the TypeOfService property provides an indication of the abstract parameters of the quality of service desired. These parameters ...

the TypeOfService property 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.  The default value is 0. 
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. 

Precedence 
111 - Network Control 
110 - Internetwork Control 
101 - CRITIC/ECP 
100 - Flash Override 
011 - Flash 
010 - Immediate 
001 - Priority 
000 - Routine  
 
For a detailed description of the various serive types, refer to RFC 791, page 12.