Skip Navigation Linkweather.gov 
NOAA logo - Select to go to the NOAA homepage NWS logo - select to go to NWS homepage
 
NWS Home Page > NWS Org > Office of Operational Systems > NOAAPORT Home Page

Transport Layer Protocol

The Satellite Broadcast Network (SBN) protocol was created for the NOAAPORT Broacast System (NBS) to provide for packet fragmentation and reassembly, to multiplex multiple product types into a single packet (for future consideration) and to multiplex multiple logical channels onto one data stream. The SBN header is divided into three functional areas: a 16-byte frame-level header that provides fixed locations for the HDLC header and locations for logical channel control; 16-byte product-definition header that uniquely defines the product(s) being transferred and permits the multiplexing of multiple products into the packet: and an optional 32-byte product-specific header that defines the specific product being transmitted. generalized SBN header structure.


Generalized SBN Header<//TH>
Frame-Level Header
(FH)		Product-Definition Header
(PDH)		Product-Specific Header
(PSH)


In application, the product-specific header is followed by the data. Each time a new product is started, the product-definition header indicates the start of a product, and the product-specific header details the AWIPS-specific information about the product. The succeeding packets then contain the data instead of the product-specific header. When all the data for a particular product are delivered, the product-definition header will indicate the end of the product.

 

Frame 1
Frame Level Header
Product Definition Header (START)
Product-Specific Header
Data
. . . . . .
. . . . . .
Frame i + 1
Frame Level Header
Product Definition Header (IN PROCESS)
Data
. . . . . .
. . . . . .
Frame N
Frame Level Header
Product Definition Header (END)
Data

The following tables provide details on these header sections. The product-specific header is AWIPS specific and conveys information about the product so that processing of that product is more efficient.

Frame-Level Header
FieldSize (octets)Description
HDLC Address1The HDLC Address field. This field is always all 1s (broadcast).
HDLC Control1The HDLC Control Field. This field is not used.
SBN version1The most significant four bits indicate the SBN version. The least significant four bits indicates the header length in 32 bit words, including the HDLC address/control fields.
SBN Control1This is a reserved field used by the transmitter to indicate the logical channel of the message packet. This field is not currently being used.
SBN command1This is the message packet command field. The following command values and associated functions are currently implemented: 
 3=Product format data transfer 5=Synchronize 
timing 10=Test message
SBN data stream1Identifies the channel (data stream): 
 1=GOES EAST 2=GOES WEST 3=Reserved 4=Non-GOES 
Imagery/DCP 5=NCEP/NWSTG 6=Reserved 7=Reserved
SBN source1Source of data transmission: 
 1=Generated at primary NCF 2=Reserved
SBN destination1Destination of data transmission: 
 0=All
SBN sequence number4Unique sequence number for each frame. This field is used in detecting lost packets. Currently ARQ or selective repeat is not implemented.
SBN run2Unique run identifier. This field will be incremented each time the sequence number is reset.
SBN checksum2Checksum is used for frame validation (for future consideration).

Product-Definition Header
FieldSize (octets)Description
Product-Definition Header Version Number1The most significant 4 bits identify the product definition version. The least significant 4 bits indicate the header length in 32-bit words.
Transfer Type1Identifies the status of the product transfer: 
 1=Start of a new product 2=Product transfer 
still in progress 4=End (last packet) of this product 8=Product error 16=Product 
Retransmit 32=Product Abort
Header Length2Total length of product header in bytes for this frame, including options.
Block Number2Used during fragmentation and reassembly to identify the sequence of the fragmented blocks.
Data Block Offset2Offset in bytes where the data for this block can be found.
Data Block Size2Number of data bytes in the data block.
Records per Block1Number of records within the data block. This permits multiple records per block.
Blocks per Record1Number of blocks a record spans. Records can span multiple blocks.
Product Sequence Number4Unique product sequence nmuber for this product within the logical data stream. Used for retransmission.

Product-Specific Header
FieldSize (octets)Description
Option Field Number1These three fields precede the first block of a product.
Option Field Type1
Option Field Length2
Product-Specific Header Version1AWIPS product-specific header version number.
Product-Specific Header Flag1Header flag indicating start of a specific product (1), that transfer is in progress (2), and the completion of a specific product transfer (4).
Product-Specific Data Length2Length of AWIPS data header (in bytes).
Number of Bytes per Record2For GOES images, this is the number of bytes per scan line.
Product-Specific Type1Identifies the type of the product 
 Type: 1=GOES EAST 2=GOES WEST 3=Non-GOES Imagery/DCP 
4=NCEP/NWSTG 5=NEXRAD
Product-Specific Category1Identifies the category of the product, ie., image, graphic, text.
Product Code2Identifites the code of the product.
Fragments2Total number of fragments this product was broken into. 
 0=multiple products in 
this frame #=number of fragments -1=unknown
Next Header Offset2Offset in bytes from the beginning of this product-specific header to the next product-specific header. Reserved for future consideration.
Base Product Sequence Number4Product sequence number as sent by NCF
Base Product Source2Product source identification
Product Start Time4Time that product started being processed
Product NCF Receive Time4Time that product started being received at NCF
Product NCF Transmit Time4Time that product started transmit at NCF
Process Control Flag2Control Flag: 
 0=OK 1=Abort 
receive list 2=Discard
Put-Buffer-Last2Last Buffer to put on list
Buffer: First on list2Buffer number currently at head of list
Buffer: Expected Total2Total Buffers expected for the product
Product-Specific Run ID4Unique product-specific run identifier.



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services

   
National Weather Service
Office of Operational Systems (OPS2)
1325 East-West Highway
Silver Spring, MD 20910
Email Web Master
Last Modified: August 8, 2007 9:00am 		Disclaimer
Credits
Information Quality
Glossary		Privacy Policy
Freedom of Information Act (FOIA)
About Us
Career Opportunities