Transcript slides - Department of Computer Science and Electrical Engineering

IP Multicasting for Wireless
Nodes
George Xylomenos and George C.Polyzos
Computer Systems Laboratory
Dept. of Computer Science & Engineering
University of California, San Diego
Outline
•
•
•
Introduction
IP Mobility and Problems
IP Multicasting
–
–
•
Local Multicasting Mechanisms
Global Multicasting Mechanisms
Alternative Models and Conclusion
IP Mobility and Problems
CH
MR
HA
FA
MH
Figure 1:Mobile IP
IP Mobility and Problems (contd..)
• Two problems
– Suboptimal triangular routing
– Lack of de-registration at FA
IP Multicasting
• To deliver datagrams from an arbitrary
sender to a dynamic set of receivers
• Tasks
– Track group membership
– Route datagrams to group members
IP Multicasting (contd...)
• Local Multicasting Mechanisms
– Deals with group membership management and
local datagram delivery
• Global Multicasting Mechanisms
– For delivering multicast datagrams from their
senders to all interested local routers or group
managers
Local Multicasting Mechanisms(native)
•
•
•
•
Group Manager
Periodic query-reply messages
No need of explicit leave messages
Change needed for Point-to-Point(PtP) links
– Separately addressed unicast datagram for each
host
– Per host information
Local Multicasting for Mobile Hosts
• Limited bandwidth and battery power
• Wastage of power and bandwidth due to
periodic query-reply messages
• Changes proposed
– Explicit join and leave messages
– More accurate group membership information
• Either native or modified approach can be
used depending on ratio of group members
to total MH population
Global Multicasting Mechanisms
• Multicast routers communicate by setting up
tunnels among multicasting routers also called as
virtual links
• Proposed approaches
– DVMRP ( Distance Vector Multicast Routing Protocol)
• Based on Reverse Path Broadcasting
• Best paths to senders are discovered by a distance vector
algorithm
• Tracks routes to networks to save routing space
Global Multicasting Mechanisms (contd...)
• Proposed approaches (contd...)
– MOSPF( Multicast Open Shortest Path First)
• Based on OSPF which uses link state
• All routers know the complete topology
• On demand calculation of the shortest path tree from
sender to all receivers
• To reduce routing table size, may track routes to
networks
Global Multicasting Mechanisms(contd...)
• Proposed approaches (contd...)
– CBT ( Core Based Trees)
• Single tree rather than one tree per sourcedestination pair
• Router called Core is chosen in ad hoc way for each
group
• Reverse shortest path tree rooted at core is
calculated
• Routing is worse as all messages must first reach the
core
• Simpler routing and tree management
Multicasting from Mobile Hosts
•
•
Problems with DVMRP and MOSPF due
to the usage of source address for routing
Solutions
1. Disguise the multicasts as originating from
FN
2. Usage of complete MH addresses instead of
network prefix for routing
Multicasting from Mobile Hosts (contd...)
CH3
CH2
CH3
MR
HA
FA
MH
Figure 2
Multicasting Reception on Mobile Hosts
Home Agent Routing
CH
MR
HA2
HA1
FA
MH1
MH2
Figure 3: Home
Agent Routing
MH3
Home Agent Routing (contd...)
• Advantages
– Interoperability
– Changes to be done to MH and HA rather than
every FA the MH visits
• Disadvantages
– Sub optimal triangular routing
– Tunnel convergence problem
Foreign Agent Routing
CH
MR
HA2
HA1
FA
MH1
MH2
Figure 4: Foreign
Agent Routing
MH3
Foreign Agent Routing (contd...)
• Advantages
– Resemblance to IP multicasting model
– Purely local optimization can be done
– Avoids Tunnel convergence problem
• Disadvantages
– Wireless network provider may not provide
multicast service to visiting MHs due to
bandwidth overhead
Combined Routing
CH
MR
HA2
HA1
FA
MH1
MH2
Figure 5:
combined routing
MH3
Combined Routing (contd...)
CH
MR
HA2
HA1
FA
MH1
MH2
Figure 6:
combined routing
Combined Routing (contd...)
• Advantages
– Local multicast optimizations can be done at FA
without disturbing global mechanisms
• Disadvantages
– Suboptimal triangular routing
– Overhead associated with setting up and tearing
down of tunnels
Comparison of Approaches
Home Agent
Routing
Foreign agent
Routing
Combined Routing
Minor
Minor
Major
Modified Entities
HA, MH
FA
HA, FA, MH
Protocol Overhead
Yes
No
Yes
Delivery Overhead
Yes
No
No
Multicast Routing
Suboptimal
Optimal
Suboptimal
Local Operation
Suboptimal
Optimal
Optimal
Locality Model
Home Network
Foreign Network
Both Networks
Modification Scale
Table 1: comparison of multicast
reception approaches
Alternate Models and Conclusion
• Other models like Columbia Mobile IP can
be considered for modifications
• Possible to ensure interoperability with
unmodified hosts, without sacrificing
efficiency