Chapter no 1

 

2. Advantages of a Client-Server System Using a LAN

Compared to a large centralized timesharing system, a client-server model using a LAN offers the following advantages:

  • Improved Performance
    Each client has its own CPU and can perform many tasks locally. This reduces the load on the central server and results in faster response times for users.

  • Scalability and Flexibility
    It is easier to upgrade or add new clients without affecting the overall system. Services can be distributed across multiple servers (e.g., one for printing, another for files), which simplifies system management and increases reliability.

4. Additional QoS Parameter Needed Based on Traffic Type

Besides bandwidth and latency, different applications require specific Quality of Service (QoS) parameters:

  • (i) Digitized Voice Traffic – Jitter
    Jitter is the variation in arrival time of packets. High jitter can cause voice distortion or gaps during a conversation, affecting call quality.

  • (ii) Video Traffic – Packet Loss
    Packet loss leads to frame drops, video freezing, or degraded visual quality. Video applications require steady, continuous data flow.

  • (iii) Financial Transaction Traffic – Reliability and Integrity
    Transactions must be delivered accurately and in full. Even a small data error can lead to serious issues. Reliability ensures delivery, and integrity ensures that data is not altered in transit.

6. Best-Case Delay in a Satellite Network

In a satellite-based client-server system:

  • Satellite Height: 40,000 km above the Earth.

  • Speed of Light: ~300,000 km/s.

  • One-Way Propagation Delay:
    40,000 km300,000 km/s=0.133 seconds\frac{40,000 \, \text{km}}{300,000 \, \text{km/s}} = 0.133 \, \text{seconds}

  • Round-Trip Delay (RTT):
    0.133×2=0.266 seconds=266 milliseconds0.133 \times 2 = 0.266 \, \text{seconds} = 266 \, \text{milliseconds}

Conclusion: The best-case response delay is approximately 266 milliseconds for a single round-trip signal transmission.

8. Time Required to Inspect All Topologies Between 5 Routers

  • Possible Connections:
    Between 5 routers, there are 5×(5−1)2=10\frac{5 \times (5 - 1)}{2} = 10 possible pairs.

  • Choices per Pair:
    Each pair can have one of 4 possibilities: high-speed line, medium-speed line, low-speed line, or no line.

  • Total Topologies:
    410=1,048,5764^{10} = 1,048,576 possible topologies.

  • Time Per Topology:
    100 milliseconds.

  • Total Time:
    1,048,576×100 ms=104,857,600 ms=104,857.6 seconds1,048,576 \times 100 \, \text{ms} = 104,857,600 \, \text{ms} = 104,857.6 \, \text{seconds}

  • Converted to Hours:
    104,857.63600≈29.13 hours\frac{104,857.6}{3600} \approx 29.13 \, \text{hours}

Conclusion: It would take approximately 29.13 hours to inspect all possible topologies.

10. Two Reasons for Using Layered Protocols and One Disadvantage

  • Advantage 1 – Modularity:
    Layered design allows each layer to focus on a specific function, making protocol development, testing, and debugging easier.

  • Advantage 2 – Interoperability:
    Different vendors can implement each layer independently, provided they conform to the standards. This enables devices from different manufacturers to work together.

  • Disadvantage – Overhead and Performance:
    Each layer adds its own header and processing, which can lead to increased latency and bandwidth usage, making the system less efficient in some cases.

12. Are Byte Stream and Message Stream Services Identical?

  • Not Identical:
    A reliable byte stream (like TCP) treats data as a continuous sequence of bytes without message boundaries. A reliable message stream (like SCTP or message-based protocols) maintains the boundaries of individual messages.

  • Example:
    If you send two messages "Hello" and "World" over a message stream, the receiver gets two separate messages.
    Over a byte stream, the receiver might receive "HelloWorld", "Hel" + "loWor", etc., requiring reassembly at the application level.

Conclusion: They differ in how they handle message boundaries, which affects application-level processing.

14. In Fig. 1-19, a service is shown. Are any other services implicit in this figure?

  • Answer:
    Even if only one service is explicitly shown in the figure, several implicit services are involved. For example, if the figure shows a transport layer service, the network and data link layers below are implicitly providing services like routing, error detection, and data framing to support the transport service.

Conclusion: Yes, other services are implicit because each upper-layer service depends on the services provided by lower layers in the protocol stack.

16. Fraction of Bandwidth Used for Headers in an n-Layer Protocol

  • Message Size (M): Given in bytes.

  • Header Size per Layer (h): Given in bytes.

  • Number of Layers (n): Given.

  • Total Header Overhead: n×hn \times h bytes.

  • Total Transmission Size: M+(n×h)M + (n \times h)

  • Header Fraction:
    n×hM+n×h\frac{n \times h}{M + n \times h}

Example:
If M=1000M = 1000 bytes, h=20h = 20 bytes, and n=4n = 4:
Header fraction = 4×201000+80=801080≈0.074\frac{4 \times 20}{1000 + 80} = \frac{80}{1080} \approx 0.074 or 7.4%.

18. Minimum Bombs to Partition the Subnet in Fig. 1-25(b)

  • Assumption: Each bomb destroys one node and all its connected links.

  • Goal: Partition the network into two disconnected sets.

  • Answer:
    The minimum number of bombs required depends on the network’s connectivity. In Fig. 1-25(b), which shows a highly connected mesh network, the node connectivity (minimum number of nodes whose removal disconnects the graph) is 3.

Conclusion: It would take at least 3 bombs to partition the subnet into two disconnected sets.

20. File Acknowledgement Strategies: Per-Packet vs. Whole File

  • Strategy 1 – Per-Packet Acknowledgement:
    Each packet sent is acknowledged by the receiver. This ensures that any lost packet can be retransmitted immediately, increasing reliability but adding overhead and latency.

  • Strategy 2 – Whole File Acknowledgement:
    No acknowledgement for individual packets; the entire file is acknowledged after complete reception. This reduces overhead but increases the risk of undetected loss and rework if any packet is corrupted.

Conclusion:
Per-packet acknowledgement offers higher reliability and better error control, while whole file acknowledgement offers better efficiency but higher risk of loss and retransmission.

22. Length of a Bit in Original 802.3 Standard (in Meters)

  • Transmission Speed: 10 Mbps

  • Propagation Speed: Two-thirds the speed of light
    =23×3×108 m/s=2×108 m/s= \frac{2}{3} \times 3 \times 10^8 \, \text{m/s} = 2 \times 10^8 \, \text{m/s}

  • Time for 1 Bit:
    110×106=1×10−7 seconds\frac{1}{10 \times 10^6} = 1 \times 10^{-7} \, \text{seconds}

  • Distance Bit Travels in That Time:
    2×108×1×10−7=20 meters2 \times 10^8 \times 1 \times 10^{-7} = 20 \, \text{meters}

Conclusion: In the original 802.3 Ethernet standard, a bit is 20 meters long in the cable.

24. Does 802.11 Share Ethernet’s One-Frame-at-a-Time Property?

  • Ethernet (Wired):
    Uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection). Only one frame can be transmitted at a time on the medium.

  • 802.11 Wireless:
    Uses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).
    It also tries to ensure that only one frame is transmitted at a time, but:

    • Wireless Limitations: Due to signal interference, hidden node problems, and varying signal strengths, collisions can still happen even with CA.

    • Shared Medium: Only one successful transmission at a time is generally allowed.

Conclusion:
Yes, 802.11 shares this property functionally, but achieves it differently using collision avoidance due to the challenges of wireless communication.

26. Standardized and Non-Standardized Systems Outside Computing

Examples of Standardized Systems

  • Electrical Outlets and Plugs: Standard voltage and pin configuration allow universal device use.

  • Shipping Containers: Standardized sizes allow global transport across ships, trucks, and trains.

  • Credit Cards: Standard dimensions and magnetic strip formats enable worldwide compatibility.

Examples of Non-Standardized Systems

  • Railway Gauges: Different track widths in countries/regions prevent train interoperability.

  • Mobile Charging Ports (Historically): Multiple types (Micro-USB, Lightning, etc.) before USB-C standardization.

  • TV Broadcast Standards: NTSC, PAL, and SECAM formats make TVs incompatible across countries.

28. Impact of Changing Services at Layer k

  • Layer k-1 (Below):

    • Might need to adapt to new data formats or service requirements from the changed layer.

    • May not function correctly without updates, leading to incompatibility.

  • Layer k+1 (Above):

    • Depends directly on the services provided by layer k.

    • Any change in service interface or behavior could break communication protocols or require changes in upper-layer applications.

Conclusion:
Changes in a service at layer k can affect both adjacent layers, potentially leading to cascading updates throughout the protocol stack.

30. Disadvantages of Using Small, Fixed-Length ATM Cells

  • Increased Overhead:
    Each small cell (53 bytes total, with 5 bytes of header) has a high percentage of overhead compared to its payload (48 bytes).

  • Fragmentation:
    Larger data (like files, videos) must be broken into many small cells, increasing processing complexity.

  • Inefficient for Variable-Length Data:
    Small fixed-length cells are not optimal for data streams like images or text files, which vary in size and structure.

Conclusion: While ATM cells reduce jitter and delay in real-time traffic, they are inefficient for general-purpose data transfer due to fragmentation and overhead.

32. Networks Used at School or Workplace (Example Answer)

Network Types

  • LAN (Local Area Network): Used within buildings and labs for fast communication.

  • Wi-Fi (802.11): Provides wireless access across the campus or office.

Topologies

  • Star Topology: Each computer connects to a central switch or router.

  • Extended Star: For larger areas, multiple switches are used in a hierarchical structure.

Switching Methods

  • Packet Switching: Most networks use this method to break data into packets and route them independently.

  • Circuit Switching: Rare in modern networks but may exist for voice applications.

Note: You can update this with your actual school's or workplace's setup.

34. IETF Project Example (Sample Answer)

Project Chosen: QUIC Protocol (Quick UDP Internet Connections)

  • Problem Addressed:
    Traditional TCP faces delays due to connection setup and congestion control mechanisms, especially on lossy mobile networks.

  • Proposed Solution:
    QUIC is a transport protocol developed by Google and standardized by the IETF. It runs over UDP and integrates security (TLS), multiplexing, and improved congestion control into one protocol.

  • Benefits:

    • Faster connection setup

    • Reduced latency

    • Better performance on mobile and wireless networks

    • Built-in encryption and improved security

Conclusion: QUIC aims to replace TCP in many use cases by offering better speed, security, and reliability.

36. Important Peering Points Used for Routing in the Internet

What Are Peering Points?

Peering points are physical network infrastructure where multiple Internet Service Providers (ISPs) and content providers exchange traffic. These points reduce the number of hops between networks and improve performance.

Examples of Major Peering Points

  • DE-CIX (Frankfurt, Germany)
    One of the world’s largest Internet Exchange Points (IXPs), connecting over 1000 networks.

  • LINX (London Internet Exchange)
    A key hub in Europe, providing high-speed routing between ISPs and data centers.

  • AMS-IX (Amsterdam Internet Exchange)
    Among the busiest exchanges globally, offering seamless traffic exchange in Europe.

  • Equinix Internet Exchange (United States)
    Operates in cities like Ashburn, Chicago, Dallas, and San Jose; vital for North American traffic.

  • HKIX (Hong Kong Internet Exchange)
    Major peering hub in Asia, connecting local and international networks efficiently.

Why Are They Important?

  • They reduce latency by shortening data paths.

  • They improve reliability by offering alternate paths during congestion or failures.

  • They reduce costs for ISPs by minimizing the need to send traffic through upstream providers.

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