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APPENDIX Usage Tips
Communication with other makes of Inmarsat-B terminals
HSD communications time may increase depending on communications content when
the HSD modem is used in a network. In this case, normal telephone and fax communica-
tions are disabled (except distress), thus frequency of communications and communica-
tions time must be carefully considered when drawing up communications plans. If
communications overlap one another, it may be necessary to install an additional MES.
Landline
Most landlines use ISDN circuits, and rules of operation vary with country. Thus several
ISDN terminals may be necessary.
Circuit delay
It takes about 15~20 sesconds for an HSD call to reach land terminal once the call is
initialed by an MES.
Propagation delay
A delay of about 15-20 seconds occurs on transmission of file from HSD terminal to
coast earth station.
A delay of 240 msec exists on the satellite circuit line between the MES and coast earth
station. A 100 msec delay occurs in Tx processing and Rx processing in the IB-681.
Furthermore, a propagation delay may occur on the landline between the land terminal
and coast earth station depending on the distance between them.
TCP/IP protocol
• When throughput is slow due to propagation delay, enlarge the size of the TCP window
to compensate for the delay. TCP size setting depends on protocol stack and OS. Con-
sult respective operator’s manual for advice.
• When using a remote router, raising the communications cue (buffer) setting can speed
up throughput time. However, in some cases it may be necessary for the ship and land
terminals to have the same router. Some routers cannot be used for Inmarsat HSD
communications, especially those which cannot accommodate circuits which have large
propagation delay. Consult with router maker and dealer to determine suitable router.
• For further details consult the network manager.
Router setting for network connection
Example:
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Figure 24Sample of connection
HSD DATA 2
HSD
MODEM
IB-681
RS-449
Router
CISCO 1601
To comm. unit
10BASE-T
to LAN
