IP Precedeence in Intserv and Diffserv

[deepinder]

Hi everybody

I have an question on QOS. Interserv uses TOS IP Precedence field to classify the traffic while Diffserv uses DSCP to classify the traffic as diffserv dont have IP Precedence field as TOS is rewritten. But in some cisco books and on cisoc documentation itslef i found saying that Diffserv supports both, so if any body can clear this doubt.

Best Regards

[mheusinger · Accepted solution]

Hi,

IntServ does not use the TOS Byte to classify traffic. Instead the traffic description is signalled throughout the path from sender to receiver through RSVP.

DiffServ does allow to classify traffic according to the bit pattern in the TOS byte (among other classification options). There have been some approaches when it comes to bit pattern in the TOS Byte.

First there was TOS, then the bit patern was redefined into IP precedence and then DSCP came along.

BUT those are "just" different names to different bit patterns in the original TOS Byte. An Example:

Binary TOS Byte value: 10100000

Naming: IP precedence 5 OR class selector 5 (in the DSCP context).

So yes, DiffServ is downward compatible to IP precedence and can use both for classification.

Hope this helps! Please use the rating system.

Regards, Martin

P.S.: Some links for further reading:

Resource-Reservation Protocol (RSVP)

http://www.cisco.com/en/US/tech/tk1330/tsd_technology_support_technical_reference_chapter09186a0080759873.html

Implementing DiffServ for End-to-End Quality of Service Overview

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800bd9ed.html

[deepinder]

Thanks Martin

Got ans in one stroke.

Regards

Ashish