SKR 5302: Advanced Distributed Computing

3.1. Networking issues for distributed systems

• Performance
  • Latency 
    • Delay that occurs after a send operation is executed and before data starts to arrive at the destination computer
    • Determined by software overheads, routing delays, etc.
  • Data transfer rate
  • Speed at which data can be transferred between two computers in the network once transmission has begun, usually quoted in bits per second.
  • Determined by its physical characteristics 

• The time required for a network to transfer a message containing length bits between two computers: 
  • Message transmission time = latency + length / data transfer rate
• Latency is often of equal or greater significance than transfer rate in determining the performance
  • Many messages transferred are small in size
• Total system bandwidth 
• Total volume of traffic that can be transferred across the network in a given time.
• The time required to access shared resources on a local network remains a thousand times greater than that required to access resources in local memory.
• Networks often outperform hard disks; local web server or file server with a large-in-memory cache can match or outstrip access to files stored on a local hard disk. 
  
  
• Scalability
  • Future traffic is expected to grow at least in proportion to the number of active users.
  • For Internet, some substantial changes to the addressing and routing mechanisms are in progress in order to handle the next phase of the Internet’s growth.
    
    
• Reliability
  • The reliability of most physical transmission media is very high.
  • Errors are usually due to failures in the software at the sender or receiver or buffer overflow
    
    
• Security
  • Firewall
  • To enable distributed applications to move beyond the restrictions imposed by firewalls.
  • There is a need to produce a secure networking environment in which a wide range of distributed applications can be deployed, with end-to-end authentication, privacy and security. 
    • Cryptographic techniques
    • The need to protect the routers against unauthorized interference
    • The need for secure links to mobile devices
      
      
• Mobility
• Wireless networks provide connectivity to mobile devices 
• But the addressing and routing schemes of the Internet are not well adapted to their need for intermittent connection to many different subnets.
• The Internet’s mechanisms need to be extended to support mobility and further growth in the use of mobile devices will demand further development.
  
  
• Quality of service
  • Include the ability to meet deadlines when transmitting and processing streams of real-time multimedia data.
  • Major new requirements on computer networks
  • Required guaranteed bandwidth and bounded latencies.