1. Scope
1.1. Design Goals
The VPIM directory Schema (VPIMDIR) is accessed from outside the
enterprise or service provider domain using the recipient's telephone
number.
Once the identity of the VPIM directory server is known, the email
address, capabilities, and spoken name confirmation information can
be retrieved. This query is expected to use LDAP [LDAP], a
connection-oriented protocol. The protocol transaction includes
multiple packet round-trips to execute the query and retrieval and is
considered to be the highest latency element of the messaging
service. Further, retrieval of the confirmation information may
require the return of a spoken name segment of up to 20kbytes (5
seconds at 4kbytes/second). Over a sufficiently engineered Internet
connection, a 1250 ms response time is believed to be achievable over
the Internet at large.
A service provider's namespace is expected to include entries for
tens of millions of subscribers in a flat namespace based on the VPIM
inter-domain address form: telephone_number@domain_name. A large
corporation may have a hundred-thousand entries, while a large
service provider may have tens of millions of entries in a single
domain. It is expected that there will be a single public address
validation service for a given service provider's network. It is
believed that existing directory technology, including horizontal
scalability through replication, will provide sufficient transaction
throughput within the required latency requirements to address this
need. The only fundamental, new requirement this application imposes
on directory servers, beyond similar existing services, is the
ability to return the recipient's spoken name. Preliminary
investigation suggests that storage and retrieval of a spoken name
will not add appreciable latency; however, it will add to the need
for storage capacity.
DNS provides well-documented redundancy and load-balancing
capabilities for the VPIMDIR. However, the latency requirements to
the end-user may not permit client-side fail-over to a secondary
server and may require the directory server to be implemented as a
high-availability service.
