Electronic Cables, Network Topologies, and Internet Protocols: A Comprehensive Guide

Posted on Aug 13, 2024 in Computers

– The most important characteristics in an electronic cable are the following ones: impedance, attenuation, and capacitance. Could you describe them?

Impedance: The resistance to the movement of electrons in an AC circuit. It is represented by the letter Z. Like resistance, its unit of measurement is the ohm, represented by Omega.

Attenuation: Refers to the resistance to the flow of electrons, and why a signal becomes degraded (to fade away) as it travels along the conduit. Its unit of measurement is the db/m.

Capacitance: How much energy it is hold in the cable. It is represented by the letter C and its unit of measurement is the picofarads pF.

– Give a physical description of the following cables: twisted pair, coaxial, and optical fiber. Explain the role of each material.

Twisted pair: It consists of four pairs of thin wires. The wire pairs are twisted for two reasons. First, to provide protection against crosstalk, which is the noise generated by adjacent pairs of wires. Second, network data is sent using two wires in a twisted pair. One copy of the data is sent on each wire, and two copies are mirror images of each other. If the two wires are twisted together, noise seen on one wire is also seen on the other wire. There are: UTP (the most popular because it is more flexible) and STP (for long distance).

Coaxial cable: It has four parts:

• -At the centre of the cable is a solid copper wire core (kernel) whose role is to transmit data.
• -Surrounding that conductor is a layer of flexible plastic insulation.
• -A woven copper braid shield is wrapped around the insulation. It helps to reduce the amount of outside interference.
• -Covering this shield is the PVC jacket, to protect from water, hits…

Fiber-Optic cable:

• -The core is the light transmission element at the centre, and all the light signals travel through the core. This core is made from silica and other elements.
• -The cladding. Light rays traveling through the fiber core reflect off this core-to-cladding interface where the core and cladding meet.
• -Buffer material, usually plastic, that helps shield the core and cladding from damage. The material used is often Kevlar.
• -The outer jacket, protects the fiber against abrasions, solvents, and other contaminants.

– What is the difference between UTP and STP? Any consequence? The difference between UnshieldTP and ShieldTP is the shielding. The shielding reduces electrical noise. This noise reduction provides a major advantage of STP over unshielded cable. However, shielded cable is more difficult to install than unshielded cable because the metallic shielding needs to be grounded. The insulation and shielding considerably increase the size, weight, and cost of the cable. Despite these disadvantages, shielded copper cable is still used.

– When crimping RJ-45 UTP cables, how can you create straight-through and crossover cables? Describe some situations in which they are used.

Crossover cables provide a network connection between two similar devices, such as computer to computer or switch to router. It directly connects two network devices of the same type to each other over Ethernet. Crossover cables are commonly used when temporarily networking two devices in situations where a network router, switch, or hub is not present. Crossover cables have the 1st and 3rd wires crossed, and the 2nd and 6th wires crossed.

Straight-through cable: When using the straight-through cable, the transmit pins of the workstation will connect to the receive pins on the switch allowing data to be sent. The receive pins on the workstation are connected to the transmit pins on the switch via straight through cable, allowing the workstation to receive data.

Loopback cable: A loopback cable redirects the output back into itself. This effectively gives the NIC the impression that it is communicating on a network, since it’s able to transmit and receive communications.

-What is the difference between single-mode and multimode fiber-optic cable?The part of an optical fiber through which light rays travel is called the core of the fiber. Light rays cannot enter the core of an optical fiber at all angles. The rays can enter the core only if their angle is inside the fiber’s numerical aperture. These optical paths are called modes. If the diameter of a fiber’s core is large enough so that many paths exist that light can take as it passes through the fiber, it is called multimode fiber. Single-mode fiber has a much smaller core that allows light rays to travel along only one path (one mode) inside the fiber.

– Describe the basic types of networks as far as their size is concerned: PAN, LAN, CAN, MAN, and WAN. Give some examples. From smaller to bigger range:

• PAN: Personal Area Network. Bluetooth, for example, creates a PAN. Range: 10m.
• LAN: Local Area Network. Range: from a room to a building. 100m
• CAN: Campus Area Network (universities, hospitals, military stations). Connects different LANs. Range: 2km.
• MAN: Metropolitan Area Network. Cities. Business. “Headquarters”. For example, it provides access to the headquarters from the Factory, the warehouse, the offices, etc. Range: 10km.
• WAN: Wide Area Network. Connects around the world. Range: 1000km.

– Compare simplex, half-duplex, and full-duplex transmissions.

• Simplex: The capability of transmission is only one direction between a sending station and a receiving station. Broadcast television is an example of a simplex technology.
• Half-duplex: A capability for data transmission in only one direction at a time between a sending station and receiving station.
• Full-duplex: The capability for simultaneous data transmission between a sending station and receiving station.

– Data are delivered by means of packets in a network. Provide a technical description of”packe”. Each piece of information transmitted on an Ethernet network is sent in a packet. A packet is a chunk of data enclosed in one or more wrappers. Three parts:

• HEADER: It contains instructions about the data carried in a packet.
• Length of packet: Is used to check if the packet arrived correctly. (The address can be IP or MAC)
• Packet number: Is used because you cannot receive the packets in order.
• Frame: Second layer (MAC)
• Packet: Third layer (sender’s and receivers IP address)
• PAYLOAD: Contains the amount of data which is determined by the protocol. The actual data that the packet is delivering to the destination.
• CRC (Cyclic Redundancy Check): Is used to hash function. It’s the most common error checking used in packets.

– Describe the OSI model.

We can describe the OSI model by its layers.

1. Application layer: Where the APIs are found. Applications call functions in the API to send network graphic.
2. Presentation layer: Converts the data from the Application layer to a form suitable for transmission over the network. TRANSLATION. FORMAT OF DATA.
3. Session layer: Controls communication between two applications. Creates a connection between two devices.
4. Transport layer: Ensures data arrives in the same order it was sent and it’s not duplicated. FRAGMENTATION. Unit: segments.
5. Network layer: Determines the path used to transfer the data over the network. ROUTING AND LOGICAL ADDRESSING.
6. Data link layer: Provides checking (the CRC value is created here) and groups bits into frames to be sent over the network. MAC addresses. Switches and bridges.
7. Physical layer: Sends the data over the network media to the party. Hubs and repeaters (relayers) belong to this one. Unit: bits.

– Compare the two main transport protocols (i.e. TCP and UDP). An advantage that UDP has over TCP is that, because it does not concentrate on establishing a connection, it can transmit more information in a smaller amount of time than TCP. TCP is useful for transmitting large amounts of data reliably, but with the penalty of large ACK overhead consuming bandwidth. UDP is useful for transmitting small amounts of data when reliability is less crucial, UDP lacks the overhead caused by ACKs.

Describe the following application protocols in TCP/IP: SMTP, POP3, IMAP4, FTP, HTTP, HTTPS, and DNS.

• SMTP: Simple Mail Transfer Protocol. It is used to send mails across a TCP/IP network.
• POP3: Post Office Protocol 3. It is an internet protocol used to read email over a TCP/IP network.
• IMAP4: Internet Message Access Protocol version 4. It is an alternative protocol used for reading email over a TCP/IP network. IMAP4 supports additional features not available using POP3, such as server-based folders for storing email.
• FTP: File Transfer Protocol. It is used to transfer files over a TCP/IP network.
• HTTP: Hypertext Transfer Protocol. It is used to deliver web pages from a web server to a web browser.
• HTTPS: Hypertext Transfer Protocol Secure. It is an internet protocol designed to deliver web pages in an encrypted format.
• DNS: Domain Name System. It is used to convert a fully qualified domain name to an IP address.

– Describe the following Internet protocols: ARP, RARP, ICMP, and IGMP.

• ARP: Determines the data link layer addresses for known IP addresses. ARP is used to bind (associate) the physical (MAC) addresses with a specific logical (IP) address. When the data packet is sent to a particular destination, ARP matches the addressing information against the ARP cache for the appropriate MAC address. If no matches are made, ARP sends a broadcast message on the network looking for the particular destination. A host responds with the correct address and sends a reply to ARP.
• RARP: (Reverse address Resolution Protocol) Determines the network addresses when data link layer addresses are known. A protocol in TCP/IP stack that provides a method for finding IP addresses based on MAC addresses.
• ICMP: Internet Control Message Protocol is a network layer protocol that reports errors. When datagram delivery errors occur, ICMP reports these errors to the sender of the datagram. ICMP does not correct the encountered network problem.
• IGMP: The Internet Group Management Protocol (IGMP) is a communications protocol used by hosts and adjacent routers on IP networks to establish multicast group memberships.

– Compare the role and format of IP addresses and MAC addresses.

Although IP works in a network layer and MAC works in a physical layer, the role is the same: to identify every device that connects to a network or LAN. The IP addresses are controlled by the AIANA (for instance in Spain) and the MAC addresses are controlled by the IEEE. The first is known as a software address and the last as a hardware address or physical address. The IP addresses are 4 bytes long and the MAC addresses are 6 bytes long.

– How and why can you ping an IP address? We will make a ping test when we want to know if we are connected to another device in the network. If the ping is successful, we can communicate with that device (send and receive data). To ping other devices, we need to know the IP address of the target, then we have to go to our computer console (cmd.exe in Windows). In the computer console, we have to type ping + IP address of the target. If the ping has been successful, we will see that we have received a response, but if the ping failed, we will see that it was impossible to reach the device.

– Compare subnet mask classes A, B, and C. How do they relate with IP addresses?The subnet mask indicates the network portion of an IP address. Usually, all hosts within a LAN use the same subnet mask.

• -255.0.0.0: Class A, which indicates that the first octet of the IP address is the network portion. You have up to two by 24 hosts possible.
• -255.255.0.0: Class B, which indicates that the first two octets of the IP address are the network portion. You have up to two by 16 hosts possible.
• -255.255.255.0: Class C, which indicates that the first three octets of the IP address are the network portion. You have up to two by 8 hosts possible.

– Describe in detail how TCP communication occurs: TCP 3-Way Handshake.

HANDSHAKE: Establishing a normal TCP connection requires three steps.

1. The first host (FH) sends the second host (SH) a”synchroniz” (SYN) message with its own sequence number, which the second host receives.
2. (SH) replies with a synchronize-acknowledgment (SYN-ACK) message with its own sequence number and acknowledgment number, which (FH) receives.
3. (FH) replies with an acknowledgment message with acknowledgment number, which (SH) receives, and doesn’t need to reply to.

– Describe the main physical topologies (e.g. bus, star, ring, and mesh) according to parameters such as cost, set-up, scalability, maintenance, and performance.

BUS: A bus topology connects all the devices using a single cable. The main cable segment must end with a terminator that absorbs the signal when it reaches the end of the line or wire. If there is no terminator, the electrical signal representing the data bounces back at the end of the wire, causing errors in the network.

STAR: Is made up of a central connection that is a device such as a switch. Although a star topology costs more to implement than the physical bus topology, the advantages of a star topology make it worth the additional cost. Because each host is connected to the central device with its own cable, when the cable has a problem, only that host is affected. However, if a central device fails, the whole network becomes disconnected.

RING: A topology in which hosts are connected in the form of a ring or circle. Unlike the physical bus topology, the ring topology has no beginning or end that needs to be terminated.

MESH: Connects all nodes to each other for redundancy and fault tolerance. The advantage is that every node is connected physically to every other node, which creates a redundant connection. If any link fails, information can flow through other links to reach its destination. The disadvantage is that for anything more than a small number of nodes, the amount of media for the links and the number of connections on the lines becomes overwhelming.

– Explain how communication takes place between two computers within an Ethernet network. Remember that Ethernet uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection).

1. A media-access mechanism wherein devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit.
2. If two devices transmit at once, a collision occurs and is detected by all colliding devices.
3. This collision subsequently delays retransmissions from those devices for some random length of time.
4. The retransmission delay when a collision occurs is called the backoff.

– Explain how communication takes place between two computers in a Token Ring network.

CSMA/CD logic helps prevent collisions and also defines how to act when a collision does occur. The CSMA/CD algorithm works like this:

1. A device with a frame to send listens until Ethernet is not busy.
2. When the Ethernet is not busy, the sender begins sending the frame.
3. The sender listens to make sure that no collision occurred.
4. Once the sender hears the collision, they each send a jamming signal, to ensure that all stations recognize the collision.
5. After the jamming is complete, each sender randomizes a timer and waits that long.
6. When each timer expires, the process starts over with Step 1.

– How do switches work? Describe some core functions such as learning, flooding, filtering, forwarding, and aging.

Switches work the same way as hubs, but they can identify the intended destination of the information that they receive, so they send that information to only the computers that are supposed to receive it. The functions are:

• Learning: It reads the MAC and saves it to the lookup table. Now the switch knows where to find the node. (Source MAC, segment, Port, Timestamp)
• Flooding: Send packet to all of the segments except by which it has arrived. The correct Node sends an acknowledgment to the source node.
• Filtering: When you have the lookup table complete, find the value MAC in the table.
• Forwarding: The source node consults the MAC of the target node into the switch table and then sends the packet directly.
• Aging: The switch has a user-configurable timer that erases the entry after a certain length of time with no activity from that node. This frees up available memory resources.

How does a switch work?

A hub can’t identify the source or intended destination of the information it receives, so it sends the information to all of the computers connected to it, including the one that sent it. A hub can send or receive information, but it can’t do both at the same time.

Describe the difference between static and dynamic routing.  

• Static routing: When an administrator has to provide the routes to the routers in a routing table and there are only those options. Routes are hard-coded.
• Dynamic routing: The router uses algorithms based on some parameters in order to find the best route for each packet. Protocol: RIP. Static is a stronger network. If a node disconnects, dynamic is better. For a very scalable network, we prefer the dynamic.

State some advantages and disadvantages between these two types of wireless data transmission media: infrared and radio frequency.

Laser requires line of sight. Receiver and transmitter must be one in front of each other. The range is shorter using laser. Light cannot go through solid objects.

Laser: one-to-one communication. RF: one-to-many communication.

The higher the frequency, the higher the data rate (data transfer or throughput), the lower the range.

Describe some terms such as “extension point”, “dead spot”, and “roaming” used in wireless networks.

• WAP: Wireless Access Point. Router. Connected to the wired network. 300m range
• Extension Point: Other Access Point BUT not connected to the internet. It’s a repeater (amplifies the signal). It’s connected to the WAP (wireless network). Their ranges must overlap. The overlapping must be at least 10%.
• Deadspot: A place inside the range which does not have any signal.
• Roaming: You can walk with your device and it connects (automatically) to more than one different WAP in the same network.

Explain how communication takes place between two computers with the CSMA/CA standard in wireless networks.

A carrier sensing is used, but nodes attempt to avoid collisions by transmitting only when the channel is sensed to be”idl”.

Compare 802.11 standards (a, b, and g) according to their frequency, channels, data rate, and other characteristics.

• 802.11b – 2.4GHz: This kind of frequency is more likely to (or prone to) have interferences. Data rate is higher.
• 802.11g – 2.4GHz: It’s backwards compatible with b because they emit in the same frequency. The throughput is larger (54Mbps). 3 clean channels.
• 802.11a – 5GHz: It is not so congested as b or g, then less interferences. Higher throughput. 12 clean channels. Shorter range and not backwards compatible. Better without obstacles.

Describe the step-by-step process to configure a WAP as an Extension Point.

1. Enter the CMD and type “ipconfig” and look for the “default gateway IP” (usually 192.168.1.1).
2. Type the WAP’s IP in your browser. Press Enter. You’ll get to a login interface. Usually, the user and password is “admin”. Log in.
3. You’ll get to a Settings interface.
4. Look for these settings: “SSID”, information about security, channel, frequency (b, g, n, a,…), IP mask (get it from the “ipconfig”).
5. Connect the laptop with the EP via your ethernet cable.
6. Set the IP to 192.168.1.2
7. Type this IP into the browser and paste the info copied in step 4. Use a different channel and IP address.

The main problem with radio frequency connection is interference. Bluetooth uses a technique called Frequency Hopping Spread Spectrum (FHSS) to avoid this problem. Describe this technique.

The device is hopping from one frequency to another. It uses a pseudo-random selection of frequencies. At the beginning, the frequencies are chosen randomly, but after that, this sequence is repeated. Thus, the possible interferences last such a short period of time that they are not perceptible. The distance between two different lines is the hop time. The dwell time is the length of the line. Increasing the dwell time is worse. Increasing the hop time is also worse.

ISDN uses the same UTP wiring as POTS, yet it can transmit data at much higher speeds. How?

In the beginning (BRI), the raw (theory max) throughput was 144Kbps. It used three channels (64, 64, and 16Kbps). Two B-channels (Bearer [to bear=to carry]) and one D-channel (Data). One B-channel is for voice and the other one is for data. Thus, you could talk and surf the internet at the same time. It is a symmetric technology. To increase the upstream and downstream, you had to bond the channels (“channel aggregation”). If you bond them, you would lose the phone line. NOWADAYS, we use PRI, which has 1 B-channel and 30 68Kbps B-channels.

What is the main problem for users of cable Internet?

This broadband service shares bandwidth between telephone and Internet of all customers of an area or neighbors are connected at the same demark. The data transfer is reduced as the users join to the service. The opposite is the ADSL service that it doesn’t share the bandwidth with the others.

Describe internal and external factors which can affect your Internet speed at home.

Inside your computer:

Outside your computer:

• • #Number of devices connected to the same AP.
  • #Damaged wires (bended,…).
  • #Loose connectors.
  • #The UTP category.
  • #Wire length.
  • #A wireless network.
  • #The AP firmware.
• • #Contention.
  • #Bad weather.
  • #Demarc and local loop physical problems.
  • #Distance between the demarc and the ISP and between the demarc and the user.

Describe the “Caesar cipher” formula when encrypting the plaintext “SECRET” when the key is 10.

Every letter has a number assigned from 0 to 26 (a to z respectively). You’ve got a key, and you have to add it to the number of each letter. It is a permutation algorithm.

If you know the position of the original character and the key, you can program this algorithm:

How do symmetric-key and public-key systems work?

A symmetric key is a shared key. This means that the sender and the receiver own the same key. It’s used for encryption and decryption.

An asymmetric pair key consists of a public key and a private key. A public key is sent to all the nodes in the network. The private key is possessed by the receiver’s node. The public key is used for encryption and the private for decryption.

Compare advantages and disadvantages between symmetric-key and public-key encryptions (e.g. security, speed, and number of keys).

Advantages and disadvantages:

• Security: The asymmetric-key is more secure because the private key is never sent across the network. The public key is less secure because the key is sent across the network and a hacker can intercept the key and decrypt the information.
• Speed: Symmetric encryption is faster because it uses simpler operations, such as XOR, on smaller numbers (64 or 128 bits). Asymmetric encryption usually uses complex mathematical operations, such as power and modulus, on very large numbers (2048 bits).
• Number of keys: Depending on what kind of key is used in encryption, it is necessary to assign a number of keys for a group of n people.

Explain how SSL establishes encrypted communication between a server and a client.

The server has an SSL certificate and a private key. The certificate contains information about the institution which releases the certificate, etc. AND a public key. The server sends the SSL certificate. The client takes the SSL certificate and takes the public key.

The browser now generates a symmetric key. Then sends the symmetric key encrypted with the public key. The server decrypts the symmetric key with the private key. Now they communicate using the symmetric key during the session.