Презентация на тему DBA In EPON & LR-PON

LR-PON
DBA
Sahand University of Technology- Sep. 2010

to multipoint optical network with no active element from

source to destination

Interior elements such as passive splitters, combiners and splitters

PON technology is one of solutions for “Last Mile” problem

Sahand University of Technology- Sep. 2010

Technology- Sep. 2010

University of Technology- Sep. 2010

20 km
DSL range is 5.5Km
PON minimizes fiber deployment
Shared

channel from SC to OLT
Provides higher bandwidth
Single wavelength provides at least 1 Gb/s
Allows video broadcasting
In downstream direction from OLT to ONUs
Easy upgrade to higher bitrates
By deploying additional wavelengths

Sahand University of Technology- Sep. 2010

layer
APON
BPON
GPON
EPON


EPON
Introduced by Glen Kramer (2001)
Transmits Ethernet frames
Ethernet frames

form 90% of total traffic
No frame conversion

Sahand University of Technology- Sep. 2010

separate optical fibers and passive couplers are used
A single

coupler and a single fiber for both directions with one wavelength for upstream transmission and another for downstream transmission, i.e., 1310nm and 1550 nm

Multiple Access
In the upstream, multiple ONUs transmit data packets to the OLT
Due to the directional property of a passive combiner, data packets from an ONU can't reach to the other ONUs, conventional contention-based multiple access, e.g., CSMA/CD, doesn't suitable for EPON

Sahand University of Technology- Sep. 2010

to implement
Cost and scalability(adding new ONU problem)
TDM
Each ONU has

a fraction of channel bandwidth
Synchronization, more complicated than WDM
CDM
Security
Inter channel interference increases by increasing number of user

Sahand University of Technology- Sep. 2010

the IEEE802.3ah Ethernet in the First Mile Task Force
Applications
Auto-discovery,

Registration, Ranging (RTT computation)
Register
Register request
Register ack

DBA
Report message
Head of frame
Tail of frame
Gate message
Fixed granting
Gate assignment granting
Limited granting

Sahand University of Technology- Sep. 2010

polling
Interleaved polling with stop.

Scheduling modes
Online
Offline
Sahand University of Technology- Sep.

2010

aforementioned protocols work in offline manner!

IPACT

Sahand University of Technology-

Sep. 2010

due to clock drifting
Adjust the OLT receiver



Sahand University of

Technology- Sep. 2010

light upstream load
Gate blocking behind data packets
Solution:
Dedicated control channel

for Gate messages

Disconnected ONU
OLT can stop polling disconnected ONU in every cycle(simple solution)
OLT must distinguish between corrupted Report and disconnected ONU
OLT polls disconnected ONU less frequently

Sahand University of Technology- Sep. 2010

where multiple wavelength are deployed I a fiber and

each of them works in TDM.
Higher upstream bandwidth than simple IPACT
IGFS:
Uses gaps that are created by dissimilarity in RTTs to utilize upstream channel
More efficient than WDM IPACT
DPA
Divides ONUs in two subgroup with some overlap
OLT performs DBA for a group, while receives data from other one
In some cases removes channel idle time

Sahand University of Technology- Sep. 2010

has been proposed that employs some early allocation mechanism

in which a light- loaded ONU can be scheduled instantly without waiting for the end of the scheduling cycle, but this scheme might lose efficiency at high network load

In [2] a DBA was introduced which predicts and schedules constant bit- rate (CBR) traffic to transmit during the idle time, but it works on a more detailed traffic classification and a certain traffic pattern


[1]: C. Assi, Y. Ye, S. Dixit, and M. Ali, “Dynamic bandwidth allocation for quality-of-service over ethernet PONs,” IEEE J. Select. Areas Commun., vol. 21, no. 9, pp. 1467-1477, Nov. 2003.
[2]:A. Shami, X. Bai, C. Assi, and N. Ghani, “Jitter performance in ethernet passive optical networks,” J. Lightware Technol., vol. 23, no. 4, pp. 1745-1753, Apr. 2005.

Sahand University of Technology- Sep. 2010

bursty traffic
Best Effort(BF), not delay sensitive data, i.e., email
Inter

ONU scheduling vs. Intra ONU scheduling

Sahand University of Technology- Sep. 2010

Technology- Sep. 2010

is implemented in GAR (Grant After Report) way
Amount of

EF traffic in the system is deterministic, therefore GBR (Grant Before Report) mechanism can be used
It is possible to define maximum queuing time for EF packets
AF and BE traffic behavior is nondeterministic, standard GAR technique is used

HG protocol defines two subcycles, one for EF traffic(GBR mechanism) and one for AF/BE traffic(using GAR mechanism)

Sahand University of Technology- Sep. 2010

beginning of the next cycle in every ONU, first

grants bandwidth for EF traffic, the reminder of transmission window is allocated for AF and BF

Sahand University of Technology- Sep. 2010

network technology, Long-Reach PON (LR-PON). The strength of optical

technology is its ability to displace electronics and simplify the network by combining network tiers

The access and metro networks can be combined into one through the use of an extended backhaul fiber, possibly 100 km in length to incorporate protection paths and mechanisms, used with a PON

Also called “Super PON”

Sahand University of Technology- Sep. 2010

can find the impact of increased RTT on packet

delay.

Single thread

Sahand University of Technology- Sep. 2010

is negligible because it is 0.1 ms with 10-km

span
LR-PON increases the idle time to 1 ms with 100 km of OLT-ONU distance, which results in 10x the idle time in traditional PON.

Sahand University of Technology- Sep. 2010

continuously allocates a small amount of extra bandwidth to

each ONU
If the ONU has no traffic to send, it transmits idle frames during its excess allocation
Observing a large number of idle frames from the given ONU, the OLT reduces its bandwidth allocation else OLT increases its bandwidth allocation when observing the given ONU is not sending idle frames

No requirements on an ONU and no need for the control loop between OLT and ONU
There is no way for the OLT to know how best to assign bandwidth across several ONUs that need more bandwidth

terms of lower packet delay & guaranteed fairness) in

a LR-PON, an idea is to allow an ONU to send its Request before the previous Gate message is received

Sahand University of Technology- Sep. 2010

the idle time

Keeps the fairness, because the transmission of

Gate messages is interleaved with upstream data transmission in another polling process

The number of threads can be increased depending on the network environment, such as
Hardware processing time
Required delay bound

Sahand University of Technology- Sep. 2010

(Request) are 64-byte medium-access control (MAC) frames. Besides the

information of source, destination, timestamp
MPCP reserves 44-byte “opcode-specific fields” for specific MPCP functions

Multi-thread polling scheme uses the reserved 44 bytes:
REPORT:
Requested window size 2-byte
Thread number: 1-byte
Gate:
Granted window size: 2-byte
Grant start time: 2-byte
Thread number: 1-byte

Sahand University of Technology- Sep. 2010

cycle time of each thread is set to value

t. The relation of t and the total number of threads N is:



Tprocess is the Request processing time at the OLT

Sahand University of Technology- Sep. 2010

use of not only the information of Requests in

the current thread, but also the one in subsequent threads before the time the OLT calculates bandwidth allocation
For example, consider that three threads T1, T2, and T3. Before OLT calculates bandwidth allocation in T1, Requests in T2 have arrived, which report the latest information of ONUs’ packet queues

This information will be counted in the bandwidth allocation in T1. Thus, packets arriving at ONUs in T2 will not be queued until Gates of T2 are received; instead, they can be transmitted in T1. So, the average packet delay can be further optimized

Sahand University of Technology- Sep. 2010