UNIT V:Advanced Wireless Technologies:

VoIP Architecture and Applications, Vehicular network, Delay tolerant network. 6 Hrs

1Apr 21, 2023

VoIP Architecture and Applications:

Voice Over Internet Protocol (VoIP) Issues and Challenges

William McCrum

2Apr 21, 2023

3

IP-based Network

IP-based Network

Drivers Affecting Network Changes

• Network Simplification

• Lower start-up and operating costs

• Regulations

• Leap frog competition

• Fast service introduction and customization

• Improved codec compression techniques

• Faster processing power

• Traffic control mechanism

• Lower LD voice service rate

• Multimedia services

• Data traffic exceeds voice traffic

• Corporate Networks

End User

Service ProviderTechnology

The telecom network is undergoing extensive changes to meet new market and service demands.

The telecom network is undergoing extensive changes to meet new market and service demands.

Apr 21, 2023

4

Network Architecture Evolution

Optical fibre

IP

SONET/SDH

ATM/FR

OXC

WDM mux AMPWDM demux

IP

FR

ATM

FR

TDM

DataServices

PSTN/ISDNServices

MobileServices

TDM

ServiceLayer

NetworkLayer

TransportLayer

SONET/SDH

CATVServices

Optical fibre

IP

SONET/SDH

ATM/FR

OXC

WDM mux AMPWDM demux

OXC

WDM mux AMPWDM demux

IPIP

FR

ATM

FRFR

ATM

FR

TDMTDM

DataServices

PSTN/ISDNServices

MobileServices

TDM

ServiceLayer

NetworkLayer

TransportLayer

SONET/SDHSONET/SDH

CATVServices

Today – Single Service Networks Future – Multi-Service Networks

Optical fibre

IP

ATM/FR

OXC

WDM mux AMPWDM demux

IP

ATM

FR

DataServices

MobileServices

NewApplications

ServiceLayer

NetworkLayer

TransportLayer

VoIPCATVServices

SONET/SDH

SONET/SDH

Optical fibre

IP

ATM/FR

OXC

WDM mux AMPWDM demux

OXC

WDM mux AMPWDM demux

IPIP

ATM

FR

ATM

FR

DataServices

MobileServices

NewApplications

ServiceLayer

NetworkLayer

TransportLayer

VoIPCATVServices

SONET/SDH

SONET/SDHSONET/SDH

Apr 21, 2023

5

Enters VoIP…What is it?

• Many names, different meaning to different people:– Soft-switching– Next Generation Voice Network– IP Telephony– Voice over Internet– Voice over Internet Protocol– Voice over Packet– IP Communications

Various implementations of VoIP systems and user expectations.

Various implementations of VoIP systems and user expectations.

Apr 21, 2023

6

VoIP Network Architecture – 3 Key Functional Elements

Circuit-SwitchedNetwork

IP Network

SS7

IP Phone

PC Client

Media Gateway Controller / Softswitch / Gatekeeper

• Instructs Media Gateways on how to set-up, handle, and terminate individual media flows

Media Gateway Controller / Softswitch / Gatekeeper

• Instructs Media Gateways on how to set-up, handle, and terminate individual media flows

Media Gateway (MG)

• Translates between TDM voice and packet data

• Establish media path

Media Gateway (MG)

• Translates between TDM voice and packet data

• Establish media path

Signalling Gateway

• Inter-works with the SS7 network for call control

Signalling Gateway

• Inter-works with the SS7 network for call control

IP

• Different signalling and control standards between network elements:

- H.323, MGCP, IETF Megaco/ITU-T H.248, SIP, SIP-T …

- Different VoIP realizations and physical architecturesApr 21, 2023

7

VoIP Realizations• PC Applications• PSTN Bypass

– Toll– Enterprise– Broadband VoIP– Cable VoIP

• Next Generation Network – Circuit-Switch Replacement– Service creation and customization

Smart Edge, Dumb network(Intelligence in CPE)

Smart Network, Dumb Edge(Centralized Intelligence)

Smart Network, Smart Edge(Distributed Intelligence)

•Combining network and CPE (edge) intelligence allows service customization and new service revenue

•Varieties of VoIP deployments

Apr 21, 2023

PC Applications – PC to PC (Internet to Internet)

• User– Free calls between PCs– Low voice quality and reliability

• Technology– PC client software (e.g. Microsoft NetMeeting) for voice

and multimedia communications between PCs with the same client software

– VoIP processing performed in PCs• Network

– Network traffic carried in public Internet– No legacy PSTN

CentralOffice

CentralOffice

Modem(DSL, cable)

Modem(DSL, cable)

Internet

8

9

PSTN Bypass – PC to Phone

VoIPGateway

GateKeeper

Modem(DSL, cable)

• User

– Voice calls between PC and PSTN phone

– A fee normally charged

– Voice quality varies, depending on service provider networks

• Technology

– PC client software

– VoIP processing performed in PCs

• Network

– Network traffic carried in public Internet or in managed IP network

– Requires VoIP Gateway to interwork with PSTN

CentralOffice

CentralOffice

Internet/IP

Apr 21, 2023

10

PSTN Toll Bypass – Phone to Phone

• User– Cheaper long distance voice calls via pre-paid calling cards– Service offered since 1995 due to high international LD tariff– May require to dial up to 24-digits for call establishment– Voice quality varies– VoIP technology invisible to users

• Network– Global coverage and interconnection among allied VoIP

service providers

VoIPGateway

GateKeeper

VoIPGateway

VoIP Service Provider

CentralOffice

CentralOffice

IP

Apr 21, 2023

11

PSTN Bypass – Enterprise IP PBX

• VoIP PBX provides Media Gateway and router functions• Supports voice and data services• Voice and data traffic between enterprise sites is carried by the IP

network. • PSTN carries overflow voice traffic and off-net calls• Well suited for road warriors

– Access corporate network resources– Make VoIP long distance calls on any Internet access to

corporate phones or public PSTN phones.

PBXIP Phone

EnterpriseEnterprise HQHQ

IP

PSTNIP Phone

EnterpriseEnterprise BranchBranchVoIP PBX

Apr 21, 2023

12

PSTN Bypass – Broadband VoIP Service Provider

• New breed of VoIP service provider exploiting over providers’ broadband access

• User Features:– Low local and LD residential

rates – Extensive call feature set – Choice of area codes

independent of customer location

• Cons to users:– Reliability - best effort service

• Dependent on access provider network reliability

• Affected by power outage

Vonage VoIP Network

PSTN

Analog Telephone Adaptor

DSL/CableModem

Router

VoIPGtwy

DSL/CableInfrastructure

Phone to Phone

Apr 21, 2023

13

Cable IP Telephony – Converged IP Architecture

Cable Headend

CMTS

IPMTA

Customer Premise

RouterCMS

MGC

Media Gateway

Regional Headend or Data Center

IP Services(Internet, e-mail, etc.)

data

voice

HFC

MTA: Multimedia Terminal AdapterCMS: Call Management ServerHFC: Hybrid Fibre-CoaxMGC: Media Gateway Controller

Signalling Gateway

Source: Lemur Networks

PSTN

Video Services

Router

Cable Operator implements a single IP infrastructure and offers innovative new services (voice, data, video) to compete with telcos.

Cable Operator implements a single IP infrastructure and offers innovative new services (voice, data, video) to compete with telcos.

Apr 21, 2023

VoIP Examples

• Xbox Voice

• Windows messenger

• AOL Instant Messenger

• Motorola Phone Adapter (Vonage)

• Cisco Phone

Apr 21, 2023 14

In brief:

• VoIP is one of many higher-level communications capabilites among devices connected to the Internet.

• VoIP is not an application.• VoIP is a capability that is part of many applications. • VoIP capabilities are already pervasive.

– Microsoft Windows Messenger (part of XP)– AOL Instant Messenger– Xbox and Sony Playstation

Apr 21, 2023 15

Vehicular NetworksVehicular NetworksWhy Vehicular Networks: Emergence of Vehicular NetworksApplications: Congestion detection, Vehicle platooning, Road hazard warning, Collision alert, Stoplight, assistant, Toll collection, Deceleration warning, Emergency vehicle warning, Border clearance, Traction updates, Flat tire warning, Merge assistance ,etc.Adversaries: Greedy drivers, Snoops, Pranksters, Industrial Insiders, Malicious Attackers, etc. Attacks: Denial of Service (DoS), Message Suppression Attacks, Alteration Attacks, etc.Vehicular Network Challenges: Authentication vs. Privacy, Availability, Mobility, Key Distribution, Low Tolerance for Errors, Bootstrap, etc

Ref: Challenges in Securing Vehicular Networks, Challenges in Securing Vehicular Networks, Bryan Parno, Adrian Perrig, Carnegie Mellon University.

Apr 21, 2023 16

Emergence of Vehicular Networks• In 1999, FCC allocated 5.850-5.925 GHz band to promote safe

and efficient highways– Intended for vehicle-to-vehicle and vehicle-to-infrastructure

communication

• Emerging radio standard for Dedicated Short-Range Communications (DSRC)– Based on an extension of 802.11

• Must consider security, or these networks will create more problems than they solve

Apr 21, 2023 17

Why Vehicular Networks?

• Safety– On US highways (2014):

• 42,800 Fatalities, 12.8 Million Injuries• ~$230.6 Billion cost to society

• Efficiency– Traffic jams waste time and fuel– In 2013, US drivers lost a total of 13.5 billion hours

and 15.7 billion gallons of fuel to traffic congestion

• Profit– Safety features and high-tech devices have

become product differentiatorsApr 21, 2023 18

Applications

• Congestion detection

• Vehicle platooning

• Road hazard warning

• Collision alert

• Stoplight assistant

• Toll collection

• Deceleration warning

• Emergency vehicle warning

• Border clearance

• Traction updates

• Flat tire warning

• Merge assistanceApr 21, 2023 19

Congestion Detection• Vehicles detect congestion when:

– # Vehicles > Threshold 1– Speed < Threshold 2

• Relay congestion information – Hop-by-hop message forwarding– Other vehicles can choose alternate routes

Apr 21, 2023 20

Deceleration Warning• Prevent pile-ups when a vehicle

decelerates rapidly

21

Why Security?• Adding security as an afterthought is rarely pretty

• Utility and ubiquity of vehicular networks will make them likely targets for attack

• Attacks may have deadly consequences

Apr 21, 2023 22

Outline

• Introduction

• Applications

• Adversaries and Attacks

• Vehicular Network Challenges

• Properties Supporting Security

• Security Primitives

• Related Work & Conclusions

Apr 21, 2023 23

Adversaries

• Greedy drivers

Apr 21, 2023 24

Adversaries

• Greedy drivers• Snoops (watch secretly)

• Pranksters (practical Joking)

• Industrial Insiders (Corporate officers)• Malicious Attackers

Apr 21, 2023 25

Attacks

• Denial of Service (DoS)– Overwhelm computational or network capacity– Dangerous if users rely on the service

• Message Suppression Attacks– Drop congestion alerts

• Fabrication– Lie about congestion ahead or lie about identity

• Alteration Attacks– Replay transmissions to simulate congestion

Apr 21, 2023 26

Outline• Introduction• Applications• Adversaries and Attacks• Vehicular Network Challenges

– Authentication vs. Privacy– Availability– Mobility– Key Distribution– Low Tolerance for Errors– Bootstrap

• Properties Supporting Security• Security Primitives• Related Work & ConclusionsApr 21, 2023 27

Challenges: Authentication vs. Privacy

• Each vehicle should only have one identity– Prevents Sybil attacks (e.g., spoofed congestion)– Allows use of external mechanisms (e.g. law

enforcement)

• Drivers value their privacy– Legal requirements vary from country to country– Vehicles today are only partially anonymous– Lack of privacy may lead to lack of security

Apr 21, 2023 28

Challenges: Availability

• Applications will require real-time responses

• Increases vulnerability to DoS

• Unreliable communication medium– Studies show only 50-60% of vehicles in range

will receive a vehicle’s broadcast

Apr 21, 2023 29

Challenges: Mobility

• Mobility patterns will exhibit strong correlations• Transient neighborhood

– Many neighbors will only be encountered once, ever– Makes reputation-based systems difficult

• Brief periods of connectivity– Vehicles may only be in range for seconds– Limits interaction between sender and receiver

Apr 21, 2023 30

Challenges: Key Distribution

• Manufacturers– Requires cooperation and interoperability– Users must trust all manufacturers

• Government– MV License distribution– Handled at the state level, so also requires cooperation

and interoperability– Running a Certificate Authority is non-trivial (Seriously)

Apr 21, 2023 31

Challenges: Low Tolerance for Errors

• Strong need for resiliency– With 200 million cars in the US, if 5% use an

application that works 99.99999% of the time, still more likely to fail on some car

– Life-and-death applications must be resilient to occasional failures

• Focus on prevention, rather than detection & recovery– Safety-related applications may not have

margin for driver reaction time

Apr 21, 2023 32

Challenges: Bootstrap• Initially, only a small number of vehicles will have DSRC• Limited support deployment of infrastructure• Ad hoc network protocols allow manufacturers to incorporate

security without deviating from their business model

Apr 21, 2023 33

Security Primitives: Secure Message Origin

• Prevents attacks– Road-side attacker cannot spoof vehicles– Attacker cannot modify legitimate

messages to simulate congestion

• Beacon-based approach

Sig(Kbeacon, time, )

Apr 21, 2023 34

Security Primitives: Secure Message Origin• Alternately, use entanglement

– Each vehicle broadcasts:• Its ID• Ordered list of vehicles it has passed

– Establishes relative ordering– Add resiliency by evaluating consistency of reports

Apr 21, 2023 35

Security Primitives: Anonymization Service• Many applications only need to connect information to a

vehicle, not to a specific identity– Authenticate to anonymization service with permanent ID– Anonymization service issues temporary ID– Optionally include escrow for legal enforcement

• Ideal environment: toll roads– Controlled access points– All temporary IDs issued by the same authority

IDApr 21, 2023 36

Security Primitives: Anonymization Service

• To provide finer granularity, use reanonymizers– Anonymization service issues short-lived certificates– Reanonymizer will provide a fresh ID in response to a

valid certificate

ID

ID’Apr 21, 2023 37

Additional Security Primitives

• Secure Aggregation– Securely count vehicles to report congestion

• Key Establishment– Temporary session keys for platooning or automatic

cruise control

• Message Authentication and Freshness– Prevent alteration and replay attacks

Apr 21, 2023 38

Delay-Tolerant Networks (DTNs)

Apr 21, 2023 39

Today’s Internet

• Successful at interconnecting communication devices across the globe

• Based on TCP/IP protocol suite and wired links

• Connected in end-to-end, low-delay paths between sources and destinations

• Low error rates and relatively symmetric bidirectional data rates

Apr 21, 2023 40

Evolving Wireless Networks Outside the Internet

• Independent networks, each supporting specialized communication requirements and adapted to a particular homogeneous communication region

• Support long and variable delays, arbitrarily long periods of link disconnection, high error rates, and large bidirectional data-rate asymmetries

Apr 21, 2023 41

Evolving Wireless Networks Outside the Internet

• Examples– Terrestrial civilian networks connecting mobile

wireless devices– Wireless military battlefield networks connecting

troops, aircraft, satellites, and sensors– Outer-space networks, such as the

InterPlaNetary (IPN) Internet project• Require the intervention of an agent that can

translate between incompatible networks characteristics and act as a buffer for mismatched network delays

Apr 21, 2023 42

The Concept of a Delay-Tolerant Networks (DTN)

• A network of regional networks supporting interoperability among them

• An overlay on top of regional networks, including the Internet

• accommodate long delays between and within regional networks, and translate between regional network communication characteristics

Apr 21, 2023 43

Concept

Delay-Tolerant Network (DTN)– is an overlay on top of regional networks

• built on top of region-specific lower layers• messages are called bundles

44Apr 21, 2023

Concept

Delay-Tolerant Network (DTN)– is a network of regional networks

45Apr 21, 2023

Concept

Delay-Tolerant Network (DTN)– was originally designed to support the

InterPlanetary Internet (IPN)

46Apr 21, 2023

Internet vs. DTN

Internet– is mainly based on packet switching– nodes are continuously connected– IP protocol is used on the network layer– excessive network traffic in case of errors

47Apr 21, 2023

Internet vs. DTN

DTN– uses the store-and-forwarding method– messages might be sent to unavailable end

hosts– hop-to-hop retransmission in case of errors

48Apr 21, 2023

Internet vs. DTN

DTN– isn’t necessarily built on top of TCP/IP

49Apr 21, 2023

Internet vs. DTN

Communication on the Internet is mainly based on packet switching

DTNs use store-and-forward message switching– very similar to the way email systems work

50Apr 21, 2023

Features

• Intermittent connectivity– Opportunistic contacts– Scheduled contacts

• Non-conversational protocol

• Security

51Apr 21, 2023

Why a Delay-Tolerant Network (DTN)?

• The Internet’s underlying assumptions– Continuous, bidirectional end-to-end path– Short round-trips– Symmetric data rates– Low error rates

• The characteristics of evolving and potential networks– Intermittent connectivity– Long or variable delay– Asymmetric data rates– High error rates

• New architectural concept is needed!Apr 21, 2023 52

Store-And-Forward Message Switching

• The problems of DTNs can be overcome by store-and-forward massage switching

• DTN routers need persistent storage for their queues because– A communication link may not be available for a

long time– One node may send or receive data much faster

or more reliably than the other node– A message, once transmitted, may need to be

retransmitted for some reasons

Apr 21, 2023 53

The Bundle Layer

• A new protocol layer overlaid on top of heterogeneous region-specific lower layers, with which application programs can communicate across multiple regions

Apr 21, 2023 54

Bundles and Bundle Encapsulation

• Bundles (messages) consist of– A source-application’s user data– Control information, provided by the source

application for the destination application– A bundle header, inserted by the bundle layer

Apr 21, 2023 55

A Non-Conversational Protocol

• DTN bundle layers communicate between themselves using simple sessions with minimal or no round-trips

• Any acknowledgement from the receiving node is optional, depending on the class of service selected

Apr 21, 2023 56

DTN Nodes

• An entity with a bundle layer– Host – sends and/or receives bundles, but

does not forward them. Optionally supports custody transfers.

– Router – forwards bundles within a single DTN region. Optionally supports custody transfers.

– Gateway – forwards bundles between tow or more DTN regions. Must support custody transfers.

Apr 21, 2023 57

Delay Isolation via Transport-Layer Termination

• DTN routers and gateways terminate transport protocols at the bundle layer

Apr 21, 2023 58

Custody Transfers

• The bundle layer supports node-to-node retransmission by means of custody transfers

• If no ACK is returned before the sender’s time-to-ACK expires, the sender retransmits the bundle

• A bundle custodian must store a bundle until– Another node accepts custody, or– Expiration of the bundle’s time-to-live

• Do not guarantee end-to-end reliability

Apr 21, 2023 59

Moving Points of Retransmission Forward

• The bundle layer uses reliable transport-layer protocols together with custody transfers to move points of retransmission progressively forward toward the destination

Apr 21, 2023 60

Internet vs. DTN Routing

• The protocol stacks of all nodes include both bundle and transport layers

• DTN gateways can run different lower-layer protocols (below the bundle layer) on each side of their double stack, which allows gateways to span two regions that use different lower-layer protocols

Apr 21, 2023 61

Classes of Bundle Services

• Custody Transfer

• Return Receipt

• Custody-Transfer Notification

• Bundle-Forwarding Notification

• Priority of Delivery

• Authentication

Apr 21, 2023 62

• Thanks!

63Apr 21, 2023