DISPERSITY ROUTING:PAST and PRESENT

2011-04-25Seungmin Kang

In This Paper Why dispersity routing was considered

How changes in networks have made disper-sity routing less usefule and more difficult to implement

Disperity routing is currently(2007) being pro-posed for MANET’s and delay tolerant net-works

Dispersity Routing The earliest use of dispersity routing was as

an alternative to adaptive routing To equalize the load on the network To reduce the queuing delays

Dispersity routing has been proposed as a means of increasing the available transmis-sion rate between a source and destination by obtaining the cut-set of the rates between a source and destination rather than the rate of a single link

Dispersity Routing Multi-path routing rule for ARPA-net(Advanced Research

Projects Agency Network)

Distributes the data between a source and destination over several paths through the network instead of concentrating it on a single path

There are two types of disperity routing Non-redundant dispersity routing Redundant dispersity routing

A source partitions the message into smaller, apporximately equal length, sub-messages and transmits the sub-messages on different paths to the destination

Non-redundant Dispersity Routing Non-redundant dispersity routing over 4 channels

Non-redundant Dispersity Routing Adaptive Routing

Equalizes the load on the network by re-routing messages through less congested regions of the network

Dispersity Routing Equalizes the load by spreading each message over more

of network

When the link utilization are equalized, dispersity routing results in smaller queuing delays than adap-tive routing Because the queues serve a larger number of smaller cus-

tomers

Redundant Dispersity Routing Redundant dispersity routing over 4 channels

Can use era-sure correction procedures to

determine missing sub-

messages

Redundant Dispersity Routing Divide a message into fewer sub-messages

than there are paths

Redundancy is more useful to deal with the unexpected If the traffic on a single path becomes extremely

high, the user can receive the message on the other paths and does not have to wait until the message on the most congested path is received

Changes in Physical Layer In the early 1970’s

Use microwave transmission DWDM (Dense Wavelength Division Multiplexing)

has increased the transmission rates that the fibers can carry

Programmable facilities switches have reduced the time needed to supply private lines to the users

Theses changes have reduced the need to the dispersity routing To increase the bandwidth available to users To disperse larger users over a network in order to

avoid blocking the other network users

Changes in Physical Layer In the early of 1990’s

Applications, such as transferring medical images, required higher rate access link to avoid unac-ceptable user delays

Increasing the access rate could result in a small number of users congesting the backbone links

Dispersity routing was considered for these applications To increase the transmission rate available to high

speed medical applications To eliminate the delay caused by transmission er-

rors in time critical applications

Changes in the Use of the Network Packet networks have changed from specialized

networks, serving a few hundred users, to ubiqui-tous networks, and serve hundreds of millions of users

The link transmission rates have increased The average message lengths have increased The link utilization have remained about the same The average number of users sharing a link has in-

creased The variance of the link utilization and the queuing de-

lays have become small Eliminate the need for dispersity routing

Wireless Networks - MANETS Redundant dispersity routing has been proposed to

survive path changes in MANET’s (Mobile Adhoc NET-work) A source set up multiple disjoint paths Redundant sub-message deliver the data after a path has

failed

Two problems Maintaining multiple disjoint paths

Maintaining multiple disjoint paths in MANET’s, using the current re-source discovery and routing mechanism, is unreasonable

The limited bandwidth in MANET’s Should use ARQ strategies, rather than forward erasure correction

Wireless Networks - MANETS Can use non-redundant dispersity routing and

partial retransmission to survive path failures

The advantage of non-redundant dispersity routing over single path transmissions Following a transmission error, we retransmit a

smaller fraction of the message Following a path failure, the source and destina-

tion continue to communicate, although at a re-duced rate

Wireless Networks – Robotic Routing Multi-path geographic routing on a field with

obstacles1. Trace an obsta-

cle

2. The infor-mation is re-tained in the

message

3. The informa-tion is returned to the source

4. The source uses the infor-mation to se-

lect forwarding location

Wireless Networks – Robotic Routing Robotic Routing

Determines a path around an obstacle when a node cannot locate a forwarding node that is closer to the destination

The routing procedure applies rules developed for robotics to packet forwarding E.g) robot to trace an obstacle by placing its right hand on the ob-

stacle (in wireless network, this rule is used to determine the next node on a path)

Robotic routing is used to both guarantee that a mes-sage finds a path when one exists and to plan subse-quent communication between the source and destina-tion

Wireless Networks – Robotic Routing Robotic Routing

Missed paths and routing loops in robotic routing

Missed path

Disal-lowed!

Wireless Network Robotic routing on a grid structure

Impossible for communications paths between

grid elements to jump over one

another

Rule :Above, be-low, right of left of our cur-rent grid

Intermittently Connected Networks Do not have reverse path and cannot imple-

ment ARQ techniques used in non-redundant dispersity routing

Require the forward erasure-correction capa-bilities in redundant dipersity routing

Redundant dispersity routing can be used to trade-off delay and resources

Conclusion Changes in networks have made dispersity rout-

ing less attractive in wired networks

MANET’s and intermittently connected networks have characteristics that originally made disper-sity routing attractive and justify applying disper-sity routing in the new environment