Network Basics

  1. Why Network?
  2. Basic Components
  3. Wiring and Implementation
  4. Signalling Techniques
  5. Access Control Methods
  6. Protocols
  7. OSI Model
Why Network? Share Network Resources
Networks allow the sharing of printer devices. High end laser, color printers and specialized printers may be shared on a network.
Share Network Resources
Data Storage devices
Large hard drives, CD-ROM drives other data storage devices may be made availiable to all the users on a network.
Share Network Resources
Modem and Fax Resources
Modems may be made availiable for dialing out from a workstation on the network. Fax server may share a common fax line for sending faxes from the network.
Share Network Resources
Host Computer Access
One of the major reasons one may use a network is to allow access to host computers such as mainframes, mini-computers, workstations, AS/400s, Supercomputers, rendering engines or any other network computing resources.
Share Network Resources
Information servers
Access to information servers such as database servers, document image servers, World Wide Web servers, search engines.
Share Network Resources
Communications servers
Access to communications systems such as Electronic mail, Video and Audio servers, Network Telephony and remote network access.
Application sharing
Standard comercial applications such as Excel, WordPerfect, etc. may be stored on network server drives. Custom applications may be made accessible from servers as well.
Application sharing
There is a potential cost savings because you may not need a software license for every machine on the network. Only for the number of simulatneous use copies needed.
Exchanging Data and Information
Data exchange
Database servers are repositories for many kinds of data. When these servers are on the network, access to the information can be gained from any networked workstation.
Exchanging Data and Information
Data exchange
Some people may add or change data while others are viewing the data.
Access Hosts
Host Access
Networked workstation may be used as a terminal to log on to a host computer. The workstation emulates a terminal.
Access Hosts
Host Access
Workstation may run client software and interact with the host as a server.
Access Hosts
Host Access
Multiple hosts may used simulataneously from a single workstation.
Basic Components
Computing Devices
Any device which is conected to the local area network
  • Computers
  • Printers
  • Modems
  • Network Interconnectivity devices
Computing Devices
These devices must have some mechanism for connecting to the local area network
  • Built-in Connectivity
  • Additional connectivity card needed
Computing Devices
Built-in Connectivity
Network Connection often built-in to printers, modems some computers
  • No need for extra connectivity device (NIC)
  • Limited to the installed connection type
Computing Devices
Add-on Connectivity
Must purchase separate part to connect device to network. For computers this is called a
Network Interface Card (NIC)
  • Card must match BUS type of computer
  • Flexible design to attach to many networks

Each NIC has a unique burned-in address called the Media Access Control (MAC) address

Computing Devices
This connectivity is necessary in order to connect the two major parts of a LAN. Whether the connectivity is built-in or added on, it's purpose is to connect the computing devices to the cable system.
Cable System
The cable system is broadly defined as the transmission media or the actual communications channel of the network. This is the paths that the information flows across.
Cable System
The cable system provides the connection between all of the computing devices.
Wiring and Topologies Transmission Media
Copper uses pulses of electricity or changes in electrical state to pass information from one point to another.
Major types of copper wire used in networks
  • Coax
  • Unshielded Twisted Pair
  • Shielded Twisted Pair
Fiber Optics
Fiber Optics use pulses of light in glass or plastic to transfer information from one point to another.
Fiber Optics
Two major classifications of Fiber Optics
  • Multi-mode
  • Single-mode
A Comparison of Copper vs. Fiber Optics
Copper Fiber
Cost per foot Lower Higher
Cost per MB transfer possible Higher Lower
Bandwidth Less Greater
Security Less Secure More Secure
Electrial Interference Can be a problem Rarely a problem
Distance Shorter Greater
Topology - Star
Each computing device has one wire connecting it to a central wiring hub or some kind

The blue room represents a wiring closet. Notice that each room has at least one wire running from it to the wiring closet.

Topology - Bus
A single wire is used to connect all of the computing devices to one another

The blue room represents a wiring closet. A single wire passes through each room with computing devices.

Topology - Ring
A single cable is used to connect all of the computing devices to one another. The cable forms a complete loop.

The blue room represents a wiring closet. The ring, or loop of cable passes by each computing device.

Topology - Daisy Chain
A single cable is used to connect all of the computing devices to one another. The continuity of the cable is broken at each device.

The blue room represents a wiring closet. The cable is broken, attached to a computing device then run to the next.

Topology - Snowflake or Tree
A Star of Stars topology

One star topology network is connected to one cable from another star network. Complex interconnections can be found in tree topologies.

Once a system of computing devices and cabling has been built, a method of getting the information onto the transmission media must exist. This is called the signalling technique.
  • Analog vs. Digital
  • Digital
  • Analog
Only descrete values representing 1's and 0's exist on the network media.
Values ranging between 1 and 0 may be represented on the network media.
Digital Network
When the signalling technique in a local area network implementation is digital, the network is known as a BASEBAND network.
Baseband = Digital
Baseband Network
In a baseband network, only representations of 1 or 0, ON or OFF exist on the network media. These may be pulses of electricity or light.
Baseband Network
Examples of baseband networks are Token Ring and Ethernet
Analog Network
When the signalling technique in a local area network implementation is analog, the network is known as a BROADBAND network. Broadband networks require the precence of a carrier signal.
Broadband = Analog
Broadband Network
In a broadband network, carrier waves create logical data paths for information to flow through. Many carrier waves may exist on a single wire at a time.
Broadband Network
An example of a broadband network is the Cable TV system. As you tune in different channels you are looking at the data carried by different carrier waves. All the channels come into your home on a single piece of RG-6 coax cable.
Using either an Analog(broadband) or Digital (baseband) signalling technique in combination with some encoding mechanism (such as differential manchester). The computing devices can now get data out onto the transmission channel. If it were not for Access Control Methods there would be no control over how workstations access the communications channel which would lead to chaos and mass confusion.
Access Contol Methods
Access Control Methods
Access Control Methods maintain the ability of all computing devices in a network to share information. Using an agreed upon method, information may be exchanged with minimal control overhead. ACMs are usually implemented in the firmware of NICs.
Carrier Sense
Multiple Access
with Collision Detection
  1. Carrier Sense - Listens to see if anyone else is transmitting
  2. Multiple Access - Everyone has access to the communication channel at the same time
  3. Collision Detection - Ability to detect when a transmission fails
Workstation wants to transmit some data
  1. Listens to see if anyone else is transmitting, if it is all clear then...
  2. Data is transmitted onto the communications channel
  3. Workstation listens to it's own message to see if there was a collision
  4. No collision? then process finished
  5. If there is a collision, workstation waits a random period of time then returns to step 1.
Is the access control method used in Ethernet.
Token Passing
The technique used to control access to the communications channel with Token Passing is that only one workstation at a time may transmit information. The workstation holding the "token" is the only station enabled to transmit.
Token Passing
  1. A free token is passed from workstation to workstation
  2. If a workstation wants to transmit some data, it waits for the free token
  3. It inserts it's data into the token (now called a frame)
  4. Sends the frame onto the ring.
Token Passing
Free Token Recovery
  1. The receiver of the data copies the data out of the frame
  2. A change is made to indicate that the frame is now returning to the sender
  3. The original transmitting station removes the data and releases a new free token
Token Passing
Is the access control method used in Token Ring
Access Control Methods
Using access control methods, information may be passed from station to station with assurance of delivery. The information that is being passed is know as protocols.
Protocols are the "languages" used by computers to communicate with one another. In order to be understood, two computers must use the same protocol.
Translation between two protocols is possible using a gateway.
Some examples of common protocols:
  • IPX - Novell Netware
  • TCP/IP - The Internet
  • AppleTalk - Apple Macintosh
  • VinesIP - Banyan Vines
  • SNA - IBM Mainframes
Most protocols are designed and built around a common architectural model. This model is known as the OSI Model.
Open Systems Interconnect (OSI) Model OSI Perspectives OSI Perspectives OSI Importance OSI Model
OSI Model
OSI Model Picture

[Physical] [Logical/Data Link] [Network] [Transport] [Session] [Presentation] [Application]

  1. Physical Layer
    Concerned with the transmission of unstructured bit stream over the physical link.
    • Voltage levels
    • Signal duration
    • Timing issues
    • Mechanical definitions
  2. Logical/Data Link Layer
    Provides for the reliable transfer of data across the physical link. Send blocks or frames of data with:
    • Syncronization
    • Error Control
    • Flow Control
    • Framing the data
  3. Network Layer
    Concerned with moving data between the sub-networks. Provide link independence for the upper layers.
    • Routing data between addresses
    • Controlling flow of data
    • Route Discovery and selection
  4. Transport Layer
    Ensures that data units are delivered error free and in sequence.
    • Reliable connection establishment
    • Initiation and management of data transfer
    • Termination of connection
  5. Session Layer
    Concerned with the dialog between two end systems. Controls some management functions.
    • Conversation management
    • Accounting functions
    • Session recovery
  6. Presentation Layer
    Concerned with presenting the data in the appropriate format.
    • Encryption/decryption
    • Character sets
    • Compression
  7. Application Layer
    Provides support for end user processes
    • *Not* the end user process
    • Provides communications services to applications