Table O-1: OSI Reference Model Layers

Layer

Functional Focus

7 Application

Semantics: Applications and end user processes such as e-mail, file transfer, and

authentication

6 Presentation

Syntax: Data format (coding) and display, code conversion, encryption, compression

5 Session

Dialog coordination: Establishing, maintaining, coordinating, and terminating dialogues

and data exchanges

4 Transport

Reliable data transfer: End-to-end error detection and correction, and flow control,

ensuring the integrity of the complete datastream

3 Network

Routing and relaying: Message routing, error detection, and control of internodal traffic

2 Data Link

Technology-specific transfer over a link or channel: Framing, error control, flow control,

data sequencing, time-out levels, and data formatting (encoding and decoding)

1 Physical

Physical connections: Electrical and mechanical aspects of the interface of a device to

a transmission medium

See also application layer, data link layer, ISO, ITU-T, network, network architecture, Network Layer, Physical Layer, Presentation Layer, protocol, Session Layer, SNA, software, standard, subnetwork, TCP/IP, Transport Layer, X.200, and x series.

74570c15.qxd 9/11/07 12:26 PM Page 353

• 1A
• 1A1
• 1A2
• 1Base5 (1 Mbps; Baseband; 500 meters)
• 1B+D
• 1. Domain Name System. The naming convention that divides the Internet into logical domains identified in Internet Protocol version 4 (IPv4) as a 32-bit portion of the total address.The standard convention is user@organization.domain, where user is the name of the end user, organization is the name of the enterprise or other organization owning or sponsoring the address, and domain is the type of entity owning or sponsoring the address.The administration of the DNS is the responsibility of Internet Corporation for Assigned Names and Numbers (ICANN). See also domain, ICANN, Internet, and IPv4. 2.
• 1. In storage, irrelevant material, usually zero (0) bits, added to a data block in order to fill it to a minimum size, to force certain fields of control data or user data into certain positions or sizes, or to prevent the user data from duplicating a bit pattern that has a specific control meaning. See also block. 2.
• 1 cps, 1 Hz
• 1+ Dialing
• 1G (1st Generation)
• 1G (1st Generation)
• 1-persistent carrier sense multiple access (1-Persistent CSMA)
• 1-Persistent CSMA (1-Persistent Carrier Sense Multiple Access)
• 1+ WATS
• 1xEV-DO (one carrier EVolution-Data Optimized)
• 1xRTT (one times Radio Transmission Technology)
• 2
• 20
• 2:1
• 2:1
• 2:1
• 218–219 MHz Service
• 22
• 23B+D
• 23B+D