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An Application of the Five Fundamental Rules of Wide Area Network Design. Henry Jacobsen November 1996. The Five Fundamental Rules. All networks become hierarchies Networks are designed top down Administration is more important than design Networks are administered bottom up

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an application of the five fundamental rules of wide area network design

An Application of the Five Fundamental Rules of Wide Area Network Design

Henry Jacobsen

November 1996

the five fundamental rules
The Five Fundamental Rules...
  • All networks become hierarchies
  • Networks are designed top down
  • Administration is more important than design
  • Networks are administered bottom up
  • Routing rules must be defined and followed
types of networks
Types of Networks
  • Mux and 3/1 DACS Network (DS-3s)
  • 1/0 and 3/0 DACS Network (DS-1s)
  • Telephone Network (Circuit Switched)
  • Store & Forward (Message Switched)
  • X.25 and Frame Relay (Packet Switched)
  • ATM (Cell Switched)
3 1 dacs
3/1 DACS

Digital Access Cross-connect System

DS-3s

DS-3s

DS-1s

DS-1s

A 3/1 DACS allows DS-1s to be rearranged and

redistributed among various DS-3s. A 3/1 DACS

has both DS-3 and DS-1 interfaces.

slide7

Hub-and-Spoke Design

Maximizes individual link

efficiency

slide8

Spanning Tree Network Design

Minimizes network spans

the five fundamental rules9
The Five Fundamental Rules...
  • All networks become hierarchies
  • Networks are designed top down
  • Administration is more important than design
  • Networks are administered bottom up
  • Routing rules must be defined and followed
two axioms of network design
The efficiency of a path increases with traffic intensity

Random traffic

Stochastic serving processes

This is sometimes referred to as the fundamental rule of traffic engineering

Relative cost/mile and price/mile tends to decrease as a function of bandwidth

equipment costs

general pricing

Two Axioms of Network Design
network cost considerations
Network Hubbing

Number of ports

Type of ports

Cost Elements

Fixed costs

Recurring costs

Reconfiguration charges

Mileage Elements

Route miles

Cost per channel

Cost Elements

Fixed costs

Recurring costs

Reconfiguration charges

Network Cost Considerations
top down design
Top-Down Design

Major nodes and major routes

tend to account for the majority

of network costs. An optimal

design is dominated by how

this traffic is served.

top down design13
1-Hub Selection

(Heuristic)

Size, location

Connection costs

2-Hub Meshing

Dictated policy

Essential for reliable routing

3-Homing

Simple spanning tree

Community of interest, costs

4-Intermediate Routes

May cause design iteration

Avoid over designing the network

Top - Down Design
hub selection
Hub Selection
  • Dominant (largest) nodes in the network
  • High connectivity to other nodes
  • Good geographic coverage to reduce network backhaul
  • The number hubs is important but not critical (See Weber’s Law)
hub meshing
Hub Meshing
  • Rule: All high-level nodes are meshed.
    • Proper hub selection should guarantee these to be the most efficient routes in the network.
    • Mesh serves as primary or overflow routes for subtending nodes on different hubs.
    • Mesh routing eliminates excessive switching.
    • Mesh is essential for robust (fault tolerant) routing.
node to hub homing
Traffic Volume

Community of Interest

Intra-regional Overflow Server

Inter-regional Traffic Aggregator

Cost Factors

The cost of facilities from node to hub can over-ride traffic issues

Node-to-Hub Homing
joe weber s law of networking
Joe Weber’s Law of Networking
  • All networks cost the same
  • Weber’s law presumes a good basic design
  • There are many designs having a similar cost
  • There is a law of diminishing return in network design
jacobsen law of networking
Jacobsen Law of Networking

Network administration is

more important than design

  • Design data will always be lacking or in error
  • Sensitivity analysis to mis-administration
  • Ease of administration and redesign is critical to controlling cost and performance
bottom up administration
1-Growth is always analyzed on the basis of point-to-point demand

2-Augments are always made to first-choice routes

3-Excessive overflow routing is an indication of poor administration

4-Intermediate routes will be added as a network grows in size

Bottom-Up Administration
network routing rules
Network Routing Rules
  • Rules preserve network economics
  • Rules define network robustness
  • Rules provide accurate growth planning
  • Rules prevent networking difficulties
    • e.g.. Circular Routing
    • Avoid overly-complex routing rules
    • How deep??? Typically four or less
the five fundamental rules21
The Five Fundamental Rules...
  • All networks become hierarchies
  • Networks are designed top down
  • Administration is more important than design
  • Networks are administered bottom up
  • Routing rules must be defined and followed