cis 81 fundamentals of networking chapter 4: network access rick graziani cabrillo college...

CIS 81 Fundamentals of NetworkingChapter 4: Network Access

Rick Graziani

Cabrillo College

[email protected]

Fall 2013

Chapter 4

4.1 Physical Layer Protocols 4.2 Network Media 4.3 Data Link Layer Protocols 4.4 Media Access Control 4.5 Summary

Comparing the two models

At the network access layer, the TCP/IP protocol suite does not specify which protocols to use when transmitting over a physical medium.

Only describes the handoff from the internet layer to the physical network protocols.

OSI Layers 1 and 2 discuss the necessary procedures to access the media and the physical means to send data over a network.

3

4

Focus on Data Link LayerIP

IP

Data Link Layer: Post-It Label on IP “box” (demo)Physical Layer: Roll or toss tennis balls (demo)

5

DataHTTP Header

TCP Header

IP Header

Data Link Header

Data Link Trailer

IP PacketData Link Header

Data Link Trailer


Data Link Trailer


Data Link Trailer


Data Link Trailer


Data Link Trailer


Data Link Trailer

DataHTTP Header

TCP Header

IP Header

Data Link Header

Data Link Trailer

Reminder of encapsulation/decapsulation

Getting it Connected

Connecting to the Network

A physical connection can be a wired connection using a cable or a wireless connection using radio waves.


Connecting to the Network

Switches and wireless access points are often two separate dedicated devices, connected to a router.

Many homes use integrated service routers (ISRs),


Network Interface Cards

Network Interface Cards (NICs) connect a device to the network. Ethernet NICs are used for a wired connection whereas WLAN

(Wireless Local Area Network) NICs are used for wireless.


Network Interface Cards

Connecting to the Wireless LAN with a Range Extender

Wireless devices must share access to the airwaves connecting to the wireless access point. Slower network performance may occur

A wired device does not need to share its access Each wired device has a separate communications channel over

its own Ethernet cable.

The Physical Layer

The OSI physical layer provides the means to transport the bits that make up a data link layer frame across the network media.

Purpose of the Physical Layer

Physical Layer Media

The physical layer produces the representation and groupings of bits for each type of media as:

Copper cable: The signals are patterns of electrical pulses. Fiber-optic cable: The signals are patterns of light. Wireless: The signals are patterns of microwave transmissions.


Physical Layer Standards

Upper OSI layers are performed in software designed by software engineers and computer scientists.

TCP/IP suite are defined by the Internet Engineering Task Force (IETF) in RFCs


Physical Layer Standards

Standard organization

Networking Standards

ISO• ISO 8877: Officially adopted the RJ connectors (e.g., RJ-11, RJ-45)• ISO 11801: Network cabling standard similar to EIA/TIA 568.

EIA/TIA

• TIA-568-C: Telecommunications cabling standards, used by nearly all voice, video and data networks.

• TIA-569-B: Commercial Building Standards for Telecommunications Pathways and Spaces

• TIA-598-C: Fiber optic color coding• TIA-942: Telecommunications Infrastructure Standard for Data Centers

ANSI • 568-C: RJ-45 pinouts. Co-developed with EIA/TIA

ITU-T • G.992: ADSL

IEEE• 802.3: Ethernet• 802.11: Wireless LAN (WLAN) & Mesh (Wi-Fi certification)• 802.15: Bluetooth

Who maintaining physical layer standards? Different international and national organizations, regulatory government

organizations, and private companies

Fundamental Principles of Layer 1

Physical Layer Fundamental Principles

MediaPhysical Components

Frame Encoding Technique

Signalling Method

Copper cable

• UTP• Coaxial• Connectors• NICs• Ports• Interfaces

• Manchester Encoding• Non-Return to Zero (NRZ)

techniques• 4B/5B codes are used with

Multi-Level Transition Level 3 (MLT-3) signaling

• 8B/10B• PAM5

• Changes in the electromagnetic field

• Intensity of the electromagnetic field

• Phase of the electromagnetic wave

Fiber Optic cable

• Single-mode Fiber• Multimode Fiber• Connectors• NICs• Interfaces• Lasers and LEDs• Photoreceptors

• Pulses of light• Wavelength multiplexing using

different colors

• A pulse equals 1.• No pulse is 0.

Wireless media

• Access Points• NICs• Radio• Antennae

• DSSS (direct-sequence spread-spectrum)

• OFDM (orthogonal frequency division multiplexing)

• Radio waves


Physical Layer Fundamental Principles

Encoding or line encoding - Method of converting a stream of data bits into a predefined "codes”.

Signaling - The physical layer must generate the electrical, optical, or wireless signals that represent the "1" and "0" on the media.


Encoding and Signaling

http://www.flukenetworks.com/content/neal-allens-network-maintenance-and-troubleshooting-guide-revealed





Bandwidth

Bandwidth is the capacity of a medium to carry data. Typically measured in kilobits per second (kb/s) or megabits per

second (Mb/s).


Throughput

Throughput is the measure of the transfer of bits across the media over a given period of time.

Due to a number of factors, throughput usually does not match the specified bandwidth in physical layer implementations.

http://www.speedtest.net/ http://ipv6-test.com/speedtest/

http://www.speedtest.net/

http://ipv6-test.com/speedtest/


Types of Physical Media

Different types of interfaces and ports available on a 1941 router

Network Media

Copper Cabling

Copper Cabling

Characteristics of Copper Media

Signal attenuation - the longer the signal travels, the more it deteriorates - susceptible to interference

Crosstalk - a disturbance caused by the electric or magnetic fields of a signal on one wire to the signal in an adjacent wire.

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Copper Cabling

Copper Media

Counter the negative effects of different types of interference some cables are wrapped in metallic shielding

Counter the negative effects of crosstalk, some cables have opposing circuit wire pairs twisted together which effectively cancels the crosstalk.

Copper Cabling

Unshielded Twisted-Pair (UTP) Cable

Read this section… good stuff!

Copper Cabling

Shielded Twisted-Pair (STP) Cable

Foil Shields

Braided or Foil Shield

Copper Cabling

Coaxial Cable

Copper Cabling

Cooper Media Safety

UTP Cabling

Properties of UTP Cabling

Read this section… more good stuff!

UTP Cabling

UTP Cabling Standards

UTP Cabling

UTP Connectors

UTP Cabling

Types of UTP Cable

UTP Cabling

Testing UTP Cables

Fiber Optic Cabling

Properties of Fiber Optic Cabling

Fiber Optic Cabling

Fiber Media Cable Design

Please read this section…. More good stuff!

Fiber Optic Cabling

Types of Fiber Media

Fiber Optic Cabling

Network Fiber Connectors

Fiber Optic Cabling

Testing Fiber Cables

Fiber Optic Cabling

Fiber versus CopperImplementation issues Copper media Fibre-optic

Bandwidth supported 10 Mbps – 10 Gbps 10 Mbps – 100 Gbps

DistanceRelatively short(1 – 100 meters)

Relatively High(1 – 100,000 meters)

Immunity to EMI and RFI LowHigh

(Completely immune)

Immunity to electrical hazards LowHigh

(Completely immune)

Media and connector costs Lowest Highest

Installation skills required Lowest Highest

Safety precautions Lowest Highest

Wireless Media

Properties of Wireless Media

• IEEE 802.11 standards• Commonly referred to as Wi-Fi.• Uses CSMA/CA• Variations include:

• 802.11a: 54 Mbps, 5 GHz• 802.11b: 11 Mbps, 2.4 GHz• 802.11g: 54 Mbps, 2.4 GHz• 802.11n: 600 Mbps, 2.4 and 5 GHz• 802.11ac: 1 Gbps, 5 GHz• 802.11ad: 7 Gbps, 2.4 GHz, 5 GHz, and 60 GHz

• IEEE 802.15 standard• Supports speeds up to 3 Mbps• Provides device pairing over distances from 1 to

100 meters.

• IEEE 802.16 standard• Provides speeds up to 1 Gbps• Uses a point-to-multipoint topology to provide

wireless broadband access.

Wireless Media

Types of Wireless Media

Wireless Media

802.11 Wi-Fi Standards

StandardMaximum

SpeedFrequency

Backwards compatible

802.11a 54 Mbps 5 GHz No

802.11b 11 Mbps 2.4 GHz No

802.11g 54 Mbps 2.4 GHz 802.11b

802.11n 600 Mbps 2.4 GHz or 5 GHz 802.11b/g

802.11ac 1.3 Gbps(1300 Mbps)

2.4 GHz and 5.5 GHz

802.11b/g/n

802.11ad 7 Gbps(7000 Mbps)

2.4 GHz, 5 GHz and 60 GHz

802.11b/g/n/ac

The Data Link Layer

The OSI physical layer provides the means to transport the bits that make up a data link layer frame across the network media.

Purpose of the Data Link Layer

The Data Link Layer

The data link layer is responsible for the exchange of frames between nodes over a physical network media.


Data Link SublayersNetwork

Data Link

LLC Sublayer

MAC Sublayer

Physical

Data Link layer has two sublayers (sometimes): Logical Link Control (LLC) – Software processes that provide services

to the Network layer protocols. Frame information that identifies the Network layer protocol. Multiple Layer 3 protocols, (ICMP, IPv4 and IPv6) can use the same

network interface and media. Media Access Control (MAC) - Media access processes performed by

the hardware. Provides Data Link layer addressing and framing of the data

according to the protocol in use.


Providing Access to Media

At each hop along the path, a router: Accepts a frame from a medium De-encapsulates the frame Re-encapsulates the packet into a

new frame Forwards the new frame

appropriate to the medium of that segment of the physical network

Data Link Layer

Layer 2 Frame Structure

The data link layer prepares a packet for transport across the local media by encapsulating it with a header and a trailer to create a frame.

Topologies

Controlling Access to the Media

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Media Access Control

Media Access Control - Regulates the placement of data frames onto the media.

The method of media access control used depends on: Media sharing

Do more than two nodes share the media? If so, how? (Switches, hubs, etc.)

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Serial vs multi-access

Point-to-Point networks Only two nodes /30 subnets are common (later) Protocols: PPP, HDLC, Frame Relay

Multi-access networks (LANs) Multiple nodes Subnets mask range depends upon the number of hosts (nodes) Protocols: Ethernet, 802.11 (wireless), Frame Relay Multipoint

Point-to-Point

Multi-access

Topologies

Physical and Logical Topologies

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Physical Topology

The physical topology is an arrangement of the nodes and the physical connections between them.

Layer 2 Switch

Multilayer Switch

Serial Connections

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Logical Topology

A logical topology - The way a network transfers frames from one node to the next. Defined by Data Link

layer protocols. Media Access

Control used. Type of network

framing

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Point-to-Point topology

A point-to-point topology connects two nodes directly together. The media access control protocol can be very simple. Frames from one devices are for the device at the other end.

Point-to-point topologies, with just two interconnected nodes, do not require special addressing.

11111111

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Logical Point-to-Point Networks

Point-to-point networks may include intermediate devices. No affect on logical topology. The logical connection (in some cases) may be a virtual circuit.

A virtual circuit is a logical connection created within a network between two network devices.

The two nodes exchange the frames with each other. Data Link Destination address is the device at the other end of

the virtual circuit.

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Multi-access Topology

A logical multi-access topology - Enables a number of nodes to communicate by using the same shared media. “Data from only one node can be placed on the medium at any

one time.” (This is only true when using CSMA/CD (hubs), NOT true

with switches. Wireless uses CSMA/CA) Every node “may” see all the frames that are on the medium. Data Link Destination Address denote which device the frame is for.

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Multi-access Addressing

Multi-access networks require an address to specifically identify the destination.

2222

3333

4444

5555

6666

22226666

LAN Topologies

Logical Topology for Shared Media

LAN Topologies

Contention-Based Access

Characteristics Contention-Based Technologies• Stations can transmit at any time• Collision exist• There are mechanisms to resolve

contention for the media

• CSMA/CD for 802.3 Ethernet networks• CSMA/CA for 802.11 wireless networks

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Media Access Control

The media access control methods used by logical multi-access topologies are typically: CSMA/CD - Hubs CSMA/CA - Wireless Token passing – Token Ring

Later

WAN Topologies

Half and Full Duplex

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Duplex Transmissions

Simplex Transmission: One way and one way only. One way street

Half-duplex Transmission: Either way, but only one way at a time. Two way street, but only one way at a time (land slide). Ethernet hubs use half-duplex

Full-duplex Transmission: Both ways at the same time. Two way street Ethernet switches use full-duplex Most serial links are full-duplex

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Data Link Frame Fields

Data Link frame header fields may include: Start Frame field - Indicates the beginning of the frame Source and Destination address fields - Indicates the source

and destination nodes on the media Priority/Quality of Service field - Indicates a particular type of

communication service for processing Type field - Indicates the upper layer service contained in the

frame Logical connection control field - Used to establish a logical

connection between nodes Physical link control field - Used to establish the media link Flow control field - Used to start and stop traffic over the media Congestion control field - Indicates congestion in the media

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Framing- The Trailer

The signals on the media could be subject to: Interference Distortion Loss

This would change the bit values that those signals represent.

The trailer is used to determine if the frame arrived without error. Error detection.

The Frame Check Sequence (FCS) field is used to determine if errors occurred in the transmission and reception of the frame.

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Cyclic Redundancy Check

Cyclic redundancy check (CRC) is commonly used. Sending node includes a logical summary of the bits in the frame. Receiving node calculates its own logical summary, or CRC.

Compares the two CRC values. Equal – Accepts the frame Different – Discards the frame

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Ethernet Protocol for LANs

Ethernet is a family of networking technologies that are defined in the IEEE 802.2 and 802.3 standards.

Uses 48 bit addressing (Ethernet MAC addresses) for Source and Destination

More next week!

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Point-to-Point Protocol for WANs

Point-to-Point Protocol (PPP) is a protocol used to deliver frames between two nodes.

PPP can be used on various physical media, including: Twisted pair Fiber optic lines Satellite transmission

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Wireless Protocol for LANs

802.11 is an extension of the IEEE 802 standards. It uses the same 48-bit addressing scheme as other 802 LANs. Contention-based system using a Carrier Sense Multiple

Access/Collision Avoidance (CSMA/CA)

CIS 81 Fundamentals of NetworkingChapter 4: Network Access

Rick Graziani

Cabrillo College

[email protected]

Fall 2013

cis 81 fundamentals of networking chapter 4: network access rick graziani cabrillo college...

Documents

data link layer protocols

data link layer frame

network access layer

physical layer protocols

osi physical layer

physical network protocols

network media

internet layer