---
# System prepended metadata

title: 多媒體期末考前
tags: [學業共筆]

---

## Ch7 review question
:::info
第七章的題目會佔總考題的百分之50
:::
R2. For 128 quantization levels, what is the size of each sample signal?

> 128 levels = $2^7$ = 7 bits

**R3.** Suppose an analog audio signal is sampled 8,000 times per second, and each sample is quantized into one of 512 levels. What would be the resulting bit rate of the PCM digital audio signal?

> 512 levels = $2^9$ = 9 bits, 9 X 8000 = 72000 = 72Kbps

**R4**. Many Internet companies today provide streaming video, including YouTube(Google), Netflix, and Hulu. Streaming stored video has three key distinguishing features. List them.

> Streaming, Interactivity, and Continuous playout (直播、互動性和連續撥放)

R5. What are advantages of client buffering?

> 透過預先儲存一部分的影音，在網路環境有波動時影片依舊能持續播放一段時間，降低使用者的delay

R6. In video streaming applications, why is HTTP streaming more popular than
UDP streaming?

> 較不容易被防火牆擋下且降低成本

R8. Consider the simple model for HTTP streaming. Suppose the server sends bits at a constant rate of 2 Mbps and playback begins when 8 million bits have been received. What is the initial buffering delay $tp$?

> 8 million = 8M, 8M / 2Mbps = 4 sec


R9. What is prefetching video? How does it help?

> 使用者可以使用補充比消耗的速度的差距預先儲存未來會撥放的影音內容，並可以在之後網速不穩或緩慢時利用

**R12.** What mechanisms are used at the receiver side to eliminate packet jitter?

>  (一) 產生區塊時標上序號. 每一次產生序號時序號會依次增加.
(二) 產生區塊時標上時戳(time stamp). 傳輸方在區塊標上該區塊產生的時間.
(三) 接收方延遲撥放區塊

**R13**. What are the two types of loss anticipation schemes used in VoIP?

> 1. Forward error correction (FEC)
> 2. interleaving. 

R14. Section 7.3 describes two FEC schemes. Briefly summarize them. Both schemes increase the transmission rate of the stream by adding overhead.Does interleaving also increase the transmission rate?

> 1. (1)First scheme: send a redundant encoded chunk after every n chunks; the redundant
> chunk is obtained by exclusive OR-ing the n original chunks. 
> 每n個區塊傳送一個多餘的加密區塊；多餘的區塊可以被exclusive OR原本的n個區塊得出
> (2)Second scheme: send a lower-resolution low-bit rate scheme along with the original stream. 
> 2. NO

**R15**. What are the four main RTP header fields?

> payload type
> sequence number
> timestamp source
> identifier fields.

**R16**. What is the role of a SIP registrar? How is the role of an SIP registrar different
from that of a home agent in Mobile IP?

> 1. SIP registrar 會持續追蹤其Domain內使用者的IP
> 2. It also forwards INVITE messages (for users in its domain) 給予(使用者正在使用中)的IP位址，此功能其較於類似於DNS authoritative name server的功能

**R17.** In Section 7.5, we discussed non-preemptive priority queuing. What would be preemptive priority queuing? Does preemptive priority queuing make sense for computer networks?

> 1. 替封包分配權重，較高權重的會被優先傳送
> 2. NO

**R18**. Give an example of a scheduling discipline that is nor work conserving.

> time division multiplexing

R19. What is the purpose of RSVP

> providing quality-of-service guarantees.

## Ch7 problem

### P1

![image](https://hackmd.io/_uploads/ByUVkpBV0.png)

a. 從左圖可以知道每個時間間格為d，而成功在時間間隔內達到的有第1,4,5,6 block

b.經過觀察，總共有六個block在預期的時間內(t1 + 6d)內收到

c.在t1 + 4d時，就已經先收到第五個block，因此最大儲存為2個blocks

d.在t1 + 3d時，所有block都準時收到

### P3


![image](https://hackmd.io/_uploads/Hkg9kVaSVR.png)

a. The server’s average send rate is  H/2

### P4(可能會考)

![image](https://hackmd.io/_uploads/rJVpXpHN0.png)

When the average TCP throughput is roughly ==twice the media bit rate==, streaming over TCP results in minimal starvation and low buffering delays.

### P6(可能會考)

![image](https://hackmd.io/_uploads/B12f4prER.png)

![image](https://hackmd.io/_uploads/Bk1IUhYV0.png)


![image](https://hackmd.io/_uploads/B138S3YVR.png)


### P11(可能會考)

![image](https://hackmd.io/_uploads/rk1KNTSER.png)

b. Packets 3, 4, 6, 7, and 8  will not be received in time

c. Packets 3, 6

d. No packets will arrive after their playout time if playout time begins at t=10


### 

## ch7 P18,19,20(三選一)

### P18

![image](https://hackmd.io/_uploads/rJ2qujS4A.png)

:::warning
第7個封包會優先於第5個封包，但是題目裡沒有說明，爛題目
:::

:::info
建議可以先寫出傳輸的順序，再去算他的delay

Round robin: 不同class輪流送
:::

![image](https://hackmd.io/_uploads/rJaqd3FN0.png)


### P19

![image](https://hackmd.io/_uploads/rJlnvsBEA.png)

![image](https://hackmd.io/_uploads/BJtIl6YVA.png)


### P20

![image](https://hackmd.io/_uploads/SkKdwjrNA.png)



![image](https://hackmd.io/_uploads/SylNHTFNC.png)

![image](https://hackmd.io/_uploads/B1AESpKNA.png)

![image](https://hackmd.io/_uploads/BJvJbTF40.png)

:::warning
9,10 求解，為何不是一起出來?
![image](https://hackmd.io/_uploads/B1fdsTt4A.png)
:::

## Questions related to power point file or textbook(12選5)

### 問題一
List 3 application types for multimedia networking. 

* streaming, stored 
* conversational
* streaming live

### 問題二(同R4)
List 3 key distinguishing features of streaming stored video.

* Streaming, Interactivity, and Continuous playout

### 問題三(同R5)
What are advantages of client buffering? 

* 透過預先儲存一部分的影音，在網路環境有波動時影片依舊能持續播放一段時間，降低使用者的delay

### 問題四(同R6)
In video streaming applications, why is HTTP streaming more popular than UDP streaming? 

* 較不容易被防火牆擋下且降低成本

### 問題五
What is DASH for streaming multimedia? 

* DASH: Dynamic, Adaptive Streaming over HTTP

### 問題六
What is the solution to stream content to hundreds of simultaneous users?

* CDN

### 問題七
List 3 CDN cluster selection strategies, i.e. how does CDN DNS select good CDN nodes? 

* geographically closest to client
* shortest delay to client
* IP anycast

### 問題八(同R12)
What mechanisms are used at the receiver side to eliminate packet jitter? 

>  (一) 產生區塊時標上序號. 每一次產生序號時序號會依次增加.
(二) 產生區塊時標上時戳(time stamp). 傳輸方在區塊標上該區塊產生的時間.
(三) 接收方延遲撥放區塊

### 問題九
How does receiver determine whether packet is first in a talkspurt? 

* if no loss, receiver looks at successive timestamps
* with loss possible, receiver must look at both time stamps and sequence numbers

### 問題十(類似R14)
What is FEC to recover from VoIP packet loss? How does simple FEC work?

* send enough bits to allow recovery without retransmission
* for every group of n chunks, create redundant chunk by exclusive OR-ing n original chunks
### 問題11(同R13)
What are 2 types of loss anticipation schemes used in VoIP?

1. Forward error correction (FEC)
2. interleaving. 

### 問題12(同R15)
What are the 4 main RTP header fields?

* payload type
* sequence number
* timestamp source
* identifier fields.



## 單元 1 5G 垂直應用系統簡介 

### 問題一
List three dimensions to Performance Improvements of 5G and give 3 examples with Usage Scenarios for each dimension. 

* eMBB(enhanced Mobile Broadband)
    * video, smart office, Connected city
* mMTC(massive Machine Type Communications)
    * ITS, smart sensors, Connected city
* URLLC(Ultra-Reliable and Low Latency Communications)
    * ITS, smart grid, remote operation

![image](https://hackmd.io/_uploads/H1j5IZRNR.png)


### 問題二
What are the 5G targets in terms of peak data rate, user experienced data rate, latency, mobility and connection density, defined in ITU-R IMT-2020 Standard. 

* peak data rate
    * Maximum achievable data rate: **20Gbit/s**
* user experienced data rate
    *  Achievable data rate across the coverage area (hotspot cases): **1Gbit/s**
    *  Achievable data rate across the coverage area **100 Mbit/s**
* latency
    * Radio network contribution to packet travel time: **1ms**
* mobility
    * Maximum speed for handoff and QoS requirements: **500km/h**
* connection density
    * Total number of devices per unit area : $10^6 Devices/km^2$

![image](https://hackmd.io/_uploads/rJ27-0KV0.png)


### 問題三(基本必考)
Illustrate the non-roaming service-based 5G System Architecture with UE, RAN and DN as well as AMF, SMF, UPF functions with N3, N6 and N9 interfaces.

:::info
只要會畫架構就好，不用寫敘述
:::

![image](https://hackmd.io/_uploads/SyLNmAKEC.png)


### 問題四(可能會考)
a. List 3 QoS flows supported by 5G QoS model and corresponding definition. 

* GBR QoS 
* Non-GBR QoS
* Reflective QoS

b. Which 5G function controls the QoS flows? 

* SMF

c. What is the identification of QoS flows? 

* QFI(QoS Flow ID)

d. what is the parameter used for QoS Characteristics Mapping. 

* QoS profile
* QoS rule(s)
* PDRs (Packet Detection Rules)

## 單元4


### 4-1-2 接取網路：NR 及 Xn 
What are the two frequencies for 5G NR? 

* FR1: Lower frequencies (below 6 GHz)
* FR2: Higher Frequencies (above 24 GHz)

### 4-1-3 核網設計：5GC 及 NG(基本必考)

Illustrate different 5G Architecture Options defined in TR38.801. (Unit 3, p.10)

![image](https://hackmd.io/_uploads/B1dyNeq4A.png)

## 單元 3 eMBB 垂直應用網路技術 

### 問題一
What is the typical deployment scenarios of eMBB to (a) provide services for those areas where the terrestrial service is not available? (b) provide services for general aviation aircrafts such as helicopters or small air plans? (c) provide services for very large areas with low density of users, including humans and machines? 

A: B

![image](https://hackmd.io/_uploads/HJfo_hrEA.png)

### 問題二(可能會考)
a. What is the Packet Delay Budget for 5QI=86? 

* 5ms

b. What kind of Resource Types for this 5QI to QoS characteristics mapping. 

*  Delay Critical GBR

c. Give 2 example services. 

* Discrete Automation
* V2X messages


![image](https://hackmd.io/_uploads/S1e0OH3SVC.png)

### 問題三
What are the typical power, coverage area, and number of simultaneous users served for Macrocell? 

Macrocell: 
* Typical Power: 20 – 40 watts
* Coverage Area: 25 – 40 km
* Typical number of simultaneous users served: >200 per sector

![image](https://hackmd.io/_uploads/BJpIU3HNA.png)



### 問題四(可能會考)
What are the Characteristics of ‘Small Cells’? 

* Easy to deploy
* SON capability
* Synchronized to the macro network
* Flexibility on backhaul capability

![image](https://hackmd.io/_uploads/ByVGD2B40.png)


### 問題五(可能會考)
List 4 types of Small Cells.

* Femtocells
* Picocells
* Microcells 
* Meadowcells


### 問題六(可能會考)
What are the typical power, coverage area, and number of simultaneous users served for wi-fi? 

* typical power: 200 毫瓦
* coverage area: 100m
* number of simultaneous users: 250

![image](https://hackmd.io/_uploads/r1CxdnBNA.png)

### 問題七
What are the typical power, coverage area, and number of simultaneous users served for femtocell? 

* typical power: 100毫瓦
* coverage area: 50m
* number of simultaneous users: 8 for residental, 16 for enterprise

![image](https://hackmd.io/_uploads/SJu4_3rER.png)

### 問題八(可能會考)
What are 3 factors to determine the Size of a Cell 

* Antenna   height and tilt
* Frequency
* Power

![image](https://hackmd.io/_uploads/H1nwdhH4C.png)



