Convergence
Technologies
Lesson 1:
Convergent Network
Traffic Protocols
Objectives
• Compare and contrast circuit-switched and packetswitched technologies, including ways that packets traverse
multiple WAN links, and call and call flow descriptions
• Define the Realtime Transport Protocol (RTP) and the
Realtime Transport Control Protocol (RTCP)
• Identify the components of Session Initiation Protocol (SIP)
and describe the format of an SIP Uniform Resource Identifier
(URI)
• Identify the functions of signaling protocols for converged
networks (e.g., Session Initiation Protocol [SIP], H.323, H.225,
H.320, H.450, Media Gateway Control Protocol [MGCP],
Media Gateway Control [Megaco])
• Compare and contrast the functions of gatekeepers,
gateways and proxies in relation to SIP and H.323 devices
• Compare and contrast SIP, H.323 and Megaco/MGCP
Convergence
Technologies
Defining Convergence
• Convergence – The integration of telephony and
data technologies
• Integration includes:
– Placing the voice network (telephony), the
video network (television, satellite) and the
Internet (rich media) onto common platforms
Convergence
Technologies
Smart Network and Dumb Network
Convergence
Technologies
Circuit-Based vs.
Convergence Calling
• Circuit-switched network – uses a dedicated physical path
to send and receive information
• Circuit-based calls:
– Provide very good voice quality
– May fail if the destination is busy or the network fails at
any point in the connection
• Packet-switched network – places addressing information
into data packets
• Convergence-based calls:
– Dynamically reroute packets to other network nodes if a
network node fails
– Result in increased latency because packetization and
compression add processing time to the signal
Convergence
Technologies
Transport Through a
Packet-Switched Network
• Packets are encapsulated in Ethernet frames
– At Layer 4, source and destination port
numbers are added
– At Layer 3, source and destination IP addresses
are added
– At Layer 2, source and destination MAC
addresses are added
Convergence
Technologies
User Datagram Protocol
• UDP header is very simple, consisting of source
and destination port numbers, a length field, and
a checksum field
Convergence
Technologies
Realtime Transport Protocol (RTP)
• Used to transport voice and video payloads for
real-time applications
• Provides end-to-end delivery services
• Runs over both UDP and TCP
• Uses even port numbers that are generally
assigned dynamically
• Default port is 5004
• RTP profiles define a set of codes for each type of
payload
Convergence
Technologies
RTP Packets
• RTP packets are encapsulated in UDP packets
Convergence
Technologies
Realtime Transport Control
Protocol (RTCP)
•
•
•
•
Does not transport any data itself
Partners with Realtime Transport Protocol (RTP)
Monitors the media stream
Provides feedback on the Quality of Service (QoS)
being provided by RTP
• While RTP uses an even port number, RTCP always
uses the next odd port number
• Default port is 5005
Convergence
Technologies
Session Initiation Protocol (SIP)
• Signaling protocol only — does not deliver media
streams, nor does it control the delivery of media
streams
• Initiates and manages sessions (or connections)
between 2 or more participants
• Primary function is to set up, modify and tear
down a connection
• Developed by the IETF, SIP is modeled after
Hypertext Transfer Protocol (HTTP)
Convergence
Technologies
SIP Related Protocols
• Session Description Protocol (SDP)
– Describes the characteristics of end points in a
session
• Multiprotocol Label Switching (MPLS)
– Can provide QoS for SIP connections
• Resource Reservation Protocol (RSVP)
– Can provide QoS for SIP connections
• Differentiated Services (DiffServ)
– Can provide QoS for SIP connections
Convergence
Technologies
SIP ports and URIs
• SIP uses both UDP and TCP ports 5060 by default
• SIP URI takes the following format:
sip:user@host
• SIP URI examples:
sip:555-1110@ctpcertified.com
sip:charles.chaplin@64.128.206.2
sip:charles.chaplin@sip.ctpcertified.com
Convergence
Technologies
SIP Components
• User agents
– User agent client (UAC): initiates an SIP request
– User agent server (UAS): responds to SIP request
• Servers:
– Proxy: perform routing, authentication and
accounting functions
– Redirect: relays information to a user agent,
such as the IP address of the party to be called
– Registrar: enables a client to let a proxy or
redirect server know how the client can be
reached
Convergence
Technologies
SIP Messages
• Requests
– INVITE
– ACK
– BYE
– Cancel
– Options
– Register
• Each request (except for an ACK request) requires
a response
Convergence
Technologies
SIP Messages (cont'd)
• Responses are composed of a 3-digit Status Code
and an associated Reason Phrase
Convergence
Technologies
SIP Calls
Session Invitation
• Consists of one
INVITE request,
usually sent to an
SIP proxy
• A 200 OK response
is generated when
the called party
answers the phone
• Media streams are
sent directly
between end
points
Convergence
Technologies
H.323
• Defines the following:
– How an audiographic call is set up across a
network
– How to negotiate capabilities
– How to transmit data and control conferencing
– Which default audio and video codecs to use
Convergence
Technologies
H.323 Architecture
• Terminals
– H.323 end points
– Can be a stand-alone device (IP phone) or a
logical device within a PC
– Includes audio and video codecs
– Must support H.245 for capabilities negotiation
– Uses Q.931 for call signaling and setup
– Uses H.225 RAS for communicating with
gatekeepers
– Must support RTP and RTCP
Convergence
Technologies
H.323 Architecture (cont'd)
• Gateways
– Connect and translate protocols between
dissimilar networks
– Provide protocol translation, media format
conversion and data transfer between H.323
and non-H.323 networks
– Optional element; not required for connections
within one LAN
– Required to establish connections between
terminals in H.323 networks and terminals in
networks with different protocols
Convergence
Technologies
H.323 Architecture (cont'd)
• Gatekeeper functionality:
– Admission control
– Address translation
– Bandwidth control
– Zone management
– Call control for point-to-point conferences
– Codec translation
– Call authorization
– Bandwidth and call management
– Accounting and billing
– Call routing
• Multipoint Control Unit (MCU) – required whenever three or
more H.323 terminals are connected
Convergence
Technologies
H.323 Protocol Stack
Convergence
Technologies
H.225 RAS
• RAS messages (requests and responses) are sent between
end points and gatekeepers via UDP
– Gatekeeper messages are sent for gatekeeper discovery
(GRQ, GCF, GRJ)
– Registration messages are sent for negotiating a
registration with a gatekeeper (RRQ, RCF, RRJ)
– Admission messages are requests and replies for address
translation (ARQ, ACF, ARJ)
– Status messages are used to monitor end point status
during calls that are routed through a gatekeeper (IRQ,
IRR)
– Disengage messages signal the end of a call (DRQ, DCF)
Convergence
Technologies
H.323 Calls
• In a typical call:
– A client contacts a gatekeeper and requests
an address using H.225 RAS admission request
(ARQ)
– Gatekeeper forwards address to the client
– Client establishes session using H.225
– Session is negotiated using H.245
Convergence
Technologies
H.323 Calls (cont'd)
H.225 call signaling is used between terminals to
set up and tear down a connection
Convergence
Technologies
H.323 Calls (cont'd)
H.245 call control signaling is used for negotiating
capabilities and master/slave determination
Convergence
Technologies
Media Gateway
Control Protocol (MGCP)
• Media Gateway Control Protocol (MGCP) – a
signaling protocol used in IP telephony systems
– MGCP controls media gateways by sending
signals from a media gateway controller
– MGCP is a master/slave protocol
– MGCP assumes that call logic and call state
are maintained by intelligent end points
Convergence
Technologies
Network Call Signaling (NCS)
• Network Call Signaling (NCS) – a protocol that creates
embedded agents to use MGCP in a network
Convergence
Technologies
Megaco/H.248
• Enhanced version of MGCP
• Result of a joint effort between IETF and ITU
• Megaco enables the separation of call control
from media conversion
• Megaco instructs an MG to connect streams
coming from outside a packet or cell data
network onto a packet or cell stream such as
Realtime Transport Protocol (RTP) streams
Convergence
Technologies
SIP vs. H.323 vs. Megaco
Convergence
Technologies
Summary
 Compare and contrast circuit-switched and packetswitched technologies, including ways that packets traverse
multiple WAN links, and call and call flow descriptions
 Define the Realtime Transport Protocol (RTP) and the
Realtime Transport Control Protocol (RTCP)
 Identify the components of Session Initiation Protocol (SIP)
and describe the format of an SIP Uniform Resource Identifier
(URI)
 Identify the functions of signaling protocols for converged
networks (e.g., Session Initiation Protocol [SIP], H.323, H.225,
H.320, H.450, Media Gateway Control Protocol [MGCP],
Media Gateway Control [Megaco])
 Compare and contrast the functions of gatekeepers,
gateways and proxies in relation to SIP and H.323 devices
Convergence
Technologies
Lesson 2:
Implementing VoIP
Objectives
• List essential steps for qualifying a network's ability to support
convergence (e.g., cable inspection, existing and maximum
device capacity, replacing hubs with switches, Power over
Ethernet [PoE] requirements, VLAN creation, conducting
network reconnaissance)
• Describe the features of Telephony Application
Programming Interface (TAPI) and Messaging Application
Programming Interface (MAPI) in a converged solution
• Implement Telephone Number Mapping (ENUM), elements
of global and private numbering plans, Local Number
Portability (LNP)/Wireless LNP, end-point addressing, path
selection, calling classes, digit manipulation, overlapping
number ranges
• Identify common G.7xx codecs and their bandwidth
requirements in a converged environment (e.g., G.711,
G.729, G.729a, G.726 and others)
Convergence
Technologies
Objectives (cont'd)
• Describe the impact of compression on voice quality, and
identify issues involved when converting voice to analogue
and digital formats
• Identify benefits and drawbacks of various codecs in
relation to bandwidth and voice quality
• Calculate and estimate bandwidth usage for various
codecs, including considerations of overhead, connection
quality, and other factors that affect theoretical calculations
(e.g., capacity planning, choosing connection speeds)
• Recommend codecs for use with local/in-network/withinLAN calls, and for across WAN connections
• Explain wireless convergence technologies, including Digital
Enhanced Cordless Telecommunications (DECT) and DECT
layers, Personal Wireless Telephone (PWT), Generic Access
Profile (GAP), expected ranges for interference-free
communication, and the MHz ranges for each standard
Convergence
Technologies
Objectives (cont'd)
• Identify the elements of the IP Multimedia Subsystem (IMS)
• Explain real-time faxing, according to standards such as ITU
T.38
• Explain store-and-forward faxing, according to standards
such as ITU T.37
• Identify the features, benefits, problems and management
of presencing, including single sign-on, features available in
various devices
• List unified message methods and benefits (e.g., fax, voice,
text, video)
• Identify common and essential videoconferencing codecs,
standards and practises (e.g., Moving Picture Experts Group
[MPEG], Quarter Common Intermediate Format [QCIF],
etc.), and choose the appropriate codecs for various
bandwidths
Convergence
Technologies
Objectives (cont'd)
• Summarize television/video-calling standards and practises
• Identify multimedia conferencing standards, including all
subsets of T.120 (e.g., T.123, T.124, T.135)
• Explain fundamentals of Internet Protocol television (IPTV),
including set-top box, Video on Demand (VoD), accepted
codecs (e.g., Video Codec [VC-1])
• Identify the purpose and function of voice and
videoconferencing hardware (e.g., Multipoint Control Unit
[MCU], set-top box, Session Border Controller [SBC])
• Compare and contrast traditional and IP-based private
branch exchange (PBX) systems
• Identify convergent terminal equipment and software,
including analogue telephone adapter (ATA), single line
adapter, soft phones (WiFi, PDA, PC-based), analogue
phones, time division multiplexer (TDM), protocol-specific
handsets (e.g., SIP, Megaco)
Convergence
Technologies
Objectives (cont'd)
• Explain power issues, including redundancy planning, Power
over Ethernet (PoE)/802.3af, PoE classes, expected voltage,
wattage, power sourcing equipment (PSE), powered
devices (PDs)
Convergence
Technologies
Planning a
Convergent Network
• Major phases of an implementation plan include
these steps:
– Identifying expectations
– Determining bandwidth requirements
– Performing a network health check
– Creating a phased deployment plan
Convergence
Technologies
Identifying Expectations
• Identify how network(s) will be used
• Identify specific protocols that will be used
• Identify and explain potential challenges
Convergence
Technologies
Determining Bandwidth Requirements
•
•
•
•
•
•
•
Identify current digital connection
Determine bandwidth required by existing network
Monitor current network performance
Evaluate current network performance
Calculate additional requirements for VoIP
Take wide area network (WAN) links into account
Take growth into account
Convergence
Technologies
Performing a Network Health Check
•
•
•
•
•
•
•
•
•
•
•
•
Check network cabling
Replace hubs with Layer 2 switches
Implement VLANs
Prioritize VLAN traffic
Check routers
Identify the entity that manages Internet router
Examine current IP addressing scheme
Examine Domain Name System (DNS)
Examine firewall
Identify whether NAT will be implemented
Identify whether VPNs must be supported
Identify whether any part of the LAN will be wireless
Convergence
Technologies
Creating a Phased Deployment Plan
• Create a detailed, approved implementation
plan
• Use a test network
• Deploy incrementally
• Do not begin with the sales department
Convergence
Technologies
TAPI and MAPI
• Telephony Application Programming Interface
(TAPI) is an API used for connecting a Windows PC
to telephone services
• Messaging Application Programming Interface
(MAPI) is a Windows API that allows different
e-mail applications to work together to distribute
mail
Convergence
Technologies
Numbering Plans
• Private numbering plans
allow a company to create
its own numbering system
• Extensions can be created
based on an organisation’s
needs
• Number plan defines the
format of telephone
numbers
• Implementing VoIP involves
designing a numbering
plan and a dial plan.
• Dial plan must include rules
for dealing with:
– End point addressing
– Path selection
– Calling classes
– Digit manipulation
– Overlapping number
ranges
Convergence
Technologies
Telephone Number Mapping (ENUM)
• Maps E.164 telephone numbers into the Domain
Name System (DNS)
• Creates a dynamic mapping of E.164 addresses to
IP addresses
• ENUM domain names are hosted in the e164.arpa
domain
– A telephone number such as +1 (602) 555-1212
is converted into the ENUM domain name
2.1.2.1.5.5.5.2.0.6.1.e164.arpa
– ENUM domain name resolves to one or more
DNS NAPTR records
Convergence
Technologies
G.7xx Codecs
• Various codecs provide different amounts of
compression
• Compression allows more voice traffic, but can
also:
– Introduce delay
– Adversely affect voice quality
– Put a significant strain on CPU resources,
depending on the complexity of the algorithm
and the amount of compression
Convergence
Technologies
Comparison of G.7xx Codecs
Convergence
Technologies
Calculating VoIP Bandwidth Requirements
• Calculations for bandwidth requirements must
factor in:
– Codec, sample period and frame size
– Frames per packet
– IP overhead
– Ethernet overhead
– Number of simultaneous calls
– Silence suppression
– Compressed headers
Convergence
Technologies
Wireless Convergence Technologies
• Components
– Radio exchange
– Base stations (transceivers)
– Portable phones
• Digital Enhanced Cordless Telecommunications (DECT) is an
ETSI standard for digital portable phones
– Generic Access Profile (GAP) guarantees interoperability
between any handset and any base station, regardless
of make or model
– Operates in the 1880 MHz to 1900 MHz band in Europe,
Africa, Australia and Asia (except China)
– Operates in the following bands in North America: 902
MHz to 928 MHz, 2400 MHz to 2483.5 MHz, 5725 MHz to
5850 MHz
Convergence
Technologies
IP Multimedia Subsystem (IMS)
• IP Multimedia Subsystem (IMS) is a network architecture
designed to enable convergence of voice and data
applications and various mobile network technologies
• IMS architecture includes 3 layers:
– Connectivity layer (also called the transport layer)
composed of routers, media gateways and switches
– Control layer composed of network control servers that
manage call setup, modification and release
– Application layer (also called the service layer)
composed of application and content servers that
deliver services within the network
Convergence
Technologies
Facsimile
• Fax transmissions impose special demands on VoIP
because fax standards were designed for circuitswitched connections
• T.30 standardizes the way in which faxes are sent
across standard circuit-switched telephone lines
• T.38 designed for real-time fax transmissions over
an IP network
• T.37 designed for store-and-forward fax
transmission over an IP network
Convergence
Technologies
Presencing
• Presence information is a status indicator that
conveys a person’s willingness and ability to
engage in communications
• Presencing can span different communication
channels
• Multiple Points of Presence (MPOP) describes how
multiple communications devices can combine
state to provide a multidimensional view of a
user’s availability status
• Presencing requires collaboration among a
number of devices and the presence services with
which each of them is connected
• Presencing raises privacy concerns
Convergence
Technologies
Unified Messaging
• In unified messaging (UM), all messaging media
can come together in the form of a unified
mailbox and/or alert service
• Unified messaging offers
– Single delivery
– Single repository
– Single access
– Single notification
Convergence
Technologies
Video Services
• Video codecs and standards include:
– H.261
– Common Intermediate Format (CIF)
• Quarter CIF (QCIF)
• Sub Quarter CIF (SQCIF)
• 4CIF
• 16CIF
– H.263
– Moving Picture Experts Group (MPEG)
• MPEG-1
• MPEG-2/H.262
• MPEG-4
– H.264/MPEG-4 Advanced Video Coding (AVC)
– Realtime Streaming Protocol (RTSP)
Convergence
Technologies
T.120 Multimedia Conferencing Standards
• Key features:
– Support for real-time communication between
two or more entities
– Support for application sharing, electronic
whiteboarding, file exchange and chat
– Support for interoperability between end points
from multiple vendors
– Support for a broad range of transport options
– Co-existence with other standards
Convergence
Technologies
T.120 Architecture
Additional protocols:
• T.128: Multipoint application sharing
• T.134: Text chat application entity
• T.135: User-to-reservation system transactions with T.120
conferences
• T.136: Remote device control application protocol
• T.137: Virtual meeting room management services and
protocol
Convergence
Technologies
Internet Protocol TV (IPTV)
• Internet Protocol TV (IPTV) can include
– Live broadcast (uses Internet Group Messaging
Protocol [IGMP] version 2)
– Video on Demand (uses Realtime Streaming
Protocol [RTSP])
• Requires a set-top box or PC to receive content
from a media server
• Common codecs include: H.264/MPEG-4 AVC,
MPEG-2, VC-1
Convergence
Technologies
Common Convergence Devices
• Videoconferencing hardware
– Multipoint Control Unit (MCU)
– Session Border Controller (SBC)
• IP PBX or traditional PBX
• Terminal equipment
– VoIP phones
– Digital phones
– analogue telephones and adapters
– Soft phones
– Single line adapter
– Time division multiplexer
Convergence
Technologies
Power Issues for Convergent Networks
• Redundant power
– Uninterruptible power supply (UPS)
• Power over Ethernet (PoE)
– Power Sourcing Equipment (PSE) provides power
– Powered Devices (PD) use the power provided
– Maximum power supplied is 15.4 watts at 48 volts
– Five power classes (0-4)
– Two power modes (Mode A and Mode B)
• PSE capable of determining the mode a PD uses
– Injector supplies power into the appropriate wires of the
Ethernet cable
– Deployment of PoE requires a power budget to ensure
that PSE can supply sufficient power to all PDs
Convergence
Technologies
Summary
 List essential steps for qualifying a network's ability to support
convergence (e.g., cable inspection, existing and maximum
device capacity, replacing hubs with switches, Power over
Ethernet [PoE] requirements, VLAN creation, conducting
network reconnaissance
 Describe the features of Telephony Application
Programming Interface (TAPI) and Messaging Application
Programming Interface (MAPI) in a converged solution
 Implement Telephone Number Mapping (ENUM), elements
of global and private numbering plans, Local Number
Portability (LNP)/Wireless LNP, end-point addressing, path
selection, calling classes, digit manipulation, overlapping
number ranges
 Identify common G.7xx codecs and their bandwidth
requirements in a converged environment (e.g., G.711,
G.729, G.729a, G.726 and others)
Convergence
Technologies
Summary (cont'd)
 Describe the impact of compression on voice quality, and
identify issues involved when converting voice to analogue
and digital formats
 Identify benefits and drawbacks of various codecs in
relation to bandwidth and voice quality
 Calculate and estimate bandwidth usage for various
codecs, including considerations of overhead, connection
quality, and other factors that affect theoretical calculations
(e.g., capacity planning, choosing connection speeds)
 Recommend codecs for use with local/in-network/withinLAN calls, and for across WAN connections
 Explain wireless convergence technologies, including Digital
Enhanced Cordless Telecommunications (DECT) and DECT
layers, Personal Wireless Telephone (PWT), Generic Access
Profile (GAP), expected ranges for interference-free
communication, and the MHz ranges for each standard
Convergence
Technologies
Summary (cont'd)
 Identify the elements of the IP Multimedia Subsystem (IMS)
 Explain real-time faxing, according to standards such as ITU
T.38
 Explain store-and-forward faxing, according to standards
such as ITU T.37
 Identify the features, benefits, problems and management
of presencing, including single sign-on, features available in
various devices
 List unified message methods and benefits (e.g., fax, voice,
text, video)
 Identify common and essential videoconferencing codecs,
standards and practises (e.g., Moving Picture Experts Group
[MPEG], Quarter Common Intermediate Format [QCIF],
etc.), and choose the appropriate codecs for various
bandwidths
Convergence
Technologies
Summary (cont'd)
 Summarize television/video-calling standards and practises
 Identify multimedia conferencing standards, including all
subsets of T.120 (e.g., T.123, T.124, T.135)
 Explain fundamentals of Internet Protocol television (IPTV),
including set-top box, Video on Demand (VoD), accepted
codecs (e.g., Video Codec [VC-1])
 Identify the purpose and function of voice and
videoconferencing hardware (e.g., Multipoint Control Unit
[MCU], set-top box, Session Border Controller [SBC])
 Compare and contrast traditional and IP-based private
branch exchange (PBX) systems
 Identify convergent terminal equipment and software,
including analogue telephone adapter (ATA), single line
adapter, soft phones (WiFi, PDA, PC-based), analogue
phones, time division multiplexer (TDM), protocol-specific
handsets (e.g., SIP, Megaco)
Convergence
Technologies
Summary (cont'd)
 Explain power issues, including redundancy planning, Power
over Ethernet (PoE)/802.3af, PoE classes, expected voltage,
wattage, power sourcing equipment (PSE), powered
devices (PDs)
Convergence
Technologies
Lesson 3:
Traffic, Troubleshooting
and Security
Objectives
• Define latency, jitter and wander
• Implement methods for reducing or eliminating latency, jitter
and wander (e.g., implementing a jitter buffer, implementing
QoS, traffic shaping, VLANs)
• Explain the impact of large frames on real-time
communications
• Identify factors that affect the bandwidth of voice and
video calls on convergent networks (e.g., latency, protocol
incompatibility, MTU, codec choice, compression, QoS
issues, packet reordering, loss of feature set)
• Use accepted industry standards such as the Mean Opinion
Score (MOS) to determine voice and video quality, including
MOS for popular codecs, standard MOS numbers, R-value
and subjective video quality
Convergence
Technologies
Objectives (cont'd)
• Identify common network bottlenecks in convergent
networks, including solutions (e.g., monitoring network
devices and protocols, creating a baseline, changing
configuration, upgrading hardware)
• Analyze traffic in a convergent network and resolve
problems using a packet sniffer, monitoring software, and
hardware solutions
• Troubleshoot convergent communications over wireless
networks
• Identify problems in contacting emergency services through
convergent networks
• Parse a Call Detail Record (CDR) and list relevant entries
Convergence
Technologies
Objectives (cont'd)
• Identify types and effects of attacks in convergent networks,
including man-in-the-middle attacks (e.g., packet sniffing,
TCP connection hijacking, registration hijacking), voice mail
compromises, viruses, brute-force and dictionary attacks,
zero-day attacks, illicit servers, toll fraud and unsolicited calls
• Define denial-of-service (DOS) and distributed DOS (DDOS)
attacks, and identify ways to counteract them, including
common traffic types used (e.g., SYN, UDP or ICMP flood),
reconfiguring core upstream routers, using alternative sites,
intentional and unintentional DOS
• Explain the practise and impact of VLAN hopping
• Explain the significance and impact of MAC address
movements, additions and changes
• Identify types of intrusion detection (e.g., host-based,
network-based, defining effective signatures, proactive
detection)
Convergence
Technologies
Objectives (cont'd)
• Back up, upgrade and scan systems to thwart attacks,
including backup types, system patches, service packs,
firmware upgrades, optimal backup schedule
Convergence
Technologies
VoIP Variables
• VoIP variables – conditions that cause problems in
voice communications
• VoIP variables include:
– Delay – the amount of wait time between the
time a signal is sent and received
– Latency – the amount of time required for data
to be transmitted across a network
– Jitter – variability in the arrival rate of data
packets transmitted over a network
– Wander – variability of more than one second
in the arrival rate of data packets transmitted
over a network (long-term jitter)
Convergence
Technologies
Delay
• Fixed delays
– Propagation delay – caused by the distance between
the request and the server fulfilling the request
– Serialization delay – the time required to physically place
voice call bits on a trunk line
– End point processing delay – caused by compressing/
decompressing and encoding/decoding data
– Packetization delay – the time required to place digital
traffic into a particular medium
• Variable delays
– Queuing delay – the time packets wait for other packets
to be placed onto a trunk line
– Router processing delay – the time required for a router
to apply QoS settings, or to process packets that have
arrived out of order
Convergence
Technologies
Latency
• Latency results when multiple delays occur
• The most significant source of latency is the digital
signal processing that occurs in gateways and
routers
• Round-trip latency is the total delay experienced
by two users on a phone call
• Round-trip latency in the PSTN is typically less than
150 milliseconds, except on international calls
• ITU recommends that for good voice quality in
VoIP calls, one-way latency must not exceed 150
milliseconds
Convergence
Technologies
Jitter
• Jitter occurs when packets in a voice transmission
take different paths over a network, causing them
to arrive out of sequence
• A jitter buffer can correct this variability by
providing a space in memory that allows packet
resequencing
Convergence
Technologies
Packet Handling in the Enterprise
• A chief cause of delay and jitter is queuing at the
router
• By default, routers process queues on a first in first
out (FIFO) basis
• Implementing QoS on routers improves voice
quality
• Convergent QoS technologies include:
– Creating VLANS
– Assigning prioritization
– Setting IP precedence values
– Employing traffic-shaping algorithms
Convergence
Technologies
Wander
• Wander is due to synchronization problems in the
network clocks used to control transmissions
• When wander is detected, the signal must be
reclocked, or synchronized, at the next network
element to avoid propagating the wander activity
• The Network Time Protocol (NTP) ensures that
systems are accurate to within milliseconds
• NTP servers belong to two strata:
– Stratum 1 – clocks that are the most accurate;
often GPS-enabled timekeeping systems
– Stratum 3/3E – VoIP gatekeepers, gateways
and PBXs
Convergence
Technologies
Large Data Packets
• Voice packets can get “stuck” behind large data
packets and incur significant delay
• Segmenting large data packets on the network
can help control latency and jitter of voice
services
Convergence
Technologies
Other Throughput Considerations
• Additional factors that affect the quality of voice
transmissions include:
– Choice of codec
– Complexity of compression algorithm
– Lack of QoS support on the network
– Overutilization of routers
– Packet reordering (caused by congestion and
queuing at routers)
– Protocol and codec incompatibility
– MTU setting
– Loss of feature set
Convergence
Technologies
Connection QoS:
Using Multiple Connections
• Connection QoS ensures that the gateway can
protect calls from network problems in several
ways, including:
– Trunk busy-out
– Alternative gateway selection
– Fallback to the PSTN
• The gateway prevents a trunk from servicing a call
if:
– The IP network fails
– The gateway detects an internal problem
Convergence
Technologies
Mean Opinion Score (MOS)
MOS is an industry standard numerical
measurement of voice quality
Convergence
Technologies
R-value
• R-value is another industry standard for measuring
voice quality
• R-values are derived from direct measurements of
equipment and traffic parameters
• R-value score ranges from 1 (worst) to 100 (best)
• One MOS point is roughly equal to 20 R-value
points, but the correlation is not linear
Convergence
Technologies
Mean Opinion Scores for Popular Audio
Codecs
Convergence
Technologies
Maintaining and Troubleshooting
Convergent Networks
• Monitoring is an important aspect of maintaining
convergent networks
• The first step in monitoring is establishing a baseline
– A baseline is a record of normal network
activity that serves as an example for
comparing future network activity
Convergence
Technologies
Establishing a Baseline
• Baseline measurement statistics should include
data on:
– Traffic analysis/end-to-end performance
• Identifies latency, percentage of packet loss
and link utilization
• Tools include: ping and traceroute, and
hardware monitoring mode
– Device performance
• Identifies factors such as CPU and memory
usage
Convergence
Technologies
Device Configuration
• Device configuration directly affects the performance of
convergent networks
• Check configurations of
– Switches
• Ensure VLANs are properly configured
• Ensure proper communication mode (full-duplex, halfduplex, auto-negotiation) settings on switch ports
– End points
• Ensure each end point has a valid IP address
• Ensure that communication mode on NIC is set
properly
• Install firmware or software updates as they become
available
Convergence
Technologies
Troubleshooting Convergence in
Wireless Networks
• In wireless networks, points for troubleshooting include:
– Access points (APs):
• Should support enterprise-level QoS
• Should provide overlapping coverage
• Should be deployed in sufficient number
• Should be able to reject calls when becoming
overloaded
• Should support roaming
– Environment
• Check for sources of interference
– Handsets
• Ensure proper configurations (for example, encryption
keys)
• Install available updates/upgrades
Convergence
Technologies
Call Detail Records
• Call Detail Records include information about the
the following call details:
– Time
– Date
– Call duration
– Number dialed
– Caller ID information
– Extension
– Line/trunk location
– Cost
– Call completion status
Convergence
Technologies
Security in Convergent Networks
• Security is a set of procedures designed to protect
transmitted and stored information, as well as
network resources
• In convergent networks, security includes
preventing:
– Call interception
– Phone fraud
– Network attacks
Convergence
Technologies
Protocol Review
• Inherent weaknesses in IPv4 include:
– Transmission Control Protocol (TCP) handshake
– often manipulated by hackers
– Internet Protocol (IP) – does not sign or encrypt
packets, and packets are easily manipulated
– User Datagram Protocol (UDP) – often used to
conduct scans of systems, and UDP packets
can be forged to wage distributed denial-ofservice attacks
– Address Resolution Protocol (ARP) – does not
authenticate the hosts it resolves and is subject
to ARP cache poisoning
Convergence
Technologies
Overview of Network Attacks
• Network attacks include:
– Spoofing attacks
• IP spoofing
• ARP spoofing
• DNS spoofing
– Man-in-the-middle (hijacking) attacks
• Password sniffing
• Connection termination
• Connection hijacking
• Packet insertion
• Poisoning
– Password-guessing attacks
• Brute-force attacks
• Dictionary attacks
Convergence
Technologies
Malicious Code
• Types of malicious code include:
– Viruses
– Worms
– Illicit servers
– Trojan horses
• To avoid malicious code, use:
– Virus and worm protection
– Application management and testing
– Configuration management
– File signature checking software
Convergence
Technologies
Denial-of-Service (DOS) Attacks
• Purpose of a denial-of-service attack is to:
– Crash a server and make it unusable to
everyone
– Assume the identity of the system being
crashed
– Install a Trojan
• Flooding is the process of sending an
overwhelming number of packets to a system
• Flooding techniques include:
– SYN flood
– Ping flood
– UDP flood
Convergence
Technologies
Distributed Denial-of-Service (DDOS)
Attacks
• Involve the cooperation of several systems to wage a
coordinated attach that generates an overwhelming
amount of network traffic
• DDOS attacks involve:
– A controlling application
– An illicit service
– A zombie
– A target
• DOS and DDOS attacks can be diagnosed by:
– Using a packet sniffer to view traffic
– Using the netstat command to view connections
– Using intrusion-detection systems
Convergence
Technologies
VLAN Hopping
• VLAN hopping is an attack in which a hacker
intercepts packets as they are sent from one VLAN
to another on a trunk
• To avoid VLAN hopping:
– Disable autotrunking
– Remove the native VLAN setting (VLAN 1) from
any trunk port
Convergence
Technologies
MAC Address Movements
• Sudden changes in MAC addresses, such as two
systems suddenly exchanging IP addresses, can
indicate that someone is attempting to poison the
ARP cache
• Monitoring the ARP cache with a tool such as
Arpwatch can guard against ARP spoofing
Convergence
Technologies
Intrusion Detection
• Intrusion detection strategies rely on:
– Signature detection
– Anomaly detection (less common)
• IDS applications require a current signature database
• IDS application types are:
– Host-based
• Captures traffic only on host, not on the network wire
– Network-based
• Does not capture traffic on switched networks
• Port mirroring enables captures and monitoring on
switched networks
Convergence
Technologies
Maintaining Your Networks
• Essential tasks for maintaining a convergent network include:
– Scan systems regularly to detect unusual behaviour
– Upgrade equipment as necessary
– Install system patches and service packs
– Keep antivirus files current
– Install firmware upgrades
– Perform regular backups
• Full
• Differential
• Incremental
– Verify that backups are successful
– Ensure careful (off-site) storage of backup media
– Choose an optimal backup schedule
Convergence
Technologies
Summary
 Define latency, jitter and wander
 Implement methods for reducing or eliminating latency, jitter
and wander (e.g., implementing a jitter buffer, implementing
QoS, traffic shaping, VLANs)
 Explain the impact of large frames on real-time
communications
 Identify factors that affect the bandwidth of voice and
video calls on convergent networks (e.g., latency, protocol
incompatibility, MTU, codec choice, compression, QoS
issues, packet reordering, loss of feature set)
 Use accepted industry standards such as the Mean Opinion
Score (MOS) to determine voice and video quality, including
MOS for popular codecs, standard MOS numbers, R-value
and subjective video quality
Convergence
Technologies
Summary (cont'd)
 Identify common network bottlenecks in convergent
networks, including solutions (e.g., monitoring network
devices and protocols, creating a baseline, changing
configuration, upgrading hardware)
 Analyze traffic in a convergent network and resolve
problems using a packet sniffer, monitoring software, and
hardware solutions
 Troubleshoot convergent communications over wireless
networks
 Identify problems in contacting emergency services through
convergent networks
 Parse a Call Detail Record (CDR) and list relevant entries
Convergence
Technologies
Summary (cont'd)
 Identify types and effects of attacks in convergent networks,
including man-in-the-middle attacks (e.g., packet sniffing,
TCP connection hijacking, registration hijacking), voice mail
compromises, viruses, brute-force and dictionary attacks,
zero-day attacks, illicit servers, toll fraud and unsolicited calls
 Define denial-of-service (DOS) and distributed DOS (DDOS)
attacks, and identify ways to counteract them, including
common traffic types used (e.g., SYN, UDP or ICMP flood),
reconfiguring core upstream routers, using alternative sites,
intentional and unintentional DOS
 Explain the practise and impact of VLAN hopping
 Explain the significance and impact of MAC address
movements, additions and changes
Convergence
Technologies
Summary (cont'd)
 Identify types of intrusion detection (e.g., host-based,
network-based, defining effective signatures, proactive
detection)
 Explain the practise and impact of VLAN hopping
 Back up, upgrade and scan systems to thwart attacks,
including backup types, system patches, service packs,
firmware upgrades, optimal backup schedule
Convergence
Technologies
Convergence Technologies
 Convergent Network Traffic Protocols
 Implementing VoIP
 Traffic, Troubleshooting and Security
Convergence
Technologies