Routing and WAN connections
BAT54-Rail/F..
Release
7.54
06/08
11.15
Manual definition of the MTU
453
11.14.11Contact assignment of BAT modem
adapter kit
Contact assignment for BAT interlink or modem connection:
11.15Manual definition of the
MTU
Many Internet providers operate their own backbone; however, their custom-
ers dial in to the network over the access nodes provided by third-party tele-
communications providers. The two-stage dial-in procedure can lead to
problems with the realized data rate:
D When dialing into the nodes of Deutsche Telekom, for example, a BAT
negotiates a permissible maximum transmission unit (MTU), which de-
fines the greatest possible size of unfragmented data packet. This MTU
is then observed by the BAT.
D When the data packets are forwarded to the actual provider, an additional
header is added which increases the size of the data packets again. For
the data packets to meet with the permitted size, they must now be frag-
mented into smaller units. This additional fragmentation can cause losses
in the data-transfer speeds.
This problem can be avoided by entering a fixed MTU for each remote site.
Device signal sub-d 9 plug Device or modem signal sub-d 9 plug
TxD 3 RxD 2
RxD 2 TxD 3
RTS 7 CTS 8
CTS8 RTS7
DTR 4 DCD 1
DCD 1 DTR 4
GND 5 GND 5
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