Control Architecture in Optical Burst Switched WDM Networks

Control Architecture in Optical Burst. Switched WDM Networks Yijun Xiong Marc Vandenhoute Hakki C. Cankaya 2/5/2022 1

Focus Ø Focus of the paper is on § OBS protocols § Design of the control network 2/5/2022 2

Topics Covered Ø Review of Optical Burst Switching Ø Architecture of Optical Core Routers Ø Data Channel Scheduling Algorithms Ø Architecture of Electronic Edge Routers Ø Burst Assembly Technique Ø Performance Study 2/5/2022 3

Terminology Ø Burst: A collection of data packets having the same egress address and some common attributes likes Qo. S requirements Ø Burst consists of burst header and burst payload Ø Burst header is referred as Burst Header Packet and burst payload is data burst 2/5/2022 4

Terminology Continued Ø Channel: Represents a certain unidirectional transmission capacity (bits per second) between two adjacent routers Ø Data channels: Channels carrying data bursts Ø Control Channels: Channels carrying BHPs and other control packets 2/5/2022 5

Terminology Continued Ø Channel group: Set of channels with a common type and node adjacency Ø Data Channel Group and Control Channel group Ø The channels of a DCG as well as its corresponding CCG could be physically carried on the same fiber or on different fibers 2/5/2022 6

What is OBS? Ø Bursts of data consisting of multiple packets are switched through the network all-optically Ø A control message is transmitted ahead of the burst in order to configure the switches along the burst’s route Ø Offset time allows the header to be processed at each node while the burst is buffered electronically at the source 2/5/2022 7

OBS continued Ø The data burst follows header after some offset time without waiting for acknowledgment Ø Therefore no FDLs are necessary at the intermediate nodes to delay the burst while the header is being processed. 2/5/2022 8

OBS 2/5/2022 9

Why OBS? Ø Bursty Internet Traffic Ø No need to dedicate a wavelength for each end to end connection Ø Avoid buffering, no fiber delay lines needed at intermediate nodes Ø Need for all optical, high speed switching network 2/5/2022 10

Burst Header Packet (BHP) Ø Burst Header packet contains § Routing information § OBS specific information as its payload which includes burst offset time, data burst duration/length, data channel carrying the burst, the bit rate at which the burst is sent and Qo. S Ø A burst header should explicitly reserve the switching resources in advance 2/5/2022 11

Burst offset time Ø Depends on design of optical core routers § If FDLs are used the main function of offset time is to resolve BHP contentions on outgoing CCGs of Optical Core Routers. § Without FDLs the burst offset time is proportional to the number of hops the burst will traverse in the OBS network 2/5/2022 12

Transmission of data bursts and their headers (BHPs) on a WDM link 2/5/2022 13

Illustration of burst transmission in an OBS network 2/5/2022 14

An example of the data burst format at layers 2 and 1. 2/5/2022 15

A general (NXM) architecture of optical core routers 2/5/2022 16

A general architecture of optical routers 2/5/2022 17

An example of the optical switching matrix 2/5/2022 18

Block diagram of the switch control unit (centralized control) 2/5/2022 19

Mismatch of time-to-switch and optical switching matrix configuration time 2/5/2022 20

Data Channel Scheduling Ø LAUC (Latest Available Unscheduled Channel) Algorithm Ø LAUC-VF (Latest Available Unscheduled Channel with Void Filling) Algorithm 2/5/2022 21

LAUC Ø Only one real value-the unscheduled time is maintained for each data channel of an outgoing DCG Ø The basic idea is to minimize gaps or voids by selecting the latest available unscheduled data channel for each arriving data burst 2/5/2022 22

LAUC continued Ø For a DCG with K-k data channels Ø tj- unscheduled time of jth channel, where j=1, 2, …K-k Ø Given the arrival time t of a data burst with duration L to the optical switching matrix, the scheduler finds the outgoing data channels that have not been scheduled at time t 2/5/2022 23

LAUC continued Ø If one such channel found § Scheduler selects latest available channel Ø Latest available channel is channel having the smallest gap between t and the end of last data burst just before t Ø The channel’s latest unscheduled time updated to t+L 2/5/2022 24

LAUC continued Ø If all channels were scheduled already at time t § Arriving data burst has to be delayed by a multiple of FDLs say i until at least one unscheduled data channel is found Ø If 1≤i≤B, the scheduler will select the latest available channel to transmit the data burst § Channel’s unscheduled time updated to t+i. D+L § If i>B, burst is discarded 2/5/2022 25

Illustration of LAUC algorithm, (a) channel 2 is selected, (b) channel 3 is chosen. 2/5/2022 26

LAUC continued Ø Advantages § Simplicity § Easy to implement Ø Disadvantages § Inefficient use of data channels as the gaps are not utilized § Larger the FDL the bigger the void § Less effective due to higher burst loss ratio 2/5/2022 27

FF algorithm Ø A simple version of LAUC Ø Data channels are searched in given order and first eligible channel found will carry data burst instead of latest available unscheduled channel 2/5/2022 28

LAUC-VF Ø Similar to LAUC except that voids can be filled by new arriving data bursts Ø Basic idea is to minimize voids by selecting the latest available unused data channel for each arriving data burst Ø Simplifies burstification 2/5/2022 29

LAUC-VF continued Ø Given arrival time t of a data burst and duration L to a optical switching matrix, the scheduler first finds the outgoing data channels that are available for the time period (t, t+L) Ø If at least one such data channel is found, the scheduler selects latest available data channel 2/5/2022 30

Illustration of LAUC-VF algorithm 2/5/2022 31

LAUC-VF continued Ø DCG has 5 data channels Ø D 3 and D 4 ineligible at t Ø D 2 is chosen because t-t 2<t-t 1<t-t 5 Ø If all the data channels are ineligible at time t, the scheduler tries to find the out going channels that are eligible at time t+D (time period of (t+D, t+D+L)) and so on 2/5/2022 32

LAUC-VF continued Ø IF no data channels are found eligible up to (t+B. D, t+B. D+L) then the burst and corresponding BHP are dropped 2/5/2022 33

LAUC-VF 2/5/2022 34

LAUC-VF Ø Ch_Search(x)- Function which searches for the eligible latest available unused channel at time x Ø Returns outgoing data channel if found else returns -1 Ø t-data burst arrival time to the optical switching matrix Ø j-outgoing data channel selected 2/5/2022 35

Variations of LAUC-VF Ø Above algorithm does not distinguish between scheduled and unscheduled channels Ø Some variations of LAUC-VF § Data channels are searched in order of scheduled and unscheduled channels for a given time instant § FF-VF: The data channels are searched in an order either fixed or round robin and first eligible channel is chosen 2/5/2022 36

Variations continued § The data channels are still searched in the order of scheduled and unscheduled channels. For eligible scheduled channel the channel with minimum gap is chosen. The LAUC still applies for the eligible unscheduled channel § The first eligible scheduled channel is chosen. If all scheduled channels are ineligible then first eligible unscheduled channel is chosen. Round robin can be used for each type of channels 2/5/2022 37

Electronic edge routers Ø Represents deaggregation and transit points between OBS network and legacy domain of any internetworking architecture. Ø Connects multiple subnetworks running on top of legacy link layer protocols to the OBS network 2/5/2022 38

Functional architecture of edge routers (sending part) 2/5/2022 39

Functional architecture of edge routers (receiving part) 2/5/2022 40

Burst Assembly Ø A burst assembly mechanism is proposed based on § Egress edge router addresses § Assembly time intervals § Maximum data burst size Ø Suppose there are G destinations and S different Qo. S classes, each burst assembler needs S. G buckets to sort arriving packets 2/5/2022 41

Burst Assembly continued Ø Assume burst assembly time of bucket i is Ta(i) µs. Ta(i) determines burst arrival rate lambda. Ø 1≤i≤S. G Ø Timer of bucket i Tc(i) Ø Length of bucket i lb(i) 2/5/2022 42

A Non periodic Time-Interval Burst Assembly Mechanism 2/5/2022 43

Burst Assembly continued Ø Burst assembly time increases linearly with the number of destinations and the number of Qo. S classes Ø The increase in the burst assembly time will introduce longer packet delay in edge routers Ø How to choose burst assembly time 2/5/2022 44

Performance Study 2/5/2022 45

The simulated OBS network 2/5/2022 46

Performance study • N x N optical router • Assumed that performance of core router will be insensitive to the number of edge routers G, and Ta • Three main sources of burst loss – Congestion on outgoing data channels – Congestion on outgoing control channels – BHP loss or excessive delay due to SCU internal congestion 2/5/2022 47

Burst loss ratio under selfsimilar traffic (Ta = 2µs). 2/5/2022 48

Burst loss ratio under selfsimilar traffic (T = 8 µs) 2/5/2022 49

Burst loss ratio under selfsimilar traffic (load = 0. 86) 2/5/2022 50

Impact of buffer size B on burst loss ratio 2/5/2022 51

Impact of number of data channels per DCG 2/5/2022 52

Conclusions Ø OBS provides an attractive alternative for realizing optical packet switched WDM networks Ø Important issues to be solved before OBS becomes practical § § Burstification Burst offset time management Data and control channel scheduling Limitations of FDLs 2/5/2022 53

Conclusions Ø Viewing the OBS network as two coupled overlay networks § A pure optical network transferring data bursts § A hybrid control networks transferring burst headers (BHP) Ø Coordination between these two is crucial Ø Traffic and congestion control is challenging Ø Network restoration is challenging 2/5/2022 54

Future work Ø Issues to be studied § How to support Qo. S and Multicast traffic in OBS § New optical multicast architectures § How to choose burst offset time 2/5/2022 55

Thank you 2/5/2022 56