Download Document

Part 2. Converged networks and services
4. Convergence of fixed networks
4.1. Network characteristics
# PSTN/ISDN
# Data networks
4.2. PSTN/Internet convergence for data services
# Internet access
4.3. PSTN/Internet convergence for voice services
# VoIP and IP Telephony
4.4. QoS issues and Reliability
4.5. Estimation of Call Quality
4.1. Network characteristics
•
•
•
•
PSTN – more then 100 years history
Basic principals – circuit switching, connection-oriented
Three phases on the session
Reservation of network resources:
# analog voice channel – 4 kHz
# digital voice channel – 64 kbps
• Guaranteed level of QoS (delay/loss)
• Very high availability – outage is less then 5 min/year
(Bellcore – 3 min/year)
PSTN
LE
LE
PBX
PSTN
PBX
Branch office
PBX
HQ office
4.1. Network characteristics (Cntd)
• Data networks – 60s, ARPA
• Basic principals – packet switching, connectionlessoriented (IP)
• No resource reservation for the transmission
• No guarantee for delay and loss – it’s not critical for
data, but critical for other possible apps
Data network
Server
App server
Router
Router
Public/private network
Modem/router
Branch office
Res. house
HQ office
Web Browser, MS Outlook, LOTUS
H.323, SIP, RTP, RSVP, MGCP,
MEGACO/H.248
HTTP, FTP
TCP
UDP
IP
Ethernet, ATM, FR, PPP
Physical layer
4.1. Network characteristics (Cntd)
Characteristics of PSTN and IP networks
Bandwidth
PSTN
IP Network
Fixed
Variable
Technology
Circuit-switched
Call handling
Connection-oriented
Quality
Guaranteed limit
on delay, jitter and loss
Packet-switched
Connectionless-oriented
No guarantee
on transmission quality
4.2. PSTN/Internet convergence for data services:
Narrowband Internet access
trunk
(ISDN PRI)
Access
PoP
LEX
(local area)
LEX
ISP
trunk
(SS7)
LEX
Central
PoP
(local area)
Access
PoP
LEX
LEX
LEX
PSTN
LEX
(local area)
LEX
LEX
Access
PoP
LEX - Local Exchange
PoP – Point-of-Presence
ISP – Internet Service Provider
Internet access methods
Narrowband
dial-in access
Access Devices
ISP PoP
Corporate PoP
POTS/ISDN
POTS
ISDN
PSTN
xDSL
cable
modem
Broadband
access
X
X
access
server /
router
CATV
PSTN
X
Broadband
access
ISP backbone
ISP
modem bank/
access server/
router
ATM/FR/LL
Virtual PoP
(VPOP)
Narrowband
dial-in access
with
virtual POP
FR/ATM/LL
Home Network
Corporate
leased line
access
Intermediate Network
FR - Frame Relay
LL – Leased line
4.3. PSTN/Internet convergence for voice services
A. Converged network
App server
Server
Router
Router
IP-based public/private network
Modem/Router
Gateway
LAN
LAN
PC
Gateway
LAN
PBX
Branch office
Res. house
HQ office
B. Network scenarios for VoIP
Internet
Voice
Voice
POP
RAS
RAS
Voice IWU
(Gateway)
MGCP
Voice IWU
(Gateway)
Gatekeeper
Call Processing
Name’s Server
OAM Server S
64 kbit/s speech
Voice over IP
Message interface to central server
PSTN/ISDN
PSTN/ISDN
POP
0
u
r
c
e
Destination
PC to PC
Phone to PC
PC to Phone
Phone to Phone
C. VoIP protocols
•
IP is designed to be media-independent transport
mechanism (different transport technologies can be
use)
•
Call control or call processing technique maps
telephone numbers or user names into IP
source/destination addresses
• Call control is implemented by call-control software
running on servers (gatekeepers)
•
Gatekeepers communicate with voice gateways,
end-user handsets or PCs using call-control protocols.
VoIP protocols:
1. H.323, ITU-T
• H.323 - first call control standard for multimedia networks.
Was adopted for VoIP by the ITU in 1996
• H.323 is actually a set of recommendations that define how
voice, data and video are transmitted over IP-based networks
• The H.323 recommendation is made up of multiple call control
protocols. The audio streams are transacted using
the RTP/RTCP
• In general, H.323 was too broad standard without sufficient
efficiency. It also does not guarantee business voice quality
H.323 call setup process
VoIP protocols:
2. SIP - Session Initiation Protocol, IETF (Internet
Engineering Task Force)
• SIP - standard protocol for initiating an interactive user session
that involves multimedia elements such as video, voice, chat,
gaming, and virtual reality. Protocol claims to deliver faster callestablishment times.
• SIP works in the Session layer of IETF/OSI model. SIP can
establish multimedia sessions or Internet telephony calls. SIP
can also invite participants to unicast or multicast sessions.
• SIP supports name mapping and redirection services. It makes
it possible for users to initiate and receive communications and
services from any location, and for networks to identify the
users wherever they are.
VoIP protocols :
2. SIP - Session Initiation Protocol, IETF (Internet
Engineering Task Force) (Cntd)
•SIP – client-server protocol, Rq from clients, Rs from servers.
Participants are identified by SIP URLs. Requests can be sent
through any transport protocol, such as UDP, or TCP.
•SIP defines the end system to be used for the session, the
communication media and media parameters, and the called
party's desire to participate in the communication.
•Once these are assured, SIP establishes call parameters at
either end of the communication, and handles call transfer and
termination.
•The Session Initiation Protocol is specified in IETF Request
for Comments (RFC) 2543.
SIP Proxy operation
SIP Redirect Server
VoIP protocols :
3. MGCP/Megaco/H.248
• MGCP - Media Gateway Control Protocol, IETF
[Telcordia (formerly Bellcore)/Level 3/Cisco]
• MGCP – control protocol that specifically addresses the
control of media gateways
• Megaco/H.248 (IETF, ITU) - standard that combines
elements of the MGCP and the H.323, ITU (H.248)
• The main features of Megaco - scaling (H.323) and
multimedia conferencing (MGCP)
How MGCP coordinates the Media
Gateways
Which Standard?
1. H.323
H.323, with its roots in ISDN-based video-conferencing,
has served its purpose of helping to transition
the industry to IP telephony. Today, however, its
circuit switched heritage makes H.323 complex to
implement, resource intensive, and difficult to
scale.
Vendors and service providers are now de-emphasizing
H.323’s role in their IP voice communications
strategies.
Which Standard?
(Cntd.)
2. SIP
SIP is ideal for IP voice and will play an important
role for next generation service providers and distributed
enterprise architectures. SIP suffers from some
of the limitations of H.323 in that it has become a
collection of IETF specifications, some of which are
still under definition. The other similarity with
H.323 is that SIP defines intelligent end points and
vendors have found this approach to be more costly
and less reliable.
Which Standard?
(Cntd.)
MGCP/MEGACO/H.248
In contrast to SIP, the MGCP/MEGACO standards
both centralize the control of simple telephones.
This is popular in environments where both cost and
control are important issues, which is certainly the
case in the enterprise environment where the PC can
be used to augment features and
functionality.
H.323 vs. SIP
VoIP components
Gatekeeper
Gatekeeper
Intranet/
Internet
(IP Network)
VoIP
Terminals
Router
Router
VoIP
Terminals
Gateway
(Voice IWU)
PSTN/
ISDN
Gateway
(Voice IWU)
ATM
PBX
VoIP components and their functions
IP Gateway
•
•
•
•
•
Packetizes voice
Supports telephone signaling
Applies audio compression
Provides connection control (mapping signaling protocols and addresses:
E.164
IP address)
Tags voice packets using QoS mechanisms (DiffServ, Priority,…)
Router
• Recognizes voice packet and tags it accordingly
•
•
•
Prioritizes packets as needed
Manages bandwidth allocation
Provides queuing of traffic overflow
Gatekeeper - media gateway controller
• MGC acts as the master controller of a media gateway
•
•
•
Supervises terminals attached to a network
Provides a registration of new terminals
Manages E.164 addresses among terminals
D. VoIP scenarios: Phone-to-Phone
Voice
(a)
A
PSTN/ISDN
POP
Voice
B
POP
RAS
RAS
(b)
Voice IWU
(Gateway A)
MGCP
Voice IWU
(Gateway B)
PSTN/ISDN
A
Internet
(a)
VoIP Server
(Gatekeeper)
Basic Call "Phone-to-Phone"
 A-Subscriber dials IWU E.164 number
 Normal Call Setup (a) between A-Subscriber and A-IWU
 Announcement from A-IWU to user
 Input of A-Subscriber E.164 Number, PIN and B-Subscriber E.164 Number (via multifrequency code)
 (SP) Call setup (b) within the Internet between A-IWU and B-IWU (routing functions
are in gatekeeper)
 Normal Call Setup (a) between B-IWU and B-Subscriber.
B
VoIP scenarios: PC-to-Phone
Voice
(b)
A
PSTN/ISDN
(a)
POP
RAS
Voice IWU
(Gateway)
B
POP
RAS
(b)
Voice IWU
(Gateway)
PSTN/ISDN
Internet
A
Voice
VoIP Server
(Gatekeeper)
Basic Call "PC-to-Phone"
 PC needs VoIP software (support on of Signaling Protocols)
 Normal Internet login (a) of A-Subscriber
 Access to VoIP Server
 Input PIN and B-Subscriber E.164 Number
 (SP) Call setup (b) within the Internet between A-subscriber and B-IWU (routing
functions are in gatekeeper)
 Normal Call Setup (a) between B-IWU and B-Subscriber.
(a)
B
VoIP scenarios: Phone-to-PC
Voice
(a)
A
PSTN/ISDN
POP
(b)
POP
RAS
B
RAS
(b)
Voice IWU
(Gateway)
MGCP
Voice
Voice IWU
(Gateway)
(a)
PSTN/ISDN
A
Internet
VoIP Server
(Gatekeeper)
Basic Call "Phone to PC"
 PC needs VoIP software (support on of Signaling Protocols)
 Normal Internet login (a) of B-Subscriber and registration at gatekeeper (E.164 to IP
address mapping)
 A-Subscriber dials IWU E.164 number
 Normal Call Setup (a) between A-Subscriber and A-IWU
 Input of A-Subscriber E.164 Number, PIN and B-Subscriber E.164 Number
 (SP) call setup (b) within the Internet between A-IWU and B-subscriber PC (routing
functions and address mapping are in gatekeeper)
B
E. Difference between VoIP and IP-T
• Voice over IP (VoIP) indicates that an analog voice signal has been digitized and
converted into the packet format used by IP. This is done in order to allow telephony and
other audio signals to be transported over the same network as regular data traffic.
Thus, VoIP refers to a conversion and transportation process.
• IP-Telephony is a service and it refers to VoIP over the public Internet. Although
technically feasible, the call quality is considered to be too variable for serious use by
business professionals. This comes from the fact that voice traffic has to be given
priority over data. However, VoIP is employed over managed IP infrastructures, e.g.
corporate intranets and the backbone networks of carriers.
•
Unfortunately, the terms VoIP and IP-Telephony are often used interchangeably.
Business VoIP and IP-T
• Business VoIP service is defined as a high quality, reliable service capable of
sustaining mission-critical communications. High quality is defined as clear audio with
the absence of echo. A reliable service connection provides an error free transmission
with no service interruptions.
• IP-Telephony uses IP as the transport mechanism but it uses the public data
network (i.e., the Internet) to transmit voice packets. Because the Internet is an
unmanaged, non-voice engineered conglomerate of many networks, it cannot
guarantee bandwidth and timely delivery of voice packets, resulting in unacceptable
voice quality for business communications.
• By transmitting voice over a private managed IP data network, you can control all of
the network characteristics required to ensure high-quality, reliable voice
communications over a data network.
TeleGeography VoIP market predictions for 2005
In 2005 the international VoIP traffic will exceed 40 billion minutes with more than 30%
annual growth.
Roadblocks to Convergence
Quality of Service (QoS): The converged network must deliver the same QoS as the
traditional Public Switched Telephone Network (PSTN); without it, video- and voiceover-IP are simply not viable. In an IP-based network, this requires handling data
packets - to reduce loss, latency and jitter - with a QoS significantly higher than most
data transmission networks are designed to support.
Reliability and Availability: The converged network must provide redundancy and
fault-tolerance with "five nines" (99.999%) availability. While this is the standard level
for most voice systems, many data networks lack the infrastructure to deliver such
high availability across the entire system.
Bandwidth: The converged network must provide the necessary bandwidth to
accommodate voice and video applications, which can demand considerably more
than most data applications. While some efficiency schemes have proved useful in
lowering the required bandwidth, most have been unable to effectively balance
transmission speeds with voice and video quality.
Security: In traditional IP networks, packets are transmitted across shared segments,
where the possibility exists that someone could decode packets and access secure
information. A converged network must provide a new measure of encryption and
security for voice traffic.
4.4. QoS issues and Reliability
• The number one issue operators have is:
guarantee of Quality of Service
How to support voice traffic on backbone ?
Actually, this is the number two issue
• The number one issue is:
Reliability of the data network
• Why?
QoS makes only sense if the network is up and running
all the time, hence reliable
A. Reliability
• Reliability in PSTN networks is already for 10s of
years equal to the famous 99.999%, also called
the 5 nines
• Operators are so used to this reliability that they
take it for granted
• Why is it so important?
–
–
–
–
99%
99.9%
99.99%
99.999%
means downtime of
means downtime of
means downtime of
means downtime of
3.7 days per year
9 hours per year
53 minutes per year
5.5 minutes per year
• Traditional IP data equipment does not offer 5
nines reliability
Nines of availability and corresponding
downtime
Reliability is a fundamental philosophy
Manufacturer Selection Criteria (Q61, n-11)
Product Reliability
Reliability moved up
the value scale
and
now rates
highest for Tier_1
Service Providers
100
82
Best Price-to-Performance Ratio
Financial Stability
73
Leading-Edge Technology
73
Manufacturer’s Products
Already Installed
64
Pre-and post-sales
service and support
64
Manufacturer reputation
45
Manufacturer’s future
product offering
45
Leasing and Financing Options
27
Lowest Price
27
Sales and Marketing Services
Source: Contingency Planning Research, a division of
Eagle Rock Alliance Ltd
Source: Infonetics Research, November 2001
The Tier 1 Service Provider Opportunity, US/Canada 2001
Network Integration and
Design Services
18
9
0%
25%
50%
75%
100%
Percent of Respondents Rating 6 to 7
Reasons for system unavailability
Source: Gartner Group
• User Errors and Process: Change management, process inconsistency
• Technology: Hardware, network links, environmental issues, natural disasters
• Software Application: Software issues, performance and load, scaling
On average, computer system reliability is estimated at around 98.5%. This number
includes not only the data networks and their components, but all the core business
applications, servers, and mainframes.
Why are traditional IP Routers Unreliable?
7% Customer Premises Equipment
Unknown 2%
Malicious 2%
Congestion 5%
 Network Engineering

36% Router Operations
 Software/hardware
updates
 Configuration errors
MPLS traffic
engineering


Software upgrades
Hardware upgrades
Physical Links 27%


21% Router Failures
 Hardware fault intolerance
 Software quality
Diversity of paths
Fast Restoration


Software process isolation and redundancy
99.999 percent available hardware
Source: University of Michigan
Common causes of downtime in IP networks
Source: University of Michigan and Sprint study, October 2004
More than half of the problems causing downtime in IP networks
- 59% - pertain to routing management issues.
More deeply, 36% of these problems are attributable to router
misconfigurations, and 23% come from a category broadly
described as "IP routing failures." By contrast, of the remaining
41% of problems, link failures of some form account for 32%,
and "other causes" comprise the remaining 9%.
Benefits of network reliability and losses due to
failures
– Reductions in capital expenditure
• eliminates requirement for duplicate
hardware configurations to support
redundancy
– Reductions in ongoing operational
costs
• lower maintenance due to reduced
number of network elements
• true non-service-interrupting upgrades
• reduced floor space, cooling and power
requirements
– Revenue opportunities
• no data session interruption during control
plane switchover will allow customers to
achieve 99.999 percent availability
• increased customer retention
– Ability to offer low-risk SLAs
• Five nines SLA
Business
Brokerage operations
Credit card/sales
authorisation
Pay-per-view
Home shopping (TV)
Airline reservations
Tele-ticket sales
Package shipping
Automated teller machines
Source FCA
Cost per minute
of downtime ($)
107,333
46,333
2500
1883
1500
1150
467
242
Commonly used techniques to “solve” reliability
• Instead of one reliable router, provide a
reservation for each router
• Not quite the solution, isn’t it ?
– double the price
– need for extra interfaces for interconnection
– but more importantly in case of failure, it takes time to
reroute the traffic from one to the other, in the
meantime the ongoing calls are affected
• outage time can be quite long