Bidirectional Light-Trails Dzmitry Kliazovich, Fabrizio Granelli, University of Trento, Italy GLOBECOM’05 November 29, 2005 Hagen Woesner, Imrich Chlamtac CREATE-NET

Dzmitry Kliazovich November 29, 2005 Outline Light-Trails and Internet Traffic Bidirectional Light-Trails  Bidirectional Synchronious Protocol (BLSP) Conclusions

Dzmitry Kliazovich November 29, 2005 Light-Trails Light-Trail – an opened optical bus for unidirectional multi-point communications Established out-of-band in separate control channel Ref.: A. Gumaste and I. Chlamtac, "Light-trails: a novel solution for IP-centric communication," in Workshop on High Performance Switching and Routing (IEEE, New York, 2003).

Dzmitry Kliazovich November 29, 2005 Light-Trails Advantages  Wavelength reuse based on spatial separation  On-demand channel access Drawbacks  Unfairness – nodes located upstream always get priority in channel access  No upstream signaling

Dzmitry Kliazovich November 29, 2005 Internet Traffic Internet Traffic Behavior  Client-server applications  Request-response protocols (HTTP, FTP, POP)  Dominant TCP protocol (>85%) acknowledges data in backward direction  Multimedia applications (Videoconferencing, VoIP) More than 90% of Internet traffic is bidirectional! Requires two light-trails in opposite directions between sender and receiver

Dzmitry Kliazovich November 29, 2005 Bidirectional Light-trails (BDLT) BDLT – an organization of two separate light-trails connecting a set of nodes in two directions (uplink and downlink) allowing bidirectional communication

Dzmitry Kliazovich November 29, 2005 Bidirectional Light-trails (BDLT) Bidirectional Light-Trail Set Up  Select two available wavelength: one in forward, another one in backward direction  Start switch configuration upon control packet reception  Last node generates the acknowledgement Set Up time: T set-up = 2h(t p + t pr ) h – number of hops; tp – propagation delay between nodes tpr – packet processing delay

Dzmitry Kliazovich November 29, 2005 Bidirectional Light-trails (BDLT) Light-Trail Dimensioning  Similar to Light-trail set up using control packets Dimensioning Metrics  Traffic Monitoring  Bandwidth Utilization Unidirectional Light-Trail  Only downstream nodes observe traffic at the upstream part  Light-trail end can be extended Bidirectional Light-Trail  Bidirectional In-band Signaling  Full control on light-trail size / bandwidth utilization

Dzmitry Kliazovich November 29, 2005 Bidirectional Light-trail Synchronous Protocol Supports data communications at the link layer as well as signaling Superframe is divided into:  Reserved Bandwidth Period – scheduled channel access  Unreserved Bandwidth Period – on-demand channel access Reserved Bandwidth Period  Bandwidth Reservation Requests  Schedule Announcement  Data Delivery

Dzmitry Kliazovich November 29, 2005 Bidirectional Light-trail Synchronous Protocol The size of Reserved BW period is variable  Based on reservation request received in prev. superframe Data delivery slots are flexible (not as in fixed TDM)

Dzmitry Kliazovich November 29, 2005 Bidirectional Light-trail Synchronous Protocol Communication Overhead Link Speed (Gbps) Number of nodes Overhead (bytes) Overhead (%) Utilization (%)

Dzmitry Kliazovich November 29, 2005 Evaluation Results OPNET simuations Light-Trail: 5 nodes, 80 km length Superfame size: 125 us Simulation focus  Fairness  Channel Access Delay  Bandwidth Utilization

Dzmitry Kliazovich November 29, 2005 Evaluation Results Bandwidth Sharing (Per-node Fairness)

Dzmitry Kliazovich November 29, 2005 Evaluation Results Channel Access Delay  Mostly determined by the node’s position from the light-trail head  Less dependant on the superframe size

Dzmitry Kliazovich November 29, 2005 Evaluation Results Goodput and Bandwidth Utilization

Dzmitry Kliazovich November 29, 2005 Conclusions Bidirectional Light-Trails (BDLT) are proposed as an extension of the Light-Trail concept in order to take advantages from in-band signaling motivated by bidirectional nature of the Internet traffic Ongoing research deals with bidirectional architectures as well as with other types of access protocols which can minimize channel access delays

Dzmitry Kliazovich November 29, 2005 Thank you!