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CprE 458/558: Real-Time Systems. Real-Time Networks – WAN Channel establishment. 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 - PowerPoint PPT Presentation
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CprE 458/558: Real-Time Systems (G. Manimaran) 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
Source Routing
S
D
Connection 11
•The source has the entire network state information (cost, delay, etc.. of each edge)
Choose the entire path
from source to destination
CprE 458/558: Real-Time Systems (G. Manimaran) 6
Distributed / Hop-by-hop Routing
S
D
Connection 11
CprE 458/558: Real-Time Systems (G. Manimaran) 7
Hierarchical Routing
S
D
CprE 458/558: Real-Time Systems (G. Manimaran) 8
Hierarchical Routing
S
D
Routingbased on precise state
Routing based on precise state
Routing based on aggregate
state
1
CprE 458/558: Real-Time Systems (G. Manimaran) 9
QoS Source Routing
S
D
Connection 1
With some QoS
requirements
1
•The source has the entire network state information (cost, delay, etc.. of each edge)
Choose the path from source to destination that
satisfies the QoS requirements based on some heuristic function
CprE 458/558: Real-Time Systems (G. Manimaran) 10
QoS Hop-by-hop Connection setup
S
D
Connection 1
With some QoS
requirements
1
No outgoing edge satisfies the required
QoSTherefore, back off
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
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