Computer Network Fundamentals

Question 1

What is the purpose of networks?

Answer 1

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.

Question 2

Client

Answer 2

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.

Question 3

Server

Answer 3

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.

Question 4

Hub

Answer 4

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.

Question 5

Switch

Answer 5

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.

Question 6

Router

Answer 6

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.

Question 7

Media

Answer 7

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.

Question 8

WAN link

Answer 8

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.

Question 9

LAN

Answer 9

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)

Question 10

IEEE

Answer 10

IEEE stands for the Institue of Electrical and Electronics Engineers, and it is an internationally recognized standards body.

Question 11

WAN

Answer 11

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)

Question 12

WLAN

Answer 12

A local area network made up of wireless networking devices is a wireless local area network (WLAN).

Question 13

SAN

Answer 13

You can construct a high-speed, reliable network for the express purpose of transmitting stored data. This network is called a storage area network.

Question 14

CAN

Answer 14

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.

Question 15

MAN

Answer 15

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.

Question 16

PAN

Answer 16

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).

Question 17

Physical Topology

Answer 17

The way components are physically interconnected determines the physical topology.

Question 18

Logical Topology

Answer 18

The actual traffic flow decides the logical topology.

Question 19

Bus Topology

Answer 19

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.

Question 20

Ring Topology

Answer 20

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.

Question 21

Token Ring Network

Answer 21

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.

Question 22

Dual Ring Topology

Answer 22

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.

Question 23

Star Topology

Answer 23

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.

Question 24

Hun-and-Spoke Topology

Answer 24

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.

Question 25

Full Mesh Topology

Answer 25

A Full-Mesh topology directly connects every site to every other site. Because each site connects directly to every other site, an optimal path can be selected, as opposed to relaying traffic via another site. A Full-Mesh topology is highly fault-tolerant. multiple links in the topology could be lost, and every site might still be able to connect to every other site. The number for required WAN connections can be calculated with the formula n(n-1)/2.

Benefits:

• An optimal route exists between any two sites.
• High Fault Tolerance.
• Each link is independent of the other links making troubleshooting easy.

Drawbacks:
-A Full-Mesh network can be difficult and expensive to scale because the addition of one new site requires a new WAN link between the new site and every other existing site.

Question 26

Partial-Mesh Topology

Answer 26

A Partial-Mesh WAN topology is a hybrid of the hub-and-spoke and full-mesh topology. Specifically, a Partial-Mesh topology can be designed to offer an optimal route between selected sites while avoiding the expense of interconnecting every site to every other site. When designing a Partial-Mesh topology, a network designed must consider network traffic patterns and strategically add links interconnecting sites that have higher volume of traffic between themselves.

Benefits:

• Optimal routes between selected sites with higher intersite traffic volumes while avoiding the expense of interconnecting every site to every other site.
• More redundant that a hub-and-spoke topology.

Drawbacks:

• Less fault-tolerant than a full-mesh topology.
• More expensive than a hub-and-spoke topology.

Question 27

Ad Hoc Wireless Topology

Answer 27

The simplest of wireless topologies is the ad hoc wireless network. This means that the wireless nodes are in charge of sending and receiving traffic to each other, without the assistance of infrastructure devices, such as switches or access points. Some network engineers refer to the ad hoc topology as simply a wireless peer-to-peer (P2P) type of network.

Example:
Apple’s AirDrop.

Question 28

Infrastructure Wireless Topology

Answer 28

With the infrastructure topology, you have specialized wireless equipment for permitting wireless communications to take place. Many homes today feature a wireless local area network (WLAN). A wireless access point (WAP) allows the various computers (and other wireless devices) to communicate with each other through the WAP acting like a hub device. This WAP connects to the service provider (SP) of the home user with a wired connection.

Example:
-A coaxial cable could connect to the broadband cable service for high-speed Internet connectivity.

Question 29

Mesh Wireless Topology

Answer 29

A specific type of ad hoc wireless topology is the mesh. This topology is more sophisticated than the ad hoc in that specialized nodes help move the traffic throughout the topology. Note that these devices are not as fancy as the access points found in an infrastructure type of topology.

Question 30

Client/Server Networks

Answer 30

A client-server network, where a dedicated file server gives shared access to files, and a networked printer is available as a resource to the network’s clients. Commonly used by businesses because resources are found on one or more servers, administration is simpler than trying to administer network resources on multiple peer devices. However, client/server networks come with extra expense of dedicated server resources.

Benefits:

• Scales easily, additional client licenses.
• Administration is simplified, because parameters, such as file-sharing permissions and other security settings, can be administered on a server as opposed to multiple clients.

Drawbacks:

• The Single server can become a single point failure.
• Cost more than Peer-to-Peer networks.

Question 31

Peer-to-Peer Networks

Answer 31

Peer-to-Peer networks allow interconnected devices (for example, PCs) to share their resources with one another. Those resources could be files or printers. Peer-to-Peer networks are seen in smaller businesses and homes. The popularity of these peer-to-peer networks is fueled in part by client operating systems that support filed and print sharing. As the number of devices (that is, peers) increases, the administrative burden increases.

Benefits:

• Installed easily because resource sharing is made possible by the clients’ OS, and knowledge of advances NOSs is not required.
• Cost less than client/server networks.

Drawbacks:
Scalability is limited because of the increased administrative burden of managing multiple clients.
-The devices providing network resources might be performing other tasks not related to resource sharing (word processing). Less performance than client/server.