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Unformatted text preview: he tcpdump output later in
monetary cost Hex
value Telnet/Rlogin 1 0 0 0 0x10 FTP
0x08 any bulk data 0 1 0 0 0x08 TFTP 1 0 0 0 0x10 SMTP
data phase 1
zone transfer 1
0x00 any IGP 0 0 1 0 0x04 SNMP 0 0 1 0 0x04 BOOTP 0 0 0 0 0x00 NNTP 0 0 0 1 0x02 Application Figure 3.2 Recommended values for type-of-service field.
The interactive login applications, Telnet and Rlogin, want a minimum delay since they're used
interactively by a human for small amounts of data transfer. File transfer by FTP, on the other
hand, wants maximum throughput. Maximum reliability is specified for network management
(SNMP) and the routing protocols. Usenet news (NNTP) is the only one shown that wants to
minimize monetary cost.
The TOS feature is not supported by most TCP/IP implementations today, though newer systems
starting with 4.3BSD Reno are setting it. Additionally, new routing protocols such as OSPF and ISIS are capable of making routing decisions based on this field.
In Section 2.10 we mentioned that SLIP drivers normally provide type-of-service queuing, allowing interactive
traffic to be handled before bulk data. Since most implementations don't use the TOS field, this queuing is done ad
hoc by SLIP, with the driver looking at the protocol field (to determine whether it's a TCP segment or not) and then
checking the source and destination TCP port numbers to see if the port number corresponds to an interactive
service. One driver comments that this "disgusting hack" is required since most implementations don't allow the
application to set the TOS field. file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ip_inter.htm (3 of 19) [12/09/2001 14.46.37] Chapter 3. IP: Internet Protocol The total length field is th...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12