Mar 11, 2003 - Alternative routing based intra-contention resolution scheme by suggesting a control header packet format. âThe blocking probability is ...
Contention Resolution for Optical Burst Switching Networks Using Alternative Routing (Mar. 11, 2003) Yonsei Univ. Computer Communication Lab. Kim Hyo Jin NGI seminar
1
Contents Abstract & INTRODUCTION OPTICAL BURST SWITCHING ALTERNATIVE ROUTING IN OBS NETWORKS SIMULATION AND RESULTS CONCLUSION NGI seminar
2
1
Abstract & INTRODUCTION Dense Wavelength Division Multiplexing(DWDM) technology Exploit the huge potential bandwidth 9 Without any opto-electro-optic(O/E/O) conversions. 9
Optical Burst Switching(OBS) 9 9 9
To build very high capacity routing switches. Good solution in high-speed optical Internet backbone. Eliminate the electronic bottleneck 9
9
at switching node without O/E/O conversion
Guarantee the Class of Service(CoS) 9
without any buffering. NGI seminar
3
Propose : 9 Alternative
routing based intra-contention resolution scheme by suggesting a control header packet format 9 The
blocking probability is significantly reduced. Additional delay
< 10% x Basic offset time
for the alternative path
NGI seminar
4
2
OPTICAL BURST SWITCHING OBS composition 9
OBS network
9
Each burst
9
9
9
Optical core routers and electronic edge routers Control header packet and a data burst
Control header contains 9
Information of the data burst length and offset time
Packets are 9 9
Assembled into bursts at the network ingress. Disassembled back into packets at the network egress. NGI seminar
5
Two coupled overlay networks 9
9
A pure optical network transferring data bursts and a hybrid control network transferring control header packets. Control network 9
A packet switched network Controls the routing and scheduling of data bursts in the all optical network
9
Advantages
9
9
9 9
based on the control header packet’s information Mature electronic control technologies Promising optical transport technologies NGI seminar
6
3
Fig. 1 : three burst switching techniques 9A
burst can cut through intermediate routers. NGI seminar
7
(a) In-Band Terminator(IBT) based burst switching 9 Bandwidth 9 9
is reserved
As soon as IBT Followed end of the data burst
9 Limitation 9
Be processed all optically 9 Not support optical processing
NGI seminar
8
4
(b) Tell-And-Go(TAG) based burst switching 9
Operating steps ① ② ③
9 9
Source node sends a control packet over the control channel to reserve a bandwidth. Corresponding data burst is transmitted without waiting for the acknowledgement. The source node sends a release packet to the destination.
Ex) Just-In-Time(JIT) protocol Disadvantage 9
Large signaling overhead NGI seminar
9
(c) Reserve-Fixed-Duration(RFD) based burst switching 9
Bandwidth is reserved 9
9
Information of reservation time 9
9
Carried by control packet
Ex) Just-Enough-Time(JET) protocol 9 9
9
fixed time duration at each router
Eliminates the signaling overhead Improve the resource utilization
Disadvantage 9
Complexity increased. NGI seminar
10
5
Many challenges to implement the OBS network 9 Edge
router
9 Burst
offset time management, burstification and burst assembly mechanism
9 Core
router
9 Data
burst and control header packet scheduling, protection and restoration mechanism and contention resolution scheme NGI seminar
11
We focused… 9
Contention resolution 9
9
The core router has no fiber delay line(FDL) and the offset time is fixed at the ingress router.
Classify the contention in intermediate core routers. The inter-class contention caused by different class bursts. 9 The intra-class contention caused by same class bursts. 9
9
To prevent the inter-class contention Additional QoS offset time can be used and high priority bursts can avoid blocking caused by low priority bursts. 9 No published result yet. 9
NGI seminar
12
6
ALTERNATIVE ROUTING IN OBS NETWORKS Our three methods for solving the intra-contention problem in core routers ① ② ③
The wavelength converter FDL The deflection routing
We proposed.. 9
An alternative routing scheme 9
Combines wavelength converters and the enhanced deflection routing algorithm. NGI seminar
13
If contention occurs at intermediate core routers, the data burst is blocked. 9 Because
it can’t change its path.
In our algorithm 9 Every
core router has hop by hop routing functions. 9 The routing table has two different paths for each destination. NGI seminar
14
7
NGI seminar
15
Operating steps 9
If contention occurs at certain intermediate core router, the hop by hop routing functions are performed. 9
9
9
One is routed through the short path and the other is routed through the alternative path obeying certain policy(time critical burst, number of hops, etc.)
If next node does not encounter any contention, the rerouted data burst will be routed through the shortest path. The control packets contain the number of rerouting times 9
Thus if the number of rerouting is over the threshold value, the rerouted bursts are just drop to prevent looping and early arrival of data bursts.
Better than deflection routing NGI seminar
16
8
“Routing offset time” 9 The 9 to
additional offset time make up the time by alternative routing.
9 Depends
on
9 the
network size and the header processing time 9 Ingress edge routers decide the offset time 9 Prevents
the data burst surpasses the control header. NGI seminar
17
NGI seminar
18
9
Message type 9 9
The header packet type Uniquely determines the exact layout of the message.
QoS 9
Following data burst’s priority.
Input port and Input wavelength identifier 9
Indicate the incoming data burst’s port and wavelength.
Offset time 9
The separation time between control header and data burst 9
Consists of the basic offset time and routing offset time.
Burst length 9
Length of data burst
Hop count 9
Prevent bursts not to lose their destination router or the looping environment.
Source address and Destination address 9
Addresses of the source and the destination. NGI seminar
19
SIMULATION AND RESULTS Java language 9
To evaluate the performance of blocking probability 9
Each time slot is equal to the burst duration. For simplify the simulation Exponential distribution and Pareto distribution with Hurst parameter H=0.9. NGI seminar 20
10
Fig. 5 and Fig. 6 9
Blocking probability is reduced by 10 and 2 times 9
9
When offered load is 0.1 and 0.9.
Self-similar traffic with H=0.9, 9
The proposed alternative routing scheme performs very well. NGI seminar
21
Fig. 7 9
Alternative Path makes the additional delay(additional hop counts) performance. NGI seminar
22
11
CONCLUSION An intra-contention resolution scheme 9 By
introducing additional routing offset time in bufferless intermediate core routers in the OBS network. 9 Using “Routing offset time” 9 Effective
to significantly reduce the blocking probability for the exponential NGI seminar
