最新-Fundamental QoS Routing Experiment基本的QS路由实验-PPT文档资料

• 36 node, highly connected network • Trunk capacity = 15Mbps • Non uniform traffic requirement • Two routing strategies are compared:
– Minhop routing (no CAC) – QoS routing
- end-to-end delay, - available buffer size, - available bandwidth
Bellman-Ford Algorithm (with delay)
Bellman Equation : Dih+1 =min[d(i ,j) + Dhj]
1
2 10 4
With QoS routing:
– optimal route; “focused congestion” avoidance – efficient Call Admission Control (at the source) – efficient bandwidth allocation (per traffic class) – resource renegotiation easier
• Packet forwarding: (a) source routing (per flow) (b) MPLS (per class)
Application I: IP Telephony
• M-CAC at source; no bandwidth reservation along path
– However, B/F generates solutions by increasing hop distance; thus, the first found feasible solution is “hop” optimal (ie, min hop)
• Polynomial performance for most common sets of MC (multiple constraints e.g. bandwidth and delay )
2) Link State Update - describes sender’s cost to its neighbors
3) Link State Ack. - acknowledges Link State Update
4) Database description - lets nodes determine who has the most recent link state information
35
QoS Simulator: Voice Source Modeling
Voice connection requests arrive according to a Poisson process, or at fixed intervals Once a connection is established, the voice source is modeled as 2 state Markov chain
• Call Acceptance Control (CAC)
• Packet Forwarding: source route or MPLS
OSPF Overview
5 Message Types
1) “Hello” - lets a node know who the neighbors are
QoS Routing and Forwarding
2019
Benefits of QoS Routing
Without QoS routing:
– must probe path & backtrack; non optimal path, control traffic and processing OH, latency

TALK

SILENCE
1/ = 352 ms 1/ = 650 ms 1 voice packet every 20ms during talk state
Simulation Parameters
10 Minute Simulation Runs Each voice connection lasts 3 minutes OSPF updates are generated every 2 seconds (30 minute OSPF update interval in Minhop scheme) New voice connections generated with fixed interarrival (150 ms) Measurements are in Steady-state (after 3 minutes) 100 msec delay threshold 3 Mbit/sec bandwidth margin on each trunk The candidate source destination pairs are : (8,20),(0,34),(3,32), (4,32), (5,32), (10,32), (16, 32)
• To replace the Dijkstra algorithm using BellmanFord constrained path computation algorithm: it computes constrained min hop paths to all destinations at each node based on topology map
Multiple Constraints QoS Routing
Given:
- a (real time) connection request with specified QoS requirements (e.g., Bdw, Delay, Jitter, packet loss, path reliability, etc)
Implementation of OSPF in QoS Simulator
Link State Update is sent every 2 seconds No ack is generated for Link State Updates Link State Update may include (for example):
CAC and Packet Forwarding
• CAC: if feasible path not found, call is rejected; alternatively, source is notified of constraint violation, and can resubmit with relaxed constraint (call renegotiation)
Link State Update is sent every 30 minutes or upon a change in a cost of a path
Link State Update is the only OSPF message which is acknowledged
Routers on the same LAN use “Designated Router” scheme
1
12 42
3 3 25
D21=1
D41=00
D11=0 1 1 3
2
4
one hop
D31=3 D51=00
3
5
Dhi
D
D12=0 1
1
D22=1 2
10
D42=11 4
two hops
1 3
D32=22 D52=5
3
5
D23=1
D43=7
D13=0 1 11 3
2
4
three hops
2
D33=22 D53=4
5) Link State Request - requests link state information
OSPF Overview (cont)
“Link State Update Flooding”1A2
C
1
B
2
2
3
E
3
D
OSPF Overview (cont)
“Hello” message is sent every 10 seconds and only between neighboring routers
Min BW = 90 > 30)
A B
Constraints: Delay (D) <= 25, Available BW >= 30 We look for feasible path with least number of hops
The Components of QoS Routing
– OSPF (Open Shortest Path First): for intra-AS routing – is a link-state protocol that uses flooding of link state
information and a Dijkstra least cost path algorithm
- Queue size of each outgoing queue (averaged over 10s sliding window)
- Throughput on each outgoing link (averaged over 10s sliding window)
- Total bandwidth (capacity of the link) Source router can use above information to calculate