Chapter 7

Chapter 7

7.2

Calculate the RTT if the SLIP link between bsdi and slip is set to 9600 bits/sec. Assume the default of 56 bytes of data.

A:

86 bytes divided by 960 bytes/sec, times 2 gives 179.2 ms. When ping is run at this speed, the printed values are 180 ms.

7.3

The current BSD ping program allows us to specify a pattern for the data portion of the ICMP message. (The first 8 bytes of the data portion are not filled with the pattern, since the time at which the packet is sent is stored here.) If we specify a pattern of 0xc0 , recalculate the answer to the previous exercise. ( Hint : Reread Section 2.4.)

A:

(86 + 48) bytes divided by 960 bytes/sec, times 2 gives 279.2 ms. The additional 48 bytes are because the final 48 bytes of the 56 bytes in the data portion must be escaped: 0xc0 is the SLIP END character.

7.4

Does the use of compressed SLIP (CSLIP, Section 2.5) affect the ping times that we observed in Section 7.2?

A:

CSLIP only compresses the TCP and IP headers for TCP segments. It has no effect on the ICMP messages used by ping.

7.5

Examine Figure 2.4. Do you expect any difference between a ping of the loopback address, versus a ping of the host's Ethernet address?

A:

On a SPARCstation ELC a ping of the loopback address yields an RTT of 1.310 ms, while a ping of the host's Ethernet address yields an RTT of 1.460 ms. This difference is the additional processing done by the Ethernet driver, to determine that the datagram is really destined for the local host. You need a version of ping that outputs microsecond resolution to measure this .



TCP.IP Illustrated, Volume 1. The Protocols
TCP/IP Illustrated, Vol. 1: The Protocols (Addison-Wesley Professional Computing Series)
ISBN: 0201633469
EAN: 2147483647
Year: 1993
Pages: 378

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