DISPERSITY ROUTING: PAST and PRESENT Seungmin Kang

In This Paper  Why dispersity routing was considered  How changes in networks have made dispersity routing less usefule and more difficult to implement  Disperity routing is currently(2007) being proposed for MANET’s and delay tolerant networks

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 transmission 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 adaptive routing  Because the queues serve a larger number of smaller customers

Redundant Dispersity Routing  Redundant dispersity routing over 4 channels Can use erasure 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 unacceptable 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 errors in time critical applications

Changes in the Use of the Network  Packet networks have changed from specialized networks, serving a few hundred users, to ubiquitous 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 increased  The variance of the link utilization and the queuing delays 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 NETwork)  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 resource 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 destination continue to communicate, although at a reduced rate

Wireless Networks – Robotic Routing  Multi-path geographic routing on a field with obstacles 1. Trace an obstacle 2. The information is retained in the message 3. The information is returned to the source 4. The source uses the information to select 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 obstacle (in wireless network, this rule is used to determine the next node on a path)  Robotic routing is used to both guarantee that a message finds a path when one exists and to plan subsequent communication between the source and destination

Wireless Networks – Robotic Routing  Robotic Routing  Missed paths and routing loops in robotic routing Missed path Disallowed!

Wireless Network  Robotic routing on a grid structure Impossible for communications paths between grid elements to jump over one another Rule : Above, below, right of left of our current grid

Intermittently Connected Networks  Do not have reverse path and cannot implement ARQ techniques used in non-redundant dispersity routing  Require the forward erasure-correction capabilities in redundant dipersity routing  Redundant dispersity routing can be used to trade-off delay and resources

Conclusion  Changes in networks have made dispersity routing less attractive in wired networks  MANET’s and intermittently connected networks have characteristics that originally made dispersity routing attractive and justify applying dispersity routing in the new environment