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Network Access

35 important questions on Network Access

What is a physical connection?

A physical connection can be a wired connection using a cable or a wireless connection using radio waves.

What is a wired network?

For example, in many corporate offices employees have desktop or laptop computers that are physically connected, via cable, to a shared switch. This type of setup is a wired network. Data is transmitted through a physical cable.

What is an integrated service router (ISRs)?

ISRs offer a switching component with multiple ports, allowing multiple devices to be connected to the local area network (LAN) using cables, as shown in Figure 2. Additionally, many ISRs also include an AP, which allows wireless devices to connect as well.

What is a NIC?

Network Interface Cards (NICs) connect a device to the network. Ethernet NICs are used for a wired connection, as shown in Figure 1, whereas WLAN (Wireless Local Area Network) NICs are used for wireless. An end-user device may include one or both types of NICs.

Explain the diffrence in peformance between a wired and a wireless connection.

All wireless devices must share access to the airwaves connecting to the wireless access point. This means slower network performance may occur as more wireless devices access the network simultaneously. A wired device does not need to share its access to the network with other devices. Each wired device has a separate communications channel over its Ethernet cable. This is important when considering some applications, such as online gaming, streaming video, and video conferencing, which require more dedicated bandwidth than other applications.

Explain the OSI physical layer.

The OSI physical layer provides the means to transport the bits that make up a data link layer frame across the network media. This layer accepts a complete frame from the data link layer and encodes it as a series of signals that are transmitted onto the local media. The encoded bits that comprise a frame are received by either an end device or an intermediate device.

Explain the process that data undergoes from a source node to a destination node.

The user data is segmented by the transport layer, placed into packets by the network layer, and further encapsulated into frames by the data link layer.

The physical layer encodes the frames and creates the electrical, optical, or radio wave signals that represent the bits in each frame.

These signals are then sent on the media, one at a time.

The destination node physical layer retrieves these individual signals from the media, restores them to their bit representations, and passes the bits up to the data link layer as a complete frame.

Name the three basic forms of network media.

Copper cable: The signals are patterns of electrical pulses.

Fiber-optic cable: The signals are patterns of light.

Wireless: The signals are patterns of microwave transmissions.

The physical layer standards address three functional areas: Physical components

The physical components are the electronic hardware devices, media, and other connectors that transmit and carry the signals to represent the bits. Hardware components such as NICs, interfaces and connectors, cable materials, and cable designs are all specified in standards associated with the physical layer. The various ports and interfaces on a Cisco 1941 router are also examples of physical components with specific connectors and pinouts resulting from standards.

The physical layer standards address three functional areas: Encoding

Encoding or line encoding is a method of converting a stream of data bits into a predefined "code”. Codes are groupings of bits used to provide a predictable pattern that can be recognized by both the sender and the receiver. In the case of networking, encoding is a pattern of voltage or current used to represent bits; the 0s and 1s.

The physical layer standards address three functional areas: Signaling

The physical layer must generate the electrical, optical, or wireless signals that represent the "1" and "0" on the media. The method of representing the bits is called the signaling method. The physical layer standards must define what type of signal represents a "1" and what type of signal represents a "0". This can be as simple as a change in the level of an electrical signal or optical pulse. For example, a long pulse might represent a 1 whereas a short pulse represents a 0.

What determines the bandwidth of a network?

The properties of the physical media

The technologies chosen for signaling and detecting network signals

What factors influence throughput?

The amount of traffic

The type of traffic

The latency created by the number of network devices encountered between source and destination

Why would copper media be used?

Networks use copper media because it is inexpensive, easy to install, and has low resistance to electrical current. However, copper media is limited by distance and signal interference.

What is signal attenuation (copper media)?

The longer the signal travels, the more it deteriorates. This is referred to as signal attenuation.

What can be done to counter the negative effects of EMI and RFI?

To counter the negative effects of EMI and RFI, some types of copper cables are wrapped in metallic shielding and require proper grounding connections.

What can be done to counter the negative effects of crosstalk?

To counter the negative effects of crosstalk, some types of copper cables have opposing circuit wire pairs twisted together, which effectively cancels the crosstalk.

What are the three main types of copper media used in networking?

Unshielded Twisted-Pair (UTP)

Shielded Twisted-Pair (STP)

Coaxial

Explain the Unschielded Twisted-Pair Cable.

Unshielded twisted-pair (UTP) cabling is the most common networking media. UTP cabling, terminated with RJ-45 connectors, is used for interconnecting network hosts with intermediate networking devices, such as switches and routers.

In LANs, UTP cable consists of four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath that protects from minor physical damage. The twisting of wires helps protect against signal interference from other wires.

Explain the Shielded Twisted-Pair Cable

Shielded twisted-pair (STP) provides better noise protection than UTP cabling. However, compared to UTP cable, STP cable is significantly more expensive and difficult to install. Like UTP cable, STP uses an RJ-45 connector.
STP cables combine the techniques of shielding to counter EMI and RFI, and wire twisting to counter crosstalk. To gain the full benefit of the shielding, STP cables are terminated with special shielded STP data connectors. If the cable is improperly grounded, the shield may act as an antenna and pick up unwanted signals.

The following are the main cable types that are obtained by using specific wiring conventions(UTP cable):

Ethernet Straight-through: The most common type of networking cable. It is commonly used to interconnect a host to a switch and a switch to a router.

Ethernet Crossover: A cable used to interconnect similar devices. For example to connect a switch to a switch, a host to a host, or a router to a router.

Rollover: A Cisco proprietary cable used to connect a workstation to a router or switch console port.

Light pulses representing the transmitted data as bits on the media are generated by either:

Lasers

Light emitting diodes (LEDs)

In general, a wireless LAN requires the following network devices:

Wireless Access Point (AP): Concentrates the wireless signals from users and connects to the existing copper-based network infrastructure, such as Ethernet. Home and small business wireless routers integrate the functions of a router, switch, and access point into one device as shown in the figure.

Wireless NIC adapters: Provide wireless communication capability to each network host.

What is the Data link layer of the OSI model (Layer 2) responsible for (7)?

Allowing the upper layers to access the media

Accepting Layer 3 packets and packaging them into frames

Preparing network data for the physical network

Controlling how data is placed and received on the media

Exchanging frames between nodes over a physical network media, such as UTP or fiber-optic

Receiving and directing packets to an upper layer protocol

Performing error detection

What is a node?

The Layer 2 notation for network devices connected to a common media is called a node. Nodes build and forward frames. As shown in Figure 2, the OSI data link layer is responsible for the exchange of Ethernet frames between source and destination nodes over a physical network media.

The data link layer is divided into two sublayers:

Logical Link Control (LLC) - This upper sublayer communicates with the network layer. It places information in the frame that identifies which network layer protocol is being used for the frame. This information allows multiple Layer 3 protocols, such as IPv4 and IPv6, to utilize the same network interface and media.

Media Access Control (MAC) - This lower sublayer defines the media access processes performed by the hardware. It provides data link layer addressing and access to various network technologies.

Explain what happens to provide access to media?

Router interfaces encapsulate the packet into the appropriate frame, and a suitable media access control method is used to access each link. In any given exchange of network layer packets, there may be numerous data link layers and media transitions.
At each hop along the path, a router:

Accepts a frame from a medium

De-encapsulates the frame

Re-encapsulates the packet into a new frame

Forwards the new frame appropriate to the medium of that segment of the physical network

WANs are commonly interconnected using the following physical topologies:

Point-to-Point - This is the simplest topology that consists of a permanent link between two endpoints. For this reason, this is a very popular WAN topology.

Hub and Spoke - A WAN version of the star topology in which a central site interconnects branch sites using point-to-point links.

Mesh - This topology provides high availability, but requires that every end system be interconnected to every other system. Therefore, the administrative and physical costs can be significant. Each link is essentially a point-to-point link to the other node.

What is a physical Point-to-Point Topology?

Physical point-to-point topologies directly connect two nodes.

What is Logical Point-to-Point Topology?

The end nodes communicating in a point-to-point network can be physically connected via a number of intermediate devices. However, the use of physical devices in the network does not affect the logical topology.

What is a multi-access network?

Some network topologies share a common medium with multiple nodes. These are called multi-access networks. Ethernet LANs and WLANs are examples of a multi-access network. At any one time, there may be a number of devices attempting to send and receive data using the same network media.
Some multi-access networks require rules to govern how devices share the physical media.

What do data link protocols do?

Data link layer protocols add a trailer to the end of each frame. The trailer is used to determine if the frame arrived without error. This process is called error detection and is accomplished by placing a logical or mathematical summary of the bits that comprise the frame in the trailer. Error detection is added at the data link layer because the signals on the media could be subject to interference, distortion, or loss that would substantially change the bit values that those signals represent.

What does a transmitting node do?

A transmitting node creates a logical summary of the contents of the frame, known as the cyclic redundancy check (CRC) value. This value is placed in the Frame Check Sequence (FCS) field to represent the contents of the frame. In the Ethernet trailer, the FCS provides a method for the receiving node to determine whether the frame experienced transmission errors.

What does the data link layer do?

The data link layer provides addressing that is used in transporting a frame across a shared local media. Device addresses at this layer are referred to as physical addresses. Data link layer addressing is contained within the frame header and specifies the frame destination node on the local network. The frame header may also contain the source address of the frame.

Name five data link layer protocols:

Ethernet

802.11 Wireless

Point-to-Point Protocol (PPP)

HDLC

Frame Relay

The question on the page originate from the summary of the following study material:

CCNA 1

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