1. CprE 458/558: Real-Time Systems
Real-Time Networks – WAN
Channel establishment
CprE 458/558: Real-Time Systems (G. Manimaran)

2. QoS metrics: types of constraint
Metrics and their nature
End-to-end delay: additive metric, path metric
Delay jitter: additive metric, path metric
Bandwidth: convex (min), link metric
Packet loss: multiplicative, path metric
Theorem: A problem with two or more path constraints is NP-Complete, assuming the constraints are independent and the values are real.
CprE 458/558: Real-Time Systems (G. Manimaran)

3. QoS routing problem instances
Given a graph G(V,E), with each edge labeled with (cost, delay, available bw).
Bandwidth-constrained least-cost routing
Polynomial time problem
Solution: Remove edges that don’t satisfy BW constraint and then run shortest path algorithm on the reduced graph.
Delay-constrained, BW-constrained, least-cost routing
NP-complete problem
Heuristics exists
CprE 458/558: Real-Time Systems (G. Manimaran)

4. Channel establishment – QoS routing
Source Routing
Source computes the routing path
Obtaining global state is difficult
Not scalable
Distributed Routing (hop-by-hop)
Each node decides what is the next hop
Lack of global knowledge  inferior paths
Scalable
Hierarchical Routing
Based on aggregate state information
Scalable (works well for inter-domain routing)
Compromise between source and distributed routings
CprE 458/558: Real-Time Systems (G. Manimaran)

5. Choose the entire path from source to destination
Source Routing
Connection 1 1 S D
The source has the entire network state information (cost, delay, etc.. of each edge)
CprE 458/558: Real-Time Systems (G. Manimaran)

6. Distributed / Hop-by-hop Routing
Connection 1 1 S D
CprE 458/558: Real-Time Systems (G. Manimaran)

7. CprE 458/558: Real-Time Systems (G. Manimaran)
Hierarchical Routing S D
CprE 458/558: Real-Time Systems (G. Manimaran)

8. Hierarchical Routing Routing based on precise state 1
Routing based on aggregate state S
Routing based on precise state D
CprE 458/558: Real-Time Systems (G. Manimaran)

9. QoS Source Routing
Choose the path from source to destination that satisfies the QoS requirements based on some heuristic function
Connection 1
With some QoS requirements 1 S D
The source has the entire network state information (cost, delay, etc.. of each edge)
CprE 458/558: Real-Time Systems (G. Manimaran)

10. QoS Hop-by-hop Connection setup
No outgoing edge satisfies the required QoS
Therefore, back off
Connection 1
With some QoS requirements 1 S D
CprE 458/558: Real-Time Systems (G. Manimaran)

11. Channel establishment – Resource reservation
Once a feasible path is found, resources such as bandwidth, buffers are reserved along the path
Resource Reservation Protocol (RSVP)
Receiver-driven protocol
Supports multicast as well as unicast
Provides different type of reservation styles
CprE 458/558: Real-Time Systems (G. Manimaran)