AFDX networks

Transcription

AFDX networks

UNIVERSIDAD
DE CANTABRIA
AFDX networks
By: J. Javier Gutiérrez (gutierjj@unican.es)
Computers and Real-Time Group, University of Cantabria
ArtistDesign Workshop on Real-Time System Models for
Schedulability Analysis
Santander, 7-8 February 2011
GRUPO DE COMPUTADORES Y TIEMPO REAL
UNIVERSIDAD DE CANTABRIA
By: J. Javier Gutiérrez
8/feb/11
1
Introduction to AFDX networks
UNIVERSIDAD
DE CANTABRIA
AFDX (Avionics Full Duplex Switched Ethernet) is a
communications network defined in the ARINC-664, Part 7
standard:
• point to point full duplex Ethernet links (redundant)
• special purpose switches with preconfigured routing
• two main types of communication ports:
- Sampling Port: the arriving message overwrites the current
message stored in the buffer
- Queueing Port: the arriving message is appended to a FIFO queue
• UDP/IP protocol is used for transmission
• traffic regulation is made in transmission via Virtual Links
8/feb/11
2
Traffic regulation in AFDX
UNIVERSIDAD
DE CANTABRIA
Each virtual link (VL) is characterized by two parameters:
• the largest Ethernet frame (Lmax): a value in bytes that can be
transmitted on the VL
• the Bandwidth Allocation Gap (BAG):
- the minimum interval in milliseconds between Ethernet frames
transmitted on the VL
- a power of 2 value in the range [1,128]
Each virtual link has a FIFO queue for all the fragmented packets:
• the same VL can be shared by several ports, tasks or partitions
- It can cause a poor schedulability of the system
• there is no way to prioritize messages on a VL
8/feb/11
3
Maximum jitter
UNIVERSIDAD
DE CANTABRIA
The maximum allowed jitter on each VL at the output of the end
system should comply with both of the following formulas:
∑
( ( 20 + Lmax i ) ⋅ 8 )
i ∈ { set of VLs }
MaxJitter ≤ 40μs + ------------------------------------------------------------------------N bw
MaxJitter ≤ 500μs
• Nbw is the speed of the Ethernet link in bits per second
• 40 μs is the typical minimum fixed technological jitter
8/feb/11
4
Ethernet frame
UNIVERSIDAD
DE CANTABRIA
64 bytes
7 bytes
1 byte
6 bytes
Start
Destination
Preamble Frame
Delimiter Address
6 bytes
Source
Address
46 bytes
2 bytes
Type
(0x800
IP V4)
IP
Structure
20 bytes
UDP
Structure
4 bytes
AFDX Payload
1 to 17 bytes
Padding
0 to 16
SN
1
Frame
Check
Seq
12 bytes
Inter Frame Gap
8 bytes
1518 bytes
6 bytes
1 byte
Start
Destination
Preamble Frame
Delimiter Address
7 bytes
6 bytes
Source
Address
2 bytes
Type
(0x800
IP V4)
1500 bytes
IP
Structure
20 bytes
UDP
Structure
AFDX Payload
1471 bytes
4 bytes
Frame
SN
Check
1
Seq
12 bytes
Inter Frame Gap
8 bytes
• Lmax should be in the interval [64,1518]
8/feb/11
5
Sub-Virtual Links
UNIVERSIDAD
DE CANTABRIA
A virtual link can be composed of a number of Sub-Virtual Links
Each Sub-VL has:
• a dedicated FIFO queue
• a round robin algorithm working over IP fragmented packets
8/feb/11
6
Latency in the transmission
UNIVERSIDAD
DE CANTABRIA
If fragmentation is not required and the messages are produced at
a frequency that is equal to or lower than the BAG of the VL:
MaxLatency ≤ BAG + MaxJitter + L T
• LT is the technological latency in the transmission (it should be
lower than 150μs).
If fragmentation is required or messages are produced in bursts,
the latency for packet p (with p-1 packets waiting in the VL FIFO
queue):
MaxLatency ( p ) ≤ p ⋅ BAG + MaxJitter + L T
8/feb/11
7
AFDX switch
UNIVERSIDAD
DE CANTABRIA
Transmissions to or from the switch are made using the full
capacity of the physical link
Packets are delivered in a store and forward way:
• the hardware latency of the switch should be taken into account
A new source of jitter appears in the FIFO queue where packets
should wait to be sent to the destination end system
8/feb/11
8
Latency in the reception
UNIVERSIDAD
DE CANTABRIA
Once a message is completely received, it is enqueued at the
corresponding AFDX port
• it could potentially overflow
The technological latency of the end system in reception, LR,
should be lower than 150μs
8/feb/11
9
Modelling
UNIVERSIDAD
DE CANTABRIA
The model is similar to the one for the analysis of tasks
We consider two types of messages:
• Synchronized:
- the release times of these messages are relative to a general and
common reference of time
- an offset to represent the interval between the start of the MAF
(Major Frame) and the earliest release of the message
• Non-synchronized: messages can be released at any time
8/feb/11
10
Modelling (cont’d)
UNIVERSIDAD
DE CANTABRIA
Different types of parameters to model AFDX communication:
• message stream parameters
b
b
b
b
- Mi, pi, Npi, Ni, M i , p i , Np i , N i , Ti, Φi, Ji, Source(σi), Li, Lib
• VL parameters
- BAGj, Lmaxj, SourcePorts(VLj), DestinationPorts(VLj)
• hardware parameters
b
b
- Nbw, LT, LTmin, JTech, LR, L R , L S
• Ethernet frame and protocol parameters
- OEth, OProt, Nmin
8/feb/11
11
Latency Model
UNIVERSIDAD
DE CANTABRIA
SENDING END SYSTEM
RECEIVING END SYSTEM
SWITCH
CSend
LVL
AFDX API
Ethernet
Hardware
LTr
LSW
LTr
LRec
CReceive
Ethernet
Hardware
AFDX API
Physical Links
• 5 steps in the communication process
• 2 contention points: queueing in the sending end system (LVL)
and queueing in the switch (LSW)
8/feb/11
12
AFDX in MAST-2
UNIVERSIDAD
DE CANTABRIA
• Processing Resources
- Network: AFDX_Link
- Network_Switch: AFDX_Switch
• Scheduling Policy
- AFDX_Policy
• Scheduling Parameter
- AFDX_Virtual_Link
• Schedulable Resource
- Communication_Channel
• Event Handler
- Message_Event_Handler: Message_Delivery, Message_Fork
8/feb/11
13
AFDX in MAST-2: Network
8/feb/11
UNIVERSIDAD
DE CANTABRIA
14
AFDX in MAST-2: Scheduling Policy
8/feb/11
UNIVERSIDAD
DE CANTABRIA
15
AFDX in MAST-2: Scheduling Policy
(cont’d)
UNIVERSIDAD
DE CANTABRIA
AFDX_Policy:
• messages are scheduled through virtual links
• messages are scheduled in FIFO order when they are originated
at an AFDX switch
This policy may only be assigned to a scheduler that has an
AFDX_Link as its host
8/feb/11
16
AFDX in MAST-2: Scheduling
Parameters
8/feb/11
UNIVERSIDAD
DE CANTABRIA
17
AFDX in MAST-2: Schedulable
Resource
8/feb/11
UNIVERSIDAD
DE CANTABRIA
18
AFDX in MAST-2: Schedulable
Resource (cont’d)
UNIVERSIDAD
DE CANTABRIA
DEFAULT_COMMUNICATION_CHANNEL:
• used for communications through AFDX links when the
message is originated at an AFDX switch
• the implicit scheduling policy is FIFO ordering for the messages
8/feb/11
19
AFDX in MAST-2: Switch
UNIVERSIDAD
DE CANTABRIA
It is capable of delivering messages arriving at an input port to one
or more output ports
The delivery operations are specified through special-purpose
message event handlers
MAST does not require to define the network topology (it is implicit
in the end-to-end-flow)
It is assumed a shared memory switch in which messages do not
need to be copied
Contention occurs when several messages need to be sent to the
same output port, in which case a queue is used at the output port
8/feb/11
20
AFDX in MAST-2: Switch (cont’d)
8/feb/11
UNIVERSIDAD
DE CANTABRIA
21
AFDX in MAST-2:
Message_Event_Handler
8/feb/11
UNIVERSIDAD
DE CANTABRIA
22
Example: sending a message through a
switch
CPU1
Message
Task1
Task1
Step:
Regular_P
Thread
Fixed_P_P
SWITCH
M1
Step:
AFDX Link
Comm_Chan
AFDX Policy
MD1
Message_E_H:
Switch
8/feb/11
UNIVERSIDAD
DE CANTABRIA
CPU2
Task2
M2
Step:
AFDX Link
Default_C_C
FIFO
Task2
Step:
Regular_P
Thread
Fixed_P_P
23

AFDX networks

Transcription

Similar documents

Study abroad in Ecuador - Summer 2016

Applicant Guide Cruz del Sur - erasmus mundus cruz del sur

Cantabria - World Travel Market

Leadership Ethics Strategy Innovation

Slides

June 2012 - American University Washington College of Law

MBA doble titulacion

Escuela de Modelaje Matemtico

spatial patterns of the accessibility of the population to health

printed version in PDF.

“Study Plans” of the Universidad Pedagogica Nacional Francisco

Eagle Happenings Newsletter 01/05/16

AFDX White Paper - Phoenix Communications Services

The Evolution of Avionics Networks From ARINC 429 to AFDX

cavieres_cl - Repositorio Académico