Dynamic PMTU Cache for Content Delivery Networks
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Solution Overview
Problem
Content delivery networks face delays due to lost or dropped data packets that are too large for network paths, leading to repeated retransmissions and decreased Quality of Service (QoS) when serving content objects to end-user systems.
Innovation Solution
A packet size digest is established and shared among servers within a content delivery network to determine and store the maximum packet sizes for network paths to end-user systems, allowing for efficient packet transmission by avoiding packet fragmentation and retransmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If packets are transmitted with default large sizes, then network throughput is improved, but packet loss increases due to exceeding MTU limits
Solution Approach 1:
The system performs preliminary PMTU discovery before content delivery by sending probe packets through the network path to determine the maximum transmission unit. This advance measurement allows servers to pre-calculate appropriate packet sizes, preventing packet loss during actual content delivery while maintaining high throughput.
Solution Approach 2:
The system dynamically adjusts packet size parameters based on discovered PMTU values for different network paths. By changing the packet size parameter from a fixed default value to a dynamically determined value matched to specific network conditions, the system optimizes both throughput and reliability.
2Measurement precision
If each server independently determines maximum packet size, then accuracy of packet sizing is improved, but time delay increases due to repeated discovery processes
Solution Approach 1:
The system merges the PMTU discovery function into a centralized DNS resolver that handles queries from multiple servers. Instead of each server independently performing packet size discovery, the consolidated resolver caches and serves PMTU information to multiple servers, reducing redundant discovery operations while maintaining accurate path-specific measurements.
Solution Approach 2:
The DNS resolver performs PMTU discovery in advance and caches the results, so when multiple servers need to deliver content to the same destination, they can reuse the pre-determined packet size information without repeating the discovery process, significantly reducing time delays.
3Reliability
If packet size is reduced to fit all network paths, then packet loss is reduced, but network efficiency decreases due to increased overhead
Solution Approach 1:
The system applies local quality by determining specific packet sizes for specific network paths rather than using a uniform size for all paths. Each server can use path-specific PMTU information to optimize packet sizes for its particular routes, maximizing efficiency while ensuring reliability on each individual path.
Solution Approach 2:
The system changes the packet size parameter dynamically based on the specific network path and destination, rather than using a fixed conservative size. This allows each transmission to use the largest possible packet size for its particular path, optimizing efficiency while maintaining reliability.
4Stability of the object's composition
If PMTU information is cached centrally, then consistency across servers is improved, but system complexity increases due to additional cache management
Solution Approach 1:
The DNS resolver performs multiple functions: it resolves domain names to IP addresses and simultaneously discovers and caches PMTU information. By making the resolver universal, the system avoids adding dedicated cache management infrastructure, reducing overall system complexity while maintaining consistent PMTU information across all servers.
Solution Approach 2:
The DNS resolver automatically performs PMTU discovery and cache management without requiring external intervention or complex coordination protocols. The resolver serves itself by integrating the discovery function into its existing operation, simplifying the system architecture while ensuring consistent information is available to all clients.
Data Source
AI summary
Methods, systems and computer program products for delivering content objects over the Internet are disclosed. Use of a packet size digest allows for look-up of known or discovered maximum packet sizes for network paths to various receiving systems by servers within one or more points of presence of a content delivery network, such that the packet size information can be advantageously re-used by the multiple servers to reduce delays associated with lost packets and time spent determining a path maximum packet size or maximum transmission unit by each of the multiple servers within the point of presence as they transmit content objects over the Internet.