diffserv field and ip version

Answered Question
Dec 28th, 2008
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hi every body!

I want to know which ip version first supported the use of diffser field which used to be called Tos before.

thanks a lot!

Correct Answer by Joseph W. Doherty about 8 years 5 months ago

Giuseppe's post lists many of the RFCs, but just wanted to emphasis it's still the TOS Octet, but different RFCs have redefined how the bits of the octet (byte) might be used.


For more history, you might also start with this Wiki reference: http://en.wikipedia.org/wiki/Type_of_Service. You might want to espeically note in this reference, "For a full history of the TOS byte, see section 22 of RFC 3168"

Correct Answer by Giuseppe Larosa about 8 years 5 months ago

Hello Sarah,

in original IPv4 specifications the byte is defined as the TOS byte.


A definition of the TOS byte is in RFC 1349


Later the TOS byte in IPv4 header has been reengineered to provide support for the 6 bits DSCP in the most significant 6 bits.


For Diffserv when it has been introduced IPv6 was already in definition so the RFC 2474 defines diffserv for both IPv4 and IPv6


DiffServ RFC's


* RFC 2474-Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers

* RFC 2475-An Architecture for Differentiated Services

* RFC 2597-Assured Forwarding PHB Group

* RFC 3140-Per Hop Behavior Identification Codes (Obsoletes RFC 2836)

* RFC 3246-An Expedited Forwarding PHB (Obsoletes RFC 2598)

* RFC 4594-Configuration Guidelines for DiffServ Service Classes



Then later the last two bits have been redefined to host ECN bits that allow to signal congestions in the IP header to provide a way to help in flow control.

But the usage of ECN is not so wide up to now even if it is an interesting option.


see RFC 3168 for ECN


Hope to help

Giuseppe


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Correct Answer
Giuseppe Larosa Sun, 12/28/2008 - 22:22
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Hello Sarah,

in original IPv4 specifications the byte is defined as the TOS byte.


A definition of the TOS byte is in RFC 1349


Later the TOS byte in IPv4 header has been reengineered to provide support for the 6 bits DSCP in the most significant 6 bits.


For Diffserv when it has been introduced IPv6 was already in definition so the RFC 2474 defines diffserv for both IPv4 and IPv6


DiffServ RFC's


* RFC 2474-Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers

* RFC 2475-An Architecture for Differentiated Services

* RFC 2597-Assured Forwarding PHB Group

* RFC 3140-Per Hop Behavior Identification Codes (Obsoletes RFC 2836)

* RFC 3246-An Expedited Forwarding PHB (Obsoletes RFC 2598)

* RFC 4594-Configuration Guidelines for DiffServ Service Classes



Then later the last two bits have been redefined to host ECN bits that allow to signal congestions in the IP header to provide a way to help in flow control.

But the usage of ECN is not so wide up to now even if it is an interesting option.


see RFC 3168 for ECN


Hope to help

Giuseppe


Correct Answer
Joseph W. Doherty Mon, 12/29/2008 - 05:19
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Giuseppe's post lists many of the RFCs, but just wanted to emphasis it's still the TOS Octet, but different RFCs have redefined how the bits of the octet (byte) might be used.


For more history, you might also start with this Wiki reference: http://en.wikipedia.org/wiki/Type_of_Service. You might want to espeically note in this reference, "For a full history of the TOS byte, see section 22 of RFC 3168"

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