CS610 - Computer Network
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Q & A
Short Question & Answers
Q28: What is meant by Bridges STARTUP and STEADY State?
When a bridge first boots the address lists are empty (startup state). The bridge forwards frames to the other segment if it cannot find its destination address in its lists. After some time when the bridge has received at least one frame from every computer, it has the lists built (steady state) it forwards frames as far it is necessary.
Q29: What is the concept of IP Address Hierarchy?
The IP address hierarchy guarantees two important principles:
1. Each computer is assigned a unique address.
2. Although network number assignment must be coordinated globally, suffixes can be assigned locally.
Q30: What is the concept of packet switches?
To span long distances or many computers, networks must replace shared medium with packet switches. Each switch moves an entire packet from one connection to another. That’s why they are called packet switches. A packet switch consists of a small computer with network interfaces, a memory and a program dedicated to packet switching function.
Q31: 1.Why TCP called end to end Protocol? 2. Why more preference given to TCP as comparative to UDP? 3. How is TCP a reliable protocol?
1. TCP established connection between nodes before transmission or receiving the data, due to this feature, it is called end-to-end protocol.

2. TCP provides reliability as it follows connection oriented protocol paradigm that is why TCP is given preference over UDP.

3. TCP is a connection-oriented protocol. A connection can be made from client to server, and from then on any data can be sent along that connection. TCP Provide a Reliability due to connection oriented features.
Q32: What is the main difference between TCP and UDP?
TCP (Transmission Control Protocol): TCP is a connection-oriented protocol. A connection can be made from client to server, and from then on any data can be sent along that connection. TCP Provide a Reliability due to connection oriented features.

UDP (User Datagram Protocol): A simpler message-based connectionless protocol. Messages (packets) can be sent across the network in chunks. UDP is Unreliable – as it could get lost on the way.
Q33: The maximum payload of a TCP segment is 65,495 bytes. Why was such a strange number chosen?
A TCP segment must fit inside an IP packet. The TCP header is a fixed-format of 20- bytes, and the IP header is also 20 bytes long. Since the maximum length of an IPv4 packet is 65,535 bytes, this leaves only 65,535-20-20 = 65,495 bytes left for TCP payload.
Q34: Why does UDP exist? Would it not have been enough to just let user processes send raw IP packets?
UDP instead of raw IP is used because the UDP header contains the port information for the source and destination machines. This allows the machines to know which processes the packet came from and should be sent to. This information is not available anywhere in the header for the raw IP packet. It would not have been enough to just let user processes send raw IP packets
Q35: Write down some characteristics of UDP.
UDP is connectionless protocol: The sender isn’t aware of the other party’s status and sends the data anytime it wants to. Real-time communication is possible. The port number is marked on the data and the data is encapsulated to IP packet and sent. Reliability of communication is not guaranteed. Data can be lost.
Q36: Describe permanent virtual circuits (PVC).
ATM can provide customers with virtual circuits that look like traditional leased digital circuits. Such permanent virtual circuits (PVC) last as long as the customer pays the periodic fee for its use. The forwarding tables are automatically restored after power of equipment failure. The forwarding table entries for such permanent VC’s are statically configured, the terms used by Telco’s for this is provisioning. Provisioning requires two steps: 1. To determine a complete path (that is, identify the switches that will be used). 2. To choose appropriate VPI/VCI for each step in the path, and configure each adjacent pair of switches (easy, since each switch rewrites the VCI/VPI).
Q37: How much data can be present on an original Ethernet segment at one time?
To find out, compute the delay-throughput product. The original Ethernet operate at 10 megabits per second, and a segment was limited to 500 meters. Assume the signals propagate down the cable at 66 percent of the speed of light.\ One Ethernet cable is sometimes called a segment. This segment is limited to 500 meters in length. The minimum separation between connections is 3 meters.
Q38: Define the term Jitter.
The term Jitter is used for variance in transmission delays. Jitter is significance for voice, video and data. Jitter can occur when a packet is delayed because the network is busy.
Q39: Give a comparison of wiring Schemes.
Thick Ethernet wiring scheme: This uses thick coax cable. AUI cable or transceiver or drop cable connects from.

NIC to transceiver: AUI cable carries digital signal from NIC to transceiver. The transceiver generates analog signal on coax cable. The wires in AUI carry digital signals power and other control signals. Thick Ethernet also requires terminators to avoid signal reflectance.

Thin Ethernet wiring scheme: Thin Ethernet uses thin coax cable that is cheaper and easier to install than thick Ethernet coax. In thin Ethernet wiring scheme transceiver electronics are built into NIC and NIC connect directly to network medium. Coax cable use connector on NIC. Coax runs directly to back of each connected computer by T-connector. The T-connector directly attaches to NIC.
Course Instructor

Mr. Hammad Khalid Khan
M.S Electrical Engineering
Oklahoma State University USA

Computer Networks & Internets with Internet Applications by Douglas E.Comer

Computer Networks by Andrew S. Tanenbaum

Networking: A Top-Down Approach Featuring the Internet by James F. Kurose and Keith W. Ross