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Questions and Answers
What is the primary requirement for file transfer applications in terms of data loss?
No loss
Which type of applications can tolerate some loss of data?
Real-time audio/video and stored audio/video
What is the primary advantage of using UDP over TCP?
Faster transmission due to lack of reliability checks
What is the purpose of flow control in TCP?
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What is the primary requirement for interactive games in terms of time sensitivity?
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What is the main difference between TCP and UDP in terms of congestion control?
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What is the requirement for web documents in terms of throughput?
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What is the primary requirement for real-time audio/video applications in terms of throughput?
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What is the primary purpose of the transport layer in terms of application requirements?
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What is the main advantage of using TCP over UDP in terms of reliability?
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Study Notes
Caching
- Caching reduces response time and traffic on an institution's access link.
- Typically, cache is installed by an ISP (university, company, residential ISP).
- Caching enables "poor" content providers to effectively deliver content.
Caching Example
- Assumptions: average object size is 100K bits, average request rate from browsers to origin servers is 15/sec, average data rate to browsers is 1.50 Mbps, RTT from institutional router to any origin server is 2 sec, and access link rate is 1.54 Mbps.
- Consequences:
- LAN utilization is 15%.
- Access link utilization is 99%.
- Total delay includes Internet delay, access delay, and LAN delay.
Fatter Access Link
- Assumptions: average object size is 100K bits, average request rate from browsers to origin servers is 15/sec, average data rate to browsers is 1.50 Mbps, RTT from institutional router to any origin server is 2 sec, and access link rate is increased to 154 Mbps.
- Consequences:
- LAN utilization is 15%.
- Access link utilization is 9.9%.
- Total delay is reduced.
Local Cache
- Assumptions: cache hit rate is 0.4, or 40% of requests are satisfied at the cache.
- Calculating access link utilization and delay with cache:
- Access link utilization is 0.58.
- Total delay is approximately 1.2 secs.
Network Applications
- Principles of network applications
- Web and HTTP
- Electronic mail (SMTP, POP3, IMAP)
- DNS
- P2P applications
- Video streaming and content distribution networks
- Socket programming with UDP and TCP
Electronic Mail
- Three major components:
- User agents
- Mail servers
- Simple mail transfer protocol (SMTP)
- User Agent:
- Data integrity and throughput
- Some apps require 100% reliable data transfer
- Other apps can tolerate some loss
Transport Service Requirements
- Common applications and their requirements:
- File transfer: no loss, elastic, and no time sensitivity
- E-mail: no loss, elastic, and no time sensitivity
- Web documents: no loss, elastic, and no time sensitivity
- Real-time audio/video: loss-tolerant, specific throughput, and time-sensitive
- Stored audio/video: loss-tolerant, specific throughput, and time-sensitive
- Interactive games: loss-tolerant, specific throughput, and time-sensitive
- Text messaging: no loss, elastic, and no time sensitivity
Internet Transport Protocols
- TCP service:
- Reliable transport between sending and receiving process
- Flow control: sender won't overwhelm receiver
- Congestion control: throttle sender when network is overloaded
- Does not provide: timing, minimum throughput guarantee, security, or connection setup
- UDP service:
- Unreliable data transfer between sending and receiving process
- Does not provide: reliability, flow control, congestion control, timing, throughput guarantee, security, or connection setup
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Description
This quiz covers the concept of client-server architecture, the role of caching in reducing response time and traffic, and its importance in content delivery.
