brezak@apollo.uucp (John Brezak) (07/22/88)
Maybe someone has some ideas on this. If you have a transport layer (TP4) that can
work over different networks, how do you know which network to send something
over ?
( transport user )
|
+---------------------+
| Transport |
+---------------------+
| |
| |
+---------------+ +----------------+
| CLNS | | X.25 |
+---------------+ +----------------+
This seems like a valid profile. And is referenced in US GOSIP. I know that each
network would have a different NSAP. But how does the transport layer know which
network that the destination PDU has to go through ?
--
============================================================================================
John Brezak UUCP: {mit-eddie,yale,uw-beaver}!apollo!brezak
Apollo Computer Inc. ARPA: brezak@apollo.com
Chelmsford, MA Phone: (617) 256-6600sklower@sequoia.Berkeley.EDU.berkeley.edu (Keith Sklower) (07/28/88)
In article <3d63cf41.1223a@apollo.uucp> brezak@apollo.uucp (John Brezak) writes:
+ Maybe someone has some ideas on this. If you have a transport layer (TP4)
+ that can work over different networks, how do you know which network to
+ send something over ?
+
+ [Shows TP over CLNS and X.25]
+
+ I know that each network would have a different NSAP. But how does the
+ transport layer know which network that the destination PDU has to go
+ through?
+
+ John Brezak UUCP: {mit-eddie,yale,uw-beaver}!apollo!brezak
+ Apollo Computer Inc. ARPA: brezak@apollo.com
+ Chelmsford, MA Phone: (617) 256-6600
+
When 4.3BSD establishes a TCP connection, it attempts to establish a
route to the destination. Based on the NSAP, maybe TP should consult
the routing layer for guidance. Berkeley is already considering
extending the routing entries for useful protocol specific (read TCP)
parameters (like round trip times, congestion tolerance parameters).
So, if we can make connection oriented and packet switched interfaces
share some kind of common routing lookup based on address, we might be
able to place some TP-oriented parameters like prefered class (0 for
for an X.25 network layer?), or suggested packet size for connection
negotiation in TP.
Another alternative is to punt and provide some means of telling TP
a priori which way to go. In BSD, this might be done by means of a
setsockopt before doing a connect() call on an AF_ISO socket.
Keith Sklower UUCP: ucbvax!sklower
ARPA: sklower@okeeffe.Berkeley.EDU
zweig@csed-1.IDA.ORG (Jonathan Zweig) (07/29/88)
Not only might it be tricky for the transport layer to figure out which of the two networks the peer lies on, but what if it's possible to reach it via BOTH nets? Then it has to choose.... It seems like a very good question to me. Johnny Zweig