Sierra Wireless DART 300 User Manual

 

2110212 Rev 1.0 

 

Page 37 

This section covers: 
•  Communication protocols and protocol stacks. 
•  Protocol Features of UDP, TCP, SLIP, and PPP in DART 300, their advantages and 

disadvantages. 

•  Packet Assembly and Disassembly (PAD) features. 

The details of the features of the DART 300 are each covered with: 

•  A brief description of the feature 
•  A detailed discussion of it with respect to configuration and impact on other features 
•  Sample(s) of AT command sequences to implement the feature 

Data communication protocols are generally discussed in relation to the Open Systems 
Interconnection (OSI) model.  The OSI model was introduced in 1978 as a long-term project of 
the International Organization for Standardization (ISO).  It divides the communications process 
into seven distinct layers, stacked one above the other, hence the term protocol stack.  This is very 
different from the computer processing use of the term stack for a LIFO buffer. 

This is the window between the end-user application and the 
communications process.  It includes functions such as login and 
password checks, and resource allocation. 

Application programs 
for file transfer, 
e-mail, etc. 

Responsible for terminal management such as character set 
interpretation (i.e. ASCII, ANSI) and code conversion. 

Session management includes data-flow synchronization, mapping 
addresses with names, handling graceful and abrupt disconnections, 
and data buffering.  This layer organizes data into Session Protocol 
Data Units (SPDUs). 

Telnet, FTP, SMTP, 
etc. 

Transport Protocol Data Units (TPDUs) are assembled at this layer.  
This can include multiplexing and de-multiplexing, error detection 
and recovery, and packet reordering where the network can receive 
packets along different routes, which can arrive out of sequence. 

UDP, TCP 

Data is organized into packets, which are data frames with network 
headers and trailers added including network addressing.  The 
duties include flow control, handling network service data units, 
notifying the transport layer of errors, and possibly sequenced 
delivery. 

IP, SLIP, PPP 

This layer arranges the bits into frames.  It also establishes and 
releases one or more link connections. 

Network Interface 
Cards, Modems 

This is the physical connection layer concerned with carrying the 
communication of digital data. 

Transmission Media: 
Twisted Pair, Fiber 
Optics, Cellular 
Radio, etc.