Topic 3 Communication

What is a LAN?

A Local Area Network

What is a WAN?

A Wide Area Network

What's the difference between a LAN and a WAN?

A Local Area Network is sited on a single site while a Wide Area Network is sited on multiple sites

LAN and WAN are the main two types of networks. What are the additional types?

- PAN (Personal Area Networks) - Very small area

- MAN (Metropolitan Area Networks) - Within a Metropolitan district

- VPN( Virtual Private Networks) - Implements WAN to allow people to Login to a network remotely

What are the specialist hardware used to construct networks?

- Switches

- Hubs

- Routers

- Gateways

- Bridge

Switches

A switch analyses each packet of data and sends it to the computer it was intended for

Hubs

A hub copies all packets of data to all devices on the network

Routers

A router stores the addresses of computers on the network and transfers data between devices

Gateways

A gateway joins together two networks that use different base protocols, e.g. links a LAN to WAN

Bridge

A bridge joins together two networks that use the same base protocols, e.g. links LAN to LAN

What are the types of network topology?

- Ring

- Bus

- Star

- Mesh

Ring network topolgy

It is where each node connects to exactly two other nodes, providing a single pathway for signals through each node

Advantage of ring networks

High transfer speeds

Disadvantage of ring networks

Entire network can fail if one node fails

Bus Network Topology

It is in which nodes are directly connected to a common linear cable (or bus).

Advantage of Bus Networks

Cheap and easy to set up

Disadvantages of Bus Networks

- Slow under heavy traffic due to collisions

- Break in the main bus will break the network

Star Network Topology

Where one or more central switch, hub or computer acts as a central conduit to transmit messages

Advantages of Star Networks

- Very reliable

- High transfer speeds are possible due to fewer collisions

- Easy to identify faults

Disadvantages of Star Networks

- Can be expensive to set up as switches and cabling is expensive

- If main switch fails, the network fails

- Bottlenecking can occur if too much data is passing through the central switch

Mesh Network Topology

Each node relays data for the network. All mesh nodes cooperate in the distribution

of data in the network

Advantage of Mesh Networks

It is very reliable as a network can 'self-heal' by reconfiguring itself around broken paths

Disadvantages of Mesh Networks

- Complex

- Expensive

- Difficult to set up

- A large part of the network may be redundant

Why is connectivity important?

Connectivity is important for the transfer of data. Without connectivity, data could not be easily exchanged between computers without the use of removable storage

What do wired connections use?

Wired connections use a wired connection protocol e.g. Cat6 cabling using Ethernet

What do wireless connections use?

Wireless does not use cabling but requires both the transmitting and receiving machine to have wireless network adapter cards and normally additional wireless routing equipment is required

Disadvantage of wireless connections

Wireless is generally slower than wired in terms of bitrate although the advantage of greater freedom can offset this

What was the globally accepted standard?

Circuit switching was a globally accepted standard until superseded by packet switching

Circuit Switching

Circuit switching requires a series of connections to be made to form a single route and that all data traverses the same route.

This is susceptible to interception and failure as failure of any one connection results in failure of the entire route

Packet Switching

Packet switching differs in that the data is broken into packets that all traverse different routes.

The data is reassembled once it arrives at the destination. Packet switching is less susceptible to interception and is more robust because if a route fails then the packet can use an alternate route

What is the importance of network protocols?

Network protocols are vital to allow computers on

networks to communicate.

Without shared common protocols, computers would not be able to communicate

What are the types of network protocols?

- Wi-Fi

- TCP/IP

- HTTP

- HTTPS

- POP3

- SMTP

- IMAP

Wi-Fi

Wireless, two common standards are Bluetooth and 801.11.

TCP/IP

Transmission Control Protocol/ Internet Protocol - Is the basic communication language or protocol of the Internet

HTTP

Hypertext Transfer Protocol - allows webpages to be shared across different computers and browsers

HTTPS

A secure variant of HTTP - it works together with another protocol, Secure Sockets Layer (SSL), to transport data securely

POP3

Post Office Protocol 3 - is a protocol for receiving email, in which email is received and stored by an email server with a client downloading messages when ready

SMTP

Simple Mail Transfer Protocol -mail servers use SMTP to send and receive mail messages, mail applications typically use SMTP only for sending messages to a mail server

IMAP

Internet Message Access Protocol - transfers emails between computer systems via the internet. The IMAP protocol however is generally used for email retrieval and storage as an alternative to POP.

Ethernet

Wired (cable connection) protocol

What are the typical contents of a TCP/IP packet?

The typical contents of a TCP/IP packet are:

(Sam Desired Data to reassemble To Do Coding)

• The source address

• The destination address

• Information which enables the data to be reassembled into its original form

• Other tracking information

• The data itself

• A checksum that checks that the data has not been corrupted

What are the 5 layers of the TCP/IP model?

- Application (Animals)

- Transport (That)

- Network (Need)

- Data link (Do)

- Physical (Pay)

Application layer

The Application layer is the group of applications requiring network communications

Transport Layer

The Transport layer establishes the connection between applications on different hosts

Network Layer (IP)

The Network layer is responsible for creating the packets that move across the network

Data Link Layer

The Data Link layer is responsible for creating the frames that move across the network

Physical Layer

The Physical layer is the transceiver that drives the signals on the network

Routing traffic on a network

Understand that during routing, networks will

search for the shortest path and the fastest nodes to transfer data. Together the path between nodes and the speed of the nodes are assessed by the device transmitting data.

Computers will look for the route with the lowest

cost (that is the shortest path and fastest nodes)

and transmit data via this lowest cost route.

Explain how a DNS resolves addresses when a user attempts to visit a website

- The browser checks the local /cached host file to check if it already holds the IP address

- If not, the local (ISP) DNS server is queried for the IP address

- If the local DNS server does not hold the IP address then the query is passed to another DNS server at a higher level

- This process is repeated until the IP address is resolved

- The address is passed on to DNS severs lower in the hierarchy

- When the full address has been resolved, the IP address is then passed to your browser

- The browser then connects to the IP address of the server and downloads the website