CCNA 2

Why do we have a network? A network is a collection of devices that can communicate together. A network is the fabric that ties business applications together. Networks are like roads. Roam was great because they built roads.
Personal computers connect to the network using a NIC (Network Interface Card). The cable that runs between the switch and the PC is an Ethernet cable. A switch allows local connectivity, or in other words, connects components in a LAN. Servers connected to the subnet provides applications and services.

A router is used for connecting multiple LANs. A router provides connectivity to the internet and other WAN services. Routers connect to the WAN through a serial interface. Buildings typically have WAN ports on the wall which the routers can connect to. The port is that stretched all the way to the central office (CO).

Clouds are typically used to describe the internet. The internet is a network of networks. No one owns the internet. Components in a cloud are typically not required to accurately describe a topology. The internet is ever changing and you will always have different throughput all the time.

You can buy a leased line which guarantees a level of service (determined by a SLA, which stands for Service Level Agreement). A dedicated leased line however costs a lot of money.

Applications that use the network include:
-Web browser and FTP
-Database Applications
-Instant Messenger
-Email
-Online Games

Within a company, you can have an intranet. Intranet refers to an internet-like environment that is internal to a company.

A byte is 8 bits, and a kilobyte is 1024 bytes. A megabyte is 1024 kilobytes and a gigabyte is 1024 megabytes. Each byte is typically a clear-text character.

Speed in a network is measured in bits, kilobits and megabits. Capitalization of the "b" character is done to differentiate megabyte (MB) and megabits (Mb). In certain environments, a kilobyte may be 1000 bytes. In this case, 1024 bytes is denoted as a kibibyte (KiB).

The effective data throughput is determined by the slowest link in the connection. Bandwidth, however, is just one of the three factors that determine link quality. Two other factors are delay (latency, jitter (variable-latency)) and availability.

Applications have very specific delay requirements are online gaming and VoIP. Applications that can tolerate delay but requires bandwidth are FTP file transfer and web surfing. All applications are sensitive to availability issues.

A bus topology refers to a typically thinnet network. Thinnet networks make use of coaxial cables bunched together known as a thicknet. In a ring topology, all devices are connect together in a ring. Protocols such as Token Ring or Fiber Distributed Data Interface (FDDI, pronounced as "Fiddy") make use of the ring topology. The most popular topology is the star topology where all devices connect to either a hub or a switch.

Modern network topologies are a hybrid of multiple network topologies. You can have switches connected in a ring, and devices connected to the switch like a star.