Lecture Outline. Topology Design: I. Topologies and Reliability. Another Case: Mobile Performance Optimization. Jeremiah Deng.

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1 Lecture Outline Topology Design: I 1 Review Jeremiah Deng 2 University of Otago 3 1 / 22 Review Another Case: Mobile Performance Optimization 2 / 22 Topologies and Reliability T. Everts, Rules for mobile performance optimisation, Communications of ACM, 56(8), July 2013 An overview of speed page loading Reduce requests Consolidate resources Use browser cacheing and CDN Eliminate redirect Reduce payload Compress images & text Resize images... Star: Has the least traffic congestion Single point of failure at the centre Bus: worst topology for link capacity Tree has only one path for each node Mesh good for backbones, but expensive! (N nodes, O(N 2 ) links) Ring Has lower capacity demand Economical (N nodes, N links) Also provides redundant paths 4 / 22 6 / 22

Eliminate redirect Reduce payload Compress images & text Resize images.

2 Reliability of Rings Southern Cross Cable System E.g., a ring with 200 nodes, links all with 99% availability Nodes A and B separated by 100 links, the availability will be 1 ( ) 2, i.e., = (!) For large networks, more than 1 ring will be required to achieve good availability. 1.2 Tbit by 2010 Owned by Telecom NZ, Optus, MCI WorldCom Outsourced to Alatec and Fijitsu Designed to have network availability of %. If one cable network breaks, full redundancy (self-healing) is immediately available via alternative pathways. 7 / 22 Across the Ditch... 8 / 22 Network Reliability Analysis Assume failure events of separate components are statistically independent. Algorithm: based on simple laws of calculating probabilities of compound events P(U V ) = P(U)P(V ) Availability(U and V) = Availability(U) Availability(V) P(U V ) = P(U) + P(V ) P(U)P(V ) For links with small unavailability values - Unavailability of sequential links: Unavailability(U) + Unavailability(V) Unavailability of parallel links: Unavailability(U) Unavailability(V) Working on unavailability is easier and usually accurate enough. 9 / / 22

999%. If one cable network breaks, full redundancy (self-healing) is immediately available via alternative pathways. 7 / 22 Across the Ditch.

3 Application of the Algorithm A Network Example E.g., links having 99% reliability A network with parallel links Equivalent to a single-link network of equivalent availability (union prob.) 99% + 99% 99% 99% = 99.99% Or equivalent unavailability of product of two individual unavailabilities 1 (.01.01) = 99.99% A network with serial links An availability equal to the product of two individual availabilities 99% 99% = 98.01% Equivalent to a single combined link with added unavailability: 1 ( ) = 98.0% What is the reliability between A and B? Start with the red trail across top. 11 / 22 An Equivalent Network 12 / 22 Further Deduction Red trail across top: add unavailability = % (availability) Next: simplify E-C links Unavailability for E-C links ( ).001 = % Next: Combine the lower path Unavailability for green path: = Final result: Availability(A,B) = %. 13 / / 22

99% A network with serial links An availability equal to the product of two individual availabilities 99% 99% = 98.01% Equivalent to a single combined link with added unavailability: 1 (.01 +.

4 Redundant Topologies Introducing redundancy into network topology increases reliability. As networks grow larger, reliability becomes more important esp. in networks on which other network depend. Solutions Redundant topology. Load balancing. Hierarchical design. Eliminate the possibility of having a single point of failure (SPF) on the network. Duplicate any required component whose failure may disable critical applications. A WAN trunk A core router A channel service unit Application servers A power supply... Expensive to deploy and maintain Tradeoff with affordability 16 / 22 Backup Paths 17 / 22 Loading Balancing A partial mesh can provide fast automatic failover. A backup link often uses a different technology and has less capacity. E.g. a dial-up line in parallel with a leased line. Always test backup paths! A secondary goal of redundancy design is to improve performance with load balancing across parallel links. Use what you pay for. Uses one of the OSI layers to make decision. Can be done using either software or hardware. Can direct traffic flowing into network to available servers. 18 / / 22

Duplicate any required component whose failure may disable critical applications. A WAN trunk A core router A channel service unit Application servers A power supply.

Load Balancing on Layer 7 Content Delivery Networks Network deployment Size & diversity Edge servers Network performance monitoring Internet traffic conditions Dynamic load balancing Fault tolerance

5 Load Balancing on Layer 7 Content Delivery Networks Network deployment Size & diversity Edge servers Network performance monitoring Internet traffic conditions Dynamic load balancing Fault tolerance Intelligent routing Fresh & synchronized content Internet traffic enters the router. Business intelligence Layer 7 device looks into packet and directs it to the appropriate server Comprehensive Service Level Agreement Traffic arrives at server in correct priority. 20 / / 22 Summary WAN topology availability Redundancy design Backup paths Load balancing Content delivery networks Next: Spanning trees Hierarchical design in LANs 21 / 22

Business intelligence Layer 7 device looks into packet and directs it to the appropriate server Comprehensive Service Level Agreement Traffic arrives at server

Industrial Ethernet How to Keep Your Network Up and Running A Beginner s Guide to Redundancy Standards

Redundancy = Protection from Network Failure. Redundancy Standards WP-31-REV0-4708-1/5 Industrial Ethernet How to Keep Your Network Up and Running A Beginner s Guide to Redundancy Standards For a very