Chapter 4: Network Access - Intro. to Networks v6

Wireless Media

Carries *electromagnetic* signals that represent binary digits of data comms. using *radio or microwave frequencies*.

Rollover

Cisco proprietary cable used to connect a workstation to a router or switch console port.

Role of *physical* layer --> Receiving

OSI 1 - Receives signals across the connecting media. Decodes the signal back into data. Then passes the frame to data link layer.

Role of *physical* layer --> Sending

OSI 1 - To control how the data is transmitted onto the physical media by encoding the *binary digits* which represent data *into signals*.

Role of *data link* layer --> Receiving

OSI 2 - Accepts the frame from the physical layer for acceptance and processing.

Role of *data link* layer --> Sending

OSI 2 - To prepare data for transmission and control how that data accesses the physical media.

Node

OSI 2/Data Link layer notation for network devices connected to a common media.

OTDR

Optical Time Domain Reflectometer - Used to test each fiber-optic cable segment by injecting a test pulse of light into the cable. Measures *backscatter & reflection* of light detected as a function of time. Calculates approximate distance of faults along cable.

NIC

(Network Interface Card) *Ethernet NICs* for wired connection - *WLAN (Wireless LAN) NICs* for wireless. Allows computer to connect to some networking cable/signal. NIC then sends/receives data over the cable/signal at the direction of the computer.

Half-duplex Communication

Both devices can transmit and receive on the media but *cannot* do so simultaneously/ONLY *one at a time*. Used in... - legacy bus topologies - Ethernet Hubs - WLANs Operate using SAME duplex mode

Ethernet Straight-through

The most common type of networking cable. Connects a network host to a network device. Both ends T568A or both ends T568B.

CSMA/CA

(*Carrier Sense Multiple Access/Collision Avoidance* - Contention-based media access method/protocol) Used by *WLAN/WiFi/IEEE 802.11*

CSMA/CD

(*Carrier Sense Multiple Access/Collision Detection* - a Contention-based media access method) If 2+ devices transmit simultaneously, both will detect on the network via their NICs either comparing data transmitted with data received OR recognizing signal amplitude > normal. Collision = data corrupted and needs to be resent. Used in half-duplex Ethernet LANs

Duplex Multimode LC Connectors

(Fiber-Optic Connector) - *Lucent Connector...* - Similar to a LC simplex connector, but using a duplex connector. B/C light travels in one direction, 2 fibers reqd. to support full duplex operation (connector accepts both the transmitting & receiving fibers in a single connector).

LC Simplex Connector

(Fiber-Optic Connector) - *Lucent Connector...* - Smaller version SC connector. AKA: little/local connector.

ST Connector

(Fiber-Optic Connector) - *Straight Tip* - One of the first connector types. Locks w/a "twist-on/twist-off" bayonet-style mechanism.

SC Connector

(Fiber-Optic Connector) - *Subscriber* - aka "square connector/standard connector". Widely used LAN & WAN connector. Uses push-pull mechanism. Used w/MMF & SMF.

ISR

(Integrated Service Router) A device that offers both wired and wireless connectivity. Offers a *switching* component/Ethernet Switch for multiple devices to connect to LAN via cables AND includes an AP (access point) for wireless devices to connect.

Contention-based Access

(MAC method for *shared media*) All nodes operating in half-duplex compete for the use of the medium, but only one device can send at a time. Has a process if 2+ transmit at once/*collision*. Used by... - Ethernet LANs using Hubs - WLANs EXs: CSMA/CD & CSMA/CA - Does NOT scale well under heavy media use.

Controlled Access

(MAC method for *shared media*) Each node has its own time to use the medium. *Inefficient* b/c device must *wait its turn* to access medium. Used by... - Legacy Token Ring LANs

Purpose of the Data Link Layer

(OSI 2) "taxicab to airport" - provides structure to 1's/0's sent over media - allows upper layers to access media - Accepts OSI 3/Network packets & packages them into *frames*//preps network data for the physical network - Exchanging Ethernet frames b/t nodes over a physical network media - Performs *error detection*

STP

(Shielded Twisted-Pair) Better noise protection that UTP but more expensive & harder to install. Shielding prevents EMI/RFI. Uses RJ45 connectors. Cables are terminated w/special shielded STP data connectors. If not grounded, may act as antenna.

UTP

(Unshielded Twisted Pair) Most Common networking media. Terminated w/*RJ45* connectors. Interconnects network hosts w/intermediate network devices. *4 pairs* of color-coded wires. Twisting helps prevent crosstalk.

WAP

(Wireless Access Point) A network device that provides connectivity of wireless clients to connect to a data network. As wireless device *further from WAP*, connection and/or bandwidth decreases (+) wireless devices must *share airwaves* connecting to WAP |\| more devices, slower network performance <-- *wired* devices do *NOT share access*/have separate comms. channels over Ethernet cable

Coaxial cable

(aka "coax") Name comes from the fact that there are 2 conductors that share the same axis. Nearly replaced by UTP. Used in *wireless installations* (attach antennas to wireless devices, carries RF energy b/t antennas) and *cable internet installations* (inside customer homes, but outside home being replaced by *fiber-optics*)

Signal attentuation

(subset of Copper Cabling) - The longer/greater distance a signal travels, the more it deteriorates. Why copper has strict distance limitations.

Crosstalk

(subset of Copper Cabling) a disturbance caused by the electric or magnetic fields of a signal on one wire to the signal in an adjacent wire.

EMI/RFI

(subset of Copper Cabling)(Electromagnetic interference & radio frequency interference)Signals that can distort/corrupt the data signals being carried by copper media. EX: radio waves, electromagnetic devices (fluorescent lights or electric motors)

Virtual Circuit

(subset of Logical Pt-to-Pt) A logical connection created within a network b/t 2 network devices. The 2 nodes on either end exchange frames.

Latency

(subset of throughput) - The amount of time, to include delays, for data to travel from one given point to another.

Goodput

(subset of throughput) - The measure of usable data transferred over a given period of time. *Goodput* = *throughput* MINUS traffic overhead for est. sessions acknowledgments encapsulation

Full-duplex Communication

*Both* devices can transmit and receive on the media at the *same time*. Data link layer assumes media available for transmission at any time. Used in *Ethernet Switches* by default but can they can also operate in half-duplex mode. Operate using SAME duplex mode

Category 5 & 5e (UTP)

*Both* for *data transmission* *Cat5* --> used commonly in 100BASE-TX Fast Ethernet installations. Supports 100 Mb/s & can support 1000 Mb/s but NOT recommended *Cat5e* --> supports 1000 Mb/s

Areas of Concern for Wireless Media

- *Coverage area* - *Interference* (cordless phones, fluorescent lights, microwaves, and more) - *Security* - *Shared Medium* (WLANs operate in *half-duplex*/ONLY one device can send/recieve at a time |\| more users = less bandwidth for each user)

*Generic* Frame Field Types

- *Frame start/stop indicator flags* - *Addressing*: source/dest. nodes on the media - *Type*: IDs layer 3 protocol in data field - *Control*: IDs special flow control services (QoS or VoIP) <-- get priority - *Data*: Frame payload (packet header, segment header, & data) - *Error Detection*: *CRC* (Cyclic Redundancy Check) value placed in FCS field (Frame Check Sequence)

Common WAN Topologies

- *Point-to-Point* - *Hub & Spoke*: A version of the star topology. Central site interconnects branch sites via pt-to-pt links. - *Mesh*: Each link is a pt-to-pt link to the other node. High availability but also high admin. & physical costs. - *Hybrid*: variation/combination of any of the above

Common LAN Topologies

- *Star* - Early on Ethernet Hubs, Now Ethernet switches. Easy to install, troubleshoot, and is scalable. - *Extended Star* - additional Ethernet switches connect other stars - *Bus* - All end systems chained together & terminated on each end. Switch NOT reqd. Early on used coax cables. - *Ring* - Does NOT need to be terminated. Used in legacy Fiber Distributed Data Interface (FDDI) & Token Ring networks

Types of Wireless Media

- *WiFi*/*WLAN* (IEEE *802.11* standard): Uses the contention-based protocol *CSMA/CA* - *Bluetooth*/*WPAN* (IEEE *802.15* standard): Uses device-pairing process to comm. distances from 1-100 meters - *Wi Max*/Worldwide Interoperability for Microwave Access (IEEE *802.16* standard): Uses *point-to-multipoint* topology (+)cellular & satellite comms. but outside of this chapter's scope

WLAN requires which network devices?

- *Wireless Access Point* (WAP/AP): concentrates user's wireless signals & connects them to existing copper-based network infrastructure - *Wireless NIC adapter*: provides wireless network capability to each host

Data Link Layer (OSI 2)/Direct Access (TCP/IP) Standard Orgs

- Institute of Electrical & Electronics Engineers - International Telecommunications Union - International Organization for Standardization - American National Standards Institute

The two major types of Fiber-Optic cables.

- Single-mode fiber (SMF) - Multimode Fiber (MMF)

Process of data from Source to Destination Nodes

-User data *segmented* by *transport* layer, put into *packets* by *network* layer, put in *frames* by *data link* layer -*Physical layer encodes* frames, *creates* electrical, optical, or radio wave *signals* to rep. bits in each frame -Signals sent on media, one at a time -Process reversed at dest. node

A physical connection can be...

...a *wired* connection using a cable or a *wireless* connection using radio waves

How UTP prevents EMI/RFI

1. *Cancellation* - When two wires in an electrical circuit are paired close together, their magnetic fields are the exact opposite of each other and |\| cancel each other and any outside EMI/RFI signals 2. *Varying # of twists/wire pair* - Precise specs. on # of twists/meter(3.28 ft) of cable. Twisting enhances cancellation effect.

The 2 basic media access control methods for *shared media*/*Multi-access Networks*

1. *Contention-based Access 2. *Controlled Access*

The 2 sublayers of the Data Link Layer

1. *Logical Link Control/LLC* 2. *Media Access Control/MAC*

2 ways to determine which MAC method/Layer 2 protocol to use

1. *Logical Topology* - How the connection b/t nodes appears to the data link layer. 2. *Media Sharing/Physical Media type* - How the nodes share the media. (point-to-point = WAN or shared = LAN)

3 common types of fiber-optic termination & splicing errors

1. *Misalignment* 2. *End gap* - media doesn't completely touch at the splice or connection 3. *End finish* - Media ends not well polished, or dirt is present at the termination

3 Functional Areas Addressed by Physical Layer Standards

1. *Physical Components* 2. *Encoding/Line Encoding* 3. *Signaling*

The 2 fundamental types of topologies

1. *Physical Topology* 1. *Logical Topology*

The 3 Basic Forms of Network Media

1. Copper Cable 2. Fiber-optic Cable 3. Wireless

The 3 basic parts of all data link layer *frames*

1. Header 2. Data - *ALL* data link layer protocols encapsulate the Layer 3 PDU in this field 3. Trailer

How are the light pulses representing the transmitted data as bits on Fiber Media generated?

1. Lasers 2. LEDs (Light Emitting Diodes)

3 Main Copper Media Types

1. Unshielded Twisted-Pair (UTP) 2. Shielded Twisted-Pair (STP) 3. Coaxial

Encoding/Line Encoding (1/3 Fnl. Areas of Phys. Layer)

A method of converting a stream of data bits into a predefined code. Pattern of voltage or current used to rep. bits(0's & 1's). EX: *Manchester Encoding* - 0 bit = *high-to-low* voltage transition 1 bit = *low-to-high* " "

Why don't Ethernet LANs using *switches* use a contention-based media access control method?

Because the switch and the host NIC operate in *full-duplex mode*.

Standards at Physical Layer

Consists of electronic circuitry, media, and connectors developed by engineers.

Physical Components (1/3 Fnl. Areas of Phys. Layer)

Electronic hardware devices, media, & connectors that transmit signals to rep. bits. (NICs, interfaces, connectors, cable designs & materials)

Photodiodes

Electronic semiconductor devices that detect the light pulses in fiber media and converts them to voltages.

Standard org. that defines the electrical characteristics of copper cabling.

IEEE

LLC

Logical Link Control - Upper sublayer of Data link layer - Comm.s w/network layer. Places info in frame that ID's which network layer protocol being used (IPv4/v6)

MAC

Media Access Control (...method) - Defines technique for getting the frame on/off the media//if and how nodes share the media. Provides data link layer addressing. Like traffic rules for cars.

MMF

Multimode Fiber provides bandwidth up to 10 Gb/s over link length of 550 meters.

Multi-access Networks

Network topologies that share a *common medium* with *multiple nodes*. EXs: LANs & WLANs

Fiber-Optic Cabling (general)

Optical fiber - a flexible, but very thin, transparent strand of glass w/bits encoded on the fiber as light impulses. - Less attenuation/transmits greater distances than Copper cabling. - higher bandwidth than any other media - Immune to EMI & RFI - durable |\| deployable in harsh conditions

See Textbook for Layer 2 Addresses & LAN vs WAN Frames

Pgs 199-202

Function of OSI (1) Physical Layer

Provides the means to transport the bits that make up a data link layer (OSI 2) frame across the network media. Physical layer accepts a complete frame from data link layer, encodes it as a series of signals, then transmits signals onto local media.

How UTP cabling is rated and its major categories.

Rated according to its performance/ability to carry higher bandwidth rates. Cat3 Cat 5 & 5e Cat 6

Fiber Patch Cords

Required for interconnecting infrastructure devices. The colors distinguish b/t SMF & MMF patch cords Yellow = SMF Orange or aqua = MMF *Protect w/small plastic cap when not in use*

Copper Cable

Signals are patterns of electrical pulses. (+)'s - Inexpensive Easy to install Low resistance to electrical current (-)'s - Distance Signal Interference

Fiber-Optic Cable

Signals are patterns of light.

Wireless Media

Signals are patterns of microwave transmissions.

SMF

Single Mode Fiber

(blank) stipulates the commercial cabling standards for LAN installations and is the standard most commonly used in LAN cabling environments.

TIA/EIA-568

Bandwidth

The *capacity* of a network medium to carry data. Digital B.width = amt. of data can flow from one place to another in given amt of time. Though of as "speed" but that's *wrong*. Ex: 10Mb/s vs 100Mb/s - All bits sent at speed of electricity. Diff is # of bits transmitted per second. Physical media properties, tech, and laws of physics determine available B.Width.

Logical Point-to-Point Topology

The end nodes could be connected physically by a number of intermediate devices. But notice that doesn't affect the logical topology.

Throughput

The measure of the transfer of bits across the media over a given period of time. Cannot be faster than the slowest link in path from source to destination. Influenced by type & amt. of traffic (+) *latency*

Signaling (1/3 Fnl. Areas of Phys. Layer)

The method of representing the bits/what type of signals reps. 0 & 1. EX: *Morse Code*. *Modulation* - process by which the characteristics of on wave (signal) modifies another wave (carrier).

Physical Topology

The physical connections and how end devices & intermediary devices are interconnected. Usually point-to-point or star.

Dispersion

The spreading out of a light pulse over time. The more dispersion, the greater the loss of signal strength. Big difference b/t SMF & MMF.

Logical Topology

The way a network transfers frames from one node to the next. Consists of virtual connections b/t nodes of a network. Logical signal paths defined by data link layer protocols. *This topology influences the type of network framing & MAC method used*.

Category 6 Cable (UTP)

Used for data transmission. Added separator b/t each pair of wires = functioning at higher speeds Supports 1000Mb/s -10 Gb/s but 10 Gb/s NOT recommended

Category 3 Cable (UTP)

Used for voice comms. Most often for phone lines.

Ethernet Crossover

Used to interconnect similar devices. Connects 2 hosts or 2 intermediary devices. One end T568A, other end T568B.