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

PBXLELE

PBX PBX

PSTN

Branch office HQ office

4.1. Network characteristics (Cntd)

• Data networks – 60s, ARPA• Basic principals – packet switching, connectionless-

oriented (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

ServerRouter Router

App server

Branch office HQ officeRes. house

Modem/router

Public/private network

Ethernet, ATM, FR, PPP

Physical layer

TCP UDP

HTTP, FTPH.323, SIP, RTP, RSVP, MGCP,

MEGACO/H.248

Web Browser, MS Outlook, LOTUS

IP

4.1. Network characteristics (Cntd)

Characteristics of PSTN and IP networks 

  PSTN IP Network

Bandwidth Fixed Variable

Technology Circuit-switched Packet-switched

Call handling Connection-oriented Connectionless-oriented

Quality Guaranteed limit No guarantee on delay, jitter and loss on transmission quality

4.2. PSTN/Internet convergence for data services: Narrowband Internet access

(local area)

LEXLEX

LEXLEX

(local area)

(local area)LEXLEX

LEXLEX

ISP

LEXLEX

AccessPoP

AccessPoP

LEXLEXLEXLEX

LEXLEX

AccessPoP

AccessPoP

AccessPoP

AccessPoP

CentralPoP

CentralPoP

PSTN

trunk(ISDN PRI)

trunk(SS7)

LEXLEX LEX - Local ExchangePoP – Point-of-PresenceISP – Internet Service Provider

Internet access methods

Home Network Intermediate Network

modem bank/access server/router

Access Devices

ISP

X

ATM/FR/LLATM/FR/LL

ISP PoPCorporate PoP

accessserver /router

POTSISDN

xDSLcablemodem

X

CATVCATV

FR - Frame RelayLL – Leased line

Virtual PoP(VPOP)

FR/ATM/LL

POTS/ISDN

Narrowbanddial-in accessNarrowbanddial-in access

Narrowbanddial-in access

withvirtual POP

Narrowbanddial-in access

withvirtual POP

Broadbandaccess

Broadbandaccess

Corporate leased line

access

Corporate leased line

access

ISP

bac

kbon

eIS

P b

ackb

one

PSTN

PSTNX

BroadbandaccessBroadbandaccess

4.3. PSTN/Internet convergence for voice servicesA. Converged network

GatewayGateway

LAN PC LANLAN LAN

Modem/Router

RouterServer

Router

App server

Res. house

PBX

Branch officeHQ office

IP-based public/private network

PS

TN

/IS

DN

B. Network scenarios for VoIP

GatekeeperCall ProcessingName’s ServerOAM Server

RAS

POP

PS

TN

/IS

DN

Internet

64 kbit/s speechVoice over IPMessage interface to central server

PC to Phone

Phone to PhonePhone to PC

PC to PC

VoiceVoice

Voice IWU(Gateway)

RAS

POP

Voice IWU(Gateway)

MGCP

S0urce

Destination

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 call-establishment 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 transitionthe industry to IP telephony. Today, however, itscircuit switched heritage makes H.323 complex toimplement, resource intensive, and difficult to scale.Vendors and service providers are now de-emphasizingH.323’s role in their IP voice communicationsstrategies.

Which Standard?(Cntd.)

2. SIPSIP is ideal for IP voice and will play an importantrole for next generation service providers and distributedenterprise architectures. SIP suffers from someof the limitations of H.323 in that it has become acollection of IETF specifications, some of which arestill under definition. The other similarity withH.323 is that SIP defines intelligent end points andvendors have found this approach to be more costlyand less reliable.

Which Standard?(Cntd.)

MGCP/MEGACO/H.248In contrast to SIP, the MGCP/MEGACO standardsboth centralize the control of simple telephones.This is popular in environments where both cost andcontrol are important issues, which is certainly thecase in the enterprise environment where the PC canbe used to augment features and functionality.

H.323 vs. SIP

VoIP components

Intranet/Internet

(IP Network)

Intranet/Internet

(IP Network)Router

Gatekeeper

VoIPTerminals

Router

Gateway(Voice IWU)

PSTN/ISDN

PSTN/ISDN ATMATM

PBX

VoIPTerminals

Gatekeeper

Gateway(Voice IWU)

VoIP components and their functionsIP 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

PS

TN

/IS

DN

VoIP Server(Gatekeeper)

RAS

POP

PS

TN

/IS

DN

InternetVoice

Voice

Voice IWU(Gateway A)

RAS

POP

Voice IWU(Gateway B)

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 multi-

frequency 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.

A B

A B

MGCP

(a) (b) (a)

VoIP scenarios: PC-to-Phone

PS

TN

/IS

DN

VoIP Server(Gatekeeper)

RAS

POP

PS

TN

/IS

DN

InternetVoice

Voice

Voice IWU(Gateway)

RAS

POP

Voice IWU(Gateway)

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.

(b)

(b)

(a)

(a)

AB

AB

VoIP scenarios: Phone-to-PC

PS

TN

/IS

DN

VoIP Server(Gatekeeper)

RAS

POP

PS

TN

/IS

DN

InternetVoice

Voice

Voice IWU(Gateway)

RAS

POP

Voice IWU(Gateway)

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 call setup (b) within the Internet between A-IWU and B-subscriber PC (routing

functions and address mapping are in gatekeeper)

MGCP

(a)

(a)

(b)

(b)A

B

A 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 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.

Business VoIP and IP-T

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 ConvergenceQuality of Service (QoS): The converged network must deliver the same QoS as the traditional Public Switched Telephone Network (PSTN); without it, video- and voice-over-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% means downtime of 3.7 days per year– 99.9% means downtime of 9 hours per year– 99.99% means downtime of 53 minutes per year– 99.999% means downtime of 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

Source: Infonetics Research, November 2001 The Tier 1 Service Provider Opportunity, US/Canada 2001

0% 25% 50% 75% 100%

Product Reliability

Best Price-to-Performance Ratio

Financial Stability

Leading-Edge Technology

Manufacturer’s ProductsAlready Installed

Pre-and post-salesservice and support

Manufacturer reputation

Manufacturer’s futureproduct offering

Leasing and Financing Options

Lowest Price

Sales and Marketing Services

Network Integration andDesign Services

100

82

73

73

64

64

45

45

27

27

18

9

Percent of Respondents Rating 6 to 7

Manufacturer Selection Criteria (Q61, n-11)

Source: Contingency Planning Research, a division of Eagle Rock Alliance Ltd

Reliability moved up the value scale

andnow rates

highest for Tier_1Service Providers

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, scalingOn 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

36% Router Operations Software/hardware

updates Configuration errors

21% Router Failures Hardware fault

intolerance Software quality

Physical Links 27%

Congestion 5% Network Engineering

Malicious 2%Unknown 2%

Source: University of Michigan

MPLS traffic engineering

Diversity of paths Fast Restoration

Software process isolation and redundancy 99.999 percent available hardware

Software upgrades Hardware upgrades

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 operationsCredit card/sales authorisationPay-per-viewHome shopping (TV)Airline reservationsTele-ticket salesPackage shippingAutomated 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