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1.2.- Components of the Traffic Engineering Process Model

  
To support the Traffic Engineering Process Model described so far, we require a system which its key components are:
  • A measurement subsystem.
  • A modelong and analysis subsystem.
  • An optimization subsystem.
Measurement
The operational state of a network can be conclusively determined only through measurement. It provides feedback data which is used by the other control subsystems. Measurement is needed to determine the quality of network services and to evaluate the effectiveness of traffic engineering policies.
When a measurement subsystem needs to be developed the following questions should be considered:
  • Why is measurement needed in this particular context?
  • What parameters are to be measured?
  • How should the measurement be accomplished?
  • Where should the measurement be performed?
  • When should the measurement be performed?
  • How frequently should the monitored variables be measured?
  • What level of measurement accuracy and reliability is desirable?
  • What level of measurement accuracy and reliability is realistically attainable?
  • To what extend can the measurement permissibly interfere with the monitored network components and variables?
  • What is the acceptable cost of measurement?
Measurement can be done at different level of abstraction. It could be performed as follows:
  1. At the packet level characteristic.
  2. At the flow level characteristic.
  3. At the user or customer level characteristic.
  4. At the traffic aggregate level characteristic.
  5. At the component level characteristic.
  6. At the network wide characteristic.
  

Modeling, Analysis and Simulation
A network model is an abstract representation of the network which captures relevant network features, attributes and characteristics. The model facilitates analysis and/or simulation which can be used to predict network performance under various conditions as well as to guide network expansion plans.
Models can be classified as structural and behavioral. Structural models focus on the organization of the network and its components. Behavioral models focus on the dynamics of the network and the traffic workload.
Network simulation tools are extremely useful for traffic engineering. A good network simulator can be used to mimic and visualize network characteristics under various conditions in a safe and non-disruptive manner. They can be used to:
  1. Validate de effectiveness of planned solutions.
  2. To verify network upgrade which may not achieve the desired objetives.
  3. To reveal pathologies such as single point of failure which may require additional redundancy and/or potential bottlenecks and hot spots which may require additional capacity.
  4. To identify planned links which may not actually be used by the existing routing protocol.
  5. To conduct scenario based and perturbation based analysis.
  6. To perform sensitivity studies.
  7. To investigate and identify how best to make the network evolve and grow, in order to accomodate projected future demands.
Optimization
Network optimization involves resolving issues by transforming such issues into concepts that enable the identification and implementation of a solution. In corrective optimization, the goal is to remedy a problem that has occurred or that is incipient. In perfective optimization, the goal is to improve network performance even when explicit problems do not exist and are not anticipated.
Network performance optimization is an iterative and continual process consisting of real-time optimization sub-processes and non-real-time network planning subprocesses. The difference between these subprocesses is the relative time-scale in which they operate and in the granularity of actions, as follows:
Real-Time Optimization Subprocesses:
  1. Control the mapping and distribution of traffic over the existing network infrastructure to avoid and/or relieve congestion.
  2. Assure satisfactory service delivery and optimize resource allocation and utilization.
  3. Resolve random incidents such as fiber cuts or shift in traffic demand that occur irrespective of how well a network is designed.
  4. Solve problems in small to medium time-scales ranging from micro-seconds to minutes or hours.

Examples: Queue management, IGP/BGP metric tunning, MPLS explicit LSPs defining, etc.
Network Planning Subprocesses:
  1. Initiate actions to systematically evolve the architecture, technology, topology, and capacity of a network.
  2. Refine solutions and improve situations taken by the Real-Time Optimization Subprocesses to provide an immediate remedy. Because a prompt response is necessary, the real-time solution may not be the best possible solution and should be refined and/or improved.
  3. Expand the network to support traffic growth and changes in traffic distribution over time.
Network planning and real-time performance optimization are mutually complementary activities. A well-planned and designed network makes real-time optimization easier, while a systematic approach to real-time network performance optimization allows network planning to focus on long term issues rather than tactical considerations. Systematic real-time network performance optimization also provides valuable inputs and insights toward network planning.
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