measured.
Throughput – Refers to how much data can be transferred from one location to another in a given amount of time (http://www.techterms.com/definition/throughput).
Time Stamp – It contains information about when the measurement was done. It is a subclass of Date Time Description defined by the W3C Time Ontology. See also Date Time Description inhttp://www.w3.org/TR/owl-time/.
Town – The town or city where the node is located. It can be also a subclass of the entity P.PPL defined by Geonames.http://www.geonames.org/export/codes.html
Trace Route – In computing, traceroute is a computer network diagnostic tool for displaying the route (path) and measuring transit delays of packets across an Internet Protocol (IP) network. http://en.wikipedia.org/wiki/Traceroute
Trace Server – It is the node information used by PingER that refers to the URL for requesting a traceroute from the described node to another.https://confluence.slac.stanford.edu/display/IEPM/PingER+NODEDETAILS.
Unit – The unit in which the metric is measured.
Unpredictability – The calculation of the distance of each predictability point from the coordinate (1,1). We normalize to a maximum value of 1 by dividing the distance by sqrt(2). It gives a percentage indicator of the unpredictability of the ping performance (http://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#unpredict). Seehttp://www.slac.stanford.edu/comp/net/wan-mon/unpredict.html for more details.
Unreachability - By looking at the ping data to identify 30 minute periods when no ping responses were received from a given host, one can identify when the host was down. Using this information one can calculate ping unreachability= (# periods with Node down / total number of periods), # Down periods, Mean Time Between Failure (MTBF or Mean Time To Failue MTTF)) and Mean Time To Repair (MTTR). Note that MTBF = sample_time/ping_unreachability where for PingER sample time is 30 minutes. The reachability is very dependent on the remote host, for example if the remote host is renamed or removed, the host will appear unreachable yet there may be nothing wrong with the network. Thus before using this data to provide long term network trends the data should be carefully scrubbed for non-network effects (http://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#availability).
Zero Packet Loss Frequency – also known as Quiescent Network Frequency. When we get a zero packet loss sample, we refer to the network as being quiescent (or non-busy). We can then measure the percentage frequency of how often the network was found to be quiescent. A high percentage is an indication of a good (quiescent or non-heavily loaded) network (http://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#quiescent).