RE: QoS in Shared Media

["Jay Wang" <jwang@opixnetworks.com>]

Dunno what is the problem. To support diffserv, the underneath
transport (MAC layer and lower), does not have to have a
sophisticated traffic management matching diffserv PHBs. The fact
that cisco's DPT (or others RPR version for that matter), a MAC
layer technology, that supports only two transmit queueing priorities,
hence is not a disqualifier for supporting diffserv on the higher level,
where you suggested otherwise. In a share-media environment, from
diffserv's perspective, what we need from below is a link layer
that may ensure a quantifiable and stable guaranteed throughput for the
target nodes, regardless of the other sharing nodes. This is what is
missing in the original IEEE-802-style LAN. The DPT, on the other hand,
assures total_ring-BandWidth/node_num for each node. Given that, the
business of diffserv traffic management, e.g., BA classification,
policing, color-based RED dropping, PHB scheduling, and so on and so forth,
can be conducted as they should have been at the connected nodes.

- jay


-----Original Message-----
From: Juha Heinanen [mailto:jh@lohi.eng.telia.fi]
Sent: Friday, May 04, 2001 10:52 PM
To: Jay Wang
Cc: HANSEN CHAN; Fred Baker; Naidu, Venkata; 'mpls@uu.net';
te-wg@ops.ietf.org
Subject: RE: QoS in Shared Media


Jay Wang writes:

 > Well, RPR gives you bandwidth endurance at the link level, a shared
 > media in this case. On higher level, you may conduct your QoS as
 > appropriate, Diffserv, Intserv, or else. One does not preclude the other,
 > IMO.

how about if someone would like to give different bandwidth assurance to
more than one independent traffic class?  also, within a diffserv
traffic class, droping of packets is based on the drop presedence of the
packet, not based on behind which nodes the packets arrived.

as i said before, node based fairness can only be applied to the highest
dp packets within each class.  dpt (and also rpr if it adopts dpt) thus
supports diffserv only in a very limited sense.  as far as i remember,
it is the only ieee mac standard, where the specification tells how many
queues the switch has.

-- juha


-----Original Message-----
From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET]On Behalf Of Juha
Heinanen
Sent: Friday, May 04, 2001 12:01 PM
To: HANSEN CHAN
Cc: Fred Baker; Naidu, Venkata; 'mpls@uu.net'; 'te-wg@ops.ietf.org'
Subject: Re: QoS in Shared Media

HANSEN CHAN writes:

 > How about the work in IEEE 802.17 RPR? I believe it will be a
shared-media
 > technology. Does that mean they will have a hard time to achieve QoS
 > guarantees?

last time that i checked, the rpr proposal (based on cisco dpt) had two
classes of service (strict priority and best effort). that is clearly
not adequate for diffserv.  node based fairness applied to the best
effort class.  in diffserv, node based fairness makes sense only for the
highest dp packets in each traffic class.

-- juha