Glossary
- ACK
- A control bit (acknowledge) occupying no sequence space, which
indicates that the acknowledgment field of this segment specifies
the next sequence number the sender of this segment is expecting to
receive, hence acknowledging receipt of all previous sequence numbers.
- address
- The unique code assigned to each device or workstation connected
to a network. A standard IPv4 address is a 32-bit address field containing
two parts. The first part is the network address, and the second part
is the host number. An IPv6 address is a 128-bit address field that
supports a much higher number of addresses than IPv4, and IPv6 addresses
also support additional features like multicast and anycast addressing.
- advisor
- Advisors collect and analyze feedback from individual
servers, and inform the manager function.
- agent
- In systems management, a user that, for a particular interaction,
has assumed an agent role.
- An entity that represents one or more managed objects by (a) emitting
notifications regarding the objects and (b) handling requests from
managers for management operations to modify or query the objects.
- alias
- An additional name assigned to a server. The alias makes the server
independent of the name of its host machine. The alias must be defined
in the domain name server.
- API
- Application programming interface. The interface (calling
conventions) by which an application program accesses operating system
and other services. An API is defined at source code level and provides
a level of abstraction between the application and the kernel (or
other privileged utilities) to ensure the portability of the code.
- backup
- In a high availability configuration, this is the partner of the
primary machine. It monitors the status of the primary machine and
takes over if necessary. See also high availability, primary.
- bandwidth
- The difference between the highest and lowest frequencies of a
transmission channel. This is the amount of data that can be sent
through a given communication circuit per second.
- begin range
- In rules-based load balancing, a lower value specified on a rule.
The default for this value depends on the type of rule.
- binary logging
- Allows server information to be stored in binary files, and then
be processed to analyze the server information that is gathered over
time.
- Caching proxy
- A caching proxy server that can help speed up end-user
response time through highly-efficient caching schemes. Flexible PICS
filtering helps network administrators control access to Web-based
information at one central location.
- CGI
- Common Gateway Interface. A standard for the exchange of information
between a Web server and an external program. The external program
can be written in any language supported by the operating system,
and performs tasks not usually done by the server, such as forms processing.
- CGI script
- A CGI program written in a scripting language such as Perl or
REXX that uses the Common Gateway Interface to perform tasks not usually
done by the server, such as forms processing.
- client
- A computer system or process that requests a service of another
computer system or process. For example, a workstation or personal
computer requesting HTML documents from a Lotus® Domino® Go
Webserver is a client of that server.
- cluster
- A group of TCP or UDP servers that are used for the same purpose
and are identified by a single hostname. See also cell.
- cluster address
- The address to which clients connect.
- clustered server
- A server that Load Balancer groups with other servers into a single,
virtual server. Load Balancer balances TCP or UDP traffic among these
clustered servers.
- consultant
- Collects server metrics from the servers that are being load balanced
and sends server weight information to the switch that performs the
load balancing.
- controller
- A collection of one or more consultants.
- cross port affinity
- Cross port affinity is the affinity (sticky) feature
expanded to cover across multiple ports. See also sticky time.
- daemon
- Disk And Execution Monitor. A program that is not involved explicitly,
but lies dormant waiting for some condition(s) to occur. The idea
is that the perpetrator of the condition need not be aware that a
daemon is lurking (though often a program will commit an action only
because it knows that it will implicitly invoke a daemon).
- default
- A value, attribute, or option that is assumed when none is explicitly
specified.
- destination address
- The address of the high availability partner machine to which
heartbeats and responses are sent.
- Dispatcher
- A component of Load Balancer that efficiently balances
TCP or UDP traffic among groups of individual linked servers. The
Dispatcher machine is the server running the Dispatcher code.
- domain name server
- DNS. A general-purpose distributed, replicated, data query service
chiefly used on Internet for translating hostnames into Internet addresses.
Also, the style of hostname used on the Internet, though such a name
is properly called a fully qualified domain name. DNS can be configured
to use a sequence of name servers, based on the domains in the name
being looked for, until a match is found.
- dotted-decimal notation
- The syntactical representation for a 32-bit integer that consists
of four 8-bit numbers, written in base 10 and separated by periods
(dots). It is used to represent IPv4 addresses.
- dscontrol
- Provides the interface to the Dispatcher component of Load Balancer.
- dsserver
- Handles the requests from the command line to the executor, manager,
and advisors.
- end range
- In rules-based load balancing, a higher value specified on a rule.
The default for this value depends on the type of rule.
- Ethernet
- A standard type of local area network (LAN). It allows multiple
stations to access the transmission medium at will without prior coordination,
avoids contention by using carrier sense and deference, and resolves
contention by using collision detection and transmission. Software
protocols used by Ethernet systems vary, but include TCP/IP.
- executor
- One of several functions. The executor routes requests
to the TCP or UDP servers, and also monitors the number of new, active,
and finished connections and does garbage collection of completed
or reset connections. The executor supplies the new and active connections
to the manager function.
- FIN
- A control bit (finis) occupying one sequence number, which indicates
that the sender will send no more data or control occupying sequence
space.
- FIN state
- The status of a transaction that has finished. When a transaction
is in FIN state, the garbage collector can clear the memory reserved
for the connection.
- Firewall
- A computer that connects a private network, such as a business,
to a public network, such as the Internet. It contains programs that
limit the access between two networks. See also proxy gateway.
- FQDN
- Fully Qualified Domain Name. The full name of a system, consisting
of its local hostname and its domain name, including a top-level
domain (tld). For example, "venera" is a hostname and "venera.isi.edu"
is an FQDN. An FQDN should be sufficient to determine a unique Internet
address for any host on the Internet. This process, called "name
resolution", uses the Domain Name System (DNS).
- FTP (File Transfer Protocol)
- An application protocol used for transferring files to and from
network computers. FTP requires a user ID and sometimes a password
to allow access to files on a remote host system.
- gateway
- A functional unit that interconnects two computer networks with
different architectures.
- GRE
- Generic Routing Encapsulation. A protocol which allows an arbitrary
network protocol A to be transmitted over any other arbitrary protocol
B, by encapsulating the packets of A within GRE packets, which in
turn are contained within packets of B.
- heartbeat
- A simple packet sent between two machines in high availability
mode used by the standby machine to monitor the health of the active
machine.
- high availability
- A feature in which one Load Balancer machine can take over the
function of another, if the primary machine is no longer available.
- host
- A computer, connected to a network, that provides an access point
to that network. A host can be a client, a server, or both simultaneously.
- host name
- The symbolic name assigned to a host. Host names are resolved
to IP addresses through a domain name server.
- HTML (Hypertext Markup Language)
- The language that is used to create hypertext documents. Hypertext
documents include links to other documents that contain additional
information about the highlighted term or subject. HTML controls the
format of text and position of form input areas, for example, as well
as the navigable links.
- HTTP (Hypertext Transfer Protocol)
- The protocol used to transfer and display hypertext documents.
- HTTPS (Hypertext Transfer Protocol, Secure)
- The protocol used to transfer and display hypertext documents
using SSL.
- ICMP
- Internet Control Message Protocol. A message control
and error-reporting protocol between a host server and a gateway to
the Internet.
- IMAP
- Internet Message Access Protocol. A protocol allowing
a client to access and manipulate electronic mail messages on a server.
It permits manipulation of remote message folders (mailboxes), in
a way that is functionally equivalent to local mailboxes.
- Internet
- The worldwide collection of interconnected networks that use the
Internet suite of protocols and permit public access.
- intranet
- A secure, private network that integrates Internet standards and
applications (such as Web browsers) with an organization's existing
computer networking infrastructure.
- IP
- Internet Protocol. A connectionless protocol that routes data
through a network or interconnected networks. IP acts as an intermediary
between the higher protocol layers and the physical layer.
- IP address
- Internet Protocol address. The unique address that specifies the
actual location of each device or workstation in a network. It is
also known as an Internet address.
- IPSEC
- Internet Protocol Security. A developing standard for
security at the network or packet processing layer of network communication.
- LAN
- Local Area Network. A computer network of devices connected
within a limited geographical area for communication and which can
be connected to a larger network.
- loopback alias
- An alternative IP address associated with the loopback
interface. The alternative address has the useful side affect of not
advertising on a real interface.
- loopback interface
- An interface that bypasses unnecessary communications functions
when the information is addressed to an entity within the same system.
- MAC address
- Media Access Control address. The hardware address of
a device connected to a shared network medium.
- managed node
- In Internet communications, a workstation, server, or router that
contains a network management agent. In the Internet Protocol (IP),
the managed node usually contains a Simple Network Management Protocol
(SNMP) agent.
- manager
- Sets weights of servers based on internal counters in
the executor and feedback that is provided by the advisors. The executor
then uses the weights to perform load balancing.
- mark down
- To break all active connections to a server and stop any new connections
or packets from being sent to that server.
- mark up
- To allow a server to receive new connections.
- metric
- A process or command that returns a numeric value that
can be used in load balancing on the network, for example, the number
of users currently logged on.
- metric address
- The address where the metric server connects.
- metric collector
- Resides in the consultant and is responsible for collecting a
metric or metrics.
- Metric Server
- Formerly known as Server Monitor Agent (SMA). Metric
server provides system specific metrics to the manager.
- MIB
- Management Information Base. A collection of objects that can
be accessed by means of a network management protocol.
- A definition for management information that specifies the information
available from a host or gateway and the operations allowed.
- netmask
- For IPv4, a 32–bit mask used to identify the subnetwork address
bits in the host portion of an IP address.
- network
- Hardware and software data communication system. Networks are
often classified according to their geographical extent, local area
network (LAN), metropolitan area network (MAN), wide area network
(WAN) and also according to the protocols used.
- Network Address Translation
- NAT, or Network Address Translator, Virtual LAN. A hardware device
currently being developed and used to extend the Internet addresses
already in use. It allows duplicate IP addresses to be used within
a corporation and unique addresses outside.
- Network Address Port Translation
- NAPT, also known as port mapping. This allows you to configure
multiple server daemons within one physical server to listen on different
port numbers.
- network management station
- In the Simple Network Management Protocol (SNMP), a station that
runs management application programs that monitor and control network
elements.
- network proximity
- The proximity of two networked entities, such as a client and
server, which determines by measuring round-trip time.
- NFA (nonforwarding address)
- The primary IP address of the machine, used for administration
and configuration.
- NIC
- Network Interface Card. An adapter circuit board installed in
a computer to provide a physical connection to a network.
- NNTP
- Network News Transfer Protocol. A TCP/IP protocol for transferring
news items.
- packet
- The unit of data that is routed between an origin and
a destination on the Internet or any other packet-switched network.
- PICS
- Platform for Internet Content Selection. PICS-enabled
clients allow the users to determine which rating services they want
to use and, for each rating service, which ratings are acceptable
and which are unacceptable.
- ping
- A command that sends Internet Control Message Protocol (ICMP)
echo-request packets to a host, gateway, or router with the expectation
of receiving a reply.
- POP3
- Post Office Protocol 3. A protocol used for exchanging network
mail and accessing mailboxes.
- port
- A number that identifies an abstracted communication device. Web
servers use port 80 by default.
- primary
- In a high availability configuration, the machine that starts
out as the machine actively routing packets. Its partner, the backup
machine, monitors the status of the primary machine and takes over
if necessary. See also backup, high availability.
- priority
- In rules-based load balancing, the level of importance placed
upon any given rule. The evaluates rules from the first priority
level to the last priority level.
- private network
- A separate network on which Load Balancer communicates
with clustered servers for performance reasons.
- protocol
- The set of rules governing the operation of functional units of
a communication system if communication is to take place. Protocols
can determine low-level details of machine-to-machine interfaces,
such as the order in which bits from a byte are sent; they can also
determine high-level exchanges between application programs, such
as file transfer.
- Quality of Service (QoS)
- The performance properties of a network service, including throughput,
transit delay and priority. Some protocols allow packets or streams
to include QoS requirements.
- quiesce
- To end a process by allowing operations to complete normally.
- reach
- An advisor that issues pings to a given target and reports whether
that target is responding.
- reach address
- In a high availability configuration, the address of the target
to which the advisor should issue pings to see if the target is responding.
- return address
- A unique IP address or hostname. It is configured on the Load
Balancer machine and used as its source address when load balancing
the client's request to the server.
- RMI
- Remote Method Invocation. Part of the Java™ programming
language library which enables a Java program
running on one computer to access the objects and methods of another Java program running on a different computer.
- root user
- The unrestricted authority to access and modify any part
of the AIX®, Red Hat Linux,
or Solaris operating system, usually associated with the user who
manages the system.
- route
- The path of network traffic from origin to destination.
- router
- A device which forwards packets between networks. The forwarding
decision is based on network layer information and routing tables,
often constructed by routing products.
- RPM
- Red Hat Package Manager.
- rule
- In rules-based load balancing, a mechanism for grouping servers
such that a server can be chosen based on information other than the
destination address and port.
- rule type
- In rules-based load balancing, an indicator of the information
that should be evaluated to determine whether a rule is true.
- scalable
- Pertaining to the capability of a system to adapt readily to a
greater or lesser intensity of use, volume, or demand. For example,
a scalable system can efficiently adapt to work with larger or smaller
networks performing tasks of varying complexity.
- server
- A computer that provides shared services to other computers over
a network; for example, a file server, a print server, or a mail server.
- server address
- The unique code assigned to each computer that provides shared
services to other computers over a network; for example, a file server,
a print server, or a mail server. The server address can be either
the IP address or the host name.
- server machine
- A server that Load Balancer groups with other servers into a single,
virtual server. Load Balancer balances traffic among the server machines.
Synonymous with clustered server.
- service
- A function provided by one or more nodes; for example, HTTP, FTP,
Telnet.
- shell
- The software that accepts and processes command lines
from a user's workstation. The bash shell is one of several UNIX shells
available.
- site name
- A site name is an unresolvable host name that the client will
request. For example, a web site has 3 servers (1.2.3.4, 1.2.3.5,
and 1.2.3.6) configured for site name www.dnsload.com. When
a client requests this site name, one of the three server IP addresses
will be returned as the resolution. The site name must be a fully
qualified domain name, for example: dnsload.com. An unqualified
name, for example, dnsload is invalid for a site name.
- Site Selector
- A DNS-based load balancing component of . Site Selector
balances the load on servers within a wide area network (WAN) using
measurements and weights that are gathered from the Metric Server
component running on those servers.
- SMTP
- Simple Mail Transfer Protocol. In the Internet suite of protocols,
an application protocol for transferring mail among users in the Internet
environment. SMTP specifies the mail exchange sequences and message
format. It assumes that the Transmission Control Protocol (TCP) is
the underlying protocol.
- SNMP
- Simple Network Management Protocol. The Internet standard protocol,
defined in STD 15, RFC 1157, developed to manage nodes on an IP network.
SNMP is not limited to TCP/IP. It can be used to manage and monitor
all sorts of equipment including computers, routers, wiring hubs,
toasters and jukeboxes.
- source address
- In a high availability configuration, the address of the high
availability partner machine that sends heartbeats.
- SPARC
- Scalable processor architecture.
- sscontrol
- Provides the interface to the Site Selector component of .
- SSL
- Secure Sockets Layer. A popular security scheme developed by Netscape
Communications Corp. along with RSA Data Security Inc. SSL allows
the client to authenticate the server and all data and requests to
be encrypted. The URL of a secure server protected by SSL begins with
https (rather than HTTP).
- sticky time
- The interval between the closing of one connection and the opening
of a new connection during which a client will be sent back to the
same server used during the first connection. After the sticky time,
the client may be sent to a server different from the first.
- strategy
- In a high availability configuration, a keyword for specifying
how recovery takes place following the failure of the active machine.
- subnet mask
- For IPv4, a 32–bit mask used to identify the subnetwork address
bits in the host portion of an IP address.
- SYN
- A control bit in the incoming segment, occupying one sequence
number, used at the initiation of a connection, to indicate where
the sequence numbering will start.
- TCP
- Transmission Control Protocol. A communications protocol used
on the Internet. TCP provides reliable host-to-host exchange of information.
It uses IP as the underlying protocol.
- TCP/IP
- Transmission Control Protocol/Internet Protocol. A suite of protocols
designed to allow communication between networks regardless of the
communication technologies used in each network.
- TCP server machine
- A server that links with other servers into a single, virtual
server. balances TCP traffic among the TCP server machines. Synonymous
with clustered server.
- Telnet
- Terminal emulation protocol, a TCP/IP application protocol for
remote connection service. Telnet allows a user at one site to gain
access to a remote host as if the user's workstation were connected
directly to that remote host.
- timeout
- The time interval allotted for an operation to occur.
- TOS
- Type of service. A one byte field in the IP header of
the SYN packet.
- TTL
- A DNS TTL (time to live) is the number of seconds a client can
cache the name resolution response.
- UDP
- User Datagram Protocol. In the Internet suite of protocols, a
protocol that provides unreliable, connectionless datagram service.
It enables an application program on one machine or process to send
a datagram to an application program on another machine or process.
UDP uses the Internet Protocol (IP) to deliver datagrams.
- URI
- Universal Resource Identifier. The encoded address for any resource
on the Web, such as HTML document, image, video clip, program, and
so forth.
- URL
- Uniform Resource Locator. A standard way of specifying the location
of an object, typically a web page, on the Internet. URLs are the
form of address used on the World-Wide Web. They are used in HTML
documents to specify the target of a hyperlink which is often another
HTML document (possibly stored on another computer).
- VPN
- Virtual Private Network (VPN). A network comprised of
one or more secure IP tunnels connecting two or more networks.
- WAN
- Wide Area Network. A network that provides communication services
to a geographic area larger than that served by a local area network
or a metropolitan area network, and that may use or provide public
communication facilities.
- WAP
- Wireless Application Protocol. This is an open international standard
for applications that use wireless communication. For example, this
standard includes internet access from a mobile phone.
- WAS
- WebSphere® Application Server.
- Web
- The network of HTTP servers that contain programs and files, many
of them hypertext documents that contain links to other documents
on HTTP servers. Also World Wide Web.
- wizard
- A dialog within an application that uses step-by-step
instructions to guide a user through a specific task.
- WLM
- Workload Manager. An advisor that is provided with Load
Balancer. It is designed to work only in conjunction with servers
on OS/390® mainframes running the MVS™ Workload
Manager (WLM) component.
|
