Q1: In the following charts,
(a) if MOS >=4, which codec will you choose to reach the best bandwidth utilization. Explain the reason with sufficient details.
(b) Between G.711 5 ms frames and G.711 20 ms frames, which one has better bandwidth utilization?
(c) Between G.711 20 ms frames and G.729 20 ms fames, which one has better bandwidth utilization? ‘ms’ means millisecond.
[NB: Please use the pdf file captioned “WK9_Part2_QoS_KPI” and other resources you may find online]
The answer may take format highlighted below:
A1: (a)
The first diagram shows the relationship between a codec and MOS score (which measures voice quality). G.7xx are the voice codec. A voice codec is to do Analog to Digital Conversion (Coding) and Digital to Analog conversion (decoding). Coding + decoding = CODEC.
G.711 64 kbps has MOS = 4.3.
G.729AB 8 kbps has MOS =4.0
G.7231A 6.3 kbps bit rate has MOS = 4.0
G.7231A 5.3 kbps bit rate has MOS= 3.5
The first requirement is MOS >=4.0. So, only one of the above codec doesn’t meet the requirement.
G.711 has 64 kbps. It is used in the legacy telephony system. The voice quality is superior. However, it also used the highest # of bits to transmit the same voice. Similar to video. If you use more pixels to represent a video frame, the video quality will be superb. The trade off is that it uses up lots of bandwidth to transmit the video frames.
Our second requirement is that we want to have the best bandwidth efficiency, meaning that we will use the lowest # of bandwidth (in other words, transmit the smallest # of bytes through the channels). Therefore, you want to choose the lowest bit rate to transmit. That’s the answer to (a).
(b) You should take a look of the snap shots along with my explanation. Look at the above left table. G.711 5 millisecond (ms) codec means every 5ms, the codec forms a VoIP packet. The G.711 20 ms codec means every 20 ms, the codec forms a VoIP frame. In each packet, the IP/UDP/RTP headers are added. If you take the first 5 ms codec and collect the VoIP frmaes for 20 ms, then you get 4 frames and 4 times of what 5 ms packet has. The 5 ms codec has 44 bytes of IP/UDP/RTP headers and 40 bytes of VoIP payload (all VoIP data) for a total of 84 bytes. So, for 20 ms, this codec collect 84 x 4 = 336 bytes of packet.
The G.711 20 ms codec has one IP/UDP/RTP header 44 bytes and 40 x 4 = 160 bytes of VoIP data for a total of 44 + 160 = 204 bytes of packet in 20 ms.
So, is G.711 5 ms codec or G.711 20 ms codec more efficient (fewer packets) to send for the same amount of analog voice after converted to VoIP packets? If sending your VoIP packets is charged by # of bytes, which codec will you choose? That’s the answer. Think about the old telephone system that it was charged by minutes, while today it is charged by # of packets.
(C ) compares G.711 20 ms codec with G.729 20 ms codec. Both of the 20 ms codec forms a VoIP packet every 20 ms. So, both has only one set of IP/UDP/RTP headers, that is 44 bytes. G.711 20 ms codec has 160 bytes of VoIP payload, while G.729 20 ms codec has 20 bytes of VoIP payload. Can you tell which one has fewer total # of packets (more efficient)? That’s the answer.
If you look at the graph above the table, G.711 has 64 kbps, while G.729 has 8 kbps. It’s obvious that G.729 uses fewer bytes / second. In other words, G.729 quality is lower than G.711. It is the trade off between quality and efficiency (data bit rate
Q2: Describe cellular network 4G LTE security protocols in terms of all security associations between two end points, authentication protocols, encryption protocols, client-authenticate-server, server-authenticate-client, and any special security features in sufficient details. [Please use the slide captioned “WK11_Park3_LTE_Security_v2” and other resources online to answer this question]
NOTE: Use the diagram below to construct your answer. There are 5 Security Associations (SA). Describe them.
A1:
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