Comtech EF Data SLM-5650C CyberLynx, Installation And Operation Manual

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SLM-5650C / SLM-5650C-ODU Satellite Modem
Revision 1
Appendix C C–4 MN-SLM-5650C
See RFC 4814 “Hash and Stuffing: Overlooked Factors in Network Device
Benchmarking” for a derivation of this probability
.
Considering both sources of HDLC Overhead means that, for a packet length “ L ”, the ratio of input
bits to encapsulated output bits is expressed as “Equation 2”:
F
H
=L/[L+3+L/62] = L/[(63/62)L+3]
Unlike framing overhead, HDLC Overhead reduces the effective throughput of packet bits relative
to the programmed modem data rate. Packet Throughput, in packet bits/second, is expressed as
“Equation 3”:
Packet Throughput=(Programmed Modem Data Rate)*FH
HDLC Overhead – referred to as “Equation 4” – is expressed as a percent overhead of the
modem date rate:
HDLC OH[%]=(1-F
H
)*100 =([(1/62)L+3]/[(63/62)L+3])*100
The HDLC Overhead ranges from approximately 6% for L=64 to approximately 1.8% for
L=1518 .
C.4 Product Support
For further information about the modem overhead support of interfaces and framing options,
please call
CEFD Product Support using the information shown in the Preface.