Difference between revisions of "QoS"
The Wiki of Unify contains information on clients and devices, communications systems and unified communications. - Unify GmbH & Co. KG is a Trademark Licensee of Siemens AG.
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Call Admissin Control makes sure that existing flows will keep their quality by rejecting any additional high priority flow. In the terms of telephony, the call is rejected and will either receive a busy signal or is rerouted. | Call Admissin Control makes sure that existing flows will keep their quality by rejecting any additional high priority flow. In the terms of telephony, the call is rejected and will either receive a busy signal or is rerouted. | ||
| − | Siemens HiPath 8000 has implemented a Call Admission Control which works in hub-and-spoke or star topologies. Topologies are abstracted to zones with unlimited bandwidth ressources which are interconnected by bottlenecks. If phone A_1 resides in zone_A only, if the bandwidth needed does not exceedand phone B_1 resides in zone_B and those zones are interconnected with a bottleneck link of 150 kbps, the call of 100 kbps is admitted, if no other call is using the bottleneck link. Now, a second phone A_2 in zone_A wants to start an other 100 kbps call to phone B_2 in zone_B. Since the needed bandwidth would exceed the left bandwidth ressources of 50 kbps, the call will be rejected, preserving the call quality of the first call. | + | === Centralized Static Call Admission Control === |
| + | Siemens HiPath 8000 has implemented a centralized static Call Admission Control which works in hub-and-spoke or star topologies. Topologies are abstracted to zones with unlimited bandwidth ressources which are interconnected by bottlenecks. If phone A_1 resides in zone_A only, if the bandwidth needed does not exceedand phone B_1 resides in zone_B and those zones are interconnected with a bottleneck link of 150 kbps, the call of 100 kbps is admitted, if no other call is using the bottleneck link. Now, a second phone A_2 in zone_A wants to start an other 100 kbps call to phone B_2 in zone_B. Since the needed bandwidth would exceed the left bandwidth ressources of 50 kbps, the call will be rejected, preserving the call quality of the first call. | ||
In the case of the HiPath 8000 solution, telephones are classified to be members of certain zones based on IP-addresses or telephone numbers. | In the case of the HiPath 8000 solution, telephones are classified to be members of certain zones based on IP-addresses or telephone numbers. | ||
| − | A standard way of performing Call Admission Control is Ressource ReserVation Protocol (RSVP), i.e. the "IntServ Model". With RSVP, each end system that seeks to send a data flow will send an RSVP PATH message to its communication partner. Network elements along the path that are RSVP aware will add route records to the RSVP PATH messages; others will route the packets like normal IP packets. The communication parter will respond to the RSVP message with a RESV packet and will send it back along the recorded path. RSVP aware network elements now will perform the reservation, if enough bandwith is available or will indicate the failure in the RSVP RESV packet. | + | Cisco CallManager makes use of the very same centralized static Call Admission Control and also is limited to hub-and-spoke or star topologies. |
| + | |||
| + | === Network based dynamic Call Admission Control === | ||
| + | A standard way of performing Call Admission Control is '''Ressource ReserVation Protocol (RSVP)''', i.e. the "IntServ Model". With RSVP, each end system that seeks to send a data flow will send an RSVP PATH message to its communication partner. Network elements along the path that are RSVP aware will add route records to the RSVP PATH messages; others will route the packets like normal IP packets. The communication parter will respond to the RSVP message with a RESV packet and will send it back along the recorded path. RSVP aware network elements now will perform the reservation, if enough bandwith is available or will indicate the failure in the RSVP RESV packet. | ||
RSVP has gained a bad reputation of not being scalable. However, Cisco argues, that the bad reputation is because RSVP had been used for Call Admission Control as well as Queuing and Scheduling. When using RSVP for Call Admission Control only it will be scalable and they recommend to use the "DiffServ model" based on packet marking for Queuing and Scheduling | RSVP has gained a bad reputation of not being scalable. However, Cisco argues, that the bad reputation is because RSVP had been used for Call Admission Control as well as Queuing and Scheduling. When using RSVP for Call Admission Control only it will be scalable and they recommend to use the "DiffServ model" based on packet marking for Queuing and Scheduling | ||
Revision as of 14:28, 8 February 2007
Contents
General
Quality of Service (QoS) refers to control mechanisms in data networks that try to ensure a certain level of performance to a data flow in accordance with requests from the application program. Data equipment tries to ensure the requested level of performance among others by performing
- Call Admission Control,
- Classification of Packets,
- Rewriting (reclassification),
- Queuing and Scheduling,
- Traffic Shaping.
Call Admission Control
Mechanisms like Queuing and Scheduling help to discriminate high prority or "real-time" traffic from other data traffic. However, if the sum of all high priority flows exceed the capabilites of network links or elements, those techniques will fail. In this case, an additional high priority flow will degrade the quality of all existing flows.
Call Admissin Control makes sure that existing flows will keep their quality by rejecting any additional high priority flow. In the terms of telephony, the call is rejected and will either receive a busy signal or is rerouted.
Centralized Static Call Admission Control
Siemens HiPath 8000 has implemented a centralized static Call Admission Control which works in hub-and-spoke or star topologies. Topologies are abstracted to zones with unlimited bandwidth ressources which are interconnected by bottlenecks. If phone A_1 resides in zone_A only, if the bandwidth needed does not exceedand phone B_1 resides in zone_B and those zones are interconnected with a bottleneck link of 150 kbps, the call of 100 kbps is admitted, if no other call is using the bottleneck link. Now, a second phone A_2 in zone_A wants to start an other 100 kbps call to phone B_2 in zone_B. Since the needed bandwidth would exceed the left bandwidth ressources of 50 kbps, the call will be rejected, preserving the call quality of the first call.
In the case of the HiPath 8000 solution, telephones are classified to be members of certain zones based on IP-addresses or telephone numbers.
Cisco CallManager makes use of the very same centralized static Call Admission Control and also is limited to hub-and-spoke or star topologies.
Network based dynamic Call Admission Control
A standard way of performing Call Admission Control is Ressource ReserVation Protocol (RSVP), i.e. the "IntServ Model". With RSVP, each end system that seeks to send a data flow will send an RSVP PATH message to its communication partner. Network elements along the path that are RSVP aware will add route records to the RSVP PATH messages; others will route the packets like normal IP packets. The communication parter will respond to the RSVP message with a RESV packet and will send it back along the recorded path. RSVP aware network elements now will perform the reservation, if enough bandwith is available or will indicate the failure in the RSVP RESV packet.
RSVP has gained a bad reputation of not being scalable. However, Cisco argues, that the bad reputation is because RSVP had been used for Call Admission Control as well as Queuing and Scheduling. When using RSVP for Call Admission Control only it will be scalable and they recommend to use the "DiffServ model" based on packet marking for Queuing and Scheduling
