Homework1

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Author:
erika01
ID:
111766
Filename:
Homework1
Updated:
2011-10-24 15:14:21
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Kumar CNP
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Problems and Solutions
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  1. What does this image represent?



    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?

    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?

    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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