DCN286 INTRODUCTION TO DATA COMMUNICATION

TECHNOLOGY

Network Physical Layer

Connection

Purpose of Physical Layer

The role of the OSI physical layer is to encode the binary digits that represent data link layer frames into signals and to transmit and receive these signals across the physical media---- cooper wires, optical fiber, and wireless that connect network devices.

Network Access Layer

The network access layer is concerned with all of the issues that an IP packet requires to actually make a physical link to the network media.

It includes the LAN and WAN technology details, and all the details contained in the OSI physical and data link layers.

Popular Copper Media Standards

TIA (Telecommunications Industry Association) and EIA (Electronic Industries Alliance) work together to publish commercial building telecommunications cabling standards TIA/EIA-568-B which defines how to use the pins on the connectors on the ends of the cables.

IEEE (Institute of Electrical and Electronic Engineers) publishes LAN standards such as IEEE802.3 which will define cable requirement.

Coaxial cable

Gradually outdated from LANCan run for longer distances than either

STP or UTPLess expensive than fiber-optic cable

though it is expensive than STP or UTPStill popular for TV and home internet

service

STP (Shielded Twisted Pair) cable

Shielding provides better electrical signals by reducing noise and attenuation.

Shielding makes the cable more expensive, heavier and hard to bend.

UTP (Unshielded Twisted Pair)

Flexible and easy installOffer the same data speedsInexpensiveRJ45 connector (RJ11 is for phone cable).

UTP Implementation

UTP Implementation

Straight-through CableSwitch to RouterSwitch to PC or ServerHub to PC or Server

Cross-over CableSwitch to Switch; Switch to Hub; Hub to HubRouter to Router; PC to PC; Router to PC

Roll-over Cable (Configuration Purposes)PC to Router; PC to Switch

UTP Implementation

Straight-Through cableA cable that maintains the pin connection all the

way through the cable.Cat 5 and Cat5e: Only wires 1, 2, 3, and 6 are

usedGigabit Ethernet uses all the wiresTo connect devices such as PC or routers to

other devices as hub or switches.

UTP Implementation

Cross-over cableA cable that crosses the critical pair to properly align,

transmit, and receive signals on the device with line connections

Pin 1 at one end and Pin 3 at the other endPin 2 at one end and Pin 6 at the other endUsed to connect similar devices:

Switch to switchHub to hub

TIA/EIA568-A and B pin outs

Pin # Function 568A wire color 568 B wire color

1 TD+ White/Green White/Orange

2 TD- Green Orange

3 RD+ White/Orange White/Green

4 Unused Blue Blue

5 Unused White/Blue White/Blue

6 RD- Orange Green

7 Unused White/Brown White/Brown

8 Unused Brown Brown

Straight through cable

Can be used to connect PC and other network equipments to LAN hub/switch

Wire 1 and 2 are used to transmit dataWire 3 and 6 are used to receive data

Cross-over cable

It is used to connect two same equipments such as PC-to-PC.

Both ends need to send data on pin 1 and 2; receive data on pin 3 and 6.

In 568B, one end has white/orange and orange on pin 1 and 2; another has white/orange and orange on pin 3 and 6.

In 568B, one end has white/green and green on pin 3 and 6; another end has them on pin 1 and 2.

Rollover cable

Usually used as console cable.Change the sequence on another end.

Rollover or Console Cable

The cable used between a terminal and a console port is a rollover cable with RJ-45 connectors.

Rollover cable (or Console cable) has a different pinout than the straight-through or crossover cable.

The pinout for a rollover cable is:1 to 8, 2 to 7, 3 to 6, 4 to 5, 5 to 4, 6 to 3, 7 to 2,

and 8 to 1.

Connector and Adapter

The 8 Position 8 Contact (8P8C) (often called RJ45) connector

Cross over adapter

Optic media

Fiber-optic cable has the strongest ability to resist EMI (electromagnetic interference), RFI (Radio Frequency Interference)

Fiber’s bandwidth is much higher than any other media.

Fiber is highly secure and it is easy to detect intrusion.

Fiber uses light signal transmission and its attenuation is much less than electrical signals. Its length could be very long

Optical fiber cable components

Core: usually made by silicon dioxide (from sand)

Cladding: coated on the core to reflect light and seal it inside

Buffer: physical protect cladding and core

Jacket: prevent damage from abrasion, solvents and other contaminants

Optical Fiber Connector (Optional)

LC/PC connector and SC/PC connectors have caps covering the ferrules

Other connectors are ST, SC, MT, MT-RJ, MU, etc, etc

Multimode fiber

Fiber with large (greater than 10 μm) core diameter may allow light coming in with different angles. (It must be in limit of acceptance cone)

Single mode fiber

Fiber with a core diameter less than about ten times the wavelength of the propagating light and it can only allow light coming in from one direction.

LAN Connectivity Devices

RepeatersHubsSwitchesBridgesRouters

Repeaters

A repeater can be used to increase the length of your network by eliminating the effect of attenuation on the signal.

It connects two segments of the same network, overcoming the distance limitations of the transmission media.

Some repeaters also serve as transmission media adapters, connecting two different types of media.

Repeaters

Repeaters can connect segments that have the same access method. (CSMA/CD, Token Passing, Polling, etc.)

DisadvantagesRepeaters do not filter data Its use is inappropriate when there is a heavy network traffic.

Repeater

10base5 – 500meter cable length limit;10base2 - 200meter cable length limit;10BaseT - 100meter cable length limit;

Repeater is to amplify signal and extend the cabling distance.

Working in layer 1 (Physical) of TCP/IP model

Repeaters

Figure11-6

Hub

Central connection of Ethernet LAN.Physically Star topology and could be

logically RING, Bus and/or StarMay have built-in repeaterWorking in layer 1 (Physical) of TCP/IP

model

Hubs

A hub is used as a central point of connection among media segments.

Cables from network devices plug in to the ports on the hub.

Hubs are referred as Concentrators or multi-port repeater

Hubs receive signals from connected devices and transmit them to the other connected devices

Hubs

Regenerate and repeat signalsPropagate signals through the networkCan not filter network trafficCan not determine the best pathAre used as network concentration points.

Hubs

Types of Hubs

Passive Hubs

Active Hubs

Intelligent Hubs (Switches)

Passive Hub

It functions only as a connection point for the signals

The signal pass through a passive hub without regeneration or amplification.

Active Hub

It regenerates or amplifies the signal before they are retransmitted.

Drawback:The noise is also regenerated

Switch

Think switch as a hub with bridge functioning on each port (interface):

1. Switch will offer central connection to all hosts.

2. Switch will only forward frame according to destination MAC address on per-port base.

3. Will regenerate signals (repeater function)

4. Most switches are working in layer 2 (Data Link) of TCP/IP model.

Switches

GOLDMAN: DATACOMM FIG. 11-03

broadcast source

LAN switch

B

B

B

broadcast source

LAN switch

LAN Switch

broadcast traffic

Broadcasts to all ports on LAN switch.

Single Switch Virtual LANs

Broadcasts only to members of Virtual LAN.

broadcast traffic

A

Virtual LAN assignments

Virtual LAN "A" is a multi-switch Virtual LAN

B

B

B

broadcast source

LAN switch

Multi-Switch Virtual LANs

A

C

C

LAN switch

C

C

Proprietary switch-to-switch communications

high-speed backbone network

A

A

A

A

A

A

A

Forwarding Frame based on DestinationMAC Address

The switch maintain table, called a MAC table, that maps destination MAC addresses with ports used to connect to each node. For each incoming frame, the destination MAC address in the frame header is compared to the list of addresses in the MAC table. If a match is found, the port number in the table that is paired with MAC address is used as exit port for the frame.

The MAC table can be referred to by many different name. It also called Switch table or Bridge table.

Switch Operation

To accomplish Frame Forwarding, Ethernet LAN switches use five basic operations:

Learning: The Mac table must be populated with MAC addresses and their corresponding ports. The learning process allows these mappings to be dynamically acquired during normal operation.

Aging: The entries in the MAC table acquired by the learning process are time stamped. This time stamp is used as a means for removing old

Continues Slide-37

entries in the MAC table. After it is made in the MAC table, a procedure begins count down, once it reaches count 0, the entry is aged out and remove from the table.

Flooding: If a switch does not have a MAC address entry in its MAC table that matches the destination MAC address of received frame, the switch will flood the frame. Flooding involves sending a frame to all ports except the port on which the frame arrived.

Switch Continues

Selective Forwarding:

Selective forwarding is the process of examining the destination MAC address of a frame and forwarding it out to the appropriate port.

Filtering: In some cases, a frame is not forwarded. This process is called frame filtering e.g. a switch does not forward a frame to the same port on which it arrived. A switch will also drop a corrupt frame. If a frame fails a CRC check, the frame is dropped.

Ethernet Bridge

Intelligent device to forward frame according to destination Media Access Control (MAC) address

Forwarding: If the destination MAC address has a port different to the originate port, the frame will be sent.

Filtering: If the destination MAC address is reachable with the same interface when it arrived, the frame will be discarded.

Working in layer 2 (Data Link) of TCP/IP model

Layer 2 Bridging

Bridges

GOLDMAN: DATACOMM FIG. 09-01

20% of LAN traffic travels

between LANs

80% of LAN traffic stays on local LAN

bridge LAN B

Segmentation

Micro-Segmentation

LAN switch

FDDI modules (100 Mbps)

backbone network router

backbone network router

10BaseT module (10Mbps)

10BaseT module (10Mbps)

LAN A

Server Isolation

LAN switch or router

hub hub

Hierarchical Networking

10BaseT hub 10BaseT hub

Router

Redirect packets according to destination logical address (IP address).

Can build routing path between different network segments (subnets)

Can act as firewallCan work as VPN (server) connectionWorking in layer 3 (Network) of TCP/IP

model

Routers

Figure 11-7

Wireless tech introduction

InfraredBluetoothMicrowaveRadioWi-Fi

In general, wireless network is secondary because of two concerns: speed and security. But, it does offer mobility and convenience.

Wireless Networking MediaRadio frequency (RF)LaserInfrared (IR)Satellite/Microwaves

Wireless transmission techniques to carry wireless signals

Wireless signals are electromagnetic waves that travel through the air.

Wireless Networking Media

InfraredLine of sightShort distancesNo obstacles between transmitter and receiver

RadiofrequencyAllows devices to be in different room or even

buildingsLimited radioCan be single or multiple (Spread spectrum)

frequencies

Single Frequency

Is subject to outside interference and geographic obstructions

Insecure (Easily monitored by others)

Spread Spectrum

Multiple frequenciesMore secure

Security in the Wireless Environment

The first level of security in a wireless LAN consists of protecting the radio frequency waveform itself.

Security in the Wireless Environment

Wireless Access PointsWireless BridgesEncryption WEP – Wireless Equivalence PrivacyEAP – Extensible Authentication Protocol

(IEEE 802.1X)

Wireless LAN Topology

Wireless Bridges

Wireless Security

If you think someone might eavesdrop on your LAN radio links…..

Encryption is the key

Wireless Security Approaches

WEP – Wired Equivalency Privacy

IEEE 802.1X or Extensible Authentication Protocol (EAP)

Wireless Equivalent Privacy

WEPIt is a security mechanism defined with the IEEE

802.11 standard.Designed to protect over the over-the-air

transmissions between wireless LAN access points and NICs.

IEEE 802.11b requires 40-bit encryption keysCisco supports the optional 128-bit standard.

WEP Goals

Deny access to the network by unauthorized users who do not possess the appropriate WEP key.

Prevent the decoding of captured WLAN traffic hat is WEP-encrypted without the possession of the WEP key.

Should be supplemented with additional higher-level security mechanisms such as VPNs or Firewalls.

802.1X/EAPExtensible Authentication Protocol

It is an alternative WLAN security approach to WEP

802.1X/EAP focuses on providing:Centralized authenticationDynamic key distribution

It is a standard for port-based network access control

Cabling the WAN

Wide Area Network (WAN) Services

To connect one network to a remote network

Provide different connection methods

Different cabling standards from those of LANs