# DIGITAL TCP/IP Services for OpenVMS
Concepts and Planning

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inetd: A UNIX internet daemon. A server process listens for client requests for specific services. When inetd receives a request for a service, it starts the appropriate server process.

initial sequence number: The first sequence number used for sending or receiving on a connection.

interface: The boundary between two parts of a system across which communication is possible; may be defined through hardware or software.

Interior Gateway Protocol (IGP): The protocol used to propagate network reachability and routing information within an autonomous system; RIP is among the most popular.

intermediate system: An OSI system that performs Internet layer forwarding. A routing system receives data packets from a system on one subnet and passes them on to a system on another subnet; it receives data packets from a source end system, or from the previous intermediate system on the route, and passes them on to the destination end system, or to the next intermediate system on the route.

internet: A shortened form of internetwork; a network of networks; interconnected TCP/IP networks that function as one large virtual network. Differs from the Internet by their lack of connectivity with the global Internet.

Internet: The worldwide network of networks and gateways that use the TCP/IP protocol suite and function as one virtual network; provides universal connectivity and three levels of network services: unreliable, connectionless packet delivery; reliable, full-duplex stream delivery; and application level services such as electronic mail that build on the first two. The Internet connects many universities, government research labs, military installations, and private businesses.

Internet architecture: A four-layered communications model that consists of the following: Application layer, Transport layer, Internet layer, and Network Interface layer.

Internet Architecture Board (IAB): The technical body that oversees the development of the Internet suite of protocols (commonly referred to as "TCP/IP"). It has a research task force and an engineering task force, each responsible for investigating a particular area.

Internet Autonomous System: A system that consists of a set of gateways, each of which can reach any other gateway in the same system using paths by means of gateways only in that system. The gateways of a system cooperatively maintain a routing database using an interior gateway protocol.

Internet Control Message Protocol (ICMP): An extension to the Internet Protocol; used by gateways to communicate with the network software in hosts.

Internet header length: An IP header field that indicates the number of 32-bit words making up the Internet header.

Internet layer: The layer in the TCP/IP network model where data is transferred between hosts across networks. Also referred to as Network Interface layer.

Internet number: See IP address.

Internet Protocol (IP): A connectionless best-effort packet switching protocol that resides in the Internet layer and has two major functions: internet addressing and fragmentation of messages.

interoperability: The ability of software and hardware on multiple machines from multiple vendors to communicate meaningfully.

InterNIC Registration Services: The Internet Network Information Center; organization that provides the Internet community with registration, directory, database and information services.

I/O status block (IOSB): A data structure associated with the $QIO system service. The IOSB holds information about how the I/O request completes.

IP: See Internet Protocol.

IP address: An address that identifies the connection between the network controller of a node using TCP/IP and the network cable. The 32-bit address is composed of two parts: network number and host number.

IP datagram: The basic unit of information passed across the Internet; contains source and destination addresses, the data, and fields that define the length of the datagram, the header checksum, and flags to say whether the datagram can be (or has been) fragmented. An IP datagram is to the Internet what a hardware packet is to a physical network. See also datagram.

IP trailer protocol: A protocol in which the protocol header follows the data.

KA9Q: A popular implementation of TCP/IP and associated protocols for amateur radio systems.

Kbps: See Kilobits per second.

kernel: The software that provides the standard API for application programs. Generally speaking, the kernel embodies the policy and structure of an operating system. In a narrower sense, the kernel provides a programmatic interface to any hardware resources available. In a UNIX system, the kernel is a program that contains the device drivers, the memory management routines, the scheduler, and system calls; always running while the system is operating.

Kilobits per second (Kbps or Kb/s): The measure of data transmission rate.

LAN: See local area network.

layer: (1) The grouping of related communication functions that provide a well defined service to a client independently of the protocols and other means used to provide it. (2) A software protocol levels that make up network architectures; each layer performs certain functions for the layers above and below it.

limited use protocol: A classification in Internet standards for protocols that are for use in limited circumstances; possibly due to their experimental state, specialized nature, limited functionality, or historic state.

line printer daemon (LPR/LPD): The UCX remote printing services for UNIX and OpenVMS client hosts.

line speed: The maximum rate at which data can be reliably transmitted over a line; varies with the capability of the modem or hardware device that performs the transmitting.

link: A directory entry referring to a file; one file may have several links to it.

little endian: The format for storage or transmission of binary data in which the least significant byte comes first. The reverse convention is called big endian.

local address: The address of a host within a subnet.

local area network (LAN): A self-contained group of computers and communications devices (such as modems, routers, servers, and repeaters) that offers a high-speed, reliable communications channel. LANs span a limited distance such as a building or group of buildings, but can be connected to wide area networks (WANs) with gateways. Contrast with wide area network (WAN).

local data: Any data stored locally by a system.

local network: A network directly attached to a host or gateway.

local node: A node at which the user is located.

local subnet: A subnet directly attached to a host or gateway.

logical connectivity: The ability of nodes to communicate.

logical link: A temporary connection between processes on source and destination nodes (or between two processes on the same node).

Logical Link Control: The upper portion of the Data Link layer that presents a uniform interface to the user of the data link service, usually the Internet layer.

loop node: A local node that is associated with a particular address and is treated as if it were a remote node. All traffic to the loop node is sent over the associated address; used for loopback testing.

loopback: A program that sends packets to a remote host on the Internet and looks for replies; works by means of the echoing facility provided by the ICMP protocol and is a way to determine if an Internet host is reachable from your host. See also packet internet groper.

LPR/LPD: See remote line printing or line printer daemon.

mail bridge: A mail gateway that forwards electronic mail between two or more networks while ensuring that the messages it forwards meet certain administrative criteria; specialized form of mail gateway that enforces an administrative policy with regard to what mail it forwards.

mail exchange record (MX record): The Domain Name Service resource record type indicating which host can handle mail for a particular domain or host.

mail exchanger (MX): The DIGITAL TCP/IP Services for OpenVMS implementation of a mail exchanger that allows hosts in a local network to forward mail to systems that might not be directly connected to the local network.

mail exploder: The part of an electronic mail delivery system that allows a message to be delivered to a list of addressees. Users send messages to one address (e.g., hacks@somehost.edu) and the mail exploder handles delivery to the individual mailboxes.

mail gateway: A host that connects two or more electronic mail systems (especially dissimilar mail systems on two different networks) and transfers messages between them.

mail path: A series of hosts used to direct electronic mail from one user to another.

Management Information Base (MIB): A database used by the Simple Network Management Protocol (SNMP) to check network statistics and configurations. An SNMP management station can query a MIB or set it in an SNMP agent (for example, router). Standard, minimal MIBs have been defined (MIB I, MIB II), and vendors often have custom entries. In theory, any SNMP manager can talk to any SNMP agent with a properly defined MIB.

Management Information Base II (MIB II): Data that can be accessed by a network management protocol; for UCX, the database maintained by a gateway running SNMP.

management station: The workstation of a human network manager running SNMP.

master file directory (MFD): The root of an OpenVMS file system on a particular physical device.

master server: The name server that is the authority for a specific domain space. See also BIND server.

maximum transmission unit (MTU): The largest possible unit of data that can be sent on a given physical medium. See also fragmentation.

MBUFs: See memory buffers.

memory buffers (MBUFs): The portions of memory that act as queues for data arriving at a port before the process is ready to claim that data.

message: A message block, or a series of message blocks, that constitute a logical grouping of information; each is delimited by communications control characters.

MFD: See master file directory.

MIB: See Management Information Base.

MIB II: See Management Information Base II.

MIME: Multipurpose Mail Extensions; a specification for the transfer of nontext files with regular Internet e-mail.

mode: A protection placed on a file.

modem (modulator/demodulator): A device that translates digital signals (electrical impulses) generated by a computer into analog signals (tones) that can be transmitted over telephone lines, and vice versa.

mount: An NFS process that makes a remote directory available to local users.

MTU: See maximum transmission unit.

multicast: A transmission of network traffic intended for multiple hosts (but not all connected hosts) within a network or internet.

multicast address: An address that designates a subset of nodes that are all listening for packets destined to this address.

multicast addressing: An addressing mode in which a data packet is targeted to a group of nodes that are of the same type, for example, all level 1 routers or all level 2 routers.

multihomed host: A host that has two or more hardware connections to a network; requires multiple IP addresses.

multiplexing: Using a single connection to carry several data streams and the mechanism for assigning these streams to that connection.

multipoint circuit: A circuit that connects multiple systems.

multiprocessing system: A network consisting of multiple processors.

MX record: See mail exchange record.

NAK: See negative acknowledgment.

name resolution: The process of mapping a host name to its corresponding address. See Domain Name Service.

namespace: A commonly distributed set of names in which all names are unique.

negative acknowledgment (NAK): The response to receipt of a corrupted packet of information. See also acknowledgment.

network: A group of computer systems that can communicate with each other; can be composed of computers in a single building (local area networks or LANs), or computers thousands of miles apart (wide area networks or WANs). The Internet is a worldwide collection of computer networks that can intercommunicate.

network address: A unique identifier of a specific system on a network, usually represented as a number or series of numbers. See also IP address.

network architecture: The specification of a network's functions and its parts, together with the ways in which the network is organized; specifies the layers of different functions in the network, ranging from data transmission at the lowest levels to user applications at the highest levels.

network class: A definition of the type of network addressing scheme being used; high-order bits in the network number designate the network class of the IP address.

network database: The UCX database that allows users to refer to networks by name rather than network number; contains network names, IP addresses for the networks, and any alias names for the networks.

network delay: The time it takes to get a unit of data from the source of a transmission to the destination; usually refers to delay from the network and not by system-dependent application processing delays at source and destination nodes.

network diameter: The distance (number of hops) between the two nodes in the network with the greatest reachability distance. The reachability distance is the path with fewest number of hops between two nodes.

Network File System (NFS): A protocol developed by Sun Microsystems that allows a computer system to access files over a network as if they were on its local disks.

Network Information Service (NIS): A set of services in the Network File System that propagate information out from masters to recipients; used for the maintenance of system files on complex networks.

Network Interface layer: The layer in the TCP/IP architecture model that provides the mechanism for connecting the hosts to the networks.

network management: See MIB II and Simple Network Management Protocol (SNMP).

network mask: A mask used to determine the subnet in the IP address; each bit that is turned on (binary one) in the mask is interpreted as part of the network and subnet address. Synonymous with subnet mask.

network meltdown: The state of complete network overload; the network equivalent of thrashing. See also broadcast storm.

network number: The part of an IP address that designates the network to which the destination host belongs.

network performance: The description of how a network performs, as measured against the expectations or requirements of users, customers, designers, or implementors, or as claimed by sales and marketing personnel. The criteria for network performance include parameters such as throughput, response time, and resource utilization.

network status notification: Information about the state of logical and physical links over which two tasks communicate. A nontransparent task can use this information to take appropriate action under conditions such as third-party disconnections and a partner's exiting before I/O completion.

network task: A nontransparent task that can process multiple inbound connection requests; that is, it has a declared network name or object number.

Network Time Protocol (NTP): The protocol that ensures accurate local timekeeping with reference to radio and atomic clocks located on the Internet; capable of synchronizing distributed clocks within milliseconds over long time periods.

NFS: See Network File System.

NFS client: The software that requests remote file services from an NFS server. Client system users access files that physically reside on an NFS server system.

NFS server: The software that provides remote file services to NFS clients.

NFS server (OpenVMS server): A computer system that offers services to NFS clients within an Internet environment; can be a single host, a whole OpenVMS cluster system, or members of an OpenVMS cluster system.

NIS: See Network Information Service.

nobody: A UNIX convention used when file ownership is not known; maps to an account with a UID and GID of --2.

node: (1) A system on a network; also referred to as a host. (2) One member in an OpenVMS cluster system.

node address: The required unique numeric identification of a specific node in the network.

node name: The alphanumeric identification associated with the node address for one-to-one mapping.

nonadjacent nodes: Nodes without direct lines between them; can communicate only if intermediate systems forward the data along the path between the source and the destination.

nontransparent task: A form of device-dependent I/O that uses system services for network-specific functions; can initiate and complete a logical link connection, exchange messages between two tasks, and terminate the communication process. Application that has direct access to network-specific information and operations, such as optional user data on connects and disconnects and interrupt messages, to monitor the communications process; can receive and process multiple inbound connection requests.

normalization: The estimation of the change in a counter value over a specified time period.

nslookup: The DIGITAL TCP/IP Services for OpenVMS utility that allows you to interactively query domain name servers (BIND servers) and helps you set up and manage the BIND server software.

NTP: See Network Time Protocol.

null modem: A simple form of modem connection where only the data interchange circuits, and not the modem control circuits, are used.

octet: A single 8-bit unit of data; used in networking (rather than bytes) because some systems have bytes that are not 8 bits long.

open network: A network made up of nonproprietary, interoperable systems.

open system: A nonproprietary, interoperable system with communications software.

Open System Interconnection (OSI): A suite of protocols, designed by ISO committees, to be the international standard of computer network architecture.

OpenVMS cluster: A configuration of OpenVMS processors.

OpenVMS cluster alias: An alias that allows remote hosts to address the cluster members as one host, as well as any cluster member individually.

OpenVMS file system: The OpenVMS files and directories on a mounted OpenVMS volume. These files and directories reside on a Files-11 On-Disk Structured (ODS-2) disk.

origination: The beginning point of communications on a circuit.

packet: A unit of data sent across a network.

Packet Internet Groper (PING): A program used to test reachability of a destination by sending an ICMP echo request and waiting for a reply. See also loopback.

packet looping: A condition in which a packet revisits a node. See also aged packet.

packet size: The amount of data in a packet.

packet switching: A communication paradigm in which packets are individually routed between hosts, with no previously established communication path.

path: The physical lines between source nodes and destination nodes; can comprise a sequence of connected nodes. The path that the data takes through the network is transparent to users.

path cost: The sum of the circuit costs along a path between two nodes.

path length: The total distance (the number of circuits) between a source node and a destination node, measured in hops. Each line between systems, including routing nodes and end nodes, equals one hop. See also network diameter.

path name: A unique designation that identifies a directory or subdirectory. UNIX path names are composed of a series of fields separated by slashes (/); each field designates a file name that is uniquely contained in the previous field (directory).

path splitting: The ability to split the transmission load destined for a single node over several paths of equal path cost. Any destination node receiving data that has been split over several paths must support out-of-order packet caching.

PC-NFS Daemon: The server software that handles authentication and printing requests from personal computer implementations of NFS.

physical address: A unique address of each physical connection of a node to the physical medium.

physical connection: The Physical layer communications path between two systems.

physical connectivity: The Physical layer connectivity that is a result of nodes being attached to each other via active lines and nodes.

PING: See Packet Internet Groper.

point-to-point circuit: A circuit that connects only two nodes. A point-to-point configuration requires a separate physical connection between each pair of nodes. Point-to-point systems communicate directly with other systems. Contrast with multipoint circuit.

point-to-point line: A line that connects two systems by using a single circuit.

Point-to-Point Protocol (PPP): A method for transmitting datagrams over serial point-to-point lines where a line is established between a remote host (usually over a telephone line) and another host acting as a gateway to a remote host.

polling: Connecting to another system to check for things such as mail or news.

POP: See Post Office Protocol.

port: The end point of a communication link between two processes.

Portmapper Service: A service that client programs can use to determine the port number that another service uses. Clients use the Portmapper Service for NFC, PC-NFS, and RPC applications.

post: To send a message to a mailing list or newsgroup. Distinguished in context from "mail."

Post Office Protocol (POP): The TCP/IP-based protocol for client stations to read mail from a server.

PPP: See Point-to-Point Protocol.

primary server: A BIND name server that maintains the database for a zone; secondary servers copy their information from primary servers. See also BIND server, cache server, forwarder server, and secondary server.

printcap database: The DIGITAL TCP/IP Services for OpenVMS database that maps local queues to printers on remote hosts; specifies local queues for LPD printing from remote hosts.

privileged port: A port in which the remote host has done some level of checking against the application using the port; privileged port numbers range from 1 to 1023.

process: The context within a system in which a specific computing session occurs; provides the context in which an application executes.

protocol: A set of rules that controls the communications between computers. Also, a set of conventions between communicating processes regarding the format and contents of messages to be exchanged.

Protocols can describe low-level details of machine-to-machine interfaces, such as the order in which the bits from a byte are set across a wire, or high-level exchanges between applications programs such as the way in which two programs transfer a file across the Internet.

protocol data unit (PDU): The unit of data sent across a network. Also called a packet.

protocol machine: The set of data structures and routines that implements a specific protocol and controls the progress of a communication between peer entities.

protocol overhead: The part of communications data or processing not directly consumed by the users but necessary to successfully bring about the transfer of user information.

protocol port: An abstraction that transport protocols use to distinguish among multiple destinations within a given host computer. Internet protocols identify ports using small positive integers. Usually the operating system allows an application program to specify which port it wants to use. Some ports are reserved for standard services such as electronic mail.

protocol transparency: The quality in a communications device or system that allows various higher-level protocols to coexist on the same wire. The protocols are transparent to the device or system.

protocol sequence: An ordered list of protocol identifiers.

protocol stack: The set of functions, one at each layer of the protocol stack, that work together to form a set of network services; each layer of the protocol stack uses the services of the module beneath it.

protocol transparency: The degree to which users of underlying protocols are aware of the specifics of those protocols.

proxy: The mechanism whereby one system acts on behalf of another system in responding to protocol requests. UCX uses a proxy mechanism to provide an OpenVMS identity (account) for each UNIX client by adding the name and identification codes of the client to a proxy database.

proxy ARP: The technique in which one machine, usually a router, answers Address Resolution Protocol (ARP) requests intended for another machine. By "faking" its identity, the router accepts responsibility for routing packets to the "real" destination. Proxy ARP allows a site to use a single IP address with two physical networks. Creating a subnet would normally be a better solution.

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