1. A Practical Approach for Providing QoS: MPLS and DiffServ
MPLS Maximizing the Performance and
Profitability of Optical and Data Networks
July , 2001
Dublin, Ireland
A Practical Approach for Providing QoS: MPLS and DiffServ
Thomas Telkamp
Director Data Architecture and Technology
Global Crossing Telecommunications, Inc.

2. Agenda Global Crossing MPLS deployment Quality of Service?
A Practical Approach
Network Design and Capacity Planning
Differentiated Services
MPLS for Traffic Engineering
Fast Reroute and Per-Class TE
Queuing and Scheduling
Conclusion

3. Global Crossing IP Backbone Network
PEC
AC-1
AC-2
North American Crossing
PC-1
MAC
EAC
PAC
SAC
Based on announced network

4. GBLX MPLS Deployment Operational since 2Q 1999
Traffic Engineering
IP TTL issues
Worldwide MPLS mesh 1Q 2001
Currently over 6000 LSPs
Network:
Cisco and Juniper routers
OC-48 wavelengths
Covering Asia, US, South America and Europe
New Services: VPN (L2/L3)

5. MPLS Traffic Engineering

7. Quality of Service. Based on a paper with XiPeng Xiao (Photoris, Inc
Quality of Service? Based on a paper with XiPeng Xiao (Photoris, Inc.) and Lionel M. Ni (Michigan State University)
Best Effort (e.g. Internet)
Real-time/Mission-critical traffic (e.g. Voice)
Increase revenue by value-added services
Two extremes:
Overprovisioning of bandwidth without additional mechanisms
Sophisticated mechanisms such as per-flow classification/policing/queuing and scheduling

8. What Causes Problems? Overloaded servers, or access to servers
Web, , etc.
TCP stack implementations
Link failures
fiber cuts
transmissions equipment failures
Router failures
complex software
early deployment of features
configuration

9. A Practical Approach Good Network Design
Differentiated Services (DiffServ)
Traffic Engineering
Traffic Protection (Fast Reroute)
Class-based Queuing
Not:
Extremely complex schemes (e.g. per-flow)
affecting equipment reliability
difficult to configure and manage

10. Network Design Avoid single points of failure
No bottlenecks in normal condition
Overprovisioning
with use of TE network can handle all traffic, even when the most critical links fails
Routing (IGP and BGP)
Security and Denial of Service attacks
Capacity Planning

11. Differentiated Services
How many classes?
What are the targeted applications for each class?
Can end users distinguish between classes?
Example:
Class 1: Real-time
application: voice
Class 2: Assured
application: trading, non-interactive audio and video
Class 3: Best Effort
application: Internet

12. MPLS Deployment Traffic Engineering Two LSP meshes: LSP Hierarchy
Avoid congestion caused by uneven traffic distribution
Macro control
Constraint based LSP setup
Two LSP meshes:
Real-time traffic vs Assured/Best Effort
Classification based on interface or multi-field lookup
Different metrics
LSP Hierarchy
Scalability and VPNs

13. MPLS LSP Deployment

14. Traffic Protection IGP convergence (OSPF/IS-IS) takes seconds
But can be improved by timer and SPF tuning
see Packet Design paper
MPLS Fast Reroute
Link or Node protection
Pre-configured patch LSPs (sub-optimal)
Use for real-time traffic only, or for all traffic (based on implementation)

15. MPLS Fast Reroute
Protecting router switches traffic to pre-configured patch LSP after failure detection (fast)
Ingress router reroutes LSP (slow)

16. Per-Class Traffic Engineering
Avoid concentration of real-time traffic at any link
Set upper limit on bandwidth reservations per class
E.g. max. 40% of a link for VoIP traffic
IETF Internet Draft(s) on ‘Diff-Serv-aware MPLS Traffic Engineering’ (Francois Le Faucheur, et al.)

17. Class-based Queuing Prefer ‘higher’ classes during congestion
sub-optimal fast-reroute period
major failures
Different queuing/scheduling mechanisms
Strict Priority Queuing
Jitter control for EF traffic
WRR/WFQ
and combinations
Configuration issues...

18. Random Early Detection
Buffer Management
prevent tail-drop
TCP oscillations and synchronization
RED drops based on average queue length
WRED drops with different probability for each class
Only during congestion
Not used to guarantee bandwidth!

19. Conclusion
Use combination of good network design, over-provisioning and MPLS/DiffServ
Use Traffic Engineering to prevent congestion
Use fast reroute and priority queuing for real-time traffic
Use WRR/WFQ to differentiate between Assured and Best Effort traffic
Too complex and too many features will make the network unreliable/unstable

20. Questions?