You would need to define Pool B's Mediation Pool FQDN (e.g. the Los Angeles Pool) as
an additional "Backup" Peer in the SBC for Pool A (Boston).
(ie. You will define Pool B's Med Pool FQDN in the Lync SG
"Fed IP/FQDN" section, and also as another "Host" in the
SIP Server Table used in that Lync SG. Define this additional
"Backup" Host in the SST as "Priority" 2, and enable
"Priority" Load Balancing under the SST definition in the Lync SG.)
Same in reverse...have Pool A's Med Pool FQDN as an additional
Backup Peer defined in Pool B's SBC Lync SG & SST.
By using the "Priority" mechanism on the Lync SG, you
will always send into Lync on this SBC, via the preferred Primary Mediation Pool, as
long as at least one server in this Mediation Pool is replying to SIP Option. If all
fail SIP Options, then the SBC will know this site is down, and will begin to
send calls in to Lync via the Backup sites' Mediation Pool servers.
It will then Failback to the preferred Primary pool's servers,
when they begin to respond to SIP Options again, so this is automatic.