FiWiIntegrated Fiber-Wireless Access Networks

Supporting Inter-ONU Communications

Introduction

• FiWi access networks introduce wireless-optical-wireless communication

• FiWi access networks enable traffic to be sent from the source wireless client to an ingress ONU, then to the egress ONU close to the destination wireless client, and finally delivered to the destination wireless client

• FiWi supports direct inter-ONU communication in the optical sub network

Introduction

• Optical access provides huge bandwidth, but it is costly to achieve deep fiber penetration. Wireless access can support flexible and ubiquitous communication in small community areas with a low deployment cost

• However, interference and low bandwidth limit wireless network’s deployment scalability

• A FiWi access network consists of a wireless sub network as the front end and an optical sub network as the back end

Introduction

• The FiWi must be able to efficiently support upstream, downstream, and peer-to-peer communications

• The integration of PONs and WMNs in FiWi access networks provides an opportunity to reduce the impact of interference on the network throughput

• The FiWi can potentially reduce the delay for some p2p communications since the transmission in the PON network can be much faster than that in the multi-hop wireless network.

Agenda

• Related work and preliminary knowledge• WDM/TDM PON architecture for efficient support of direct

inter-ONU communication• Wavelength assignment (and traffic grooming) in the optical

sub network• Dynamic Bandwidth Allocation (DBA) protocol supporting

inter-ONU communication• Dynamic egress ONU selection and routing in WMNs• Simulation

Related work

PON architecture:• Conventional PONs implement inter-ONU communication by

sending the traffic from the source ONU to the OLT, which then sends it back to the destination ONU– This implementation, suffers from OEO conversion delay and round-

trip transmission delay

• Some PON architectures are developed to support such communication by broadcasting optical signals from one ONU to all ONUs through star coupler (SC) which is deployed at the remote node (RN)– Such designs cause large power loss and can only be applied to TDM

PON

Related work

• A WDM EPON is proposed that supports direct inter-ONU communication, the transmission cycle is divided into two sub-cycles, one for upstream transmission, the other for inter-ONU communication

• Zaho has developed a novel WDM PON with internetworking capability. A 2n×2n AWG, where n is the number of ONUs, is placed at the RN and two distributed fibers are connected to each ONU in such architecture, Based on the cyclic property of AWG, direct inter-ONU communication can be implemented.

Related work

– If two ONUs are connected to the same port of the AWG router to share wavelength for inter-ONU communication, they can not receive signals from each other since the wavelength they use to transmit inter-ONU traffic can not be routed to the port they are connected to.

DBA:• A centralized DBA protocol was proposed for inter-ONU

communication where report messages are sent to the OLT and grant message is sent back to the ONUs from the OLT. – This protocol is vulnerable to OLT failure

Related work

Wavelength assignment:• A hybrid optical-wireless access network supporting load

balancing with WDM/TDM PON as the optical sub network is proposed by Shaw. ONUs can dynamically share wavelengths by tuning to different wavelengths. Such a dynamic wavelength sharing among ONUs is feasible because passive splitters are deployed at the RN, which is subject to power loss.

WDM/TDM PON architecture

WDM/TDM PON architecture

Wavelength assignment

• Assume that upstream traffic and downstream traffic are symmetric

• There are n ONUs in a PON and there are ω available wavelengths for transmission

• Let and B be the bandwidth of a wavelength• Let K be the be the split ratio of a wavelength (K×ω > n)• Let is the estimated traffic load of • Let be 1 if is associated with wavelength

Wavelength assignment is to assign n ONUs onto ω wavelengths

such that the traffic load on each wavelength is less than B

Wavelength assignment

• The problem can be formulated as follows:

Subject to:

Wavelength assignment

• We modify Sorted Greedy LoadBalance algorithm which is used for load balancing problem to solve the wavelength assignment problem

• Modified algorithm:

Decentralized DBA protocol

• Works in a synchronized manner – request message transmission is followed by data transmission in each

transmission cycle

• In each transmission cycle, at most ω ONUs are able to transmit data to their destination ONUs

Stages:• Transmitting request messages: In this stage, the request

message from each ONU will reach all other ONUs including the ONUs in its own group

Decentralized DBA protocol

• Executing bandwidth allocation algorithm: In this stage, based on the gathered request messages, each ONU will independently execute the same decentralized bandwidth allocation algorithm

• Transmitting data: During this period, ONUs will send traffic to other ONUs according to the decision made by the bandwidth allocation algorithm

Decentralized DBA protocol

Request Message Transmission:• Each source ONU’s weight t is initially set to i/n• If has backlogged traffic and loses the bid at current

transmission cycle, is updated to , otherwise is reset to i/n

• Two phase: In the first phase, each ONU in group i tunes to wavelength and sends its request message to all ONUs in its adjacent next group, group j, where j=i+1.

• In the second phase, one ONU in each group will represent the group to forward received request messages to its adjacent group

Decentralized DBA protocol

Example:• 7 ONUs are grouped

as the following:

Decentralized DBA protocol

Suppose ONU i wants to send to ONU j at group k

For all requests with dest. ONU belonging to group k if

has the highest values, ONU i can send its traffic else changes its weight to and waits for the next transmission cycle

Dynamic egress ONU selection

• If the destination ONUs of many requests belong to the same group, such requests contend for the same wavelength and inter-ONU communication may experience longer delay

• One remedy solution will be to dynamically determine the egress ONU

• To support dynamic egress ONU selection at ingress ONU, each ONU needs to maintain the following two tables:

1. Traffic demand table: Each ONU will maintain a traffic demand table which records the volume of backlogged traffic destined to each group

Dynamic egress ONU selection

Example:

Simulation

Simulation Setting:• The simulation is conducted in ns-2.34• In the WMN sub network of the constructed FiWi network• There are two gateways (ONUs)• There are eight wireless mesh routers which are uniformly

distributed 400×200 m2 square region• DSDV protocol is used for wireless routing• The size of each wireless packet is set to 1000 bytes• Each ONU has 2 wavelengths (us & ds), each with 16 Mbps

allocated bandwidth

Simulation

• The propagation delay from the OLT to each ONU is set to 100 µs

• Each PON frame is set to be 15000 bytes• We assume that when a wireless packet arrives at an ONU,

there is some traffic from other fixed users or wireless clients and a PON frame is formed immediately for transmission

Simulation

• The propagation delay from the OLT to each ONU is set to 100 µs

• Each PON frame is set to be 15000 bytes• We assume that when a wireless packet arrives at an ONU,

there is some traffic from other fixed users or wireless clients and a PON frame is formed immediately for transmission

Large scale Simulation

Large scale Simulation

Large scale Simulation

• 100 wireless clients• 16 ONUs• 4 wavelengths • Each at 1Gb/s• TDMA mode• The propagation delay between the OLT and ONUs varies in

the interval of [50 µs, 100 µs]• Traffic arrived at each ONU from the wireless sub network

follows Poisson distribution

Large scale Simulation

Large scale Simulation

Large scale Simulation

Large scale Simulation