Intro Networking Class

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Do routers forward layer 2 frames?: no
What does the OSI Transport layer do?: Defines the end-to-end station establishment guidelines between two end stations, to create a connection or session. Monitors reliable or unreliable delivery, error correction before retransmit. Examples include TCP, UDP, SPX
What is a port number?: an identifier attached to an upper-layer segment to identify the application it's associated with.
discuss reliable versus unreliable transport protocol: a reliable protocol (such as TCP) has feedback about the quality of the transport. An unreliable protocol (such an UDP) does not.
what is the 3-way handshake?: within the TCP/IP protocol suite, establishes a connection. accomplished by the sending and receiving of sunchronization and acknowledgement packets.
Describe an IP address: a 32-bit address divided into four 8-bit segments called octets, identifies a specific network and host. Then a 32-bit subnet mask that is also divided into four 8-bit octets, used to determine which bits represent the network and which represent the host. it's a string of 1s followed by 0s, the division between them marks the boundary between network and host portions of the address.
what is a router?: operates at the network level to track and record different networks and choose the best path to those networks.
what is a metric (in terms of routers)?: refers to cost or distance to target network, used to determine best path. common metrics include hops (how many networks you'll go through), delay (time taken), or bandwith (a value associated with the speed of a link).
What does the OSI network session do?: Determines how to transport traffic between devices that are not locally attached in the same broadcast domain. Provides logical addressing which routers use for path determination. Examples include IP and IPX
What is a LAN?: Local Area Network. Network used within a building or campus. Generally connects to centralized data center with mainframe computers and application servers.
What is a WAN?: Wide Area Network. May use permanant or dialup connections.
Name the three layers of a hierarchical network model.: 1. Core layer
2. Distribution layer
3. Access layer
Describe the Access layer of a network.: The point at which end users are connected to the network. AKA the desktop layer. Traffic to and from local resources is confined between the resources, switches, and end users.
Describe the Distribution layer of a network.: AKA workgroup layer - positioned between core and access layer, performs functions such as routing, filtering, and WAN access. The layer that provides policy-based connectivity, it determines if and how packets can access the core services of the network.
Describe the Core layer of a network: AKA the backbone layer. switches traffic as fast as possible to the appropriate global service (AKA enterprise service).
What is the OSI Reference Model?: a conceptual network framework. A layered model that serves as a way to understand how an internetwork operates.
What are the seven layers of the OSI reference model?: Application layers:
1. application
2. presentation
3. session

Data flow layers:
4. Transport layer
5. Network layer
6. Data link
7. Physical
What do the 4 lower layers of the OSI model define?: ways for end stations to establish connections to each other in order to exchange data.
What do the 3 upper layers of the OSI reference model define?: How applications within the end stations will communicate with each other and with the users.
What does the OSI application layer do?: it's the user interface, where the user or application interfaces with the protocols to gain access to the network. examples include FTP, HTTP, Telnet.
What does the OSI presentation layer do?: it's the layer that defines how data is presented, as well as any special data processing such as encryption. examples include ASCII, JPEG, EBCDIC.
What does the Session layer of OSI do?: establishes, manages, and terminates communications sessions between presentation layer entities. service requests and responses. example: application access scheduling, coordination between a database server and a database client.
Describe elements of a network layer address segment.: 1. IP header
2. source address (identifies both the network and the particular host (device) within the network
3. destination address
4. data
What does a protocol stack do?: provides communications between network devices. it's a set of rules that define how information travels across the network. example TCP/IP.
What are headers and trailers?: fields in a PDU that hold control information.
what layer of the OSI stack do bridges and layer 2 switches function in?: Data link layer.
Define PDU.: Protocol data units - control information that is added to the user data. examples include the MAC (media access control) header, and FCS (frame check sequence) trailer.
define encapsulation.: the method of passing data down the OSI stack and adding headers and trailers.
What is layer 2 switching?: hardware-based bridging.
Define ASIC: Application-specific integrated circuit - a a chip to be programmed ot perform a specific function as it is built. technology in switches which allow gigabit speeds with low latency.
define peer layers: similar layers in every device that allow encapsulation and de-encapsulation of data.
What does the OSI physical layer do?: defines the media type, connector type, and signaling type. move bits between devices, specifies voltage, wire speed, and pin-out cables.
What are the standards that define the physical connections in ethernet implementations?: IEEE 802.3 (CSMA/CD) - define a bus topology LAN that operates at a baseband signaling rate of 10 Mbps.
What is Thinnet?: 10base2 wire standard, allows network segments up to 185 meters on coax.
What is Thicknet?: 10base5 wire standard, allows network segments up to 500 meters on large coax cable with devices tapping into the cable to receive signals.
what is 10baseT?: inexpensive twisted-wire standard carries ethernet signals up to 100 meters back to a hub.
what is an AUI?: attachment unit interface - how an ethernet cable attaches to a device.
What is a collision domain?: a group of devices connected to the same physical media such that if two devices access the media at the same time, the result is a collision of the two signals.
What is a broadcast domain?: A group of devices in the network that receive one anothers broadcast messages.
What is a hub?: allows the concentration of many devices into a centralized device, connects all the devices to one physcial bus structure. does not manipulate or view the traffic that crosses the bus, concerned only with propegating the physical signalling.
what is CSMA/CD: carrier sense multiple access collision detection. technology used by stations connected to a single hub, to check for activity before sending information (to prevent collisions).
what is a backoff algorithm?: in the event that a collision is detected by a station, the backoff algorithm determines when they will retransmit the damaged frames so as to minimize the chances of another collision.
What does the OSI data link layer do?: Provides the communications between workstations at the first logical layer above the bits on a wire. Combines bits into bytes and bytes into frames, provides access to media using a MAC address, error detection but not correction. examples HDLC.
What are the two sublayers of the data link layer?: 1. Media Access control (MAC) (802.3) - responsible for how the data is transported over the physical wire. communicates downward to the physical layer.
2. Logical Link Control (802.2) - responsible for logically identifying different protocol types and encapsulating them in order to be transmitted across the network. Uses Service Access Point (SAP) identifier.
functions of a switch or bridge: 1. filtering - if a destination device is on the same segment as a frame, the bridge blocks the frame from going on to other segments.
2. if destination device is on a different segment, bridge forwards the frame.
3. flooding - if destination address unknown to the bridge, frame is forwarded to all segments except the one on which it was received.
What is the purpose of a bridge?: avoid collisions by directing path of frames and reducing total traffic.
characteristics of a bridged/switched network: 1. each segment is its own collision domain.
2. all devices connected to the same bridge are in the same broadcast domain.
3. all segments must use the same data link layer implementation.
What are the elements of a MAC sublayer frame?: 1. preamble - a series of 1s and 0s that warn station that a frame is coming.
2. MAC layer address includes 6 hex destination address and 6 hex source address. source addresses are BIA (burned-in address), ROM on card, vendor assigned. Organizationally unique identifier (OUI) addresses are administered by IEEE.
3. length field
4. data field including LLC control information, other upper-layer control information, and the user data
5. 4 byte FCS field - contains a cyclic redundant check value, used to check for frame damage.
WHat are the two types of LLC sublayer frames?: SAP (service access point) and
SNAP (subnetwork access protocol)
which frame your system uses depends on the applications you have running.
How does SNAP format differ from SAP?: destination and source SAP addresses set to AA hex and control field is set to 03 hex. then there's a OUI ID (vendor code) and a type field code that allows for the inclusion of the ethertype, which defines which upper-layer protocol receives the data.
Describe format of SAP frame: 1. Destination SAP (1 byte)and Source SAP (1 byte) together act as pointers to upper level protocols in a station.
2. control field - 1 or 2 byte.
3. data
4. CRC (cyclic redundancy check) value
3 principal categories of physical layer implementations of ethernet.: 1. ethernet (DIX) and IEEE 802.3 - 10 mbps, coax, UTP, or fiber
2. 100 Mbps Ethernet (IEEE 802.3u) - known as fast ethernet, operates over UTP or fiber
3. 1000 Mbps Ethernet - aka gigabit ethernet
who sets standards for ethernet cabling media?: the electronic industries association and the newer telecommunications industry association (EIA/TIA) standards body. categories of cabling are defined from EIA/TIA-568 commercial building telecommunications wiring standards.
what does UTP stand for: unshielded twisted-pair cable. requires an RJ-45 connector. no sheilding is needed because of the cancellation effect of the twisted pairs which minimizes the absorption of radiation of electrical energy from the surrounding environment.
define crosstalk: interference measured on a wire that is located near the wire sending a signal.
what are tip conductors and ring conductors: the two types of wire pairs in UTP. terms originated from phone technology; tip wires are positive and ring wires are negative.
Define and describe encapsulation: As the data moves down the OSI model, it is broken into chunks and information added to each chunk (like headers which tell the destination, and ending bits containing checksum information), which wrap the data for transport. At the other end the opposite process happens. Ultimately this wasn't designed for modern stuff like streaming video.
What does ISO stand for?: open system interconnection reference model.

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