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.