Multipoint Communications in a Beyond-3G Internetwork Elias C. Efstathiou & George C. Polyzos Mobile Multimedia Laboratory Department of Informatics Athens University of Economics and Business Athens 10434, Greece [email_address] http://mm.aueb.gr/ Tel.: +30 10 8203 650, Fax: +30 10 8203 686
Assumption : a multicast router exists in the visited subnet
MHs simply use IGMP and (re-)subscribe to any number of groups
Disadvantage 1 : delay, packet losses, tree rearrangement
Disadvantage 2 : “get-ahead” and “lag-behind” problems
(2) MIP-BT – “Bi-directional tunneled multicast”
Assumption 1 : the MH’s HA is a multicast router
IGMP requests are tunneled to the HA
The HA joins groups on MH’s behalf
Assumption 2 : MH must decapsulate the multicast packets sent to it through the tunnel - even if it uses an FA for M-IP decapsulation
Disadvantage 1 : potential packet duplication
Disadvantage 2 : potential tunnel convergence
Packet Duplication and Tunnel Convergence FA MH MH MH MH HA HA HA FA MH MH HA Both visiting MHs belong to the same home network and are members of the same multicast group but because of tunneling the FA has no way of knowing this Visiting MHs belong to different home networks but they are members of the same multicast group causing multiple HA-FA tunnels to carry the same datagrams
Multicast addresses do not appear different from unicast addresses
Simple mapping of IP identifiers to forwarder ports
C-IP has keep-alive mechanisms similar to IGMP
Adapt the C-IP “route-update” packet mechanism
MHs send these packets but instead of using their own IP address in the source field, they use the multicast group address instead
When, with C-IP forwarding, they reach the C-IP gateway, the gateway (M-IP FA) may then subscribe to a group, if it’s not receiving it already.
No need for IGMP. Reuse C-IP soft state mechanisms.
Multicast groups can be “virtual” C-IP hosts
C-IP forwarders should handle IP address-to-multiple ports mappings
C-IP gateway must be a multicast router
MHs use their IP stack in an “unconventional” way
Packet duplication only when paths towards receivers diverge!
Cellular IP and Mobile Multicast (cont’d) Global Multicast Routing Protocol 188.8.131.52 transmission source Foreign Agent and Cellular IP Gateway BS1 BS4 BS3 Mobile Host BS2 Mobile Host Mobile Host The 3 MHs subscribe to 184.108.40.206 by sending route_update with 220.127.116.11 as the source IP address. BSs update tables accordingly for virtual MH “18.104.22.168”: BS1 BS2 BS2 BS3 and BS4 BS3 and BS4 do link-local broadcast The FA/CIP-GW grafts to new multicast trees every time a route_update with a new group arrives. IGMP-like soft-state assured through C-IP mechanisms.