Telecom Chapter 5 - Ethernet (802.3) Switched LANs

Terminal Crosstalk Interference

<-- Propagation effect. Interference by other wire pairs in the cord is crosstalk interference. Crosstalk interference at the two ends where the wires are untwisted is terminal crosstalk interference. Major problem. So limit untwisting of wires to 1.25cm. Worse at the ends (terminal) of the cable where wires are untwisted to put them into RJ-45, ethernet connectors. With no twisting, there is no protection from crosstalk interference. this is all physical layer 1

Noise

<-- Propagation effect. Random electromagnetic energy in the wire adds to the signal and may produce errors. Microwave near wireless access point. So limit cord distance to 100m. this is all physical layer 1

Radiative Attenuation

<-- Propagation effect. Signal may become too low to be received properly. So limit cord distance to 100m. Each pair of copper wire cable radiates radio signals, dissipating the signal. This causes _________ which increases with propagation distance. Twisting wires helps cancel out effects of this. this is all physical layer 1

Digital Signaling

A few possible states (any power of two) Used for Gigabit Ethernet. Binary transmission is a special case of digital signaling. Not all signaling is binary, but all signaling is digital. a = 2^b a = number of possible alternative states. b = number of bits transmitted in each CC

802.1X Authentication

AKA 802.1X Port-Based Network Access Control (NAC). Supplicant must be verified by an authentication server before being allowed to use the workgroup switch to which it is attached. If server accepts, authorizes switch to authorize access to the port. Attacker cannot walk up to any Ethernet wall jack, plug in, and bypass the firewall.

Absorptive Attenuation

Absorption of the light by the core's glass, but this glass is very pure so it is a very small amount.

Tag Fields

Add priority, not frequently used. VLAN tagging is frequently used for security. - Tag Protocol ID field indicates that frame is tagged. - Tag Control Information field gives the info.

ARP Cache Poisoning

Before an attack, the victim's ARP cache correctly tells them that the router IP Address has the DLink layer EUI-48 (MAC) address. Victim sends packets in frames to that MAC address. I.e.... Attacker sends the victim an ARP update. This changes the victim's router DL layer EUI-48 (MAC) address to the DL layer EUI-48 (MAC) address of the attacker. Subsequent packets to the router will go in frames addressed to the attacker, who can read them before sending them on to the router.

Types of UTP

Cat5e, Cat6, Cat6A

Workgroup Switches

Connect Individual hosts to the network. Dealing with layer one connections.

Access Links

Connect individual hosts to their workgroup switches (UTP)

Trunk Links

Connect switches to other switches (fiber)

Multimode Fiber

Cores admitting several modes. Quality standards are optical multimode (OM) standards. OM3 and OM4 multimode fiber are sold today. Used in LANs because of the short distance, modal dispersion doesn't effect the receiver's understanding of the signal too much. this is all physical layer 1

Modal Dispursion

Different directions internal light in a fiber optic cable go, so has this as a time gap. Light can only enter the core at certain angles (modes). This creates arrival time delays called _______. Signals can become unreadable.

Core Switches

Switches connecting to other switches. Fiber optic cables often running between them.

Power over Ethernet (PoE)

_______ is a technology for wired Ethernet local area networks (LANs) that allows the electrical current necessary for the operation of each device to be carried by the data cables rather than by power cords. Made AP installations easier and more flexible, especially on ceilings.

4-Pair Unshielded Twisted Pair (UTP)

8 copper wires, carries signals as voltages. Home-made ethernet. Difference b/w this and OF is distance. And OF is signal pulses through glass. Max distance in LAN is 100m. Lower cost. Same speed as OF.

Data Link Layer Standard

802.3 MAC Standard (single standard regardless of signaling) while many standards in the Physical Layer. NO MAX distances for DLinks in switched networks, only limited at the Physical layer level.

Link Aggregation (Switch Bonding)

Allows to increase total speed and bandwidth at core switches w/o need to install higher capacity switches or cabling. Uses software in switches. 1) Increases overall bandwidth between switches and servers. 2) Eliminate single points of failures between switches

Rapid Spanning Tree Protocol (RSTP)

Also think of as reliability. A protocol that allows the switches within a local area network to virtually remove redundant paths between devices. When link fails, backup link is activated, violating hierarchy, but RSTP disables backup links until they are needed. AKA: IEEE 802.1w

Hierarchy

Ethernet requires a strict ______ switch topology. In _____ there is only a single possible path between any two hosts on a LAN. Problem: If any access or trunk lines or switches fail then the line is severed.

Single-Mode Fiber

Fiber with a diameter of 8.3 microns, no modal dispersion, signal travels much farther, 40km or longer.

Frame Forwarding

Fundamental job of an ethernet switch. Each switch makes a switching decision. 1) Host A puts destination MAC address (E5-...)in destination address field of the frame; sends frame to Switch 1 into Port 2. 2) Switch 1 looks up address in switching table. Sees that the dest. MAC add. is associated with Port 5. Sends frame to port 5. 3)Port 5 on Switch 1 connects to Port 3 on Switch 2. Frame sent to Switch 2. Now Switch 2 looks up E5-... in its switching table. Associated with Port 7, sends to Port 7. 4) Frame sent from S2P7 to S3P4. Switch 3 finds associated port. Port 6 takes to destination host.

Physical Layer Standards

Govern physical links between devices. - Connectors and plugs - Transmission media - Signaling

Manageable Switch

In Simple Network Management Protocol (SNMP). To be visible to the SNMP manager, an Ethernet switch must be a ______________, meaning that it must have an SNMP agent. Can make changes via Set commands. More expensive.

IEEE Standards Association

Its 802 LAN/MAN Standards Committee is where LAN standards come from. That committee's 802.3 Working Group is where Ethernet standards come from. Almost all P & DL layer standards are OSI standards.

Optical Fiber

Light pulses traveling through thin glass fiber. Light pulse = 1 No pulse = 0 Max distance in LAN is 200-500m. Same speed as UTP. Higher cost. ST connector - longer ferrel can stab you SC connector - short end Allows full-duplex transmissions. Not as durable as UTP.

Optical Fiber Transmission

Light travels in waves. A wave's amplitude is its power. __________ is described in terms of wavelength. Wavelength is the physical distance between comparable points on adjacent cycles. Measured in nm. LAN fiber uses 850 nm.

Local Area Network (LAN)

Networks that operate on a customer premises--the property owned by the organization that uses the network. Companies can use whatever technology standards they wish.

Optical Multimode (OM)

OM3: same speeds OM4: Same speeds over the slightly improved distance, costs more. In multimode fiver, quality standards are optical multimode (OM) standards. OM3 and OM4 fiber are sold today. Be able to differentiate which one you would need for which situation: (some Cat of) UTP, OM3, or OM4. this is all physical layer 1

Three UTP Propagation Effects

Radiative Attenuation Noise Terminal Crosstalk Interference

Virtual LAN (VLAN)

Segregate network resources by using clusters of servers and hosts that are allowed to communicate with each other. At layer 2 and does not require encryption.

Clock Cycle

Sender holds transmission state constant for a short amount of time. The receiver can read the signal at any time within the clock cycle. Transmission speed is 1 Gbps = binary transmission CC is 1 billionth of a second.

Signal Regeneration

Signal is rebuilt and transmitted when received at network component (switch or a router), then sent off, negating any attenuation effects

Parallel Transmission

Signals are sent by changing voltage or other characteristics of an electrical signal. Ethernet transmits on all four pairs in each direction simultaneously. Four times as fast compared to if it only had a single pair. Benefit is higher speed.

Ethernet

Single-network standard governed by Physical and Data Link Layer standards. Forwarding devices are switches, messages that travel to them are frames.

10GBASE-T

Speed of 10Gbps using baseband frequencies and UTP (unshielded twisted pair cabling) Cat6 or Cat6A Cat6A has additional and tighter twists and more insulation to eliminate crosstalk.

802.1AE Standard

Switch-to-Switch Protection Switches send supervisory frames to one another. Requires switches to authenticate themselves before another switch will listen to them. Encrypts traffic between switches.

Signaling

To transmit a frame over a physical link, the sender converts 0s and 1s into physical signals that propagate down a transmission link, then that device converts them back into 0s and 1s of the frame.

Binary Signaling

Two possible states

Full-Duplex Transmission

Two strands permit simultaneous two-way transmission. In optical fiber.