MAXTT

Name

MAXTT -- Set Maximum Trip Time.

Synopsis

MAXTT=n (n = 0-60000)

Availability

Used only in XROUTER.CFG.

Description

MAXTT is a global and PORT configuration keyword used in XROUTER.CFG, and a parameter which can be used in a ROUTE ADD command.

It defines the maximum accepted "trip time" (transit time) for new nodes table entries received via INP3 unicasts from neighbours. Node information with trip times that exceed this figure are not accepted into the nodes table. This parameter has no effect on data received via conventional NetRom nodes broadcasts.

MAXTT would typically be used to limit the "trip time horizon" to a smaller value than the default horizon, which is 60000 (600 seconds). Like MAXHOPS, it can be used to limit the number of node entries that are accepted via a particular port or neighbour.

For example, if an RF user lists a moderately sized nodes table via an average 1200 baud RF link, it could take several minutes to download the data. It becomes impractical to use the "N" commands in that situation. Experience has shown that a nodes table with more than 150 entries is impractical for RF users. Since Internet-based routers have low trip times to everywhere, they tend to have very large nodes tables. Thus routers on the Internet<>RF interface, and their RF neighbours, would also have over-sized tables, comprised mainly of Internet-routed nodes. Many of these nodes are in foreign-language countries of no interest to the RF user. The sysop may choose to limit the horizon to reduce the number of Internet nodes in the table.

Alternatively (and more likely since there are so few RF nodes nowadays), a sysop may decide that nodes with trip times of more than 10 seconds are too slow, and not worth having in the table, and would therefore set a MAXTT of 1000.

MAXTT can be used in 3 places: If used in the "global" section of XROUTER.CFG, it specifies a default value for all ports, overriding the default of 60000. If used in a PORT configuration block, it overrides the global default. All new routes inherit this value. Finally a MAXTT value (without the keyword) can be used in a ROUTE ADD entry, to override the PORT default. For example:

	ROUTE ADD g8pzt 5 100 ! 0 0 0 2000 5

This adds a locked in route to neighbour "g8pzt" on port 5, quality 100, with default maxframe, paclen and frack, MAXTT of 2000 and MAXHOPS of 5.

Setting a route's MAXTT to 0 effectively blocks all INP3 activity. It disables INP3 unicasts, and ignores received INP3. This is not recommended, but NetRom purists may wish to do it anyway.

Caveats

Using MAXTT to limit the no. of nodes learned via a neighbour may fail if the neighbour duplicates the INP3 data in conventional NetRom nodes broadcasts. This may enter nodes which are beyond your chosen trip time horizon into the nodes table and keep them refreshed. The only defence is to ignore data from NetRom broadcasts by setting the port QUALITY below MINQUAL, or to set the MINQUAL high. Both actions may cause the loss of some NetRom-only nodes from the table.

See also

INP3(9) -- InterNode Protocol.
MAXHOPS(7) -- Maximum Hop Count.
MINQUAL(2) -- Display / Set port Minimum Quality.
QUALITY(2) -- Display / Modify NetRom Quality.
ROUTES(2) -- Display / Modify NetRom Neighbour Routes.
XROUTER.CFG(8) -- Main Configuration File.