Networking Basics Ch.4: Network Access – Flashcards

- *Data Link Layer* (2) prepares data for transmission and controls data access to physical media - *Physical Layer* (1) receives signals across connecting media and its protocols govern how to format a frame for use with different media. provides the means to transport bits that make up data link layer frame encoding one complete frame into series of media-specific signals.

*Integrated Service Routers (ISRs)* provides AP AND switch component for connection to LAN via physical cable

- Wired network has data transmitted through physical cables connecting end device to shared switch - Wireless network has data transmitted through radio waves connecting end devices to an AP (Access Point) - Integrated Service Routers (ISRs) provides AP AND switch component w/ multi ports for connection to LAN via physical cable - Ethernet NICs (wired) and WLAN NICS (wireless) connect devices to network media

- *Transport (L4) segments* data - *Network (L3) packets * segments with IP adrss - *Data Link (L2) frames* packets - *Physical (L1) encodes * bit-represented frames onto media-specific signals (electrical/optical/radio) on which they are sent - at destination node... physical layer (L1) restores bits representation and passes complete frame to Data Link (L2)

TCP/IP standards are governed by *IETF*. OSI standards are governed by electrical and communication engineer organizations (Physical Layer Standards) or computer scientists/software engineers (upper layers)

- ISO - TIA/EIA (Telecommunications Industry Association/Electronic Industries Association - ITU (International Telecommunication Union - ANSI (American National Standards Institute) - IEEE (Institute of Electrical and and Electronics Engineers) - FCC (Federal Communication Commission) and ETSI (European Telecommunications Standards Institute) - Canadian Standards Association - European Committee for Electrotechnical Standardization (CENELEC) - Japanese Standards Association (JSA/JIS)

(1)*Physical Components*: Hardware including devices, media, connectors... -eg, NICs, UTPS, Coaxial, connectors interfaces, cable, materials/designs, ports (2)*Line/Frame Encoding*: Converting data bit stream into *code* (grouping of bits that provide predictable pattern for recognition by sender/receiver and allows user to distinguish data bits from control bits) -eg, Manchester encoding, Non-Return to Zero (NRZ) technique, 4B/5B codes used with Multi-Level Transition Level 3 (MLT-3) signaling, 8B/10B encoding, PAM5 (3) *Signaling*: Method representing bits as electrical/optical/wireless signals on media defines what represents a 1 or a 0 -eg, long pulse = 1 and short pulse = 0) -eg, intensity/phases/changes of Electromagnetic Field

- *Manchester Encoding* uses voltage transition where high>low=0 and low>high= -Transition occurs mid-period -(eg, 10 b/s Ethernet, RFID, NFC) - *NRZ (Non-Return to Zero)* Has "zero" and "one," state w/ no neutral position.

*Modulation* is when the characteristics of a signal wave modify a carrier wave - *Frequency (FM)* - *Amplitude (AM)* - *Pulse-coded modulation (PCM)* analog signal (eg, sound) is converted into a digital signal by sampling the signal's amplitude and expressing the different amplitudes as a binary number. The sampling rate must be at least twice the highest frequency in the signal.

- *Asynchronous* - data signal transmission sans associated clock signal, requires start/stop flags b/c spacing is arbitrary non-standard - *Synchronous* - odd/even spaced intervals with clock signal

*Bandwidth* is (data carrying capacity of media) is rate of bits transmitted/s not speed of bits as all bits travel at speed of electricity) *Throughput* measures bit transfer over time and is determined by traffic amount/type/latency (data A->B time) created by internetworking devices. one low-throughput segment bottlenecks otherwise high-bandwidth path *Goodput* measures usable data transferred over time and equals throughput - traffic overhead for establishing sessions/acknowledgments/encapsulation.

Copper Cabling transmits data as electric pulses received by detector in destination's network interface device +simple/economic choice of media with low resistance to electric current -susceptible to interference

-*EFI (Electromagnetic Interference)* or *RFI (Radio Frequency Interference)* from radio waves and electromagnetic devices (fluorescent lights and electric motors) - minimized via insulation and grounding connections - *Crosstalk* disturbance caused by small circular electromagnetic field of adjacent wire - minimized via opposing circuit wire pairs twisted together - Can limit electric noise susceptibility of copper cables by selecting environment-appropriate cabling, avoiding potential noise sources in building and proper cable handling/termination techniques

*UTP (Unshielded Twisted-Pair)* - most common cabling connects network host to internetworking devices w/ RJ-45 termination *STP (Shielded Twisted Pair)* - -Better noise protection than UTP but more expensive/difficult , also had RJ-45 terminals *Coaxial* - has two conductors sharing same axis and was replaced by UTP

4 twisted-pair 22/24 gauge wires w/ color-coded insulation (prevents interference between pairs) sheathed in plastic outer jacket (minor physical damage). NO SHIELD *Cancellation*(opposite magnetic fields of wires in a circuit cancel each other out) and *varying twists* counters EMI/RFI sans shielding -arrange wires on same circuit proximal so that their opposite magnetic fields cancel each other and outside EMI/RFI - varying number of twists/meter for each color-pair ISO 8877 specifies RJ-45 plug is crimped at end of cable and goes into RJ-45 Socket. wires should be as twisted and sheathed as possible to limit degradation at terminal connections

- *Ethernet Straight-Through*: common connecting end-internetworking device. Both ends T568A/B - *Ethernet Crossover*: connects similar devices via dissimilar plug standards (T568A/B) - *Rollover*: cisco proprietary connects workstation serial port to router console port via adapter

- *TIA/EIA-568* defines UTP standards (types, lengths, connectors, terminations, testings methods) - *IEEE rates UTP* by bandwidth - Cat3 - phone-line voice com - Cat5 - data transmission 100Mb/s (eg, 100BASE-TX Fast Ethernet Installation) - Cat5e(nhanced) supports 1000 Mb/s is minimally acceptable current standard - Cat6 - 100-1000 Mb/s using pair-seperatorrecommended current best practice - Cat6a - Cat7 on horizon

*Shielded Twisted Pair * -Better noise protection but more expensive/difficult RJ-45 - use shielding (for EMI/RFI interference) and twisting (for crosstalk) - terminated w/ shielded STP data connectors but shield may act pick up noise as antenna if improper cable grounding - each twisted pairs are wrapped in foil shield. all 4 pairs are wrapped in braided/foil shield - new Ethernet 10GB standard media Two kinds -STP cable shields the entire bundle of wires with foil, eliminating virtually all interference (more common). -STP cable shields the entire bundle of wires and the individual wire pairs with foil, eliminating all interference.

- has two conductors sharing same axis -(((signal-transmitting copper conductor) wrapped in plastic insulation) surrounded by braided-copper-weave OR metallic-foil that acts as circuit's 2nd wire AND shields inner conductor) outer jacket) - Installations 1) carries RF energy between antennas and radio equipment in wireless device 2) *HFC (Hybrid Fiber Coax)* replacing portions of coax cable and supporting amplification elements with optical fiber until last little length - BNC N and F type

correctly separated, connected, grounded cables w/ undamaged installations prevents... - defective device conducts improper current to other device chassis - undesirable voltage levels between devices with different power-source ground-potential - might conduct lightning strikes to device

- *Work area*: Consists of the communication outlets (wall boxes and faceplates), wiring, and connectors needed to connect network hosts using the horizontal wiring subsystem to the telecommunications room. The standard requires that two outlets be provided at each wall plate: one for voice and one for data. - *Horizontal cabling*: The cabling run from each outlet to the equipment room. The maximum horizontal distance is 90 meters (295 feet) independent of media type. An additional 6 meters (20 feet) is allowed for patch cables at the telecommunications room and at the workstation, but the combined length cannot exceed 10 meters (33 feet). - *Telecommunications room* : Sometimes referred to as the wiring closet, it provides an endpoint for horizontal cabling and backbone cabling. Typically contains patch panels and infrastructure devices such as switches and routers. Multiple telecommunications rooms exist in large organizations and connect to a central equipment room using backbone cabling. - *Backbone cabling: The backbone wiring runs up throu*gh the floors of the building (risers) or across a campus and provides the interconnection between the equipment room and telecommunications room. The distance limitations of this cabling depend on the type of cable and facilities it connects, but the popular cabling consists of optical fiber cables. - *Central equipment room*: Sometimes referred to as the network operation center (NOC), this room provides the endpoint for all backbone cabling and may contain enterprise-class switches, routers, firewall appliances, servers, and access to the provider entrance facility. - *Entrance facility*: This contains the service provider telecommunications service entrance to the building. This facility may also contain campus-wide backbone connections. This area also defines the network demarcation point, which is the interconnection to the local exchange carrier's telecommunications facilities. The demarcation point forms the boundary between the part of the network that is the responsibility of the organization and the part of the network that is the responsibility of the carrier.

- bits are encoded as light pulses on flexible thin transparent strand of pure glass (light-pipe OR wave-guide) - pulses generated by Lasers OR LEDs (Light Emitting Diode) and detected by photodiodes -longer distance, higher bandwidth, less-attenuation, EMI/RFI immunity. popular for connecting infrastructure network devices

- *Jacket*: PVC protection from abrasion/moisture/contaminants of variable composition - *Strengthening Material*: prevents stretching, kevlar - *Buffer*: shield core/cladding from damage - *Cladding*: mirror like epidermal pipe slightly dissimilar to core - *Core*: silica OR glass transmission element

- *Enterprise* - backbone of infrastructure devices - *FTTH (Fiber-to-the-Home)* - always on broadband service to home/small business - *Long-Haul* - SP's connecting countries/cities - *Submarine*

- *SMF (Single-mode Fiber)* - expensive *LASER* is sent across small core (polymeric coating) in single straight path with little dispersion. long distance - *MMF (Multimode Fiber)* - economic *LED* is sent across large core in multiple paths with more dispersion/loss of signal. shorter distances. 10 Gb/s over link lengths of up to 550 meters.

- *ST (Straight-Tip)* - early adopted. locks securely with a "twist-on/twist-off" bayonet style mechanism. - *SC (Subscriber-Connector)* - aka: square connector or standard connector. widely adopted LAN and WAN connector w/ push-pull mechanism ensuing positive insertion. Esed w/ multimode and single-mode fiber. - *LC (Lucent Connector)* - - *Simplex* - A smaller version of the fiber-optic SC connector. It is sometimes called a little or local connector and is quickly growing in popularity due to its smaller size. -* Duplex Multimode* (aqua) - Similar to a LC simplex connector, but using a duplex connector.

- *Misalignment*: The fiber-optic media are not precisely aligned to one another when joined. - *End gap*: The media does not completely touch at the splice or connection . - *End finish*: The media ends are not well polished, or dirt is present at the termination. - *OTDR (Optical Time Domain Reflectometer)* measures backscatter and reflection over injected light pulse over time detecting distance faults along cable of

-Binary digits represented as Electro-mag signals carried by radio/microwave frequencies. +is most mobile/flexible media - *Coverage Area* limited by physical barriers in unopened environment - *Interference* from common devices - *Security* - non-discriminant transmission - *Shared Medium* - WLANs operate in half-duplex (only one device can send or receive at a time. shared wireless medium means less bandwidth for each user.

apply to (1) data-radio signal encoding (2) power/freq. of transmission (3) signal reception/decoding requirements (4) antenna design/construction - *Wi-Fi (IEEE 802.11)* Wireless LAN (WLAN) technology uses contention-based protocol CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) - The wireless NIC must first listen before transmitting to determine if the radio channel is clear. If another wireless device is transmitting, then the NIC must wait until the channel is clear. CSMA/CA is discussed later in this chapter. - *Blue-Tooth (IEEE 802.15)*- Wireless Personal Area Network (WPAN) uses device pairing process 1-100m at 3Mb/s - *Mi-MAX (IEEE 802.16)* - Worldwide Interoperability for Microwave Access uses point-to-multipoint topology to provide wireless broadband access. at 1 Gb/s

- *AP (Wireless Access Point)* - aggregates end-device signals and connects to network via copper or . router-switch-AP combined - *Wireless NIC Adapters* on each host provide wireless compatibility

- *IEEE 802.11a*: - 5 GHz frequency band @ 54 Mbps. - Higher frequency, smaller coverage area, and less penetrating buildings. - not 802.11b or 802.11g interoperable - *IEEE 802.11b*: - 2.4 GHz @11 Mbps. - longer range, better building penetration than 802.11a. -* IEEE 802.11g*: - 2.4 GHz @ 54 Mbps. - same frequency/range as 802.11b but with the bandwidth of 802.11a. - *IEEE 802.11n*: - 2.4 GHz or 5 GHz @ 100 Mbps to 600 Mbps - distance range of up to 70 meters. 802.11a/b/g backward compatible. -* IEEE 802.11ac*: - 5 GHZ @ 450 Mbps and 1.3 Gbps (1300 Mbps.) - 802.11a/b/g/n backward compatible -* IEEE 802.11ad*: (aka WiGi) - uses a tri-band Wi-Fi solution using 2.4 GHz, 5 GHz, and 60 GHz @ 7 Gbps.

~ responsible for the exchange of frames between nodes over a physical network media ~ provides access to upper layers ~ packages L3 packets into frames ~ preps data for physical network ~ controls data placement and reception on media ~ exchanges frames between nodes over media (UTP OR Fiber) ~ packet reception/direction to upper Ls ~ error detection

At each hop along a path, the router... (1) accepts frame from medium (2) De-encapsulates Frame (3) Re-Encapsulates Packet into new frame (4) forwards new frame appropriate to the medium of that segment of the physical network

Layer 2 notation for network devices connected to common media which build and forward frames

- *LLC (Logical Link Control)* - This upper sublayer defines the software processes that provide services to the network layer protocols -communicates with the network layer. -places information IDing which L3 protocol is being used into the frame allowing multiple L3 protocols (IPv4, IPv6) to utilize the same network interface and media - *MAC (Media Access Control)* - defines media access processes performed by the hardware providing data link layer addressing and access to various network technologies. - *MAC* sublayer communicates with Ethernet LAN technology to send and receive frames over copper or fiber-optic cable. - The *MAC* sublayer also communicates with wireless technologies such as Wi-Fi and Bluetooth to send and receive frames wirelessly.

*Topology*: How the connection between the nodes appears to the data link layer. The arrangement/relationship of network devices and the interconnections between them. eg, LAN and WAN topologies can be viewed in two ways... *Media Sharing*: How the nodes share the media (eg point-to-point in WAN OR shared in LAN)

*Physical Topology* refers to physical connections and IDs how end/infrastructure devices (routers, switches, wireless access points) are interconnected. usually point-to-point or star. *Logical Topology* refers to way network transfers frames between nodes. This arrangement consists of virtual connections between the nodes of a network. These logical signal paths are defined by data link layer protocols. The logical topology of point-to-point links is relatively simple while shared media offers different access control methods. See Figure 2. physical topology: the actual connections and layout of devices in a network logical topology: the way that the data travels through the network

- *Point-to-Point*: permanent link between two nodes w/ - (physical topology) logical data link protocols are simple because (1) no other hosts to share media with and (2) no incoming frame destination determination to be made - (logical topology) source and destination nodes can have multiple intermediary devices. logical connection can sometimes create virtual circuit (two end nodes exchanging frames) - The media access method used by the data link protocol is determined by the logical point-to-point topology, not the physical topology. This means that the logical point-to-point connection between two nodes may not necessarily be between two physical nodes at each end of a single physical link. - *Hub-and-Spoke*: Wan version of star topology with points connected to central site via branches - *Mesh*: high availability/cost where every endpoint is interconnected

Duplex communications refer to the direction of data transmission between two devices. duplex mismatch creates inefficiency and latency on the link. - *Half-duplex communication*: devices can transmit/receive on the media but not simultaneously. Ethernet has established arbitration rules for resolving conflicts arising from instances when more than one station attempts to transmit at the same time. - *Full-duplex communication*: devices can transmit/receive on the media simultaneously. The data link layer assumes that the media is available for transmission for both nodes at any time. Therefore, there is no media arbitration necessary in the data link layer.

how the end systems are physically interconnected - *Star*: central intermediate device connecting end devices. Early star topologies used Ethernet hubs while new ones use Ethernet switches. - easy to install, very scalable (easy to add and remove end devices), and easy to troubleshoot. - *Extended Star*: In an extended star topology, additional Ethernet switches interconnect other star topologies. - *Bus*: All end systems are chained to each other and terminated in some form on each end. does not reqiure Infrastructure devices (eg, switches) to interconnect the end devices. Bus topologies using coax cables were used in legacy Ethernet networks because it was inexpensive and easy to set up - *Ring* - End systems are connected to their respective neighbor forming a ring that does not need to be terminated (unlike the bus topology). used in legacy Fiber Distributed Data Interface (FDDI) and Token Ring networks.

Multi-Access Networks share a common medium with multiple nodes communication simultaneously - *Contention-based access*: All nodes operating in *half-duplex* compete for the use of the medium and have collision plan. - *Controlled access* - (scheduled access or deterministic.) Nodes take turns using tokens - These deterministic types of networks are inefficient because a device must wait its turn to access the medium - eg, Legacy Token Ring LANs (IEEE 802.5) and FDDI -*SONET* (Synchronous Optical Network) is the standard for optical networks now obsoleting these other

- *CSMA (Carrier Sense Multiple Access)* detects media busy status and decides when chance of colliding—>corrupting data are small - *Carrier sense multiple access with collision detection (CSMA/CD)*: TEnd devices monitor media for presence of data signal. transmits when available and looks for collision in order to resend. Traditional forms (802.3) of Ethernet use this method. - *Carrier sense multiple access with collision avoidance (CSMA/CA)*: device sends Intent-to-use (Request to Send frame) over free media. recieves clearnace to submit (Clear to Send frame) THEN sends data - 802.11 (Wifi) frame receiver returns acknowledgment These don't scale well under heavy media use. as Nodes ^ probability of successful media access !^ - eg, Ethernet LANs using hubs, WLANS, and legacy Ethernet bus networks

- 1. PC1 has an Ethernet frame to send to PC3. - 2. PC1's NIC needs to determine if anyone is transmitting on the medium. If it does not detect a carrier signal, in other words, it is not receiving transmissions from another device, it will assume the network is available to send. - 3. PC1's NIC sends the Ethernet Frame, as shown in Figure 1. - 4. The Ethernet hub receives the frame. An Ethernet hub is also known as a multiport repeater. Any bits received on an incoming port are regenerated and sent out all other ports, as shown in Figure 2. - 5. If another device, such as PC2, wants to transmit, but is currently receiving a frame, it must wait until the channel is clear. - 6. All devices attached to the hub will receive the frame. Because the frame has a destination data link address for PC3, only that device will accept and copy in the entire frame. All other devices' NICs will ignore the frame, as shown in Figure 3.

- *Header*: control information (addressing) at PDU beginning (specified by the data link layer protocol for the specific logical topology and media used) ETHERNET OTHER Protocols - *Data*: IP header, transport layer segment header, and application data - *Trailer*: control information (error detection) at PDU ending

*Cyclic Redundancy Check (CRC)* -created by transmitting nodes, serves as mathematical summary of frame contents and is placed in *Frame Check Sequence (FCS).* receiving node re-calculates and cross-references

- *Frame start* and *Frame stop* indicator flags: MAC sublayer uses to identify beginning/end frame limits - *Addressing*: Mac Sublayer uses to identify source/destination nodes - *Type*: LLC sublayer uses to identify Layer 3 protocol. - *Control*: Identifies special flow control services. - *Data*: Contains the frame payload (i.e., packet header, segment header, and the data). - *Error Detection*: Included after the data to form the trailer, these frame fields are used for error detection.

- SHDSL Interface - FastEthernet Switch Ports - Management Ports - Gigabit Ethernet Interfaces - USB Type A Connector

*Ethernet* -- dominant family of networking technologies used in LAN - 802.2 and 802.3 - basic frame format and the IEEE sublayers of OSI Layers 1 and 2 remain consistent across all forms of Ethernet while data detection and placing methods vary - provides unacknowledged connectionless service over a shared media using CSMA/CD as the media access methods - Shared media requires ethernet frame header to contain source/destination MAC address (48 bit hexadecimal) *PPP* - RFC-defined unlike most EEO-defined L2 protocols - WAN associated - media-agnostic via layers architecture - PPP establishes logical connections, called sessions, between two nodes. - session hides the underlying physical media from the upper PPP protocol. - sessions provide PPP with a method for encapsulating multiple protocols over a point-to-point link. - Each protocol encapsulated over the link establishes its own PPP session - allows negotiation options - authentication - compression - multilink *802.11 Wireless*