telchemy enterprise voip performance management
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8/3/2019 Telchemy Enterprise Voip Performance Management
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Contents
Introduction...................................................... 1
Performance Management
& Enterprise IP Telephony ................................ 1
VoIP Network Requirements
& Pre-Deployment Testing .............................. 3
The New VoIP Performance Management
Architecture ..................................................... 4
Common VoIP Performance Metrics ............... 6
Performance Management
Reporting Protocols ......................................... 7
Applying the New Performance Management
Architecture To Enterprise Networks .................. 8
Problem Resolution, Detection & Diagnosis ....... 9
Summary .......................................................... 9
Application Notes
Title Managing Enterprise IP Telephony
Series VoIP Performance Management
Date June 2004
Overview
This Application Note describes the typical
issues that network managers encounter
when deploying Enterprise IP Telephony and
introduces a management framework that
allows them to detect, address, and resolve
these problems.
Application Note Managing Enterprise IP Telephony June 2004 1
Introduction
Voice over IP brings many benefits to the Enterprise,
including lower system maintenance costs, improved
network integration between branch offices and
teleworkers, and the ability to build distributed
call centers. Telephony is mission critical for most
businesses, and network managers expect that their new
“exciting” IP services deliver the quality, reliability, and
availability that they had with traditional phone service.
Thus as VoIP is deployed in the Enterprise, it is critical
to implement a performance management framework
that is sufficient to deal with the many operational
problems that arise.
This Application Note describes the typical issues
that network managers encounter when deploying
Enterprise IP Telephony and introduces a management
framework that allows them to detect, address and
resolve these problems.
Performance Management& Enterprise IP Telephony
Calls originating from IP phones are typically carried
as internal VoIP traffic to branch offices or teleworkers
in their home offices. Calls going to external numbers
or to non-VoIP sites are converted from VoIP traffic
to conventional circuit-switched telephone calls by
a gateway and routed through the public telephone
network or TDM leased lines. (Figure 1, Next Page)
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2 Application Note Managing Enterprise IP Telephony June 2004
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IP Telephony is very different from conventional data
applications in that call quality is particularly sensitive
to IP network impairments. Existing network problems
become much more obvious with the deployment of
VoIP. For network managers, this means that LANs,access links, and network equipment will probably need
to be upgraded and that more sophisticated management
and diagnostic tools are needed when deploying and
maintaining VoIP.
There are three basic categories of performance-related
problems that can occur in Enterprise IP Telephony:
1. IP Network Problems
Jitter — Variation in packet transmission
time that leads to packets being discarded
in VoIP end systems or to increases in
delay; jitter is usually due to network
congestion, but it can also be caused by
load sharing across transmission routes
with differing delays.
Packet Loss — Packets lost during
transmission due to network errors, route
changes, link failures, or Random Early
Detection (RED) in routers.
Delay — Overall packet transmission “lag
time” that leads to two-way conversational
difficulty.
2. Equipment Configuration
& Signaling Problems
VoIP Endpoint Configuration —
Performance impact based on codec type
and packet loss concealment algorithm, or
jitter buffer configuration.
Router and Firewall Configuration —
Firewalls or incorrectly configured routers
block VoIP traffic; routers need to be
configured to allow RTP packets through
Figure 1: A typical Enterprise IP telephony network
Switch
Router Router
Router
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Application Note Managing Enterprise IP Telephony June 2004 3
Bandwidth Allocation — Network may
lack sufficient bandwidth to support peak
traffic volumes.
3. Analog/TDM Interface Problems
Echo — “Echo” commonly occurs at
the boundary between the digital network
(VoIP or TDM) and analog local loops. This
becomes very obvious and annoying with the
additional delay introduced by the IP network
problems described on the previous page.
Signal Level — Abnormally high or low
voice signal levels, “clipping,” excessive
noise, and “echo” may occur due to
incorrectly configured gateway signal levels.
Network architects and managers should address call
quality and performance management problems when
they plan and deploy their IP networks, but they should be
aware that these problems may also frequently occur during
normal day-to-day network operation post-deployment.
Many VoIP-related problems are transient in nature and
can occur anywhere along the network path. For example,a user accessing a file from a server may cause a period of
congestion lasting a few seconds. This, in turn, can cause
short-term degradation in call quality for other users on the
network. Thus it is essential that network managers use
performance management tools that are able to detect and
measure these types of network impairments.
The transient nature of IP problems also means that
they are not easily detected or reproduced. In contrast
to traditional POTS, problems are not necessarily
associated with specific cables or line cards – they
can occur randomly due to the “collision” of several
different factors. Network managers could attempt to
use packet loss and jitter metrics to estimate call quality;
however, these metrics do not provide either a reliable
way to do this or enough diagnostic information to
determine the cause of the problem.
Network managers use probes and analyzers located at
specific network points to help detect and diagnose VoIP
performance problems; however, it is not cost effective to
place probes on user desktops, in small branch offices or
teleworkers’ homes.
VoIP Network Requirements& Pre-Deployment Testing
Data applications are not sensitive to real-time
transmission problems like jitter, delay and route
flapping. On the other hand, VoIP performance is very
vulnerable to these problems. When deploying VoIP,
network managers need to pay special attention to the IP
infrastructure to support their new service. In addition,
they should be prepared for increased network traffic and
potential congestion once their VoIP network is active.
When moving to VoIP, Enterprise network managers
and architects should take the following steps to ensure
network success
Step 1: Assess Inter-Site Connectivity
Many call quality-related problems occur in access links
or on limited bandwidth WAN or VPN links. If significant jitter or delay occurs on inter-site connections, this is a
strong indicator that similar problems will occur during
VoIP deployment. Budget bandwidth usage between sites
and verify that routers can prioritize RTP traffic.
Step 2: Assess Desktop Connectivity
Use a switched 100BaseT Ethernet architecture.
Even with the use of Ethernet, problems can still
occur due to duplex mismatch, excessively long
Ethernet segments or bad cable connections.
Examine Ethernet switch statistics for evidence of
packet errors or excessive collisions and upgrade
equipment accordingly.
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4 Application Note Managing Enterprise IP Telephony June 2004
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Step 3: Pre-Deployment Performance Testing
Before deploying the network, verify network
performance using a pre-deployment tool to generate
a realistic level of simulated traffic. In addition toanalyzing performance, these tools also highlight
problem areas. Make sure to use tools, like VQmon
(described below), that are able to detect transient
problems typical of IP network behavior.
Step 4: Pilot Trial
After completing the previous three steps, conduct a
pilot trial for the network. At this stage, the trial should
be successful. Any problems during the pilot trial are
normally the result of an incorrectly configured router
or other network equipment rather than a network
performance problem.
Step 5: Deploy “Live” Network
As deployment ramps up, carefully monitor any trends
in key VoIP performance parameters, note any call
quality-related degradation and investigate accordingly.
Step 6: Maintain VoIP Network
Since VoIP networks are constantly changing and
evolving (e.g., network configuration, equipment
configuration and network traffic), continued
monitoring and maintenance of the network is essential
to maintain quality voice service after its initial
deployment.
To deploy and maintain a VoIP network successfully,
network managers need a new performance management
infrastructure that understands IP telephony issues and
call quality-related problems.
The New VoIP PerformanceManagement Architecture
A new standards-based framework has emerged within
the IP industry for VoIP Performance Management. Ituses a distributed software probe architecture to provide
cost-effective, real-time call quality feedback with
maximum network coverage. The new framework’s
monitoring functions provide real-time visibility of
network performance, detection of transient problems
and comprehensive diagnostic data.
The new framework provides new QoS reporting
protocols that are able to send data back to network
management and call control systems with minimal
network traffic overhead. The architecture features high
performance network probes located within the core
network and at major customer locations that provide
in-depth diagnosis when problems are detected.
A key benefit of the new VoIP Performance
Management Architecture is that small lightweight
monitoring functions can be integrated directly into
IP Phones, routers, gateways and similar network
elements. This “direct integration” provides probe
functionality in equipment where it would normally becost prohibitive, e.g., on every customer desktop.
Embedded Monitoring Function
VQmon® technology is a major building block
of the new performance framework; it was the
first and is the most widely deployed monitoring
function for VoIP performance management today.
VQmon’s embedded monitoring technology
enables network managers to see call quality
problems in real-time and identify the root cause
of the problem for both active and completed calls.
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Application Note Managing Enterprise IP Telephony June 2004 5
VQmon measures key characteristics of the packet
voice stream and calculates real-time performance data
that network managers can use to detect, characterize
and report transient problems. The technology provides
detailed information on service quality with lessreporting frequency, thus requiring less bandwidth.
VQmon is a high performance standards-based non-
intrusive call quality monitoring and diagnostic agent
that can be integrated directly into VoIP CPE, SLA
monitoring systems, probes, routers and generally any
system that is on the path taken by the voice packets
(Figure 2). VQmon agents are small and highly efficient
and can be integrated into existing equipment without
requiring additional CPU or memory, scaling from
systems that monitor a single call to those that support
“hundreds of thousands” of calls.
VQmon agents produce call quality metrics, including
listening and conversational quality scores. They
also provide detailed information on the severity and
distribution of packet loss and discards due to jitter
and other essential diagnostic data. Most importantly,
VQmon is able to detect transient IP problems and
assess their effects on call quality.
VQmon is an advanced VoIP perceptual quality
estimation algorithm that incorporates support for key
international standards including ITU-T P.564, ITU-T
G.107, ITU-T G.1020, ETSI TS 101 329-5 Annex E
and IETF RFC 3611. VQmon incorporates supportfor time varying IP impairments (typically caused by
network congestion) and has been independently shown
to provide significantly more accurate and stable metrics
than other algorithms such as G.107 (E Model).
Two versions of VQmon are available for VoIP
performance management: VQmon/EP (End Point)
and VQmon/SA (Stream Analysis). Both produce a
rich set of diagnostic data and support the common
VoIP performance management metrics. (A third type,
VQmon/HD, provides video performance analysis for
IPTV and IP Videoconferencing systems.)
IP Phone and Gateway Monitoring: VQmon/EP
VQmon/EP is widely integrated into IP phones
and gateways produced by leading equipment
manufacturers. VQmon/EP monitors the received
packet stream and extracts other vital information from
the VoIP codec, then uses this information to generate
accurate call quality estimates and supporting diagnosticdata.
Figure 2: VQmon’s embedded monitoring technology
VQmon/SA
“Stream Analysis”
VQmon/EP
“End Point”
IP Network
RTCP XR
CODEC
VQmon
IP Phone
VoIP GatewaySLA Monitor
Protocol Analyzer
Router
VQmon
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6 Application Note Managing Enterprise IP Telephony June 2004
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SLA Monitors, Analyzers, and Probes:
VQmon/SA
VQmon/SA is the core VoIP analysis software used in
many probes, routers, SLA monitoring systems, andanalyzers. VQmon/SA monitors the packet stream,
automatically recognizing individual call streams and the
types of codec in use. VQmon determines which packets
were lost or would be discarded due to jitter and uses this
data to determine a call quality estimate using the same
algorithms as VQmon/EP.
Common VoIP Performance Metrics
The new VoIP Performance Management Architecture
incorporates a common set of VoIP performance metrics
supported by multiple QoS reporting protocols; i.e., the
same information is available regardless of the protocol
used for reporting (Figure 3). These metrics are:
Percentage Of Packets Lost By the
Network
Percentage Of Packets Discarded By the
Jitter Buffer Due To Late Arrival
Both these metrics help to identify the degree
to which a call is being affected by network
packet loss or jitter. They also eliminate the
need to “guess” how much effect jitter is
having on packet discard rate.
Mean Length and Density of Bursts,
(where a burst is defined as an interval of
time during which the packet loss/discard
rate is high enough to cause audio quality
degradation.)
Mean Length and Density Of Gaps
Between Bursts
Both these metrics help to identify the
extent to which a call is degraded by
loss/discard and provide some insight into
the user experience. Transient network
congestion is a common problem resulting
in a period of high loss/discard lasting for
several seconds during which call quality
is degraded; these transient call quality
problems are reported as “bursts.”
VoIP
Endpoint
Network Probeor Analyzer
Network Management
System
Call Server andCDR Database
VoIP Gateway
Signaling-based
QoS ReportingSNMP with
RTCP XR MIB
G.799.1
Trunking Gateway
RTCP XR (RFC3611)
Media Path Reporting
Embedded monitoring
with VQmon®
Figure 3: The new
VoIP Performance
Management
reporting protocols
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Application Note Managing Enterprise IP Telephony June 2004 7
Round Trip Delay Between VoIP
Endpoints
End System Delay Within a VoIP Endpoint
Both these metrics help to identify the
sources of excessive delay which can lead
to conversational difficulty and greatly
intensify the effects of echo.
Signal Level
Noise Level
Echo Level
These three metrics enable detection of
problems due to excessive variations in
signal, noise or echo level. They also allow
mid-stream probes to detect signal, echo
and noise level problems without needing
to decode voice packets. These metrics
will be essential to support network
management when networks use the
secure RTP framework.
Call Quality Metrics In Either R Or MOS
Scaling
These metrics provide an immediate view
of call quality. If it is apparent that there is
a problem, then the other metrics can be
used for diagnosis.
Jitter Buffer Configuration and Packet
Loss Concealment Algorithm
This information is used to determine
if poor call quality is due to incorrect
configuration of the end system,
and to allow mid-stream probes
to automatically detect endpoint
configuration.
Performance ManagementReporting Protocols
Reporting protocols have been developed for
the media path, signaling system, and network management. It is important to realize that these are
complementary; i.e., they are designed to be used
together.
RTCP Reporting Extensions (RTCP XR)
The RTCP XR protocol (RFC3611) is a media path
reporting protocol that exchanges call quality metrics
between VoIP endpoints. RTCP XR provides several
useful functions:
Enables collection of call quality reports
by the remote endpoint, e.g., a trunking
gateway, or by intermediate probes
Provides ability to pass transparently
through firewall routers
Supports the diagnosis of echo-related
problems
Enables network probes to obtain analog
signal information without the need to
decode voice packets
Compatibility with the emerging Secure
RTP security framework.
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8 Application Note Managing Enterprise IP Telephony June 2004
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Signaling Protocol QoS Reporting
Several new QoS Reporting protocols have been
developed within ITU and IETF that support call
quality reporting to call management systems,e.g., softswitches. These protocols provide call
quality information directly to the systems that
maintain CDR databases and link service quality
information directly to specific users and their
calls. QoS reporting protocols for H.323 (H.460.9
Annex B) and Megaco (H.248.30) were approved
in early 2004, and new protocols for SIP and
MGCP are expected in mid- to late-2004.
SNMP and the RTCP XR MIB
An RTCP XR Management Information Base
(MIB) is under development within the IETF for
use in gateways or probes to support the retrieval
of metrics via SNMP. For example, RTCP XR
could be used to relay call quality information
from an IP phone to the gateway that forms the
network end of a VoIP connection; and SNMP
would be used to retrieve call quality information
from the gateway for both in-bound and out-
bound packet streams.
Applying the New PerformanceManagement ArchitectureTo Enterprise Networks
The new VoIP performance management architectureis very useful in providing real-time visibility of user
perceived quality in an Enterprise network (Figure 4).
VQmon is integrated into the IP phone
on a user desktop or at a teleworker’s
home. During an active call, call quality
is measured at the IP phone on the user
desktop.
VQmon is integrated into the IP-PBX
gateway. For calls going out onto the
PSTN, call quality is measured at the
IP-PBX gateway. This helps to detect
echo and other typical problems.
VQmon is integrated into branch office
gateways/routers. VQmon measures the
quality of calls at remote locations. This
helps to detect congestion in access links.
VQmon is integrated into a probe, switch
NMS/OSS
IP Phones withembeddedmonitoring SQProbe
IP Phones withembeddedmonitoring
IP Phone
SIP RTCPReporting
Central Location Branch Oce
Teleworker
Embedded Voice QualityMonitoring with VQmon
SQmediator
SIP RTCPReporting
Web
Service API
RTCP XR Reportingbetween Endpoints
IP VPN
Figure 4: The New
Performance Management
Architecture for Enterprise
Networks
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Application Note Managing Enterprise IP Telephony June 2004 9
or router at key demarcation points to help
with problem isolation.
The IP PBX call management system
collects QoS reports sent by the signaling protocol.
VQmon is integrated into VoIP test
equipment (probes and analyzers). When
problems are reported and detailed
analysis is needed, Network Operations
and Field Service personnel use this test
equipment to capture and analyze call
streams.
Problem Resolution, Detection & Diagnosis
The new VoIP Performance Management Framework
provides the basis for detecting and diagnosing different
types of call-quality related problems:
Access Link Congestion
—If the access links to the IP network site have
insufficient bandwidth, the jitter level will increase.
This will typically cause IP phones to discard a high
proportion of packets and can increase the size of the
jitter buffer adding more delay. Network Managers
can diagnose congestion problems using VQmon
generated call quality reports sent from either an IP
phone, router or gateway.
Duplex Mismatch or Bad Ethernet
Segment on LAN
—If Ethernet switches are not configured properly
or Ethernet segments are too long, there may be ahigh rate of packet loss that severely impacts call
quality. Network Managers can diagnose these
problems using VQmon generated call quality
reports sent from IP Phones.
Echo in PSTN
—If there is a problem on a remote analog loop, the IP
phone on a customer site may experience audible echo.
Network Managers can diagnose echo problems usingVQmon-generated call quality reports sent from the IP
phone and from the trunking gateway.
Summary
The new VoIP Performance Management Architecture
provides an ideal solution for quality monitoring and
problem diagnosis for Enterprise IP telephony service.
Important call quality and diagnostic data is obtained in
real-time from key points on the packet stream and routed
to network management systems.
Network managers can obtain a reasonable level of
problem diagnosis simply by using data from VoIP call
quality reports; however, in-depth problem analysis
requires the use of probes and analyzers that support the
new Performance Management Framework as well as
the use of VQmon for call quality analysis.
Many of the industry’s equipment manufacturers are
already implementing elements of the new management
framework in IP phones, gateways, routers, probes and
analyzers.
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AcronymsCDR Call Detail Record
IETF Internet Engineering Task Force
IP Internet Protocol
ITU International
Telecommunications UnionLAN Local Area Network
MIB Management Information Base
PBX Private Branch Exchange
POTS Plain Old Telephone Service
PSTN Public Switched Telephone
Network
QoS Quality of Service
RED Random Early Detection
RTP Real Time Protocol
SLA Service Level Agreement
SNMP Simple Network Management
Protocol
TDM Time Division Multiplexer, -ing
VoIP Voice Over Internet Protocol
VPN Virtual Private Network
VQmon/EP VQmon End Point
VQmon/SA VQmon Stream Analysis
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Notes
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References
[1] IETF RFC3611 RTP Control Protocol Reporting
Extensions (RTCP XR), November 2003
[2] ITU-T G.799.1 “Functionality and Interface
Specifications for GSTN Transport Network
Equipment for Interconnecting GSTN and IP
Networks”
[3] ITU-T H.460.9 Annex B Support for online
QoS-monitoring reporting within H.323 systems:
Extended Performance Metrics
[4] ITU-T H.248.30 RTCP Extended Performance
Metrics Packages
[5] IETF SIPPING draft-johnston-rtcp-summary.02.txt
[6] ETSI, “Quality of Service (QoS) measurement
methodologies,” ETSI TS 101 329-5 V1.1.1
(2000-11), November 2000.
[7] ITU-T, “The E-Model, a computational model for use
in transmission planning,” Recommendation G.107
Application Note Managing Enterprise IP Telephony June 2004 11
About Telchemy, Incorporated
Telchemy, Incorporated is the global leader in VoIP
and IP Video fault and performance management with
its VQmon®
family of multimedia quality monitoring
and analysis software. Telchemy is the world's first
company to provide voice quality management
technology that considers the effects of time-varying
network impairments and the perceptual effects
of time-varying call quality. Founded in 1999, thecompany has products deployed worldwide and markets
its technology through leading networking, test and
management product companies.
Visit www.telchemy.com.
sales@telchemy.com
info@telchemy.com
Phone
+1-866-TELCHEMY
+1-678-387-3000
Fax
+1-678-387-3008
Telchemy Incorporated
2905 Premiere Parkway
Suite 280
Duluth, GA 30097
USA
Information
Telchemy, VQmon, SQprobe, and SQmediator are registered trademarks and SQmon and the Telchemy logo are
trademarks of Telchemy, Incorporated. VQmon and SQmon contain technology described in four or more patents and
pending patents. © 2008 Telchemy, Incorporated, all rights reserved.
Telchemy Application Notes
Series Understanding VoIP Performance
Title Voice Quality Measurement
Title Impact of Delay on VoIP Services
Title Impact of Echo on VoIP Services
Title Data and Fax Modem Performance on VoIP
Services
Title Voice Quality Estimation in Wireless & TDM
Environments
Series VoIP Performance Management
Title Managing Enterprise IP Telephony
Title Managing IP Centrex & Hosted PBX Services
Title Managing Cable Telephony Services
Title Managing Wireless LANs and Wi-Fi Services
Title Six Steps to Getting Your Network Ready for
Voice over IP
Download application notes @ www.telchemy.com
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