19-09-2012, 11:16 AM
DiffServ QoS in internet
DiffServ.ppt (Size: 750 KB / Downloads: 256)
Why do we need QoS ?
IP revolution - from “IP over everything” to “everything over IP”
Current Internet guarantee: Best Effort only.
Some applications require more:
Guarantee delay, jitter
Guarantee bandwidth
Guarantee loss rate
(VoIP, Conference-Calls, VPN, VOD…)
Although QoS is available in lower layers (ATM, FR, Ethernet) we need a media independent IP QoS
Little History
An 8 bit field in the IP-header
Seems like a good idea for future use.
Lots of initial research in the late 80s and early 90s.
Often takes a telecommunications view of the network.
ATM QoS and Integrated services were developed based on these results (1995).
Focus on per-flow, hard QoS.
Effort was driven by perceived application needs.
In the last years (from 1998), the focus has shifted towards Differentiated services.
Focus is on QoS for flow aggregates, e.g., all the flows belonging to one customer.
From 2000 , you can buy a router that support DiffServ (Cisco)
What is needed to support QoS
Between the network and its clients - Traffic contract
Traffic specification/desired QoS/supported QoS
At network edge:
Signaling and admission control
Packet classification/marking
Traffic shaping
Traffic policing
IntServ
Per-flow QoS guarantees
Reservation of resources using RSVP
Two service models:
controlled-load service: performance is as good as unloaded network
guaranteed service: firm bound of throughput and delay
IntServ drawbacks
Scalability
RSVP support along the path
Maintaining “soft” reservations
Complexity
Support for each flow
Need to administrate allocations
What is DiffServ?
Aggregate connections flows to different classes
Different demand can be guaranteed to each class
Guarantees implementations are per hop behavior
Each flow gets required services statistically