Glossary

Also known as VLAN tagging. An IEEE standard (and process) which allows multiple bridged networks to transparently share the same physical network link without leakage of information between networks and, in common usage, the name of the encapsulation protocol used to implement this mechanism over Ethernet networks.

Access Control List.

Address Resolution Protocol. An IP protocol for finding a host’s link layer (hardware) address when only its Internet Layer or some other Network Layer address is known.

When new writes can be made without having to wait for the secondary or remote storage site to also finish its writes.

A type of disk storage replication, where write is considered complete as soon as local storage acknowledges it. Remote storage is updated, but probably with a small lag. Performance is greatly increased, but in case of losing a local storage, the remote storage is not guaranteed to have the current copy of data and most recent data may be lost.

The process of validating the claimed identity of an end user or a device wuch as a host, server, switch, router, etc.

The act of granting access rights to a user, groups of users, system, or program.

Within the NX Series appliances, the ability of an appliance to discover and register with the Global Management System (GMS) server when first deployed.

The process by which terminating devices automatically negotiate for maximum bandwidth.

A rate of data transfer, throughput, or bit rate, measured in bits per second.

A binary digit, taking a logical value of either "1" or "0" (also referred to as "true" or "false" respectively). It is also a unit of measurement, the information capacity of one binary digit.

When configuring for gigabit etherchannel bonding, lan0 plus lan1 bond to form blan0, which uses the lan0 IP address.

In-line deployment of an appliance, placing it between an Ethernet LAN switch and a WAN edge router.

When configuring for gigabit etherchannel bonding, wan0 plus wan1 bond to form the virtual interface, bwan0, which uses the wan0 IP address.

Refers to hardware bypass. If there is a major problem with the appliance hardware, software, or power, all traffic goes through the appliance without any processing. Additionally, you can manually put the appliance into Bypass as an aid to troubleshooting.

A common problem with naively designed application protocols is that they are too “chatty”. That is, they imply too many “round-trip” cycles.

Common Internet File System. CIFS is the remote file system access protocol used by Windows servers and clients to share files across the network. Some specific capabilities of CIFS include file access, record locking, read/write privileges, change notification, server name resolution, request batching, and server authentication

A set of techniques for mitigating the impacts of latency across the WAN. They include read-aheads and write-behinds to pipeline CIFS requests and the respective acknowledgements. This dramatically minimizes roundtrip delays when using CIFS over a WAN.

See Command Line Interface.

An application or system that accesses a remote service on another computer system, known as a server, by way of a network.

A method of configuring the appliance by typing in commands via the local serial interface or remote SSH session. [Peribit]

Class of Service (CoS) is a way of managing traffic in a network by grouping similar types of traffic (for example, e-mail, streaming video, voice, large document file transfer) together and treating each type as a class with its own level of service priority. Unlike Quality of Service (QoS) traffic management, Class of Service technologies do not guarantee a level of service in terms of bandwidth and delivery time; they offer a "best-effort." On the other hand, CoS technology is simpler to manage and more scalable as a network grows in structure and traffic volume. One can think of CoS as "coarsely-grained" traffic control and QoS as "finely-grained" traffic control.

A technique that applies compression across various flows of traffic.

The transfer of data at a steady high-speed rate sufficient to support such applications as high-definition television (HDTV) or the continuous backup copying to a storage medium of the data flow within a computer. Data streaming requires some combination of bandwidth sufficiency and, for real-time human perception of the data, the ability to make sure that enough data is being continuously received without any noticeable time lag.

An independent, self-contained message sent over the network whose arrival, arrival time, and content are not guaranteed.

A gateway is a router on a computer network, serving as an access point to another network.

Dynamic Host Configuration Protocol. A TCP/IP protocol that enables PCs and workstations to automatically get temporary or permanent IP addresses (out of a pool) from centrally administered servers.

Domain Naming System or Domain Name Server. It serves as the "phone book" for the Internet by translating human-friendly computer hostnames into IP addresses.

Differentiated Services Code Point. A 6-bit value that encoudes Per-Hop Behavior (PHB) into the 8-bit Differentiated Services (DS) field of the IP packet header. The DS field is the same as the TOS (Type of Service) field.

The main purpose of a domain name is to provide a recognizable names to mostly numerically addressed Internet resources. This abstraction allows any resource (for example, website) to be moved to a different physical location in the address topology of the network, globally or locally in an intranet, in effect changing the IP address.

The capability to switch over automatically to a redundant or standby computer server, system, or network upon the failure or abnormal termination of the previously active server, system, or network. Failover happens without human intervention and generally without warning, unlike switchover.

Forward Error Correction. When Adaptive Forward Error Correction (FEC) is enabled, the appliance introduces a parity packet, which helps detect and correct single-packet loss within a stream of packets, reducing the need for retransmissions. Silver Peak dynamically adjusts how often this parity packet is introduced in response to changing link conditions. This maximizes error correction while minimizing overhead.

In a packet switching network, packet flow or traffic flow is a sequence of packets from a source computer to a destination, which may be another host, a multicast group, or a broadcast domain. As packets traverse successive communication links towards their destination, the packets from one flow (for example, A1, A2, A3) will be intermingled with packets from other flows also traversing the network to form a multiplexed stream (for example, A1, B7, C9, A2, C10, A3). This represents a form of statistical multiplexing because the link is shared as required.

File Transfer Protocol. A network protocol used to exchange and manipulate files over a TCP computer network, such as the Internet. An FTP client may connect to an FTP server to manipulate files on that server.

Bidirectional, simultaneous two-way communications.

Also called protocol converters, can operate at any layer of the OSI model. The job of a gateway is much more complex than that of a router or switch. Typically, a gateway must convert one protocol stack into another.

Global Management System.

Generic Routing Encapsulation. Tunneling protocol developed by Cisco that can encapsulate a wide variety of protocol packet types inside IP tunnels, creating a virtual point-to-point link to Cisco routers at remote points over an IP internetwork.

Graphical User Interface.

A circuit designed for data transmission in both directions, but not at the same time.

If there is a major problem with the appliance hardware, software, or power, all traffic goes through the appliance without any processing. Additionally, you can manually put the appliance into Bypass as an aid to troubleshooting.

This technique can provide additional bandwidth gains by reducing packet header information using specialized compression algorithms.

For maximizing uptime, deploying NX appliances redundantly in 1+1 or N+1 configurations, with failover and load balancing.

In computer networking, a network host, Internet host or host is a computer connected to the Internet. A network host can host information as well as client and/or server software.

The host address, or more properly the host id portion of an IP address is the portion of the address used to identify hosts (which can be any device requiring a Network Interface Card, such a personal computer or networked printer) on the network.

HyperText Transfer Protocol. The protocol web browsers use to communicated with web servers.

HyperText Transfer Protocol Secure. A combination of the HyperText Transfer Protocol and a cryptographic protocol, for accessing a secure web server.

Internet Control Message Protocol. An internet protocol used by networked computers’ operating systems to manage errors and generate control messages.

A global network of interconnected computers, enabling users to share information along multiple channels.

Internet Protocol. Network layer protocol in the TCP/IP stack that enables a connectionless internetwork service.

An Internet Protocol (IP) address is a numerical identification and logical address that is assigned to devices participating in a computer network utilizing the Internet Protocol for communication between its nodes.

Internet Protocol Security Protocol.

Internet Virtual Private Network.

Traffic received from the LAN.

Traffic transmitted to the LAN.

A time delay between the moment something is initiated, and the moment one of its effects begins or becomes detectable. Network latency is the time it takes for information to go from a sender to a receiver and back.

A technique to spread work between two or more computers, network links, CPUs, hard drives, or other resources, in order to get optimal resource utilization, maximize throughput, and minimize response time. Using multiple components with load balancing, instead of a single component, may increase reliability through redundancy. The balancing service is usually provided by a dedicated program or hardware device.

A WAN prone to dropped and out-of-order packets. This is most common on shared networks, like MPLS and Internet VPNs.

Messaging Application Programming Interface. A Microsoft Windows program interface that enables you to send e-mail from within a Windows application and attach the document you are working on to the e-mail note. Applications that take advantage of MAPI include word processors, spreadsheets, and graphics applications.

Management Information Base. A type of database for managing devices in a communications network.

Messaging and groupware software for Windows from Microsoft. The Exchange server is an Internet-compliant messaging system that runs under Windows systems and can be accessed by web browsers, the Windows In-box, Exchange client or Outlook. The Exchange server also stores files for sharing.

MultiProtocol Label Switching is an IETF initiative that integrates Layer 2 information into Layer 3 (IP) packets.

Maximum Transmission Unit. The largest size packet that a device can transmit on a network.

Addresses high WAN latency and TCP chattiness. This is achieved using standard TCP acceleration techniques, such as adjustable windows and selective acknowledgements.

Protects traffic from collateral congestion in a shared service provider network by mitigating the impact of dropped and out-of-order packets.

Addresses limited bandwidth. This technology uses advanced fingerprinting algorithms to examine all incoming and outgoing WAN traffic. Network Memory localizes information and transmits only modifications between locations.

Network File System. The file sharing protocol in a UNIX network.

Out-of-Order [packets]

Same as Router mode. In an out-of-path deployment, policy-based routing (PBR), VRRP, or WCCP redirect the traffic to the Silver Peak appliance for processing.

When packets are small, packet headers consume substantial bandwidth in comparison to the amount of end-user data transferred. Packet coalescing combines multiple user packets traveling between the same two sites into a single coalesced packet. Used in conjunction with header compression, this amortizes a single header over multiple packets thus decreasing overhead, and therefore bandwidth requirements. Packet coalescing is particularly beneficial for web applications, VoIP, and interactive applications, like Citrix.

Traffic that is sent to the WAN without being optimized.

Uses algorithms to identify relatively short byte sequences that are repeated frequently over time. These sequences are then replaced with shorter segments of code to reduce the size of transmitted data. Simple algorithms can find repeated bytes within a single packet; more sophisticated algorithms can find duplication across packets and even across flows

Policy-based routing is a technique used to make routing decisions based on policies set by the network administrator.

Forces the WAN interface to go down when the corresponding LAN interface goes down, or vice versa. By default, this option is enabled on the Configuration - System page.

A programs used to test whether a particular network destination is online, by sending an Internet Control Message Protocol (ICMP) echo request and waiting for a response. [Peribit]

Packet Order Correction. To avoid retransmissions that occur when packets arrive out of order, Silver Peak NX appliances use Packet Order Correction (POC) to resequence packets on the far end of a WAN link, as needed.

Quality of Service is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow. QoS involves several functions: 1) classification of packets into traffic classes based on characteristics such as source, destination addresses, and/or applications and 2) queuing and service mechanisms that are used to apply service policies based on these classifications, including bandwidth allocation.

Remote Authentication Dial In User Service (RADIUS) is a networking protocol that provides centralized Authentication, Authorization and Accounting (AAA) management for computers to connect and use a network service. It is a client/server protocol that uses UDP as transport.

Out-of-path deployment, where data traffic is redirected by using policy-based routing (PBR), Web Cache Coordination Protocol (WCCP), or Virtual Router Redundancy Protocol (VRRP).

Round-trip time. the time it takes to send a packet to a remote host and receive a response; used to measure delay on a network at a given time. [Peribit]

Server Message Block. An application-level network protocol mainly used to provide shared access to files, printers, serial ports, and miscellaneous communications between nodes on a network.

Server Message Block, version 2.

Simple Mail Transfer Protocol. A de facto standard for electronic mail (e-mail) transmissions across the Internet.

Simple Network Management Protocol. A standard TCP/IP protocol for network management. Network administrators use SNMP to monitor network devices, performance, and security, and to manage configurations and collect statistics.

Secure Socket Layer. These are cryptographic protocols that provide secure communications for such things web browsing, email, and other data transfers over the internet.

A portion of a network that shares a common address component. On TCP/IP networks, subnets are defined as all devices whose IP addresses have the same prefix. For example, all devices with IP addresses that start with 100.100.100. would be part of the same subnet. Dividing a network into subnets is useful for both security and performance reasons. IP networks are divided using a subnet mask.

A network device that filters and forwards frames based on the destination address of each frame. The switch operates at Layer-2 (data link layer) of the Open System Interconnection (OSI) model.

Terminal Access Controller Access-Control System Plus is a protocol which provides access control for routers, network access servers and other networked computing devices via one or more centralized servers. TACACS+ provides separate authentication, authorization and accounting services. It uses TCP for its transport. Transactions between the TACACS+ client and TACACS+ servers are also authenticated through the use of a shared secret.

Transmission Control Protocol. The error-correcting Transport layer (Layer-4) in the TCP/IP protocol suite. It ensures that all data arrive at the other end accurately and completely intact.

A set of techniques for mitigating the impacts of latency across the WAN. They include adjustable window sizing and selective acknowledgements.

Transmission Control Protocol/Internet Protocol. A protocol suite for communication between computers, used as a standard for transmitting data over networks and as the basis for standard Internet protocols.

A terminal emulation protocol used on the Internet and TCP/IP-based networks. A Telnet program allows a user at a terminal or PC to log in to a remote computer and run a program and execute other Unix commands.

The average rate of successful message delivery over a communication channel.

Encapsulating one type of network protocol (called the payload protocol) within a different delivery protocol. Reasons to use tunneling include carrying a payload over an incompatible delivery network, or to provide a secure path through an untrusted network.

User Datagram Protocol. Part of the TCP/IP protocol suite, it was created to provide a way for applications to access the connectionless features of IP. UDP provides for exchange of datagrams without acknowledgements or guaranteed delivery.

Virtual Local Area Network. A means by which LAN users on different physical LAN segments are afforded priority access privileges across the LAN backbone so that they appear to be on the same physical segment of an enterprise-level logical LAN.

See 802.1q encapsulation.

Voice-Over-Internet-Protocol. A protocol optimized for the transmission of voice through the Internet or other packet-switched networks.

Virtual Router Redundancy Protocol is a standard redundancy protocol designed to increase the availability of servicing hosts on the same subnet.

Traffic received from the WAN.

Traffic transmitted to the WAN.

Web Cache Communications Protocol. A Cisco-developed content-routing protocol that provides a mechanism to redirect traffic flows in real-time. It has built-in load balancing, scaling, fault tolerance, and service-assurance (failsafe) mechanisms.