1. Introduction to Computers
Introduction to Networking (continued)

2. Network Addressing
Every computer on a network has to have an address to be able to be identified. We need a way to be able to send a message to a specific computer over a network. This address is called an IP address
We can think of IP addresses in the same way that we think of mailing addresses for houses
Just like a house address consists of a street name to indicate the area, and then a number indicating the house, IP addresses indicate both our network and the computer we want to communicate with. This means that, just like houses can share numbers so long as they are on different streets, computers can share numbers so long as they are on different networks

3. IP Address Format
Series of four numbers separated by dots. Each number can be between 0 and 255 as a decimal
In binary, these numbers form octets, or sets of eight decimal numbers
= 0
= 255
The first part of the IP address is called the network address or subnet address and will indicate the network. The second part is called the host address and indicates the host

4. Network Scope
One way we can designate networks is by their size, or scope
Subnet - A subnet is a part of the network where all of the computers share the same subnet address, in much the same manner that all of the houses on the same street share the same street address in their addresses.
LAN - Subnets can be connected to each other by a device called a router. We can connect multiple networks together using multiple routers. When several networks within the same organization are connected together, they're collectively referred to as a LAN, which stands for Local Area Network.

5. Network Scope (Larger)
MAN - There will be many local area networks within the same city and they're probably all interconnected together. All of the networks within the same metropolitan area connected together constitute a Metropolitan Area Network, sometimes called a MAN
WAN - We can connect these LANs and MANs together into an even larger network. The connections between them are called Wide Area Network links, or WAN links. The collection of connected networks is called a WAN

6. Network Connections
We can also separate networks by how they are connected
An internetwork is when we have separate networks under the control of separate organizations connected over WAN links
An intranet is a collection of private networks all owned by the same organization. Unlike an internetwork, access would be private not public. Either by isolation from public networks or by security measures
An extranet is an intranet that allows access from public networks. Since it is still a private network, we would need a means of verifying users and only allowing access to authorized users

7. The Internet
The internet is the largest example of an internetwork. It is a collection of networks all managed by different entities: large corporations, schools, non-profit groups and even individuals
To connect to the internet, you will go through an ISP (Internet Service Provider). ISPs don't manage the main part of the Internet network. Instead, they manage an access point to the Internet for individuals and companies
When you connect to the internet, you will typically have a security boundary that separates your private network from the public internet network. The devices on your private network can reach out and communicate to computers on the public network, but without allowing access, computers outside your private network can’t make a connection with the computers inside

8. Network Topologies Logical vs Physical
When we talk about mapping a network, we have to make a distinction between two separate kinds of topology - physical and logical
The physical topology of the network is a description of how the network media connects hosts together
The logical topology of the network is a description of how the hosts see the network, and how they are able to communicate on it
The logical topology is going to be limited by the physical topology. The logical topology can only be as open and connected as the physical, although the logical topology can be more restrictive than the physical if we need it to be

9. Bus Topology All devices connect to a single central cable or “bus”
Least cable length
Easiest to create if devices are linear
Difficult to identify location of problems
Terminators required for both ends of cable to absorb signals and stop bouncing
Not scalable - additional devices slow network down (only one device can send information at a time)
Main cable is a single failure point
Not secure, since messages get passed along

10. Ring Topology Devices connected to their two neighbors
Data moves in one direction, reducing chances for packet collision
No network server or hub needed
Since devices are contacting the device next in the line, multiple devices can send information at once, making this network scalable
Every device needs to be operating to keep network operating
Isolating problems involves moving from node to node

11. Star Topology
Every device connects to a central node (A hub or switch for example) which sends information directly to the target
Potentially fastest topology since messages go direct
Most scalable and secure
One point of failure: central node. Other devices can fail without affecting network
Higher cost to maintain
Performance determined by central node device

12. Mesh Topology Messages sent from one device to another
Defined by having multiple or redundant paths from one device to another
Partial Mesh: When some redundant paths exist
Full Mesh: Every device connected directly to every device
Can handle high traffic since multiple devices can transmit simultaneously
No single points of failure
Mixed scalability: Costly but non-disruptive
Very costly due to redundant connections

13. Physical Topology VS Logical Topology
Logical bus topology - Messages are sent to all devices connected to the bus. We can use this with both bus and star physical topologies
Logical ring topology - Messages are passed from one host to the next in a predetermined order until they hit the intended target. We can use this with both ring and star physical topologies
Logical star topology - Messages are sent directly to the intended target. We can only use this topology with a physical star topology