Guide to Networking Essentials Fifth Edition Chapter 7 Network - - PowerPoint PPT Presentation

Guide to Networking Essentials Fifth Edition

Chapter 7 Network Architectures

Guide to Networking Essentials, Fifth Edition 2

Objectives

• Compare and contrast media access methods

used in network architectures

• Describe the operation of Ethernet
• Differentiate between Ethernet standards and

speeds

• Explain the four Ethernet frame types and how

they are used

Guide to Networking Essentials, Fifth Edition 3

Objectives (continued)

• Describe the token ring architecture and its

components

• Describe the AppleTalk network architecture
• Explain the function of Fiber Distributed Data

Interface

• Describe other LAN and WAN architectures and

their role in today’s networks

Guide to Networking Essentials, Fifth Edition 4

Putting Data on the Cable: Access Methods

• Given that network architectures communicate in

a number of different ways, some factors in network communications must be considered

– How computers put data on the cable – How they ensure that the data reaches its destination undamaged

Guide to Networking Essentials, Fifth Edition 5

Function of Access Methods

• How computers share the network medium must

be defined

• A collision

results from two or more devices trying to use the channel (medium) at the same time

– Splitting data in small chunks helps prevent collisions

• Channel access methods

specify when computers can access the cable/medium/data channel

– Ensure that data reaches destination by preventing computers from sending messages that might collide – Every computer on a network must use the same access method

Guide to Networking Essentials, Fifth Edition 6

Major Access Methods

• Channel access is handled at the MAC sublayer of

the Data Link layer in the OSI model

• Five major types of channel access

– Contention – Switching – Token passing – Demand priority – Polling

Guide to Networking Essentials, Fifth Edition 7

Contention

• In early networks based on contention, computers

sent data whenever they had data to send

• As networks grow, outgoing messages collide

more frequently, must be sent again, and then collide again

• To organize contention-based networks, two

carrier access methods were created

– CSMA/CD – CSMA/CA

Guide to Networking Essentials, Fifth Edition 8

Switching

• Switching: nodes are interconnected through a a

switch, which controls access to the media

– Contention occurs only when multiple senders ask to reach the same receiver simultaneously or when the simultaneous transmission requests exceed the switch’s capability to handle multiple connections

• Advantages: fairer, centralized management

(enables QoS), switch can have connection ports that operate at different speeds

• Disadvantage: higher cost

Guide to Networking Essentials, Fifth Edition 9

Token Passing

Guide to Networking Essentials, Fifth Edition 10

Token Passing Illustrations

Guide to Networking Essentials, Fifth Edition 11

More Token Passing Illustrations

Guide to Networking Essentials, Fifth Edition 12

Demand Priority

• Demand priority: channel access method used

solely by the 100VG-AnyLAN 100 Mbps Ethernet standard (IEEE 802.12)

– 100VG-AnyLAN runs on a star bus topology – Intelligent hubs control access to the network

• Hub searches all connections in a round-robin fashion
• When an end node has data to send, it transmits a

demand signal to the hub

• The hub then sends an acknowledgement that the

computer can start transmitting its data

– The major disadvantage of demand priority is price

Guide to Networking Essentials, Fifth Edition 13

Demand Priority Illustration

• Graphic from

– www.microsoft.com/mspress/books/sampchap/4077.aspx#SampleChapter

• Hub receives two

frames to transmit (to the next hub)

• Higher-priority

frame is sent first

Guide to Networking Essentials, Fifth Edition 14

Polling

Guide to Networking Essentials, Fifth Edition 15

Choosing an Access Method

Guide to Networking Essentials, Fifth Edition 16

Choosing an Access Method (continued)

Guide to Networking Essentials, Fifth Edition 17

The Ethernet Architecture

• 1960s –

1970s: many organizations worked on methods to connect computers and share data

– ALOHA network at the University of Hawaii – 1972: Metcalfe and Boggs develop an early version

• 1975: 1st commercial

version (3 Mbps, up to 100 computers,

• max. 1 km of total cable)
• DIX developed standard based on Xerox’s

Ethernet (10 Mbps)

• 1990: IEEE defined the 802.3 specification

– Defines how Ethernet networks operate at layers 1-2

Guide to Networking Essentials, Fifth Edition 18

Overview of Ethernet

• Ethernet is the most popular network architecture

– Advantages: easy to install, scalable, broad media support, and low cost – Supported transmission speeds: 10 Mbps to 10 Gbps – Uses the NIC’s MAC address to address frames – Ethernet variations are compatible with one another

• Basic operation and frame formatting is the same
• Cabling, speed of transmission, and method by which

bits are encoded on the medium differ

Guide to Networking Essentials, Fifth Edition 19

Ethernet Operation

• Ethernet is a best-effort delivery system

– It works at the Data Link layer of the OSI model

• Relies on the upper-layer protocols to ensure reliable

delivery of data

• Understanding the following concepts is

important:

– How Ethernet accesses network media – Collisions and collision domains – How Ethernet handles errors – Half-duplex and full-duplex communications

Guide to Networking Essentials, Fifth Edition 20

Accessing Network Media

• Ethernet uses CSMA/CD in a shared-media

environment (a logical bus)

– Ethernet device listens for a signal or carrier (carrier sense) on the medium first – If no signal is present, no other device is using the medium, so a frame can be sent – Ethernet devices have circuitry that detects collisions and automatically resends the frame that was involved in the collision

Guide to Networking Essentials, Fifth Edition 21

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

Guide to Networking Essentials, Fifth Edition 22

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

• CSMA:

– This is the "Carrier-Sense Multiple Access" part – Listen for prior transmission

• if none, go ahead and transmit
• if medium in use, "back off" and try again later
• worst case: two hosts listen at the same time; neither

hears anything; both begin to transmit at the same time

• CD

– This is the "Collision Detection" part – Listen to your own transmission

• if interference is detected, "back off" and try again later
• "Exponential Backoff":

– If a host backs off more than once (e.g. repeated collisions), wait up to twice as long after each time

Guide to Networking Essentials, Fifth Edition 23

CSMA/CD simulation

• In this screen capture,

transmissions from node 1 and node 4 have just collided.

– Node 3 is about to detect the collision – Nodes 2 and 4 will detect it next – The Senders, nodes 1 and 5, will be the last to notice

• Source:

– www.informatik.uni- mannheim.de/pi4/animations/e thernet/index.html

Guide to Networking Essentials, Fifth Edition 24

Collisions and Collision Domains

Guide to Networking Essentials, Fifth Edition 25

Ethernet Error Handling

• Collisions are the only type of error for which

Ethernet automatically attempts to resend the data

• Errors can occur when data is altered in medium

– Usually caused by noise or faulty media connections – When the destination computer receives a frame, the CRC is recalculated and compared against the CRC value in the FCS – If values match, the data is assumed to be okay – If values don’t match, the data was corrupted

• Destination computer discards the frame
• No notice is given to the sender

Guide to Networking Essentials, Fifth Edition 26

Half-Duplex Versus Full-Duplex Communications

• When half-duplex communication is used with

Ethernet, CSMA/CD must also be used

• When using a switched topology, a computer can

send and receive data simultaneously (full-duplex communication)

– The collision detection circuitry is turned off because collisions aren’t possible – Results in a considerable performance advantage

Guide to Networking Essentials, Fifth Edition 27

Ethernet Standards

• Each Ethernet variation is associated with an IEEE

standard

• The following sections discuss many of the

standards, some of which are obsolete or had limited use

• Keep in mind that Ethernet over UTP cabling has

been the dominant technology since the early 1990s, and will likely to continue to be for the foreseeable future

Guide to Networking Essentials, Fifth Edition 28

IEEE 802 Elements

• From the online document

standards.ieee.org/getieee802/download/802.2-1998.pdf

Guide to Networking Essentials, Fifth Edition 29

Ethernet and IEEE 802.3 – milestones

1970

ALOHAnet (Norm Abramson, UHawaii)

1973

Ethernet (Metcalfe, Xerox PARC)

1982

Ethernet II (DEC/Intel/Xerox)

1983

802.3 10Base5

1985

802.3a 10Base2

1990

802.3i 10Base-T

1995

802.3u 100Base-TX, -T4, -FX (Fast Ethernet)

1998

802.3z 1000Base-X (optical fiber) (GigE)

1999

802.3ab 1000Base-T

2003

802.3ae 10Gbps over optical fiber (10GigE)

2006

802.3an 10GBase-T

2010 ?

802.3ba 40 Gbps, 100 Gbps

Guide to Networking Essentials, Fifth Edition 30

(an Intel Marketing image)

Guide to Networking Essentials, Fifth Edition 31

10 Mbps IEEE Standards

• Four major implementations of 10 Mbps Ethernet

– 10Base5: Ethernet using thicknet coaxial cable – 10Base2: Ethernet using thinnet coaxial cable – 10BaseT: Ethernet over UTP cable – 10BaseF: Ethernet over fiber-optic cable

• Of these 10 Mbps standards, only 10BaseT and

10BaseF are seen today

– "legacy" installations that aren't worth upgrading

• 10Base2 and 10Base5 are essentially obsolete

Guide to Networking Essentials, Fifth Edition 32

10Base-T, 10Base-F

Guide to Networking Essentials, Fifth Edition 33

100 Mbps IEEE Standards

• The most widely accepted Ethernet standard

today is 100BaseT, which is also called fast Ethernet

– The current IEEE standard for 100BaseT is 802.3u

• Subcategories:

–100BaseTX: Two-pair Category 5 or higher UTP –100BaseT4: Four-pair Category 3 or higher UTP –100BaseFX: Two-strand fiber-optic cable

– Because of its widespread use, the cable and equipment in fast Ethernet are inexpensive – Architecture of choice for all but heavily used servers and multimedia applications

Guide to Networking Essentials, Fifth Edition 34

100BaseTX

• 100BaseTX is the standard that’s usually in mind

when discussing 100 Mbps Ethernet

• Requires two of the four pairs bundled in a

Category 5 twisted-pair cable

• Although three cable types are available for

100BaseT, 100BaseTX is the most widely accepted

– Generally called fast Ethernet

Guide to Networking Essentials, Fifth Edition 35

100BaseT4

• 100BaseT4 Ethernet uses all four pairs of wires

bundled in a UTP cable

• Advantage: capability to run over Category 3

cable

– One of the biggest expenses of building a network is cable installation, so many organizations with Category 3 cabling chose to get the higher speed with the existing cable plant by using 100BaseT4 instead of 100BaseTX

Guide to Networking Essentials, Fifth Edition 36

100BaseFX

• 100BaseFX uses two strands of fiber-optic cable

– Advantages:

• Impervious to electrical noise and electronic

eavesdropping

• Can span much greater distances between devices

– Disadvantage: far more expensive than twisted-pair – Rarely used as a complete 100BaseTX replacement

• Used as backbone cabling between hubs or switches

and to connect wiring closets between floors or buildings

• Connect client or server computers to the network

when immunity to noise and eavesdropping is required

Guide to Networking Essentials, Fifth Edition 37

100BaseT Design Considerations

Guide to Networking Essentials, Fifth Edition 38

100BaseT Design Considerations (continued)

Guide to Networking Essentials, Fifth Edition 39

Gigabit Ethernet: IEEE 802.3ab and 802.3z Standards

• 802.3z-1998

– 1000BaseX specifications, including LX and SX (laser/fiber-optic), and CX (copper jumper cables)

• 802.3ab-1999

– 1000BaseT specifications, which require four pairs of 100 ohm Category 5 or higher cable

Guide to Networking Essentials, Fifth Edition 40

10 Gigabit Ethernet

• IEEE 802.3ae –

10Gbps over fiber-optic cable

– Defined to run only on fiber-optic cabling, both SMF and MMF, on a maximum distance of 40 km – Provides bandwidth that can transform how WAN speeds are thought of

• IEEE802.an –

10Gbps over twisted-pair wiring

• Runs in full-duplex mode only

– CSMA/CD is not necessary

• Primary use: as network backbone

– Also useful in storage area networks (SANs) – Good for enterprise-level servers

Guide to Networking Essentials, Fifth Edition 41

IEEE 802.3ae fiber-optic variants

• Standards

– 10GBASE-SR: Runs over short lengths (between 26 and 82 meters) over MMF

• For high-speed servers, SANs, etc.

– 10GBASE-LR: Runs up to 10 km on SMF

• For campus backbones and MANs

– 10GBASE-ER: Runs up to 40 km over SMF

• Primary applications are for MANs

– 10GBASE-SW: Uses MMF for distances up to 300 m – 10GBASE-LW: Uses SMF for distances up to 10 km – 10GBASE-EW: Uses SMF for distances up to 40 km

Guide to Networking Essentials, Fifth Edition 42

What’s Next for Ethernet?

• Implementations of 40 Gbps Ethernet are underway
• Ethernet could increase tenfold every 4-6 years

– 100 Gbps Ethernet available by 2006 to 2008, terabit Ethernet by 2011, and 10 terabit Ethernet by 2015

• In October 2005, Lucent Technologies demonstrated for

the first time the transmission of Ethernet over fiber-optic cable at 100 Gbps

– transfer data across the city faster than today’s CPUs can transfer data to memory – major implications for entertainment industry, many other areas

• Ethernet is increasingly applied to situations other than

LANs

– PoE – Power over Ethernet, provides power to remote devices – EPON – Ethernet Passive Optical Networks for multi-channel, long-distance communications – etc. …

Guide to Networking Essentials, Fifth Edition 43

Comparing the Ethernets

• The differing speeds and cabling considerations

refer to the physical (PHY) layer

– viz. the NIC hardware

• The variants share a common Media Access

Control (MAC) sublayer format

– This common format makes Ethernet appealing to network administrators – Minor format variations (Ethernet II versus 802.3/802.2) can co-exist "on the wire"

• The Wireshark

packet sniffer sees the MAC frame. It doesn't see the physical details.

Guide to Networking Essentials, Fifth Edition 44

Early compatibility issues: Ethernet Frame Types

• "Ethernet II"

– used by TCP/IP

• "Ethernet 802.3" (a.k.a.

"802.3 raw")

– used by IPX/SPX on Novell NetWare 2.x and 3.x networks

• "Ethernet 802.2"

– used by IPX/SPX on Novell NetWare 3.12 and 4.x networks – Supported by default in Microsoft NWLink

• "Ethernet SNAP"

– used in EtherTalk and mainframes

• Frame types are distinguished by their headers
• All frame types support a frame size between 64 and 1518

bytes, and can be used by all network architectures mentioned previously

Guide to Networking Essentials, Fifth Edition 45

Ethernet II versus 802.3 headers

• Ethernet II and 802.3 frames are very similar

– Ethernet II Preamble is identical to 802.3 Preamble + Start-Frame-Delimiter – Type / Length values differentiate

• Values <= 1500 must be 802.3 lengths
• Values > 1500 must be Ethernet II types

Guide to Networking Essentials, Fifth Edition 46

802.3 and 802.2 Headers

• IEEE standards divide

the OSI "Datalink" layer into the "Logical Link Control" sublayer and the "Media Access Control sublayer

• 802.3 standards specify

MAC headers for a frame

• 802.2 standards specify

LLC headers that go within a MAC frame

Guide to Networking Essentials, Fifth Edition 47

"Ethernet 802.2" frames

• Ethernet 802.2 frames comply completely with

the Ethernet 802.3 standard

• The IEEE 802.2 group didn’t address Ethernet,
• nly the LLC sublayer of the OSI model’s layer 2

– Since Novell had already decided to use the term Ethernet 802.3 to describe Ethernet "raw", it’s generally accepted that Ethernet 802.2 means a fully 802.3- and 802.2-compliant Ethernet frame

• Ethernet 802.2 frames contain an LLC header,

with three LLC fields, inside an 802.3 frame

– Each field is one byte long, so the maximum payload is reduced from 1500 bytes to 1497 bytes

Guide to Networking Essentials, Fifth Edition 48

Ethernet SNAP

• Ethernet SubNetwork Address Protocol (SNAP) is

generally used on the AppleTalk Phase 2

• It contains enhancements to the 802.2 frame,

including a protocol type field, which indicates the network protocol used in the frame’s data section

Guide to Networking Essentials, Fifth Edition 49

Distinguishing Between Frame Types

1. Receive good frame. 2. Analyze frame. Perform the following steps, in order:

1. If the EtherType/Length value is greater than 0x05DC (decimal 1500), then process the frame as Ethernet II. Otherwise, it's an 802.3 length. – Ethernet II "EtherType" values are greater than 0x05DC – Examples: 0x0800 for IP, 0x8137 for NetWare IPX/SPX 2. If the Length field is followed by an IPX header (0xFFFF), interpret the frame as "802.3 raw" carrying Netware IPX/SPX traffic. – Standard SSAP and DSAP values do not include hexadecimal FF, so the 802.3 (Raw) frame can be distinguished from LLC frames (Ethernet SNAP, 802.2). 3. Otherwise, if the DSAP and SSAP values are 0xAA, the frame is interpreted as a SNAP frame. 4. Any other DSAP/SSAP combination is interpreted as a 802.2 frame.

Guide to Networking Essentials, Fifth Edition 50

Wireless LANs

• Radio transmitters cannot transmit and receive
• n the same channel/frequency simultaneously

– Cellphones use two channels to provide simultaneous talk/listen functionality

• CSMA –

Carrier-Sense Multiple Access – is still possible, and necessary

• CD –

Collision Detection – is not possible

– CA – Collision Avoidance – is used instead

• Range is variable, depending on local

environment

• Privacy is much harder to provide

Guide to Networking Essentials, Fifth Edition 51

IEEE 802.11 – milestones

• IEEE 802.11 defines a MAC sublayer

similar to 802.3

• 802.11 frames carry 802.2 LLC payloads
• Increasing performance for 802.11, just like for 802.3

1997

802.11 1 Mbps, 2 Mbps; 2.4GHz

1999

802.11b 5.5 Mbps, 11 Mbps; 2.4GHz

2001

802.11a 54 Mbps; 5GHz

2003

802.11g 54 Mbps; 2.4 GHz; compatible w/ 802.11b

2010?

802.11n MIMO; 2.4GHz & 5GHz; compatible w/ 802.11a/b/g; up to 600Mbps?

Guide to Networking Essentials, Fifth Edition 52

Wireless Ethernet: IEEE 802.11

• Ad-hoc

mode allows nodes to communicate directly with each other

– true bus topology – not commonly used

• Managed

mode employs an access point (AP) as the center

• f a star topology network
• No fixed segment length

– Maximum of 300 feet without obstructions

• Can be extended with large, high-quality antennas
• Stations can’t send and receive at the same time

– CSMA/CA is used instead of CSMA/CD

• 802.11b/a/g use handshaking before transmission

– Station sends AP an RTS and it responds with CTS

• Standards define a maximum transmission rate, but

speeds might be dropped to increase reliability

Guide to Networking Essentials, Fifth Edition 53

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

• Wireless (Radio) systems cannot detect collisions

– theoretical problems – practical (cost) concerns

• Transmission-and-Acknowledgement is the basic

solution

– "Collision tolerance" ?

• Nodes that detect transmissions in progress must

wait a fixed amount of time before attempting their own transmissions

– Allow for the acknowledgement to be sent

• Optional features improve performance

– RTS/CTS

Guide to Networking Essentials, Fifth Edition 54

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

• Used in wireless LANs
• Sending hosts signal intent to transmit with RTS

("Ready To Send") frame

– RTS declares length (time duration) of transmission – Access point (if any) acknowledges with CTS ("Clear To Send") frame that also declares the duration

• Other hosts wait until transmission has finished

– Time duration, in the RTS/CTS frames, tells other hosts how long to wait

• The overhead created by these additional intent-

to-transmit frames reduces network throughput significantly

Guide to Networking Essentials, Fifth Edition 55

802.11 CSMA/CA: 3 Terminals

• In this network, the WAP

can hear all three hosts; each host can hear the WAP and the other hosts

• Hosts with data will send

RTS "Ready-To-Send" frames

– Any host hearing an RTS must wait until it's done – the "CSMA" part – RTS's may still collide, in effect nullifying each one

• WAP will acknowledge
• ne RTS with a CTS

"Clear-To-Send" frame

– Other hosts must wait as long as specified in the CTS before trying another RTS – the "CA" part

Guide to Networking Essentials, Fifth Edition 56

1. Sta1, Sta2, Sta3 all try at the same time 2. Sta1 waits little time, sends another RTS 3. WAP sends CTS to Sta1 4. Once Sta1 is finished, WAP sends an ACK; then Sta2 and Sta3 send more RTS's 5. Sta2, Sta3 back off… 6. WAP sends CTS for Sta2's 3rd RTS 7. Sta2 finishes, receives an ACK; Sta3 sends another RTS 8. WAP sends a CTS to Sta3; Sta3 begins transmitting

CSMA/CA Busy Network

Guide to Networking Essentials, Fifth Edition 57

802.11 CSMA/CA: Hidden Terminals

• In this network, the WAP

can hear all three hosts (and the hosts can hear the WAP), but none of them can hear each other

• The hosts are "hidden"

from each other

– Hosts can send RTS's, but cannot tell whether any

• ther host is sending also

– Only the WAP detects any RTS collisions

• WAP will broadcast a CTS

that all hosts hear

– Hosts must wait as long as specified in the CTS, even though they can't hear the sending host's transmission

Guide to Networking Essentials, Fifth Edition 58

CSMA/CA Hidden Terminals

1. Sta1, Sta2 send

• verlapping RTS's

2. Neither hears a response, so they "countdown" 3. Each sends another

• verlapping RTS

4. No response, so countdown… 5. Sta1 sends an RTS first, WAP sends a CTS, so Sta2 keeps waiting 6. Sta1 receives an ACK; Sta2 resumes and finishes its countdown before sending another RTS

Guide to Networking Essentials, Fifth Edition 59

MIMO

• Multiple-In, Multiple-

Out transmission

– Multiple antennas for transmission and reception take advantage of reflected signals – Better throughput and range for given power levels

• Part of the 802.11n

standard for wireless networks

Guide to Networking Essentials, Fifth Edition 60

The Token Ring Architecture

Guide to Networking Essentials, Fifth Edition 61

Token Ring Function

• A token passes around the ring

– If an “in use” token is received from NAUN, and the computer has data to send, it attaches its data to the token and sends it to its NADN – If received token is in use, NIC verifies if it is the destination station

• If not, the computer re-creates the token and the data

exactly and sends them to its NADN

• If it is, data is sent to the upper-layer protocols

–Two bits in data packet are toggled and token is sent to NADN; when original sender receives it, it frees the token and then passes it along

Guide to Networking Essentials, Fifth Edition 62

Beaconing

Guide to Networking Essentials, Fifth Edition 63

Hardware Components

• A hub can be a multistation access unit (MSAU) or

smart multistation access unit (SMAU)

• IBM’s token ring implementation is the most

popular adaptation of the IEEE 802.5 standard

– Minor variations but very similar to IEEE specs

• IBM equipment is most often used

– 8228 MSAU has 10 connection ports, eight of which can be used for connecting computers – The RO port on one hub connects to RI port on the next hub, and so on, to form a ring among the hubs

• IBM allows connecting 33 hubs

Guide to Networking Essentials, Fifth Edition 64

Cabling in a Token Ring Environment

Guide to Networking Essentials, Fifth Edition 65

The Token Ring Architecture (summary)

Guide to Networking Essentials, Fifth Edition 66

The AppleTalk Environment

• Designed for use in Macintosh networks (1983)
• Can be run over several physical architectures;

commonly run over Ethernet (EtherTalk)

• Easy to implement
• Dynamic scheme used to determine device’s

address

• AppleTalk Phase 1 supported only 32 computers

per network, and only with LocalTalk cabling

– With hubs/repeaters, increased the number to 254

• AppleTalk Phase 2, EtherTalk, and TokenTalk

(1989) allow more than 16 million computers

Guide to Networking Essentials, Fifth Edition 67

LocalTalk

• LocalTalk uses STP in a bus topology to allow

users to share peripherals and data in a small home or office environment

– CSMA/CA channel access method

• Avoids more collisions, but cumbersome

– Maximum transmission speed of 230.4 Kbps

• Thus, this architecture was used primarily in small,

Macintosh-only environments

Guide to Networking Essentials, Fifth Edition 68

EtherTalk and TokenTalk

• EtherTalk is the AppleTalk protocol running over a

10 Mbps IEEE 802.3 Ethernet network

• TokenTalk is the AppleTalk protocol running over

a 4 or 16 Mbps IEEE 802.5 token ring network

• Both implementations require using a different

NIC

– Since 1996, Apple Computer has offered systems with built-in Ethernet NICs or with options to add Ethernet or token ring to its systems at a low cost – Mac OS X with an Ethernet interface can freely participate in a Windows-based network

Guide to Networking Essentials, Fifth Edition 69

The Fiber Distributed Data Interface (FDDI) Architecture

Guide to Networking Essentials, Fifth Edition 70

The Fiber Distributed Data Interface (FDDI) Architecture (continued)

Guide to Networking Essentials, Fifth Edition 71

Networking Alternatives

• Many other network architectures are available
• Some are good for specialized applications, and
• thers are emerging as new standards
• Topics

– Broadband technologies (cable modem and DSL) – Broadcast technologies – ATM – ATM and SONET Signaling Rates – High Performance Parallel Interface (HIPPI)

Guide to Networking Essentials, Fifth Edition 72

Broadband Technologies

• Baseband systems use a digital encoding scheme

at a single fixed frequency

• Broadband systems use analog techniques to

encode information across a continuous range of values

– Signals move across the medium in the form of continuous electromagnetic or optical waves – Data flows one way only, so two channels are necessary for computers to send and receive data – E.g., cable TV

Guide to Networking Essentials, Fifth Edition 73

Cable Modem Technology

Guide to Networking Essentials, Fifth Edition 74

Digital Subscriber Line (DSL)

• Competes with cable modem for Internet access

– Broadband technology that uses existing phone lines to carry voice and data simultaneously – Most prominent variation for home Internet access is Asymmetric DSL (ADSL)

• Splits phone line in two ranges: Frequencies below 4

KHz are used for voice transmission, and frequencies above 4 KHz are used to transmit data

• Typical connection speeds for downloading data range

from 256 Kbps to 8 Mbps; upload speeds are in the range of 16 Kbps to 640 Kbps

Guide to Networking Essentials, Fifth Edition 75

Broadcast Technologies

• By definition: one-way transmissions

– This changed in Internet access by satellite television systems

• Work on the principle that most traffic a user

generates is to receive files, text, and graphics

– The average user’s computer sends very little traffic – User connects to service provider through a modem – Service provider sends data by satellite to the user’s home at speeds up to 400 Kbps – E.g., service offered by DirectTV, through its DirectPC add-on products

Guide to Networking Essentials, Fifth Edition 76

Asynchronous Transfer Mode (ATM)

• High-speed network technology for LANs and

WANs

– Connection-oriented switches

• Dedicated circuits are set up before communicating

– Data travels in fixed-size 53-byte cells (5 byte- header)

• Enables ATM to work at extremely high speeds

–Quick switching –Predictable traffic flow

• Enables ATM to guarantee QoS

– Used quite heavily for the backbone and infrastructure in large communications companies – LAN emulation (LANE) required for LAN applications

Guide to Networking Essentials, Fifth Edition 77

ATM and SONET Signaling Rates

Guide to Networking Essentials, Fifth Edition 78

High Performance Parallel Interface (HIPPI)

• HIPPI (late 1980s): high-speed interface

developed for supercomputers and high-end workstations

– Serial HIPPI is a fiber-optic version that uses point- to-point optical links for bandwidth up to 800 Mbps

• In early 1990s, it was used as a network backbone and

for interconnecting supercomputers –With the advent of Gigabit Ethernet, interest in HIPPI as a LAN backbone decreased

– HIPPI-6400 (1998): up to 6.4 Gbps transfer rates

• Known as Gigabyte System Network (GSN)

– HIPPI and GSN are now exotic networking products and aren’t often found in typical corporate networks

Guide to Networking Essentials, Fifth Edition 79

Summary

• Cable access methods determine how a network

architecture gains access to the network medium

• A network architecture defines how data is

placed, transmitted, and at what speed, and how problems in the network are handled

• DIX introduced Ethernet, which later became the

IEEE 802.3 standard, transmitting data at 10 Mbps

– Standards for 10Mbps, 100Mbps, 1000Mbps (Gigabit), and 10G indicate the supported network mediums

• 10 Gigabit Ethernet runs only over fiber-optic cable

and only in full-duplex mode

Guide to Networking Essentials, Fifth Edition 80

Summary (continued)

• Token ring networks are reliable, fast, and

efficient

– Capable of transmitting at 4 Mbps or 16 Mbps

• Macintosh computers use AppleTalk to

communicate

• FDDI is an extremely reliable, fast network

architecture that uses dual counter-rotating rings

• Cable modem technology delivers high-speed

Internet access to homes and businesses

• ATM, a high-speed network technology designed

both for LANs and WANs, uses connection-

• riented switches