Next: M-DHCP
Up: Multiparty Multimedia Session
Previous: IETF Conferencing Architecture
Mark Handley (ISI) presented some ideas on a multicast address allocation
architecture. This must be
- Robust
- Scalable, so we can allocate a significant portion of the address
space efficiently
- Available, even in the presence of failures
At present we overload SAP to do address allocation, which works okay, but
the API is messy. There is a new solution being proposed, which uses a
three layer allocation heirarchy:
- An application asks for an address using DHCP to an allocation server
- The allocation server speaks "AAP" (a varient of SAP) to discover
which addresses are avilable and to request and defend those
addresses.
- The address allocation server listens to advertisments from MBGP
routers which speak GUM and MASC to discover which address prefixes
are avilable and to allocate and defend addresses on a domain wide
scale.
The actual allocation is performed using a varient of the IPRMA algorithm.
Mark Handley provided a brief description of this algorithm, full details
of this are provided in his thesis, and will be documented more publically
in due course.
Because AAP works on a much slower timescale to SAP it's relatively immune
to packet loss. The problem of lost packets prevents scaling of SAP to very
large numbers of addresses allocated. The AAP allocates prefixes, from
which SAP allocates individual addresses.
This requires SAP and AAP to be separate, so that SAP announcements can be
global, whilst the equivalent AAP announcement is more local. This is a
major change to SAP. The current SAP draft is expected to be put forwards
as an experimental RFC, whilst this redesign takes place.
Colin PERKINS
Thu Aug 28 16:00:07 BST 1997