Homework1

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  1. What does this image represent?



    Image Upload 1
    Its the TCP Header
  2. Describe the meaning of the different fields in the TCP Header.
    • Source Port (16 bits): Holds the port number of the source point.
    • Destination Port (16 bits): Holds the port number of the destination point.
    • Sequence Number (32 bits):
    • (i) if SYN flag = 0, this is the sequence number of the first data byte.
    • (ii) if SYN flag = 1, this is the initial sequence number (ISN) and the seq. # of the actual first data byte is ISN+1.
    • Acknowledgement Number (32 bits): If the ACK flag=1, this fields holds the sequence number of the next data byte the receiver is expecting.
    • Header Length (4 bits): Specifies the size of the TCP Header in 32-bit words
  3. Continue... Describe the meaning of different fields in the TCP Header.
    • Reserved (6 bits): Reserved for future use.
    • Flags (6 bits): Holds the control bits used to
    • identify the purpose of the segment.
    • (i)URG: Indicates Urgent Pointer field is valid
    • (ii)ACK: Indicates Acknowledgement field is valid
    • (iii)PSH: Segment requests a PUSH
    • (iv)RST: Resets the connection
    • (v)SYN: Synchonizes sequence numbers
    • (vi)FIN: No more data from sender
    • Window (16 bits): Contains the size of hte receive window, wich specifies the # of bytes destination is willing to accept.

    Checksum (16 bits): Used for error detection of the header and data.

    Urgent Pointer (16 bits): Specifies the position where urgent data (data delivered as quickly as possible) ends.

    • Options + Padding (variable): Options have 3 fields
    • (i) Option-Kind: type of option, not optional
    • (ii)Option-Length: total length of the option
    • (iii)Option-Data: cotains value of option, if applicable
    • Padding: field composed of zeros that are used to ensure that the TCP header ends and data begins.
  4. What does the image represent?

    Image Upload 2
    This is the UDP Header!
  5. Describe the meaning of the different fields in a UDP header.
    Source Port (16 bits): Holds the port number of the source point.

    Destination Port (16 bits): Holds the port number of the destination point.

    Segment Length (16 bits): Contains the length of the entire UDP segment, including header and data.

    Checksum (16 bits): Used for error detection.
  6. What does this image represent?

    Image Upload 3
    This is the IPv4 Header!
  7. Mention briefly the significance of different fields in the IPv4 Header.
    • Version (4 bits): Indicates the version number.
    • InternetHeader Length (IHL) (4 bits): Length of the header in 32-bit words.

    Type of Service (8 bits): Specifies reliability, precedence, delay and throughput parameters.

    Total length (16 bits): Total datagram length in bytes.

    Identification (16 bits): Sequence number that identifies a datagram.

    • Flags (3 bits): used to control/identify fragments.
    • (i) Bit 0: Reserved
    • (ii) Bit 1: Dont Fragment (DF)
    • (iii) Bit 2: More Fragments (MF)
  8. Continue...Mention briefly the significance of different fields in the IPv4 Header.
    Fragment Offset (13 bits): byte count that indicates where in the original datagram this fragment belongs.

    Time to Live (TTL): Number of hops a packet may be routed over that limits its lifetime to prevent routing loops.

    Protocol (8 bits): Defines the next protocol that is to receive the data field.

    Header Checksum (16 bits): Error detector for the header only.

    Source Address (32 bits): IP address indicating the sender of the packet.

    Destination Address (32 bits): IP address indicating the receiver of the packet.

    • Options Padding (variable): The Options part holds the options requested by the sender.
    • The Padding part is used to ensure that the header is a multiple of 32 bits.
  9. Mention 3 significant differences between IPv4 and IPv6 protocol.
    • Address Space: IPv4 addresses are 32 bits (4bytes) in length while IPv6 are 128-bits (16 bytes) in length.
    • Header format: IPv6 has simplifier header format than Ipv4
    • Security Capabilities: IPv6 includes features that support authentication and privacy.
  10. How many unique IP addresses can be supported by IPv4 and IPv6?
    • IPv4: 232=4,294,967,296
    • IPv6: 2128= ~ 3.4×1038
  11. Briefly mention the significance of IEEE LLC/SNAP header.
    • This header allows the upper layers to know where to find the data.
    • * LLC-Logical Link Control (24 bits):
    • (i) DSAP-Destination Service Access Point (1byte): Acts as a pointer to memory buffer in the receiver.
    • (ii) SSAP-Source Service Access Point (1byte): specifies the source of hte sending process.
    • (iii) Control Byte (1byte): indicates the type of LLC frame.

    *OUI-Organizationally Unique ID (24 bits): number that identifies a vendor, manufacturer, or other organization.

    *Type (16 bits)
  12. Find how computers on LAN use CSMA/CD Protocol for transfer of Ethernet
    Packets. (IEEE Standard 802.3)
    • a. Nodes listen to the network to check if it is
    • free.

    • b. If no other transmission is detected, a node
    • starts transmitting.

    • c. If more than one node senses that no
    • transmission is occurring, both can start transmitting at the same time.

    • d. When two nodes start transmitting at the same
    • time, the transmissions overlap and cause a collision.

    • e. If a collision occurs, one of the nodes
    • recognizes the interference and transmits a bit sequence (jam) that ensures the
    • other node recognizes the collision too.

    • f. After a random delay, the nodes attempt to
    • retransmit the information and the process begins again.
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Homework1
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