# Bài giảng Computer Networks 1 (Mạng Máy Tính 1): Lecture 3.2 - Dr. Phạm Trần Vũ

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## Bài giảng Computer Networks 1 (Mạng Máy Tính 1): Lecture 3.2 - Dr. Phạm Trần Vũ

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Bài giảng Computer Networks 1 (Mạng Máy Tính 1): Lecture 3.2 do Dr. Phạm Trần Vũ biên soạn nhằm cung cấp cho các bạn những kiến thức về Networking Technologies. Bài giảng phục vụ cho các bạn chuyên ngành Công nghệ thông tin và những bạn quan tâm tới lĩnh vực này.

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## Nội dung Text: Bài giảng Computer Networks 1 (Mạng Máy Tính 1): Lecture 3.2 - Dr. Phạm Trần Vũ

1. Computer Networks 1 (Mạng Máy Tính 1) Lectured by: Dr. Phạm Trần Vũ
2. Lecture 3: Networking Technologies Reference: Chapter 4 - “Computer Networks”, Andrew S. Tanenbaum, 4th Edition, Prentice Hall, 2003.
3. Faculty of Computer Science and Engineering - HCMUT Content  Channel Allocation Problem  Multiple Access Protocols
4. Faculty of Computer Science and Engineering - HCMUT Two types of transmission technology Point-to-Point Link Broadcast Link
5. Faculty of Computer Science and Engineering - HCMUT Channel Allocation Problem Who's first?
6. Faculty of Computer Science and Engineering - HCMUT Channel Allocation Problem Static Method Dynamic Method
7. Faculty of Computer Science and Engineering - HCMUT Static Channel Allocation in LANs and MANs KEY: Each user is assigned with a equal-portion of the bandwidth Plus: Minus: 1. Simple 1. Ineffective bandwidth 2. No utilization interference 2. Some users will be denied in high traffic
8. Faculty of Computer Science and Engineering - HCMUT Dynamic Channel Allocation in LANs and MANs Key assumptions 1. Station Model 2. Single Channel Assumptions 3. Collision Assumption 4. Continuous Time vs Slotted Time 5. Carrier Sense vs No Carrier Sense
9. Faculty of Computer Science and Engineering - HCMUT Multiple Access Protocols ALOHA Carrier Sense Multiple Access Protocols Collision-Free Protocols
10. Faculty of Computer Science and Engineering - HCMUT ALOHA Idea: Users can transmit whenever they have data to send Aloha!! Two types of ALOHA: Pure ALOHA Slotted ALOHA The main difference between them is time and time and time
11. Faculty of Computer Science and Engineering - HCMUT Pure ALOHA frame Send & then wait for collision wait a random collision? yes time n o end continuous time no global time synchronization
12. Faculty of Computer Science and Engineering - HCMUT Pure ALOHA – vulnerable period t – frame time, to – starting time
13. Faculty of Computer Science and Engineering - HCMUT Slotted ALOHA 1. Time is divided to equal intervals (slots) 2. Need time synchronization 3. Frames can only be transmitted at starts of time slots
14. Faculty of Computer Science and Engineering - HCMUT Slotted ALOHA – who's next?
15. Faculty of Computer Science and Engineering - HCMUT Channel utilization
16. Faculty of Computer Science and Engineering - HCMUT CSMA with Collision Detection (CSMA/CD) Idea: A station stop transmitting its How? frame immediately after a collision is detected to save time and bandwidth This is the basis of But: half-duplex Ethernet LAN
17. Faculty of Computer Science and Engineering - HCMUT Propagation Delay & CD
18. Faculty of Computer Science and Engineering - HCMUT Collision-free Protocols The basic bit-map control Idea: At the contention period, all station announce their needs to transmit. And then at the transmission period all registered stations take turn to send their frames. Drawback: suffer n bits delay in contention period
19. Faculty of Computer Science and Engineering - HCMUT Collision-Free Protocols The binary countdown protocol Unique binary station addresses with the same length Rules: Compete by “OR” with • other bits in the same order If there is a “0 to 1 • transformation” in the result → give up
20. Faculty of Computer Science and Engineering - HCMUT The Adaptive Tree Walk Protocol Distributed Depth-first tree walk