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Identifying Application Impacts on Network Design

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  1. Identifying Application Impacts on Network Design Designing and Supporting Computer Networks – Chapter 4

  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

  3. 4.1.2 Explain How Applications and Traffic Flow Can Affect the Network Design • Application performance for end users is based on • Availability--when they need it? • Responsiveness—responding as quickly as expected? • When is Application Performance considered critical? • When it is critical to the company being able to do business • Measurement: user satisfaction, throughput, technical metrics

  4. 4.1.2 Characteristics of Different Application Categories • Client-to-client (IP Telephony) • Client-to-distributed server (servers and Users on same LAN) • Client-to-server farm (organizational mail servers like Microsoft Exchange) • Client-to-enterprise edge (external mail servers and public web servers)

  5. 4.1.2 Characteristics of Different Application Categories Characterize applications by gathering information: • Organizational input—existing documentation about the network • Network audit—gathers information about network devices, monitors traffic and reveals details of the current network configuration • Traffic analysis—provides information about how the applications and protocols use the network • Cisco IOS Software Embedded tools—that conducts audits and traffic analysis • Network-Based Application Recognition (NBAR) is a Cisco utility that recognizes web-based and other difficult-to-classify protocols that utilize dynamic TCP and UDP port assignments • NetFlow—provides a set of services for IP applications • Network traffic accounting • Usage-based network billing • Network planning • Security • Denial of Service monitoring capabilities • Network Monitoring

  6. 4.1.3 How Traffic Flow Can Affect the Network Design • Internal traffic: identify areas where high bandwidth is needed, and possible bottlenecks • Generated by local hosts going to other hosts with the network • External traffic: determine placement of firewalls and DMZ networks • Traffic initiated by users outside the local network coming into the internal network • Local traffic being sent to remote networks • Such as a person in your company going to a competitor’s site or to an external email account like gmail)

  7. 4.1.4 How Application Characteristics Affect Network Design • Installed hardware affects application performance • Hardware delays can be caused by Processing time a router takes to forward traffic and older switches unable to handle traffic loads • Choose hardware after analyzing technical requirements

  8. 4.2.1 Identifying Application Impacts on Network Design Transaction-processing applications: • Immediate response to user requests by computer • Each request by user is a transaction • Can require additional operations to take place in response to the original request • Redundancy and security required

  9. 4.2.1 Transaction Processing • Atomic Transactions—guarantees that if the transaction isn’t performed complete, the entire transaction is void • A transaction that is to delete multiple records fails to complete, then none of the records are deleted • Consistent Transaction—ensures incomplete transactions are not allowed, if it is incomplete, the system returns to the state it was before the transaction began • Isolated Transaction—kept secure from all other transaction on the network. Includes the use of ACLs, encryption and firewalls • Durable Transaction—Once the transaction is completed, it will not be undone (even if there is a system failure) • A person orders tickets and the information is all taken down. Later the network goes down…the person’s tickets are still reserved

  10. 4.2.1 Transaction Processing • Redundancy—consider the impact of each transaction on the network • Reduction or elimination of network downtime • Increased availability of applications • No single points of failure • Servers handling transaction processing should have an alternate path to receive or deliver traffic • Rapid Spanning Tree Protocol—(RSTP)prevents Layer 2 switching loops that can occur with redundant switches • Hot Standby Routing Protocol (HSRP)—can provide layer 3 redundancy in the network by providing immediate or link-specific failover and a recovery mechanism

  11. 4.2.1 Transaction Processing • Security—protecting the privacy and integrity of the transaction information and the transaction database • VPNs use tunneling—often referred to as “Port Forwarding” • The transmission of data through a public network that is intended for a private network • Accomplished by encapsulating the private network data and protocol information within the public network transmission units • Intrusion Detection Systems (IDS) are used to monitor network traffic for suspicious activity and alerts the administration • Firewalls are used to filter traffic based on set of criteria • ACLs can filter harmful traffic that is trying to enter the network and block specific traffic from exiting the network.

  12. 4.2.2 Real Time Streaming and Voice Applications • Traditional telephone system Infrastructure may need to be upgraded • Such as switches, cabling to support gigabit traffic • Need to support Power over Ethernet (PoE) if switches are properly equipped • VoIP requires voice-enabled routers if using Traditional telephones (analog voice converted to IP Packets) • If using IP telephony, phone performs voice-to-IP conversion (eliminates the need for voice-enabled routers) • Real-time streaming applications such as video surveillance and IP telephony • Traffic must be forwarded with minimal latency (less than 150 ms) and jitter • May require • Special hardware devices • Special connections • Physical redundancy

  13. 4.2.2 Real Time Streaming and Voice Applications • Real-time Video Protocols transport streaming media • Real-Time Transport Protocol (RTP) • Real-Time Transport Control Protocol (RTCP) • Both enable control and scalability of the network resources • Incorporates QoS to minimize latency • Includes priority queuing, custom queuing, low latency queuing and class-based weighted fair queuing • All video of the events held in the stadium to be viewed in real-time from anywhere in the stadium

  14. 4.2.3 File Transfer and Email • Unpredictable bandwidth usage—user initiated and can’t be reliably predicted • Large packet size • FTP and other file transfer traffic uses large packet sizes for efficient transfer which causes delay for other traffic • HTTP transfers • copying from shared networks • Response-time requirements are low • Centralization of file and mail servers in a secure location • Redundancy to ensure reliable service

  15. 4.2.3 File Transfer and Email • Email—obviously one of the most popular network services • Has revolutionized how people communicate • Requires several applications and services • Post Office Protocol (POP) • Simple Mail Transfer Protocol (SMTP) • Email Client Processes—application used to access email service to compose, send messages, and place in user’s mailbox • Email Server Processes—server transfers and delivers mail to the client

  16. 4.2.3 File Transfer and Email • Secure file/mail servers in a centralized location (server farm) • Protect from unauthorized access both physically and logically • Create redundancy in the server farm so files will not be lost • Configure redundant paths to the servers

  17. 4.2.4 HTTP and Web Traffic • Network media—layer 3 devices to control internal and external traffic flows • Redundancy—both in components and power sources • Security—ACLs, firewalls, IDS and physically secured from unauthorized access

  18. 4.2.5 Microsoft Domain Services • Active Directory Services requires DNS to locate domain controllers to provide authentication and authorization services • Broadcast generation • Tight integration between ADS, DNS, and DHCP • Requires common TCP/UDP ports be open

  19. 4.3.1 What is QoS and Why do we need it? • Goal: provide priority service, including dedicated bandwidth, controlled jitter and latency, and reduced packet loss to selected traffic • First step to implementing QoS in traffic queues--- • IDENTIFY THE TRAFFIC REQUIREMENTS

  20. 4.3.1 What is QoS and Why do we need it? Implementing traffic queues: • Identify traffic requirements • Define traffic classes • Define QoS policies • Users perceive service quality based on: • Speed with which the network reacts to their request • The availability of the applications they want to use • Some Cisco Devices, such as routers, have built-in QoS mechanisms

  21. 4.3.1 What is QoS and Why do we need it? • IP Telephony Requirements • Requires more than a simple connection between users • Delays cause voice to break up and words to be distorted • Low jitter • Low latency • One-way delay no greater than 150 ms • Streaming Video Requirements • Sent from prerecorded files • Can be live broadcast converting video into compressed digital signal in multicast (so multiple users can view at same time) • Traffic queues help manage priority traffic on converged networks • Two network applications most affected by congestion and delays • IP TELEPHONE • LIVE VIDEO WEBCAST

  22. 4.3.2 Traffic Queues • Voice and Data Traffic—requires real-time, no time to retransmit packets with errors. VoIP uses UDP as a best-effort transport protocol • Must be processed at rate it is sent • File Transfer—large files, use error checking and retransmission features of TCP • Fine for files, not fine for voice!

  23. 4.3.2 Traffic Queues • Queues are used to manage traffic flow with QoS • Hardware queues send data in order it is received (TxQ) • Software queues allow data to be sent based on the priority set by administrator • PQ—Priority Queuing • CQ—Custom Queuing • Implementing QoS in Traffic queues means the designer must prioritize traffic • Identify traffic requirements needed for different types • Place in appropriate classes • Define the QoS policies to be applied to each class

  24. 4.3.3 Priorities and Traffic Management Priority Queuing is useful for time-sensitive and mission-critical protocols • Queue type • Traffic assignment • Size • Filter traffic into high, medium, normal and low priorities

  25. 4.3.3 Priorities and Traffic Management • AutoQoS • Simple, intelligent, CLI that enables LAN and WAN QoS for VoIP • Incorporates the Cisco best practices for implementing quality of service • Easy for customers to configure their networks for voice and video • Reduces deployment cost and time frame by as much as 2/3’s when compared to manual approach

  26. 4.3.4 Where Can QoS be implemented? • Layer 2 devices—switches at the Access Layer support QoS based on IEEE 802.1p Class of Service (CoS) • Layer 3 devices—support QoS based on Physical interface, IP address, logical port numbers • Classification—process by which traffic is grouped • Allow partition of traffic into multiple priority levels or classes of service

  27. 4.4.1 Converged Network Considerations • Strong performance • Security features • Mandatory use of QoS mechanisms

  28. 4.4.2 Requirements of an IP Telephony Solution • Power and capacity planning • Identifying contending traffic flows • Selecting components for the IP telephony solution • Components of an IP telephony solution can include: • IP phones • Voice Gateway • Connects a VoIP system to the PSTN • Multipoint control unit (MCU) • Supports audio and Video Conferencing • Call agent • processes calls specifically for a VoIP network • IP Communicator • Software-based VoIP • Application servers • Video endpoint • Software telephone

  29. 4.4.2 Requirements of an IP Telephony Solution • Isolating traffic—simplest method to avoid a conflict • Separate VLANs • QoS can prioritize the IP telephony traffic as it crosses the network • NA can identify and troubleshoot network problems more easily

  30. 4.4.2 Requirements of an IP Telephony Solution • Traditional Telephony • Central control unit called private branch exchange (PBX) • Routes calls (digital or analog) based on type • Physical address of the phone is dependent on the wire to which it is connected which complicates changes • VoIP • Voice enabled routers convert analog voice from traditional telephones into IP packets • QoS can prioritize the IP telephony traffic as it crosses the network • NA can identify and troubleshoot network problems more easily • IP Telephony • Replaces traditional phones with IP phones • Uses Cisco Unified Communications Manager to manage phones centrally • Integrates voice and voice-messaging applications • Uses an IP phone to perform voice-to-IP conversion • Simplified moves, additions and changes • Reduces cost

  31. 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 on servers in a centrally located server farm Called store-and-forward Minimizes load on system resources Unicast packets to a specific user requesting the service 4.4.3 Video - Live and On-Demand

  32. 4.4.4 Supporting Remote Workers with Voice and Video • Assess bandwidth requirements for WAN connection • Permanent link or on-demand • Asynchronous dialup • ISDN BRI • Cable modems • DSL • Wireless and satellite • VPN

  33. 4.5.1 What is Traffic Flow? • Traffic Flow—movement of data from one location in the network to another • Path typically defined by a Network Layer IP address • Traffic Control—QoS mechanisms are designed to ensure the smooth flow of application traffic on the network • Application Traffic Flows—estimate volume of application traffic during the design to help with congestion

  34. 4.5.1 What is a Traffic Flow • Diagram the flow of traffic to and from hosts and servers within the LAN • Document both existing and new traffic • Analyze the proposed design, identify where network can be improved

  35. 4.5.2 Diagramming Internal (intranet) Traffic • Traffic being sent from host to host and host to server • Traffic within the network is easy to identify • What can you determine by diagramming internal traffic flow? • Areas where network congestion may occur • Locations where high-bandwidth connections are required

  36. 4.5.3 Diagramming Traffic Flows To and From Remote Sites • Primarily transactional processes • Mission critical • Calculate amount of traffic flowing from remote sites as part of the external traffic flows into the internal network

  37. 4.5.4 Diagramming External Traffic Flows • Diagram outgoing traffic flows destined for the Internet • Diagram incoming traffic flows from the Internet to locally-provided services • Assess the need for redundancy and security to facilitate the traffic that is generated • Example of external traffic • User connecting to competitors web servers • User in your company logging into a web-based email (gmail)

  38. 4.5.5 Diagramming Extranet Traffic Flows • Diagram extranet traffic flows to and from selected trusted partners, customers, and vendors

  39. 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.