User Manual

Appendix E: Glossary

Packet

E-20

Psion Teklogix 9160 Wireless Gateway User Manual

• Layer 5, the Session layer, defines protocols for initiating, maintaining, and

ending communication and transactions across the network. Some common

examples of protocols that operate on this layer are network file system

(NFS) and structured query language (SQL). Also part of this layer are

communication flows like single mode (device sends information bulk),

half-duplex mode (devices take turns transmitting information in bulk), and

full-duplex mode (interactive, where devices transmit and receive simulta-

neously).

• Layer 6, the Presentation layer, defines how information is presented to the

application. It includes meta-information about how to encrypt/decrypt and

compress/decompress the data. JPEG and TIFF file formats are examples of

protocols at this layer.

• Layer 7, the Application layer, includes protocols like hypertext transfer

protocol (HTTP), simple mail transfer protocol (SMTP), and file transfer

protocol (FTP).

Packet

Data and media are transmitted among nodes on a network in the form of packets.

Data and multimedia content is divided up and packaged into packets. A packet

includes a small chunk of the content to be sent along with its destination address

and sender address. Packets are pushed out onto the network and inspected by each

node. The node to which it is addressed is the ultimate recipient.

Packet Loss

Packet Loss describes the percentage of packets transmitted over the network that did

not reach their intended destination. A 0 percent package loss indicates no packets

were lost in transmission. QoS features are designed to minimize packet loss.

PHY

The Physical Layer (PHY) is the lowest layer in the network layer model (see OSI).

The Physical Layer conveys the bit stream - electrical impulse, light or radio signal -

- through the network at the electrical and mechanical level. It provides the