BIT RATE CALCULATION WITH BARIX DEVICES
With this document we want to explain how to calculate the total bit rate flowing on an Ethernet cable connected to a Barix device.
The total bit rate is equal at the audio bit rate plus the overhead due to the encapsulation of audio packet inside the layers of OSI stack [1].
We have used for the test an Instreamer 100 (with standard firmware) configured first in RAW UDP and then in RTP, and an Exstreamer 1000 (with STL firmware).
RAW UDP STREAMING MODE
For the structure of the Ethernet packet see here: [2]
The Total Ethernet Overhead per packet is 300 bit.
For the structure of the IP packet see here: [3]
The Total IP Overhead per packet is 160 bit.
For the structure of the UDP packet see here: [4]
The Total UDP Overhead per packet is 64 bit.
Total Bit of Overhead per Packet = Ethernet Overhead + IP Overhead + UDP Overhead = 524 bit
The Audio Bit rate is expressed in bit/sec but the Overhead is expressed in bit/packet.
So we have to translate the Overhead (bit/packet) in Overhead rate (bit/sec).
For this we need to know the amount of packet/sec, that depends by Audio Format and is measurable with Network Protocol Analyzer software like Wireshark.
The values of Audio Data for audio format, sampling frequency and quality (MP3 bitrate average), come from Instreamer Manual (firmware V3.10 – page 18 - [5])
For MPEG1/2 Layer3 (MP3) the following range is supported as Variable Bit Rate in IPAM100 based devices:
28kbps (MPEG2@16KHz mono) - 192kbps (MPEG1@48KHz stereo)
Overhead/sec = Overhead/Packet x Packet/sec
Total Bit Rate (Kbit/sec) = Audio Data Rate (Kbit/sec) + Overhead/sec (Kbit/sec)
(1 Kbit = 1000 bit)
| Audio Format
|
Audio Data Rate (Kbit/sec)
|
Packet/sec (Wireshark)
|
Overhead (bit)
|
Total Bit Rate (Kbit/sec)
|
| PCM 16 bit 8 KHz, mono
|
128
|
13.551
|
524
|
135.1
|
| PCM 16 bit 24 KHz, mono
|
384
|
42.213
|
524
|
406.12
|
| uLaw 8 KHz, mono
|
64
|
6.7
|
524
|
67.5
|
| ALaw 8 KHz, mono
|
64
|
6.7
|
524
|
67.5
|
| ALaw 24KHz, mono
|
192
|
20.28
|
524
|
202.62
|
| uLaw 24 KHz, mono
|
192
|
20.28
|
524
|
202.62
|
| MPEG1 48KHz quality 0, stereo
|
88
|
16.46
|
524
|
96.62
|
| MPEG1 48KHz quality 4, stereo
|
144
|
22.56
|
524
|
155.82
|
| MPEG1 48KHz quality 7
|
192
|
27.81
|
524
|
206.57
|
| MPEG1 48KHz quality 4, mono
|
96
|
16.08
|
524
|
104.42
|
| MPEG1 44.1KHz, quality 0, mono
|
65
|
12.27
|
524
|
71.43
|
| MPEG1 44.1KHz, quality 4, mono
|
90
|
15.76
|
524
|
98.25
|
| MPEG1 44.1KHz, quality 7, mono
|
140
|
25
|
524
|
153.1
|
| MPEG2 16KHz quality 0, mono
|
28
|
5.8
|
524
|
31.03
|
| MPEG2 16KHz quality 4, mono
|
44
|
7.58
|
524
|
47.97
|
| MPEG2 16KHz quality 7
|
64
|
11.5
|
524
|
70
|
Without Ethernet Overhead
| Audio Format
|
Audio Data Rate (Kbit/sec)
|
Packet/sec (Wireshark)
|
Overhead (bit)
|
Total Bit Rate (Kbit/sec)
|
| PCM 16 bit 8 Khz, mono
|
128
|
13.551
|
224
|
131.4
|
| PCM 16 bit 24 Khz, mono
|
384
|
42.213
|
224
|
393.46
|
| uLaw 8 Khz, mono
|
64
|
6.7
|
224
|
65.5
|
| ALaw 8 Khz, mono
|
64
|
6.7
|
224
|
65.5
|
| ALaw 24KHz, mono
|
192
|
20.28
|
224
|
196.54
|
| uLaw 24 Khz, mono
|
192
|
20.28
|
224
|
196.54
|
| MPEG1 48KHz quality 0, stereo
|
88
|
16.46
|
224
|
91.69
|
| MPEG1 48KHz quality 4, stereo
|
144
|
22.56
|
224
|
149.05
|
| MPEG1 48KHz quality 7, stereo
|
192
|
27.81
|
224
|
198.23
|
| MPEG1 48KHz quality 4, mono
|
96
|
16.08
|
224
|
99.6
|
| MPEG1 44.1KHz quality 0, mono
|
65
|
12.27
|
224
|
67.75
|
| MPEG1 44.1KHz quality 4, mono
|
90
|
15.76
|
224
|
93.53
|
| MPEG1 44.1KHz quality 7, mono
|
140
|
25
|
224
|
145.6
|
| MPEG2 16KHz quality 0, mono
|
28
|
5.8
|
224
|
29.3
|
| MPEG2 16KHz quality 4, mono
|
44
|
7.58
|
224
|
45.7
|
| MPEG2 16KHz quality 7, mono
|
64
|
11.5
|
224
|
66.58
|
RTP STREAMING MODE
For the structure of the RTP packet see here: [6]
The Total RTP Overhead per packet is 128 bit (counting also the MP3 MPA wrapper inside the RTP payload, which has an extra 32 bit header).
Total Bit of Overhead per Packet =
Ethernet Overhead + IP Overhead + UDP Overhead + RTP Overhead = 652 bit
The values of Audio Data for audio format, are the same of above, since the transmission protocol doesn't affect audio bit rate.
Overhead/sec = Overhead/Packet x Packet/sec
Total Bit Rate (Kbit/sec) = Audio Data Rate (Kbit/sec) + Overhead/sec (Kbit/sec)
(1 Kbit = 1000 bit)
| Audio Format
|
Audio Data Rate (Kbit/sec)
|
Packet/sec (Wireshark)
|
Overhead (bit)
|
Total Bit Rate (Kbit/sec)
|
| MPEG1 48KHz quality 0, stereo
|
88
|
41.7
|
652
|
115.2
|
| MPEG1 48KHz quality 4, stereo
|
144
|
41.7
|
652
|
171.2
|
| MPEG1 48KHz quality 7, stereo
|
192
|
41.7
|
652
|
219.2
|
| MPEG1 48KHz quality 4, mono
|
96
|
41.7
|
652
|
123.2
|
| MPEG1 44.1KHz quality 0, mono
|
65
|
38.3
|
652
|
90
|
| MPEG1 44.1KHz quality 4, mono
|
90
|
38.3
|
652
|
114.97
|
| MPEG1 44.1KHz quality 7, mono
|
140
|
38.3
|
652
|
164.97
|
| MPEG2 16KHz quality 0, mono
|
28
|
27.8
|
652
|
46.12
|
| MPEG2 16KHz quality 4, mono
|
44
|
27.8
|
652
|
62.12
|
| MPEG2 16KHz quality 7, mono
|
64
|
27.8
|
652
|
82.12
|
| Audio Format (STL)
|
Audio Data Rate (Kbit/sec)
|
Packet/sec (Wireshark)
|
Overhead (bit)1
|
Total Bit Rate (Mbit/sec)2
|
| ALaw 8 Khz, mono
|
64
|
50
|
620
|
0.09
|
| PCM MSB 16 bit 8 KHz mono
|
128
|
50
|
620
|
0.16
|
| PCM MSB 16 bit 11.025 KHz mono
|
176.4
|
50
|
620
|
0.2
|
| PCM MSB 16 bit 12 KHz mono
|
192
|
50
|
620
|
0.22
|
| PCM MSB 16 bit 16 KHz mono
|
256
|
50
|
620
|
0.29
|
| PCM MSB 16 bit 22.050 KHz mono
|
352.8
|
50
|
620
|
0.38
|
| PCM MSB 16 bit 24 KHz mono
|
384
|
50
|
620
|
0.41
|
| PCM MSB 16 bit 32 KHz mono
|
512
|
50
|
620
|
0.54
|
| PCM MSB 16 bit 44.1 KHz mono
|
705.6
|
70
|
620
|
0.75
|
| PCM MSB 16 bit 48 KHz mono
|
768
|
75
|
620
|
0.81
|
| PCM MSB 16 bit 8 KHz stereo
|
256
|
50
|
620
|
0.29
|
| PCM MSB 16 bit 11.025 KHz stereo
|
352.8
|
50
|
620
|
0.38
|
| PCM MSB 16 bit 12 KHz stereo
|
384
|
50
|
620
|
0.41
|
| PCM MSB 16 bit 16 KHz stereo
|
512
|
50
|
620
|
0.54
|
| PCM MSB 16 bit 22.050 KHz stereo
|
705.6
|
70
|
620
|
0.75
|
| PCM MSB 16 bit 24 KHz stereo
|
768
|
75
|
620
|
0.81
|
| PCM MSB 16 bit 32 KHz stereo
|
1024
|
100
|
620
|
1.08
|
| PCM MSB 16 bit 44.1 KHz stereo
|
1411.2
|
137
|
620
|
1.5
|
| PCM MSB 16 bit 48 KHz stereo
|
1536
|
150
|
620
|
1.63
|
1 - in PCM and A/uLaw streaming mode, there is not MPA wrapper.
2 - 1 Mbit = 1000 Kbit.
Without Ethernet Overhead
| Audio Format
|
Audio Data Rate (Kbit/sec)
|
Packet/sec (Wireshark)
|
Overhead (bit)
|
Total Bit Rate (Kbit/sec)
|
| MPEG1 48KHz quality 0, stereo
|
88
|
41.7
|
352
|
102.67
|
| MPEG1 48KHz quality 4, stereo
|
144
|
41.7
|
352
|
158.67
|
| MPEG1 48KHz quality 7, stereo
|
192
|
41.7
|
352
|
206.67
|
| MPEG1 48KHz quality 4, mono
|
96
|
41.7
|
352
|
110.67
|
| MPEG1 44.1KHz quality 0, mono
|
65
|
38.3
|
352
|
78.48
|
| MPEG1 44.1KHz quality 4, mono
|
90
|
38.3
|
352
|
103.48
|
| MPEG1 44.1KHz quality 7, mono
|
140
|
38.3
|
352
|
153.48
|
| MPEG2 16KHz quality 0, mono
|
28
|
27.8
|
352
|
37.78
|
| MPEG2 16KHz quality 4, mono
|
44
|
27.8
|
352
|
53.78
|
| MPEG2 16KHz quality 7, mono
|
64
|
27.8
|
352
|
73.78
|
| Audio Format (STL)
|
Audio Data Rate (Kbit/sec)
|
Packet/sec (Wireshark)
|
Overhead (bit)1
|
Total Bit Rate (Mbit/sec)2
|
| ALaw 8 Khz, mono
|
64
|
50
|
320
|
0.08
|
| PCM MSB 16 bit 8 KHz mono
|
128
|
50
|
320
|
0.14
|
| PCM MSB 16 bit 11.025 KHz mono
|
176.4
|
50
|
320
|
0.2
|
| PCM MSB 16 bit 12 KHz mono
|
192
|
50
|
320
|
0.2
|
| PCM MSB 16 bit 16 KHz mono
|
256
|
50
|
320
|
0.27
|
| PCM MSB 16 bit 22.050 KHz mono
|
352.8
|
50
|
320
|
0.36
|
| PCM MSB 16 bit 24 KHz mono
|
384
|
50
|
320
|
0.4
|
| PCM MSB 16 bit 32 KHz mono
|
512
|
50
|
320
|
0.52
|
| PCM MSB 16 bit 44.1 KHz mono
|
705.6
|
70
|
320
|
0.72
|
| PCM MSB 16 bit 48 KHz mono
|
768
|
75
|
320
|
0.8
|
| PCM MSB 16 bit 8 KHz stereo
|
256
|
50
|
320
|
0.27
|
| PCM MSB 16 bit 11.025 KHz stereo
|
352.8
|
50
|
320
|
0.36
|
| PCM MSB 16 bit 12 KHz stereo
|
384
|
50
|
320
|
0.4
|
| PCM MSB 16 bit 16 KHz stereo
|
512
|
50
|
320
|
0.52
|
| PCM MSB 16 bit 22.050 KHz stereo
|
705.6
|
70
|
320
|
0.72
|
| PCM MSB 16 bit 24 KHz stereo
|
768
|
75
|
320
|
0.8
|
| PCM MSB 16 bit 32 KHz stereo
|
1024
|
100
|
320
|
1.05
|
| PCM MSB 16 bit 44.1 KHz stereo
|
1411.2
|
137
|
320
|
1.45
|
| PCM MSB 16 bit 48 KHz stereo
|
1536
|
150
|
320
|
1.58
|
1 - in PCM and A/uLaw streaming mode, there is not MPA wrapper.
2 - 1 Mbit = 1000 Kbit.
The PDF version of the original document is downloadable here [[media:bit_rate_calculation_3_0.pdf]].
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