University of Roma
“Sapienza”
DIET
Network traffic engineering
Lecturer: Andrea Baiocchi
DIET - University of Roma “Sapienza”
E-mail: [email protected]
URL: http://net.infocom.uniroma1.it/corsi/ing_traffico/
Lecture 1
Introduction to network traffic engineering
a.a. 2013/2014
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Traffic engineering: what is it?
• Traffic engineering deals with the application of
probability and optimization theories to analysis and
design of service systems.
• Analysis
– Calculate/estimate performance
• Design
– Evaluation of which resources to use and how much of them.
• Service systems
– Input-output function with given quality specs
– Examples: protocol, router, server, network
Network traffic engineering - Andrea Baiocchi - a.a. 2013/2014
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Network Traffic Engineering
• Applied to networking
– From isolated network elements to protocols, to networks
• Service system abstraction
– Allows generale results, applicable to different domains
• e.g., transportation networks, logistics, power distribution
networks, supply chains and inventory management, workflow
systems
– Methodologies are applicable to different problems
• e.g., Markov chains and processes, renewal processes, queueing
theory, convex optimization, graph theory
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NTE target
• The aim of NTE is to build mathematical models, given
a service system specification:
– Structure, policies, intrinsic service capacity
– Statistical description of demand
• service request arrivals
• amount of required service
• The model gives mathematical rules to tie together:
– DEMAND (USERS)
– SYSTEM CAPACITY (RESOURCES)
– PERFORMANCE METRICS (QUALITY)
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Example
• A base station of a cellular network, covering a single
cell
• Demand assignment resource management, with equal
rate communication channels assigned for a whole
session
• Arrivals?
• Service?
• Appropriate model?
• Performance metrics?
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Application objective
• The final objective is to design service system that
meet given service grade constraints at a minimum cost
(minimization of required resources) for the
given/expected demand.
• To that purpose, we need:
– Methods to quantify and forecast demand (service
characterization, measurements);
– Method to evaluate the system capacity (e.g., models of system,
lab measurements, filed trials, simulations);
– Methods to evaluate the service grade offered by a given
configuration of the system with given demand
– Methods for recovery actions, to restore the capabilities of the
systems after congestion and or mulfunctioning.
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Example (follows)
• Minimize number of channels for given set-up failure
probability
• Hand-offs: how can we deal with them?
• Demand quantification: mobility pattern, service
preferences, session duration
– More complex if more flexibility allowed: different rates,
priorities
• Evaluation of service grade: Erlang model
• Recovery actions: some channels are turned-off; the
base station fails (e.g., power failure)
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Erlang loss model usage
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The art of modeling
• From system description to a mathematical model
Key: simplifying assumptions and hypotheses
• Requires:
– In-depth technical knowledge of system working and context;
– Mathematical skills to adopt the most useful models.
• A system model can be analyzed by
– Theoretical means (e.g., queueing theory)
– Computer aided simulations
– Lab/field experiments
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Example (follows)
• Aim: optimize use of spectrum
• Full knowledge of radio resource management
– MAC protocol or multiple access scheme
– Types of service, requirements.
– Radio channel modeling (attenutation, shadowing, fading)
– Physical layer modeling (e.g., Shannon limit capacity)
• Full knowledge of user behavior patterns
– Mobility
– Traffic demand
– Desired QoE/QoS, willingness to pay
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NTE approaches pros and cons
APPROACH
Theoretical model
grossly simplified
gain insight
Simulation model
laborious, costly
many details
accounted for
Lab/field trial
very expensive,
inflexible, costly
the ultimate word
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Modeling approach
Observation
Model
Analysis
Results
Check
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NTE tasks
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NTE tools
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Example
• Let us now work out an example: delay equalization of
a packet stream
• Applications: streaming audio/video
• Technical approach:
– Introduce additional, variable delay at receiving end
• Issues:
– Late packets
– Receiver buffer sizing
Network traffic engineering - Andrea Baiocchi - a.a. 2013/2014