Operation of TRIP

A TRIP Speaker(LS) establishes intra-domain and inter-domain “peering sessions” with
other TRIP Speakers to exchange routing information. The peering sessions are established
to exchange routes to telephony destinations. The peers update each other of new
routes learned by them. Each peer may in-turn learn about new routes from other peers
or through gateways registering telephony prefixes to them or through a static configuration
on the Location Servers. The peers also “withdraw” the routes they advertised to
the other peer on learning about the unavailability of the routes.TRIP peering sessions
use TCP for transport.

Apart from conveying the telephony destinations (prefixes) that a Location Server can
reach, a routing update also carries some more information about that route, called the
“attributes” associated with the route like capacity, cost, etc. These attributes are helpful
in describing characteristics of the route as well as in correct operation of the protocol.
They also help in enforcing policies and network design.

TRIP qualifies inter-domain sessions as running E-TRIP sessions ( External TRIP ) and
intra-domain sessions as I-TRIP (internal TRIP ).Figure 1 shows two ITADs. ITAD 1
has two Location Servers. Gateways G1 and G2 register with LS2 and Gateways G3 and
G4 register with LS1. LS1 and LS2 have I-TRIP peering. LS1 peers with LS3 in ITAD2
(E-TRIP peering).

Figure 1 TRIP operation

Internal TRIP uses a link state mechanism to flood database updates over an arbitrary
topology same as open shortest path first. An attempt is made to synchronize routing
information among TRIP LSs within an ITAD to maintain a single unified view. To
achieve internal synchronization, internal peer connections are configured between LSs
of the same ITAD such that the resulting intra-domain Location Server topology is connected
and sufficiently redundant. When an update is received from an internal peer,
the routes in the update are checked to determine if they are newer than the version already
in the database. Newer routes are then flooded to all other peers in the same ITAD.

While updates within an ITAD are flooded onto internal peers, external TRIP updates
are point-to-point like Border Gateway Protocol. TRIP updates received by an ITAD
X from ITAD Y can be passed on to ITAD Z with or without any modifications ( with
X and Z not sharing any peering relation ). Thus a route ”advertisement” might reach a
peer after hopping through various TRIP Speakers in different ITADs.

Thus TRIP can be used for inter-domain as well as intra-domain routing. It is also
possible to use TRIP on a gateway as a registration protocol. When used in this way,
the TRIP Protocol shall run on the gateway in a “send-only” mode, only sending routing
information ( prefixes supported by the gateway ) to it’s peer ( a Location Server ).

TRIP – Telephony Routing over IP protocol


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