Supporting DiffServ with Per-Class Traffic Engineering in MPLS

Outlines

• The paper is proposing a new MPLS traffic engineering scheme to meet the demand for Quality of Service (QoS).

• This scheme is a modified version of a previously proposed QoS routing algorithm.

• The proposed scheme enhances E-LSP with per-class TE and load balancing.

• Compared with the original E-LSP and E-LSP with load balancing for the support of EF, AF, and BE.

• Simulation results are shown.

Background

• MPLS and DiffServ together provide a potential model that supports QoS over IP network.

• DiffServ model divides traffic into a small number of classes and allocates resources on a per-class basis.

• Because DiffServ has a few different classes, a packet’s “class” can be marked directly in the packet.

• The mark in the packet is called a Differentiated Service Cod Point, or DSCP, that has 6-bit long within the IP header.

• DSCP identifies a “per-hop behavior” or PHB.

• The standard PHBs include:• Expedited Forwarding (EF): Packets are forwarded with

minimal delay and low loss.

• Assured Forwarding (AF): Packets have different classes and different drop preferences.

• Best Effort (BE): No special treatment.

• DSCPs is carried in the IP header, but MPLS LSRs don’t examine that. we need a way to determine the PHB from the label header.

• Two ways to solve that: E-LSP, and L-LSP.

Background (2)

• E-LSP: The EXP field of the MPLS Shim Header conveys to the label-switch router (LSR) the PHB to be applied to the packet.

• L-LSP - That the packet’s scheduling treatment is inferred by the LSR exclusively from the packet’s label value while the packet’s drop precedence is conveyed in the EXP field of the MPLS Shim Header or in the encapsulating link-layer-specific selective drop mechanism.

Background (3)

Features of the proposed Scheme

• Labeling:• The EXP field encodes the scheduling treatment

and drop precedence just as in E-LSP.

• Load balancing by Service Classes:• Traffic flows of different service classes is

distributed over different LSPs.

• Routing:• Uses a simple constraint-based routing algorithm

that is modified from an “Optimal QoS Routing Algorithm” previously developed [10].

Optimal QoS Routing Algorithm

• It solves the QoS multicast routing problem that requires two constraints; delay and bandwidth.

• It is called also Maximum-Bandwidth with Delay Constraint algorithm, MBDC.

MBDC Algorithm:

The Proposed Algorithm

i. Prunes the topology database of all links that don’t have sufficient residual/reservable bandwidth or that is administratively forbidden (including excess delay) for the LSP;

ii. Find the minimum-cost path towards the LSP’s egress router (use propagation delay as the cost for each link);

Iii. If several equal-cost paths remain, select the one with the fewest number of hops;

Iv. If several equal-cost paths remain, apply the load- balancing rule: choose the path that has the maximum residual bandwidth;

V. Steps i to iv are repeated for each LSP computation, beginning from the highest service class;

Performance Evaluation• Three schemes are simulated:

• Original E-LSP

• E-LSP with multiple path load balancing

• E-LSP with per-class traffic engineering, the proposed scheme

Simulation Results

Flow 1 (EF):

Case 3a, 3b,and 3c have the smallest delay and delay jitter.

Throughput is the same for all schemes.

Simulation Results (2)

Flow 2 (AF):

All schemes have similar delay and throughput.

The proposed scheme yields better delay jitter.

Flow 3 (BE):

Delay and delay jitter are reduced dramatically with the proposed scheme.

Throughput also is improved.

Simulation Results (3)

Simulation Results (4)

Flow 4 (BE):

The proposed scheme in case 3a has dramatically reduced Delay and delay jitter.

While facing more AF flows, in case 3b, Throughput, delay, and delay jitter are close to scheme 1.

Simulation Results (5)Flow 5 (BE/AF/EF):

When flow 5 is BE flow 3.

When flow 5 is AF the proposed scheme in case 3b has much better performance.

When flow 5 is EF LSP is shifted to 4-9-8, and flow 2,3,4 will have more BW.

Conclusion

• The proposed a per-class TE scheme that enhances E-LSP demonstrates better utilization of the network resources.

• It is able to accommodate more QoS flows while offering better performance to existing flows.