Assume 18 bytes for the Layer 2 header and a 10-millisecond voice payload, how much bandwidth
should be allocated to the strict priority queue for three VoIP calls that use a G.722 codec over an
Ethernet network?
A.
331.2 kb/s
B.
347.8 kb/s
C.
261.6 kb/s
D.
274.7 kb/s
E.
238.4 kb/s
Explanation:
http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094a
e2.shtml
Total packet size = (L2 header: MP or FRF.12 or Ethernet) + (IP/UDP/RTP header) + (voice payload size)
PPS = (codec bit rate) / (voice payload size)
Bandwidth = total packet size * PPS
Total packet size = (18) + (40) + (160) = 218 bytes (1744 bits)
PPS = 64 Kbps / 160*8 = 50 PPS
Bandwith = 1744 * 50 = 87,2 kbps * 3 = 261,6 kbps
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Total packet size = (L2 header: MP or FRF.12 or Ethernet) + (IP/UDP/RTP header) + (voice payload size)
PPS = (codec bit rate) / (voice payload size)
Bandwidth = total packet size * PPS
Total packet size = (18) + (40) + (80) = 138 bytes (1104 bits) (coz 160 is for 20ms, the question is asking for 10ms)
PPS = 64 Kbps / 80*8 = 100 PPS
Bandwith = 1104 * 100 * 3 = 110.4 kbps * 3 = 331.2 kbps
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