Communicating over the Network.

Local Area Network (LAN)

A LAN is a network confined to a relatively small space. (still like an island but a little bigger);
Lan’s are a single enterprise that is locally administered.

Problem faced with a LAN – How to share information in different geographic areas.

Three LAN components

a. Devices
b. Media
c. Services

Two types of Devices:

End Devices:

PCs, Servers, Printers, Phones, PDAs, Laptops, etc.
End Devices are often refered to as a HOST.

Intermedia Devices:

Relied on for connection
Work behind the scenes
Connect HOST to network and connect multiple networks to form an internetwork

- Network access Devices (Hub, Switch, Access Point (AP))
- Internetworking Devices (Routers)
- Communication Servers and Modems
- Security Devices (Firewalls).

Intermedia Devices manage data flows through the network.
Intermedia Devices use destination Host address and information about the network to determine data path.
Intermedia Devices Perform a variety of functions:

Regenerate and retransmit data signals.
Maintain information about pathways through network.
Notify other devices of errors or failures.
Re-direct data along when a link fails.
Classify and direct messages according to QoS.
Permit or deny data based on security settings.

Media:

Copper – electrical impulses
Fiber – pulses of light
Wireless – electromagnetic waves

Network Media

Each type has different features and benefits.

Criteria for choosing a network media:
Distance the media can successfully carry signals.
Operational environment.
Bandwidth required (data to move).
Cost of media and installation.

Wide Area Network (WAN):

Connect two or more geographical LANs;
Telecommunications Service Providers (TSP) interconnect LANs;
Organizations LEASE connections through a TSP;
Organization maintains policies and administration of their LANs but policies within TSP network are those of the TSP
WANs use specifically designed network devices that are integral to the function of an organizations network.

Internet:

An intricate and extensive WAN spanning the globe;
Created by the interconnection of networks belonging to Internet Service Providers (ISPs);
This diverse infrastructure requires consistent and commonly recognized technologies and protocols as well as the cooperation of many agencies.

Intranet:

Refers to a private group of LANs, WANs accessible only by members, employees or others with authorization.

NOTE: Internetwork, data network or networks may be interchangeable. The usage depends on the context and terms may often be interchanged.

Extranet: similar to Intranet but allow certain outside groups access to their network.

Function of Protocol in Network Communications:

Protocol – Set of rules for communications.
Communications follow rules: Phone, email, mail, networks.
Without protocols a computer cannot rebuild the stream of bits from another PC.
Successful communications between hosts requires many different protocols.
A group of inter-related protocols is called a Protocol suite.
One way to visualize how protocols interact on a particular host is to view it as a stack.

Network Protocols Provide:

The format for the messages.
The process for sharing info about pathways.
How and when error messages are passed.
Setup and termination of data transfers.

Protocol Suites and Industry Standards:

Many protocols use others or industrial standards.
Standard is a process or protocol that has been endorsed by a standards organization:

IEEE, Institute of Electrical and Electronic Engineers.
IETF, Internet Engineering Task Force.
ISO, Internet Organization for Standards.

Protocol Interaction:

EG. Web Brosers and Web Servers interaction require multiple protocols working together: HTTP, TCP, IP, Ethernet.

Technology Independent Protocol:

May not say how, but says what is required. EG. Web Services need a browser to speak HTTP but doesn’t specify the OS or browser type.

Networking Models:

Communications follow rules, but it often uses a layered approach. EG. Conversation between 2 people – Idea ? Decision to Communicate ? Sound.

Benefits to using a layered Model:

Assists in protocol design.
Fosters competition because products from different vendors can work together.
Prevents technique or capability changes in one layer from affecting other layers above or below.
Provides a common language to describe networking functions and capabilities.

Protocols and Reference Models:

Protocol models closely match a particular protocol suite.
Typically represent all the functionality required to interface human with data.
TCP/IP model describes the TCP/IP suite
A reference model helps maintain consistency within all types of network protocols and services.
Open System Interconnection (OSI) model is the most widely known reference model.

TCP/IP Model:

Open standard dating to the ‘70s,
Standards are discussed in open RFC (Requests For Comments).

Layers:
Application
Transport
Internet
Network access (Network interface)

Communications process involves moving down one stack and up the other stack on the other side.

Protocal Data Units (PDUs)

Unique packages of data and each layer that often contains Headers, Identifiers and Control information.

Encapsulation:

Act of enclosing in a capsule – (definition from Websters).
Lower layers encapsulate the data from higher levels.
PDUs are layered specific encapsulation.
Moving down the stack we encapsulate PDUs.
Moving up the stack we decapsulate PDUs.

TCP/IP Layer PDU Type
*** encapsulation occurs at each level to include the PDU from the previous layer.***
Application Data
Transport Segment
Interenet Packet
Network Access Frame
Bits

A good acronym to rember this is
Do Some People Fry Bacon

Layers with TCP/IP and OSI model

Describe the process of sending and receiving messages:

Open System Interconnection (OSI)

Layer level PDU

Application 7 Data
Presentation 6 Data
Session 5 Data
Transport 4 Segment
Network 3 Packet
Data Link 2 Frame
Physical 1 Bits

Developed by OSI for a protocol stack.
Protocol fizzled, but model is huge.
Memorize both names and layer numbers.
PDNTSPA (as known – Please Do Not Throw Sausage Pizza Away (level 1 to 7) or All People Seem To Need Data Personnel (level 7 to 1).
Know PDUs at each layer.

Compare OSI and TCP/IP Models.

Addressing and Naming Schemes:

Data sent from source to destination can be divided into pieces and mixed with other messages.
Billions of these pieces are on the network at any time.
Critical that each piece is addressed to its destination.
3 types of addresses needed to deliver the data from an application on one Host to another.
These addresses or PDU identifiers occur at 3 layers.

1. Phsical Address:
identifies layer 2 PDUs/Frames – EG. Ethernet MAC address;
primarily for moving Data with a single local network.
2. Network Address:
identifies layer 3 PDUs/Packets – EG. IP Address;
primarily used to move Data between networks;
allow intermediary devices to locate and direct traffic.
3. Application Address
Layer 4 is concerned with getting Data to right application;
Layer 4 PDUs/Segment – EG. Use Port numbers to keep processes or services separate.

Some methods to Check the Stacks

Application layer protocol HTTP, FTP, Telnet can be used to check connectivity all the way to Layer 7 (Application Layer).
Utils like Ping, Tracert confirm Layer 3 (Network layer).

Tags: wan, cisco, 802.1q, ip, switch, router

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