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.