DNET
Encyclopedia
DNET is a proprietary
software suite
of network protocols created by DIAB
, originally deployed on their Databoard products. It was based upon X.25
, which was particularly popular in European telecommunications circles at that time. In that incarnation it was rated at 1 Mbit/s over RS-422.
In the 80's, ISC Systems Corporation (ISC) purchased DNET as part of their purchase of DNIX
, and ported it to run over Ethernet
. ISC's choice of DNET over TCP/IP was in part due to the relative light weight of the DNET protocol stack
, allowing it to run more efficiently on the target machinery. DNET was also auto-configuring
so there was no manual configuration of the local network, all that was required was that each machine in a network be given a unique name. This simplicity was advantageous in ISC's market.
Being based on X.25
, DNET was connection
-oriented, datagram
-based (as opposed to a byte stream
), supported out-of-band
(interrupt) messages, and provided link
-down notifications to its clients
and servers
so that applications did not have to provide their own heartbeat
s. In the financial community these were all considered advantages over, say, TCP/IP. DNET also supported Wide Area Network
s (WAN) using X.25
point-to-point communication links
, either leased line
or dialup (see also Data link
). (WAN support did require manual configuration of the gateway
machines.)
DNET provided named network services
, and supported a multicast
protocol for finding them. Clients
would ask for a named service, and the first respondent (of potentially many) would get the connection
. Servers
could either be resident, in which case they registered their service name(s) with the protocol stack
when they were started, or transient, in which case a fresh server was forked/execed
for each client connection.
DNET at ISC consisted of the following services:
There were many more services than these at a typical DNET installation - these are representative.
Handler, usually mounted on /netphys, and was responsible for providing all Layer 2 and Layer 3
X.25
protocol
handling. It talked to the Ethernet
and HDLC device drivers. It also provided the service name registry, and the WAN
gateway functionality. Resident server
s could also utilize, at their instigation, a Layer 3
protocol stack
(called 'serverprot') between themselves and netman, allowing them to support up to 4095 client
connections through one file descriptor
(to netman). Such servers were called complex resident servers, so named in honor of the relatively complicated (though not large) bit of protocol code that had to be included to handle the multiplexing
and flow control
. Simple resident and transient servers consumed a file descriptor
per client connection. It was possible to run more than one netman process, for testing or other special purposes. (Such a process would be configured to use different Ethertype
and handler mount points, at a minimum.) The /usr/lib/net/servtab file was the usual location for the configuration file controlling WAN
configuration and transient servers.
Client applications would open /netphys/servicename, this would normally result in an open connection to a server somewhere, possibly even on the same machine. Resident servers would open /netphys/listen/servicename, this would register their service name with netman. Transient servers were pre-registered via their entry in servtab, and would be forked/execed
with their connection already established by netman. Machine-specific services (such as ncu---network login) would contain the machine name as part of the service name, installation-specific services (such as dmap---a site's machine status servers) would not.
Service name resolution was handled entirely between netman processes. A client's representative would multicast
the desired service name to the network using a MUI [Multicast Unnumbered Information] extension to X.25
. Responses indicating server availability would be directed (not multicast) back by potential server representatives. When there was more than one respondent to the multicast (as was normal for, say, dmap) the first one would be selected for opening a connection. Only one server was ever contacted per client service request. As with all UI-class messages in X.25
, packet loss was possible, so the MUI process was conducted up to three times if there was no response.
The X.25
-ness of connections, namely datagram
control, was exposed to applications (both client
and server
) as an extra control byte at the beginning of each read and write through a connection. As was customary in network header
processing, this byte was usually accessed at a -1 offset within any application's networking code, only the buffer allocation and the read(2)/write(2) calls were usually aware of it. This byte contained the X.25
M, D, and Q bits (for More, Delivery, and Qualifier). DNET never implemented the D (delivery confirmation) bit, but the other two were useful, particularly the M bit. The M bits were how datagrams were delimited. A byte-stream
application could safely ignore them. Any read with a clear M bit indicated that the read result contained an entire datagram and could be safely processed. Reads that were too small to contain an entire datagram would get the part that would fit into the buffer, with the M bit set. M bits would continue to be set on reads until a read contained the end of the original datagram. Datagrams were never packed together, you could get at most one per read. Any write with the M bit set would propagate to the other end with the M bit set, indicating to the other end that it should not process the data yet as it was incomplete. (The network was free to coalesce M'd data at its discretion.) The usual application merely wrote an entire datagram at once with a clear M bit, and was coupled with a small read loop to accumulate entire datagrams before delivery to the rest of an application. (Though not often required due to automatic fragmentation
and reassembly within the protocol stack
, this protective loop ensured that allowable exposed fragmentation was never harmful.) The Q bit was a simple marker, and could be used to mark 'special' datagrams. In effect it was a single header bit that could be used to mark metadata
.
Out-of-band
(OOB) data, which bypassed all buffering, flow control
, and delivery confirmation was accomplished via DNIX
's ioctl
mechanism. It was limited (per X.25
) to 32 bytes of data. (Asynchronous I/O
reads were usually utilized so that out of band data could be caught at any time.) As with UDP
, it was possible to lose OOB
data, but this normally could only happen if it was overutilized. (The lack of a reader waiting for it resulted in OOB
data being discarded.)
Flow control
was accomplished within the network (between netman processes, and possibly involving external X.25
WAN
links) using the usual X.25
mechanisms. It was exposed to the applications only insofar as whether the network data reads and writes blocked or not. If a request could be satisfied via the buffering abilities of the netman handler and/or the current state of the connection it would be satisfied immediately without blocking. If the buffering were exceeded the request would block until the buffers could satisfy what remained of the request. Naturally, Asynchronous I/O
could be used to insulate the process from this blocking if it would be a problem. Also, complex resident servers used the 'serverprot' X.25
flow control mechanisms internally to avoid ever blocking on their single network file descriptor
, this was vital considering that the file descriptor
was shared by up to 4095 client
connections.
-level applications could access files on remote machines via /net/machine.domain/path file names. Raccess was a DNIX
handler (for its clients), a netman client
(for packaging up the filesystem requests), and a netman server
(for executing the requests on the remote machine). The usual reference point for remote files was '/', the root of the remote machine's filesystem, though it could be anything that was required. (Changing this reference point was one way of providing a facility analogous to chroot
jails for network file accesses.) Raccess supported user ID translation and security facilities in a manner analogous to TCP/IP's .rhosts file. It was possible to run more than one raccess process, for testing or other special purposes. Examples:
(for passing standard I/O
to the remote machine), a netman server
(for receiving standard I/O
on the remote machine), a parent process
for hosting the remote process, and a DNIX
handler (so that remote programs believed themselves to be connected to tty devices). Rx supported user ID translation and security facilities in a manner analogous to TCP/IP's .rhosts file. Some examples:
or rlogin
protocols. Like rx, it was a netman client
(for passing standard I/O
to the remote machine), a netman server
(for receiving standard I/O
on the remote machine), a parent process
for hosting the remote login procedure, and a DNIX
handler (so that remote programs believed themselves to be connected to tty devices).
driver. Technically not really part of DNET, in that it was a satellite protocol merely associated with DNET installations. (As was the X.25
'safelink' file server protocol used to communicate between these same diskless workstations and their file servers.)
and periodically broadcast
(multicast
, actually, so that non-participants never even saw the messages) their presence. The same process also collected these broadcasts and (as a server) advertised the availability of the list of senders through netman. To control the load on the servers, the broadcast frequency was affected by the current size of the list in order to limit the network messages to an average of one per second. Dmap clients
would contact their nearest dmap server
(as determined by who responded first to the service name enquiry) to get the current list of machines, then would contact each machine in turn (usually maintaining four [configurable] connections in parallel for speed) to get the specific machine status they were interested in. (Unlike most other transient servers, the dmap client program was not also the transient server. The convention for DNET transient servers was that the same program was used for both sides of the link. netman automatically passed a -B command-line argument to any transient server it spawned, indicating to the process that it was the B-side process and that its standard input
file descriptor
was a network service connection. The reason for splitting dmap into A- and B-side programs was the desire to push as much of the processing [such as display formatting] onto the client as possible, a 'thick' client in other words. In this case because the client was run infrequently, and usually manually, the division was made in order to minimize the load on the servers. This extended even to minimizing the memory footprint of the transient server, which necessitated the split into A- and B-side programs.)
Proprietary software
Proprietary software is computer software licensed under exclusive legal right of the copyright holder. The licensee is given the right to use the software under certain conditions, while restricted from other uses, such as modification, further distribution, or reverse engineering.Complementary...
software suite
Software suite
A software suite or application suite is a collection of computer programs, usually application software and programming software of related functionality, often sharing a more-or-less common user interface and some ability to smoothly exchange data with each other.Sometimes software makers...
of network protocols created by DIAB
Diab
Diab is a village in the Bassar Prefecture in the Kara Region of north-western Togo.-External links:**...
, originally deployed on their Databoard products. It was based upon X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
, which was particularly popular in European telecommunications circles at that time. In that incarnation it was rated at 1 Mbit/s over RS-422.
In the 80's, ISC Systems Corporation (ISC) purchased DNET as part of their purchase of DNIX
DNIX
DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB . A version called ABCenix was also developed for the ABC1600 computer from Luxor. DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB (DIAB). A version called ABCenix...
, and ported it to run over Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
. ISC's choice of DNET over TCP/IP was in part due to the relative light weight of the DNET protocol stack
Protocol stack
The protocol stack is an implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them....
, allowing it to run more efficiently on the target machinery. DNET was also auto-configuring
Auto-configuration
Auto-configuration is the automatic configuration of devices without manual intervention, without any need for software configuration programs or jumpers. Ideally, auto-configuring devices should just "plug and play"...
so there was no manual configuration of the local network, all that was required was that each machine in a network be given a unique name. This simplicity was advantageous in ISC's market.
Being based on X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
, DNET was connection
Telecommunication circuit
A telecommunication circuit is any line, conductor, or other conduit by which information is transmitted.A dedicated circuit, private circuit, or leased line is a line that is dedicated to only one use...
-oriented, datagram
Datagram
A datagram is a basic transfer unit associated with a packet-switched network in which the delivery, arrival time, and order are not guaranteed....
-based (as opposed to a byte stream
Byte stream
In computer science, a byte stream is a bit stream, in which data bits are grouped into units, called bytes.In computer networking the term octet stream is sometimes used to refer to the same thing; it emphasizes the use of bytes having the length of 8 bits, known as octets.Formally, a byte stream...
), supported out-of-band
Out-of-band
The term out-of-band has different uses in communications and telecommunication. In case of out-of-band control signaling, signaling bits are sent in special order in a dedicated signaling frame...
(interrupt) messages, and provided link
Data link
In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit...
-down notifications to its clients
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
and servers
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
so that applications did not have to provide their own heartbeat
Heartbeat
Heartbeat may refer to:* Cardiac cycle of the heart* Heart sounds* Pulse* The interval for keeping alive a push e-mail connection* Heartbeat , a British police drama* HeartBeat Heartbeat may refer to:* Cardiac cycle of the heart* Heart sounds* Pulse* The interval for keeping alive a push e-mail...
s. In the financial community these were all considered advantages over, say, TCP/IP. DNET also supported Wide Area Network
Wide area network
A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...
s (WAN) using X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
point-to-point communication links
Link (telecommunications)
In telecommunications a link is the communications channel that connects two or more communicating devices. This link may be an actual physical link or it may be a logical link that uses one or more actual physical links...
, either leased line
Leased line
A leased line is a service contract between a provider and a customer, whereby the provider agrees to deliver a symmetric telecommunications line connecting two or more locations in exchange for a monthly rent . It is sometimes known as a 'Private Circuit' or 'Data Line' in the UK or as CDN in Italy...
or dialup (see also Data link
Data link
In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit...
). (WAN support did require manual configuration of the gateway
Gateway (telecommunications)
In telecommunications, the term gateway has the following meaning:*In a communications network, a network node equipped for interfacing with another network that uses different protocols....
machines.)
DNET provided named network services
Name server
In computing, a name server is a program or computer server that implements a name-service protocol. It maps a human-recognizable identifier to a system-internal, often numeric, identification or addressing component....
, and supported a multicast
Multicast
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
protocol for finding them. Clients
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
would ask for a named service, and the first respondent (of potentially many) would get the connection
Telecommunication circuit
A telecommunication circuit is any line, conductor, or other conduit by which information is transmitted.A dedicated circuit, private circuit, or leased line is a line that is dedicated to only one use...
. Servers
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
could either be resident, in which case they registered their service name(s) with the protocol stack
Protocol stack
The protocol stack is an implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them....
when they were started, or transient, in which case a fresh server was forked/execed
Fork-exec
Fork-exec is a commonly used technique in Unix whereby an executing process spawns a new program. fork is the name of the system call that the parent process uses to "divide" itself . After calling fork, the created child process is an exact copy of the parent except for the return value...
for each client connection.
DNET at ISC consisted of the following services:
- netman (the main networking client/server support handler)
- raccess (remote file access via /net/machine/path/from/raccess/root...)
- rx (remote execution)
- ncu (network login)
- bootserver (diskless workstationDiskless workstationA diskless node is a workstation or personal computer without disk drives, which employs network booting to load its operating system from a server...
boot serviceNetwork bootingNetwork booting is the process of booting a computer from a network rather than a local drive. This method of booting can be used by routers, diskless workstations and centrally managed computers such as public computers at libraries and schools...
) - dmap (ruptime analog)
There were many more services than these at a typical DNET installation - these are representative.
netman
netman was the main component of DNET. It was a DNIXDNIX
DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB . A version called ABCenix was also developed for the ABC1600 computer from Luxor. DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB (DIAB). A version called ABCenix...
Handler, usually mounted on /netphys, and was responsible for providing all Layer 2 and Layer 3
Network Layer
The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
protocol
Protocol stack
The protocol stack is an implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them....
handling. It talked to the Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
and HDLC device drivers. It also provided the service name registry, and the WAN
Wide area network
A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...
gateway functionality. Resident server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
s could also utilize, at their instigation, a Layer 3
Network Layer
The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
protocol stack
Protocol stack
The protocol stack is an implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them....
(called 'serverprot') between themselves and netman, allowing them to support up to 4095 client
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
connections through one file descriptor
File descriptor
In computer programming, a file descriptor is an abstract indicator for accessing a file. The term is generally used in POSIX operating systems...
(to netman). Such servers were called complex resident servers, so named in honor of the relatively complicated (though not large) bit of protocol code that had to be included to handle the multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
and flow control
Flow control
In data communications, flow control is the process of managing the pacing of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with...
. Simple resident and transient servers consumed a file descriptor
File descriptor
In computer programming, a file descriptor is an abstract indicator for accessing a file. The term is generally used in POSIX operating systems...
per client connection. It was possible to run more than one netman process, for testing or other special purposes. (Such a process would be configured to use different Ethertype
EtherType
EtherType is a two-octet field in an Ethernet frame. It is used to indicate which protocol is encapsulated in the PayLoad of an Ethernet Frame. This field was first defined by the Ethernet II framing networking standard, and later adapted for the IEEE 802.3 Ethernet networking standard.EtherType...
and handler mount points, at a minimum.) The /usr/lib/net/servtab file was the usual location for the configuration file controlling WAN
Wide area network
A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...
configuration and transient servers.
Client applications would open /netphys/servicename, this would normally result in an open connection to a server somewhere, possibly even on the same machine. Resident servers would open /netphys/listen/servicename, this would register their service name with netman. Transient servers were pre-registered via their entry in servtab, and would be forked/execed
Fork-exec
Fork-exec is a commonly used technique in Unix whereby an executing process spawns a new program. fork is the name of the system call that the parent process uses to "divide" itself . After calling fork, the created child process is an exact copy of the parent except for the return value...
with their connection already established by netman. Machine-specific services (such as ncu---network login) would contain the machine name as part of the service name, installation-specific services (such as dmap---a site's machine status servers) would not.
Service name resolution was handled entirely between netman processes. A client's representative would multicast
Multicast
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
the desired service name to the network using a MUI [Multicast Unnumbered Information] extension to X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
. Responses indicating server availability would be directed (not multicast) back by potential server representatives. When there was more than one respondent to the multicast (as was normal for, say, dmap) the first one would be selected for opening a connection. Only one server was ever contacted per client service request. As with all UI-class messages in X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
, packet loss was possible, so the MUI process was conducted up to three times if there was no response.
The X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
-ness of connections, namely datagram
Datagram
A datagram is a basic transfer unit associated with a packet-switched network in which the delivery, arrival time, and order are not guaranteed....
control, was exposed to applications (both client
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
and server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
) as an extra control byte at the beginning of each read and write through a connection. As was customary in network header
Header (information technology)
In information technology, header refers to supplemental data placed at the beginning of a block of data being stored or transmitted. In data transmission, the data following the header are sometimes called the payload or body....
processing, this byte was usually accessed at a -1 offset within any application's networking code, only the buffer allocation and the read(2)/write(2) calls were usually aware of it. This byte contained the X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
M, D, and Q bits (for More, Delivery, and Qualifier). DNET never implemented the D (delivery confirmation) bit, but the other two were useful, particularly the M bit. The M bits were how datagrams were delimited. A byte-stream
Byte stream
In computer science, a byte stream is a bit stream, in which data bits are grouped into units, called bytes.In computer networking the term octet stream is sometimes used to refer to the same thing; it emphasizes the use of bytes having the length of 8 bits, known as octets.Formally, a byte stream...
application could safely ignore them. Any read with a clear M bit indicated that the read result contained an entire datagram and could be safely processed. Reads that were too small to contain an entire datagram would get the part that would fit into the buffer, with the M bit set. M bits would continue to be set on reads until a read contained the end of the original datagram. Datagrams were never packed together, you could get at most one per read. Any write with the M bit set would propagate to the other end with the M bit set, indicating to the other end that it should not process the data yet as it was incomplete. (The network was free to coalesce M'd data at its discretion.) The usual application merely wrote an entire datagram at once with a clear M bit, and was coupled with a small read loop to accumulate entire datagrams before delivery to the rest of an application. (Though not often required due to automatic fragmentation
Fragmentation (computer)
In computer storage, fragmentation is a phenomenon in which storage space is used inefficiently, reducing storage capacity and in most cases reducing the performance. The term is also used to denote the wasted space itself....
and reassembly within the protocol stack
Protocol stack
The protocol stack is an implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them....
, this protective loop ensured that allowable exposed fragmentation was never harmful.) The Q bit was a simple marker, and could be used to mark 'special' datagrams. In effect it was a single header bit that could be used to mark metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
.
Out-of-band
Out-of-band
The term out-of-band has different uses in communications and telecommunication. In case of out-of-band control signaling, signaling bits are sent in special order in a dedicated signaling frame...
(OOB) data, which bypassed all buffering, flow control
Flow control
In data communications, flow control is the process of managing the pacing of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with...
, and delivery confirmation was accomplished via DNIX
DNIX
DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB . A version called ABCenix was also developed for the ABC1600 computer from Luxor. DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB (DIAB). A version called ABCenix...
's ioctl
Ioctl
In computing, ioctl, short for input/output control, is a system call for device-specific operations and other operations which cannot be expressed by regular system calls. It takes a parameter specifying a request code; the effect of a call depends completely on the request code. Request codes are...
mechanism. It was limited (per X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
) to 32 bytes of data. (Asynchronous I/O
Asynchronous I/O
Asynchronous I/O, or non-blocking I/O, is a form of input/output processing that permits other processing to continue before the transmission has finished....
reads were usually utilized so that out of band data could be caught at any time.) As with UDP
User Datagram Protocol
The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...
, it was possible to lose OOB
Out-of-band
The term out-of-band has different uses in communications and telecommunication. In case of out-of-band control signaling, signaling bits are sent in special order in a dedicated signaling frame...
data, but this normally could only happen if it was overutilized. (The lack of a reader waiting for it resulted in OOB
Out-of-band
The term out-of-band has different uses in communications and telecommunication. In case of out-of-band control signaling, signaling bits are sent in special order in a dedicated signaling frame...
data being discarded.)
Flow control
Flow control
In data communications, flow control is the process of managing the pacing of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with...
was accomplished within the network (between netman processes, and possibly involving external X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
WAN
Wide area network
A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...
links) using the usual X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
mechanisms. It was exposed to the applications only insofar as whether the network data reads and writes blocked or not. If a request could be satisfied via the buffering abilities of the netman handler and/or the current state of the connection it would be satisfied immediately without blocking. If the buffering were exceeded the request would block until the buffers could satisfy what remained of the request. Naturally, Asynchronous I/O
Asynchronous I/O
Asynchronous I/O, or non-blocking I/O, is a form of input/output processing that permits other processing to continue before the transmission has finished....
could be used to insulate the process from this blocking if it would be a problem. Also, complex resident servers used the 'serverprot' X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
flow control mechanisms internally to avoid ever blocking on their single network file descriptor
File descriptor
In computer programming, a file descriptor is an abstract indicator for accessing a file. The term is generally used in POSIX operating systems...
, this was vital considering that the file descriptor
File descriptor
In computer programming, a file descriptor is an abstract indicator for accessing a file. The term is generally used in POSIX operating systems...
was shared by up to 4095 client
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
connections.
raccess
raccess provided a distributed filesytem, usually mounted on /net. ShellShell (computing)
A shell is a piece of software that provides an interface for users of an operating system which provides access to the services of a kernel. However, the term is also applied very loosely to applications and may include any software that is "built around" a particular component, such as web...
-level applications could access files on remote machines via /net/machine.domain/path file names. Raccess was a DNIX
DNIX
DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB . A version called ABCenix was also developed for the ABC1600 computer from Luxor. DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB (DIAB). A version called ABCenix...
handler (for its clients), a netman client
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
(for packaging up the filesystem requests), and a netman server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
(for executing the requests on the remote machine). The usual reference point for remote files was '/', the root of the remote machine's filesystem, though it could be anything that was required. (Changing this reference point was one way of providing a facility analogous to chroot
Chroot
A chroot on Unix operating systems is an operation that changes the apparent root directory for the current running process and its children. A program that is run in such a modified environment cannot name files outside the designated directory tree. The term "chroot" may refer to the chroot...
jails for network file accesses.) Raccess supported user ID translation and security facilities in a manner analogous to TCP/IP's .rhosts file. It was possible to run more than one raccess process, for testing or other special purposes. Examples:
cat /net/grumpy/usr/adm/errmessages
vi /net/sneezy/etc/passwd
rm /net/dopey.on.weekends.com/etc/nologin
mv /net/doc/tmp/log /net/doc/tmp/log-
cd /net/bashful/tmp && ls
rx
rx provided remote command execution in a manner analogous to TCP/IP's rsh (or remsh) facility. It was a netman clientClient (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
(for passing standard I/O
Standard streams
In Unix and Unix-like operating systems , as well as certain programming language interfaces, the standard streams are preconnected input and output channels between a computer program and its environment when it begins execution...
to the remote machine), a netman server
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
(for receiving standard I/O
Standard streams
In Unix and Unix-like operating systems , as well as certain programming language interfaces, the standard streams are preconnected input and output channels between a computer program and its environment when it begins execution...
on the remote machine), a parent process
Parent process
In computing, a parent process is a process that has created one or more child processes.- Unix :In the operating system Unix, every process except is created when another process executes the fork system call. The process that invoked fork is the parent process and the newly-created process is...
for hosting the remote process, and a DNIX
DNIX
DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB . A version called ABCenix was also developed for the ABC1600 computer from Luxor. DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB (DIAB). A version called ABCenix...
handler (so that remote programs believed themselves to be connected to tty devices). Rx supported user ID translation and security facilities in a manner analogous to TCP/IP's .rhosts file. Some examples:
rx machine!who
rx machine!vi /etc/passwd
tar cf - . | rx -luser:pass machine.far.far.away.com!tar xf -
ncu
ncu (networked call unix) was the usual network remote login procedure, analogous to TCP/IP's telnetTELNET
Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility using a virtual terminal connection...
or rlogin
Rlogin
rlogin is a software utility for Unix-like computer operating systems that allows users to log in on another host via a network, communicating via TCP port 513.It was first distributed as part of the 4.2BSD release....
protocols. Like rx, it was a netman client
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
(for passing standard I/O
Standard streams
In Unix and Unix-like operating systems , as well as certain programming language interfaces, the standard streams are preconnected input and output channels between a computer program and its environment when it begins execution...
to the remote machine), a netman server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
(for receiving standard I/O
Standard streams
In Unix and Unix-like operating systems , as well as certain programming language interfaces, the standard streams are preconnected input and output channels between a computer program and its environment when it begins execution...
on the remote machine), a parent process
Parent process
In computing, a parent process is a process that has created one or more child processes.- Unix :In the operating system Unix, every process except is created when another process executes the fork system call. The process that invoked fork is the parent process and the newly-created process is...
for hosting the remote login procedure, and a DNIX
DNIX
DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB . A version called ABCenix was also developed for the ABC1600 computer from Luxor. DNIX was a Unix-like real-time operating system from the Swedish company Dataindustrier AB (DIAB). A version called ABCenix...
handler (so that remote programs believed themselves to be connected to tty devices).
bootserver
The bootserver handled boot and dump requests from the diskless workstations. It was a simple process that talked directly to the EthernetEthernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
driver. Technically not really part of DNET, in that it was a satellite protocol merely associated with DNET installations. (As was the X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
'safelink' file server protocol used to communicate between these same diskless workstations and their file servers.)
dmap
dmap provided a facility analogous to TCP/IP's ruptime facility. Dmap servers, one per disk-based machine, connected directly to EthernetEthernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
and periodically broadcast
Broadcast
Broadcast or Broadcasting may refer to:* Broadcasting, the transmission of audio and video signals* Broadcast, an individual television program or radio program* Broadcast , an English electronic music band...
(multicast
Multicast
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
, actually, so that non-participants never even saw the messages) their presence. The same process also collected these broadcasts and (as a server) advertised the availability of the list of senders through netman. To control the load on the servers, the broadcast frequency was affected by the current size of the list in order to limit the network messages to an average of one per second. Dmap clients
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
would contact their nearest dmap server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
(as determined by who responded first to the service name enquiry) to get the current list of machines, then would contact each machine in turn (usually maintaining four [configurable] connections in parallel for speed) to get the specific machine status they were interested in. (Unlike most other transient servers, the dmap client program was not also the transient server. The convention for DNET transient servers was that the same program was used for both sides of the link. netman automatically passed a -B command-line argument to any transient server it spawned, indicating to the process that it was the B-side process and that its standard input
Standard streams
In Unix and Unix-like operating systems , as well as certain programming language interfaces, the standard streams are preconnected input and output channels between a computer program and its environment when it begins execution...
file descriptor
File descriptor
In computer programming, a file descriptor is an abstract indicator for accessing a file. The term is generally used in POSIX operating systems...
was a network service connection. The reason for splitting dmap into A- and B-side programs was the desire to push as much of the processing [such as display formatting] onto the client as possible, a 'thick' client in other words. In this case because the client was run infrequently, and usually manually, the division was made in order to minimize the load on the servers. This extended even to minimizing the memory footprint of the transient server, which necessitated the split into A- and B-side programs.)