Network+ Chapter 2

Switch

A Layer 2 (Data Link) multiport device that filters and forwards frames based on MAC addresses.

Network

A collection of two or more devices interconnected by telephone lines, coaxial cables, satellite links, radio, and/or some other communication technique. A computer network is a group of computers that are connected together and communicate with one another for a common purpose. Computer networks support "people and organization" networks, users who also share a common purpose for communicating.

Datagram

A connectionless transfer unit created with User Datagram Protocol designed for quick transfers over a packet-switched network.

Frame

A defined series of binary data that is the basic container for a discrete amount of data moving across a network. Frames are created at Layer 2 of the OSI model.

Router

A device that connects separate networks and forwards a packet from one network to another based only on the network address for the protocol being used. For example, an IP router looks only at the IP network number. Routers operate at Layer 3 (Network) of the OSI seven-layer model.

Unshielded Twisted Pair (UTP)

A popular cabling for telephone and networks composed of pairs of wires twisted around each other at specific intervals. The twists serve to reduce interference (also called crosstalk). The more twists, the less interference.The cable has no metallic shielding to protect the wires from external interference, unlike its cousin, STP.

UDP (User Datagram Protocol)

A protocol used by some older applications, most prominently TFTP (Trivial FTP), to transfer files. UDP datagrams are both simpler and smaller than TCP segments, and they do most of the behind-the-scenes work in a TCP/IP network.

FCS (Frame Check Sequence)

A sequence of bits placed in a frame that is used to check the primary data for errors.

Protocol Suite

A set of protocols that are commonly used together and operate at different levels of the OSI seven-layer model.

Open Systems Interconnection (OSI) Seven-Layer model

An architecture model based on the OSI protocol suite, which defines and standardizes the flow of data between computers.

TCP/IP Model

An architecture model based on the TCP/IP protocol suite, which defines and standardizes the flow of data between computers.

Hub

An electronic device that sits at the center of a star topology network, providing a common point for the connection of network devices. In a 10BaseT Ethernet network, the hub contains the electronic equivalent of a properly terminated bus cable. Hubs are rare today and have been replaced by switches.

Open Systems Interconnection (OSI)

An international standard suite of protocols defined by the International Organization for Standardization (ISO) that implements the OSI seven-layer model for network communications between computers.

Packet

Basic component of communication over a network. A group of bits of fixed maximum size and well-defined format that is switched and transmitted as a complete whole through a network. It contains source and destination address, data, and control information.

UTP grades/categories:

Category 1 UTP - Regular analog phone lines, not used for data communications Category 2 UTP - Supports speeds up to 4 Mbps Category 3 UTP - Supports speeds up to 16 Mbps Category 4 UTP - Supports speeds up to 20 Mbps Category 5 UTP - Supports speeds up to 100 Mbps Category 5e UTP - Category 5e UTP - Supports speeds up to 100 Mbps using two pairs and for 1000 Mbps with four pairs Category 6 UTP - Can use full 100-meter length when used with 10/100/1000BaseT networks. With 10GBaseT networks, CAT 6 is limited to 55 meters. Category 6a UTP - Extends the length of 10-Gbps communication to the full 100 meters commonly associated with UTP cabling.

Subnet

Each independent network in a TCP/IP internetwork.

HTTP (Hypertext Transfer Protocol)

Extremely fast protocol used for network file transfers on the World Wide Web.

POP3 (Post Office Protocol Version 3)

One of the two protocols that receive email from SMTP servers. POP3 uses TCP port 110. While historically most email clients use this protocol, the IMAP4 email protocol is now more common.

TCP (Transmission Control Protocol)

Part of the TCP/IP protocol suite, operates at Layer 4 (Transport) of the OSI seven-layer model. TCP is a connection-oriented protocol.

Network Protocol

Special software that exists in every network-capable operating system that acts to create unique identifiers for each system. It also creates a set of communication rules for issues like how to handle data chopped up into multiple packets and how to deal with routers. TCP/IP is the dominant network protocol today.

TCP/IP Model Layer 4

The Application layer combines the features of the top 3 layers of the OSI model. It consists of the process that applications use to initiate, control, and disconnect from a remote system.

OSI Model Layer 7

The Application layer provides tools for programs to use to access the network (and the lower layers). HTTP, FTP, SMTP, and POP3 are all examples of protocols that operate at the Application layer.

OSI Model Layer 2

The Data Link layer identifies devices on the Physical layer. MAC addresses are part of the Data Link layer. Bridges operate at the Data Link layer.

EUI-48 (Extended Unique Identifier, 48-bit)

The IEEE term for the 48-bit MAC address assigned to a network interface. The first 24 bits of the EUI-48 are assigned by the IEEE as the organizationally unique identifier (OUI).

TCP/IP Model Layer 2

The Internet layer is the same as OSI's Network layer. Any part of the network that deals with pure IP packets -- getting a packet to its destination -- is on the Internet layer.

TCP/IP Model Layer 1

The Link Layer (Network Interface Layer) is similar to OSI's Data Link and Physical layers. The Link layer consists of any part of the network that deals with frames.

OSI Model Layer 3

The Network layer moves packets between computers on different networks. Routers operate at the Network layer. IP and IPX operate at the Network layer.

OSI Model Layer 1

The Physical layer defines hardware connections and turns binary into physical pulses (electrical or light). Repeaters and hubs operate at the Physical layer.

OSI Model Layer 6

The Presentation layer, which can also manage data encryption, hides the differences among various types of computer systems.

OSI Model Layer 5

The Session layer manages connections between machines. NetBIOS and sockets operate at the Session layer.

OSI Model Layer 4

The Transport layer breaks data down into manageable chunks. TCP, UDP, SPX, and NetBEUI operate at the Transport layer.

TCP/IP Model Layer 3

The Transport layer combines the features of OSI's Transport and Session layers. It is concerned with the assembly and disassembly of data, as well as connection-oriented and connectionless communication.

Broadcast Address

The address a NIC attaches to a frame when it wants every other NIC on the network to read it. In TCP/IP, the general broadcast address is 255.255.255.255. In Ethernet, the broadcast MAC address is FF-FF-FF-FF-FF-FF.

LLC (Logical Link Control)

The aspect of the NIC that talks to the operating system, places outbound data coming "down" from the upper layers of software into frames, and creates the FCS on each frame. The LLC also deals with incoming frames by processing those addressed to the NIC and erasing ones addressed to other machines on the network.

Segment

The bus cable to which the computers on an Ethernet network connect.

TCP/IP Suite

The collection of all the protocols and processes that make TCP over IP communication over a network possible.

OUI (Organizationally Unique Identifier)

The first 24 bits of a MAC address, assigned to the NIC manufacturer by the IEEE.

ROM (Read-Only Memory)

The generic term for nonvolatile memory that can be read from but not written to. This means that code and data stored in ROM cannot be corrupted by accidental erasure. Additionally, ROM retains its data when power is removed, which makes it the perfect medium for storing BIOS data or information such as scientific constants.

IEEE (Institute of Electrical and Electronics Engineers)

The leading standards-setting group in the United States.

IP Address

The numeric address of a computer connected to a TCP/IP network, such as the Internet. IPv4 addresses are 32 bits long, written as four octets of 8-bit binary. IPv6 addresses are 128 bits long, written as eight sets of four hexadecimal characters. IP addresses must be matched with a valid subnet mask, which identifies the part of the IP address that is the network ID and the part that is the host ID.

Encapsulation

The process of putting the packets from one protocol inside the packets of another protocol. An example of this is TCP/IP encapsulation in Ethernet, which places TCP/IP packets inside Ethernet frames.

De-encapsulation

The process of stripping all the extra header information from a packet as the data moves up a protocol stack.

MAC-48

The unique 48-bit address assigned to a network interface card. This is also known as the MAC address or the EUI-48.

Network Interface Card (NIC)

Traditionally, an expansion card that enables a PC to link physically to a network. Modern computers now use built-in NICs, no longer requiring physical cards, but the term "NIC" is still very common.

MAC (Media Access Control) Address

Unique 48-bit address assigned to each network card. IEEE assigns blocks of possible addresses to various NIC manufacturers to help ensure that each address is unique. The Data Link layer of the OSI seven-layer model uses MAC addresses for locating machines.

VoIP (Voice over IP)

Using an IP network to conduct voice calls.