Computer network Chapter 1

1.1 LAN Design

• Explain how switched networks support small to medium-sized businesses.
• Explain how data, voice, and video are converged in a switched network.
• Describe a switched network in a small to medium-sized business.

1.2 The Switched Environment

• Explain how Layer 2 switches forward data in a small to medium-sized LAN.
• Explain how frames are forwarded in a switched network.
• Compare a collision domain to a broadcast domain.

1.1 LAN Design

Converged Networks

Growing Complexity of Networks

• Next-generation networks need to be secure, reliable, and highly available.
• They must support a globalized workforce.
• They must be able to integrate legacy devices.

Elements of a Converged Network

(Many type of traffic in one network)

• Converged network solutions integrate voice systems, IP phones, voice gateways, video support, and video conferencing.
• Primary benefit of the converged network - just one physical network to install and manage.

Cisco Validated Designs

The Need to Scale the Network

A company with a small network with one site and a connection to the Internet might grow into an enterprise with a central location with numerous remote sites across the globe.

All enterprise networks must:

• Support the exchange of various types of network traffic
• Support critical applications
• Support converged network traffic
• Support diverse business needs
• Provide centralized administrative control

The LAN is the networking infrastructure that provides access to network resources for end users over a single floor or a building.

Hierarchical Design Model

The campus wired LAN uses a hierarchical design model to break the design up into modular layers.

• Breaking the design up into layers allows each layer to implement specific functions, which simplifies the network design for easier deployment and management.
• A hierarchical LAN design includes three layers as shown in the figure:
• Access layer
• Distribution layer
• Core layer
• Some smaller enterprise networks implement a two-tier hierarchical design and collapse the core and distribution layers into one layer.

Converged Networks

Hierarchy in the Borderless Switched Network

• Borderless switched network design guidelines are based on the following principles
• Hierarchical - Facilitates understanding the role of each device at every tier.
• Modularity - Allows seamless network expansion and integrated services.
• Resiliency – Provides an always available network.
• Flexibility - Allows intelligent traffic load sharing.

The three tiers of the hierarchical model are Access, Distribution and Core layers.

Access, Distribution, and Core Layers

1. Access Layer – provides network access to the user.
2. Distribution Layer - interfaces between the access layer and the core layer. Provides functions such as: 
• aggregating Layer 2 broadcast domains and Layer 3 routing boundaries. 
• providing intelligent switching, routing, and network access policy functions to access the rest of the network.
3. Core Layer - is the network backbone. It provides fault isolation and high-speed backbone connectivity.