Quality of service
Encyclopedia
The quality of service refers to several related aspects of telephony
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....

 and computer network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....

s that allow the transport of traffic with special requirements. In particular, much technology has been developed to allow computer networks to become as useful as telephone network for audio conversations, as well as supporting new applications with even more strict service demands.

Definitions

In the field of telephony
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....

, quality of service was defined by the ITU
Itu
Itu is an old and historic municipality in the state of São Paulo in Brazil. The population in 2009 was 157,384 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language, meaning big waterfall. Itu is linked with the highway numbered the SP-75 and are flowed...

 in 1994. Quality of service comprises requirements on all the aspects of a connection, such as service response time, loss, signal-to-noise ratio, cross-talk, echo, interrupts, frequency response, loudness levels, and so on. A subset of telephony QoS is grade of service
Grade of service
In telecommunication engineering, and in particular teletraffic engineering, the quality of voice service is specified by two measures: the grade of service and the quality of service ....

 (GoS) requirements, which comprises aspects of a connection relating to capacity and coverage of a network, for example guaranteed maximum blocking probability and outage probability.

In the field of computer networking and other packet-switched telecommunication networks, the traffic engineering term refers to resource reservation control mechanisms rather than the achieved service quality. Quality of service is the ability to provide different priority to different applications, users, or data flows
Flow (computer networking)
In packet switching networks, traffic flow, packet flow or network 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...

, or to guarantee a certain level of performance to a data flow. For example, a required bit rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

, delay
Network delay
Network delay is an important design and performance characteristic of a computer network or telecommunications network. The delay of a network specifies how long it takes for a bit of data to travel across the network from one node or endpoint to another. It is typically measured in multiples or...

, jitter
Packet delay variation
In computer networking, packet delay variation is the difference in end-to-end delay between selected packets in a flow with any lost packets being ignored...

, packet dropping probability and/or bit error rate may be guaranteed. Quality of service guarantees are important if the network capacity is insufficient, especially for real-time streaming multimedia applications such as voice over IP
Voice over IP
Voice over Internet Protocol is a family of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol networks, such as the Internet...

, online games and IP-TV, since these often require fixed bit rate and are delay sensitive, and in networks where the capacity is a limited resource, for example in cellular data communication.

A network or protocol that supports QoS may agree on a traffic contract
Traffic contract
If a service wishes to use a broadband network to transport a particular kind of traffic, it must first inform the network about what kind of traffic is to be transported, and the performance requirements of that traffic...

 with the application software and reserve capacity in the network nodes, for example during a session establishment phase. During the session it may monitor the achieved level of performance, for example the data rate and delay, and dynamically control scheduling priorities in the network nodes. It may release the reserved capacity during a tear down phase.

A best-effort network or service does not support quality of service. An alternative to complex QoS control mechanisms is to provide high quality communication over a best-effort network by over-provisioning the capacity so that it is sufficient for the expected peak traffic load. The resulting absence of network congestion
Network congestion
In data networking and queueing theory, network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates. Typical effects include queueing delay, packet loss or the blocking of new connections...

 eliminates the need for QoS mechanisms.

QoS is sometimes used as a quality measure, with many alternative definitions, rather than referring to the ability to reserve resources. Quality of service sometimes refers to the level of quality of service, i.e. the guaranteed service quality. High QoS is often confused with a high level of performance or achieved service quality, for example high bit rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

, low latency
Latency (engineering)
Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...

 and low bit error probability.

An alternative and disputable definition of QoS, used especially in application layer services such as telephony and streaming video, is requirements on a metric that reflects or predicts the subjectively experienced quality. In this context, QoS is the acceptable cumulative effect on subscriber satisfaction of all imperfections affecting the service. Other terms with similar meaning are the quality of experience
Quality of experience
Quality of experience , some times also known as quality of user experience, is a subjective measure of a customer's experiences with a service...

 (QoE) subjective business concept, the required “user perceived performance”, the required “degree of satisfaction of the user” or the targeted “number of happy customers”. Examples of measures and measurement methods are Mean Opinion Score
Mean Opinion Score
The Mean Opinion Score test has been used for decades in telephony networks to obtain the human user's view of the quality of the network. In multimedia especially when codecs are used to compress the bandwidth requirement , the mean opinion score ...

 (MOS), Perceptual Speech Quality Measure (PSQM) and Perceptual Evaluation of Video Quality (PEVQ). See also subjective video quality
Subjective video quality
Subjective video quality is a subjective characteristic of video quality. It is concerned with how video is perceived by a viewer and designates his or her opinion on a particular video sequence...

.

History

Conventional Internet routers and LAN switches operate on a best effort basis. This equipment is less expensive, less complex and faster and thus more popular than competing more complex technologies that provided QoS mechanisms. There were four “Type of service
Type of Service
The type of service field in the IPv4 header has had various purposes over the years, and has been defined in different ways by five RFCs...

” bits and three “Precedence” bits provided in each IP packet header, but they were not generally respected. These bits were later re-defined as DiffServ Code Points (DSCP) and are sometimes honored in peered links on the modern Internet.

With the advent of IPTV
IPTV
Internet Protocol television is a system through which television services are delivered using the Internet protocol suite over a packet-switched network such as the Internet, instead of being delivered through traditional terrestrial, satellite signal, and cable television formats.IPTV services...

 and IP telephony, QoS mechanisms are increasingly available to the end user.

A number of attempts for layer 2 technologies that add QoS tags to the data have gained popularity during the years, but then lost attention. Examples are Frame relay
Frame relay
Frame Relay is a standardized wide area network technology that specifies the physical and logical link layers of digital telecommunications channels using a packet switching methodology...

 and ATM
Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...

. Recently, MPLS
Multiprotocol Label Switching
Multiprotocol Label Switching is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links between...

 (a technique between layer 2 and 3) have gained some attention. However, today Ethernet may offer QoS through its 802.1p. Ethernet is, by far, the most popular layer 2 technology.

In Ethernet, Virtual LAN
Virtual LAN
A virtual local area network, virtual LAN or VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location...

s (VLAN) may be used to separate different QoS levels. For example in fibre-to-the-home switches typically offer several Ethernet ports connected to different VLAN:s. One VLAN may be used for Internet access (low priority), one for IPTV (higher priority) and one for IP telephony (highest priority). Different Internet service provider
Internet service provider
An Internet service provider is a company that provides access to the Internet. Access ISPs directly connect customers to the Internet using copper wires, wireless or fiber-optic connections. Hosting ISPs lease server space for smaller businesses and host other people servers...

s may use the different VLANs.

Qualities of traffic

In packet-switched networks, quality of service is affected by various factors, which can be divided into “human” and “technical” factors. Human factors include: stability of service, availability of service, delays, user information. Technical factors include: reliability, scalability, effectiveness, maintainability, grade of service
Grade of service
In telecommunication engineering, and in particular teletraffic engineering, the quality of voice service is specified by two measures: the grade of service and the quality of service ....

, etc.

Many things can happen to packets as they travel from origin to destination, resulting in the following problems as seen from the point of view of the sender and receiver:

Low throughput: Due to varying load from other users sharing the same network resources, the bit rate (the maximum throughput) that can be provided to a certain data stream may be too low for realtime multimedia services if all data streams get the same scheduling priority.
Dropped packets: The routers might fail to deliver (drop) some packets if their data is corrupted or they arrive when their buffers are already full. The receiving application may ask for this information to be retransmitted, possibly causing severe delays in the overall transmission.
Errors: Sometimes packets are corrupted due to bit errors caused by noise and interference, especially in wireless communications and long copper wires. The receiver has to detect this and, just as if the packet was dropped, may ask for this information to be retransmitted.
Latency: It might take a long time for each packet to reach its destination, because it gets held up in long queues, or takes a less direct route to avoid congestion. This is different from throughput, as the delay can build up over time, even if the throughput is almost normal. In some cases, excessive latency can render an application such as VoIP or online gaming unusable.
Jitter: Packets from the source will reach the destination with different delays. A packet's delay varies with its position in the queues of the routers along the path between source and destination and this position can vary unpredictably. This variation in delay is known as jitter
Jitter
Jitter is the undesired deviation from true periodicity of an assumed periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of...

 and can seriously affect the quality of streaming audio and/or video.
Out-of-order delivery: When a collection of related packets is routed through a network, different packets may take different routes, each resulting in a different delay. The result is that the packets arrive in a different order than they were sent. This problem requires special additional protocols responsible for rearranging out-of-order packets to an isochronous
Isochronous
Isochronous : From Greek iso, equal + chronos, time. It literally means regularly, or at equal time intervals. In general English language, it refers to something that occurs at a regular interval, of the same duration; as opposed to synchronous which refers to more than one thing happening at the...

 state once they reach their destination. This is especially important for video and VoIP streams where quality is dramatically affected by both latency and lack of sequence.

Applications

A defined quality of service may be desired or required for certain types of network traffic, for example:
  • Streaming media
    Streaming media
    Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...

     specifically
    • Internet protocol television (IPTV)
    • Audio over Ethernet
      Audio over Ethernet
      In audio engineering and broadcast engineering, Audio over Ethernet is the use of an Ethernet-based network to distribute real-time digital audio....

    • Audio over IP
      Audio over IP
      Streaming audio over IP networks is being increasingly used by broadcasting companies, among others, to provide high-quality audio feeds over distance across an IP network such as the Internet. The application is also known as audio contribution over IP in reference to the programming...

  • IP telephony also known as Voice over IP
    Voice over IP
    Voice over Internet Protocol is a family of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol networks, such as the Internet...

     (VoIP)
  • Videoconferencing
    Videoconferencing
    Videoconferencing is the conduct of a videoconference by a set of telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously...

  • Telepresence
    Telepresence
    Telepresence refers to a set of technologies which allow a person to feel as if they were present, to give the appearance of being present, or to have an effect, via telerobotics, at a place other than their true location....

  • Circuit Emulation Service
    Circuit Emulation Service
    Circuit Emulation Service is an emerging telecommunication technology used to transmit time-division multiplexed services such as the traditional Digital Signal and the E-carrier circuits over Asynchronous Transfer Mode networks...

  • Safety-critical applications such as remote surgery
    Remote surgery
    Remote surgery is the ability for a doctor to perform surgery on a patient even though they are not physically in the same location. It is a form of telepresence. Remote surgery combines elements of robotics, cutting edge communication technology such as high-speed data connections and elements...

     where availability
    Availability
    In telecommunications and reliability theory, the term availability has the following meanings:* The degree to which a system, subsystem, or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e., a random, time...

     issues can be hazardous
  • Network operations support systems either for the network itself, or for customers' business critical needs
  • Online games where real-time lag
    Lag (online gaming)
    In online gaming, Lag is a term used to describe delays between the action of players and the reaction of the server . Although it is commonly used to refer to delays caused by high latency, it is occasionally used to describe delays caused by insufficient processing power in the client and/or server...

     can be a factor
  • Industrial control systems
    Industrial Control Systems
    Industrial control system is a general term that encompasses several types of control systems used in industrial production, including supervisory control and data acquisition systems, distributed control systems , and other smaller control system configurations such as skid-mounted programmable...

     protocols such as Ethernet/IP
    EtherNet/IP
    EtherNet/IP is a communications protocol developed by Rockwell Automation, managed by the Open DeviceNet Vendors Association and designed for use in process control and other industrial automation applications....

     which are used for real-time control of machinery


These types of service are called inelastic, meaning that they require a certain minimum level of bandwidth and a certain maximum latency to function. By contrast, elastic applications can take advantage of however much or little bandwidth is available. Bulk file transfer applications that rely on TCP
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...

 are generally elastic.

Mechanisms

Non-IP protocols, especially those intended for voice transmission, such as Asynchronous Transfer Mode
Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...

 (ATM) or GSM, have QoS in the core protocol and do not need additional procedures to achieve it. Shorter data units and built-in QoS were some of the unique selling points of ATM for applications such as video on demand
Video on demand
Video on Demand or Audio and Video On Demand are systems which allow users to select and watch/listen to video or audio content on demand...

.

When the expense of mechanisms to provide QoS is justified, network customers and providers can enter into a contractual agreement termed a service level agreement
Service Level Agreement
A service-level agreement is a part of a service contract where the level of service is formally defined. In practice, the term SLA is sometimes used to refer to the contracted delivery time or performance...

 (SLA) which specifies guarantees for the ability of a network/protocol to give guaranteed performance/throughput/latency bounds based on mutually agreed measures, usually by prioritizing traffic.
In other approaches, resources are reserved at each step on the network for the call as it is set up.

Over-provisioning

An alternative to complex QoS control mechanisms is to provide high quality communication by generously over-provisioning a network so that capacity is based on peak traffic load estimates. This approach is simple and economical for networks with predictable and light traffic loads. The performance is reasonable for many applications. This might include demanding applications that can compensate for variations in bandwidth and delay with large receive buffers, which is often possible for example in video streaming. Over-provisioning can be of limited use, however, in the face of transport protocols (such as TCP
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...

) that over time exponentially increase the amount of data placed on the network until all available bandwidth is consumed and packets are dropped. Such greedy protocols tend to increase latency and packet loss for all users.

Commercial VoIP services are often competitive with traditional telephone service in terms of call quality even though QoS mechanisms are usually not in use on the user's connection to his ISP and the VoIP provider's connection to a different ISP. Under high load conditions, however, VoIP may degrade to cell-phone quality or worse. The mathematics of packet traffic indicate that network requires just 60% more raw capacity under conservative assumptions.

The amount of over-provisioning in interior links required to replace QoS depends on the number of users and their traffic demands. This limits usability of over-provisioning. Newer more bandwidth intensive applications and the addition of more users results in the loss of over-provisioned networks. This then requires a physical update of the relevant network links which is an expensive process. Thus over-provisioning cannot be blindly assumed on the Internet.

IP and Ethernet efforts

Unlike single-owner networks, the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 is a series of exchange points interconnecting private networks. Hence the Internet's core is owned and managed by a number of different network service provider
Network service provider
A network service provider is a business or organization that sells bandwidth or network access by providing direct backbone access to the Internet and usually access to its network access points...

s, not a single entity. Its behavior is much more stochastic
Stochastic
Stochastic refers to systems whose behaviour is intrinsically non-deterministic. A stochastic process is one whose behavior is non-deterministic, in that a system's subsequent state is determined both by the process's predictable actions and by a random element. However, according to M. Kac and E...

 or unpredictable
Predictability
Predictability is the degree to which a correct prediction or forecast of a system's state can be made either qualitatively or quantitatively.-Predictability and Causality:...

. Therefore, research continues on QoS procedures that are deployable in large, diverse networks.

There are two principal approaches to QoS in modern packet-switched IP networks, a parameterized system based on an exchange of application requirements with the network, and a prioritized system where each packet identifies a desired service level to the network.
  • Integrated services
    Integrated services
    In computer networking, IntServ or integrated services is an architecture that specifies the elements to guarantee quality of service on networks...

     (“IntServ”) implements the parameterized approach. In this model, applications use the Resource Reservation Protocol
    Resource Reservation Protocol
    The Resource Reservation Protocol is a Transport Layer protocol designed to reserve resources across a network for an integrated services Internet. RSVP operates over an IPv4 or IPv6 Internet Layer and provides receiver-initiated setup of resource reservations for multicast or unicast data flows...

     (RSVP) to request and reserve resources through a network.
  • Differentiated services
    Differentiated services
    Differentiated Services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing Quality of Service on modern IP networks...

     (“DiffServ”) implements the prioritized model. DiffServ marks packets according to the type of service they desire. In response to these markings, routers and switches use various queueing strategies to tailor performance to expectations. DiffServ Code Point (DSCP) markings use the first 6 bits in the ToS
    Type of Service
    The type of service field in the IPv4 header has had various purposes over the years, and has been defined in different ways by five RFCs...

     field of the IP(v4) packet header.


Early work used the integrated services
Integrated services
In computer networking, IntServ or integrated services is an architecture that specifies the elements to guarantee quality of service on networks...

 (IntServ) philosophy of reserving network resources. In this model, applications used the Resource reservation protocol
Resource Reservation Protocol
The Resource Reservation Protocol is a Transport Layer protocol designed to reserve resources across a network for an integrated services Internet. RSVP operates over an IPv4 or IPv6 Internet Layer and provides receiver-initiated setup of resource reservations for multicast or unicast data flows...

 (RSVP) to request and reserve resources through a network. While IntServ mechanisms do work, it was realized that in a broadband network typical of a larger service provider, Core routers would be required to accept, maintain, and tear down thousands or possibly tens of thousands of reservations. It was believed that this approach would not scale with the growth of the Internet, and in any event was antithetical to the notion of designing networks so that Core routers do little more than simply switch packets at the highest possible rates.

The second and currently accepted approach is differentiated services
Differentiated services
Differentiated Services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing Quality of Service on modern IP networks...

 (DiffServ). In the DiffServ model, packets are marked according to the type of service they need. In response to these markings, routers and switches use various queuing strategies to tailor performance to requirements. — At the IP layer, differentiated services code point (DSCP) markings use the 6 bits in the IP packet header. At the MAC layer, VLAN IEEE 802.1Q
IEEE 802.1Q
IEEE 802.1Q is the networking standard that supports Virtual LANs on an Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames...

 and IEEE 802.1p
IEEE 802.1p
IEEE P802.1p is the name of a task group active during 1995–98 responsible for adding traffic class expediting and dynamic multicast filtering to the IEEE 802.1D standard. Essentially, they provided a mechanism for implementing Quality of Service at the Media Access Control level...

 can be used to carry essentially the same information.

Routers supporting DiffServ use multiple queues for packets awaiting transmission from bandwidth constrained (e.g., wide area) interfaces. Router vendors provide different capabilities for configuring this behavior, to include the number of queues supported, the relative priorities of queues, and bandwidth reserved for each queue.

In practice, when a packet must be forwarded from an interface with queuing, packets requiring low jitter (e.g., VoIP or videoconferencing
Videoconferencing
Videoconferencing is the conduct of a videoconference by a set of telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously...

) are given priority over packets in other queues. Typically, some bandwidth is allocated by default to network control packets (such as Internet Control Message Protocol
Internet Control Message Protocol
The Internet Control Message Protocol is one of the core protocols of the Internet Protocol Suite. It is chiefly used by the operating systems of networked computers to send error messages indicating, for example, that a requested service is not available or that a host or router could not be...

 and routing protocols), while best effort traffic might simply be given whatever bandwidth is left over.

At the Media Access Control
Media Access Control
The media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...

 (MAC) layer, VLAN
Virtual LAN
A virtual local area network, virtual LAN or VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location...

 IEEE 802.1Q
IEEE 802.1Q
IEEE 802.1Q is the networking standard that supports Virtual LANs on an Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames...

 and IEEE 802.1p
IEEE 802.1p
IEEE P802.1p is the name of a task group active during 1995–98 responsible for adding traffic class expediting and dynamic multicast filtering to the IEEE 802.1D standard. Essentially, they provided a mechanism for implementing Quality of Service at the Media Access Control level...

 can be used to carry essentially the same information as used by DiffServ.

Cisco IOS
Cisco IOS
Cisco IOS is the software used on the vast majority of Cisco Systems routers and current Cisco network switches...

 NetFlow and the Cisco Class Based QoS (CBQoS) Management Information Base (MIB) are marketed by Cisco systems
Cisco Systems
Cisco Systems, Inc. is an American multinational corporation headquartered in San Jose, California, United States, that designs and sells consumer electronics, networking, voice, and communications technology and services. Cisco has more than 70,000 employees and annual revenue of US$...

.
Additional bandwidth management
Bandwidth management
Bandwidth management is the process of measuring and controlling the communications on a network link, to avoid filling the link to capacity or overfilling the link, which would result in network congestion and poor performance of the network.- Management :Bandwidth management mechanisms may be...

 mechanisms may be used to further engineer performance, to include:
  • Traffic shaping
    Traffic shaping
    Traffic shaping is the control of computer network traffic in order to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds of packets that meet certain criteria...

     (rate limiting
    Rate limiting
    In computer networks, rate limiting is used to control the rate of traffic sent or received on a network interface. Traffic that is less than or equal to the specified rate is sent, whereas traffic that exceeds the rate is dropped or delayed...

    ):
    • Token bucket
      Token bucket
      The token bucket is an algorithm used in packet switched computer networks and telecommunications networks to check that data transmissions conform to defined limits on bandwidth and burstiness ....

    • Leaky bucket
      Leaky bucket
      The leaky bucket is an algorithm used in packet switched computer networks and telecommunications networks to check that data transmissions conform to defined limits on bandwidth and burstiness . The leaky bucket algorithm is also used in leaky bucket counters, e.g...

    • TCP rate control—artificially adjusting TCP window size as well as controlling the rate of ACKs being returned to the sender
  • Scheduling algorithms:
    • Weighted fair queuing
      Weighted fair queuing
      Weighted fair queuing is a data packet scheduling technique allowing different scheduling priorities to statistically multiplexed data flows.WFQ is a generalization of fair queuing . Both in WFQ and FQ, each data flow has a separate FIFO queue...

       (WFQ)
    • Class based weighted fair queuing
    • Weighted round robin
      Weighted round robin
      Weighted round robin is a scheduling discipline. Each packet flow or connection has its own packet queue in a network interface card. It is the simplest approximation of generalized processor sharing...

       (WRR)
    • Deficit weighted round robin (DWRR)
    • Hierarchical Fair Service Curve (HFSC)
  • Congestion avoidance:
    • RED, WRED — Lessens the possibility of port queue buffer
      Computer port (software)
      In computer programming, port has a wide range of meanings.A software port is a virtual/logical data connection that can be used by programs to exchange data directly, instead of going through a file or other temporary storage location...

       tail-drop
      Tail drop
      Tail Drop, or Drop Tail, is a simple queue management algorithm used by Internet routers to decide when to drop packets. In contrast to the more complex algorithms like RED and WRED, in Tail Drop all the traffic is not differentiated. Each packet is treated identically...

      s and this lowers the likelihood of TCP global synchronization
      TCP global synchronization
      TCP global synchronization in Computer networks can happen toTCP/IP flows during periodsof congestion because each sender will reduce their transmission rate at the sametime when packet loss occurs....

    • Policing (marking/dropping the packet in excess of the committed traffic rate and burst size)
    • Explicit congestion notification
      Explicit Congestion Notification
      Explicit Congestion Notification is an extension to the Internet Protocol and to the Transmission Control Protocol and is defined in RFC 3168 . ECN allows end-to-end notification of network congestion without dropping packets. ECN is an optional feature that is only used when both endpoints...

    • Buffer tuning


While DiffServ is used in many sophisticated enterprise networks, it has not been widely deployed in the Internet. Internet peering
Peering
In computer networking, peering is a voluntary interconnection of administratively separate Internet networks for the purpose of exchanging traffic between the customers of each network. The pure definition of peering is settlement-free or "sender keeps all," meaning that neither party pays the...

 arrangements are already complex, and there appears to be no enthusiasm among providers for supporting QoS across peering connections, or agreement about what policies should be supported in order to do so.

One compelling example of the need for QoS on the Internet relates to congestion collapse. The Internet relies on congestion avoidance protocols, as built into Transmission Control Protocol
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...

 (TCP), to reduce traffic under conditions that would otherwise lead to "meltdown". QoS applications such as VoIP and IPTV
IPTV
Internet Protocol television is a system through which television services are delivered using the Internet protocol suite over a packet-switched network such as the Internet, instead of being delivered through traditional terrestrial, satellite signal, and cable television formats.IPTV services...

, because they require largely constant bitrates and low latency cannot use TCP and cannot otherwise reduce their traffic rate to help preventcongestion. QoS contracts limit traffic that can be offered to the Internet and thereby enforce traffic shaping that can prevent it from becoming overloaded, hence they're an indispensable part of the Internet's ability to handle a mix of real-time and non-real-time traffic without meltdown.

Protocols

  • The Type of Service
    Type of Service
    The type of service field in the IPv4 header has had various purposes over the years, and has been defined in different ways by five RFCs...

     (ToS) field in the IP(v4) header (now superseded by DiffServ
    Differentiated services
    Differentiated Services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing Quality of Service on modern IP networks...

    )
  • IP Differentiated services (DiffServ)
  • IP Integrated services (IntServ)
  • Resource reSerVation Protocol
    Resource Reservation Protocol
    The Resource Reservation Protocol is a Transport Layer protocol designed to reserve resources across a network for an integrated services Internet. RSVP operates over an IPv4 or IPv6 Internet Layer and provides receiver-initiated setup of resource reservations for multicast or unicast data flows...

     (RSVP)
  • Multiprotocol Label Switching
    Multiprotocol Label Switching
    Multiprotocol Label Switching is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links between...

     (MPLS) provides eight QoS classes
  • RSVP-TE
    RSVP-TE
    Resource Reservation Protocol - Traffic Engineering is an extension of the resource reservation protocol for traffic engineering. It supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature of the packet...

  • Frame relay
    Frame relay
    Frame Relay is a standardized wide area network technology that specifies the physical and logical link layers of digital telecommunications channels using a packet switching methodology...

  • X.25
    X.25
    X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...

  • Some ADSL modems
  • Asynchronous Transfer Mode
    Asynchronous Transfer Mode
    Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...

     (ATM)
  • IEEE 802.1p
    IEEE 802.1p
    IEEE P802.1p is the name of a task group active during 1995–98 responsible for adding traffic class expediting and dynamic multicast filtering to the IEEE 802.1D standard. Essentially, they provided a mechanism for implementing Quality of Service at the Media Access Control level...

  • IEEE 802.1Q
    IEEE 802.1Q
    IEEE 802.1Q is the networking standard that supports Virtual LANs on an Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames...

  • IEEE 802.11e
    IEEE 802.11e
    IEEE 802.11e-2005 or 802.11e is an approved amendment to the IEEE 802.11 standard that defines a set of Quality of Service enhancements for wireless LAN applications through modifications to the Media Access Control layer. The standard is considered of critical importance for delay-sensitive...

  • HomePNA
    HomePNA
    The HomePNA Alliance is an incorporated non-profit industry association of companies that develops and standardizes technology for home networking over the existing coaxial cables and telephone wiring within homes.-Overview:HomePNA does not manufacture products, although its members do...

     Home networking over coax and phone wires
  • The ITU-T
    ITU-T
    The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....

     G.hn
    G.hn
    G.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...

     standard provides QoS by means of “Contention-Free Transmission Opportunities” (CFTXOPs) which are allocated to flows which require QoS and which have negotiated a “contract” with the network controller. G.hn also supports non-QoS operation by means of “Contention-based Time Slots”.
  • Audio Video Bridging
    Audio Video Bridging
    Audio Video Bridging is a common name for the set of technical standards developed by the Institute of Electrical and Electronics Engineers Audio Video Bridging Task Group of the IEEE 802.1 standards committee. The charter of this organization is to "provide the specifications that will allow...


End-to-end quality of service

End-to-end quality of service can require a method of coordinating resource allocation between one autonomous system
Autonomous system (Internet)
Within the Internet, an Autonomous System is a collection of connected Internet Protocol routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the Internet....

 and another.
The Internet Engineering Task Force
Internet Engineering Task Force
The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...

 (IETF) defined the Resource Reservation Protocol
Resource Reservation Protocol
The Resource Reservation Protocol is a Transport Layer protocol designed to reserve resources across a network for an integrated services Internet. RSVP operates over an IPv4 or IPv6 Internet Layer and provides receiver-initiated setup of resource reservations for multicast or unicast data flows...

 (RSVP) for bandwidth reservation, as a proposed standard in 1997.
RSVP is an end-to-end
End-to-end principle
The end-to-end principle is a classic design principle of computer networking which states that application specific functions ought to reside in the end hosts of a network rather than in intermediary nodes, provided they can be implemented "completely and correctly" in the end hosts...

 bandwidth reservation protocol. The traffic engineering version, RSVP-TE
RSVP-TE
Resource Reservation Protocol - Traffic Engineering is an extension of the resource reservation protocol for traffic engineering. It supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature of the packet...

, is used in many networks to establish traffic-engineered Multiprotocol Label Switching
Multiprotocol Label Switching
Multiprotocol Label Switching is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links between...

 (MPLS) label-switched paths.
The IETF also defined Next Steps in Signaling (NSIS) with QoS signalling as a target. NSIS is a development and simplification of RSVP.

Research consortia such as "end-to-end quality of service support over heterogeneous networks" (EuQoS, from 2004 through 2007) and fora such as the IPsphere Forum
IPsphere Forum
The IPsphere Forum was an international non-profit consortium of computer network equipment manufacturers, IT companies and communications service providers...

 developed more mechanisms for handshaking QoS invocation from one domain to the next. IPsphere defined the Service Structuring Stratum (SSS) signaling bus in order to establish, invoke and (attempt to) assure network services.
EuQoS conducted experiments to integrate Session Initiation Protocol
Session Initiation Protocol
The Session Initiation Protocol is an IETF-defined signaling protocol widely used for controlling communication sessions such as voice and video calls over Internet Protocol . The protocol can be used for creating, modifying and terminating two-party or multiparty sessions...

, Next Steps in Signaling and IPsphere's SSS with an estimated cost of about 15.6 million Euro and published a book.

A research project Multi Service Access Everywhere (MUSE) defined another QoS concept in a first phase from January 2004 through February 2006, and a second phase from January 2006 through 2007.
Another research project named PlaNetS was proposed for European funding circa 2005.
A broader European project called "Architecture and design for the future Internet" known as 4WARD had a budgest estimated at 23.4 million Euro and was funded from January 2008 through June 2010.
It included a "Quality of Service Theme" and published a book.

Circumvention

Strong cryptography
Strong cryptography
Strong cryptography or cryptographically strong are general terms applied cryptographic systems or components that are considered highly resistant to cryptanalysis....

 network protocols such as Secure Sockets Layer
Transport Layer Security
Transport Layer Security and its predecessor, Secure Sockets Layer , are cryptographic protocols that provide communication security over the Internet...

, I2P
I2P
I2P is a mixed-license, free and open source project building an anonymous network .The network is a simple layer that applications can use to anonymously and securely send...

, and virtual private network
Virtual private network
A virtual private network is a network that uses primarily public telecommunication infrastructure, such as the Internet, to provide remote offices or traveling users access to a central organizational network....

s obscure the data transferred using them. As all electronic commerce
Electronic commerce
Electronic commerce, commonly known as e-commerce, eCommerce or e-comm, refers to the buying and selling of products or services over electronic systems such as the Internet and other computer networks. However, the term may refer to more than just buying and selling products online...

 on the Internet requires the use of such strong cryptography protocols, unilaterally downgrading the performance of encrypted traffic creates an unacceptable hazard for customers. Yet, encrypted traffic is otherwise unable to undergo deep packet inspection
Deep packet inspection
Deep Packet Inspection is a form of computer network packet filtering that examines the data part of a packet as it passes an inspection point, searching for protocol non-compliance, viruses, spam, intrusions or predefined criteria to decide if the packet can...

 for QoS.

Doubts about quality of service over IP

The Internet2
Internet2
Internet2 is an advanced not-for-profit US networking consortium led by members from the research and education communities, industry, and government....

 project found, in 2001, that the QoS protocols were probably not deployable inside its Abilene Network
Abilene Network
Abilene Network was a high-performance backbone network created by the Internet2 community in the late 1990s. In 2007 the Abilene Network was retired and upgraded network was known as the "Internet2 Network".-History:...

 with equipment available at that time.
Equipment available at the time relied on software to implement QoS. The group also predicted that “logistical, financial, and organizational barriers will block the way toward any bandwidth guarantees” by protocol modifications aimed at QoS.
They believed that the economics would encourage network providers to deliberately erode the quality of best effort traffic as a way to push customers to higher priced QoS services. Instead they proposed over-provisioning of capacity as more cost-effective at the time.

The Abilene network study was the basis for the testimony of Gary Bachula to the US Senate Commerce Committee
United States Senate Committee on Commerce, Science and Transportation
The United States Senate Committee on Commerce, Science, and Transportation is a standing committee of the United States Senate in charge of all senate matters related to the following subjects:* Coast Guard* Coastal zone management* Communications...

's hearing on Network Neutrality
Network neutrality
Network neutrality is a principle that advocates no restrictions by Internet service providers or governments on consumers' access to networks that participate in the Internet...

 in early 2006. He expressed the opinion that adding more bandwidth was more effective than any of the various schemes for accomplishing QoS they examined.

Bachula's testimony has been cited by proponents of a law banning quality of service as proof that no legitimate purpose is served by such an offering. This argument is dependent on the assumption that over-provisioning isn't a form of QoS and that it is always possible. Cost and other factors affect the ability of carriers to build and maintain permanently over-provisioned networks

Mobile (cellular) QoS

Mobile cellular service providers may offer mobile QoS
Mobile QoS
Quality of service mechanism controls the performance, reliability and usability of a telecommunications service. Mobile cellular service providers may offer mobile QoS to customers just as the fixed line PSTN services providers and Internet Service Provides may offer QoS...

 to customers just as the fixed line PSTN services providers and Internet Service Provides (ISP) may offer QoS. QoS mechanisms are always provided for circuit switched services, and are essential for non-elastic services, for example streaming multimedia.

Mobility adds complication to the QoS mechanisms, for several reasons:
  • A phone call or other session may be interrupted after a handover
    Handover
    In cellular telecommunications, the term handover or handoff refers to the process of transferring an ongoing call or data session from one channel connected to the core network to another...

    , if the new base station
    Base station
    The term base station can be used in the context of land surveying and wireless communications.- Land surveying :In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to derive correction information for nearby portable GPS...

     is overloaded. Unpredictable handovers make it impossible to give an absolute QoS guarantee during a session initiation phase.
  • The pricing structure is often based on per-minute or per-megabyte fee rather than flat rate
    Flat rate
    A flat fee, also referred to as a flat rate or a linear rate, refers to a pricing structure that charges a single fixed fee for a service, regardless of usage. Rarely, it may refer to a rate that does not vary with usage or time of use...

    , and may be different for different content services.
  • A crucial part of QoS in mobile communications is Grade of Service
    Grade of service
    In telecommunication engineering, and in particular teletraffic engineering, the quality of voice service is specified by two measures: the grade of service and the quality of service ....

    , involving outage probability (the probability that the mobile station is outside the service coverage area, or affected by co-channel interference, i.e. crosstalk) blocking probability (the probability that the required level of QoS can not be offered) and scheduling starvation. These performance measures are affected by mechanisms such as mobility management
    Mobility management
    Mobility management is one of the major functions of a GSM ora UMTS network that allows mobile phones to work. The aim of mobility management is to track where the subscribers are, allowing calls, SMS and other mobile phone services to be delivered to them....

    , radio resource management
    Radio resource management
    Radio resource management is the system level control of co-channel interference and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless networks and broadcasting systems...

    , admission control, fair scheduling, channel-dependent scheduling etc.

Standards

Quality of service in the field of telephony
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....

, was first defined in 1994 in the ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....

 Recommendation E.800. This definition is very broad, listing 6 primary components: Support, Operability, Accessibility, Retainability, Integrity and Security.
A 1995 recommendation X.902 included a definition is the OSI reference model.
In 1998 the ITU published a document discussing QoS in the field of data networking. X.641 offers a means of developing or enhancing standards related to QoS and provide concepts and terminology that will assist in maintaining the consistency of related standards.

The main QoS-related IETF Request For Comments
Request for Comments
In computer network engineering, a Request for Comments is a memorandum published by the Internet Engineering Task Force describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems.Through the Internet Society, engineers and...

 (RFC)s are Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers (RFC 2474), and Resource ReSerVation Protocol (RSVP) (RFC 2205); both these are discussed above. The IETF has also published two RFCs giving background on QoS: RFC 2990: Next Steps for the IP QoS Architecture, and RFC 3714: IAB Concerns Regarding Congestion Control for Voice Traffic in the Internet.

Open source software

  • Linux
    Linux
    Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

     Advanced Routing & Traffic Control (from 2000 to 2005)
  • Linux Bandwidth Arbitrator (2003 through 2005)
  • Zero Shell
  • mod qos
    Mod qos
    mod_qos is a quality of service module for the Apache HTTP server implementing control mechanisms that can provide different priority to different requests.-Description:...

     adding QoS to the Apache HTTP Server
    Apache HTTP Server
    The Apache HTTP Server, commonly referred to as Apache , is web server software notable for playing a key role in the initial growth of the World Wide Web. In 2009 it became the first web server software to surpass the 100 million website milestone...


See also

  • Application service architecture
    Application service architecture
    Application service architecture is an emerging discipline within IT that involves a top down approach to monitoring, controlling, securing, and optimizing applications in transit...

  • Best-effort
  • BSSGP
    BSSGP
    Base Station System GPRS Protocol. Information between SGSN and BSS. This protocol provides radio related Quality of Service and routing information that is required to transmit user data between a BSS and an SGSN. It does not carry out any form of error correction....

  • Bufferbloat
    Bufferbloat
    Bufferbloat is a phenomenon in a packet-switched computer network whereby excess buffering of packets inside the network causes high latency and jitter, as well as reducing the overall network throughput...

  • Class of Service
    Class of service
    -Class of service :As related to network technology, CoS is a 3-bit field within an Ethernet frame header when using 802.1Q tagging. The field specifies a priority value of between 0 and 7 inclusive that can be used by quality of service disciplines to differentiate traffic.While CoS operates only...

  • Deep packet inspection
    Deep packet inspection
    Deep Packet Inspection is a form of computer network packet filtering that examines the data part of a packet as it passes an inspection point, searching for protocol non-compliance, viruses, spam, intrusions or predefined criteria to decide if the packet can...

     (DPI)
  • Grade of service
    Grade of service
    In telecommunication engineering, and in particular teletraffic engineering, the quality of voice service is specified by two measures: the grade of service and the quality of service ....

     (GoS)
  • Mean Opinion Score
    Mean Opinion Score
    The Mean Opinion Score test has been used for decades in telephony networks to obtain the human user's view of the quality of the network. In multimedia especially when codecs are used to compress the bandwidth requirement , the mean opinion score ...

     (MOS)
  • Mobile QoS
    Mobile QoS
    Quality of service mechanism controls the performance, reliability and usability of a telecommunications service. Mobile cellular service providers may offer mobile QoS to customers just as the fixed line PSTN services providers and Internet Service Provides may offer QoS...

  • Network neutrality
    Network neutrality
    Network neutrality is a principle that advocates no restrictions by Internet service providers or governments on consumers' access to networks that participate in the Internet...

  • QPPB
    QPPB
    QoS Policy Propagation via BGP , is a mechanism that allows propagation of quality of service policy and classification by the sending party based on access lists, community lists and autonomous system paths in the Border Gateway Protocol , thus helping to classify based on destination instead of...

  • Quality of Experience
    Quality of experience
    Quality of experience , some times also known as quality of user experience, is a subjective measure of a customer's experiences with a service...

     (QoE)
  • Series of tubes
    Series of tubes
    "Series of tubes" is a phrase coined originally as an analogy by then-United States Senator Ted Stevens to describe the Internet in the context of opposing network neutrality. On June 28, 2006, he used this metaphor to criticize a proposed amendment to a committee bill...

  • Streaming media
    Streaming media
    Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...

  • Subjective video quality
    Subjective video quality
    Subjective video quality is a subjective characteristic of video quality. It is concerned with how video is perceived by a viewer and designates his or her opinion on a particular video sequence...

  • Tiered Internet
    Tiered Internet
    Tiered Internet is a proposed Internet architecture that would allow telecommunications providers to divide traffic over their lines into different tiers. High speed tiers can be dedicated for websites with large broadband applications such as voice and streaming video.-External links:* *...

  • Traffic shaping
    Traffic shaping
    Traffic shaping is the control of computer network traffic in order to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds of packets that meet certain criteria...


Further reading


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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