Ram: /* Receiving */ Clarified that leaves should never be forwarded /PI/UDP messages

2014-01-15T22:41:31Z

Receiving: Clarified that leaves should never be forwarded /PI/UDP messages

← Older revision		Revision as of 22:41, 15 January 2014
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	immediately.		immediately.

	If the ping was received from a TCP neighbour and contains a /PI/UDP child packet,		If the ping was received by a hub from a TCP neighbour and contains a /PI/UDP child packet,
	but no /PI/RELAY tag, a /PI/RELAY tag should be added and the packet forwarded to		but no /PI/RELAY tag, a /PI/RELAY tag should be added and the packet forwarded to
	all neighbouring hubs. If a /PI/RELAY tag was present, the node should send a /PO		all neighbouring hubs. If a /PI/RELAY tag was present, the node should send a /PO
	packet with a /PO/RELAY tag to the UDP address identified in the /PI/UDP child		packet with a /PO/RELAY tag to the UDP address identified in the /PI/UDP child
	packet.		packet.

			Note that leaf nodes should '''never''' be forwarded /PI packets with a /PI/UDP child: these need to be handled by hubs only.

	== Payload ==		== Payload ==

Dcat at 04:06, 1 January 2009

2009-01-01T04:06:26Z

← Older revision		Revision as of 04:06, 1 January 2009
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	~~[[LNI\|<< LNI]] \| [[PO\|PO >>]] \| [[Root_packets_index\|Packet Index]]~~		{{Packets}}


	= /PI - Ping =		= /PI - Ping =

Spooky: nav

2005-09-05T23:37:02Z

nav

← Older revision		Revision as of 23:37, 5 September 2005
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			[[LNI\|<< LNI]] \| [[PO\|PO >>]] \| [[Root_packets_index\|Packet Index]]


	= /PI - Ping =		= /PI - Ping =

Dcat at 18:01, 19 March 2005

2005-03-19T18:01:01Z

New page

= /PI - Ping =

The ping packet is used to verify the presence of the addressed node, testing that:

* The destination node is online
* The destination node can receive the transmission
* The local node can receive the reply

Aside from performing a "keep-alive" function on TCP links, pings can be used to
solicit inbound UDP datagrams to test the local node's ability to receive UDP. Many
NAT systems will route UDP traffic from nodes with whom a persistent TCP stream
has been established, so it is necessary to test inbound traffic from nodes with which
there is no TCP connection. This is achieved by sending a ping with a /PI/UDP packet
to a connected hub via TCP, which will forward the request to its neighbours who
then reply to the originator via UDP.

== Sending ==

On a TCP stream connection, if one end has not received a valid packet from the
other after an internally determined period of time, it has the option of sending a
keep-alive ping to verify the other end's presence. If a pong is not received in a
timeout period it may close the connection.

If a node needs to verify that it is able to receive UDP datagrams from nodes with
which it does not have a TCP stream connection, it may send a ping packet with a
/PI/UDP child packet. If it then receives a /PO (pong) packet with a /PO/RELAY child
tag and there is no TCP connection to the sender, it can assume it is able to receive
UDP.

== Receiving ==

Upon receiving a keep-alive ping, a node should respond with a keep-alive pong
immediately.

If the ping was received from a TCP neighbour and contains a /PI/UDP child packet,
but no /PI/RELAY tag, a /PI/RELAY tag should be added and the packet forwarded to
all neighbouring hubs. If a /PI/RELAY tag was present, the node should send a /PO
packet with a /PO/RELAY tag to the UDP address identified in the /PI/UDP child
packet.

== Payload ==

This packet has no payload at the current time.

== Children ==

The ping packet has two child packets defined at the current time:

* /PI/RELAY
* /PI/UDP

== /PI/RELAY - Relayed Ping Marker ==

If a /PI packet contains a /PI/RELAY child marker, the ping has been relayed for a
third party. The receiving node should reply to the original party rather than the
sender. The original party should be contacted via UDP with the address contained in
the /PI/UDP child. If the /PI/UDP child is absent, the packet is invalid.

=== Sending ===

The /PI/RELAY child should be added to a /PI packet when relaying a ping to hub
neighbours at the request of a leaf.

=== Receiving ===

Upon receiving a /PI packet with a /PI/RELAY tag, a /PO (pong) packet should be
sent via UDP to the node identified in the /PI/UDP child.

=== Payload ===

This packet has no payload at the current time.

=== Children ===

This packet has no known children at the current time.

== /PI/UDP - Ping Response Address ==

The /PI/UDP child packet specifies the return address for a relay able or relayed
ping.

=== Sending ===

Add a /PI/UDP child packet to a /PI packet to request a relayed "two hop" ping.

=== Receiving ===

The /PI/UDP child packet indicates that a /PI packet needs to be relayed.

=== Payload ===

The /PI/UDP packet contains an endpoint address.

=== Children ===

This packet has no known children at the current time.

PI - Revision history

Ram: /* Receiving */ Clarified that leaves should never be forwarded /PI/UDP messages

Dcat at 04:06, 1 January 2009

Spooky: nav

Dcat at 18:01, 19 March 2005