Specifications

SLAA137A

4 MSP430 Internet Connectivity

Table 1. Functions of Internet Reference Model Layers

Layer Name Function Example

Application layer Contains a lot of protocols defined by different

applications to provide their services.

HTTP, telnet, e-mail (SMTP, POP)

Transport layer Makes the communication between endpoints

possible.

Transmission control protocol (TCP),

user datagram protocol (UDP)

Internet layer Delivery and routing of datagrams between

Internet nodes.

Internet protocol (IP), Internet control

message protocol (ICMP), address

resolution protocol (ARP)

Network layer Host-specific implementation of transmission of

datagrams.

Ethernet (IEEE 802.3), point-to-point

protocol (PPP), AX.25

Beginning with the application where data is sent, each layer adds its own header to the

segment. This is called data encapsulation (Figure 2). By receiving a frame for example from

ethernet, the TCP/IP stack has to evaluate and remove step by step the headers of the different

layers to extract the payload. A recommended source for background information about the

TCP/IP software architecture is Reference [1].

DataHeader

Data

DataHeader

Header

HeaderHeader

Application Layer

Transport Layer

Internet Layer

Network Layer

Send

Receive

Figure 2. Data Encapsulation

2.1 Ethernet

Today, ethernet is the most common medium to transfer data in a local area network (LAN). It

belongs to the network layer in the Internet reference model. The standard IEEE 802.3 defines

possible bit rates, the physical realization of bit coding, and the frame format used. Ethernet

shares the bus and each network node has the same rights to access the media by the carrier

sense multiple access with collision detection (CSMA/CD) method. If a collision is detected, the

sending nodes stop transmitting and use a special back-off algorithm for retransmission. The

data stream is Manchester coded and transferred using differential two-wire lines (twisted pair

cable, RJ45) or coaxial cables (RG58, BNC).