Computer Network Fundamentals Flashcards
- What is the purpose of a network? - What are some examples of network components? - How are networks defined by geography? - How are networks defined by topology? - How are networks defined by resource location? (31 cards)
What is the purpose of networks?
A network’s purpose is to make connections:
- File sharing between two computers.
- Video sharing between computers located in different parts of the world.
- Surfing the Web, and Instant Messaging between computers with IM software installed.
- Email.
- Voice over IP (VoIP), to replace traditional telephony systems.
Client
The term client defines the device an end user uses to access a network. This device might be a workstation, laptop, smartphones with wireless capabilities, or a variety of other end-user terminal devices.
Server
A server, as the name suggests, serves up resources to a network. These resources might include email access as given by an email server, web pages as offered by a web server, or files available on a file server.
Hub
A hub is an older technology that interconnects network components such as clients to servers. Hubs vary in their number of available ports. However, for scalability, you can interconnect hubs, up to a point. If you chain too many hubs together, network errors can result.
A hub is a LAYER 1 device. A hub receives traffic in a port ( that is, a receptacle to which a network cable connects) and repeats that traffic out all other ports. The hub is considered OBSOLETE for the LAN network.
Switch
Like a hub, a switch interconnects network components, and switches are available with a variety of port densities. A switch learns which devices live off of which ports. It does this by inspecting traffic that comes into the port (inbound) and recording the source address. It then looks at the destination address and, if the switch knows the destination address, it forwards the traffic out of the appropriate port, not out of all the other ports. A switch is a LAYER 2 device, which means that it makes forwarding decisions based on addresses that are physically burned into a Network Interface Card (NIC) installed in a host (that is, any device that transmits or receives traffic on a network). This burned-in address is a Media Access Control (MAC) address
NOTE: Today’s switches are capable of functioning at higher layers of the network model but are still mostly considered Layer 2 Devices.
Router
A Router is a LAYER 3 Device, which means that it makes its forwarding decisions based on logical network addresses. Most modern networks use Internet Protocol (IP) addressing. Therefore, most Routers know what logical IP networks live off which Router interfaces. Then, when traffic comes into a Router, the Router examines the destination IP address of the traffic and, based on the Router’s database of networks (that is, the routing table), it intelligently forwards the traffic out of the appropriate interface.
Media
The previously mentioned devices need to be interconnected via some sort of media. This media could be copper cabling. It could be a fiber-optic cable. Media might not even be cable, as is the case with wireless networks, where radio waves travel through the media of air.
WAN link
An interconnection between two devices in a Wide Area Network(WAN). Today, most networks connect to one or more other networks. For example, if your company has two locations, and those two locations are interconnected, via a Multiprotocol Label Switching (MPLS) network, the link that interconnects those networks is typically referred to as a Wide Area Network (WAN) link.
LAN
A LAN interconnects network components within a local area (for example: within a building).
Common LAN Technologies:
- Ethernet (IEEE 802.3)
- Wireless Networks (IEEE 802.11)
IEEE
IEEE stands for the Institue of Electrical and Electronics Engineers, and it is an internationally recognized standards body.
WAN
A WAN interconnects network components that are geographically separated. For example, a corporate headquarters might have multiple WAN connections to remote office sites.
Examples of WAN Technologies:
- Multiprotocol Label Switching (MPLS)
- Asynchronous Transfer Mode (ATM)
WLAN
A local area network made up of wireless networking devices is a wireless local area network (WLAN).
SAN
You can construct a high-speed, reliable network for the express purpose of transmitting stored data. This network is called a storage area network.
CAN
The university covered several square miles and had several dozen buildings. Within many of these buildings was a LAN. However, those building-centric LANs were interconnected. By these LANs being interconnected, another network type was created, a CAN. Besides an actual university campus, you might also find a CAN in an industrial park or business park.
MAN
More widespread than a CAN and less widespread than a WAN, a MAN interconnects locations scattered throughout a metropolitan area. One example of a MAN technology is Metro Ethernet, which features much higher speeds than the traditional WAN technologies that might have been used in the past to connect such locations. If a service provider could interconnect locations scattered across a metropolitan area using a high-speed network, such as a 10Gbps (that is, 10 billion bits per second) network, the interconnection of those locations would form a MAN.
PAN
A PAN is a network whose scale is even smaller than a LAN. The main distinction of a PAN, however, is that its range is typically limited to just a few meters.
Examples of PAN:
- A connection between a PC and a digital camera via a universal serial bus (USB).
- A PC connected to an external hard drive via a FireWire connection.
- A Bluetooth connection between your cell phone and your car’s audio system is considered a wireless PAN (WPAN).
Physical Topology
The way components are physically interconnected determines the physical topology.
Logical Topology
The actual traffic flow decides the logical topology.
Bus Topology
A bus topology typically uses a cable running through the area needing connectivity. Devices that need to connect to the network then tap into this nearby cable. Early Ethernet networks relied on bus topologies. A network tap might be in the form of a T connector or a vampire tap.
Benefits:
- Less cabling is required, compared to other topologies.
- Depending on the media a bus topology can be less expensive.
Downfalls:
- Potential single point failure.
- Troubleshooting can be difficult due to the inspection of multiple network taps.
- Adding devices can cause outages
- Not scalable
- An error on one device can affect all devices.
Ring Topology
A ring topology sends data, in a single direction, to each connected device in turn, until the intended destination receives the data. Because a ring topology allows devices on the ring to take turns transmitting on the ring, a connection for media access was not a problem, as it was for a bus topology. If a network had a single ring, however, the ring became a single point of failure. If the ring were broken at any point, the data would stop flowing.
Benefits:
- A dual ring adds a layer of fault tolerance.
- Simplified troubleshooting, due to the repeater on each device in a ring. Error is reported when the repeater on the far side of a cable does not receive any data within a certain time.
Downfalls:
-Single point failure.
Scalability Limitations, Max length, Max devices.
-A single ring may need to be divided into two interconnected rings when Max Scalability is reached.
Token Ring Network
Token Ring networks relied on a ring topology. Token Ring, however, was not the only popular ring-based topology in networks back in the 1990s.
Dual Ring Topology
Fiber Distributed Data Interface(FDDI) was another variant of a ring-based topology. Most FDDI networks (Which, as the name suggests, have fiber optics as the media) used not just one ring, but two. These two rings sent data in opposite directions, resulting in counter-rotating rings. One benefit of counter-rotating rings was that if a fiber broke, the stations on each side of the break could interconnect their two rings, resulting in a single ring capable of reaching all stations on the ring.
Star Topology
Star topology has a central point from which all attached devices radiate. In LANs, that centralized device was typically a hub back in the early 1990s. Modern networks, however, usually have a switch located at the center of the star. The star is the most popular physical LAN topology in use today, with an ethernet switch at the center of the star and unshielded twisted-pair (UTP) cable used to connect from the switch ports to the clients.
Benefits:
- A cable break only impacts the device connected via the broken cable and not the entire topology.
- Simplified troubleshooting because the central device in the star topology acts as the aggregation point of all the connected devices.
Drawbacks:
- Requires the most cabling, because each device has its own cable to connect back to the central device.
- Installation can take longer for a Star Topology because more cable runs that must be installed.
Hun-and-Spoke Topology
When interconnecting multiple sites (for example, multiple corporate locations) via WAN links, a hub-to-spoke topology has a WAN link from each remote site (that is, spoke site) to the main site (that is, the hub site) This approach is similar to the star topology used in LANs. Witch WAN links, a service provider is paid a recurring fee for each link. Therefore a hub-and-spoke topology helps minimize WAN expenses by not directly connecting any two spoke locations. If two spoke locations need to communicate between themselves, their communication is sent via the hub location.
Benefits:
- Reduced costs, minimal number of links used.
- Adding additional sites is easy because only one link needs to be added per site.
Drawback:
- Suboptimal routes must be used between remote sites because all intersite communication must travel via the main site.
- The hub site becomes a single point of failure.
- Because each remote site is reachable by only a single WAN link, there is no redundancy.
