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tags: NCTU, CS, 共筆, 陳志成, 網路
description: 交大資工課程學習筆記
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IOE 5016 Homework 1
=====

:::info
:mega: Feel free to edit / correct this page :tada:
:::

1. Briefly explain the differences between circuit switching and packet switching
- circuit-switching:
- 通訊前需要先建立連線(找路徑)
- 兩端建立起連線後，只有這個通訊可以使用這個通訊資源，無法共享資源給其他人用
- 通訊過程為 建立連線 -> 資料傳遞 -> 切斷連線
- packet-switching
- 通訊前端點(host)會對要傳輸的資料作切割(Fragment)、封裝(Encapsulation)
- 傳送過程中，不需要先建立連線，網路的傳送節點(switch)，利用封裝的 header 查找最佳的下一個節點並送出 (fate-sharing)
- 傳輸過程中，因為資料都是一包一包傳，並且節點也是透過封包標頭進行封包轉送，因此可以與其他通訊共用通訊資源
- [參考](http://acai-hsieh.blogspot.tw/2013/07/circuit-switching-vs-packet-switching.html)

2. Briefly explain the differences between TDMA, FDMA, and CDMA.
- FDMA
- Frequency (頻分多址)
- 共用傳出通道時，利用每個通訊不同頻率，接收端可以以此分別不同的通訊
- ex. 不同顏色
- TDMA
- Time (時分多址)
- 利用時間分區，配不同時間給每個通訊，每個時段傳輸不同的通訊
- ex. 不同張紙
- CDMA
- Code (碼分多址)
- 利用編碼的不同，區分不同通訊
- ex. 中文 & 英文
- [參考](https://www.csie.ntu.edu.tw/~b6506031/ExpReport/intro_1.html)
- [參考](http://blog.ittraining.com.tw/2017/01/tdma.html)

3. There are many wireless technologies and systems. Each of them generally is optimized for a specific transmission environment. Draw a figure, in which x-axis and y-axis represent the moving speed and data rate, respectively, to show their relationship.

4. What are the major differences between wireless LANs and PANs?
- PANs
- Personal Area Networks
- **Short-range** low-power radios
- ex. Bluetooth，手機、電腦開出來的基地台(wifi)
- LANs
- Local Area Network
- ex. Wifi

5. What are the major differences between low-tier and high-tier wireless systems?
- Low-tier / High-tier 是設計給已經有移動速度的無線網路
- Low-tier
- 計給行人
- 室外小於 500m，室內小於 30m
- High-tier
- 支援到車輛速度
- 大範圍
- 出現了 CN(core network) / RAN(radio access network)

6. Which wireless systems are/were available in Taiwan?
- DECT/PHS (Low-tier)
- AMPS (1G)
- GSM (2G)
- 3GPP
- WiMax
- LTE

7. What does license mean in cellular networks? Why do we need it?
- 應該是指，cellular networks 需要有 license 授權，才能使用 cellular networks 的頻段
- 如果不需要有 license 就可以自由開任意頻段，將會造成範圍內嚴重的干擾，因此對於特殊頻段(尤其是可以傳得比較遠的低頻)，應該會限制，只有有 license 的 ISP 才能使用
- [參考](http://www.hightech.tw/index.php/2012-06-06-14-12-38/25-comm-network/305-spectrum-license)

8. Briefly describe the major technical differences between 1G, 2G, 3G, and 4G systems.
- 1G: circut-switched
- 2G: circut-switched、標準出現、還沒連到 Internet
- 3G: IP-based、circut/packet-switched 並存、可上 Internet
- 4G: LTE、IP、packet-switch only、可傳 video

9. Briefly describe the relationship between AMPS, IS-41, IS-136, and IS-95.
- AMPS: 1G 台灣使用
- IS-41、IS-136、IS-95: 2G 北美標準
- IS-136: packet-switched, TDMA
- IS-95: packet-switch, CDMA
- IS-41: circut-switch

10. What is 3GPP Evolved Packet System (EPS)?
- Evolved Packet System
- 4G 開始，提供 Packet-switched 的傳輸
- 分別由 LTE(Long Term Evolution)(RAN) 與 SAE(System Architecture Evolution)(CN) 組成
- [參考(EPS, EPC, SAE)](https://www.jianshu.com/p/e62ad14b0e2b)

11. What is LTE-A?
- LTE(Long Term Evolution)-Advance
- 反正就是所有的性能都變更好...

12. Compare mobile-controlled handoff (MCHO), network-controlled handoff (NCHO), and mobile-assisted handoff (MAHO). You need to show the similarities and differences.
- MCHO
- 由手機測試訊號強弱，由手機選擇換手
- 手機沒有全盤資訊，不利於全盤規劃(有些基地台很 traffic 也許不適合換手)
- NCHO
- 由基地台測試訊號強弱，由基地台選擇換手
- 基地台需要定時測量每一台機器，整體 cost 蠻大的
- MAHO
- 由手機測試訊號強弱，由基地台選擇換手

13. In GSM, how does the network track the location of a mobile user?
- 由手機跟 BS(Base Station) 溝通，由 MSC(Mobile Switching Center) 轉手告知 PSTN(Public Switching Telophone Network) 中的 VLR(Visitor Location Register) 誰在我這個 BS 裡，VLR 在溝通手機供應商的 HLR(Home Location Register) 做註冊

14. Compare hard handoff vs. soft handoff. You need to show the similarities and differences.
- Hard Handoff
- 把舊的基地台連線切掉，再連線到新的基地台
- 可能會有空窗期
- Soft Handoff
- 先連到新的基地台，再切斷舊的基地台
- 系統設計比較難，需要避免干擾、迴圈
- similarities
- 都是 Handoff ?
- differences
- 是否同時保持兩個連結

15. What are the four major functional building blocks in the core network of 3GPP Release 5?
- Circuit-Switched(CS) Domain
- Packet-Switched(PS) Domain
- IP Multimedia Subsystem(IMS)
- Information Servers

16. Draw a picture to show the functional architecture of a User Equipment (UE) in 3GPP.
- 

17. In the circuit switching core network of 3GPP Release 5, it allows the switching and call control functions of an MSC to be separated and implemented on separate network entities. Describe how it is done and what are the benefits.
- It sperates data into control plane and user plane
- MSC server decides how to deliver the data and which path the data should go.(control plane)
- switch only deal with data transimission and it does whatever the control functions say.
- It improves the scalibity of the system. When user increase, the service porvider only need to increase the number of switch no need to increase the controller.
- It also improves the reliability since it won't affect the whole system when some of the switch broke down