2. Page 2
• IP QoS
To provide differentiated services on an IP network, the DSCP field in the header of
IP packets is used to identify packets. Each router determines the packet
forwarding behaviors for packets according to the DSCP field in aspects of
resource allocation, queue scheduling, congestion control, and link-layer selection.
• MPLS QoS
To provide differentiated services on an IP network, the information in the MPLS
encapsulation header, including labels and EXP, is used to identify packets.
MPLS QoS v.s. IP QoS
3. Page 3
• E-LSP
In MPLS QoS, the EXP field in the MPLS
encapsulation format is used to identify PHBs.
MPLS QoS supports a maximum of 8 PHBs and
cannot completely map IP QoS.
• L-LSP
In MPLS QoS, the labels in the MPLS encapsulation
format is used to identify PHBs. MPLS QoS supports
PHBs without any limit and can completely map IP
QoS.
E-LSP v.s. L-LSP
4. Page 4
MPLS QoS
Combination of MPLS and IntServ
MPLS supports QoS based on flows. Communication is set up by interconnecting the MPLS
signaling protocol (CR-LDP or RSVP-E) with the IP signaling protocol (RSVP). Then, end-to-end
QoS is available.
The QoS based on flows has the scalability problem.
Combination of MPLS and DIffServ: MPLS CoS
Both MPLS and DIffServ have proper scalability and similar processing. That is, packets are
aggregated at network edges (DSCP or label) and are processed at the network core (PHB based
on DSCP or forwarding based on label).
MPLS equipment (LSR) only makes the forwarding decision according to the MPLS shim header.
Hence, which PHB should be adopted is based on the shim header.
In the industry, there are two solutions to mapping a DS domain with six fields to the EXP with
three fields, that is, E-Infered-LSP and L-Infered-LSP.
DIffServ provides QoS based on classes and thus features good scalability, but lacks an effective
mechanism for end-to-end deployment.
5. Page 5
Comparison of QoS Service Models
IntServ
The IntServ model provides the QoS based on flows and has the scalability problem.
DiffServ
The DiffServ model provides the QoS based on classes and has proper scalability,
but lacks an effective mechanism for end-to-end deployment.
MPLS TE
The traditional routing protocols (such OSPF and IS-IS) mainly ensure network
connectivity and reachability and use insensitive parameters as the basis for SPF
computation. As a result, defects such as unbalanced network load and route
instability are caused. MPLS TE uses the capability of the LSPs to support explicit
routes to direct traffic on the network with limited resources. In this manner, MPSL
TE matches the network load with the physical network resources and improves
the service quality of the network.
Though adopting the DiffServ QoS model, the OptiX OSN 1500/2500
supports configuration and delivery of MPLS TE.
The OptiX OSN 3500 adopts the QoS with combination of MPLS
TE and DS.
