Network Performance Models Overview

Best Effort Performance

• Best Effort performance model allows maximum traffic flow but has the downside of potential performance degradation.
• When the number of concurrent traffic flows increases, the available capacity decreases.
• When the demand for resources exceeds the available capacity, network congestion starts to occur.

Guaranteed Performance

• Uses a Call Admission Control (CAC) mechanism.
• Maximum number of users/calls allowed until system resources are fully loaded.
• No additional users/calls are allowed until resource availability has been restored.

Best Effort vs. Guaranteed

• Best Effort is best for networks with fluctuating traffic demands but can suffer from slow responses if the demand is high.
• Guaranteed performance is preferable for applications demanding consistent performance but limits the number of users/calls.
• A hybrid approach, Predictable Effort, balances both approaches.

Audit Trail Significance

• Audit trails allow for tracing decisions and identifying rationale for design choices.
• Audit trails should include information about technologies, costs, and time spent.
• This documentation can be used to answer questions about the network's design.
• Audit trails document requirements, problem definitions, goals, decisions, and data.

Systems Methodology

• Network and its environment (e.g. users, applications, devices) should be analyzed as a system.
• Traditional network view focuses primarily on the network itself.
• A systems methodology takes a broader perspective focusing on interactions and dependencies between the network and its environment.

System Components

• User-Application Interface: interacts through displays and user interfaces
• Application-Device Interface: communicates through APIs and QoS mechanisms
• Device-Network Interface: utilizes device drivers for communication with the network

Comparison to OSI Model

• OSI model defines seven layers, while system levels focus on the interaction between users, applications, devices, and the network.
• OSI layers are not directly tied to system levels.
• System levels emphasize user application and network interactions.

Network Service Characteristics

• Service characteristics describe individual network performance and functionality.
• Service characteristics act as network requirements. Relevant examples include:
  • Providing 1.5 Mb/s peak capacity to a user.
  • Guaranteeing a maximum round trip time (RTT) of 100 msec.
  • Defining a specific security level for a group of users.

Service Metrics

• Service metrics measure specific characteristics within the network to monitor, analyze, and manage services.
• Service metrics are necessary for accounting and billing purposes.
• Ensure that all network components can support the requested services.

Service Levels

• A service level defines a set of service characteristics.
• Service levels are offered by service providers to customers as packages with varying features.

Hierarchy of network Levels

• The network is organized in hierarchical levels (Access, Core, etc.)
• Each level has its own bandwidth and capabilities with specific requirements.

Network Design Sections

• Conceptual Model: Defines network requirements, traffic flows, and potential risks.
• Logical Model: Outlines relationships within and between network functions (routing, management, etc.)
• Physical Model: Defines specific technologies, equipment, and interconnection strategies.

Overview of Network Analysis

• Analyzes the current state of the network, any problems present, desired outcomes, and user, application, and device requirements.

Overview of Network Architecture

• Defines an end-to-end structure with relationships between network functions and interactions.

Overview of Network Design

• Defines the physical details, evaluates and selects technologies, sets interoperability strategies, and outlines evaluation criteria.

Need for Diversity

• Diversity improves network performance by connecting networks at different levels.
• Diversity provides redundancy in case of failures and distributes traffic flow across the network.

Network Complexity

• Network complexity increases with each new generation of network technology.
• Each generation represents a level of complexity:
  • 1st Generation - Connectivity
  • 2nd Generation - Interoperability
  • 3rd Generation - Services
  • 4th Generation - Decision-making

Defensibility in Network Architecture and Design

• Defensibility ensures the decision-making process, including data collection and design choices, is well-documented and justified.
• Defensible designs rely on a strong audit trail to support each design choice.