IP Differentiated Services over a WDM Passive Optical Star

1
IP Differentiated Services over a WDM Passive
Optical Star

• Josué KURI, Maurice GAGNAIRE
• Ecole Nationale Supérieure des Télécommunications
• 46 rue Barrault - 75634 Paris CEDEX 13, FRANCE
• Tel [phone] Fax [phone]
• E-mail kurigagnaire_at_enst.fr
  http//www.enst.fr/kuri

2
Outline

• IP Differentiated Services (Diffserv).
• Network Model.
• MAC protocol.
• Signaling
• Scheduling
• Service Disciplines
• Buffer Management
• Performance Evaluation.
• Conclusions.

3
IP Differentiated Services

• Differentiation in terms of
• Throughput, delay, jitter and/or loss.
• Relative priority of access to network resources.
• Service meaningful to users based on
• Classification and conditioning of packets at
  ingress.
• Service disciplines and buffer management in
  interior nodes.

4
IP Differentiated Services

• Per Hop Behavior (PHB) The externally observable
  forwarding behavior (delay, jitter, loss) applied
  to a particular aggregate.
• Expedited Forwarding PHB The aggregates
  departure rate must be equal/greater than a
  configured rate.

REF(in)
REF(out)
Rcfg
?
EF-capable node
5
IP Differentiated Services

• Assured Forwarding PHB group Resources (buffer
  space and BW) are allocated to four classes.
  Packets are assigned to classes and marked with
  one of three possible dropping precedence levels.

Drop 1
AF1
Drop 2
Drop 3
Drop 1
AF2
Drop 2
Drop 3
Drop 1
AF3
Drop 2
Drop 3
Drop 1
AF4
Drop 2
Drop 3
6
Network Model

• POS with N nodes

Control (?c )
FT
FR
Data (?i )
FT
TR
Star coupler
FT Fixed Transmitter FR Fixed Receiver TR
Tunable Receiver
7
Network Model

• Data channels (?i) and control channel (?c) are
  slot synchronized.

?1
Data Channels
. . .
?n
Control Channel
?c
time
8
Signaling

• Signaling-Reservation Decoupling (SRD)12.

L
Control channel
S
R
Control data unit
SIG
RES
r
s
...
...
SIG RES fields
mini-slot 1
mini-slot N
R1
R2
Reservation Sub-fields
Destination _at_
Packet length
PHB ID
Log2(N)
Log2(M)
Log2(P)
9
Signaling
Packet arrived

time
time
time
Packet
time
10
Scheduling

• Once the reservation messages have been
  broadcast, the nodes build backlog matrices Bi(t).

BEF(t)
BAF1(t)
BAF4(t)
Dest
Dest
Dest
Src
Src
Src
11
Scheduling

• An extended version of RSA13 is executed on the
  backlog matrices.
• Transmissions in BEF(t) are first scheduled.
• Transmissions in BAFi(t) (1 ? i ? 4) are then
  scheduled according to the proportion of
  resources of each class.

12
Service Disciplines

• Node configuration

?c
Control block
EF
AF1
?i
AF2
AF3
AF4
13
Buffer Management

• Tail Dropping is used in the EF queue.
• AF queues implement Random Early Detection
  (RED)14.

Packet arrival
14
Performance Evaluation

• The performance under EF, AF and combined EF/AF
  traffic is evaluated.
• Network parameters

15
Performance Evaluation

• EF traffic generated by CBR sources.
• AF traffic according exponential packet
  interarrival time with two packet length
  distributions16.

16
Performance Evaluation

• Bounds on attained rate of EF traffic

2500
EF
1

2
EF
3

2
EF
4

2
EF
2000
1

3
EF
2

3
1500
Mb/s
1000
500
0
0
0.1
0.2
0.3
0.4
0.5
0.6
time
17
Performance Evaluation

• Instantaneous rate of EF traffic under different
  load conditions.

18
Performance Evaluation

• Loss Probability (LP) of four AF classes with WWW
  and bulk traffic.

LAN / WWW
Bulk
-1
-1
AF
(40)
AF
(40)
10
10
1
1
AF
(30)
AF
(30)
2
2
AF
(20)
AF
(20)
3
3
AF
(10)
AF
(10)
-2
-2
10
10
4
4
-3
-3
10
10
Loss probability
Loss probability
-4
-4
10
10
-5
-5
10
10
-6
-6
10
10
0.5
0.6
0.7
0.8
0.9
1
0.5
0.6
0.7
0.8
0.9
1
Offered load
Offered load
19
Performance Evaluation

• Loss Probability of AF traffic (LAN / WWW) with
  EF backgroung traffic.

20
Conclusions

• We presented a MAC protocol for a WDM POS with
  support for the Diffservs EF and AF PHBs.
• The maximum rate attained by sources of EF
  traffic depends on the number of transmissions
  concurrently using the involved transmitter and
  receiver.
• Jitter in EF traffic is mainly "self-induced".

21
Conclusions

• For the AF PHB group, different levels of
  forwarding assurance, in terms of LP, is achieved
  with different allocation of resources.
• Moreover, lower LP is observed for traffic with
  larger packets.