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+
+Network Working Group Bill Duvall
+Request for Comments: 2 SRI
+
+
+ [unknown title]
+
+
+[page 1 missing]
+
+1 LINKS
+
+ 1a Control Links
+
+ 1a1 Logical link 0 will be a control link between any two HOSTs on
+ the network
+
+ 1a1a Only one control link may exist between any two HOSTs on
+ the network. Thus, if there are n HOSTs on the network, there
+ are n-1 control links from each HOST.
+
+ 1a2 It will be primarily used for communication between HOSTs for
+ the purposes of:
+
+ 1a2a Establishing user links
+
+ 1a2b Breaking user links
+
+ 1a2c Passing interrupts regarding the status of links and/or
+ programs using the links
+
+ 1a2d Monitor communication
+
+ 1a3 Imps in the network may automatically trace all messages sent
+ on link 0.
+
+ 1b Primary Links
+
+ 1b1 A user at a given HOST may have exactly 1 primary link to each
+ of the other HOSTs on the network.
+
+ 1b1a The primary link must be the first link established
+ between a HOST user and another HOST.
+
+ 1b1b Primary links are global to a user, i.e. a user program
+ may open a primary link, and that link remains open until it is
+ specifically closed.
+
+
+
+
+
+Duvall [Page 1]
+
+RFC 2
+
+
+ 1b1c The primary link is treated like a teletype connected over
+ a normal data-phone or direct line by the remote HOST, i.e. the
+ remote HOST considers a primary link to be a normal teletype
+ user.
+
+ 1b1d The primary link is used for passing (user) control
+ information to the remote HOST, e.g. it will be used for
+ logging in to the remote host (using the remote hosts standard
+ login procedure).
+
+ 1c Auxilliary Links
+
+ 1c1 A user program may establish any number of auxilliary links
+ between itself and a user program in a connected HOST.
+
+ 1c1a These links may be used for either binary or character
+ transmission.
+
+ 1c1b Auxilliary links are local to the sub-system which
+ establishes them, and therefore are closed when that subsystem
+ is left.
+
+2 MANIPULATION OF LINKS
+
+ 2a Control links
+
+ 2a1 The control link is established at system load time.
+
+ 2a2 The status of a control link may be active or inactive
+
+ 2a2a The status of the control link should reflect the
+ relationship between the HOSTs.
+
+ 2b Primary Links
+
+ 2b1 Primary links are established by a user or executive call to
+ the monitor
+
+ 2b1a The network identification number of the HOST to be linked
+ to must be included in the call
+
+ 2b1b An attempt to establish more than one primary link to a
+ particular HOST will be regarded as an error, and the request
+ will be defaulted
+
+ 2b1c Standard Transmission Character Set
+
+
+
+
+
+Duvall [Page 2]
+
+RFC 2
+
+
+ 2b1c1 There will be a standard character set for
+ transmission of data over the primary links and control
+ links.
+
+ 2b1c1a This will be full (8 bit) ASCII.
+
+ 2b1d (get link) The protocol for establishing a link to HOST B
+ from HOST A is as follows
+
+ 2b1d1 A selects a currently unused link to HOST B from its
+ allocation tables
+
+ 2b1d2 A transmits a link-connect message to B over link 0.
+
+ 2b1d3 A then waits for:
+
+ 2b1d3a A communication regarding that link from B
+
+ 2b1d3b A certain amount of time to elaspse
+
+ 2b1d4 If a communication regarding the link is received from
+ B, it is examined to see if it is:
+
+ 2b1d4a A verification of the link from B.
+
+ 2b1d4a1 This results in a successful return from the
+ monitor to the requestor. The link number is returned
+ to the requestor, and the link is established.
+
+ 2b1d4b A request from B to establish the link. This
+ means: that B is trying to establish the same link as A
+ independently of A.
+
+ 2b1d4b1 If the network ID number of A(Na) is greater
+ than that of B(Nb), then A ignores the request, and
+ continues to await confirmation of the link from B.
+
+ 2b1d4b2 If, on the other hand, Na<Nb, A:
+
+ 2b1d4b2a Honors the request from B to establish the
+ link,
+
+ 2b1d4b2b Sends verification as required,
+
+ 2b1d4b2c Aborts its own request, and repeats the
+ allocation process.
+
+
+
+
+
+Duvall [Page 3]
+
+RFC 2
+
+
+ 2b1d4c Some other communication from B regarding the
+ link.
+
+ 2b1d4c1 This is an error condition, meaning that
+ either:
+
+ 2b1d4c1a A has faulted by selecting a previously
+ allocated link for allocation,
+
+ 2b1d4c1b B is transmitting information over an un-
+ allocated link,
+
+ 2b1d4c1c Or a message regarding allocation from B
+ to A has been garbled in transmission.
+
+ 2b1d4c2 In this case, A's action is to:
+
+ 2b1d4c2a Send a link disconnect message to B
+ concerning the attempted connection
+
+ 2b1d4c2b Consider the state of HOST B to be in
+ error and initiate entry to a panic routine(error).
+
+ 2b1d5 If no communication regarding the link is received
+ from B in the prescribed amount of time, HOST B is
+ considered to be in an error state.
+
+ 2b1d5a A link disconnect message is sent to B from A.
+
+ 2b1d5b A panic routine is called(error).
+
+ 2c Auxilliary Links
+
+ 2c1 Auxilliary links are established by a call to the monitor from
+ a user program.
+
+ 2c1a The request must specify pertinent data about the desired
+ link to the monitor
+
+ 2c1a1 The number of the primary link to B.
+
+ 2c1b The request for an auxilliary link must be made by a user
+ program in each of the HOSTs (A and B).
+
+ 2c1c If Na > Nb, then HOST A proceeds to establish a link to
+ HOST B in the manner outlined above (getlink).
+
+
+
+
+
+Duvall [Page 4]
+
+RFC 2
+
+
+ 2c1d If Na<Nb, then A waits:
+
+ 2c1d1 For HOST B to establish the link (after looking to see
+ if B has already established the corresponding link).
+
+ 2c1d2 For a specified amount of time to elapse.
+
+ 2c1d2a This means that HOST B did not respond to the
+ request of HOST A.
+
+ 2c1d2b The program in HOST A and B should be able to
+ specifiy the amount of time to wait for the timeout.
+
+3 ERROR CHECKING
+
+ 3a All messages sent over the network will be error checked initally
+ so as to help isolate software and hardware bugs.
+
+ 3b A checksum will be associated with each message, which is order
+ dependent.
+
+ 3b1 The following algorithm is one which might be used:
+
+ 3b1a A checksum of length 1 may be formed by adding successive
+ fields in the string to be checked serially, and adding the
+ carry bit into the lowest bit position of the sum.
+
+ +--------------+
+ | |
+ +---FIELD 1----+
+
+ ADD +--------------+
+ | |
+ +----FIELD 2---+
+
+ +-+--------------+
+ | | |
+ +-+--------------+
+ \
+ \ +--+
+ ADD CARRY---> | |
+ +--+
+
+ +--------------+
+ | |
+ +----RESULT----+
+
+ 3b1a1 This process is known as folding.
+
+
+
+Duvall [Page 5]
+
+RFC 2
+
+
+ 3b1a2 Several fields may be added and folded in parallel, if
+ they are folded appropiately after the addition.
+
+ +---------+---------+---------+---------+
+ | FIELD 4 | FIELD 3 | FIELD 2 | FIELD 1 |
+ +---------+---------+---------+---------+
+
+ +---------+---------+---------+---------+
+ | FIELD 8 | FIELD 7 | FIELD 6 | FIELD 5 |
+ +---------+---------+---------+---------+
+ ADD
+ +-+---------+---------+---------+---------+
+ | | | | | |
+ +-+---------+---------+---------+---------+
+ | | | | |
+ | | | | v
+ | | | | +---------+
+ | | | | | |
+ | | | | +---------+
+ | | | |
+ | | | \ +---------+
+ | | | `-> | |
+ | | | +---------+
+ | | |
+ | | \ +---------+
+ | | `-----------> | |
+ | | +---------+
+ | |
+ | \ +---------+
+ | `--------------------->| |
+ | +---------+
+ |
+ \ +---+
+ `-----CARRY------------------------>| |
+ +---+
+ ADD
+ +---------+---------+
+ | | |
+ +--CARRY--+---------+
+ |
+ \ +-----+
+ ADD `-----> | |
+ +-----+
+
+ +---------+
+ | |
+ +-RESULT--+
+
+
+
+
+Duvall [Page 6]
+
+RFC 2
+
+
+ 3b1a2a Using this scheme, it is assumed that, if there
+ are n fields, the carries from the first n-1 fields
+ are automatically added into the low order position of
+ the next higher field, so that in folding, one need
+ only add the [n] result fields to the carry from the
+ nth field, and then add in an appropiately sized carry
+ from that addition (and repeat the desired number of
+ times to achieve the result.
+
+ 3b1a3 A checksum computed in this manner has the advantage
+ that the word lengths of different machines may each be used
+ optimally:
+
+ 3b1a3a If a string of suitable length is chosen for
+ computing the checksum, and a suitable checksum field
+ length is selected, the checksum technique for each of
+ the machines will be relatively optimal.
+
+ 3b1a3a1 Field length: 288 bits (lowest common
+ denomenator of (24,32,36)
+
+ 3b1a3a2 Checksum length: 8 bits (convenient field size
+ for all machines)
+
+ 3b1b If a message is divided into groups of fields, and each
+ group is checksummed in this manner, an order dependent
+ checksum may be got by shifting the checksum for each group,
+ and adding it in (successively) to the checksum of the next
+ group
+
+ 3c A facility will be provided where two HOSTs may enter a mode which
+ requires positive verification of all messages. This verification is
+ sent over the control link.
+
+4 MONITOR FUNCTIONS
+
+ 4a Network I/O drivers
+
+ 4a1 Input
+
+ 4a1a Input message from IMP.
+
+ 4a1b Do error checking on message.
+
+ 4a1b1 Verify checksum,
+
+ 4a1b2 Send "message recieved" aknowledgement over control
+ link if aknowledge mode is in effect.
+
+
+
+Duvall [Page 7]
+
+RFC 2
+
+
+ 4a1c (trans)character translation
+
+ 4a1c1 There is a strong possibility that the character
+ translation may be done in the IMP.
+
+ 4a1c2 This needs to be explored further with BBN.
+
+ 4a1c3 There are two main considerations
+
+ 4a1c3a Should the translation be done by table or
+ algorithm?
+
+ 4a1c3a1 Initially it seems as though the best way to
+ go is table.
+
+ 4a1c3b How should we decide which messages should be
+ translated, i.e. is it desirable to not translate
+ everything (YES!!) and by what means can we use to
+ differentiate?
+
+ 4a1d Decode header, and pass message to correct recipient as
+ identified by source, and link.
+
+ 4a2 Output
+
+ 4a2a Build header
+
+ 4a2b Character translation
+
+ 4a2b1 See remarks under the section on output translation
+ (trans).
+
+ 4a2c Create checksum
+
+ 4a2d Check status of link
+
+ 4a2d1 If there has not been a RFNM since the last message
+ transmitted out the link, wait for it.
+
+ 4a2e Transmit message to IMP
+
+ 4a2f If aknowledge mode is in effect,wait for
+
+ 4a2f1 RFNM from destination IMP.
+
+ 4a2f2 Response from destination HOST over control line 0.
+
+
+
+
+
+Duvall [Page 8]
+
+RFC 2
+
+
+ 4b Network status
+
+ 4b1 Maintain status of other HOSTs on network
+
+ 4b1a If an IMP is down, then his HOST is considered to be down.
+
+ 4b2 Maintain status of control lines.
+
+ 4b3 Answer status queries from other HOSTs.
+
+ 4b4 Inform other HOSTs as to status of primary and auxilliary
+ links on an interrupt basis.
+
+ 4b5 Inform other HOSTs as to status of programs using primary and
+ secondary links
+
+5 EXECUTIVE PRIMITIVES
+
+ 5a Primary Links
+
+ 5a1 These require the HOST number as a parameter.
+
+ 5a1a Establish primary link
+
+ 5a1b Connect controlling teletype to primary link
+
+ 5a1c INPUT/OUTPUT over primary link
+
+ 5a1d Interrogate status of primary link
+
+ 5a1d1 Don't know what, exactly, this should do, but it seems
+ as though it might be useful.
+
+ 5a1e Disconnect controlling teletype from primary link
+
+ 5a1f Kill primary link
+
+ 5b Auxilliary Links.
+
+ 5b1 Establish auxilliary link.
+
+ 5b1a requires the HOST number as a parameter
+
+ 5b1b It returns a logical link number which is similar to a
+ file index. It is this number which is passed to all of the
+ other Auxilliary routines as a parameter.
+
+ 5b2 INPUT/OUTPUT over auxilliary link
+
+
+
+Duvall [Page 9]
+
+RFC 2
+
+
+ 5b3 Interrogate status auxilliary link.
+
+ 5b3a Don't know what, exactly, this should do, but it seems as
+ though it might be useful.
+
+ 5b4 Kill auxilliary link.
+
+ 5c Special executive functions
+
+ 5c1 Transparent. INPUT/OUTPUT over link
+
+ 5c1a This may be used to do block I/O transfers over a link
+
+ 5c1b The function of the monitor in this instance is to
+ transfer a buffer directly to its IMP
+
+ 5c1c At does not modify it in any way
+
+ 5c1c1 This means that the header and other control
+ information must be in the buffer.
+
+ 5c1d The indended use of this is for network debugging.
+
+6 INITIAL CHECKOUT
+
+ 6a The network will be initially checked out using the links in a
+ simulated data-phone mode.
+
+ 6a1 All messages will be one character in length.
+
+ 6a2 Links will be transparent to the monitor, and controlled by
+ user program via a special executive primitive.
+
+ 6a2a The initial test will be run from two user programs in
+ different HOSTs, e.g. DDT to DDT.
+
+ 6a2b It will be paralleled by a telephone link or similar.
+
+
+ [ This RFC was put into machine readable form for entry ]
+ [ into the online RFC archives by Robbie Bennet 10/1998 ]
+ [ This RFC was nroffed by Kelly Tardif, Viagenie 10/1999 ]
+
+
+
+
+
+
+
+
+
+Duvall [Page 10]
+