Coaxial and Optical Fiber Transmission Quiz

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Questions and Answers

What are the main factors limiting the performance of coaxial cables?

Performance is limited by attenuation and noise.

How do digital signals affect the placement of repeaters in coaxial cable transmission?

For digital signals, a repeater is needed every 1 km, with closer placement for higher data rates.

List two advantages of using coaxial cables over twisted pair cables.

Coaxial cables resist EMI better and support higher bandwidths.

Describe the significance of total internal reflection in optical fiber transmission.

Total internal reflection allows light to be transmitted effectively along the fiber. Signup and view all the answers

What are some benefits of using optical fiber cables compared to coaxial cables?

Optical fibers offer greater capacity, lower attenuation, and electromagnetic isolation. Signup and view all the answers

What distinguishes multimode transmission in optical fibers?

Multimode transmission allows for multiple propagation paths, each with different path lengths. Signup and view all the answers

Explain the role of Light Emitting Diodes (LEDs) in optical fiber applications.

LEDs are cheaper, have a wider operating temperature range, and last longer. Signup and view all the answers

Identify one disadvantage of coaxial cables.

Coaxial cables can be heavy, bulky, or expensive. Signup and view all the answers

What is the maximum length of a given Ethernet segment?

500 meters Signup and view all the answers

What are the speeds of the three main Ethernet versions mentioned?

10 Mbps for Original Ethernet, 100 Mbps for Fast Ethernet, and 1 Gbps for Gigabit Ethernet. Signup and view all the answers

Describe how sharing works on a traditional Ethernet.

Only one computer can transmit at a time while others must wait for the cable to be free. Signup and view all the answers

What does the frame header of an Ethernet packet contain?

The frame header contains the source address, destination address, and the frame type. Signup and view all the answers

How does the 64-bit preamble in an Ethernet frame function?

It allows the receiver's hardware to synchronize with the incoming signal. Signup and view all the answers

Explain the purpose of the 'payload' in an Ethernet frame.

The payload carries the actual data being sent in the packet. Signup and view all the answers

What is the significance of a 48-bit static addressing scheme in Ethernet?

It ensures that each device on the network has a unique identifier. Signup and view all the answers

What must occur for an adapter to pass data in the frame to the net-layer protocol?

The adapter must receive a frame with a matching destination address or a broadcast address. Signup and view all the answers

What impact does signal spreading have on data transmission rates in fiber optics?

Signal spreading limits the rate at which data can be accurately received. Signup and view all the answers

List one advantage and one disadvantage of fiber optic cables.

An advantage is their immunity to interference, and a disadvantage is the high cost of network interfaces. Signup and view all the answers

Define what a protocol is in the context of network communication.

A protocol is a set of rules that defines the format, order, and actions taken for messages sent and received among network entities. Signup and view all the answers

Why are protocols essential for Internet communication?

Protocols govern all communication activities in the Internet, ensuring consistency and reliability in data exchange. Signup and view all the answers

What role does Ethernet play in LAN technology?

Ethernet is a widely used network technology that employs bus topology for local area networks (LANs). Signup and view all the answers

Explain one reason why fiber optic connections require high-precision manufacturing.

High-precision manufacturing is necessary to ensure proper alignment and handling, which affects the performance of fiber optic connections. Signup and view all the answers

What is a bus topology in relation to local network structures?

A bus topology is a network configuration where all devices share a single communication line or cable. Signup and view all the answers

Describe the collaborative effort behind the development of the Ethernet standard.

The Ethernet standard was developed through collaboration among Digital Equipment Corporation, Intel Corporation, and Xerox Corporation. Signup and view all the answers

What are the main benefits of using twisted pair cables in LAN technologies?

Twisted pair cables are less expensive, easier to work with, and commonly used for both analog and digital signals. Signup and view all the answers

Explain the impact of twisting in twisted pair cables.

The twisting of the wires reduces crosstalk interference between adjacent pairs in the cable. Signup and view all the answers

What is the maximum distance for analog signaling using twisted pair cables?

Analog signaling requires amplifiers every 5 km to 6 km due to limited distance capabilities. Signup and view all the answers

List three disadvantages of unshielded twisted pair (UTP) cables.

UTP cables are sensitive to electromagnetic interference, unsuitable for very high-speed data transmission, and subject to stability issues in new networking standards. Signup and view all the answers

What is the data-carrying capacity of Category 5 UTP cables?

Category 5 UTP cables support LAN technologies such as 100 Mbps Ethernet. Signup and view all the answers

How often do digital twisted pair cables require repeaters?

Digital twisted pair cables need a repeater every 2-3 km for reliable transmission. Signup and view all the answers

What challenges are associated with twisted pair cables in high-speed applications?

Twisted pair cables are unsuitable for very high-speed data transmissions and are susceptible to interference and eavesdropping. Signup and view all the answers

What types of applications are supported by Category 2 UTP cables?

Category 2 UTP cables support Integrated Services and Digital Network (ISDN) and medium-speed data applications. Signup and view all the answers

What does CSMA/CD stand for and how does it help in reducing channel wastage?

CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. It reduces channel wastage by detecting collisions quickly and aborting the colliding transmissions. Signup and view all the answers

Explain why collisions may still occur in a CSMA protocol despite carrier sensing.

Collisions can occur due to the spatial layout of nodes and propagation delays, which may prevent two nodes from hearing each other's transmissions that just started. Signup and view all the answers

Describe the role of a computer in a CSMA network when attempting to transmit data.

In a CSMA network, a computer checks for the presence of a carrier wave; if none is detected (idle), it transmits a frame, otherwise, it waits for the channel to become free. Signup and view all the answers

What happens after a NIC aborts a transmission due to a collision in CSMA/CD?

After a NIC aborts a transmission due to a collision, it engages in binary exponential backoff where it randomly selects a wait time before retrying. Signup and view all the answers

How does the binary exponential backoff algorithm work in CSMA/CD environments?

The binary exponential backoff algorithm chooses a random value K from the set {0, 1, 2, ..., 2^m-1} after the mth collision, where m indicates the number of collisions encountered. Signup and view all the answers

What controls access to the network in a Token Bus network?

A token must be obtained to control access to the network. Signup and view all the answers

Explain the process of how a station sends a frame in a Token Ring (802.5) network.

The station waits for the token, sends its data frame if the token is free, and keeps the token until the frame has circled back. Signup and view all the answers

What happens when a frame reaches its intended recipient in a Token Ring network?

The recipient copies the frame and changes 4 bits in the last byte to indicate it has recognized and copied the frame. Signup and view all the answers

Describe what occurs when a token is released in a Token Ring network.

The next station on the ring with data to send has the right to take control of the ring. Signup and view all the answers

How can a station with a higher priority influence data transmission in a Token Ring network?

A station with a higher priority can remove a lower priority reservation and insert its own priority code. Signup and view all the answers

What is the role of the priority code in the access control (AC) field?

The priority code allows a waiting station to reserve the next open token based on its urgency. Signup and view all the answers

What unique feature does the Token Ring (802.5) have regarding frame recognition?

The sender examines the address-recognized bits to confirm if their frame was received successfully. Signup and view all the answers

In a Token Ring network, what prevents a station from transmitting more than one frame during its turn?

The station sets a bit in its NIC indicating it has sent data, allowing only one frame to be transmitted. Signup and view all the answers

Study Notes

Transmission Medium & LAN Technologies - Lecture 3

The lecture focuses on LAN wiring, hardware components, medium sharing, and LAN protocols.
The objectives are to discuss LAN wiring, identify major hardware components, how the medium is shared among devices, and LAN protocol operations.
The lecture covers guided transmission media, specifically twisted pair and coaxial cable. Also, it discusses optical fiber.
Lastly, it introduces LAN technologies like Ethernet. Specific standards, including Ethernet, token bus, token ring, and DQDB, are included.
The lecture also describes random access protocols like CSMA/CD.

Twisted Pair

Twisted pair consists of two insulated copper wires twisted in a spiral pattern.
The twisted pair acts as a single communication link, reducing crosstalk.
Twisted pair is usually installed in buildings during construction due to ease of work.
Analog signals need amplifiers every 5 km to 6 km. Digital signals need repeaters every 2–3 km.
Twisted pair has limited distance and bandwidth (1 MHz for analog point-to-point signaling).
Higher data rates are possible for short distances (up to 10 Gbps).
Susceptible to interference and noise (EMI).

Twisted Pair - Transmission Characteristics

Analog signals require amplifiers every 5–6 km.
Digital signals require repeaters every 2–3 km.
Limited distance, Bandwidth (1 MHz for analog point-to-point signaling).
High data rates possible for very short distances (up to 10 Gbps).
Susceptible to interference and noise.

Advantages and Disadvantages of Twisted Pair

Advantages: Common guided medium for analog and digital signals, commonly used in telephone networks, less expensive, and easier to work with.
Disadvantages: Sensitive to EMI and eavesdropping (especially unshielded), unsuitable for very high-speed data transmission, and some standards are unstable.

Unshielded Twisted Pair (UTP) & Categories

UTP cable is rated by its data-carrying capacity.
Category 1: Analog and digital voice (telephone), low-speed data.
Category 2: Integrated Services Digital Network (ISDN) and medium-speed data.
Category 3: High-speed data, LAN traffic (up to 10 Mbps).
Category 4: LAN traffic (up to 16 Mbps).
Category 5: LAN technologies like 100 Mbps Ethernet.
Category 6: LAN technologies like 10 Gbps Ethernet.

Coaxial Cable

Structure: Central copper core, insulating material, braided outer conductor, protective plastic covering.
Superior frequency characteristics than twisted pair (performance limited by attenuation/noise).
Analog signals require amplifiers every few kilometers. Better performance with increased frequency.
Digital signals require repeaters every kilometer. Better data rates supported via higher-frequency transmission.
High bandwidth possible.
More resistant to EMI than twisted pair.
Heavier, bulkier, potentially more expensive than twisted pair.

Coaxial Cable - Advantages and Disadvantages

Advantages: Mature technology/standards leading to compatibility, better EMI resistance than twisted pair, higher bandwidths than twisted pair, sturdy/resists rough treatment.
Disadvantages: Susceptible to EMI and eavesdropping like twisted pair, sometimes heavy, bulky, or expensive.

Optical Fiber

Structure: Glass or plastic core surrounded by cladding, specially designed jacket. Small size and weight.
Light transmission: Uses total internal reflection to transmit light. Light at less than critical angle is absorbed in jacket.
Benefits: High capacity (hundreds of Gbps over tens of km), lower attenuation, electromagnetic isolation, greater repeater spacing (tens of kilometers), and smaller size and weight..
Transmission characteristics: Uses total internal reflection to transmit light, effective wave guide (1014–1015 Hz). Supports infrared and visible light spectrums. Various light sources possible.
Light sources (e.g., Light Emitting Diodes (LEDs) and Injection Laser Diodes (ILDs))
Transmission modes: Step-index multimode, Graded-index multimode, and Single mode.

Optical Fiber - Advantages and Disadvantages

Advantages: Immune to interference/eavesdropping, higher bandwidths possible, smaller/lighter than other options.
Disadvantages: Network interfaces and cables relatively expensive, connections require precision manufacturing and careful handling, relatively complex to configure/install.

LAN Technologies

Ethernet (IEEE 802.3): Well-known/widely used technology, employs bus topology, invented at Xerox in the early 1970s. DEC, Intel, and Xerox created a production standard.
Ethernet standards: Original Ethernet (10 Mbps), Fast Ethernet (100 Mbps), Gigabit Ethernet (1 Gbps). Uses Carrier Sense Multiple Access/Collision Detection (CSMA/CD).
Sharing on Ethernet: Sending computer has exclusive use of cable during transmission. Other computers wait.
Ethernet frame format: Preamble, destination address, source address, type, data, and CRC. Fields have specific sizes in bits. The Ethernet frame begins with a 64-bit preamble, containing alternating 1s and 0s which allows receiving hardware to synchronize with the incoming signal. 16 bit field of header specifies the type. 48-bit static addressing scheme used. Addresses are 6 bytes. Adapters receive frame w/ matching address. Otherwise, it discards frame. Checks whether it matches broadcast address, forwards data for net-layer protocol. Checks the Frame type. CRC checked at receiver.

Protocol definition

Protocols define the format, order, of messages sent and received among network entities, and actions on msg transmission, receipt. Protocols define standards for computer network communications.

Access Networks

Frequency Division Multiplexing (FDM): Different channels transmitted in different frequency bands for Cable-based access.

Random Access Protocols

When a node has a packet to send, it transmits at full channel data rate (R) without coordination.
Two or more transmitting nodes lead to a "collision."
Protocols defining the how to detect collisions and recover via delayed retransmissions:
CSMA
CSMA/CD
CSMA/CA

CSMA (Carrier Sense Multiple Access)

Simple CSMA: Listen before transmitting, transmit if idle, defer transmission if busy.
Human analogy: Don't interrupt others.

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

Collisions detected within a short time.
Colliding transmissions aborted, reduces channel wastage.
Collision detection easy in wired, difficult in wireless.
Human analogy: The polite conversationalist.

CSMA: Collisions

Collisions may still happen despite carrier sensing due to propagation delays.
Two nodes might not hear each other starting transmission.
Collision wastes the entire transmission time.
Distance and propagation delay determine collision probability.

Carrier Sense On Multi-Access (CSMA) Algorithm

Ethernet lacks a centralized controller. Check whether the cable is currently in use.
If the cable is idle, transmit a frame.
If the cable is busy, wait for the sender to finish.
All computers attached to an Ethernet participate in a distributed coordination scheme.

Collision Detection (CD)

Collision is interference/mixture of transmission signals.
Monitoring a cable during transmission is collision detection (CD).
Collision prevents a correct reception of either frame in a garbled transmission.
CSMA/CD reduces time lost due to collisions. Sending stations immediately stop transmission when a collision is detected.

Binary Exponential Backoff with CSMA/CD

To avoid collisions, delay after collision, retransmit after random delay.
Max delay (d): computer selects random delay less than d.
To avoid a collision sequence, stations double the delay range after each collision.
Random delay between 0 and d (1st collision), 0 and 2d (2nd collision), and so on. Larger range for a few collisions makes the process more random. The range from which to select a random value gets larger after a few collisions.

Binary Exponential Backoff

Stations resend when they collide.
Mean random delay doubles up to 10 attempts.
Remains same for 6 further attempts.
After 16 failed attempts, station gives up and reports the error. A 1-persistent algorithm with binary exponential backoff which is efficient over a wide range of loads.

Why does CSMA/CD use a random delay?

Randomization prevents multiple stations from transmitting simultaneously, leading to potential collisions.
The protocol defines a maximum delay and a random delay less than it for each station after a collision. In most cases, when two stations choose a random value, the station with the smallest delay will proceed to send and the network will return to normal operation.

Token Bus (IEEE 802.4)

A token ring operates as a single shared medium.
To send, a device must wait for permission (a token).
Once permission is granted, it controls the ring.
As it transmits a frame, the bits pass around the ring.
A frame is copied and forwarded to other stations, until it reaches the intended destination.
The originating station receives a copy to confirm reception.

Token Passing in Token Ring (802.5)

Token rings use a token to regulate transmission, and the stations wait for turn (token) to communicate.
The token passes around the ring, and a station will wait for the token to become available before sending.
A three-byte token is sent whenever the network is inactive.
The station receiving data will make a copy, and checks for errors before sending a confirmation back to the sender.

Priority and Reservation

After token release, next station with data to send takes control of the ring.
Busy token can be reserved by waiting stations regardless of their position on the ring.
Each station has a priority code.
Higher priority stations can remove lower priority reservations, and equal priority stations use a first-come, first-serve approach.

References

Comer, Douglas E. Computer Networks and Internets. Prentice Hall, 3rd ed.
Comer, Douglas E. Computer Networks and Internets. Prentice Hall, 4th ed.
Stallings, William. Data and Computer Communications. 8th ed.

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Description

Test your knowledge on coaxial and optical fiber cables, including their advantages, disadvantages, and performance factors. This quiz covers aspects of digital signals, Ethernet standards, and the role of Light Emitting Diodes in fiber applications. Enhance your understanding of how these technologies function and their significance in modern communication.