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[ns] IP headers
Hello,
I am working on my final year project and I am using ns. I however need to alter
some of the values in the IP hearer for the datagrams sent over my modelled
network.
A summary of the contents of the internet header follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In particular I would like to alter the values for the 'Type of Service' field.
The Type of Service provides an indication of the abstract parameters of the
quality of service desired. These parameters are to be used to guide the
selection of the actual service parameters when transmitting a datagram through
a particular network. Several networks offer service precedence, which somehow
treats high precedence traffic as more important than other traffic (generally
by accepting only traffic above a certain precedence at time of high load). The
major choice is a three way tradeoff between low-delay, high-reliability, and
high-throughput.
Bits 0-2: Precedence.
Bit 3: 0 = Normal Delay, 1 = Low Delay.
Bits 4: 0 = Normal Throughput, 1 = High Throughput.
Bits 5: 0 = Normal Relibility, 1 = High Relibility.
Bit 6-7: Reserved for Future Use.
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
| | | | | | |
| PRECEDENCE | D | T | R | 0 | 0 |
| | | | | | |
+-----+-----+-----+-----+-----+-----+-----+-----+
Precedence
111 - Network Control
110 - Internetwork Control
101 - CRITIC/ECP
100 - Flash Override
011 - Flash
010 - Immediate
001 - Priority
000 - Routine
My aim is to send packets accross the netwok and have control over the values in
this field, ie send packets through a particular link with different type of
service tags and log the effects. I have all this set up, all I need to do is
know how to change the values in the 'type of service' field. I suspect this is
easy once you know how and where to do it.
Any help would be greatly welcome
Stephen Coulson
---------------
[email protected]
[email protected]
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http://www.geocities.com/sdcoulson_uk
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Why Rule The World When I Can Eat Baked Beans (Neil Freeman 15/11/99)