Network Dispatcher 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 IP address is a 32-bit address field.
This field contains two parts. The first part is the network address;
the second part is the host number.
- advisor
- The advisors are a function of the Dispatcher component. Advisors
collect and analyze feedback from individual servers and inform the manager
component.
- 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.
- 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.
- bottom tier
- In a two-tiered Network Dispatcher configuration, that portion of the
configuration that describes the relationship between the Network Dispatchers
and the clustered servers. See also top tier.
- C
- CBR
- Content Based Routing. A component of Network
Dispatcher which provides load balancing for HTTP based on URL content and a proxy server for POP3 and IMAP4 traffic.
- cell
- In ISS, a cell is a set of locally managed machines, or nodes,
close enough to one another on the network and close enough geographically to
be administered as a single logical unit.
- 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
- 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. Network Dispatcher balances TCP or UDP traffic among
these clustered servers.
- collocate
- When you don't have a dedicated machine, Network Dispatcher is
installed on the same machine it is load balancing. Collocate only applies
to AIX, Red Hat Linux, and Solaris operating systems.
- cross port affinity
- Cross port affinity is the affinity (sticky) feature expanded to cover across multiple
ports.
- D
- 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 Network Dispatcher that efficiently balances TCP or UDP
traffic among groups of individual linked servers. The Dispatcher
machine is the server running the Dispatcher code. Dispatcher, ISS, and
CBR are all called components of Network Dispatcher. Each of these
components have functions.
- 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 IP addresses.
- 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.
- executor
- One of several Dispatcher components. 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 component.
- 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. Once a transaction
is in FIN state, the Network Dispatcher 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.
- 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.
- H
- heartbeat
- A simple packet sent between two Dispatcher machines in high availability
mode used by the standby Dispatcher to monitor the health of the active
Dispatcher.
- high availability
- A Dispatcher feature in which one Dispatcher 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.
- I
- Internet
- The worldwide collection of interconnected networks that use the Internet
suite of protocols and permit public access.
- ICMP
- Internet Control Message Protocol. A message control and
error-reporting protocol between a host server and a gateway to the
Internet.
- IMAP4
- Internet Message Access Protocol (version 4). 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.
- 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 32-bit 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.
- ISS
- Interactive Session Support. A component of Network
Dispatcher.
- 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
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
- 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 Dispatcher 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
- In ISS, 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. Metrics are defined by use of the METRIC keyword and can be
one of the following types: LoadLeveler , Custom, or Round-robin.
- 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
- Muliple address collocation allows the customer to specify the address of the
collocated server to be different than the nonforwarding address (NFA) in the
configuration.
- mutual high availability
- Mutual high availability allows two Dispatcher machines to be both primary and backup for each other.
- N
- netmask
- For Internet subnetworking, a 32-bit mask used to identify the
subnetwork address bits in the host portion of an IP address.
- network management station
- In the Simple Network Management Protocol (SNMP), a station that executes
management application programs that monitor and control network
elements.
- NNTP
- Network News Transfer Protocol. A TCP/IP protocol for transferring
news items.
- node
- In ISS, a single machine, which may have one or more IP addresses over
time. A node is a member of one and only one cell.
- nonforwarding address (nfa)
- The primary IP address of the Network Dispatcher machine, used for
administration and configuration.
- O
- observer
- In ISS, a process that subscribes to load-balancing reports on a given
resource.
- 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 Network 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
- 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.
- resource
- In ISS, a specific device needed to provide a service.
- resourceType
- In ISS, a formalized category to which various resources can
belong. The ResourceType can be configured once and its parameters will
subsequently apply to all resources belonging to it.
- 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.
- 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. A standard IP address is a 32-bit address field.
The server address can be either the dotted decimal 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
- 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 Korn shell is one of several UNIX shells
available.
- SMA
- Server Monitor Agent. The system monitor agent which is installed
on servers running on a Red Hat Linux platform. SMA provides system
specific metrics to the Dispatcher manager.
- 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.
- source address
- In high availability for the Dispatcher, the address of the high
availability partner machine that sends heartbeats.
- SPARC
- Scalable processor architecture.
- 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).
- strategy
- In high availability for the Dispatcher, a keyword for specifying how
recovery takes place following the failure of the active machine.
- 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.
- subnet mask
- For Internet subnetworking, 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 Network Dispatcher links with other servers into a single,
virtual server. Network Dispatcher 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.
- top tier
- In a two-tiered Network Dispatcher configuration, that portion of the
configuration that describes the relationship between the ISS Monitor and the
Network Dispatchers. See also bottom tier.
- TOS
- Type of service. A one byte field in the IP header of the SYN packet.
- two-tiered configuration
- An implementation of a network using both functions of Network
Dispatcher. The Interactive Session Support (ISS) Monitor in the
top tier manages the routing of client requests to the Dispatcher
machines in the bottom tier. The Dispatcher machines route
client requests to the clustered servers.
- 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.
- V
- VPN
- Virtual Private Network (VPN). A network comprised of one or more
secure IP tunnels connecting two or more networks.
- W
- 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.
- WTE
- Web Traffic Express (WTE). 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.
- 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.