Quality of Services for IP Access Network
Original Publication Date: 2001-Oct-01
Included in the Prior Art Database: 2003-Jul-23
Information / Kommunikation
Quality of Services for IP AccessNetwork
Idee: Qi Guan, A-Wien
Until now, two separate worlds have existed for tele-communication services and networks – one for voiceand one for data.
The voice world is that of switched PSTN / ISDNnetworks, which generally provide real-time servicesand features such as call diversions, conference anddisplay services. Switched PSTN / ISDN networksguarantee quality and reliability in the form ofconstant availability of voice services for theircustomers. As a result thereof, this quality of servicehas made voice networks extremely profitable.
The other world is that of low-cost and efficient dataservices such as e-mail, file transfer and access to‘information’ resources of the World Wide Web(WWW) provided by packet-based networks, mainlythe Internet. These data networks are based on com-mercial servers and widespread programming envi-ronments. They offer a degree of flexibility whichallows the short term creation of applications.
Using slogans like ”The convergence of the network”and ”Everything over IP”, more and more traditionaltelco services (e.g.: telephony, video conference,radio/TV broadcasting, etc.) are being adapted forInternet usage. This has caused an increase in Internettraffic as the number of users and applications thatare constantly being introduced to the Internet.
In addition and due to the multitudes of new applica-tions the character of Internet traffic has also beenand still is in the process of changing to meet de-mands. Some of the new breed of Internet applicati-ons, for example IP-telephony, have very strict timingrequirements. The end-to-end latency (phone-to-phone) determines whether the conversation soundsinteractive or not. A delay of 100 msec is the thres-hold for phone companies. A delay larger the 200msec is quite noticeable and will usually cause aswitch to half-duplex conversation.
The latency of an Internet transmission depends on:
• network congestion,
• number of routers involved,
• type of prioritisation,
• delay of voice encoding, and
In order to be able to ensure acceptable IP telephoneservices the Internet must provide enough bandwidth,low delay. Generally speaking, the Internet must offer
Siemens Technik Report Jahrgang 4 Nr.13 Oktober 2001
Information / Kommunikation
2 Quality of Service Technologies
This section describes some technologies concerningQoS for IP services. The Internet Engineering TaskForce (IETF) has proposed many service models andmechanisms designed to meet the demands for Inter-net QoS. Among them are the Integrated Servi-ces / RSVP model, the Differentiated Services (Diff-Serv) model and the Multi-Protocol Label Switching(MPLS).
The ATM forum has also proposed ATM QoS servi-ces, for example, CBR (Constant Bit Rate), UBR(Unspecified Bit Rate),VBR (Variable Bit Rate) andABR (Avail...