Network+ The Fundamentals of Networking 1 of 3

Networking Basics: Networking Overview

LAN (Local Area Network)

WAN (Wide Area Network)

Server - Provides resources to other computers on the network

Workstation - any computer that can request resources and be used to do work. Workstations and Clients are different

Client - any device that can request resources

Host - any network device that has a TCP/IP address

Peer to Peer – no centralized authority. access rights are managed by computer holding the resource

Client/Server – managed from a central point. some computers are dedicated to serving others. each computer is either a client or a server.

Advantages of Client/Server vs P2P:

• More organized
• More efficient
• files and resources easier to locate
• More secure – require password and username
• Can be scaled to infinite size

Networking Basics: Types of Networks

LAN - high speed, low-error, data network confine to a small area

Type of LANs

• Ethernet
• Fast Ethernet
• Gigabit Ethernet

Network Standars are defined by the Institute for Electrical and Electronics Engineers (IEEE)

Standard Ethernet 802.3 is commonly referred to as “Ethernet”

WAN - covers a large geographic area. The Internet (public) and Private Global Corportate networks are examples of WANs.

WAN vs LAN

• WAN covers larger distance
• WAN speeds are slower
• WANs are more expensive
• LANs are usually private while WANs can be public or private

WANS require several core device to function:

• Routers - used to direct traffic on the network to its correct destination. A router is connected to at least 2 networks.
• WAN switches – used to connect routers on the WAN using virtual circuits.
• Modems - provide remote access to networks by converting digital signals to analog ones so that data can be transmitted over analog communication lines (such as telephone lines)

MAN - (Metropolitan Area Network) Covers a metropolitan area such as a City or Suburb. Larger than a LAN, smaller than a WAN

Intranet - private network consisting of interlinked LANs.

Extranet - when part of a company’s intranet becomes available to customers, suppliers or anyone outside the company.  Extranets use IP and a Firewall is used to ensure secruity.

Networking Basics: The OSI Model

OSI – Open System Interconnection model – developed in 1984 by ISO (International Organiztion for Standardization)

A standard or technology can be either proprietary or open

Proprietary - One company or a small group of companies controls the technology rights and usage

Open - available for free usage to the public

OSI Model 7 layers:

• Application
  • File, Print, message, and applacation database services. It provides network service to applications that require access to the network. It controls how these services are advertised and made available. Deals with User authentication and privacy.
  • Does not provide services to any other layer
• Presentation
  • Manages data representation. Transforms data into a mutually agreed format that each application can understand. It formats and structures data, ensuring it is readable between two hosts.
  • Examples include: ASCII (American Standard Code for Information Exchange) and EBCDIC (Extended Binary-Coded Decimal Interchange Code).
  • Organized the sytax of data transfer for the application layer. Data compression and encryption take place in this layer.
• Session
  • Provides communication between hosts. It does this by connection establishment, data transfer, and connection release.
  • Includes authentication, creation management, and termination of sessions between different applications.
  • Provides services to the Presentation Layer.
• Transport
  • aids point to point communications
  • provides reliability in the transportation of data between hosts and ensures complete data transfer.
  • Uses error detection and recovery information flow control to establish, maintain, and terminate all virutal circuits.
• Network
  • ensures data delivery by providing connectivity and path selection between two host systems
  • selects the most appropriate path for sending data and routes data packets
  • Logical addressing and resovling names to host physical address is carried out
  • works with IP addresses assigned to hosts
  • provide logical LAN to LAN communications by supporitng the routing of data between different networks
• Data-Link
  • arranges bits from the physical layer into logical chunks of data known as frames.
  • A frame is a contiguous series of data witha common function
  • framing enables the network to organize bits into logical data format and send them to the correct computer
  • controls how data is formatted and how data on the network is controlled
• Physical
  • responsible for providing the most basic element of data transport – binary transmission
  • outlines the functional, procedural, electrical, and mechanical specifications for controlling physical links
  • specifications relate to the activation, maintenance, and deactivation of physical links.
  • controlls transmission of data on to physical media

OSI has advantages

• enables compatability between different types of networks
• provides standards for users
• facillitates and understanding of how data travels within a network

Adantages of layering network functions:

• accelerates evolution: supports updates and improments to individual componenants without affecting other componenants or needing to rewrite and entire protocol.
• ensures interoperable technology: prevents changes in one layer from affecting another layer
• facillitates modular engineering: allows different types of network hardware and software to communicate with each other.
• reduces complexity: breaks network communcation into smaller, simpler components
• standarizes interfaces: provides vendors a set of standards that ensure greater compatability between the various network technologies.
• simplies teaching and learning: breaks up the task of networking into distict layers

Encapsulation - wraps the data with the required protocol information before transmitting data to the network. As moves through the layers of the OSI model each layer adds a Header (and a Trailer if applicable.)

8 Steps in the Encapsulation Process:

1. user data is sent from an application to the 7th layer of the OSI model – the Application layer
2. The Application Layer adds the header “L7″ to the user data. the L7 and the original user data become the data that is passed down to the Presentation Layer.
3. The Presentation Layer adds the Presentation Layer Header “L6″ This now become the data that is passed down to the Session Layer.
4. The Session Layer adds the Session Layer header “L5.” This now become the data that is passed down to the Transport Layer.
5. The Transport Layer adds the Transport Layer header “L4″ This now become the data that is passed down to the Network Layer.
6. The network Layer adds the Network Layer header “L3″ This now becomes the data that is passed down to the Data-Link Layer.
7. The Data-Link Layer adds the Data-Link Layer header “L2″ This now becomes the data that is passed down to the Physical Layer.
8. The Physical Layer transmits the bits onto the network media.

De-encapsulation occurs when the data is recieved. First it is check for errors then it is striped of its header.

4 Tasks of De-encapsulation

1. Checks the Data-Link trailer to see of there are any errors
2. If the data contains errors it may be discarded. The Data-Link layer may ask that the data be retransmitted
3. If the data contains NO errors then the Data-Link layer reads and interprets the control information in the data-link header.
4. The Data-Link layer strips the data of its header and trailer and then move the data up to the network layer based on the control information found in the data-link header.

During the encapsulation process the protocols at each layer exchange information called PDUs (Protocol Data Units)  between the peer layers.

PDUs are named differently depending on which layer they are going through:

• Transport = Segments
• Network = Packets
• Data-Link = Frames
• Physical = Bits

Peer to Peer communication: each layer of the OSI Model communicates with its peer layer at the destination.

TCP/IP Stack

Comprises 4 layers:

• Application
  • Mangage High Level Protocols
  • Includes aspects related to dialog control, ecoding, and resprentation
  • TCP/IP Stack groups all application aspects into one layer and ensure that application-related data is properly packaged for the layer below
• Transport
  • Handles quality of service issues such as reliability, flow-control, and any error correction
  • TCP protocol provides reliable network communication
• Internet
  • provide packet delievery and hierarchical addressing services.
  • Sends packets from any network on the internetwork and esures they arrive at the correct destination no matter what path they have taken to get there.
• Network Access (Host-to-Network Layer)
  • Looks after all the issues handled by the OSI Physical and Data-Link layers.
  • Includes the LAN and WAN protocols

Similarities between OSI Model and TCP/IP Stack:

1. Both have Application Layers (Functions of the App Layer in each model is different)
2. Both use Packet-Switched Technology. (As opposed to Circuit Switched)
3. The Transport and Network Layers are comporable in both models

Differeneces between OSI and TCP/IP Stack:

1. OSI Data-Link and Physical Layers are combined into the Network Access Layer of TCP/IP Stack.
2. OSI Presentation and Session Layers are combined into the Application Layer of TCP/IP Stack
3. TCP/IP is the standard around which the internet was developed. The OSI Model is generally only used as a guide.