Enhanced Disruption Tolerant Bundle Delivery (EDIFY) System

Discussion

Challenges to communication in extreme environments

• Traditional internet service is based some assumptions, such as reliable end-to-end path from the source to the destination, unexcessive round trip time

• In extreme and performance-challenged environments continuous end-to-end connectivity cannot be assumed

• Unreliable connection (mobile environment)• Excessive latency (satellite communication)• Power exhaustion (e.g. sensor network)• New architecture and schemes are needed to handle the

disruption and disconnection in the network (DTN).

Insufficient work in existing DTN proposal

• Current DTN naming convention may be reasonable for stationary environment but may not be enough for disruption tolerant environment where nodes move

• Does not provide details about how neighbors discover one another

• No details on routing

• No details on bundle acceptance algorithm

• Lack of multicasting support

Our Project Goals

• New naming scheme that can cope with network mobility and network isolation

• Policy-based DTN routing to deliver bundles for different service classes

• QoS-based Bundle delivery algorithm • Adaptive Bundle Scheduling Scheme for different

environments• Point-to-multipoint Bundle delivery protocol for multicast

of bundle

Naming Convention 1. Network nodes are formed into groups based on their proximity or special

needs.2. Hierarchical name tuple (Group ID, personal ID) is used where the Group

ID is unique among the different groups while the personal ID is unique only within a group.

3. When a node drifts from its original group to a new group, a temporary ID is assigned. If a whole group moves to a new place, a temporary groupID may be assigned.

4. In addition, if a group gets split into 2 or 3 groups as a result of movement, a new temporary groupID will be used by each subgroups until they merge again.

5. Different naming systems can be supported e.g. network topology, network administration, physical location and more.

6. Each node has one canonical name, this is fixed as the node moves from system to system.

7. Each node can resolute from non-canonical names to the canonical name.

Routing• Group-based routing is used to imitate group movements in reality.• Group Initiation: neighbor discovery, gateway selection• Group Maintenance: How to handle the group merging, group splitting and node drifting under

mobile environments?• Intra-group Routing: How to find a route to a node within a group?• Inter-group Routing: How to forward route request from groups to groups through gateways to

establish a route from the source to the destination?• Three methods: custodian method, multipath delivery method, mobile carrier based delivery

method

Group Initiation

Neighbor discovery phase: 1. Each node sends hello message to neighborhood, the hello message

includes node tuple(GID, PID), node type(regular or gateway) and a list of

reachable groups if the sender is a gateway node.

2. Upon receiving a hello message, a node sends a response message to

the sender of the hello message.

3. A node gets its neighbor topology when sufficient responses are received

from neighbors.

4. Periodically each node exchanges hello messages with its neighbors in

this way to maintain the neighbor topology.

Group Initiation (cont’)

Gateway selection phase: 1. A node becomes a good candidate for being a gateway if it

receives more than K hello messages from different groups.

2. Each candidate node will transmit a message to nominate itself as a gateway after some random back off to avoid collisions.

3. Each candidate will suppress its own self-nomination message if it

hears other nodes’ message first unless it has better qualifications to be a gateway e.g. it can hear more external groups than the first nominating gateway candidate.

4. If more than one candidates nominate themselves as gateways

simultaneously, a contention takes place. The tier is broken using node ID, the node with lower ID will win the contention.

Group Maintenance (case study)

1. A new node appears in a group The new node broadcasts a gateway discovery message, any

gateway that receives such a discovery message should respond with a unicast reply. The new node can register itself with the nearest gateway and be assigned a visiting identifier.

2. A node leaves a group a) The leaving node will notify the gateway before it leaves the

group. b) Periodically gateways send keep-alive messages to and

receive replies from group members to probe the existing of the group members.

3. A gateway leaves or dies If group members find that a gateway disappears, gateway

selection takes place automatically within group.

Group Maintenance (case study)

4. A node drifts from one group to another group It is similar to case 1, and in this case the gateway of the new group can provide the information of the drifting node to the gateway of the old group.

5. One group is split into two groups A new temporary groupID will be used by each subgroups until they merge again. The information of the two new groups will be propagated to the whole network.

6. Group merging When two groups overlap, they can merge into one group to save resource and simplify the management.

In our future research work, we will explore each above case and provide details.

Routing policies

• In DTN network, each node can be configured with a set of routing policies to make the routing be more flexible and useful to different routing environments.

• Based on the routing type: e.g. unicast routing, multicast routing

• Based on the traffic type: e.g. expedite traffic, reliable traffic, regular traffic

• DTN service: e.g. custodian service or non-custodian service

• Generally the policies can be either individual policies or group wide policies.

Group Based Routing

Intra-group routing (bundle delivery within group)

Inter-group routing (bundle delivery between different groups)

Intra-group RoutingEach group runs its favorite intra-group routing

protocol depending on the characteristics of the

group. • sensor network tree-based routing protocol• mobile ad hoc network AOMDV• group with large number of members

hierarchical routing protocol • group with small number of members flat

routing protocol

Inter-group Routing If the source and the destination are in the different groups, how to

discover and establish a route between the source and the destination over multiple groups?

• The source node encapsulates (src_ID, dest_ID, routing policy) into a route request (RREQ).

• If the source node and the destination node in the same group, use intra-group routing protocol to discover route.

• Otherwise, the source node will send RREQ to gateways using the intra-group routing protocol.

• Because each gateway has the routing information to neighboring groups. Upon receiving RREQ, gateways relay RREQ to other gateways in neighboring groups.

• Once the route to destined group is found, a route reply (RREP) will be sent back to the source by the reverse path in bi-directional condition or a route discovery is initiate to find the back path to the source in uni-directional condition.

Three Methods for DTN Routing• DTN characteristic: Route is not available at any particular time. The continuous end-to-

end connection is not guaranteed. Sometimes the network is partitioned into some isolated parts.

Store-and-forward Method This method provides reliable delivery upon unpredictable route

disconnections. When route is not available, the bundle is cached in intermediate

nodes until the downlink route is available.Multi-path delivery Method This method make the routing resilient to link or node failure. It can

also provide load balance. When multiple paths are available, one fails or is congested, others

are available. Mobile Carrier Based Delivery Method This method provide bundle delivery in network isolation. When the network is partitioned into some isolated groups, a mobile

carrier moves between isolated groups and relays bundles from one group to another group.

Store-and-forward method: Custodian method

• The source node assigns one or more nearby nodes to be custodians, these nearby nodes in turn request nearby downlink nodes as custodians until the message arrives at its destination;

• A custodial signal is used to indicate whether the bundle is delivered from current custodian to the downlink custodian reliably;

• The current custodian keeps the copy of the bundle and sends it to the down-link custodian;

• If a custodian receives a bundle successfully from uplink custodian, it replies a “Succeeded” custodial signal to the uplink custodian; otherwise, it replies a “Failed” custodial signal to the uplink custodian;

• If the current custodian receives a “Succeeded” custodial signal from down-link custodian, it discards the bundle and releases the resource to the referred bundle;

• If the current custodian receives a “Failed” custodial signal from down-link custodian, it retransmits the bundle.

Custodian Method

DTN1 identifies DTN2 and DTN3 as custodians.

DTN1 can still request bundles to be delivered from both DTN2 and DTN3 when it is experiencing bad links with both DTN2 and DTN3.

We do not re-discovery and re-establish end-to-end path in this case. It saves resource and make the delivery more robust.

Mobile Carrier Based Delivery Method

Source: n1 Destination: n5

n1MCn5

Bundle Acceptance Algorithm Design

Problem: • Store-and-forward method is used in routing. Intermediate nodes have

limited Storage Capacity, can not cache all bundles• How bundles are accepted by intermediate nodes influence bundle delivery

time• Some bundles need to be stored in buffer for a long time, the utilization of

the storage is reduced as a result. • Some bundles can not be dropped once accepted (e.g. reliable-class

bundle).How to improve utilization of the buffer?How to serve more expedite traffic and provide more reliable service for

reliable traffic?

General Ideas: • Keep track of the total size of all the bundles for each service class• Avoid picking up too many bundles which need to be stored for a long time • Give expedite-class bundles higher priority over other two class bundles

Fair Bundle Scheduling (QoS)

• Different DTN scenarios may require different bundle scheduling, how to guarantee the fair service in different scenarios?

• Find different fairness criteria for different scenarios

Typical Scenarios: • Wireless ad-hoc environment• Mobile-carrier environment• Other environments in future research

• Each node uses 802.11 in MAC.• Four sessions: F0, F1, F3, F5.• F0 and F5 collides with each other. how to give fair-share of the wireless link• Rough approach: n7 will piggyback service tag for F5 in its transmission to

n5 so that n6 can overhear the service tag. Each node should include the service tag of contending flows in its ack to its sender. N6 will include F5’s service tage when it acknowledges bundles it recieves from n2 so that F01 and F5 knows each other and they can be given fair-share of the available wireless link bandwidth

Fair Bundle Scheduling for Ad-hoc Environment (cont’)

• Rough Approach:

1. The carrier transmits downlink sessions to each DTN node.

2. Each DTN node piggybacks its service tag which indicates the information of its service for uplink session in the acknowledgment.

3. Depending on acknowledgment, the mobile carrier makes a scheduling and transmits an uplink schedule to all nodes that need its uplink service.

Fair Bundle Scheduling for Mobile-carrier Environment (cont’)

Point-to-Multipoint bundle Delivery protocol(Multicast)

• Two approaches: implicit tree forwarding, explicit tree formation

• Implicit tree forwarding is used to deliver bundles to all nodes within a group. A overlay network is constructed within each group. Unicast is used to deliver the bundle to receivers.

• Explicit tree formation is used to send bundles to both all nodes and multiple receivers. Core-based tree or root-based tree are formed for multicasting.

Wrap Up

• Naming convention deal with mobility and partition

• Policy-Driven Routing Framework Design

• Bundle Acceptance Algorithmic Design

• Bundle Scheduling Scheme Design

• Point-to-Multipoint Delivery Protocol Design