iss+esa+atv+docking+mpeg 2+encoder

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document title/ titre du document

ISS ESA ATV DOCKING MPEG-2 ENCODER

&

TRANSPORT STREAMOVER IP SPECIFICATION

prepared by/prparpar

Fabio Sintoni

reference/rference TN-01-13082008-ATV-EDVissue/dition 1revision/rvision 0date of issue/dateddition

13/08/2008

status/tatDocument type/typede document

Technical Note

Distribution/distribution

a45938626.doc

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s ISS ESA ATV DOCKING MPEG-2 ENCODERissue 1 revision 0 - 13/08/20TN-01-13082008-ATV-EDV

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A P P R O V A L

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T A B L E O F C O N T E N T S

1 INTRODUCTION.............................................................................................................................1

2 TECHNICAL SPECIFICATION.......................................................................................................1

2.1 Ethernet IEEE 802.3 Frame encapsulation for MPEG-2 TS over IP.......................................................3

2.2 IP addressing and UDP Ports...................................................................................................................3

2.3 MPEG-2 Transport Stream......................................................................................................................3

2.4 The UDP Packet.......................................................................................................................................6

2.5 The IP Packet...........................................................................................................................................72.6 The Ethernet Frame..................................................................................................................................9

FIGURE 2-1: ATV DOCKING VIDEO E2E DISTRIBUTION.............................................................1

FIGURE 2-2: TS STRUCTURE..........................................................................................................4

FIGURE 2-3: UDP PACKET..............................................................................................................6

FIGURE 2-4: IP PACKET..................................................................................................................7

FIGURE 2-5: IEEE 802.3 ETHERNET FRAME.................................................................................9

FIGURE 2-6: GENERIC EXAMPLE OF DECODED ETHRNET FRAME......................................10


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1 INTRODUCTION

This document has been prepared to summarize the specification of the ISS ESA ATV docking

video digital end-to-end implementation and become part of the Section four of CCSDS White

Book , chapter 2 : Examples of current spaceflight video systems .

It covers the definition of the Encoding scheme and of the MPEG-2 Transport Stream produced by

the ESA Encoder mounted in the ISS Service Module and the transmission over an IP network.

These specifications are also focusing on the definition of Ethernet Frame structure which has to be

prepared by the Ethernet interface of the encoder.

The Specifications are given in form of example. All the mentioned standards such as IEEE

802.3, IPv4, MPEG-2 TS are widely documented and detailed information are easly accessible on

the Web.

2 TECHNICAL SPECIFICATION

The current baseline for the implementation of the transport of the MPEG-2 Video from the ISS to

the ground terminals (PC and TV displays) is depicted in the figure 2.1

Figure 2-1: ATV docking Video E2E distribution

Encoder


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List of specs/parameters

1. Source signal: Analog signal from the the ATV Docking camera

distributed inside the ISS by the Video Switch (). The Video Signal

contains telemetry and ancillary information overlay produced by the SIMBOL equipment

2. The signal is: composite625 lines/ 50 Hz PAL

3. The encoder produces: MPEG-2 encoded Video

4. Frame Resolution: 720 x 576 pixel 24bit colour

5. Frame per second: 25

6. YUV colour space: 4:2:0

7. Colour conversion: RGB-24bit to YUV Conversion ITU-601 R

{R [0...255], G [0...255], B [0...255]} => {Y [16...235], U [16...240], V [16...240],

black: Y=16, white: Y = 235

8. Bit rate: constant bit rate

9. GOP: IPPPIPPPI without motion compensation (no B-frames

and motion vectors).

10. Transportation: MPEG-2 TS - MPEG-2 Encoded Video is transmitted at the

constant transport stream bitrate of4000000 Bits/second.

11. Transport stream ID Yes - Transport stream consist of a single component

(video) with fixed PID.

12. Program stream ID None- No PSI (Program Specific Information) tables need be

used.

13. MPPEG-TS Packet size: Standard - Each TS packet is 188 byte long14. 1 TS packet is written into a 1 UDP packet of 196 bytes

15. 7 UDP packets are encapsulated into a 1 IP packet

16. 1 IP packet is encapsulated into a 1 Ethernet frame

17. MTU size: 1500 Bytes

18. Every Ethernet Frame is delivers to the network by the Ethernet Interface of the Encoder

19. A single IP multicast addresses is used to group all possible destination at layer-3

20. A single Ethernet address is used to group all possible destination at layer-2

21. Every single Ethernet frame which has been send from the ESA Encoder the Russian

Smart Switch router has to be delivered to:

o Client(s) located in the Russian Segment of the ISS, belonging to the same VLAN

o OCA interface located in the American Segment of the ISS22. The Smart Switch routes IP Multicast packets from ESA Encoder with static entry of

routing table, without processing of APR (or other) protocols.

23. The protocol between the Smart Switch Router and the Edge Router is the IEEE 802.1q

trunk protocol.

24. The Edge Router routes IP Multicast packets to the OCA interface.

25. In MCC_H the IP Multicast packet is received and delivered to the ESA MPEG-2 /IP to

ASI interface hosted inside the ESA Relay.

26. The ESA Ground Segment supports the distribution of the MPEG-2 Video to the end

systems in ATC-CC and MCC-M


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27. For the end-to-end compatibility, the ESA Encoder MPEG-2 Transport Stream shall be

compatible with the Client Software and the MPEG-2 /IP to ASI interface.

2.1 Ethernet IEEE 802.3 Frame encapsulation for MPEG-2 TS over

IP.

The following paragraphs describe the preparation of a single Ethernet packet which is carrying a

payload data of 1 MPEG-2 Transport Stream packet. Addresses and UDP ports are not part of this

specification, but are taken by a working example1.

2.2 IP addressing and UDP Ports

Source IP address: Encoder IP address : 192.168.100.10Destination IP address: IP Multicast address: 239.255.100.1UDP source port 1051UDP destination port: 1234

2.3 MPEG-2 Transport Stream

The TS packet is the payload field of the UDP layer 4 packet

It works like this:

Each MPEG-2 TS packet carries 184 B of payload data prefixed by a 4 B (32bit) header. MPEG-2 Transport stream:The packet is 188 bytes = 4 header , 184 payload. Overhead 2%

1 The ATV reference video used for the MPEG-2 parameter identification has been send via IP multicast using the

VideoLAN software over a LAN in UDP Multicast. The server and the client were connected via 2 switches with a

802.1q trunk between the 2 switches. The Mpeg-2 file and the network traffic hexdump of the transmission of the file

are available on request to F. Sintoni [email protected] .
mailto:[email protected]:[email protected]


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Figure 2-2: TS Structure

The TS header has the following fields:The header starts with a well-known Synchronisation Byte (8 bits). Thishas the bit pattern 0x47 (0100 0111).A set of three flag bits are used to indicate how the payload should beprocessed.

1. The first flag indicates a transport error.2. The second flag indicates the start of a payload

(payload_unit_start_indicator)3. The third flag indicates transport priority bit.

The flags are followed by a 13 bit Packet Identifier (PID). This is used touniquely identify the stream to which the packet belongs (e.g. PESpackets corresponding to an ES) generated by the multiplexer. The PIDallows the receiver to differentiate the stream to which each receivedpacket belongs. Some PID values are predefined and are used toindicate various streams of control information. A packet with anunknown PID, or one with a PID which is not required by the receiver, issilently discarded. The particular PID value of 0x1FFF is reserved toindicate that the packet is a null packet (and is to be ignored by thereceiver).

The two scrambling control bits are used by conditional accessprocedures to encrypted the payload of some TS packets.Two adaption field control bits which may take four values:

1. 01 no adaptation field, payload only2. 10 adaptation field only, no payload3. 11 adaptation field followed by payload4. 00 - RESERVED for future use

Finally there is a half byte Continuity Counter(4 bits)

Any transport stream packet has a single fixed PID with the value 0x85(asexample, can be any).


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2.4 The UDP Packet This group of 188 bytes is the "data payload" of the UDP packet, to have a completeUDP packet, you have to had the UDP header which is very simple:

Figure 2-3: UDP Packet

In my example:source port = 1051 (example) (2 bytes) 04.1bdestination port = 1234 (2 bytes) 04.d2packet length =196 bytes (2 bytes) 00.c4

checksum (2 bytes) cf.61 example, must be calculated!

[UDP Header][payload = 188 bytes of the TS Packets] = 196 bytes in total.|

[source port][destination port][packet length][checksum][ = 188 bytes of the TS Packets]The UDP packet is now complete, but we cannot deliver it directly to any machines, since weneed to add the network information to the UDP packet.


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2.5 The IP Packet We decided to use IP as network protocol.In an IP network, we need IP addresses and some information to create an IP packet which canbe transmitted independently fro the Layer-2 implementation (Ethernet, Token Ring, FDDI, ).Our complete UDP packet of 196 bytes must be encapsulated into an IP v4 packet.

To build and IP packet we need to build the IP header and after the header put the UDPpacket. Because of the length of the IP header of 20 bytes the total length of the new packet is20 + 196 = 216 bytes.

Figure 2-4: IP Packet

Our IP Header will be:version/header length : IP version 4, header length 4 octets is:

(1 byte) 45Differ. Serv =0 (1 byte) 00Total light =216 bytes (2 bytes) 00.d8Identification = 3454 (example) (2 bytes) 0d.7eFlags/Offset = dont fragment

(1 bytes) 40.00Time to live = 254 (1 byte) feIP Subrotocol type: UDP (1 byte) 11Header checksum: (2 bytes) 32.e4 example, must be calculated!


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Source IP address (4 bytes) c0.a8.64.0a (HEX equivalent to the decimaldotted notation for 192.168.100.10)

Destination IP address (4 bytes) ef.ff.64.01 (HEX equivalent to thedecimal dotted notation 239.255.100.1)Our new IP packet is now:[IP header = 20 bytes][UDP packet= 196 bytes]

I[diff-serv][length][Id][flag][fragm.][TTL][sub-protocol][checksum][source address][destinationaddress][UDP packet= 196 bytes]

Now we have a complete IP packet, ready to be delivered to a lower layer: we have decidedto use Ethernet.


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2.6 The Ethernet FrameOur complete IP packet needs now to be encapsulated into an Ethernet Frame.

The Ethernet frame IEEE 802.3 is build like this:

Figure 2-5: IEEE 802.3 Ethernet Frame

We concentrate our attention to the header, because every Ethernet controller should preparethe preamble by itself when are set to a certain speed 910/100/1000 Mbits) It is a sequence of101010... to synch the transmitter and the receiver. Also the checksum should be calculatedby the Ethernet controller.


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Figure 2-6: Generic example of decoded Ethrnet Frame

In our case the Ethernet Header is build with:

MAC Address destination (6 bytes) 01.00.5E.7F.64.01 ( Multicast MAC address whichcorresponds to 239.255.100.1MAC Address source (6 bytes) 00.11.85.86.8F.57 ( example)Protocol Type = IP (2 bytes) 08.00

In our case the header is always the same in every frame : the encoder doesn't chance itsMAC address and since we use a Multicast MAC address as destination, it also doesn't changeand we will use IP which is "coded" as 0x08.00 according to the IEEE 802.3

In addition to that the Ethernet standard 802.3 includes 8 bytes for preamble at the beginningof the Ethernet packet and 4 bytes for the FCS ( Frame Check Sequence ) at the end.

Preamble: an alternating 1,0 pattern provides a 5MHz clock for 10Mbits ( or 50Mhz for 100Mbits or 500 for 1 Gbits) at the start of each packet, which allows the receiving devices tolock the incoming bit stream. The preamble uses either an SFD or synch field to indicate to thereceiving station that the data portion of the message will follow.Start Frame Delimiter (SFD)/Synch SFD is 1,0,1,0,1,0, etc., and the synch field is all 1s. Thepreamble and SFD/synch field are 64 bits long.

Frame Check Sequence (FCS) is a field at the end of the frame that is used to store the cyclicredundancy check (CRC).

Typically the Preamble and the FCS are prepared by the Ethernet controller "low levelroutines" and are typically stripped off when you display data dumps with a LAN Sniffer.

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