NEC IPASOLINK 400 Installation And Provisioning page 17

Frame size (L2 octets)
64
1500
8000
Table 2. GbE interface L2 capacity also depends on the frame size.
If the average frame size were only 64 octets, there would be a problem fitting the 2+0 maximum capacity
at 56 MHz and 512QAM into a single GbE interface. This is because the total L2 speed is 2 x 394 = 788M,
which would need over 1 Gbit/s at interface L1 speed (2 x 517 = 1034M). In other words two modems
could send more packets than a single GbE interface can handle.
In practise the average packet size is always much larger than 64 octets, perhaps 500-1000 octets, and then
the GbE interface can handle all the packets delivered by two modems.
The compression can become an interpretation problem when measuring the link capacity with the
smallest frame size. If the capacity is defined using the smallest frames only, that capacity cannot be
achieved with real traffic and a larger average frame size. This may cause SLA problems between the
operator and the end customer. It is recommended that the capacity is defined and measured using the
largest possible frames which will remove the L1/L2 difference. Then the real capacity achievable is always
slightly larger than the measured one.
Table 3 shows iPasolink radio capacities with each available modulation and channel spacing. This value is
practically identical with the L1 and L2 capacity when the average frame size is 1500 octets or larger.
(1024QAM and 2048QAM are preliminary values).
Modulation
QPSK
16QAM
32QAM
64QAM
128QAM
256QAM
512QAM
(1024QAM)
(2048QAM)
Table 3. iPasolink radio capacity.
L1 capacity L2 capacity
(Mbit/s) (Mbit/s)
1000 761,9
1000 986,8
1000 997,5
Radio capacity (Mbit/s)
Channel spacing
7MHz 14MHz 28MHz
10 22
22 45
27 56
33 67
39 79
45 90
- -
- -
- -
56MHz
45 91
91 183
113 228
136 274
159 320
182 366
205 412
(228) (458)
(251) (504)
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