is on the order of 10 octets, hardly a staggering amount!
Appendix C:
Determination of Network Called Address
As described in Section 10, when the P-CONNECT.REQUEST primitive is
issued the presentation provider must determine which of the network
addresses present in the called presentation address parameter to use
for the presentation connection. The first step in this
determination is to examine the quality of service parameter and
consider only those network addresses which support the corresponding
transport service. In practice, it is likely that each network
address will support exactly the same transport services, so using
quality of service as a discriminant will either permit all or none
or the network addresses present to be selected. This appendix
describes a local policy which might be employed when deciding which
network address to use.
The policy distinguishes between "underlying failures" and
"connection establishment failures". An "underlying failure" occurs
when, using the desired transport service, the initiating
presentation provider is unable to contact the responding
presentation provider. For the tcp-based service, this means that a
TCP connection could not be established for some reason. For the
udp-based service, it means that a response was not received before
final time-out. In contrast, a "connection establishment failure"
occurs when the responding presentation provider can be contacted,
but the presentation connection is rejected by either the
presentation provider or the correspondent presentation user.
The policy is simple: starting with the first network address
present, attempt the connection procedure. If the procedure fails
due to an "underlying failure", then the next network address in the
list is tried. This process is repeated until either an underlying
connection is established or all network addresses are exhausted.
If, however, a "connection establishment failure" occurs, then the
presentation provider immediately indicates this failure to the
presentation user and no further network addresses are considered.
Note that this is only one conformant policy of many. For example,
the presentation provider may wish to order network addresses based
on the "intensity" associated with the members present in the set of
transport services for each network address.
Author's Address:
Marshall Rose
The Wollongong Group
1129 San Antonio Road
Palo Alto, CA 94303
Phone: (415) 962-7100
EMail: mrose@TWG.COM