Bandwidth management, Bandwidth allocation – Comtech EF Data MIDAS 4 System and Design User Manual
Page 45
System and Design Manual, Revision 2
Theory of Operation 3–3
• Pre-assigned digital SCPC channel using slotted aloha access scheme.
• Transmission in burst mode at 19.2 kbps, QPSK, FEC = 1/2.
• Messages are contained in an HDLC frame.
• As the inbound control channel operates in a contention mode, after
transmitting a message the traffic node waits for an acknowledgment
from the MIDAS Controller on the outbound control channel. A lack
of acknowledgment leads to message re-transmission after a random
delay.
B
B
a
a
n
n
d
d
w
w
i
i
d
d
t
t
h
h
M
M
a
a
n
n
a
a
g
g
e
e
m
m
e
e
n
n
t
t
MIDAS allocates satellite bandwidth and power on demand for establishing
satellite circuits. The MIDAS Controller is capable of managing 36, 54, and
72 MHz transponders. The managed bandwidth consists of one or more
segments of satellite transponder. The bandwidth segments do not have to be
contiguous. The managed bandwidth is also referred to as the owned
bandwidth.
The MIDAS Controller also supports bandwidth pools, which allows
bandwidth to be reserved for exclusive use of the customers. This allows a
better control over the grade of service.
B
B
a
a
n
n
d
d
w
w
i
i
d
d
t
t
h
h
A
A
l
l
l
l
o
o
c
c
a
a
t
t
i
i
o
o
n
n
The channel allocation unit for traffic and control channels is 2.5 kHz. The
carrier spacing (allocation factor) is user-configurable, from 1.2 to 1.5 in steps
of 0.05.
Using the specified data rate, modulation type, and coding rate, the allocated
bandwidth for a carrier is computed as follows (and rounded up to the nearest
multiple of the channelization):
Spacing
Carrier
Solomon
Reed
Rate
FEC
1
Factor
Modulation
1
Rate
Data
Bw
∗
∗
∗
∗
=
where:
Bw
Allocated bandwidth in kHz, after rounding up to the nearest multiple of the
channels.
Data Rate
User data rate in kbps.