host
Click on the red underlined text to get to the source
... DDP-516
computer which interfaces with up to four HOSTs at a particular
site, and allows HOSTs access into the network ...
... interfaces with up to four HOSTs at a particular
site, and allows HOSTs access into the network. The configuration
of the initial four-HOST ...
... HOSTs access into the network. The configuration
of the initial four-HOST network is given in figure 1. The IMPs
from a store-and-forward communications network ...
... bits long which is given to
an IMP by a HOST for transmission to another HOST. The first 32 bits
...
... an IMP by a HOST for transmission to another HOST. The first 32 bits
of the message are the leader. The leader contains the following
...
... information:
(a) HOST
(b) Message Type
...
... When a message is transmitted from a HOST to its IMP, the HOST field
of the leader names the receiving HOST ...
... HOST field
of the leader names the receiving HOST. When the message arrives at
the receiving HOST ...
... HOST. When the message arrives at
the receiving HOST, the HOST field names the sending HOST.
...
... Only two message types are of concern in this paper. Regular
messages are generated by a HOST and sent to its IMP for transmission
to a foreign HOST ...
... HOST and sent to its IMP for transmission
to a foreign HOST. The other message type of interest is a RFNM
...
... link number identifies over which of 256 logical paths (links)
between the sending HOST and the receiving HOST the message will be
...
... between the sending HOST and the receiving HOST the message will be
sent. Each link is unidirectional ...
... so that no more than one message at a time may be sent over it. This
control is implemented using RFNM messages. After a sending HOST has
sent a message to a receiving HOST ...
... HOST over a particular link, the
sending HOST is prohibited from sending another message over that
same link until the sending HOST ...
... HOST is prohibited from sending another message over that
same link until the sending HOST receives a RFMN. The RFNM is
generated by the IMP ...
... generated by the IMP connected to the receiving HOST, and the RFNM is
sent back to the sending HOST ...
... HOST, and the RFNM is
sent back to the sending HOST after the message has entered the
receiving HOST ...
... HOST after the message has entered the
receiving HOST. It is important to remember that there are 356 links
in each direction and that no relationship among these is imposed by
...
... link and RFMN mechanism is to prohibit individual
users from overloading an IMP or a HOST. Implicit in this purpose is
the assumption that a user does not use multiple links to achieve a
...
... the assumption that a user does not use multiple links to achieve a
wide band, and to a large extent the HOST-HOST protocol cooperates
with this assumption. An even more basic assumption, of course, is
...
... links to achieve a
wide band, and to a large extent the HOST-HOST protocol cooperates
with this assumption. An even more basic assumption, of course, is
that the network ...
...
In order to delimit the length of the message, and to make it easier
for HOSTs of differing word lengths to communicate, the following
formatting procedure is used. When a HOST prepares a message for
...
... for HOSTs of differing word lengths to communicate, the following
formatting procedure is used. When a HOST prepares a message for
output, it creates a 32-bit ...
... 32-bit leader. Following the leader is a binary
string, called marking, consisting of an arbitrary number of zeros,
followed by one. Marking makes is possible for the sending HOST to
synchronize the beginning of the text message with its word
...
... hardware interface between the IMP and HOST appends a one followed by
enough zeros to make the message length a multiple of 16 bits ...
... processes are to converse in both directions.
Processes within a HOST communicate with the network through a
Network ...
... Network Control Program (NCP). In most HOSTs, the NCP will be a part
of the executive, so that processes will use system calls to
...
...
In order to accomplish its tasks, a NCP in one HOST must communicate
with a NCP in another HOST ...
... HOST must communicate
with a NCP in another HOST. To this end, a particular link between
each pair of HOSTs ...
... HOST. To this end, a particular link between
each pair of HOSTs has been designated as the control link. Messages
received over the control link ...
... control commands is given in the next section.
A major issue is how to refer to processes in a foreign HOST. Each
HOST has some internal naming scheme, but these various schemes often
...
... A major issue is how to refer to processes in a foreign HOST. Each
HOST has some internal naming scheme, but these various schemes often
are incompatible. Since it is not practical to impose a common
internal process naming scheme, an intermediate name space ...
... created with a separate portion of the name space given to each HOST.
It is left to each HOST to map internal process identifiers ...
... name space given to each HOST.
It is left to each HOST to map internal process identifiers into its
name space ...
... socket is illustrated in Figure 3.
Each HOST is assigned all sockets in the name space which have field
...
... sockets in the name space which have field
(b) equal to the HOST's own identification.
A socket ...
... bits of the AEN simply provide a sizable population
of sockets for each used number at each HOST. (AEN stands for
"another eight-bit number")
...
... him throughout the network. Generally this will be the 8-bit HOST
number of his home HOST, followed by 16 bits ...
... 8-bit HOST
number of his home HOST, followed by 16 bits which uniquely identify
him at that HOST ...
... HOST, followed by 16 bits which uniquely identify
him at that HOST. Provision can also be made for a user to have a
user number not keyed to a particular HOST, an arrangement desirable
...
... him at that HOST. Provision can also be made for a user to have a
user number not keyed to a particular HOST, an arrangement desirable
for mobile users who might have no home HOST or more than one home
...
... user number not keyed to a particular HOST, an arrangement desirable
for mobile users who might have no home HOST or more than one home
HOST. This 24-bit ...
... for mobile users who might have no home HOST or more than one home
HOST. This 24-bit user number is then used in the following manner.
When a user signs onto a HOST ...
... HOST. This 24-bit user number is then used in the following manner.
When a user signs onto a HOST, his user number is looked up.
Thereafter, each process the user creates is tagged with his user
...
... Thereafter, each process the user creates is tagged with his user
number. When the user signs onto a foreign HOST via the network, his
same user number is used to tag ...
... same user number is used to tag processes he creates in that HOST.
The foreign HOST obtains the user number either by consulting a table
...
... creates in that HOST.
The foreign HOST obtains the user number either by consulting a table
at login time, as the home HOST ...
... HOST obtains the user number either by consulting a table
at login time, as the home HOST does, or by noticing the
identification of the caller. The effect of propagating the user's
...
... processes he has created. This virtual net may span an arbitrary
number of HOSTs. It will thus be easy for a user to connect his
processes in arbitrary ways, while still permitting him to connect
his processes with those in other virtual nets.
...
... The relationship between sockets and processes is now describable
(see Figure 4). For each user number at each HOST, there are 128
send sockets and 128 receive sockets ...
...
An unusual aspect of the HOST-HOST protocol is that a process may
switch its end of a connection ...
... socket to another. The new
socket may be in any virtual net and at any HOST, and the process may
initiate a switch either at the time the connection ...
... connection. The new socket must
have the same user number and HOST number, and the connection is
still established to the same process. This form of switching is
...
... The NCP concatenates <AEN 1> and <AEN 2> each with the user
number of the process and the HOST number to form 40-bit
sockets ...
... parameters. The number and format of parameters is fixed for each
operation code. A sequence of control commands destined for a
particular HOST can be packed into a single control message.
...
... arrives, the buffer space in the receiving HOST is used to queue the
waiting messages. Since only limited space is generally available,
...
... waiting messages. Since only limited space is generally available,
the receiving HOST may need to inhibit the sending HOST from sending
any more messages over the offending connection ...
... the receiving HOST may need to inhibit the sending HOST from sending
any more messages over the offending connection. When the sending
...
... any more messages over the offending connection. When the sending
HOST receives this command, it may block the process generating the
messages.
...
...
This command is also sent from the receiving HOST to the sending HOST
and negates a previous CEASE ...
... This command is also sent from the receiving HOST to the sending HOST
and negates a previous CEASE.
...
...
We assume that within each HOST there is always a process in
execution which listens to login requests. We call this process the
...
... At the user level, subroutines which manage data buffer and format
input designed for other HOSTs are provided. It is not mandatory
that the user use such subroutines, since the user has access to the
network ...
...
In addition to user programming access, it is desirable to have a
subsystem program at each HOST which makes the network immediately
accessible from a teletype-like device without special programming.
...
... starts up the TELNET subsystem at
the user's HOST.
(111) The user identifies a break character which causes any
...
... (111) The user identifies a break character which causes any
message following the break to be interpreted locally
rather than being sent on the foreign HOST.
(iv) The TELNET ...
... Characters typed on the user's teletype are transmitted
unaltered through the PDP-10 (user HOST) and on to the
940 (serving HOST). The PDP ...
... shell program built over the network system calls. It effectively
established a shunt in the user HOST between the remote user and a
distant serving HOST.
...
... established a shunt in the user HOST between the remote user and a
distant serving HOST.
Given the basic system primitives, the TELNET ...
... Given the basic system primitives, the TELNET subsystem at the user
HOST and a manual for the serving HOST, the network can be profitably
...
... TELNET subsystem at the user
HOST and a manual for the serving HOST, the network can be profitably
employed by remote users today.
...
... network poses special problems where a high degree of interaction
is required between the user and a particular subsystem in a foreign
HOST. These problems arise due to heterogeneous consoles, local
operating systems overhead ...
...
cause nine messages in each direction. Furthermore, each character
is handled by a user level program in the local HOST before being
sent to the foreign HOST.
...
... is handled by a user level program in the local HOST before being
sent to the foreign HOST.
Now it is clear that if this particular example were important, we
...
...
Now it is clear that if this particular example were important, we
would quickly implement rules 1 to 5 in a local HOST program and send
only complete lines to the foreign HOST. If the foreign HOST ...
... would quickly implement rules 1 to 5 in a local HOST program and send
only complete lines to the foreign HOST. If the foreign HOST program
could not be modified so as to not generate echoes, then the local
...
... HOST program and send
only complete lines to the foreign HOST. If the foreign HOST program
could not be modified so as to not generate echoes, then the local
program could not only echo ...
... program could not only echo properly, it could also throw away the
later echoes from the foreign HOST. However, the problem is not any
particular interaction scheme; the problem is that we expect many of
these kinds of schemes to occur. We have not found any general
...
... In the example above, the program to accumulate a line and generate
echoes would be the front end of some subsystem. We now take notice
of the fact that the local HOSTs have substantial computational
power, but our current designs make use of the local HOST only as a
...
... of the fact that the local HOSTs have substantial computational
power, but our current designs make use of the local HOST only as a
data concentrator. This is somewhat ironic, for the local HOST is
...
... power, but our current designs make use of the local HOST only as a
data concentrator. This is somewhat ironic, for the local HOST is
not only poorly utilized as a data concentrator, it also degrades
performance ...
... connections. The strategy is then to transport the source code for
the front end of a subsystem to the local HOST, where it would be
compiled and executed.
...
... pursuing. Testing of this conjecture and further development of NIL
will take priority after low level HOST-HOST protocol has stabilized.
...
... The hardware and software interfaces between HOST and IMP is an area
of particular concern for the HOST ...
... between HOST and IMP is an area
of particular concern for the HOST organizations. Considering the
diversity of HOST computers to which a standard IMP ...
... of particular concern for the HOST organizations. Considering the
diversity of HOST computers to which a standard IMP must connect, the
hardware ...
... interface was made bit serial and full-duplex. Each HOST
organization implements its half of this very simple interface.
...
... interface is equally simple and consists of messages
passed back and forth between the IMP and HOST programs. Special
error and signal messages are defined as well as messages containing
normal data. Messages waiting in queues ...
... The effect of the present software interface is the needless
rebuffering of all messages in the HOST in addition to the buffering
in the IMP ...
... times at the IMP. The Network Control Program at one HOST (e.g.,
UTAH) needs waiting RFNM's before all other messages. At another
...
... user who is next to be run.
What is needed is coding representing the specific needs of the HOST
on both sides of the interface to make intelligent decisions about
...
... duplex, character by character, interactions over the net. At the
very least, the IMP/HOST protocol should be expended to permit each
side to assist the other in scheduling messages over the channels.
...