LAN DESIGN – first step

5 ISB – school year 2006/07

LAN design

1. LAN Design Goals and Components

2. Network Design Methodology

3. Layer 1 Design

4. Layer 2 Design

5. Layer 3 Design

LAN Design Goals and Components

• Main requirements of the networks are: scalable, manageable , reliable

• There is not a unique solution, each network has distinct design requirement

• The first step is to establish and document the goals of the design

Typical LAN Design Goals

• Functionality - the network must work, must provide user-to-user and user-to-application connectivity with reasonable speed and reliability

• Scalability- the network must be able to grow

• Adaptability - the network must be designed with an eye toward future technologies

• Manageability- the network should be designed to facilitate network monitoring and management

Critical components of LAN design

The critical components of the overall LAN design for high-speed technologies and multimedia-based applications are:• the function and placement of

servers

• Collision detection and Segmentation

• Bandwidth versus Broadcast domains

Placement of servers

Servers provide file sharing, printing, communication, and application services.

Servers can be categorized into two distinct classes: enterprise servers and workgroup servers.

An enterprise server supports all the users on the network by offering services, such as e-mail or Domain Name System (DNS).

A workgroup server supports a specific set of users.

Placement of servers

Enterprise servers should be placed in the main distribution facility (MDF).

Workgroup servers should be placed in the intermediate distribution facilities (IDFs) closest to the users accessing the applications on these servers.

Within the MDF and IDFs, the Layer 2 LAN switches should have 100 Mbps or more allocated for these servers.

Collision detection

• too many client packets looking for services,

• too many server packets announcing services,

• too many routing table updates,

• too many other broadcasts dependent on the protocols, such as Address Resolution Protocol.

The designer has to decrease collision detection and media contention on networks. The possible causes of excessive collisions and broadcasts are:

Collision detection

As traffic increases on the shared media, the rate of collisions also increases. An excessive number of collisions will reduce available bandwidth. In most cases, the actual available bandwidth is reduced to a fraction (about 35% to 40%) of the full 10/100 Mbps.

This reduction in bandwidth can be remedied by segmenting the network by using bridges, switches, or routers.

Segmentation

Segmentation is the process of splitting a single collision domain into two or more collision domains.

Bandwidth Domain vs Broadcast Domain

A bandwidth domain (collision domain in Ethernet ) is everything associated with one port on a bridge or switch.

A broadcast domain is everything associated with one port on a router.

Gathering and analyzing requirements

Beginning steps for a LAN design are:

• gathering the users' requirements and expectations 

• analyzing requirements 

• designing the Layer 1, 2, and 3 LAN structure

• documenting the logical and physical network implementation

Gathering and analyzing requirements

Information to be gathered:

• organization's history and current status,

• projected growth,

• operating policies and management procedures,

• office systems and procedures,

• viewpoints of the people who will be using the LAN

Gathering and analyzing requirements

You need to answer the following questions:

• Who are the people who will be using the network?

• What is their level of skill?

• What are their attitudes toward computers and computer applications?

• Have some data and operations been declared mission critical ?

Focus on identifying the resources and constraints of the organization, existing computer

hardware/software and human resources.

Physical topologies used in networking

The next step is to decide on an overall LAN topology (typically star or extended-star).

Design the layer 1 topology

The physical cabling design issues include the typeof cabling to be used (typically copper or fiber) and the overall structure of the cabling.

Design the layer 1 topology

Layer 1 cabling media include types such as Category 5 unshielded twisted-pair (UTP) and fiber-optic cable, along with the TIA/EIA-568-A standard for layout and connection of wiring schemes and maximum distance.

Diagramming a standards-based Ethernet cable run from the workstation

to the HCC

HCC, VCC, MDF and IDF

It is usual to have more than one wiring closet .

So multiple areas are created.

Main wiring closet is called MDFs (Main Distribution Facility), and secondary are referred to as IDFs (Intermediate Distribution Facility).

HCC, VCC, MDF and IDF

TIA/EIA 568-A Standards

specify that IDFs should be

connected to the MDF by using

vertical cabling, also called backbone

cabling.

HCC, VCC, MDF and IDF

A vertical cross-connect (VCC)

is used to interconnect the various IDFs to

the central MDF. For cable length

issues, fiber-optic cabling

normally is used in VCCs.