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
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
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
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Example: | Router | CISCO 1601 | CISCO SYSTEMS |
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IOS soft | SFC1601C11.33 | CISCO SYSTEMS | ||
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| Cable | CAB449MT | CISCO SYSTEMS |
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Figure 24Sample of connection
HSD
MODEM
HSD DATA 2
Router
CISCO 1601
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