Avaya ExpertNet Lite Assessment Tool

Transcription

1 IP Telephony Contact Centers Mobility Services WHITE PAPER Avaya ExpertNet Lite Assessment Tool April 2005

2 avaya.com Table of Contents Overview... 1 Network Impact... 2 Network Paths... 2 Path Generation... 2 Delay Measurements... 3 Router Monitoring... 5 Installation Planning... 5 Reports... 6 ExpertNet Lite Assessment Tool and the ExpertNet VoIP Assessment Tool... 6 Glossary & Acronyms... 6

3 avaya.com 1 Overview This document is for customers who purchase implementation services for an IP Telephony solution requiring an IP Network Readiness Assessment Basic deliverable. The tool used to deliver the basic Readiness Assessment is the ExpertNet Lite Assessment Tool. This document explains what the purpose of the ExpertNet Lite Assessment Tool software is and an overview of its operation. This is a technical document; hence some specialized knowledge is assumed. Specifically, the reader should have a sound knowledge of basic TCP/IP networking theory and practice, IP packet routing, routing protocols and related technologies. The ExpertNet Lite Assessment Tool is a software application designed to perform an IP Network Readiness Assessment. To accomplish this, the tool gathers quality of service (QoS) information from an IP network. The data gathered is then analyzed by Avaya engineers to produce an ExpertNet Lite Assessment Tool report. It is designed to run for an extended period of time, typically five to seven days (note that five days is the recommended minimum), in order to see trends in network performance. These trends are often visible when the data is summarized graphically, and such graphs are typically included in an ExpertNet Lite Assessment Tool report. The IP Network Readiness Assessment Basic deliverable is intended to assess the suitability of a given network for Voice over IP (VoIP) applications. Hence the data gathered by the ExpertNet Lite Assessment Tool is tailored towards such applications. This is a key differentiator between the ExpertNet Lite Assessment Tool and other network performance measurement tools. The ExpertNet Lite Assessment Tool provides a network discovery operation and relies on a network topology discovery tool called the Avaya ExpertNet Discovery Tool. The operation of this tool is not discussed in this document, but further information can be obtained from Avaya. The network topology discovered by this tool is read by the ExpertNet Lite Assessment Tool, and used to determine the extent of the network to be monitored. Automatic network discovery is optional in the ExpertNet Lite Assessment Tool. It is performed only when the user selects the Discover Paths menu option. Users may also enter network paths manually. When entering paths manually, the user has the choice of entering proper paths or target-type paths. When entering a proper path, the agent, using an enhanced, patented trace-route with an ability to discover load-balanced links, discovers intermediate routers. When entering a target-type path, no intermediate routers are discovered. The ExpertNet Lite Assessment Tool is comprised of two parts: an Agent, which gathers measurements data, and the Server, which resides in a secure environment within Avaya infrastructure that interprets the measurements data. The Agent is available for download on external Avaya servers. When the Agent concludes measurements gathering, it compresses the data and then encrypts it utilizing 1024 bit encryption. If the Agent PC resides on a network directly connected to the Internet, the Agent can automatically upload the encrypted dataset onto Avaya servers. The uploaded dataset is not accessible to anyone external to Avaya. The dataset is then moved to a secure server and removed from the intermediate server. The Avaya technician involved in the Network Readiness Assessment is notified once the dataset has been stored. Use of the ExpertNet Lite Assessment Tool requires a valid license for up to 30 days from the date of generation. Please contact your Avaya representative for information about obtaining a license. Documentation, release notes and context-sensitive on-line help describe the procedure for running the ExpertNet Lite Assessment Tool.

4 COMMUNICATIONS AT THE HEART OF BUSINESS 2 Network Impact The ExpertNet Lite Assessment Tool is designed to have a low impact on the network under test. This means it injects a minimal amount of traffic into the network, and has built-in safeguards to ensure that the traffic does not exceed set limits. These traffic throttling limits can be increased or decreased as required, however the defaults should be sufficient for most customer network environments. Broadly speaking, there are two types of traffic that the ExpertNet Lite Assessment Tool uses to perform its measurements. These are delay (or ping ) packets and SNMP get queries, discussed further in the Delay Measurements and Router Monitoring sections below. The traffic throttling can be adjusted independently for each of these two types of measurements. The ExpertNet Lite Assessment Tool has been designed carefully and tested extensively, to ensure that it does not alter the configuration of, or otherwise affect adversely, any device in the network. For example, all of the SNMP traffic is get requests and responses. In addition, the ExpertNet Lite Assessment Tool produces extensive logging of all of its activities. Network Paths One of the key concepts in the ExpertNet Lite Assessment Tool is that of a network path. When a packet is sent from a host, it may pass through many different links and routers before arriving at its destination. This set of hosts, routers and links is known as the network path. The network path is significant because the overall performance of the path can be affected by the performance of the individual components of the path. For example, excessive packet loss on a network path can be due to congestion on one of the intermediate routers between source and destination. Hence the concept of network path allows data from different sources to be correlated and analyzed together. One of the key assumptions of the ExpertNet Lite Assessment Tool is that measurement of network performance to and from a single point can lead to meaningful inferences about the performance of the network as a whole. This means that all paths in the ExpertNet Lite Assessment Tool originate at a single point, the PC that runs the ExpertNet Lite Assessment Tool software. All paths terminate at network edges, and the process of generating paths is described in the section Path Generation below. The ExpertNet Lite Assessment Tool is designed such that no other additional special software is needed to run in the network. Instead, the tool measures network performance by relying on the default behavior of IP implementations for each device in the path. This is discussed further below. For the ExpertNet Lite Assessment Tool purposes the concept of path applies to the Internet Protocol (IP) layer. The tool does not monitor directly any network performance or topology for network link or physical layers (terminology as defined by the ISO network stack). For example, the ExpertNet Lite Assessment Tool does not attempt to discover Ethernet topology or monitor directly Ethernet performance. It is anticipated that performance problems for layer 2 links will be indirectly apparent at the IP layer. For example, if a problematic Ethernet segment is resulting in 1% of frames being lost, this will generally be apparent at the IP layer as 1% packet loss. Path Generation In order to make meaningful interpretation of packet delay measurements, the ExpertNet Lite Assessment Tool needs to ensure that the path taken by each packet is known. Determining this path is also necessary in order

5 avaya.com 3 to monitor the correct router interfaces. This path generation process is conducted when the user executes either Discover Paths or Add Path Manually. The set of paths is generated from the topology file produced by the ExpertNet Discovery Tool or manually entered by the user. Each path starts at the agent host and ends with a host in the edge subnet. Between the Assessment Tool and the edge host/router are intermediate routers. When generating paths, the ExpertNet Lite Assessment Tool uses a patented technique of enhanced traceroute. For each edge device, packets are sent with successively incrementing TTL values. The TTL-expired message returned is used to enumerate the path taken from the Agent host to each edge subnet. At the same time, sequences of pings are sent to determine load-balanced links. It is important to note that the process used to generate paths is similar to that used when making the delay measurements. This has the benefit that the paths are verified throughout the monitoring period. Concurrently with path generation, the ExpertNet Lite Assessment Tool also attempts to detect the presence of load-balanced links. Modern routing protocols such as OSPF allow for the presence of multiple equal-cost paths between two points in the network. Routers for load balancing purposes typically utilize these links. The ExpertNet Lite Assessment Tool attempts to determine which of the multiple routes in a load-balanced link is to be used for any given packet. Generally routers implement load balancing on either a per-packet or per-destination basis. Where per-packet load balancing is used, two successive packets to the same destination can take different paths through the network. This has the potential to negatively impact VoIP applications. Per-destination load balancing provides a stable route for successive packets, however the ExpertNet Lite Assessment Tool must still determine which of the possible routes is being used for the delay measurement packets. The Agent s GUI provides Ping Status information at the path and hop level which shows whether packets are Off Path at any given time. Delay Measurements One of the main functions of the ExpertNet Lite Assessment Tool is to take periodic measurements of packet roundtrip time (referred to here as pinging ). This is conceptually similar to the output of the ping utility supplied with most operating systems, in that a timer is started when sending a packet and the value of the timer recorded when a response packet is received. Packets may be lost in transit, and this fact is recorded. From the recorded values of delay, we can calculate the statistical variance in these values, sometimes known as jitter. Thus, the ExpertNet Lite Assessment Tool makes measurements in order to calculate the most important factors that affect the quality of VoIP applications: Mean Opinion Score (MOS), delay, loss rate, and jitter. Most implementations of the ping utility use the Internet Control Message Protocol (ICMP) echo request/ reply facility. However, ICMP echo packets are not always treated by the network in a similar fashion to voice packets. Routers may be configured to forward ICMP echo packets at a lower priority than others, or drop them altogether. Hence delay measurements made with ICMP echo are not necessarily indicative of VoIP performance. A similar limitation exists when Transmission Control Protocol (TCP) is chosen for performance measurement. In order to address this limitation of ICMP echo, the ExpertNet Lite Assessment Tool uses a combination of User Datagram Protocol (UDP) request, with an ICMP reply. To measure packet round-trip time to a host, the ExpertNet Lite Assessment Tool will send a UDP packet to a closed port on that host. The host will respond with an ICMP port unreachable message. The round trip time is calculated as the elapsed time between sending the UDP request and receiving the ICMP reply.

6 COMMUNICATIONS AT THE HEART OF BUSINESS 4 Some routers disable UDP ping packets to stop malicious software (viruses, worms) from spreading. In this situation the ExpertNet Lite Assessment Tool can be directed to use ICMP pings. As noted above ICMP pings will not be as accurate as UDP, and the resulting data may not be as accurate had UDP ping been used. The ExpertNet Lite Assessment Tool also attempts to measure round-trip time (RTT) to intermediate routers along the path. A slight variation on the above technique is used for these intermediate routers. For example, let R be an intermediate router between the ELAT Agent PC and host H. Now we cannot ping R directly, because of the potential presence of per-destination load-balancing which may result in packets addressed to R directly taking a different path from the Tool to R than they would if they were addressed to host H (see Figure 1). Hence when pinging R, the UDP packets are actually addressed to H, but the time-to-live (TTL) field in the IP header of these packets are set such that a response is elicited from R, rather than the destination host H. This TTL method is similar to that used by the trace-route utility. In summary, the ExpertNet Lite Assessment Tool measures delay for each component of a path through the network from the Agent PC to a host. For intermediate routers, the TTL is set in order to elicit a TTL-expired ICMP message. For the target host, a closed UDP port is chosen in order to elicit a port-unreachable ICMP message. In each case the ICMP reply is used to make the delay measurement. UDP Packet Source: Agent Dest: Host TTL: 1 ELAT Agent (A) ICMP Packet (TTL-expired) Source: Router R Dest: Agent A Router (R) UDP Packet Source: Agent Dest: Host H Port: (high numbered) Host (H) ELAT Agent (A) Router (R) ICMP Packet (port not reachable) Source: Host H Dest: Agent A Host (H) Figure 1. The ExpertNet Lite Assessment Tool is installed and runs on a Microsoft Windows -based PC, the exact specifications of which are given in the release notes. It is important to understand that, given the highly time-sensitive nature of the delay measurements, this PC should be configured to minimize the possibility of other software affecting the measurements. Software such as virus scanners, screen savers, and other background processors can prevent the ExpertNet Lite Assessment Tool from being notified immediately when a packet is received. This introduces delay as measured by the ExpertNet Lite Assessment Tool, and hence must be disabled.

7 avaya.com 5 Router Monitoring The second major type of measurement made by the ExpertNetLite Assessment Tool uses the Simple Network Management Protocol (SNMP) to obtain performance data from routers. As mentioned above, only SNMP get queries are used, and hence should have no discernable impact on the network. The ExpertNet Lite Assessment Tool queries for interface information using standard Management Information Bases (MIBs). 3Com, Avaya, Cisco, Extreme, and Xylogics devices are also queried for CPU usage information using the manufacturer private MIBs. Other MIB variables may be added in subsequent ExpertNet Lite Assessment Tool releases. At startup, the ExpertNet Lite Assessment Tool determines what SNMP variables are supported by each device to be monitored. This ensures that only supported variables are queried for the remainder of the ExpertNet Lite Assessment Tool run time. If SNMP is not supported by, or the community string not known for a given router, then it is removed from the set of devices to be monitored. The ExpertNet Lite Assessment Tool currently supports SNMP v1 and v2c only. Installation Planning An important prerequisite for running the ExpertNet Lite Assessment Tool is that the network topology must be known and understood. Some care needs to be taken when installing the ExpertNet Lite Assessment Tool to ensure that it produces results that are most meaningful. By design, the ExpertNet Lite Assessment Tool is deployed on a single PC, measuring network performance between this PC and the network edges. The performance of other paths through the network is not measured. Hence the location of the ExpertNet Lite Assessment Tool in the network is important. While not strictly required, some preliminary plans for the deployment of VoIP applications are highly beneficial. These plans should include information such as the location of media servers, media gateways, and endpoints (both IP and traditional). Similarly traffic paths should be considered, including the possibility of endpoint-to-endpoint, endpoint-to-gateway, gateway-to-gateway, and other more complex call topologies. Also the possible location for PSTN interfaces should be considered. These plans do not have to be complete (or even vendor-specific), but should be derived from the business requirements for VoIP telephony, and an understanding of existing traffic patterns. From these preliminary plans, it should be possible to determine where to deploy the ExpertNet Lite Assessment Tool. As a general rule it is suggested that the ExpertNet Lite Assessment Tool be deployed into a network subnet, which might be considered for use by a media server. In addition, it is recommended that SNMP v1/v2c be enabled on all routers. If IP-address-based access control is in use, the IP address of the Agent PC must be added to allow access to all routers. SNMP is also required for execution of the ExpertNet Discovery Tool. The community strings used by the ExpertNet Discovery Tool are reused by the ExpertNet Lite Assessment Tool as needed. As described above, the ExpertNet Lite Assessment Tool uses UDP packets to make delay measurements. Hence it is desired for correct use of the tool that devices support these packets; in the event that UDP ping cannot be supported, the user may configure the tool to use ICMP ping. Intermediate routers must support trace-route. The network must not filter the UDP ping packets or the ICMP replies; if filtering does occur, ICMP ping must be used.

8 COMMUNICATIONS AT THE HEART OF BUSINESS 6 Reports The ExpertNet Lite Assessment Tool has the ability to generate a detailed report from the measurements data of the network. The report, which is typically customized by an Avaya engineer for the specific customer, contains an overview of the entire network, in addition to details about each path or target-type path if path discovery was not chosen. The path, or target-type path, will have annotation detailing whether the path is within specifications or not and a summary graph containing MOS, delay, jitter, and loss. For layer 3 devices that are SNMP manageable and a proper SNMP read community string was given, CPU usage and interface utilization will be included. ExpertNet Lite Assessment Tool and the ExpertNet VoIP Assessment Tool There are two suites of tools that support the Network Readiness Assessment, the ExpertNet Lite Assessment Tool which has been discussed thus far, and the ExpertNet VoIP Assessment Tool. The ExpertNet VoIP Assessment Tool has additional capabilities to support a much larger enterprise network. An overview of the capabilities that the ExpertNet VoIP Assessment Tool has is described below. 1. The set of paths measured by the ExpertNet VoIP Assessment Tool does not originate/terminate at a single point in the network. Thus, edge-to-edge network performance can be measured directly, rather than inferred from the performance characteristics to and from a single point. 2. The ExpertNet VoIP Assessment Tool discovers Ethernet topology. 3. The ExpertNet VoIP Assessment Tool performs measurements using Real Time Protocol (RTP) streams emulating real VoIP calls. 4. The ExpertNet VoIP Assessment Tool reports estimated bandwidth. For more information about the ExpertNet VoIP Assessment Tool, please contact your Avaya Client Executive or visit us at Glossary & Acronyms ExpertNet Lite Assessment Tool ExpertNet Discovery Tool ExpertNet VoIP Assessment Tool ExpertNet SM Consulting Practice ICMP IP MIBs OSPF PSTN A tool designed to gather information from Internet Protocol (IP) networks Internet Protocol discovery, visualization, analysis and display tool Detailed Internet Protocol troubleshooting and sectionalization tool The Avaya Network Consulting Practice s Services for LAN/WAN, IP Telephony, Enterprise Security planning and communications infrastructures Internet Control Message Protocol Internet Protocol Management Information Bases Open Shortest Path First (routing protocol) Public Switched Telephone Network

9 avaya.com 7 Glossary & Acronyms QoS RTP RTT SNMP TCP TTL UDP VoIP Quality of Service Real-Time Transport Protocol Round-trip time Simple Network Management Protocol Transmission Control Protocol Time-to-live User Datagram Protocol Voice over Internet Protocol

10 About Avaya Avaya enables businesses to achieve superior results by designing, building and managing their communications infrastructure and solutions. For over one million businesses worldwide, including more than 90 percent of the FORTUNE 500, Avaya s embedded solutions help businesses enhance value, improve productivity and create competitive advantage by allowing people to be more productive and create more intelligent processes that satisfy customers. For businesses large and small, Avaya is a world leader in secure, reliable IP telephony systems, communications applications and full life-cycle services. Driving the convergence of embedded voice and data communications with business applications, Avaya is distinguished by its combination of comprehensive, world-class products and services. Avaya helps customers across the globe leverage existing and new networks to achieve superior business results. COMMUNICATIONS AT THE HEART OF BUSINESS avaya.com 2005 Avaya Inc. All Rights Reserved. Avaya and the Avaya Logo are trademarks of Avaya Inc. and may be registered in certain jurisdictions. All trademarks identified by the, SM or TM are registered trademarks, service marks or trademarks, respectively, of Avaya Inc., with the exception of FORTUNE 500 which is a registered trademark of Time Inc. All other trademarks are the property of their respective owners. Printed in the U.S.A. 05/05 EF-SVC