Paper Group: 12

Data Transport in Challenged Networks

Above papers are original works of respective authors, referenced here for academic purposes only

Papers Discussed:

- Delay-Tolerant Network Architecture for Challenged Internets (ACM SIGCOMM 2003)- Interplanetary Internet: Communications infrastructure for Mars exploration (53rd International Astronautical Congress)

Chetan HiremathCSE525 – Advanced Networking, Winter 2004

Oregon Graduate Institute

Paper Group Objectives

• Issues with communication nodes deployed in mobile and extreme environments

• Propose Delay Tolerant Network Architecture (DTN), that– Allow interoperability between “challenged” networks

and Internet– Provide key services such as in-network data storage,

retransmission interoperable naming, authentication and COS

• Interplanetary Internet: An example of DTN

“Challenged Networks”

• Terrestrial Mobile Networks– Networks become unexpectedly ‘partitioned’

• Exotic Media Networks– High latencies with predictable interruptions

• Military Ad-Hoc Networks– Strong authentication and Class of Service

required

• Sensor/Actuator Networks– Have limited CPU, memory and power

resources

Characteristics of Challenged Internets

• Path and Link Characteristics– High latency, low data rate– Disconnection– Long queuing times

• Network Architectures– Interoperability considerations– Security

• End System Characteristics– Limited longevity– Low duty cycle operation– Limited resources

Tailor Internet Protocols for Challenged Networks ?

• Performance Enhancement Proxies– Violates fate sharing principle; connection state

should be maintained by end stations only– Suggested for performance improvement applications

only• Protocol Boosters

– Limits performance scalability under failure conditions• Proxies

– Too specific; not scalable• Electronic Mail

– Lack of dynamic routing • Preset mail relays, acknowledgement, etc

Delay Tolerant Message based Overlay Architecture

Region A (Internet) Region A (Internet)

Region B Region B

Region D Region D

Region C (Intranet)

Region C (Intranet)

{A, user}

{A, R1}

{A, R2}

{B, R3}

{B, R4}

{C, R5}

{D, R5}

{B, R2}

{C, R4}

{D, Space}

Delay Tolerant Network Features

• Regions and Gateways• Name Tuples• Postal Class of Service• Path Selection and Scheduling• Custody Transfer and Reliability• Time Synchronization• Security• Congestion and Flow Control• Convergence Layers and Retransmission

Structure of DTN Gateway

Scheduling and Message ForwardingScheduling and Message ForwardingRPC

ServerRPC

ServerDTN Library + RPCDTN Library + RPC

DTN App

Internet Convergence Layer

Internet Convergence Layer

Sensor NetConvergence Layer

Sensor NetConvergence Layer

Other Convergence Layer

Other Convergence Layer

Database Manager

Database Manager

TCP UDP SCTP

IP

802.11802.3 Other

FileStore

Sockets Sensor Net API

Sensor Network

Stack(TBD)

Other Transport

OrRaw

Protocols(TBD)

FileStore

DTN (Bundle) Gateway

Serial Port

Interplanetary Internet Concept

• Use Internet and related protocols to form low delay, low noise local internets on Earth and other planets

• Specialized deep space backbone network of long-haul wireless links; interconnecting local internets– Characterized by intermittent connectivity, huge

propagation delay and noisy data channels

• This “network of internets” employs a overlay concept called “bundling” to tie together this set of heterogeneous internets

Bundling

• Operates in “store and forward” mode– Messages are held at routers until forward path is

established

• Avoids need for sender to store data until an ACK is received– Operate in custodial mode– Messages can be differentiated for priority based

message transfers

• Store and forward model increases per hop error control for high error rate links– Good for deep space wireless backbones

Categories of Interoperability

• Data Handling Interfaces– Space vehicle communicates to orbiter via space link

• Long haul data links– Connect spacecraft with its ground system

• End-to-end data paths– Data flow between ground and space

• Mission management services• Describe, sharing and archiving scientific

information

Current Space Protocol Stack

Space Wireless Frequency and Modulation

Space Channel Coding

Space Link

Space Networking

Space End-to-End Security

Space End-to-End Reliability

Space File Transfer

Space Applications• Defined by CCSDS –

Consultative Committee for Space Data Systems

• Network layer allows abbreviated form of IP, as part of Space Communication Protocol Standards (SCPS)

• IPSec can be employed for end-to-end security

• SCPS extensions and TCP provide end-to-end reliability

• FTP, SCPS extensions and CFDP provide file transfer mechanisms

Mars Communication Protocol Stack

CCSDS File Delivery Protocol (CFDP)CCSDS File Delivery Protocol (CFDP)

TCP, UDPTCP, UDP CCSDS TCP TranquilityCCSDS TCP Tranquility

IPSECIPSEC CCSDS End-to-End SecurityCCSDS End-to-End Security

CCSDS Path, Network or IPCCSDS Path, Network or IPIPIP

Local Terrestrial

Link

Local Terrestrial

Link

CCSDS Long Haul Link and CodingCCSDS Long Haul Link and Coding

CCSDS proximity link and codingCCSDS proximity link and coding

CCSDS Link SecurityCCSDS Link Security

CCSDS S, X or Ka bandCCSDS S, X or Ka bandLocal WiredLocal Wired CCSDS UHFCCSDS UHF UHFWireless

UHFWireless

CCSDSLong Haul Link

CCSDSProximity Link

SONET E’net

Convergence Layer

Current “bundling” architecture

Bundle API

End-to-End ApplicationsBundle FTP, CDFP, Bundle NTP, etc

Routing

Custod

yT

ransfer

End

-to-end

Reliability

Authen

tication

Encryption

Other

Services

Licklider Transmission Protocol (LTP)

TCP

IP

UDP

• Support for real end-to-end applications, not only file transfer

• Modular architecture allows ease of evolution for individual layers

• Increased flexible custodial transfer capability than CFDP

Advantages of DTN

• Design embraces notion of message switching, in-network storage and retransmissions for challenged networks

• Leverages trends of content based naming, administrative regions from Internet

• Prototype DTN implementation provides validation of architecture and proof of concept.

Concerns / Disadvantages of DTN

• Proposes change to basic service model and system interfaces– Existing applications may not interoperate– Increases barrier to acceptance

• Diverging set of choices, relative to widely used Internet– Messages versus packets– Hop-to-hop reliability and security, as

opposed to end-to-end

Avenues for future work

• Definition of standards based stack for sensor networks allow interoperability

• Study application behavior transitioning from typical network to DTN based model

Questions ?