CCNA Chapter 1 Internetworking

Terms in this set (59)

is a hexidecimal number identifying the physical connection of a host. They operate on layer 2 of the OSI model. defines how packets are placed on the media; is a unique identifier assigned to network interfaces for communications on the physical network segment. XXX are used as a network address for most IEEE 802 network technologies, including Ethernet. Logically, XXX addresses are used in the media access control protocol sublayer of the OSI reference model.

XXX addresses are most often assigned by the manufacturer of a network interface controller (NIC) and are stored in its hardware, such as the card's read-only memory or some other firmware mechanism. If assigned by the manufacturer, a XXX address usually encodes the manufacturer's registered identification number and may be referred to as the burned-in address. It may also be known as an Ethernet hardware address (EHA), hardware address or physical address. This can be contrasted to a programmed address, where the host device issues commands to the NIC to use an arbitrary address. An example is a SOHO router, for which the ISP grants access to only one XXX address (used previously to inserting the router) so the router must use that XXX address on its Internet-facing NIC. Therefore the router administrator configures a XXX address to override the burned-in one.

A network node may have multiple NICs and each must have one unique XXX address per NIC.

XXX addresses are formed according to the rules of one of three numbering name spaces managed by the Institute of Electrical and Electronics Engineers (IEEE): XXX-48, EUI-48, and EUI-64. The IEEE claims trademarks on the names EUI-48 and EUI-64, in which EUI is an abbreviation for Extended Unique Identifier.
is an ethernet term used to describe a network collection of devices in which one particular device sends a packet on a network segment, forcing every other device on that same segment to pay attention to it. is a section of a network where data packets can collide with one another when being sent on a shared medium or through repeaters, in particular, when using early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network segment at the same time. XXX are resolved using carrier sense multiple access with collision detection in which the competing packets are discarded and re-sent one at a time. This becomes a source of inefficiency in the network.[1]

Only one device in the XXX domain may transmit at any one time, and the other devices in the domain listen to the network in order to avoid data collisions. Because only one device may be transmitting at any one time, total network bandwidth is shared among all devices. XXX also decrease network efficiency on a XXX domain; if two devices transmit simultaneously, a XXX occurs, and both devices must retransmit at a later time.

XXX domains are found in a hub environment where each host segment connects to a hub that represents only one collision domain and only one broadcast domain. XXX domains are also found in wireless networks such as Wi-Fi.

Modern wired networks use a network switch to eliminate XXX. By connecting each device directly to a port on the switch, either each port on a switch becomes its own XXX domain (in the case of half duplex links) or the possibility of XXX is eliminated entirely in the case of full duplex links.
responsible for the delivery and formatting of information to the application layer for further processing or display.[4] It relieves the application layer of concern regarding syntactical differences in data representation within the end-user systems. An example of a presentation service would be the conversion of an EBCDIC-coded text computer file to an ASCII-coded file.

The xxx is the lowest layer at which application programmers consider data structure and presentation, instead of simply sending data in form of datagrams or packets between hosts. This layer deals with issues of string representation - whether they use the Pascal method (an integer length field followed by the specified amount of bytes) or the C/C++ method (null-terminated strings, e.g. "thisisastring\0"). The idea is that the application layer should be able to point at the data to be moved, and the presentation layer will deal with the rest.

Serialization of complex data structures into flat byte-strings (using mechanisms such as TLV or XML) can be thought of as the key functionality of the presentation layer.

Encryption is typically done at this level too, although it can be done on the application, session, transport, or network layers, each having its own advantages and disadvantages.[1] Decryption is also handled at the xxx. For example, when logging off bank account sites the presentation layer will decrypt the data as it is received.[1] Another example is representing structure, which is normally standardized at this level, often by using XML. As well as simple pieces of data, like strings, more complicated things are standardized in this layer. Two common examples are 'objects' in object-oriented programming, and the exact way that streaming video is transmitted.

In many widely used applications and protocols, no distinction is made between the presentation and application layers. For example, HyperText Transfer Protocol (HTTP), generally regarded as an application-layer protocol, has presentation-layer aspects such as the ability to identify character encoding for proper conversion, which is then done in the application layer.

Within the service layering semantics of the OSI network architecture, the presentation layer responds to service requests from the application layer and issues service requests to the session layer.

In the OSI model: the xxx ensures the information that the application layer of one system sends out is readable by the application layer of another system. For example, a PC program communicates with another computer, one using extended binary coded decimal interchange code (EBCDIC) and the other using ASCII to represent the same characters. If necessary, the presentation layer might be able to translate between multiple data formats by using a common format.
allows communication in both directions, and, unlike half-duplex, allows this to happen simultaneously. Land-line telephone networks are xxx, since they allow both callers to speak and be heard at the same time, the transition from four to two wires being achieved by a Hybrid coil. A good analogy for a full-duplex system would be a two-lane road with one lane for each direction.

Two-way radios can be designed as xxx systems, transmitting on one frequency and receiving on another. This is also called frequency-division duplex. Frequency-division duplex systems can be extended to farther distances using pairs of simple repeater stations, because the communications transmitted on any one frequency always travel in the same direction.

xxx Ethernet connections work by making simultaneous use of two physical pairs of twisted cable (which are inside the jacket), where one pair is used for receiving packets and one pair is used for sending packets (two pairs per direction for some types of Ethernet), to a directly connected device. This effectively makes the cable itself a collision-free environment and doubles the maximum data capacity that can be supported by the connection.

There are several benefits to using xxx over half-duplex. Firstly, time is not wasted, since no frames need to be retransmitted, as there are no collisions. Secondly, the full data capacity is available in both directions because the send and receive functions are separated. Thirdly, stations (or nodes) do not have to wait until others complete their transmission, since there is only one transmitter for each twisted pair.

Historically, some computer-based systems of the 1960s and 1970s required full-duplex facilities even for half-duplex operation, because their poll-and-response schemes could not tolerate the slight delays in reversing the direction of transmission in a half-duplex line
provides reliable, ordered, error-checked delivery of a stream of octets between programs running on computers connected to an intranet or the public Internet. provides a communication service at an intermediate level between an application program and the Internet Protocol (IP). That is, when an application program desires to send a large chunk of data across the Internet using IP, instead of breaking the data into IP-sized pieces and issuing a series of IP requests, the software can issue a single request to xxx and let xxx handle the IP details. TRANSPORT LAYER

IP works by exchanging pieces of information called packets. A packet is a sequence of octets and consists of a header followed by a body. The header describes the packet's destination and, optionally, the routers to use for forwarding until it arrives at its destination. The body contains the data IP is transmitting.

Due to network congestion, traffic load balancing, or other unpredictable network behavior, IP packets can be lost, duplicated, or delivered out of order. xxx detects these problems, requests retransmission of lost data, rearranges out-of-order data, and even helps minimize network congestion to reduce the occurrence of the other problems. Once the xxx receiver has reassembled the sequence of octets originally transmitted, it passes them to the application program. Thus, xxx abstracts the application's communication from the underlying networking details.

xxx is utilized extensively by many of the Internet's most popular applications, including the World Wide Web (WWW), E-mail, File Transfer Protocol, Secure Shell, peer-to-peer file sharing, and some streaming media applications.

xxx is optimized for accurate delivery rather than timely delivery, and therefore, xxx sometimes incurs relatively long delays (in the order of seconds) while waiting for out-of-order messages or retransmissions of lost messages. It is not particularly suitable for real-time applications such as Voice over IP. For such applications, protocols like the Real-time Transport Protocol (RTP) running over the User Datagram Protocol (UDP) are usually recommended instead.[2]

xxx is a reliable stream delivery service that guarantees that all bytes received will be identical with bytes sent and in the correct order. Since packet transfer is not reliable, a technique known as positive acknowledgment with retransmission is used to guarantee reliability of packet transfers. This fundamental technique requires the receiver to respond with an acknowledgment message as it receives the data. The sender keeps a record of each packet it sends. The sender also keeps a timer from when the packet was sent, and retransmits a packet if the timer expires before the message has been acknowledged. The timer is needed in case a packet gets lost or corrupted.[2]

xxx consists of a set of rules: for the protocol, that are used with the Internet Protocol, and for the IP, to send data "in a form of message units" between computers over the Internet. While IP handles actual delivery of the data, xxx keeps track of the individual units of data transmission, called segments, that a message is divided into for efficient routing through the network. For example, when an HTML file is sent from a Web server, the xxx software layer of that server divides the sequence of octets of the file into segments and forwards them individually to the IP software layer (Internet Layer). The Internet Layer encapsulates each xxx segment into an IP packet by adding a header that includes (among other data) the destination IP address. Even though every packet has the same destination address, they can be routed on different paths through the network. When the client program on the destination computer receives them, the xxx layer reassembles the individual segments and ensures they are correctly ordered and error free as it streams them to an application.
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