|
Cs 552 Computer Networks Quality Of Service
|
| bet | 11/12 | | Sana | 26.12.2023 | | Hajmi | 492 Kb. | | #128375 |
Bog'liq qos-f05Edge Router - Per aggregate
- Classification
- (e.g., user)
Assumptions - Assume two bits
- P-bit denotes premium traffic
- A-bit denotes assured traffic
- Traffic conditioner (TC) implement
TC Performing Metering/Marking - Used to implement Assured Service
- In-profile traffic is marked:
- A-bit is set in every packet
- Out-of-profile (excess) traffic is unmarked
- A-bit is cleared (if it was previously set) in every packet; this traffic treated as best-effort
TC Performing Metering/Marking/Shaping - Used to implement Premium Service
- In-profile traffic marked:
- Out-of-profile traffic is delayed, and when buffer overflows it is dropped
- Metering/
- Shaper/
- Set P-bit
- out-of-profile traffic
- (delayed and dropped)
- User profile
- (token bucket)
Scheduler - Employed by both edge and core routers
- For premium service – use strict priority, or weighted fair queuing (WFQ)
- For assured service – use RIO (RED with In and Out)
- Always drop OUT packets first
- For OUT measure entire queue
- For IN measure only in-profile queue
Scheduler Example Control Path - Each domain is assigned a Bandwidth Broker (BB)
- Usually, used to perform ingress-egress bandwidth allocation
- BB is responsible to perform admission control in the entire domain
- BB not easy to implement
- Require complete knowledge about domain
- Single point of failure, may be performance bottleneck
- Designing BB still a research problem
Example - Achieve end-to-end bandwidth guarantee
Comparison: Best-Effort, Diffserv, Intserv | | | | | | | - Connectivity
- No isolation
- No guarantees
| | - Per flow isolation
- Per flow guarantee
| | | | | | | | | | | | | - Highly scalable (nodes maintain only routing state)
| | - Not scalable (each router maintains per flow state)
| Summary - Diffserv more scalable than Intserv
- Edge routers maintain per aggregate state
- Core routers maintain state only for a few traffic classes
- But, provides weaker services than Intserv, e.g.,
- Per aggregate bandwidth guarantees (premium service) vs. per flow bandwidth and delay guarantees
- BB is not an entirely solved problem
- Single point of failure
- Handle only long term reservations (hours, days)
Non-technical Factors Impacting QoS - Existing Networks
- What is available today to solve our needs? Why switch?
- Business Models
- How QoS make doing business harders
- Deployment Issues
- How QoS makes running the network harder.
|
| |
