Heading:qjk40(635)
Pup Network Directory Update Protocoly756qjk40
Page Numbers: Yes  X: 527  Y: 10.5"qjk40
Copyright Xerox Corporation 1979z18697l3033y45c(1270)\g
Inter-Office Memorandumz18592l4445y762(635)\f5b
To	Distributed Computing	Date	August 8, 1976z18592l4445d2998e21(0,65535)(1,4445)(5,11684)(6,14146)\f1 2f0t2 1t0 21t6 1f1t0 4f0t7 1t0
From	David Boggs	Location	Palo Altoz18592l4445d2998y716e25\f1 4f0t2 1t0 11t6 1f1t0 8f0t7 1t0
Subject	Pup Network Directory	Organization	Parcz18592l4445d2998e25\f1 7f0t2 1t0 21t6 1f1t0 12f0t7 1t0
Update Protocolz18592l4445
XEROX       z18592l508y644e14(2116)\f2 5f0
Filed on: <Pup>NetDirUpdate.bravoe30
e10
This memo documents the protocol by which name lookup servers update their local copies of the network directory.z18697l3033e10j(1270)
Disclaimerz18697l3033e10j\b
This version of the protocol assumes that the network directory is maintained at galactic central, from which all servers get copies.  This scheme is cheap and easy to implement for small galaxies, but as civilization spreads:  (1) it will become cumbersome: to add or change a listing, one must interact with galactic central which may be many light-years away in space with a consequent many year delay in time before the listing propagates out to the periphery (besides, galactic central will be a huge bureaucracy, slow in responding to requests) (2) the directory will get very large: everyone in the whole galaxy will be listed in each copy of the directory, which will strain the capacity of small servers to store and search in reasonable time.  In short, it is centralized.z18697l3033e9j\764i17I
The eventual solution is, of course, to distribute the network directory.  A server's network directory should be a cache containing only those names most likely to be referenced.  If a request arrives for a name not in the cache, the request should be passed on to other name lookup servers.z18697l3033e9j\40i10I66i5I
The Protocolz18697l3492d3033e9\b
When a Pup of type NetDirVersion arrives at the miscellaneous services socket, the version number in the Pup should be compared with the version number of the local network directory, and one of the following actions taken:z18697l3033e9j\19f6 13f0
If the local directory version number is greater than the version number in the incoming Pup, a reply of type NetDirVersion should be generated with the local network directory version number as data.z18697l3527e9j\110f6 13f0
If the local directory version number is equal to the version number in the incoming Pup, do nothing.z18697l3527e9j
If the local directory version number is less than the version number in the incoming Pup, probe the inter-network to find the server with the latest version, (the version advertised in the incoming Pup is newer than your version, but it may not be the newest) then ask him to send it to you.  See below for a suggested implementation to probe for newer versions.z18697l3527e9j
When a Pup of type SendNetDir arrives at the miscellaneous services socket, open an EFTP Socket with the foreign port set to the port specified in the incoming Pup, and send the local network directory.z18697l3033e9j\19f6 10f0
Periodically (every 6 hours or so) probe the inter-network for newer versions of the network directory.z18697l3033e9j
Probing for newer versionsz18697l3033e9j\b
Open a level 1 Pup socket and broadcast a Pup of type NetDirVersion to miscellaneous services on all directly connected networks.  Remember the address of the host which responds with the highest version number.  If the highest version number is less than or equal to the version number of the local directory, give up.  If a newer version is located, start an EFTP receiver (do not use the default EFTP receive socket), and send a Pup of type SendNetDir with the EFTP socket as data to the host which responded with the highest version number.  If the EFTP receiver times out, the SendNetDir Pup should be retransmitted a few times before giving up.  If a file is successfully received, it should be installed as the new network directory.z18697l3033e9j\54f6 13f0 377f6 10f0 128f6 10f0
Packet types and formatse9\b
NetDirVersion:	Pup type #240z19402l3527d3033e9
Data:	2 bytes containing a 16 bit version number.z18697l5536d4288e9j
SendNetDir:	Pup type #241z19226l3527d3033e9
Data:	6 bytes containing a port to which the recipient should EFTP his copy of the network directory.z18697l5536d4288e9j