Network PerformanceArchitecture

Ahmad M. Shaheen

200810964

December 28, 2011

Revision / Component Architectures

• Network architecture is understanding of the relationships between (architectural) components of the network.

• Component architecture is a description of how and where each function of a network is applied within that network.

• Addressing/routing

• Network management

• Performance

• Security.

Background / Performance Arch.

• It is the relationship between network components and performance requirements.

• Network Components: Users, Applications and Devices

• Performance Requirements: Capacity, Delay, RMA

Introduction

• Performance is the set of levels for capacity, delay, and RMA in a network.

• 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

- Internal & External relationships between the network and

other components.

Performance consists of

Performance Architecture

• Before applying performance mechanism we must insure that:

1) The performance mechanisms are necessary for this network

2) The performance mechanisms will solve a performance problem

3) The performance mechanisms are sufficient for this network

• If we decide to implement a performance mechanism we should

start from simple and move toward the complex architecture.

Such as:

1. implementing performance mechanisms only in selected areas

of the network

2. By using only one or a few mechanisms

3. by selecting only those mechanisms that are easy to implement, operate, and maintain.

Performance Architecture

• NOTE

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.

Performance Mechanisms

• Performance mechanisms are:

– Quality of Service (QoS)

– Resource Control (RC)

prioritization

traffic management

scheduling

queuing

– Service-Level Agreements (SLA)

– Policies

Quality of Service (QoS)

• There are two principal approaches to QoS , a parameterized system based on an exchange of application requirements with the network, and a prioritized system where each packet identifies a desired service level to the network.

There are two standard types of QoS :

1. Differentiated services (DiffServ)

implements the prioritized model. DiffServ marks packets

according to the type of service they desire.

2. Integrated services (IntServ)

implements the parameterized approach. In this model,

applications use the Resource Reservation Protocol (RSVP)

to request and reserve resources through a network.

Quality of Service (QoS)

• IntServ

• 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.

Quality of Service (QoS)

• DiffServ:

• 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.

• DiffServ and IntServ can be applied individually or together,If both

mechanisms applied together the DiffServ is first applied and

IntServ is then overlaid onto it

Resource Control / 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.

• Priority levels for users, applications, and devices determined

during requirements analysis

• Priority levels for traffic flows determined during the flow

analysis process

Resource Control / Prioritization

• 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 )

• Priority level 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

Resource Control /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

Resource Control / 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)

Resource Control / Queuing

• Queuing is storing packets within a network device while they wait for processing.

• There are a number of queuing mechanisms available

in network devices:

• First in first out (FIFO)

• Class-based queuing (CBQ)

• Weighted fair queuing (WFQ)

• Random early detect (RED)

• Weighted RED (WRED)

Resource Control / 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

Resource Control / Queuing

• 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.

• Weighted RED (WRED)

• operates in the same fashion as RED

• but supports multiple priority levels (one for each queue) for dropping packets

Resource Control / Queuing

• Generally, when a queue becomes full,

• 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.

NOTE

• 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)

Thank you all …

Ahmad M. Shaheen