1. Performance Architecture
By Dr. Shadi Masadeh 1

2. Performance Architecture
Describes how user, application, device, and (existing) network requirements for performance (capacity, delay, and RMA [reliability, maintainability, and availability]) will be met within the planned network.
The performance architecture is the newest of the component architectures, and it is rapidly evolving to include many new mechanisms to achieve network performance.

3. Performance Architecture
Objectives
We will learn:
What performance means in a network, including descriptions of mechanisms to achieve performance
How to determine the relationships both among these mechanisms and between performance and the other architectural components
How to develop the performance architecture.
Develop goals for performance that will guide the development of this architecture.

4. Performance Architecture
Background
Performance is the set of levels for capacity, delay, and RMA in a network.
Desirable to optimize these levels, to one or more sets of traffic flows, based on groups of users, applications, and/or devices.
Performance architecture: is the set of performance mechanisms to configure, operate, manage, provision, and account for resources in the network that support traffic flows.
Where these mechanisms are applied within the network, and the sets of internal and external relationships between this and other component architectures.

5. Performance Architecture
Background
Importance of developing Performance Architecture:
Determining the performance goals of a network.
Performance may be applied to:
Improve the overall performance of the network (e.g., to improve response times and throughput to all users)
Support a particular group or groups of users or applications, maybe new or planned applications
Control resource allocation for accounting, billing, and/or management purposes

6. Performance Architecture
Background
performance consists of one or more of the following (Figure 8.1):
controlling traffic inputs to the network (admission and rate controls)
adjusting the baseline performance of the network (traffic or capacity engineering)
controlling all or part of the network for delivery of specific services (prioritizing, scheduling, and conditioning traffic flows)
implementing a feedback loop to users, applications, devices, and management to modify controls as necessary.

8. Performance Architecture
Developing Goals for Performance
toward developing performance architecture, we should answer the following questions:
Are performance mechanisms necessary for this network?
What are we trying to solve, add, or differentiate by adding performance mechanisms to this network?
Are performance mechanisms sufficient for this network?
we should already have the information needed to make a decision from the requirements and flow analyses.

9. avoid implementing mechanisms just because they are interesting or new.
For example, it may be tempting to implement QoS mechanisms in a network, even when there are no clear goals or problems to solve.
start simple and work toward a more complex architecture.
Simplicity may be achieved by:
implementing performance mechanisms only in selected areas of the network (e.g, at the access or distribution [server] networks)
By using only one or a few mechanisms
by selecting only those mechanisms that are easy to implement, operate, and maintain.

10. Performance Architecture
Developing Goals for Performance
There should be information in the requirements and flow analyses that can help in determining the need for performance mechanisms in a network; include:
Clearly different sets of network performance requirements, per user, group, application, device, and/or flow
Requirements to bill and account for network service.
When you plan to implement performance mechanisms in a network, you should also determine whether or not your customer is willing to pay the costs for such mechanisms.

11. For example, does your customer have a network staff capable of configuring, operating, and maintaining QoS, SLAs, and policies?
If not, are they willing to pay the cost to acquire such staff, or outsource performance (and some portion of network management)?
Performance is not a capability that is implemented once and then forgotten; it requires continual support.
If your customer is not willing to provide that support,
it is better not to implement such mechanisms.

12. Performance Architecture
Developing Goals for Performance
when performance mechanisms are implemented and not supported, maintained, or kept current, performance in the network can actually degrade to a point where it would be better not to have any performance mechanisms at all.
Some common problems that are addressed by the performance architecture include:
Improving the overall performance of a network
Improving the performance to select users, applications, and/or devices
Changing the network from a cost center to profitability
Merging multiple traffic types over a common network infrastructure
Differentiating (and possibly charging) customers for multiple levels of service

13. Performance Architecture
Performance Mechanisms
Performance mechanisms are:
Quality of Service (QoS)
Resource Control (RC) (prioritization, traffic management, scheduling, and queuing)
Service-Level Agreements (SLA)
Policies.
Subsets of these mechanisms are usually used together to form a comprehensive approach to providing single-tier and multi-tier performance in a network.
These mechanisms provide the means to identify traffic flow types, measure their temporal characteristics, and take various actions to improve performance for individual flows, groups of flows, or for all flows in the network.

14. Performance Architecture
Quality of Service
QoS, is determining, setting, and acting upon priority levels for traffic flows.
QoS is usually associated with
IP QoS (including MPLS), type of service (ToS), and Frame Relay committed information rate (CIR).
IP-based traffic, there are two standard types of QoS (two views of network service):
differentiated services (DiffServ, or DS)
perspective of aggregating traffic flows on a per-hop basis based on traffic behavior
integrated services (IntServ, or IS)
perspective of supporting traffic flows on an individual, end-to-end basis.

15. Performance Architecture
Quality of Service
IntServ: specifies a fine-grained QoS system
every router in the system implements IntServ, and every application that requires some kind of guarantees has to make an individual reservation.
Resource Reservation Protocol "RSVP“: is the underlying mechanism to signal QoS across the network:
All machines on the network capable of sending QoS data send a PATH message every 30 seconds, which spreads out through the networks.
Those who want to listen to them send a corresponding RESV (short for "Reserve") message which then traces the path backwards to the sender.

16. Performance Architecture
Quality of Service
IntServ: specifies a fine-grained QoS system
DiffServ: coarse-grained control system.
IP packets are marked in the type of service (ToS) byte for IPv4 or in the traffic class byte in IPv6 so that they will receive the corresponding performance at each network device (or hop).
DiffServ defines a set of values for classes of traffic flows
It applies to aggregates of traffic flows (e.g., composite flows), not individual traffic flows.

17. Performance Architecture
Quality of Service
In DiffServ:
IP packets are marked in the type of service (ToS) byte for IPv4 or in the traffic class byte in IPv6
defines a set of values (termed differentiated services code points, or DSCPs) for classes of traffic flows, to be used by resource control mechanisms.
it applies to aggregates of traffic flows (e.g., composite flows), not individual traffic flows.
By aggregating flows into traffic classes
The main reason for this is for scalability
Storing and maintaining state information become more tenable
Traffic classes for DiffServ:
Best-effort: normal IP packets
Assured Forwarding (AF): assured forwarding can be used for traffic with both delay and capacity requirements (e.g., multimedia or tele∗services)
Expedited Forwarding (EF) : traffic that has delay requirements (e.g., real-time or interactive)

18. Performance Architecture
Quality of Service
In IntServ:
defines values and mechanisms for allocating resources to flows across the end-to-end path of the flow.
placing importance on supporting a flow at every network device in the end-to-end path of that flow.
it requires resources (e.g., memory, processing, bandwidth) for each flow
It requires a mechanism to communicate flow requirements
across network devices (signaling provided by RSVP and MPLS)
RSVP is used to request specific quality of service levels from network devices in the end-to-end path of a traffic flow.
Reserve state information about the requested service.
DiffServ and IntServ can be applied individually or together
If both mechanisms applied together:
In this case DiffServ is first applied and IntServ is then overlaid onto it

19. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
DiffServ and IntServ are used to apply prioritization, traffic management, scheduling, and resource control to traffic flows:
The represent the heart of providing performance in a network
Performance architecture:
may include one or more of these mechanisms, in conjunction with QoS, SLAs, and policies
These mechanisms can be:
implemented in network devices such as routers and switches
applied to the network as stand-alone hardware (traffic management devices)

20. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Prioritization:
The process of determining which user, application, device, flow, or connection gets service ahead of others, or gets a higher level of service.
Necessary since traffics compete for network resources.
limited amount of resources available in any network
who gets resources first
how much resources they get.
Begins during the requirements and flow analysis processes.
Priority levels for users, applications, and devices determined during requirements analysis
Priority levels for traffic flows determined during the flow analysis process
Two high-level views of performance:
Single-tier performance: (may apply across the entire network)
Multi-tier performance: one or more groups of traffic flows, based on groups of users, applications, and/or devices (may apply in select areas, or as an addition to single-tier )

21. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Prioritization:
Multiple levels of performance implies a need to prioritize traffic flows
Prioritization is based on importance and urgency
The basic case of prioritization when all have the same priority level
the case in best-effort networks
When greater than the general case
they will have higher priority levels.

22. Priority level may be: changed based on urgency based on:
Protocol type (e.g., TCP versus UDP)
Service, or port number
IP or MAC-layer address
Or by other information embedded within the traffic
maintained in databases and coupled with policies and SLAs
Priority levels are used by network devices:
To determine if traffic flows will be allowed on the network (admission control)
Scheduling of traffic flows onto the network
Conditioning of flows throughout the network.

23. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Traffic Management
Consists of:
Admission control: the ability to refuse access to network resources
Traffic conditioning: a set of mechanisms that modify (increase or decrease) performance to traffic flows
Admission control:
Uses priority levels to change the behavior of network access
In a best-effort network without admission control, access to the network all traffic flows have a (more or less) equal chance to get network resources.
Access is permitted, denied, or sometimes delayed, based on the relative priority of that traffic.

24. Performance Architecture
8.4.2 Prioritization, Traffic Management, Scheduling, and Queuing
Traffic Management
Traffic conditioning
Traffic flows are identified and distinguished|:
Classification is the ability to identify traffic flows
looks at various parts of the IP packet
IP addresses, port numbers, protocol types or may look deeper into a packet.
For example, voice over IP (VoIP) signaling flows may be determined by looking for session initiation protocol (SIP) identifiers
Upon identifying traffic flows
Packets may be marked/ tagged with a priority level
Examples: tagging packets with DiffServ Code Points (DSCPs) for best-effort (BE), assured forwarding (AF), and expedited forwarding (EF) priority levels.

25. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Traffic Management
After classification; traffic may be metered to determine their performance levels.
Metering: measuring the temporal performance
traffic rates and burst sizes
Metering:
is a capability provided in network devices (e.g., routers and switches)
can also be applied as a separate network device
For example, a traffic flow may be metered over a period of 1 second. Each second, the peak data rate for that flow is compared with a capacity boundary of 1.5 Mb/s, which was input into the network device from an SLA developed for that traffic flow.

26. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Traffic Management
Metering a traffic flow can determine whether or not a flow is within performance boundaries (Figure 8.4).
Conforming traffic is within performance boundaries
no action is taken
forwarded to the appropriate output queue
Non-conforming traffic is outside of performance boundaries

28. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Traffic Management
Non-conforming: (it is exceeding the specifications of an SLA)
subject to shaping or dropping
Shaping is delaying traffic to change a performance characteristic
Dropping is discarding traffic
Non-conforming traffic may also be marked, with no other action taken
To shape non-conforming traffic:
sent to a shaper queue where delay is added; (changes the performance of that traffic flow)
Consider an SLA for a traffic flow that specifies a peak rate of 1.5 Mb/s. A meter is measuring that traffic flow, and calculates a rate of:
200 packets/second∗1500 byte packets∗8 bits/byte = 24 MBits/second

29. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Traffic Management
To shape non-conforming traffic:
Consider an SLA for a traffic flow that specifies a peak rate of 1.5 Mb/s. A meter is measuring that traffic flow, and calculates a rate of:
200 packets/second∗1500 byte packets∗8 bits/byte = 24 MBits/second
This is compared with the SLA specification (1.5 MBits/second) and found to be non-conforming. Subsequent packets are then forwarded to a shaper queue, where they are delayed by an average of 10 ms. As a result, only 100 packets can be transmitted per second, and the rate of that traffic flow becomes:
100 packets/second∗1500 byte packets∗8 bits/byte = 12 MBits/second
Shaping continues either for a specified period of time or until the traffic flow is again conforming
The most serious action that can be taken on traffic is dropping, or discarding, packets
This is done when a traffic flow is seriously exceeding its performance boundary, or when the network device is congested to the point where dropping packets is necessary. Traffic conditioning functions are shown in Figure 8.5

31. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Scheduling
Scheduling is the mechanism that determines the order in which traffic is processed for transmission.
provided through network management
or as part of the QoS
Scheduling may be:
proprietary (enterprise-specific)
or standards-based use scheduling algorithms:
include weighted fair queuing (WFQ)
class-based queuing (CBQ)
The combination of QoS, prioritization, traffic management, and scheduling can be applied across a network to achieve various performance levels for traffic flows (Figure 8.6)

33. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Queuing
Queuing is storing packets within a network device while they wait for processing.
Locations where packets are stored (queues):
holding packets received from the network
processing for QoS
holding packets for transmission onto the network
There are a number of queuing mechanisms available in network devices.
For example, queue mechanisms may treat all packets in the same way
may randomly select packets for processing
may favor particular packets
the following queuing mechanisms achieve that:
First in first out (FIFO)
Class-based queuing (CBQ)
Weighted fair queuing (WFQ)
Random early detect (RED)
Weighted RED (WRED)

34. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Queuing
First in first out (FIFO) queuing: simplest queuing mechanism available
Packets are stored in a single queue
Packets are transmitted onto the network in the order that they were received (at the input queue).
Class-based queuing (CBQ):
Multiple queues with differing priorities
Priority levels are configurable in the network device and indicate the performance levels required for each traffic type
Packets of each priority level are placed in their respective queues
Higher-priority queues are processed before lower-priority queues
Weighted fair queuing (WFQ)
Assigns priorities (weights) to queues
High-priority traffic flows are processed first, and lower-priority traffic flows share the remaining resources.

35. Performance Architecture
Prioritization, Traffic Management, Scheduling, and Queuing
Queuing
Generally, when a queue becomes full (e.g., during periods of congestion),
packets are dropped either from the beginning of the queue (head) or end of the queue (tail).
In either case, the dropping of these packets is likely to be unfair to one or a few traffic flows.
As a result, random early detect (RED) was developed to randomize the packet dropping process across a queue.
RED will drop packets early (before the queue is actually full) to force traffic flows (i.e., TCP flows) to adjust by reducing their transmission rate.
Weighted RED (WRED)
operates in the same fashion as RED
but supports multiple priority levels (one for each queue) for dropping packets