Subject: QoS and Labels: A question ??

From: Arturo Nunez <[email-masked]>
Date: Tue, 23 Jan 2001 17:25:19 -0500 (EST)

Hi:
	I have a doubt about the relation between Labels and the QoS ??
	For example in  the follow network:

PC ==== Ingress LSR ---- Core Network[LSR] ------ Egress LSR === Server

	+ I have a 2 services that are running in the Server, with QoS
	different.
	+ Now if I connect from the PC,notice its one, to the Server for the 2
	services. Will I have 2 LSP ?? Hows is connected the QoS with the labels
	?

	Regards
	Arturo Nunez

---

From: "Vipul Sharma" <[email-masked]>
Date: Tue, 23 Jan 2001 17:43:37 -0500

Arturo,
	This has to do with Forward Equivalency Class (FEC). Since the 2 services
in ur PC have different QoS req. you will like them to be handled diff. in
the Core network (perhaps to reflect their QoS). So you may have two LSP,
one for each service. Each LSP corresponds to a FEC.
	There is EXP bits in the MPLS Label that is there to convey the QoS info.
Hope this helps and experts in this subj. pls. feel free to correct me if I
am wrong. Thanx.

Vip

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of Arturo
Nunez
Sent: Tuesday, January 23, 2001 5:25 PM
To: [email-masked]
Subject: QoS and Labels: A question ??

Hi:

	Regards
	Arturo Nunez

---

From: David Charlap <[email-masked]>
Date: Tue, 23 Jan 2001 19:15:01 -0500

Vipul Sharma wrote:
> 
> This has to do with Forward Equivalency Class (FEC). Since the 2
> services in ur PC have different QoS req. you will like them to be
> handled diff. in the Core network (perhaps to reflect their QoS). So
> you may have two LSP, one for each service. Each LSP corresponds to a
> FEC.

Correct.  If two packet flows are not supposed to be handled
identically, then they do not belong to the same FEC, even if they share
the same destination address.

> There is EXP bits in the MPLS Label that is there to convey the QoS

The EXP bits are for conveying DiffServ priority levels.  If you simply
want to prioritize best-effort traffic, and your switches can suport
E-LSPs, then this is the way to do it.

If you need actual QoS guarantees, or if your switches only support
L-LPSs, or if you want the two service levels to be routed
independantly, then you need to create a separate LSP for each service
level.  CR-LDP or RSVP-TE can be used for signalling the QoS
requirements for the two LSPs.

-- David

---

From: Bora Akyol <[email-masked]>
Date: Tue, 23 Jan 2001 16:33:30 -0800

>>>>> "David" == David Charlap <[email-masked]> writes:

    David> If you need actual QoS guarantees, or if your
    David> switches only support L-LPSs, or if you want the two
    David> service levels to be routed independantly, then you
    David> need to create a separate LSP for each service level.
    David> CR-LDP or RSVP-TE can be used for signalling the QoS
    David> requirements for the two LSPs.

David

You are making assumptions about a particular switch
architecture when you assert that you can not do "actual" QoS
guarantees with E-LSPs. If you have a policer and a
shaper/scheduler that can process the EXP bits as well as the
label, then doing "actual" QoS is quite possible with
E-LSPs. 

Not only that, but you can map traffic destined to the same
prefix to different EXP levels based either on Diffserv bits or
on packet content. This also applies to VLAN tags.

Bora

---

From: David Charlap <[email-masked]>
Date: Wed, 24 Jan 2001 10:33:35 -0500

> on packet content. This also applies to VLAN tags.

The meaning of the EXP bits is not signalled.  It must be preconfigured
network-wide.  And in order to be useful, they must be identical across
the entire network.  Which limits you to 8 different service levels,
network-wide.

If you use the EXP bits to define a priority level and two flows are
both assigned that level, they will be queued in best-effort fashion
relative to each other.  There is no way to guarantee the individual
flows any particular level of service.  You can only guarantee the
aggregate of one class relative to another class.

Using L-LSPs, you can request a separate label, and a separate resource
reservation for every flow, if needed.  This is the only way to
guarantee this level of service.  (Unless you're willing to limit each
DS code point to a single flow, which is a ridiculous concept.)

E-LSPs are useful, no doubt about that.  But they can not provide the
level of QoS necessary to make sure that a single specific flow can be
guaranteed the resources it requires.

-- David

---

From: Jim Boyle <[email-masked]>
Date: Wed, 24 Jan 2001 09:13:07 -0700 (MST)

That is the difference between diffserv and intserv, I believe.  Diffserv
doesn't aim to give hard guarentees to individual flows.  Diffserv, and
"E-LSPs", work.

Jim