socket pair: The client IP address and port number, and the server IP address and port number that uniquely identify a TCP connection.

socket API: An application programming interface for implementing TCP/IP protocols. Sometimes called Berkely sockets indicating where the API was developed.

source: The IP header field that contains the IP address of the datagram's point of origin.

source port: A 2-octet value in the TCP or UDP header field that identifies the upper-level application or protocol associated with the data in the segment.

spanning tree: A logical arrangement created by bridges in an extended LAN in which all LANs are connected and there are no loops.

split horizon: When a router (or group of routers work together) accepts routing information from multiple external networks, but does not pass on information learned from one external network to others. This is an attempt to prevent false routes to a network from being propagated because of gossip or counting to infinity.

splitting: The process of mapping one transport connection to several network connections.

stateless: A characteristic of a server designed to simplify crash recovery after a server crashes and reboots. The server does not keep track of the status of ongoing client interactions. Servers that do not keep track of client status are called stateless servers.

static routing: A routing method by which a system manager manually adds routes to the kernel's routing table. This method is generally used on small networks. On Open VMS systems, you use the SET ROUTE command to add static routes and on UNIX systems, you use the route command.

step: To change the time of a clock to the correct time with no intermediate adjustments. Compare with ``slew''.

stratum: The distance a host running the NTP time daemon is from an external source of Coordinated Universal Time (UTC). A stratum 1 server has direct access to an external source of UTC, such as a radio clock synchronized to a standard time signal broadcast. In general, a stratum n server is n-1 network hops away from a stratum 1 server. For example, a stratum 4 server is 3 hops away from a stratum 1 server. Also, a stratum n server is at a higher stratum than a stratum n-1 server. For example, a stratum 3 server is at a higher stratum than a stratum 2 server, and at a lower stratum than a stratum 4 server. See also ``time daemon''.

stream-oriented: The type of transport service that allows its client to send data in a continuous stream; guarantees that all data will be delivered to the other end in the same order as sent and without duplicates. Also known as a reliable transport service.

Structure of Management Information (SMI): The rules used to define the objects that can be accessed by means of a network management protocol. See also Management Information Base.

subnet: An organization of hosts within a network into logical groups. A network can be comprised of several subnets. The portion of a network, which might be a physically independent network, that shares a network address with other portions of the network and is distinguished by a subnet number. A subnet is to a network what a network is to an internet.

subnet address: A part of the Internet addressing scheme. If a site uses a single IP address for multiple physical networks, there is one subnet address for each physical network. Each such address is composed of the network part of the full address and part of the local part (host).

subnet field: A bit field in an IP address that denotes the subnet number. The bits making up this field are not necessarily contiguous in the address.

subnet mask: A method of representing the portion of the IP network address that is devoted to subnet address. Each bit that is turned on (binary one) in the mask is interpreted as part of the network and subnet address. Synonymous with network mask. See address mask.

Sun Remote Procedure Call (RPC) : An easy and popular paradigm for implementing the client/server model of distributed computing. In general, the local system (client) sends a request to a remote system (server) to execute a designated procedure, using supplied arguments, and the remote system returns the result to the local system.

superuser: A UNIX user who has been granted special privileges; has an effective UID of 0.

symbiont: A process that transfers record-oriented data to and from a mass storage device; for example, from disks to printers.

Synonym for daemon.

symbolic link: In the UNIX file system, a symbolic link is a file that contains a pointer to another file or directory. The link (also called a soft link) may be created across a different UNIX file system. Any changes to the file can be seen when you access the file through the file name or through the symbolic link. If you delete the file, the symbolic link will point to a nonexistent file.

synchronous transmission: Data transmission in which characters are transmitted at a fixed rate. The transmitter and receiver are synchronized, gaining greater efficiency than in asynchronous transmission. Synchronous transmissions send a predetermined group of "sync" characters ahead of a long stream of data. The sync characters enable the communicating devices to synchronize with each other in accordance with a time clock at each end. Contrast with asynchronous transmission.

syntax: The rules for formatting/interpreting data.

TAC: See terminal access controller.

target system: The intended destination of messages.

TCP: See Transmission Control Protocol.

TCP/IP: An Internet suite of protocols. See also Transmission Control Protocol and Internet Protocol.

TELNET: An Internet protocol for remote terminal connection. TELNET allows a user at one site to interact with remote timesharing systems at another site as if the user's terminal were directly connected to the remote host.

terminal access controller (TAC): A program and hardware that connects terminals to the Internet, usually using dialup modem connections.

terminal emulator: A program that allows a computer to emulate a terminal; a workstation thus appears as a terminal to the host.

terminal server: A device that handles terminal operations for host nodes on a LAN; can be used to connect terminal users to nodes on the same LAN and to users on nodes located off the LAN. Off-loads the terminal connection and I/O responsibilities from host nodes, and reduces the number of direct terminal connections to each host, thus saving substantial power, packaging, and cabling expense.

terminating packet: A packet whose destination is the local node.

TFTP: See Trivial File Transport Protocol.

thread: (1) A request from an NFS client to the NFS server. (2) A single unit of execution within a program.

throughput: A measure of how much data is sent, or can be sent, between two points in a specified unit of time; often used in either of two contexts:

• Rated throughput, which refers to the bandwidth or capacity of a component
• Real throughput, which refers to actual measured throughput.

time: A time value, usually a time interval. It may be specified in any one of the following forms:

number A non-negative decimal number of seconds. For example, 27, 60, or 3600. number:number A non-negative decimal number of minutes followed by a seconds value in the range of zero to 59, inclusive. For example, 0:27, 1:00, or 60:00. number:number:number A non-negative decimal number of hours followed by a minutes value in the range of zero to 59, inclusive, followed by a seconds value in the range of zero to 59, inclusive. For example, 0:00:27, 0:01:00, or 1:00:00.

time to live (TTL): A field in the IP header that indicates how long this packet should be allowed to be forwarded to other routers before being discarded.

The Time To Live (TTL) of an IP packet. Valid values are from 1 to 255 inclusive.

time daemon: The program running on a host that synchronizes the host's hardware clock to Coordinated Universal Time in accordance with the protocols known as the Network Time Protocol.

timeo: A timeout option for the NFS mount command.

TN3270: TELNET options that allows TELNET users to connect to hosts that support 3270 model terminals.

token ring: A type of LAN that has stations wired in a ring, where each station constantly passes a special message (a "token") on to the next; technically referred to as IEEE 802.5.

topology: The architecture of a network. A network topology shows the computers and the links between them within a network.

TOS (type of service) : The type of service is for internet service quality selection. The TOS is specified along the abstract parameters precedence, delay, throughput, reliability, and cost. These abstract parameters are to be mapped into the actual service parameters of the particular networks the datagram traverses. The vast majority of IP traffic today uses the default type of service.

traffic: The measurement of data flow, volume, and velocity over a communications link.

transceiver: Transmitter-receiver; a physical device required in baseband networks that takes the digital signal from a computer or terminal and imposes it on the baseband medium; connects a host interface to a LAN, such as Ethernet.

transient information: Network management information carried in an operation; is meaningful only while the operation is being performed.

transit network: A network that passes traffic between networks in addition to carrying traffic for its own hosts; must have multiple connections to the internet.

Transmission Control Protocol (TCP): A Transport layer protocol that provides the reliable, full-duplex, stream service on which many application protocols depend. TCP allows a process on one host to send a stream of data to a process on another. It is connection-oriented in the sense that before transmitting data, participants must establish a connection.

Transmission Control Protocol/Internet Protocol (TCP/IP): The acronym for the suite of application and transport protocols that run over IP, for example, FTP, TELNET, and UCP as well as TCP and IP themselves.

Transport layer: The layer in the TCP/IP architecture model where network traffic is passed between an application on one host and an application on another host.

Trivial File Transport Protocol (TFTP): The Internet protocol for file transfer with minimal capability and minimal overhead. The simple design of the facility is intended for use in application environments that do not require complex interactions among clients and servers. TFTP is a simple service running on top of UDP, using timeout and retransmission to ensure that data arrives. The sending side transmits a 512-byte, fixed-size file, and awaits an acknowledgment for each block before sending the next. The receiver acknowledges each block. See also File Transfer Protocol.

TTL: See Time to Live.

tunneling: The encapsulation of protocol A within protocol B such that A treats B as though it were a Network Interface layer. Used to get data between administrative domains that use a protocol not supported by the internet connecting those domains.

UAF: See user authorization file.

UCP: See Management Control Program.

Management Control Program: The DIGITAL TCP/IP Services for OpenVMS network management control software; includes a command-line interface.

UDP: See User Datagram Protocol.

UID: See user identification.

UNIX style file system: An OpenVMS organization of files based on the UNIX operating system.

UNIX-to-UNIX Copy Program (UUCP): A program that allows one UNIX system to copy files to or from another UNIX system.

upline dumping: A TFTP server function allowing a TFTP client to transfer data or a program image to the TFTP server's public directories. The opposite function of downline loading.

user authorization file (UAF): An OpenVMS file that contains account names and their associated attributes.

User Datagram Protocol (UDP): An Internet transport protocol. A connectionless, unreliable Transport layer protocol for the exchange of requests and replies between networked hosts. UDP, like TCP, uses IP for message delivery from one host to another; however, unlike TCP, UDP provides for exchange of datagrams without acknowledgments or guaranteed delivery of data. Each UDP message contains the data sent by a user process, a destination port number, and a source port number.

user identification (UID): A unique number that identifies a user of a UNIX system. The number along with an associated group identification number (GID) determines file access privileges. Accounting statistics and other collected information also tracts by UID.

UUCP: See UNIX-to-UNIX Copy Program.

virtual circuit: The network service that allows two processes to communicate as if they were directly connected, regardless of the structure of the underlying subnet.

WAN: See wide area network.

well-known port: A port number assigned for use by a specific network application for connections made with either UDP or TCP. Every implementation of TCP/IP that provides well-known services provides them with the well-known port numbers from 1 to 1023. The Internet Assigned Numbers Authority (IANA) manages the well-known port numbers.

wide area network (WAN): A network, usually constructed with serial lines, which covers large geographic areas.

wildcarding: A method for generalizing parts of a OpenVMS file designation to encompass a set of files by substituting a symbol to represent one or more characters. OpenVMS wildcarding symbols are % (for one character) and * (for a character string of any length, including zero).

window: A 2-octet field in a TCP header indicating the number of data octets (relative to the acknowledgment number in the header) that the sender is currently willing to accept.

write access: An Access right that grants users the ability to change data.

zone: A subdivision of the Internet hierarchy that starts at a domain and extends down to leaf domains (individual host names) or to domains where other zones begin; usually represents an administrative boundary. Contrast with domain.

zone file: A master name server file that describes the domain names for which the server has authority.

G.2 Acronyms

Table 1 Acronyms

Acronym	Meaning
ACK	acknowledgment
ACL	access control list
ACP	ancillary control process
ANSI	American National Standards Institute
API	application programming interface
ARP	Address Resolution Protocol
ASCII	American Standard Code for Information Interchange
ATM	asynchronous transfer mode
BBS	Bulletin Board System
BGP	Border Gateway Protocol
BIND	Berkeley Internet Name Domain
BOOTP	Bootstrap Protocol
bps	bits per second
BSD	Berkeley Software Distribution
CFS	container file system
CFSRTL	container file system run-time library
CSLIP	Compressed Serial Line Internet Protocol
DCE	Distributed Computing Environment
DCL	Digital Command Language
DEK	data encryption key
DES	data encryption standard
DNS	Domain Name Service
eSNMP	extensible Simple Network Management Protocol
EGP	External Gateway Protocol
FDDI	Fiber Distributed Data Interface
EOF	end of file
EOL	end of line
FQDN	fully qualified domain name
FTP	File Transfer Protocol
GID	group identification (UNIX)
IAB	Internet Architecture Board
ICMP	Internet Control Message Protocol
IGP	Internal Gateway Protocol
InterNIC	Internet Network Information Center
IP	Internet Protocol
ISDN	Integrated Services Digital Networks
IVP	installation verification procedure
Kbps	kilobits per second
LAN	local area network
LPD	line printer daemon
LPR	remote line printing
MBUF	memory buffer
MFD	master file directory
MIB	Management Information Base
MIBII	Management Information Base II
MTU	maximum transmission unit
MX	mail exchanger
NAK	negative acknowledgment
NFS	Network File System
NIS	Network Information Service
NOC	Network Operations Center
NTP	Network Time Protocol
PDU	protocol data unit
PING	packet internet groper
POP	Post Office Protocol
PPP	Point-to-Point Protocol
PSDN	Packet Switching Data Network
PWIP	PATHWORKS Internet Protocol
RARP	Reverse Address Resolution Protocol
RCP	remote copy
REXEC	remote execute
RFC	Request for Comments
RLOGIN	remote login
RIP	Routing Information Protocol
RMS	Record Management Services
RPC	remote procedure call
RSH	remote shell
RTL	run-time library
RTT	round-trip time
SLIP	Serial Line Internet Protocol
SMI	structure of management information
SMTP	Simple Mail Transfer Protocol
SNMP	Simple Network Management Protocol
TAC	terminal access controller
TCP	Transmission Control Protocol
TCP/IP	Transmission Control Protocol/Internet Protocol
TFTP	Trivial File Transport Protocol
TP	Time Protocol
TTL	time to live
UAF	user authorization file
UCP	Management Control Program
UDP	User Datagram Protocol
UID	user identification (UNIX)
UTC	Coordinated Universal Time
UUCP	UNIX-to-UNIX Copy Program
WAN	wide area network
WKS	Well Known Server
XDR	external data representation