Glossary
A
- 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.
- advisor
- The advisors are a function
of the Load Balancer. Advisors collect and analyze feedback from individual
servers and inform the manager function.
- agent
- (1) In systems management, a user that,
for a particular interaction, has assumed an agent role.
- (2) 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.
B
- backup
- In high availability for the Dispatcher,
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; 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.
C
- 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.
- CBR
- Content Based Routing. A component
of Load Balancer. CBR works with Caching Proxy to load balance incoming
requests, based on Web page content using specified rule types, to
HTTP or HTTPS servers.
- cbrcontrol
- Provides the interface
to the Content Based Router component of Load Balancer.
- cbrserver
- In Content Based Router,
handles the requests from the command line to the executor, manager
and advisors.
- ccocontrol
- In Cisco CSS Controller,
provides the interface to the Cisco CSS Switch.
- ccoserver
- In Cisco CSS Controller,
handles the requests from the command line to the Consultants.
- 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.
- Cisco CSS Controller
- A component
of IBM® Load Balancer. Cisco CSS Controller uses Load Balancer technology
to provide real-time load balancing information to the Cisco Content
Services Switch.
- Cisco CSS Switch
- Any of Cisco's
CSS 11000 series switches, used for packet forwarding and content
routing.
- 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
- In the Dispatcher, 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
- In the Dispatcher, the
address to which clients connect.
- clustered server
- A server that the Dispatcher groups
with other servers into a single, virtual server. Load Balancer balances
TCP or UDP traffic among these clustered servers.
- collocate
- When Load Balancer is
installed on the same machine it is load balancing.
- 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.
D
- 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
- In Dispatcher, handles
the requests from the command line to the executor, manager, and
advisors.
E
- 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 Load Balancer 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.
F
- 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 Load Balancer 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.
G
- 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.
H
- heartbeat
- A simple packet sent between
two Load Balancer machines in high availability mode used by the standby Load Balancer to
monitor the health of the active Load Balancer.
- high availability
- A Load Balancer feature in
which one Load Balancer can take over the function of another, should
that part fail.
- 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
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.
I
- 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.
L
- 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.
M
- 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
- One of several Load Balancer functions.
The manager sets weights based on internal counters in the executor
and feedback 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 Load Balancer manager.
- MIB
- (1) Management Information Base.
A collection of objects that can be accessed by means of a network
management protocol.
- (2) A definition for management information
that specifies the information available from a host or gateway and
the operations allowed.
- multiple address collocation
- Multiple
address collocation allows the customer to specify the address of
the collocated server to be different than the nonforwarding address
(NFA) in the configuration. See also collocate.
- mutual high availability
- Mutual
high availability allows two Dispatcher machines to be both primary
and backup for each other. See also backup, high availability,
primary.
N
- nalcontrol
- Provides the interface
to the Nortel Alteon Controller component of Load Balancer.
- nalserver
- In Nortel Alteon Controller,
handles the requests from the command line to the Consultants.
- 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 Site Selector determines
by measuring round-trip time.
- nfa (nonforwarding address)
- The primary
IP address of the Load Balancer 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.
- Nortel Alteon Controller
- A component
of IBM Load Balancer. Nortel Alteon Controller uses Load Balancer technology
to provide real-time load balancing information to the Nortel Alteon Web Switch.
- Nortel Alteon Web Switch
- The Nortel Alteon ACE
Director Series Switch and the Nortel Alteon 180 Series Switch from
the Alteon Web Switching portfolio, used for packet forwarding and
content routing.
O
- owner content
- Represents the owner name
and the content rule for an owner, which are both defined on the Cisco CSS Switch.
P
- 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 high availability for the Dispatcher,
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 Dispatcher evaluates
rules from the first priority level to the last priority level.
- private network
- A separate network
on which Dispatcher 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.
Q
- 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.
R
- reach
- In Dispatcher, an advisor that
issues pings to a given target and reports whether that target is
responding.
- reach address
- In high availability for
the Dispatcher, 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 Dispatcher machine and used
by Dispatcher 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.
S
- 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 the Dispatcher groups
with other servers into a single, virtual server. The Dispatcher balances
traffic among the server machines. Synonymous with clustered server.
- service
- (1) A function provided by
one or more nodes; for example, HTTP, FTP, Telnet.
- (2) For
Nortel Alteon Controller, a service is the function or information
requested by an end user from a site. It is identified by a virtual
IP address and a virtual port number on an end user request. On the
switch it is identified by a virtual server identifier which is an
integer and a virtual port number or service name.
- (3) For
Cisco CSS Consultant, a service is a destination location where a
piece of content physically resides. For example, a local or remote
server and port.
- 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 Load Balancer. 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 high availability for
the Dispatcher, 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 Load Balancer.
- 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).
- ssserver
- In Site Selector, handles
the requests from the command line to the site name, manager and
advisors.
- 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 high availability for the Dispatcher,
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.
T
- 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 Load Balancer links
with other servers into a single, virtual server. Load Balancer 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.
U
- 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).
V
- VPN
- Virtual Private Network (VPN).
A network comprised of one or more secure IP tunnels connecting two
or more networks.
W
- 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.
An open international standard for applications that use wireless
communication, e.g. 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
provided with Dispatcher. It is designed to work only in conjunction
with servers on OS/390® mainframes running the MVS™ Workload
Manager (WLM) component.