Editing Differentiated services (section)

===Class Selector===

{| class="wikitable"
|+ Class Selector mapping<ref name=classselector/>
! Service class
! DSCP Name
! DSCP Value
! [[IP precedence]] 
! Examples of application
|-
| Standard 
| CS0 (DF)
| 0
| 0 (000)
| [[Network Time Protocol|NTP]]<ref name=ntp/>
|-
| Low-priority data
| CS1
| 8
| 1 (001)
| File transfer ([[FTP]], [[Server Message Block|SMB]])
|-
| Network [[operations, administration and management]] (OAM)
| CS2 
| 16
| 2 (010)
| [[SNMP]], [[SSH]], [[Ping (networking utility)|Ping]], [[Telnet]], [[syslog]]
|-
| Broadcast video 
| CS3 
| 24
| 3 (011)
| {{Unbulleted list|[[RTSP]] broadcast TV|streaming of live audio and video events|[[video surveillance]]|[[video-on-demand]]}}
|-
| Real-time interactive
| CS4
| 32
| 4 (100)
| Gaming, low priority video conferencing
|-
| Signaling 
| CS5 
| 40
| 5 (101)
| Peer-to-peer ([[Session Initiation Protocol|SIP]], [[H.323]]), client-server IP telephony signaling ([[H.248]], [[MEGACO]], [[Media Gateway Control Protocol|MGCP]], [[Skinny Client Control Protocol|SCCP]])
|-
| Network control 
| CS6 
| 48
| 6 (110)
| Routing protocols ([[OSPF]], [[BGP]], [[IS-IS]], [[RIP]])
|-
| Reserved for future use
| CS7 
| 56
| 7 (111)
| 
|-
|}

DF= Default Forwarding

Prior to DiffServ, IPv4 networks could use the [[IP precedence]] field in the [[Type of service|TOS]] byte of the IPv4 header to mark priority traffic. The TOS octet and IP precedence were not widely used. The IETF agreed to reuse the TOS octet as the DS field for DiffServ networks, later splitting it into the DS field and ECN field. In order to maintain backward compatibility with network devices that still use the Precedence field, DiffServ defines the ''Class Selector'' PHB.

The Class Selector code points are of the binary form 'xxx000'.  The first three bits are the former IP precedence bits. Each IP precedence value can be mapped into a DiffServ class. IP precedence 0 maps to CS0, IP precedence 1 to CS1, and so on. If a packet is received from a non-DiffServ-aware router that used IP precedence markings, the DiffServ router can still understand the encoding as a Class Selector code point.

Specific recommendations for use of Class Selector code points are given in {{IETF RFC|4594}}.