Quality of service
Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a
, etc.In the field of
Quality of service is particularly important for the transport of traffic with special requirements. In particular, developers have introduced Voice over IP technology to allow computer networks to become as useful as telephone networks for audio conversations, as well as supporting new applications with even stricter network performance requirements.
Definitions
In the field of
In the field of
A network or protocol that supports QoS may agree on a traffic contract 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
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.[3] High QoS is often confused with a high level of performance, for example high bit rate, low latency and low bit error rate.
QoS is sometimes used in application layer services such as telephony and
History
A number of attempts for
Ethernet optionally uses
There were four
With the advent of
Qualities of traffic
In
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:
- Goodput
- Due to varying load from disparate users sharing the same network resources, the maximum throughput that can be provided to a certain data stream may be too low for real-time multimedia services.
- Packet loss
- The network may fail to deliver (drop) some packets due to network congestion. The receiving application may ask for this information to be retransmitted, possibly resulting in congestive collapseor unacceptable delays in the overall transmission.
- Errors
- Sometimes packets are corrupted due to bit errorscaused 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 it takes a less direct route to avoid congestion. In some cases, excessive latency can render an application such as VoIP or online gaming unusable.
- Packet delay variation
- 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. Delay variation can be absorbed at the receiver, but in so doing increases the overall latency for the stream.
- 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 for rearranging out-of-order packets. The reordering process requires additional buffering at the receiver, and, as with packet delay variation, increases the overall latency for the stream.
Applications
A defined quality of service may be desired or required for certain types of network traffic, for example:
- Streaming media specifically
- Voice over IP (VoIP)
- Videotelephony
- Telepresence
- Storage applications such as iSCSI and Fibre Channel over Ethernet
- Circuit emulation service
- Safety-critical applications such as remote surgery where availability 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 can be a factor
- Industrial control systems protocols such as EtherNet/IP which are used for real-time control of machinery
These types of service are called inelastic, meaning that they require a certain minimum bit rate 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 are generally elastic.
Mechanisms
Circuit switched networks, especially those intended for voice transmission, such as ATM or
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 (SLA) which specifies guarantees for the ability of a connection to give guaranteed performance in terms of throughput or latency based on mutually agreed measures.
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 for networks with predictable peak loads. This calculation may need to appreciate 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 in the face of transport protocols (such as TCP) that over time 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.
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.
Commercial VoIP services are often competitive with traditional telephone service in terms of call quality even without QoS mechanisms in use on the user's connection to their 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.[5]
IP and Ethernet efforts
Unlike single-owner networks, the Internet is a series of exchange points interconnecting private networks.[6] Hence the Internet's core is owned and managed by a number of different network service providers, not a single entity. Its behavior is much more unpredictable.
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 ("IntServ") implements the parameterized approach. In this model, applications use the Resource Reservation Protocol (RSVP) to request and reserve resources through a network.
- IP(v4) packet header.
Early work used the integrated services (IntServ) philosophy of reserving network resources. In this model, applications used 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,[7] and in any event was antithetical to the end-to-end principle, the notion of designing networks so that core routers do little more than simply switch packets at the highest possible rates.
Under DiffServ, packets are marked either by the traffic sources themselves or by the edge devices where the traffic enters the network. In response to these markings, routers and switches use various queuing strategies to tailor performance to requirements. At the IP layer, DSCP markings use the 6 bit DS field in the IP packet header. At the MAC layer, VLAN IEEE 802.1Q can be used to carry 3 bit of essentially the same information. Routers and switches supporting DiffServ configure their network scheduler to 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.,
At the
One compelling example of the need for QoS on the Internet relates to
Protocols
Several QoS mechanisms and schemes exist for IP networking.
- The DiffServ)
- Differentiated services (DiffServ)
- Integrated services (IntServ)
- Resource Reservation Protocol (RSVP)
- RSVP-TE
QoS capabilities are available in the following network technologies.
- Multiprotocol Label Switching (MPLS) provides eight QoS classes[11]
- Frame Relay
- X.25
- Some DSL modems
- ATM
- Ethernet supporting IEEE 802.1Q with Audio Video Bridging and Time-Sensitive Networking
- IEEE 802.11e
- HomePNA home networking over coax and phone wires
- The G.hn home networking 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.
End-to-end quality of service
End-to-end quality of service can require a method of coordinating resource allocation between one autonomous system and another. The Internet Engineering Task Force (IETF) defined the Resource Reservation Protocol (RSVP) for bandwidth reservation as a proposed standard in 1997.[12] RSVP is an end-to-end bandwidth reservation and admission control protocol. RSVP was not widely adopted due to scalability limitations.[13] The more scalable traffic engineering version, RSVP-TE, is used in many networks to establish traffic-engineered Multiprotocol Label Switching (MPLS) label-switched paths.[14] The IETF also defined Next Steps in Signaling (NSIS)[15] 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)
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.[20][21][22] Another research project named PlaNetS was proposed for European funding circa 2005.[23] A broader European project called "Architecture and design for the future Internet" known as 4WARD had a budget estimated at 23.4 million Euro and was funded from January 2008 through June 2010.[24] It included a "Quality of Service Theme" and published a book.[25][26] Another European project, called WIDENS (Wireless Deployable Network System),[27] proposed a bandwidth reservation approach for mobile wireless multirate adhoc networks.[28]
Limitations
Protocols like ICA and RDP may encapsulate other traffic (e.g. printing, video streaming) with varying requirements that can make optimization difficult.
The Internet2 project found, in 2001, that the QoS protocols were probably not deployable inside its Abilene Network with equipment available at that time.[29][a] The group predicted that “logistical, financial, and organizational barriers will block the way toward any bandwidth guarantees” by protocol modifications aimed at QoS.[30] 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.[29][30]
The Abilene network study was the basis for the testimony of Gary Bachula to the
Mobile (cellular) QoS
Mobile cellular service providers may offer
Mobility adds complications to QoS mechanisms. A phone call or other session may be interrupted after a handover if the new base station is overloaded. Unpredictable handovers make it impossible to give an absolute QoS guarantee during the session initiation phase.
Standards
Quality of service in the field of telephony was first defined in 1994 in ITU-T Recommendation E.800. This definition is very broad, listing 6 primary components: Support, Operability, Accessibility, Retainability, Integrity and Security.[1] 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 should assist in maintaining the consistency of related standards.[32]
Some QoS-related IETF
The IETF has also published Baker, Fred; Babiarz, Jozef; Chan, Kwok Ho (August 2006), Configuration Guidelines for DiffServ Service Classes,
See also
Notes
- ^ Equipment available at the time relied on software to implement QoS.
References
- ^ a b "E.800: Terms and definitions related to quality of service and network performance including dependability". ITU-T Recommendation. August 1994. Retrieved October 14, 2011. Updated September 2008 as Definitions of terms related to quality of service
- ^ Teletraffic Engineering Handbook Archived January 11, 2007, at the Wayback Machine ITU-T Study Group 2 (350 pages, 2.69 MB)(It uses abbreviation GoS instead of QoS)
- .
- ^ Peuhkuri M. (1999-05-10). "IP Quality of Service". Helsinki University of Technology, Laboratory of Telecommunications Technology.
- S2CID 10365270. Archived from the original (PDF) on 2012-04-30. Retrieved 2009-01-24.)
{{cite book}}
: CS1 maint: date and year (link) CS1 maint: location missing publisher (link - ^ "An Evening With Robert Kahn". Computer History Museum. 9 Jan 2007. Archived from the original on December 19, 2008.
- ISBN 978-0-12-119792-6.
However, the effort required in setting flow-based resource reservations along the route is enormous. Further, the control signaling required and state maintenance at routers limit the scalability of this approach.
- .
- .
- ^ Ben Erwin (December 16, 2008). "How To Manage QoS In Your Environment, Part 1 of 3". Network Performance Daily video. NetQoS. Archived from the original on September 29, 2011. Retrieved October 15, 2011.
- ^ "VoIP on MPLS". Search Unified Communications. Retrieved 12 March 2012.
- )
- ^ MPLS Segment Routing, Arista, 10 December 2019, retrieved 2020-04-16
- ^ ""Next Steps in Signaling" Charter".
- ^ "EuQoS - End-to-end Quality of Service support over heterogeneous networks". Project website. 2004–2006. Archived from the original on April 30, 2007. Retrieved October 12, 2011.
- ^ IPSphere: Enabling Advanced Service Delivery Archived January 13, 2011, at the Wayback Machine
- ^ "End-to-end quality of service support over heterogeneous networks". Project description. European Community Research and Development Information Service. Retrieved October 12, 2011.
- ISBN 978-3-540-79119-5.
- ^ "Multi Service Access Everywhere (MUSE)". Project website. Retrieved October 12, 2011.
- ^ "Multi Service Access Everywhere". Project description. European Community Research and Development Information Service. Retrieved October 12, 2011.
- ^ "Multi Service Access Everywhere". Project description. European Community Research and Development Information Service. Retrieved October 12, 2011.
- ^ "PlaNetS QoS Solution". Project website. 2017-07-28. Archived from the original on November 12, 2009. Retrieved October 12, 2011.
- ^ "4WARD: Architecture and design for the future Internet". Project description. European Community Research and Development Information Service. Retrieved October 15, 2011.
- ^ "Going 4WARD". Project newsletter. June 2010. Archived from the original (PDF) on May 9, 2013. Retrieved October 15, 2011.
- ISBN 978-90-481-9345-5.
- ^ "Wireless Deployable Network System". Project description. European Union. Retrieved May 23, 2012.
- .
- ^ Stanislav Shalunov (May 3, 2002). "Why Premium IP Service Has Not Deployed (and Probably Never Will)". Draft Informational Document. Internet2 QoS Working Group. Archived from the originalon August 30, 2002. Retrieved October 15, 2011.
- ^ a b Andy Oram (June 11, 2002). "A Nice Way to Get Network Quality of Service?". Platform Independent column. O'Reilly. Archived from the original on August 5, 2002. Retrieved October 15, 2011.
- ^ Gary Bachula (February 7, 2006). "Testimony of Gary R. Bachula, Vice President, Internet2" (PDF). pp. 2–3. Archived from the original (PDF) on January 7, 2010. Retrieved October 15, 2011.
- ^ "X.641: Information technology - Quality of service: framework". ITU-T Recommendation. December 1997.
Further reading
- Deploying IP and MPLS QoS for Multiservice Networks: Theory and Practice by John Evans, Clarence Filsfils (Morgan Kaufmann, 2007, ISBN 0-12-370549-5)
- Lelli, F. Maron, G. Orlando, S. Client Side Estimation of a Remote Service Execution. 15th International Symposium on Modeling, Analysis, and Simulation of Computer and Telecommunication Systems, 2007. MASCOTS '07.
- QoS Over Heterogeneous Networks by Mario Marchese (Wiley, 2007, ISBN 978-0-470-01752-4)
- XiPeng Xiao (September 8, 2008). Technical, Commercial and Regulatory Challenges of QoS: An Internet Service Model Perspective. Morgan Kaufmann. ISBN 978-0-12-373693-2.
- Braden, Robert T.; Clark, David D.; Shenker, Scott (June 1994), Integrated Services in the Internet Architecture: an Overview, RFC 1633
- Black, David L.; Wang, Zheng; Carlson, Mark A.; Weiss, Walter; Davies, Elwyn B.; Blake, Steven L. (December 1998), An Architecture for Differentiated services, RFC 2475
- Awduche, Daniel O.; Berger, Lou; Gan, Der-Hwa; Li, Tony; Srinivasan, Vijay; Swallow, George (December 2001), RSVP-TE: Extensions to RSVP for LSP Tunnels, RFC 3209
External links
- Nate Hoy. "Implementing QoS". Vonage Forum. Retrieved October 14, 2011.
- Cisco's Internetworking Technology Handbook Archived 2015-09-06 at the Wayback Machine
- Henning Schulzrinne (January 9, 2008). "Network Quality of Service". Columbia University faculty website. Retrieved October 14, 2011.
- "Quality of Service (QoS) Overview". Microsoft TechNet. March 31, 2011. Retrieved October 14, 2011.
- "Quality of Service (QoS) in High-Priority Applications" (PDF). Transition Networks. February 2003. Retrieved February 16, 2017.
- "Implementing Quality of Service for Prioritizing Network Traffic". EtherWAN. Retrieved December 15, 2022.