Chapter 4

© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 1Version 4.0

Identifying Application Impacts on Network Design

Designing and Supporting Computer Networks – Chapter 4

© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 2

Objectives Explain how applications and traffic flow can affect the

design of the network

Identify application impacts on network design

Explain how Quality of Service is implemented on the LAN/WAN

Explain the options for supporting voice and video traffic on the network

Document the network requirements of specific categories of applications and diagram the application traffic flows through the network


Explain How Applications and Traffic Flow Can Affect the Network Design

Application performance depends on availability and responsiveness

Measurement: user satisfaction, throughput, technical metrics



Four main types of application communication:

Client-to-client

Client-to-distributed server

Client-to-server farm

Client-to-enterprise edge


Characterize applications by gathering information:

Organizational output

Network audit

Traffic analysis




Internal traffic: identify areas where high bandwidth is needed, and possible bottlenecks

External traffic: determine placement of firewalls and DMZ networks



Installed hardware affects application performance

Choose hardware after analyzing technical requirements



Transaction-processing applications:

Additional operations required

Immediate response to user requests

Redundancy and security required



Real-time streaming applications:

Minimize latency and jitter

Infrastructure may need to be upgraded



File transfer and email applications:

Unpredictable bandwidth usage

Large packet size

Centralization of file and mail servers in a secure location

Redundancy to ensure reliable service



HTTP and web traffic:

Network media

Redundancy

Security



Microsoft Domain Services:

Active Directory Services

Broadcast generation

Tight integration between ADS, DNS, and DHCP


Explain how Quality of Service is Implemented on the LAN/WAN

Capability of a network to provide preferential service to selected network traffic

Dedicated bandwidth, controlled jitter and latency, and reduced packet loss



Implementing traffic queues:

Identify traffic requirements

Define traffic classes

Define QoS policies



Set priorities to manage traffic:

Queue type

Traffic assignment

Size

Filter traffic into high, medium, normal and low priorities



Where QoS can be implemented to affect traffic flow:

Layer 2 devices

Layer 3 devices


Explain the Options for Supporting Voice and Video Traffic on the Network

Network design implications of converged networking:

Strong performance

Security features

Mandatory use of QoS mechanisms



Network design implications of IP telephony:

Power and capacity planning

Identifying contending traffic flows

Selecting components for the IP telephony solution



Live video:

Streaming media files

User sees content before all packets have arrived

No need to store large media files before playing them

Uses multicast packets to many users at the same time

Video on Demand:

Either stream or download before viewing

Users can store content and view later

Unicast packets to a specific user requesting the service



Supporting remote workers with voice and video:

Assess bandwidth requirements for WAN connection

Permanent link or on-demand


Document the Network Requirements of Specific Categories of Applications

Estimate the volume of application traffic during the initial design phase.

Document projected applications and associated hardware in a network diagram.



Diagram the flow of traffic to and from hosts and servers within the LAN



Diagram the flow of traffic to and from remote sites, including VPN traffic



Diagram outgoing traffic flows destined for the Internet gateway and incoming traffic from the Internet to locally-provided services



Diagram extranet traffic flows to and from selected trusted partners, customers, and vendors


Summary End users evaluate network performance based on the

availability and responsiveness of their applications.

The choice of hardware installed on a network can affect the performance of the applications.

When adding a new application, the designer must consider the impact on the performance of existing applications.

Voice and video applications present unique requirements, as they cannot tolerate delays.

Security and reliability are primary concerns in a network supporting high volumes of web traffic.

The primary goal of QoS is to provide priority, dedicated bandwidth, controlled jitter and latency, and reduced packet loss.


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