Is the Scrambler Function in JESD204B Part of the Data Link Layer?

[senmeis]

Hi,

in some standards such as JESD204B or DVB-S2 a so called scrambler function is defined. As far as I understand this scrambler is a means of spreading spectrum but in data link layer. Is it correct?

Senmeis

 

[tech99]

I think it will prevent a series of zeros creating a DC component, which the transmission system cannot handle and which wil make clock extraction a problem. The data stream might be disconnected during maintenance, say.

 

[analogdesign]

Actually tech99 OP is correct. JESD204B has 8b-10b coding in the standard for DC balance. The optional scrambling is for EM compliance.

 

[Svein]

As far as I understand this scrambler is a means of spreading spectrum but in data link layer.

No. It is in the physical layer. The data link layer deals with bits, bytes and frames.

 

[analogdesign]

No. It is in the physical layer. The data link layer deals with bits, bytes and frames.

This may be down into the weeds (and not sure if anyone is following this thread) but OP is actually correct. In JESD204B the scrambler is in the link layer as scrambling happens before frame alignment (so we are dealing with bits, bytes, and frames here). See this discussion by Analog Devices:

https://www.analog.com/en/technical-articles/understanding-layers-in-jesd204b-specification.html

 

[Svein]

In JESD204B the scrambler is in the link layer as scrambling happens before frame alignment

Then JESD204B does not conform to the OSI layer model. From Wikipedia (https://en.wikipedia.org/wiki/Data_link_layer):

The services that the data link layer provides are:

• Encapsulation of network layer data packets into frames
• Frame synchronization
• In the logical link control(LLC) sublayer:
  • Error control (automatic repeat request, ARQ), in addition to ARQ provided by some transport-layer protocols, to forward error correction (FEC) techniques provided on the physical layer, and to error-detection and packet canceling provided at all layers, including the network layer. Data-link-layer error control (i.e. retransmission of erroneous packets) is provided in wireless networks and V.42 telephone network modems, but not in LAN protocols such as Ethernet, since bit errors are so uncommon in short wires. In that case, only error detection and canceling of erroneous packets are provided.
  • Flow control, in addition to the one provided on the transport layer. Data-link-layer flow control is not used in LAN protocols such as Ethernet, but in modems and wireless networks.
• In the medium access control(MAC) sublayer:
  • Multiple access protocols for channel-access control, for example CSMA/CD protocols for collision detection and re-transmission in Ethernet bus networks and hub networks, or the CSMA/CA protocol for collision avoidance in wireless networks.
  • Physical addressing (MAC addressing)
  • LAN switching (packet switching), including MAC filtering, Spanning Tree Protocol (STP) and Shortest Path Bridging (SPB)
  • Data packet queuing or scheduling
  • Store-and-forward switching or cut-through switching
  • Quality of Service (QoS) control
  • Virtual LANs (VLAN)