The IP over ATM Mailing List Archive by date

["Greg Wetzel, +1 908 949 6630" <gfw@qsun.ho.att.com>]

Hiroshi Esaki writes:

>Integrated of the layer is that ABR and VBR service will be 
>integrated into one VP, and within VP, switch (or router) 
>will schedule ABR traffic and VBR traffic within it ? 
>CBR service may use other VP or VC.  connectionless traffic 
>also. 
>Oh, UBR will use another VP or integrated into ABR/VBR traffic 
>pipe. 

A switch is not allowed, by definition, to look inside a virtual path
connection, that is, when it is configured as a VP switch (cross-connect)
for that VP.

In that case, it cannot know if there is 1 or 100 virtual channels within
a virtual path and hence cannot distinguish one from another for purposes
of scheduling traffic.  All traffic within a VP is scheduled according to
the same bearer class and QoS: to the VP cross-connect switch it looks
like one cell stream.  Thus in order to support differing traffic classes
(e.g., ABR, VBR, CBR) across a VP switch requires that each traffic class be
segregated into its own VP; they cannot be mixed (or integrated).

Greg Wetzel

G_F_Wetzel@att.com          +1 908 949 6630 (voice)
                            +1 908 949 1726 (fax)
AT&T Bell Laboratories
Room HO 1L-426
P.O. Box 3030
101 Crawfords Corner Road
Holmdel, NJ  07733-3030