data centric, position-based routing in space networks siva kumar tanguturi & sanjaya gajurel...

Data Centric, Position-Based Routing In Space Networks

Siva Kumar Tanguturi &

Sanjaya Gajurel

{skt8, sxg125}@eecs.case.edu

4/6/2005 EECS 600 Advanced Network Topics

Siva kumar Tanguturi & Sanjaya Gajurel

Agenda Introduction to Space Networks Background Architecture Implementation Simulation Experiments Conclusions Discussion


This is Space

Source: Kul Bhasin, Jeff Hayden., Developing Architectures and Technologies for an Evolvable NASA Space Communication Infrastructure , 22nd AIAA International Communications Satellite Systems Conference, May 2004


Space NetworksBackbone or Inter-Planetary or Deep Space

Network Earth-Mars Network Earth-Orbital Network Earth-Lagrangian-Relay-Orbital (Multi-

Hop) Network Orbital Network Access Network Inter-spacecraft & Intra-spacecraft

Network Inter-Orbital

Proximity Network or Surface Network Sensor Networks Inter-Surface Elements Networks

(robots, access points, rovers, landers, balloons etc. communicating each other)

Human-Robot Networks


Communication Problems in SpaceDeep Space

Very High and Variable Propagation Delay

High Link Error Rates or Error-Prone Links

Blackouts or Intermittent Connectivity Bandwidth Asymmetry Very Low Bandwidth/ Limited Link

Capacity High Power Requirement Security

Source: http://www.jpl.nasa.gov/history/hires/1997/VLBI.jpg


Communication Problems in Space Orbital Latency (Intermittent

connection) Gravitational Fluctuations The Sun’s interference Doppler’s effect in Satellite

Radio Signal Orbital Debris Distributed Computation

Source: Kul Bhasin, Jeff Hayden., Space Internet Architectures and Technologies for NASA Enterprises. http://mrr.nrl.navy.mil/applications.html


Communication Problems in SpaceSurface Noise & Power issue Highly mobile Weight, Cost, & Power Harsh Environment No infrastructure (Ad

Hoc topology)

Source:http://scp.grc.nasa.gov/images/portfolio/pn/pn%20main.jpg


Problems with existing TCP/IP protocol suite

The current approaches cannot support the dynamic nature of the space networks.

They work well only if the nodes and links are fixed and well-known ahead of time.

They are not intelligent to discover the links as they become available and use them for routing.


Effect of Space Environment on TCP

Effect of Error Prone Links:

TCP is designed to handle packet loss by identifying and retransmitting lost segments assuming the source of all packet loss is network congestion

Effect of Asymmetric Channels:

TCP rely on feedback in the form of cumulative acknowledgements from the receiver to ensure reliability. In addition, TCP is ack-clocked, relying on the timely arrival of acknowledgements, to make steady progress and fully utilize the available bandwidth of the path.


Effect of Space Environment of TCP Effect of Limited Link Capacity :

The packet overhead, at least 20 bytes of TCP header per packet, can consume a sizable share of a limited bandwidth channel.

Intermittent Connectivity :

Even short-term link outages pose a problem for TCP ranging from poor throughput in best case to an aborted connections in the worst case.

Extremely long and variable Propagation Delays :

For the very long propagation delay in minutes, TCP has to set its retransmission timer very long to wait for the acknowledgement. This long delay is not acceptable. Moreover, because of the changing network topology, TCP can’t estimates the optimal timeout.


Effects of Space Environment on Network Layer Naming And Addressing:

If the application on a remote planet wished to resolve an earth-based address, the long round-trip delay to query the DNS is significant in terms of available communication time.

With the use of secondary DNS on the surface, addresses updates have to be sent frequently to the secondary DNS that can consume a large portion of the limited bandwidth of the space.


Effects of Space Environment on Routing Both MANET routing protocols and BGP/OSPF do not have

mechanism to use periodicity of the links to compute paths.

They use only the active links to compute a path

They cannot adopt to network dynamics without requiring a manual intervention.

Though they are known to be highly stable and scalable, they can not be directly used in the context of space networks.


Approaches

Data-Centric approach can be used to enable energy efficient and low latency operation in proximity networks.

Position Based Routing approach can be efficiently used in the space orbital and backbone networks having predictable trajectories.


Data-Centric & Position-Based Routing Approach

In Data Centric approach a message specifies its content in terms of attributes: location, temperature and so on and there will be a in-networking processing of data.

The Positional Link-trajectory State (PLS) Protocol that is used can get the link trajectories along with their metrics such as latency, data rate, error characteristics from STK (Satellite Tool Kit) to provide the future routing information. Each node calculates the shortest path and this information is disseminated throughout the space network.


ASCoTASCoT – Autonomous Space Communication Technology

Is a routing and scheduling substrate for flexible tasking and coordination among space assets.

Scalable Able to deal with message propagation latencies. Support connectivity changes Support Heterogeneous and asymmetric link

bandwidths


AssumptionASCoT expects the underlying system to provide a variety of information and services to the ASCoT middleware.

This includes: Navigation information

characteristics of the links available and nodes on the other end, including position (current and expected), bandwidth, reliability, latency, etc.

Current position of the node Local status

power, health, load of transmission queues,etc.


Data-Centric Approach Naming the data allows the system to eliminate different

levels of binding Naming the data allows in-network processing of data.


Data-Centric ApproachExampleQuery for the average temperature of the shadowed parts in Gusev crater, Query can be flooded in the proximity network only the nodes that meet the query criteria (in Gusev crater and in shadowed

parts) will respond to the query thereby avoiding multiple steps of binding and spending energy transmitting data from nodes that are not in the shadowed parts of the crater.

Intermediate nodes also have the context to transform the data in several interesting Ways to aggregate different data items that perhaps have redundant information (e.g.

temperature data from nearby sensors) reduce information in response to resource constraints (e.g. downsample an

image because the image size exceeds available network capacity).


Data-Centric Approach

Used in Proximity Networks Energy Efficient Reduce the latency of communications


Positioning Link-trajectory State (PLS) PLS is modified to the context of space networks.

Each node independently computes shortest path tree using modified Dijkstra’s Algorithm, getting metrics like latency, data rate, and bit error rate (Satellite Tool Kit,STK).

Unlike traditional Link-State Routing (LSR), the information disseminated throughout the network is the trajectory of nodes in space, and the availability of the link end-points now or in the future.


PLS The PLS is only run in mobile space assets like satellites,

moving base stations.

PLS routing exchange information like {u,p(u),v,t,metrics(u->v)} which are flooded throughout the network.?

Tradeoffs between frequency of information exchange and network resources (energy) as well as updates accumulation.

Intelligent scheduling can be employed by which better links are waited for QoS.


Key Components of ASCoT Link Information Dissemination

Takes advantage of the space assets relative predictability by distributing information about link availability throughout the network ahead of time.

Path Computation predicted link connectivity and time-varying graphs are taken into

account for path computation. intelligent scheduling to meet the application’s QoS requirement

Message Forwarding once routing table is populated for a given metric, lookup the best

next hop towards the destination and buffer the packet until the link becomes available.


Message Switching The base station acts as a message gateway. It decodes the data-centric name for the target, encodes it as

an attribute (say temperature) along with other constraints for the query.

Diffusion Semantics is used to harvest data as follows: A node translates the query into a interest message, floods the

network & sets up gradients (navigator) in the network. Nodes (sources) reply the query as attribute-value tuple and inject it

into the network. Gradients now guide the data to the base station by matching

attributes in the data message to that of the gradients established by the interest messages.


Implementation Structure Web-Based Query

Interface Implemented in OPNET Data taken from STK

Implementation in OPNET


Implementation Structure ascot_app ascot_nav ascot_router position_manager Antenna modules


Demonstrated ASCoT Features

Its ability to deal with heterogeneous hardware. The Earth and Mars relay satellites, as well as the Mars base station, may utilize completely different transmission hardware. As long as they have a form of the IP stack and ASCoT running on top, the communication occurs seamlessly.

The reliability of the protocol in the face of dynamic network topology, short link duration and long link latencies. As relay stations become occluded or occupied with tasks of higher priority (or orientation requirements force them to cut the current link), ASCoT automatically selects a different path that uses orbiters that become available.



PLS routing exploits future link information to predictively route on paths that become available just as the message travels along, and buffers messages as it waits for the links to come up if necessary.

Automatic and efficient path discovery and link information distribution that allows PLS path computation to occur. Several parameters allow this behavior to be tuned to the current network state.



Source: http://scp.grc.nasa.gov/images/portfolio/an/an_3.jpg


Simulation Components PI : Specifies the source and the constraints of the data using

a web interface. DSN (Deep Space Network): The Madrid DSN node

participated in PLS. Earth Orbiters: Six Middle Earth Orbit (MEO) satellites Mars Orbiters: Three satellites in Aerosynchronous and five

satellites in moderately inclined lower Mars orbit. Mars Base Station: communication with rovers happen

thorough base station Surface Rovers: “Spirit” and “Opportunity” can

communicate with base station.


Simulation and Experiments (1)


Conclusions ASCoT is a new data-centric and position-based routing

architecture for future space science mission. The space missions involve large number of satellites and other nodes and the current static routing (manual ) is no more scalable.

Data-centric approach avoids the traditional address-centric energy consuming approach to make up for the energy deprived space nodes.

Planning to add design scheduling and resource allocation strategies.

Even with the limited knowledge about the future available links, ASCoT can discover paths that can be used to forward message successfully and efficiently.


Critiques This paper tries to solve the communication difficulties in

space network by emphasizing the data-centric and position-based routing approach.

The data to be communicated between the earth and the Mars is only the telemetry type. Also didn’t address the issues of real time and bulk load (picture, video) data transfers.

Direct communication facilities among the surface elements required for the space mission has not been mentioned.

Using PLS, the router is queuing packet when the satellites get occluded but didn’t mention how long. That can be hours and special store and forward router (used in DTN) may be required.


Question Session Feel free to ask the doubts and questions. We

will try to answer them Your comments are really appreciated

Thank You

data centric, position-based routing in space networks siva kumar tanguturi & sanjaya gajurel...

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