These EMBnet tutorials are mirrored at three EMBnet Nodes and one University:

Node Icon	Node Name	Country	Host to  PING
	BioBase	Denmark	biobase.dk
	HGMP-RC	The United Kingdom	www.hgmp.mrc.ac.uk
	CNR	Italy	www.area.ba.cnr.it
	ISREC	Switzerland	www.ch.embnet.org

To find the mirror "virtually closest" to your computer, you can either PING each host in turn from your local computer, choosing the one with the smallest response time, or you can infer/guess which might be best for you by checking the latest statistics on the Performance Monitoring in EMBnet page.

Just what IS PING, anyway?

Unfortunately, the PING facility is not supported (yet!) by web browsers, so there is no easy way to use the programme directly from a web page. Further, PING on large UNIX Internet hosts is often reserved for use only by system administrators. However, if you have your own PC on the Internet, you are its "system administrator" and may run a PC version of PING to do your test.

You'll find a version of PING for your PC with an ARCHIE search or Net search.

You may find after your PING tests that NONE of the mirrors is responding very quickly. Now your remaining options are to:

• try again, either later or earlier in the day, when network traffic is lower;
• try the tutorials without the graphics (turn off the automatic loading of images);
• ask your EMBnet Node administrator to have the tutorials mirrored at your node, too;
• ask your local web master to contact me.

What is PING? From the EMBnet's Performance Monitoring in EMBnet page ...

Ping is a tool for network testing, measurement and management. It utilizes the ICMP protocol's ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from a host or gateway. ECHO_REQUEST datagrams ("pings") have an IP and ICMP header, followed by an 8-byte timestamp, and then an arbitrary number of "pad" bytes used to fill out the packet.

ping: [from the TCP/IP acronym `Packet INternet Groper', prob. originally contrived to match the submariners' term for a sonar pulse] 1. n. Slang term for a small network message (ICMP ECHO) sent by a computer to check for the presence and alertness of another (the UNIX command `ping(8)' can be used to do this manually). Occasionally used as a phone greeting. See {ACK}, also {ENQ}. 2. vt. To verify the presence of. 3. vt. To get the attention of. 4. vt. To send a message to all members of a {mailing list} requesting an {ACK} (in order to verify that everybody's addresses are reachable). "we haven't heard much of anything from geoff, but he did respond with an ack both times i pinged jargon-friends." 5. n. A quantum packet of happiness. People who are very happy tend to exude pings; furthermore, one can intentionally create pings and aim them at a needy party (e.g., a depressed person). This sense of ping may appear as an exclamation; "ping!" (I'm happy; I am emitting a quantum of happiness; I have been struck by a quantum of happiness). The form "pingfulness", which is used to describe people who exude pings, also occurs. (In the standard abuse of language, "pingfulness" can also be used as an exclamation, in which case it's a much stronger exclamation than just "ping"!). Oppose {blargh}.

The funniest use of `ping' to date was described in January 1991 by Steve Hayman on the USENET group comp.sys.next. He was trying to isolate a faulty cable segment on a TCP/IP Ethernet hooked up to a NeXT machine, and got tired of having to run back to his console after each cabling tweak to see if the ping packets were getting through. So he used the sound-recording feature on the NeXT, then wrote a script that repeatedly invoked `ping(8)', listened for an echo, and played back the recording on each returned packet. Result? A program that caused the machine to repeat, over and over, "ping ... ping ... ping ..." as long as the network was up. He turned the volume to maximum, ferreted through the building with one ear cocked, and found a faulty tee connector in no time.