Glossary

Explanation of words and phrases you may come across using VisualRoute and their meaning

Discover your TTL
To discover the default TTL value of your computer, 'ping localhost' and check the TTL reply value. For older Windows computers this value is 32. For newer Windows computers, this value is 128.

DNS, Domain Name System
This System translates a domain name such as rankingtoday.com into the Internet Protocol (IP) numbers (205.234.111.141) to find the correct web site - in this case the site for Visualware. The network of computers that constitute the Internet map domain names to their corresponding IP numbers. The data is then made available to all computers and users on the Internet.

Domain
A domain is the main subdivision of internet addresses, the last three letters after the final dot, and it tells you what kind of organization you are dealing with. There are six top-level domains widely used: .com (commercial) .edu (educational),.net (network operations), .gov (US government), .mil (US military) and .org (organization). Other, two letter domains represent countries; thus;.uk for the United Kingdom, .it for Italy, .fr for France, .de for Germany, .es for Spain and so on.

FTP, File Transfer Protocol
A standard method for sending files from one computer to another on TCP/IP networks such as the Internet. FTP is also the name of the command used to initiate transfer of files. Anonymous FTP is a common practice which permits users to access some parts of an FTP site without needing an account and password for the site. Access usually is gained by using the username "anonymous" or "ftp". By convention, the user should enter their e-mail address as the password.
Hop Each time that an IP Packet moves one step through the Internet, that is considered a hop.

HTTP, HyperText Transfer Protocol
The underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands.

ICMP, Internet Control Message Protocol
ICMP is the control and error reporting protocol for IP. For example, when the TTL field of an IP Packet reaches zero, a Router will send an ICMP 'TTL expired in transit' message back to the sending IP Address.

IP Address
An IP address is just four numbers, each in the range of 0 to 255, separated by periods. For example, 161.58.180.113 is the IP Address of our VisualRoute server. An IP Address is like a postal address that identifies a building.

IP Packet
A piece of information (such as part of a web page) with 'to' and 'from' IP Address and Port Number information, and other miscellaneous information, such as TTL , etc.
Latency The time between initiating a request for data and the beginning of the actual data transfer. Network latency results when a packet is momentarily stored, analyzed and then forwarded.

Packet Loss
Packet loss kills throughput. So, having no packet loss is critical to having a connection to the Internet to responds well. A slower connection with zero packet loss can easily outperform a faster connection with some packet loss. Also, packet loss on the last hop, the destination, is what is most important. Sometimes routers in-between will not send ICMP "TTL expired in transit" messages, causing what looks to be high packet loss at a particular hop, but all it means is that the particular router is not responding to ICMP echo.

Port Number
A number from 0 to 65535. A port number helps to distinguish one program communicating across the Internet on your computer from another program. A port number at an IP address is like a named person at a postal address / building.

Reverse DNS
Name resolution software that looks up an IP address to obtain a domain name. It performs the opposite function of the DNS server, which turns names into IP addresses.
Round Trip Times Each millisecond (ms) time in the table is the round-trip time that it took (to send the ICMP packet and to get the ICMP reply packet). The faster (smaller) the times the better. ms times of 0 mean that the reply was faster than the computers timer of 10 milliseconds, so the time is actually somewhere between 0 and 10 milliseconds.

Router
A router is a device that, when interconnected to other routers, can receive IP Packets and forward them to other routers that are closer to the destination IP Address in the IP Packet.

RTT, Round-Trip Time
Is the estimated time for an Acknowledgment to be received for a given transmitted packet. When the network link is a local network, this delay will be minimal (if not zero). When the network link is the Internet, this delay could be substantial and vary widely. RTT is adaptive; it adjusts to include the PPD (Packet Processing Delay) and whatever shifting network delays contribute to the time between a packet being transmitted and receiving its acknowledgment.

SMTP, Simple Mail Transfer Protocol
A protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP.

TCP, Transmission Control Protocol
A protocol used along with the Internet Protocol (IP) to send data in the form of individual units (called packets) between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the packets that a message is divided into for efficient routing through the Internet. For example, when a web page is downloaded from a web server, the TCP program layer in that server divides the file into packets, numbers the packets, and then forwards them individually to the IP program layer.

Traceroute
An Internet utility that traces the route from the client machine to the remote host being contacted. It reports the IP addresses of all the routers in between.

TTL, Time To Live
It is an integer value between 0 and 255. Each time a Router forwards an IP Packet, the TTL value in the IP Packet is decremented by one. When TTL gets to zero, the Router discards the IP Packet and an ICMP 'TTL Expired in transit' message is sent back to the sending IP Address. This mechanism prevents an IP Packet from being routed around the Internet forever, if for some reason there is a routing loop that would just send the packet around in circles.

TTL Expired
In Transit Most computers today initialize the TTL value of outgoing IP Packets 128 or higher. If you ever see a reply above with a "TTL=5" (or some other low TTL number) this tells you that the computer being pinged should most likely have its default TTL value increased. Otherwise, anyone trying to communicate with the computer that is at a hop count higher than the TTL will not be able to communicate with the computer. For example, if you are 40 hops away from www.xyz.com, and www.xyz.com sets TTL fields in IP packets that it sends out to 32, the IP Packets will not reach you. They will 'expire in transmit' before they reach you.

TTL Reply
Ping sends an ICMP echo packet (with the TTL value set to the host default) to the host listed on the ping command line. Ping expects back an ICMP 'echo reply' packet. The millisecond time displayed is the round trip time. The "TTL=245" above says that the incoming ICMP echo reply packet has its TTL field set to 245. Because this value was decremented by one at each hop on the way back, this tells us that visualroute.com is probably setting the initial TTL value to 255.

UDP, User Datagram Protocol
UDP is a lightweight transport built on top of IP. UDP squeezes extra performance from IP by not implementing some of the features a more heavyweight protocol like TCP offers. Specifically, UDP allows individual packets to be dropped (with no retries) and UDP packets to be received in a different order than they were sent.