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QIC

Stands for Quarter Inch Cartridge, the original tape format for tape backups.

QoS

Stands for quality of service, any network mechanism for ensuring that applications or services are able to operate as expected.

QoS ACS

Stands for QoS Admission Control Service, a feature of Microsoft Windows 2000 for implementing quality of service (QoS) on an Internet Protocol (IP) network.

See Also QoS Admission Control Service (QoS ACS)

QoS Admission Control Service (QoS ACS)

A feature of Microsoft Windows 2000 for implementing quality of service (QoS) on an Internet Protocol (IP) network.

Overview

QoS Admission Control Service (QoS ACS) is a Windows 2000 service that can be used to centrally designate when, how, and by whom shared network segment resources will be used. QoS ACS is based on the Subnet Bandwidth Management (SBM) specification defined by the Internet Engineering Task Force (IETF). QoS ACS operates at the network layer and can service all transport protocols in the TCP/IP protocol suite, including Remote Display Protocol (RDP), User Datagram Protocol (UDP), and Transmission Control Protocol (TCP). A QoS ACS host (a server running Windows 2000 with the QoS ACS service installed and configured) uses the Resource Reservation Protocol (RSVP) as a message service for sending and receiving priority bandwidth requests.

Implementation

A QoS ACS host controls the bandwidth for the subnet to which it is connected. The QoS ACS host uses multicasting to send out messages called beacons to inform clients on the subnet that it is ready to receive bandwidth allocation requests. Clients on the subnet that desire access to shared network resources (such as multimedia servers) first submit their bandwidth request to the QoS ACS server so that it can determine whether sufficient bandwidth is available to allocate to the clients. Bandwidth is then allocated based on the current state of resource and bandwidth availability on the subnet and the requesting user's QoS ACS policy rights. These policy rights are defined in Active Directory directory service.

A client's request for bandwidth will be rejected if the QoS ACS host determines that the user does not have the right to reserve bandwidth on the subnetwork or if the subnetwork does not have sufficient resources to support the request at that time. If the client's request is rejected, the client must decide whether to try accessing the resource using a best-effort service level or wait until later, when priority bandwidth becomes available and can be allocated to the client. If the request is approved, the QoS ACS host logically allocates the requested bandwidth and forwards the client's resource request to the appropriate server on the network. No configuration is required for Windows clients, and non-Windows clients can request bandwidth, provided they are running suitable SBM client software.

See Also quality of service (QoS) ,Resource Reservation Protocol (RSVP)

Q-series protocols

Also called Series Q protocols, a set of protocols developed by the International Telecommunication Union (ITU) that govern the operation of Integrated Services Digital Network (ISDN).

Overview

Some of the more important Q-series protocols include the following:

Q.920/921: Specifies the User-Network Interface (UNI) data-link layer for ISDN, including the ISDN D channel's Link Access Protocol, D-channel (LAP-D) data-link layer protocol.
Q.922A: Specifies the ITU encapsulation method for frame relay networks.
Q.931: Specifies mechanisms for establishing, maintaining, and tearing down ISDN connections. This includes working with connections in the LAP-D data-link protocol, which runs on the ISDN D channel.
Q.93B: The Asynchronous Transfer Mode (ATM) signaling protocol, which specifies mechanisms for establishing, maintaining, and tearing down broadband ISDN (B-ISDN) connections.

See Also Asynchronous Transfer Mode (ATM) ,Integrated Services Digital Network (ISDN) ,International Telecommunication Union (ITU) ,Link Access Protocol,D-channel (LAPD)

quality of service (QoS)

Any network mechanism for ensuring that applications or services are able to operate as expected.

Overview

Network performance characteristics such as bandwidth, latency, and jitter (variation in delay) can have bad effects on some applications. For example, voice communications and streaming video can be frustrating when delivered over a network with insufficient bandwidth, unpredictable latency, or excessive jitter. Anyone who has used a cell phone has experienced the frustrating "dropouts" that occur from time to time, causing conversation to be difficult. Quality of service (QoS) is all about making sure that a network's bandwidth, latency, and jitter are predictable and suited to the needs of applications that use that network.

History

The general concept of network QoS originated in the telco market, where it represented a set of technologies and methods for ensuring that services provided to customers were above designated minimum levels of quality. For telephone service, this means, for example, reducing the latency of telephone line communications to less than 200 milliseconds even on long distance or overseas calls, as delays above this value result in frequent interruptions or awkward pauses in communications as callers wait for a response from the other end. It also meant reliable calls that were not accidentally disconnected, low levels of static and background noise, and minimal signal distortion as callers voices are modulated from analog to digital and back to analog again over the Public Switched Telephone Network (PSTN).

When enterprises began using telco services such as Integrated Services Digital Network (ISDN) and leased lines for connecting their geographically remote offices into a wide area network (WAN), QoS referred to the reliability of the carrier's WAN services for carrying network traffic, which was especially important for synchronous links between mainframes and remote terminals. However, QoS in its modern sense is associated with the emergence of Asynchronous Transfer Mode (ATM) networking, a technology that allows QoS parameters such as delay, jitter, and loss to be enforced for traffic traveling over the network. In essence, ATM allows "traffic contracts" to be established for different types of applications running on the network to ensure that applications that are sensitive to delay or hungry for bandwidth perform as users want them to. The fact that ATM employs fixed-size 53-byte cells is an advantage in implementing QoS on this technology, as ATM switches can generally process fixed-size cells faster than variable length ones. QoS as it refers to ATM networking basically means two things:

Prioritization: Each cell is assigned a service class, and cells belonging to a specific service class are all handled the same way by switches on the ATM network. Prioritization allows different kinds of traffic to be treated differently on an ATM network. For example, voice traffic can be given higher priority than data to ensure that voice communications are always reliable. Different kinds of data traffic can be treated similarly. For example, traffic for an accounting application can be given high priority, while Web traffic can be assigned a lower priority.
Resource reservation: An ATM connection can request and be assigned a given amount of bandwidth along the entire path between the two end nodes involved. This ensures that the application making the request will be able to perform its function during the time of the connection. Since ATM represents a homogeneous, tightly managed cell-switched system, resource reservation is achievable.

Although ATM remains the winner in the arena of network technologies that support QoS, the greatest interest today is in bringing QoS to Internet Protocol (IP) networks such as the Internet. IP was originally designed as a "best effort" delivery service with no guarantees of reliability, delay, or performance. As a result of the underlying operation of the Transmission Control Protocol (TCP) used to establish IP sessions, and because IP employs variable-length packets that are more complex for routers and local area network (LAN) switches to process than fixed-size ATM cells, it has been difficult to bring QoS to IP networks. Efforts have been underway in this regard for many years and have resulted in complex protocols such as DiffServ, Resource Reservation Protocol (RSVP), and Multiprotocol Label Switching (MPLS). These efforts are not complete, and IP QoS generally remains a technology that is complex to implement and whose promises are not quite realized. Simple packet-based IP QoS prioritization schemes work well but are difficult to scale to the enterprise level, and more complex resource reservation- based IP QoS is difficult to achieve over networks with multiple subnets and combinations of hubs, switches, and routers. This is discussed further below.

Implementation

This section will cover the details of ATM QoS and examine the efforts underway to make IP QoS a reality. Beginning with ATM, the basic QoS parameters (or traffic parameters) that can be negotiated on an ATM network include the following:

Cell Transfer Delay (CTD): The latency in seconds for a connection
Cell Delay Variation (CDV): The tolerance per second for cells that should not exceed the peak cell rate
Cell Loss Ratio (CLR): The acceptable ratio of cells delivered to cells lost in a transmission
Maximum Burst Size (MBS): The maximum number of cells per burst
Peak Cell Rate (PCR): The maximum number of cells that can be transmitted per second based on the specified peak bandwidth per second
Sustainable Cell Rate (SCR): The maximum number of cells that can be transmitted per second based on the specified sustainable bandwidth per second

To implement QoS in an ATM network, the sending node signals the network using User to Network Interface (UNI) version 4 signaling to reserve bandwidth, restrict cell loss or delay, or similar QoS parameters. The ATM switches configure themselves accordingly to ensure that the requested QoS is achieved. ATM QoS is "hard state" QoS in that connections may be denied if they violate established QoS settings for the network. Some of the kinds of QoS behaviors that can be enforced on an ATM network include

Traffic contracts: Each ATM end node in an ATM network negotiates a traffic contract with that network to specify data stream parameters such as peak bandwidth, average bandwidth, and maximum burst size. These parameters can be defined for the end node to control the type and amount of traffic that the host can send over an ATM circuit. If an ATM switch in the circuit cannot meet these requirements, it sends a message to the transmitting host indicating that the connection is refused. Each virtual channel or virtual path that is established by an ATM end node in an ATM network has its own traffic contract.
Traffic shaping: This involves ATM devices using data queues to smooth out traffic bursts and limit the peak data rate so that the conditions of the negotiated traffic contracts are met. ATM switches can use several kinds of queuing, including first-in/first-out (FIFO) queuing, prioritized queuing, and weighted fair queuing.
Traffic policing: ATM switches enforce traffic contracts so that the agreed-upon QoS conditions of each data stream are met. If these conditions are violated, ATM switches set the cell-loss priority (CLP) bit of each offending cell, which indicates that the offending cells may be dropped should congestion occur at the switch.

These mechanisms enable ATM QoS to support several different classes of QoS, such as

Constant Bit Rate (CBR): The type of traffic under consideration requires a guaranteed rate of transport and does not tolerate cell loss. To implement CBR, an ATM end station informs the ATM network of the required QoS parameters during call setup. The network then performs admission control by reserving the necessary bandwidth or refusing the connection. The end station is responsible for complying with the agreed-upon peak data rate-if it exceeds this rate, the network drops the offending cells.
Variable Bit Rate (VBR): Similar to CBR, except that maximum burst size and maximum sustainable rate are negotiated in addition to peak data rate.
Unspecified Bit Rate (UBR): Used mainly for LAN emulation (LANE) mode-that is, running IP traffic over ATM backbones. In UBR, if a cell is dropped due to congestion, the entire IP packet to which the cell belongs is retransmitted. UBR does not reserve bandwidth or establish a cell-loss ratio.
Available Bit Rate (ABR): Also used in LAN emulation mode, ABR implements periodic polling of the ATM network to adjust the data transmission rate as needed.

In the realm of IP networks, QoS can be implemented using the same basic approaches used in ATM, namely, prioritization and resource reservation. Prioritization means that the way a particular IP packet will be handled by QoS-enabled devices such as suitable routers and switches on the network is embedded within the packet itself. In other words, IP QoS prioritization works on a packet-by-packet basis, and as a packet traverses the network the various switches and routers handle the packet independently of one another (stateless QoS). Priority-based QoS is configured by setting packet-forwarding rules on the routers and switches on the network, so all such devices on the network must support this feature in order for it to work properly. Priority-based IP QoS schemes generally employ multiple queues on suitable routers and switches so that different types of traffic (packets having different priorities) are delivered to different queues on the device. The device then processes these queues in a way that ensures that traffic with high priority is processed first. Priority-based IP QoS is the basis of the IEEE 802.1p standard and is implemented at Layer 2 (the data link layer) of the Open Systems Interconnection (OSI) reference model, but there is also a Layer 3 approach to IP QoS prioritization called DiffServ, which is discussed later in this article.

By contrast, IP QoS resource reservation uses a stateful approach in which the receiving node (not the sending node) uses RSVP to contact all the various switches and routers along the path to be used, telling each device to reserve the required bandwidth for the traffic. This is complicated by the fact that the switches and routers must be able to adjust to changes in network performance should they occur. The network interface cards (NICs) of the sending and receiving hosts must also support QoS-in other words, the resource reservation type of QoS requires end-to-end support in order to work. The resource reservation approach to IP QoS using RSVP is the method utilized by the QoS Admission Control Service of Microsoft Windows 2000 to implement IP QoS on this platform.

RSVP is the basis of the integrated services (IntServ) approach to IP QoS because this feature must be "integrated" across all packet-forwarding devices on the network in order to work, including routers, switches, and NICs. The IntServ approach enables IP networks to be used as the backbone for applications ranging from voice, video, and real-time data to classical data traffic. By contrast, IP QoS prioritization employs differentiated services (DiffServ), which classifies traffic into different priority classes using the DS field in the IPv4 packet header to define how the packet will be forwarded. The DiffServ approach can be implemented on an IP network with only minor changes to routers but leaves the complexity of implementing QoS to the edges of the network. DiffServ provides only a statistically based QoS to IP networks with no firm guarantee of bandwidth or traffic handling-in contrast to IntServ, which provides guaranteed QoS, albeit in a much more complicated fashion. So it is a trade-off-DiffServ, with its statistical QoS capabilities but ease of configuration and use of existing routing and switching devices, or IntServ, with its guaranteed QoS capabilities but complex configuration and requirement of routing and switching devices that fully support RSVP.

Another approach to IP QoS is Multiprotocol Label Switching (MPLS), which was derived from Cisco's proprietary label switching technology. MPLS is designed to bring some of the advantages of circuit- switched networks to switched IP networks, including predictable delay and latency, the ability to reserve bandwidth, and QoS. All of the various approaches to IP QoS, including IntServ/RSVP, DiffServ, MPLS, and 802.1p are implemented to various degrees on routers and switches from Cisco Systems and other infrastructure vendors.

Prospects

IP QoS remains an elusive target and, in the opinion of some analysts, even an unnecessary one, considering the cost and complexity of implementing it in the enterprise. On the LAN side, the increasing availability and decreasing cost of Gigabit Ethernet (GbE) has made "throwing bandwidth at the problem" a cheaper and easier solution to network congestion than implementing IP QoS. In the WAN environment, where bandwidth is still scarce, IP QoS makes more sense. On the other hand, prices for high-end WAN services such as T3 and OC-48 are likely to drop in the near future, since the speed at which Synchronous Optical Network (SONET) can run over fiber and the number of channels that can be carried by a single strand are doubling every year. Although the emergence of Voice over IP (VoIP) as a viable enterprise technology may seem to be a driving force for the implementation of IP QoS, some network architects contend that occasional dropouts or garbled transmissions are a small price to pay compared to overhauling their whole infrastructure to support IP QoS. The best solution may be to implement basic two-level traffic prioritization (high priority for voice and video, low for data), upgrade to GbE, and leave it at that for now until IP QoS technology matures and becomes cheaper and easier to manage.

See Also 802.1p ,Asynchronous Transfer Mode (ATM) ,bandwidth ,cell (ATM) ,Gigabit Ethernet (GbE) ,Integrated Services Digital Network (ISDN) ,Internet Protocol (IP) ,jitter ,latency ,Multiprotocol Label Switching (MPLS) ,Public Switched Telephone Network (PSTN) ,Resource Reservation Protocol (RSVP) ,Transmission Control Protocol (TCP) ,wide area network (WAN)

Quarter Inch Cartridge (QIC)

The original tape format for tape backups.

Overview

Quarter Inch Cartridge (QIC) is a cartridge-based tape format that was developed in the 1970s and became widely popular in the enterprise-in fact, it is still in use in many places. QIC employs serpentine recording to record several parallel tracks on the tape, switching directions at the end of each track. QIC tape cartridges come in two basic formats:

Data cartridge (DC): A large 4 by 6 inch cassette 5/8 inch thick.
Mini cartridge (MC): A smaller 3 by 2 by 3/5 inch cassette.

There are dozens of different QIC formats based on tape capacity, transfer speed, and interface. Most QIC drives today employ Travan technology originally developed by 3M Corporation and now licensed by Imation Corporation.

For More Information

Get more information about QIC at www.qic.org

quartet signaling

A signaling method used by 100VG-AnyLAN.

Overview

Quartet signaling makes possible the transmission of data at a speed of 100 megabits per second (Mbps) while using the same transmission frequencies that are used on standard 10BaseT networks. Quartet signaling enables 100VG-AnyLan to leverage existing installations of Category 3, 4, and 5 unshielded twisted-pair (UTP) cabling for 100-Mbps transmission.

Implementation

100VG-AnyLan employs the demand priority method for controlling access to the media, which prevents collisions from occurring. Although 10BaseT Ethernet networks use only two pairs of wires in a four-pair UTP cabling-one pair for transmitting data and the other pair for receiving data and for detecting collisions on the network-100VG-AnyLAN transmits signals over all four pairs of wire in voice-grade UTP cabling, hence the term quartet signaling . In addition, quartet signaling uses a different line coding technique than the traditional Manchester coding method used in Ethernet networks. Quartet signaling uses the 5B/6B NRZ line coding method, but Manchester coding uses a 1B/2B scheme whereby 1 bit of data is encoded using two binary symbols. The 1B/2B algorithm is reliable and simple to implement but inefficient. The 5B/6B method encodes 5 bits using six binary symbols, which allows two and a half times as much information to be transmitted per wire compared to 10BaseT Ethernet (as shown in the following table).

Calculations for Line Coding Data Rates
	Manchester Coding	Quartet Signaling
Line coding	1B/2B	5B/6B
Line frequency	20 MHz	30 MHz
Data rate per pair	(¹ /₂ ) x 20 = 10 Mbps	(⁵ /₆ ) x 30 = 25 Mbps
Number of pairs used	1	4
Total data rate	1 x 10 = 10 Mbps	4 x 25 = 100 Mbps

Notes

The 100BaseT4 form of Fast Ethernet also uses all four pairs of wire in twisted-pair cabling.

See Also 10BaseT ,100VG-AnyLAN ,demand priority ,Ethernet ,line coding ,Manchester coding ,unshielded twisted-pair (UTP) cabling

queue

A collection of items waiting to be processed in a specific order.

Overview

Examples of queues in computer and networking technology are numerous and include the following:

A print queue, which consists of print jobs waiting to be sent to a print device
A messaging queue (on a mail server such as Microsoft Exchange Server), which consists of messages waiting to be sent
A backlog of packets waiting to be forwarded over a specific interface by a router
Information, function calls, or transactions sent by one application and forwarded to another by Microsoft Message Queuing (MSMQ)
A collection of fax messages waiting to be processed and sent by a fax server
A series of system messages, such as key presses and mouse clicks, sent by applications to an operating system for processing

queuing methods

Methods used by routers and local area network (LAN) switches for queuing incoming traffic.

Overview

Most LAN switches and routers implement some form of queuing to ensure that packets are not lost in times of heavy traffic. Certain forms of queuing also enable these devices to implement quality of service (QoS) through prioritizing different types of traffic by using different queues for each type. The most common queuing methods used in such devices include

First-in/first-out (FIFO) queuing: Here, incoming packets are stored in the queue and forwarded in the order in which they arrived. FIFO queuing requires no configuration and helps routers handle traffic congestion, but they do not support QoS. On Cisco routers, FIFO queuing is the default queuing method for all interfaces unless configured otherwise.
Priority queuing: Routers using this form of queuing employ multiple queues for different types of traffic, typically four queues for high, medium, normal, and low priority traffic. These traffic types can be distinguished according to incoming interface, packet size, source address, destination address, or network protocol. Queues are emptied in a fashion that ensures that higher priority traffic is given first attention, which enables these devices to support Internet Protocol (IP) QoS prioritization. Priority queuing is used by Asynchronous Transfer Mode (ATM) switches and is often used on wide area network (WAN) links to ensure that high-priority traffic such as Voice over IP (VoIP) and Enterprise Resource Planning (ERP) applications perform as expected.
Weighted fair queuing: This is a flow-based form of queuing that allows interactive traffic to be moved ahead in the queue to ensure good performance. Weighted fair queuing implements QoS by ensuring that applications that require bandwidth get enough of it to function satisfactorily. Weighted fair queuing was introduced with release 11.0 of the Cisco Internetwork Operating System (IOS).

Queuing methods other than FIFO generally do not need to be configured for wide area network (WAN) access routers if the utilization rate of the WAN link is low. The interfaces that generally benefit most from queuing are subrate interfaces, that is, speeds slower than T1 (fractional T1 being the typical example).

See Also Asynchronous Transfer Mode (ATM) , Ethernet switch ,Internetwork Operating System (IOS) , router

quota management

Managing disk storage for network users.

Overview

Quota management involves setting storage limits for individual users on file servers and other forms of network storage. Although disk space has become an inexpensive commodity over the last few years, managing large amounts of user files can become a nightmare from a management perspective. Setting quotas for users prevents them from accumulating unnecessary files and encourages them to manage their network workspace wisely. Quota management tools generally alert users when volumes are nearly full, which also frees administrators from the chore of intervening by locating and deleting unnecessary files or adding more disk space. Quotas also prevent volumes from becoming full, which can cause storage systems to crash under certain circumstances.

Marketplace

In addition to the disk quota management tools bundled with Microsoft Windows 2000, Windows XP, and Windows .NET Server, and, a number of third-party tools from different vendors are helpful for managing storage in an enterprise environment. Some popular examples include QuotaAdvisor from WQuinn, Quota Server from NORTHERN, Quota Sentinel from NTP Software, and SpaceGuard from Tools4ever.