1. Quality of Service for MultiService IP Networks 8th March 2000
John A. Clark - Technical Account Manager

2. Agenda Overview of Enterprise Quality of Service
The Differentiated Services Model
DiffServ Traffic Classification
Mapping DiffServ to/from Link Layers
RSVP for QoS Signaling
Summary

3. Enterprise Quality of Service
… What is it & Why do we need it?

4. What is driving the need for QoS?
Increasing number of network users and applications
New applications and traffic dynamics
RT, Interactive traffic (VoIP)
RT, non-Interactive traffic (Video on Demand, RealMedia)
Non-RT, Interactive traffic (Web surfing)
Non-RT, Mission Critical traffic (e-Commerce)
Non-RT, non-Mission Critical traffic (everything else)
Service Providers offering/pricing tiered levels of service
Service differentiation in Intranets
Ability to assign business priorities to traffic or users
Businesses are rapidly becoming aware of the benefits of sharing information across traditional boundaries. Those boundaries may have been within one office area or building to domestic and international locations. Fueling network growth are the applications evolving to simplify the sharing of information across logical and physical boundaries.
Some of the more dynamic applications that can have an immediate financial impact and promote collaboration among groups is video and teleconferencing. In a global economy, travel is a necessary evil. Companies looking to improve bottom line performance must become more efficient with valuable , scarce resources. Video and teleconferencing can help reduce unnecessary and expensive trips. However, both video and voice communications have very little tolerance for variations in delay. These kind of applications require special treatment if they are to be effective.
Another tool driving networks to provide Quality of Service is thew World Wide Web. The WWW is this generations ultimate answer to sharing information. Businesses have taken the concept and applied it to their own internal networks and coined it the “Intranet”. Extending a subset of the corporate resources to external sources (customers and suppliers) is a version called the “Extranet”. Network managers need to apply a set of rules to the wild and woolly communication resource they have opened. They need to make sure the traffic that drives the companies existence is given a higher priority than recipes for the world’s best chili for the weekend picnic.

5. Traffic Classification Proposal
Traffic Category
Application Examples
Required Treatment
Inter-human communications (interactive), e.g., VoIP, Video conferencing
Absolute priority with no packet discard.
Delay typically < 50ms
Real-time,
Delay Intolerant
Single-human communication (non-interactive), e.g., Steaming audio or video
Guaranteed delivery with little to no packet discard
Delay typically < 500ms
Real-time,
Delay Tolerant
Transaction processing, e.g., financial transactions, e-commerce
Guaranteed delivery with minimal packet discard
Delay typically < 5000ms
Non-Real-time, Mission Critical
Non-Real-time,
Non-Mission Critical
, Web, FTP, SNMP, etc.
Best effort delivery

6. PEN (Policy Enabled Networking) Strategy
3 Key Focus Areas
QoS and Service Classification
Define Enterprise End-to-End QoS architecture
Standardize Service Classes used across Nortel products
Packet Flow Classification
Define Queuing Mechanisms
Define Congestion Avoidance Mechanisms
Policy Enablement
Define Centralized Policy Management requirements

7. QoS/CoS: What’s the difference?
WAN
CoS
CoS
CoS
CoS
QoS
For sake of discussion, let us define the following:
CoS (Nodal):
Behavioral treatment of traffic flows through a network node
Traffic Prioritization and Discarding
QoS (Network):
Guaranteed level of traffic service performance across network
CoS plus BW reservation/admission control mechanisms
Others:
An architecture delivering fast, reliable, predictable, differentiated service over a network

8. QoS achieved using CoS Mechanisms
QoS Vision
QoS over LANs
Achieved using simple CoS mechanisms
QoS over WANs
Today: Requires BW reservation/admission control mechanisms
Future: Will only need simple CoS mechanisms
Vision will be achieved by implementing:
Best CoS and congestion avoidance mechanisms
Consistent treatment of CoS across all products
Robust Policy Management solution
Simple Message:
QoS achieved using CoS Mechanisms

9. Differentiated Services Model
… The industry direction

10. Differential Services (DiffServ) Model
End-to-End Architecture defined by RFC 2475
Defines CoS on a Per Hop basis
Relies on congestion avoidance mechanisms
Requires all network nodes to comply to be effective
“Open Loop” system
No feedback from network to determine if there is congestion
DiffServ Domain
Set of DiffServ nodes with common service provisioning policy
Policy Manager provides the policy

11. Ingress or Egress Nodes
DiffServ Domain
DiffServ Domain across Campus LAN
L2 Switch
L3 Switch
Interior LAN Nodes
(Network Core)
Ingress or Egress Nodes
(Network Edge)

12. Packet Treatment by DS Edge Nodes
Policing
Shaping
Scheduling
Marking
DSCP
Filtering based on:
S/D IP Address, TCP/UDP Port, Protocol ID, DS Field (ToS)
Policing
Does the flow conform to policy?
Marking
Mark/Re-mark DS Code Point based on policy
Congestion Management
Drop Precedence
Avoidance: RED or WRED
Shaping
Improves efficiency and conformance to policy
Scheduling
Ensures queues get serviced according to priorities

13. Packet Treatment by DS Core Nodes
Policing
Shaping
Scheduling
Shaping
Marking
DSCP
Scheduling
Congestion Management
Drop Precedence
Avoidance: RED or WRED
Shaping
Improves efficiency and conformance to policy
Scheduling
Ensures queues get serviced according to priorities

14. Per-Hop Behaviors (PHBs)
PHBs are the packet-forwarding treatment that delivers the “differentiated service” to packets at network nodes
Policing
Possible remarking of DS Code Point (DSCP)
Enqueuing treatment (e.g., drop preference)
Shaping
Scheduling
IETF has defined the following DiffServ PHBs:
Expedited Forwarding (EF) - RFC 2598
Assured Forwarding (AF) - RFC 2597
DEfault Forwarding (DE) - RFC 2474
Prioritization of traffic flows means that traffic is classified in a network, and that the entire “class of service” is given a priority. Each network node point may have its own per-hop-behaviors, depending on the requirements of the traffic and the network.
For example, the network can be set up to classify all voice traffic as high, all data traffic as low, all video traffic as medium.
Traffic can be “shaped” or smoothed out to minimize the effect of burstiness
Traffic can be marked to designate lower-priority packets that can be dropped in cases of high congestion
Traffic can be policed, to ensure that it conforms to the levels set forth by Service-Level Agreement in place
Traffic is scheduled based on classification, through the priority queuing process
The above process of classifying, marking, policing and shaping, is managed at edge and boundary routers that support DiffServ.

15. DS Field DS Field defined by RFC 2474 Supercedes existing definitions
IPv4 ToS Field (RFC 791)
IPv6 Traffic Class Octet (RFC 2460)

16. DiffServ Traffic Classification

17. Expedited Forwarding (EF) PHB - RFC 2598
“Virtual leased line” Substitute “Service”
Police and drop on network ingress
Modest buffering needed (no burst)
Typically uses strict priority queuing
Shape on egress to maintain contract with next DS Domain
Network Engineering Requirements
Egress rate must exceed ingress rate
Traffic Engineering Guidelines
For multiservice networks, EF Traffic is typically kept to a small fraction of total network traffic, e.g., 10%
However, this is completely application-dependent
Forwarding treatment requires that (at each node) egress rate exceeds ingress rate for a conforming aggregate
“Virtual leased line”
Police and drop on network ingress
Modest buffering needed (no burst)
Some form of priority queuing
Shape on egress to maintain contract to next provider
Should be kept to a small fraction of total network traffic
Proposed Standard
EFDSCP =

18. Assured Forwarding (AF) PHB - RFC 2597
Lowest
Latency
Highest
Latency
Lowest
Discard
Highest
Discard
Four traffic classes
Each with assigned guaranteed bandwidth levels
Similar to Frame Relay CIR
Three drop preferences for each traffic class
High/Medium/Low drop preference
Similar to Frame Relay DE
Token bucket policers for each priority
Enqueuing uses RED or similar mechanism
To distinguish between drop preference and control congestion
Scheduling based on bandwidth given to the priority
4 AF Classes (priority classes)
3 Drop Precedences per AF class
6-bit value located in the DS Field

19. Proposed Service Classification for Nortel
DiffServ PHBs
EF PHB
AF PHBs
DE PHB
Service Class names make configuration more intuitive

20. Congestion Avoidance Mechanisms
Required for DiffServ architecture to work properly
Drop Precedence
AF PHB offers 3 levels of drop precedence for each AF class
All DE PHB traffic is eligible to discard
No EF PHB traffic is eligible to discard
RED
Required to break global synchronization of TCP/IP sessions
Actively and randomly drops packets
WRED/MRED variants allow weighting of different queues

21. Traffic Scheduling Strict Priority Schedulers
Assigns a fixed % of total BW to a queue
Queue must be emptied prior to others being serviced
Weighted Bandwidth Schedulers
Lower priority queues borrow higher priority queue BW when available
Higher priority queues reclaim borrowed BW as needed
Two Commonly used algorithms
Weighted Round Robin (WRR)
Weighted Fair Queuing (WFQ)
Weighted Round Robin (WRR)
All queues are serviced in sequence, e.g., Q1, Q2, Q3, Q1, etc.
% BW assigned to each queue
Focus on Throughput
Weighted Fair Queuing (WFQ)
Suited for delay-intolerant interactive traffic
Low BW flows serviced before high BW flows
High BW flows share remaining BW
Focus on Latency Performance

22. Nodal Handling

23. Mapping IP to/from Link Layers
… preserving DiffServ behavior at Layer 2

24. IP/Layer 2 Traffic Classification
IP Filtering on:
Source/Destination IP Address
Source/Destination TCP/UDP Port number
DSCP
Protocol ID
Ethernet 802.1p User Priorities
8 User Priorities
Highest level queue serviced before next lower level queue
ATM
CBR, rt-VBR, nrt-VBR, ABR, UBR
Single or Multiple Virtual Circuits
Frame Relay
CIR, EIR, DE

25. Ethernet 802.1p User Priorities
6 bytes
6 bytes
4 bytes
2 bytes
bytes
Dest
MAC
Source
MAC
802.1q
TAG
Protocol
Type
Data
Priority
bits
C F I
VLAN ID
Tag
Protocol
Identifier
Tag
Control
Info
8 User Priorities (traffic classes)
DiffServ PHB mapped to/from 802.1p User Priorities

26. DSCP to 802.1p Mapping Example
Standard, power-up default mapping
Egress to non-Layer 3 “aware” L2 Switch
Required because L2 switch cannot interpret DSCP

27. DSCP to ATM CoS Mapping Example
Sample, power-up default mapping
ATM to DSCP mapping not required
IP DSCP is preserved across ATM network

28. DSCP to Frame Relay VC Mapping Example
Frame Relay does not have any native CoS mechanisms
Each VC is assigned the following for each flow
Guaranteed BW (CIR)
Burst BW (EIR)
Discard Eligibility (DE)

29. RSVP for QoS Signaling
… a new use for RSVP

30. New use for RSVP RSVP for DiffServ Used as a QoS signaling mechanism
Application or appliance uses RSVP to request:
Bandwidth
Prioritization
Authentication
Authorization
Request made to edge device in DiffServ domain
Edge device or Policy Server admit or reject request
Driven by Microsoft’s inclusion of RSVP enabling technology in Windows 2000
RSVP traditionally associated with IntServ architecture
Creates “stateful” connection-oriented end-to-end paths
IntServ never gained popularity due to limited scalability
RSVP for DiffServ
Will not maintain “stateful” end-to-end connections
RSVP used to request bandwidth, priority, authentication and authorization
DiffServ architecture will provide QoS via associated behavioral treatment of packets in each DS node

31. IP Classification w/o RSVP QoS Signaling
PBX VoIP
Sets DSCP
Upstream devices configured to respect DSCP
Supports H.323
Router (VoIP Media Gateway)
Sets DSCP based on OPS policy setting
“State” is maintained between OPS and router
L3 Switch
Sets DSCP or 802.1p User Priority based on OPS policy setting
L2 Switch
Sets DSCP and 802.1p User Priority based on OPS policy setting
Etherset
Sets DSCP or 802.1p User Priority

32. IP Classification with RSVP QoS signaling
PBX VoIP
Sets DSCP
Upstream devices configured to respect DSCP
Supports H.323
Router VoIP Media Gateway
Detects RSVP packet
Requests policy from OPS based on RSVP message
Sets DSCP based on Optivity Policy Server (OPS) policy setting
“State” is maintained between OPS and router
L3 Switch
Detects RSVP packet and forwards to OPS
OPS determines DSCP and sends via COPS
Etherset
Sets DSCP or 802.1p User Priority
Client PC
QoS signaled via RSVP
Win2000 app. sets DSCP
NIC sets 802.1p user priority
L2 Switch
Detects RSVP packet and forwards to OPS
OPS sends DSCP via COPS
Maps DSCP to user priority

33. Summary DiffServ is the predominant IP QoS Architecture
IP QoS is in the early stages of standardization
Good traffic management required to make all this work
Policy Enablement simplifies and automates network administration

34. Questions ? John A. Clark - Technical Account Manager
Thank you
Questions ?
John A. Clark - Technical Account Manager