calculate new link-cost metric for all links in E based on the updated topology, reserved bandwidth, and traffic demand k; find minimum-cost path from the calculated link metric for tr[r]
(1)WAN Network Design
WAN Network Design
Telcom 2110 Network Design University of Pittsburgh
Slides 11
WAN Network Design
• Given
– Node locations (or potential locations) – Traffic Demand (mean, peak, etc)
– Performance Goals (blocking rate, delay,etc.)
• Determine Topology
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WAN Network Design
•Design Variables
•Network Topology (possibly facility location as well) • Channel Capacity
• Routing Policy
•Performance Metrics
depends on network application and layer • Circuit Switched Network
•Call Blocking, Availability
• Packet network •Delay
• Delay Jitter • Throughput • Packet Loss
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• Minimize total cost
• Subject to Constraints … for example
– Link capacity must exceed some min, and be less than some max
– Average Packet Delay must be < maximum – Reliability requirements
– Throughput, etc
• General goals
– Short path between all sources and destinations – Well-utilized components with high speed lines to
achieve economy of scale
– These are somewhat contradictory goals
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• Consider an example to see design issues/tradeoffs all designs use same algorithm with different parameter settings
• 45 nodes labeled N1-N45
• large data centers, N1 and N45 Each data center terminates and sends Mbps
• data servers, N2, N3, N43, and N44 Each data server sends and receives 150 Kbps
• The remainder of the sites are small Each sends and receives 25 Kbps
• Assume link costs are greater than node costs • The links available:
Example of Tradeoffs/Designs
Tree type of design, cost reduced to $133,584/month The average number of hops, 7.84, is high
Design has only high speed links (T1 and 256Kbps lines) Poor reliability
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Two level design – backbone with edge nodes
Data centers and servers are interior nodes of the backbone tree Cost reduced to $96,777; average hops= 3.41
Reliability poor – if backbone link failure – large impact
Example Design 2
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Instead of tree, interior (backbone) nodes are connected with high-speed links to form a 2-connected graph
Cost = $ 112,587/month, better reliability
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Alternate connected backbone design with slightly lower cost $112,587Ỉ$108,724 per month
Example Design 4
Can Cost Be Reduced Further?
• We will look for costsimprovements by expanding the backbone • Look at the $112K Example
3 Design:
• There are large clusters centered at N2 and N45 • Can we locate a new
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TELCOM 2110 Spring 06 62
WAN Packet Design
• Note many alternative routing based
design approaches based on tradeoff of
cost,capacity, performance
• A simple extension to the routing based
approaches discussed is successive
minimum cost routing
• Route traffic – create initial topology –
evaluate performance metrics (cost, delay
etc.) try to improve by rerouting traffic
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Heuristic Algorithm
Heuristic Begin
Let D= set of traffic demands or flows; Let E= set of all potential links; {
randomly select an order of traffic demands in Dto be routed;
for each traffic demand kin the order {
if (traffic demand khas an existing route)
temporarily remove its required bandwidth along the route;
calculate new link-cost metric for all links in Ebased on the updated topology, reserved bandwidth, and traffic demand k; find minimum-cost path from the calculated link metric for traffic demand k;
if (new route has been found)
update network topology for new links and capacity; else
maintain previous solution;
}
} until ( update improvement < epsilon OR iteration > max_iteration);
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