dispersity routing: past and present 2011-04-25 seungmin kang
TRANSCRIPT
DISPERSITY ROUTING:PAST and PRESENT
2011-04-25
Seungmin 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 mes-sages 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 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 ubiq-uitous 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
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 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 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 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 desti-nation
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