Homework 7

CIS 331: Network Introduction
Lehman College, City University of New York
Fall 2013

This Homework Is Due By 11:59 PM on November 10, 2013

1. Explain the use of the pseudo-header for a UDP datagram and TCP segment. When is it used? Is it transmitted with the datagram? How does the ultimate destination obtain the contents of the pseudo-header?


2. What is the chief advantage of using protocol ports instead of process identifiers to specify the destination within a machine?


3. Explain sliding windows as used by TCP. What advantage does the use of sliding windows provide over a simple Positive Acknowledgement with Retransmission (PAR) protocol?


4. A lost TCP acknowledgement does not necessarily force retransmission. Explain why.



5. Given that a frame is formatted as follows:

   Destination Hardware Address	Source Hardware Address	Frame Type	Frame Data
   6 Bytes	6 Bytes	2 Bytes	46 - 1500 Bytes

   And given that an IP datagram is formatted as follows:

   Byte	0								1								2								3
   bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
   0	Version				Header Length				Type Of Service								Total Length
   4	Identification																Flags			Fragment Offset
   8	TTL								Type								Header Checksum
   12	Source IP Address
   16	Destination IP Address
   	IP Options (May Be Omitted)																								Padding
   20	IP Payload Data

   And given that a UDP datagram is formatted as follows:

   Byte	0								1								2								3
   bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
   0	UDP Source Port																UDP Destination Port
   4	UDP Message Length																UDP Checksum
   20	UDP Payload Data

   And given the following frame with an encapsulated IP datagram and UDP datagram:

   	46	8F	D7	8C	1D	E8	3F	48	06	30	33	A9	08	00	45	33
   	00	72	A4	9C	38	E8	BD	B4	DF	CF	1E	75	AE	CB	66	07
   	BF	9F	84	B3	BA	F4	AD	53	BB	82	67	82	5A	7B	08	29
   	E4	E0	FB	09	41	E3	57	96	52	5C	8A	0D	94	81	54	A0
   	ED	8F	C4	38	7A	B0	9F	66	D8	F4	68	4A	6F	BA	B7	B6
   	98	0D	EB	DC	F1	54	D7	B4	2D	DA	78	35	AA	EF	EC	BF
   	E9	F4	1D	87	77	E7	38	65	39	FB	B4	F8	63	6D	50	DA
   	51	40	D8	1F	AA	31	8C	22	AB	54	31	65	E7	DD	83	90
         

   1. What is the UDP source port?
   2. What is the UDP destination port?
   3. What is the UDP message length?
   4. What is the UDP checksum?
   5. If the UDP header and the IP header include no options or padding, what are the first five bytes of the datagram data?



6. Given that a frame is formatted as follows:

   Destination Hardware Address	Source Hardware Address	Frame Type	Frame Data
   6 Bytes	6 Bytes	2 Bytes	46 - 1500 Bytes

   And given that an IP datagram is formatted as follows:

   Byte	0								1								2								3
   bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
   0	Version				Header Length				Type Of Service								Total Length
   4	Identification																Flags			Fragment Offset
   8	TTL								Type								Header Checksum
   12	Source IP Address
   16	Destination IP Address
   	IP Options (May Be Omitted)																								Padding
   20	IP Payload Data

   And given that a TCP segment is formatted as follows:

   Byte	0								1								2								3
   bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
   0	TCP Source Port																TCP Destination Port
   4	Sequence Number
   8	Acknowledgment Number (If ACK is set)
   12	Data Offset				Reserved			NS	CWR	ECE	URG	ACK	PSH	RST	SYN	FIN	Window Size
   16	Checksum																Urgent Pointer (If URG is set)
   	TCP Options (May Be Omitted)																								Padding
   20	TCP Payload Data

   And given the following frame with an encapsulated IP datagram and TCP Segment:

   	38	C4	5D	49	7A	60	69	9B	25	2C	64	F1	08	00	45	98
   	00	72	75	B8	14	54	86	2F	0B	12	D2	42	94	45	79	54
   	AA	17	1A	10	2A	DA	57	C5	5A	C0	17	44	6D	96	DE	F9
   	1D	38	6A	E6	6D	9B	B4	61	F4	F2	90	E7	48	D8	46	9A
   	3F	63	ED	02	49	34	62	ED	E1	52	44	66	D7	15	0C	55
   	8A	A6	31	C8	2A	BE	25	18	6A	55	82	A8	7C	22	26	58
   	32	96	DE	4E	2C	F8	E6	66	8F	E0	E2	5F	2B	E0	83	8B
   	03	5C	2A	68	8F	2C	5D	A1	8F	2D	CF	5A	5C	F6	66	34	
         

   1. What is the TCP source port?
   2. What is the TCP destination port?
   3. What is the Sequence Number?
   4. What is the Acknowledgment Number?
   5. What flags are set?
   6. What is the Window Size?
   7. What is the checksum?
   8. What is the urgent pointer?
   9. If the TCP header and the IP header include no options or padding, what are the first five bytes of the datagram data?

Please submit the completed assignment on Blackboard as a Microsoft Word file or a PDF file. No other forms of submission will be accepted.