LAYER 7 OSI Model LAYER 6 LAYER 5 LAYER 4 LAYER 3 LAYER ...

Avionics Full DupleX Switched Ethernet (AFDX) in Manned Spacecraft · AFDX Hot Redundancy scheme duplicates links and switches, with frames always sent on both networks concurrently · Network implements a ''first valid frame wins'' scheme in reception

duplex, 100 Mbps, star architecture databus according to Part 7 of ARINC 664 specification

· Full

· Commonly

Blue Switch (Network B)

used in Avionics applications (Airbus A380, A400M, Boeing B787 Dream Liner)

· Specification

Per VL ES Transmit

Per VL ES Receive Red Switch (Network A)

based on standard Ethernet IEEE 802.3, with superimposed features like Virtual Link Concept and Redundancy Scheme

· Differences

OSI Model · Example of a typical AFDX network within an avionics environment. · End Systems provide an interface between avionics equipment and the AFDX network.

on 4 Layers of 7 Layer OSI Reference Model IEEE 802.3 Ethernet

LAYER 7

Application Layer

Differences in AFDX according to ARINC 664 Part 7

Integrity Checking (IC) occurs in the receiving ES and serves to increase · data integrity and system robustness. · The IC process for each frame occurs prior to the frame being forwarded to the Redundancy Management function. · The IC's prime function is to identify abnormal, invalid or stuck frames, which it consequently must eliminate. · The IC function interacts directly with the Redundancy Management block, which accepts only the first arriving valid frame, and discards any consequent duplicates

Network A

Sampling / Queuing / SAP; TFTP, SNMP implementation

Presentation Layer

LAYER 5

Session Layer

LAYER 4

Transport Layer

UDP and TCP implementation

LAYER 3

Network Layer

IP and ICMP implementation

LAYER 2

Data Link Layer

MAC addressing and VL concept

Application

Redundancy Management

Detects and eliminates invalid frames

Eliminates redundant frames

IP UDP/TCP Layers

Integrity Checking

MAC Layer

Network B

LAYER 6

Integrity Checking

MAC Layer

Network Management

Detects and eliminates invalid frames

Avionics Computer System controllers Avionics Subsystem

sensors

ES 1

actuators AFDX Interconnect

Avionics Computer System controllers Avionics Subsystem

sensors

At each End System output, traffic flow needs to be adjusted and packets · adequately scheduled to ensure that allocated bandwidths of all VLs are adhered to.

ES 2

actuators ES 3

Gateway

Internet

LAYER 1

· The VL Scheduler orders and multiplexes frames prior to transmission on the physical AFDX link.

· Single transfer direction (the VL 'pipe' is mono-directional) · Single subscriber in Tx mode and one or more subscribers in Rx mode

Physical Layer

· The

characteristics / features which make AFDX potentially suitable for future manned space applications include Data Integrity and Determinism are achieved through fully profiled network implementation ensuring there is no saturation possible on available data links

· Known maximum latencies and jitters

· Known

set of rules are enforced and policed by AFDX equipment

2

3

4

Scheduler MUX

BAG2 1

1 1

2

3

4

2

2

· BAG=Minimum time interval between the starting bits of two successive Ethernet frames transmitted on a single VL

ES 1

A physical 100 Mbps link of an ES can support multiple virtual links. ·

ES 4

· Since all the VLs share the physical link, individual VLs need to be isolated to prevent traffic on one VL from interfering with traffic on another VL. VL 4 VL 1

SWITCH 2

ES 6

ES 5

· This isolation between the individual VLs is achieved by specifying and limiting two parameters: · The minimum time gap between consecutive transmission of Ethernet frames on a VL (Bandwidth Allocation Gap or BAG). · The maximum size of Ethernet frames that can be transmitted on a VL (Lmax).

· BAG values range from 20 to 27 milliseconds

Port 1 Port 2

· A BAG can only be initiated when there is data to be transmitted AND the previous bag has expired

Port 3

Port 4

VL 2

Author:

1

· The most important control mechanism imposed on a per VL basis to control the bandwidth of that particular VL.

maximum delay for packet transmission

· Unique identifier called a VL ID

ES 3

VL 2 4ms BAG

R e g u l a t o r

Traffic Shaping achieved through use of Bandwidth Allocation Gaps · (BAGs)

· Fixed predefined route on the network

SWITCH 1

BAG1 BAG1 BAG1 BAG1 VL 1 1ms BAG

tables in End Systems and Switches contain predefined information on network structure and bandwidth allocation

· Strict

ES 2

Physical Link

Virtual Link

· Configuration

· Reserved, fixed bandwidth into the global AFDX network

VL 3

· Blocking the VL for the remainder of a BAG, gives the Scheduler the possibility to insert packets from other VLs onto the physical link. · Jitter may be introduced at the Scheduler output, caused by simultaneously arriving packets from different Vls being multiplexed onto the physical link.

· High · A Virtual Link is a 'pathway' which transmits a predefined set of traffic and is characterised by the following key features:

· The Traffic Regulator positions packets within the data stream to be separated by the BAG associated with that VL.

Port 5

100Mbps Ethernet Physical Link

BAG

BAG

BAG

Port 6 Port 7

1

2

3

Olga Trivailo

Supervisors: Dr. Ahmet Sekercioglu (MONASH University)

ID 18446760

Matthias Gronowski (EADS Astrium)