13.1

Wired LANs: Ethernet

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A Simple Network (LAN)

Internet

140.192.40.5192.168.0.1

192.168.0.10Crossover UTP

cable

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Typical LAN

1st floor

2nd floor

9th floor

Internet

Data center

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Campus Area Network (CAN)CDM Building DePaul

Center

LewisCenter

AdministrationBuilding

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Metropolitan Area Network (MAN)

Lincoln Park

Loop

Rolling Meadow

Lake Forest

Naperville

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Wide Area Network (WAN)

WAN

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Success of Ethernet

Easy to understand, implement, manage, and maintain

Low-cost network implementations Extensive topological flexibility for

network installation Interoperability and operation of

standards-compliant products, regardless of manufacturer

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LAN Services Users do not see the network, and

they are interested in the services. What are the essential LAN services?

Printer sharing File sharing Application sharing Internet Surfing Intranet Web Database

Backup Fax Service Telephony Conferencing Management Miscellaneous

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Network Components

Cables Network Interface Cards (NIC) Network hardware

Hubs Switches Routers Gateways Printers Storage devices (NAS and SAN)

Network Operating System (NOS) Software

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Network Operating System

Network

Software programs that control resources shared over the network.

Application

Protocols

Drivers

Example: Windows, NetWare, UNIX, Linux, MacOS

Application

Protocols

Drivers

Clients

Server

McGraw-Hill ©The McGraw-Hill Companies, Inc., 200011

History of Ethernet

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ALOHA Network (’68-’72)Radio frequency w/ speed = 4.8-9.6K bps

Outbound channel: one-to-many transmissionIn-bound: same channel frequency with contention

Inventor:Norman Abramson

terminal

IBM 360

Slotted Aloha followed after Aloha. Throughput jumped from 18% to 37%.

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First Ethernet at Xerox

Inventor: Bob Metcalfe Location: Xerox Palo Alto Research Lab Time: May 22, 1973, The first Local

Area Network for personal computer (called ALTO) and printer (called EARS).

Speed: 2.94Mbps Importance: carrier sense (listen first

before transmitting)

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Standardization of Ethernet Intel – Chip technology DEC – System engineering and

hardware supplier Xerox – Ethernet technology 1980 - The Ethernet blue book (DIX) Speed – 10Mbps 1981 – IEEE 802.3 subcommittee 1983 – IEEE 10Base5 1989 – ISO 88023

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Figure 13.1 IEEE standard for LANs

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Figure 13.2 HDLC frame compared with LLC and MAC frames

13.17

Figure 13.3 Ethernet evolution through four generations

13.18

Figure 13.4 802.3 MAC frame

13.19

Figure 13.5 Minimum and maximum lengths

13.20

Frame length:Minimum: 64 bytes (512 bits)

Maximum: 1518 bytes (12,144 bits)

Note

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Figure 13.6 Example of an Ethernet address in hexadecimal notation

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Figure 13.7 Unicast and multicast addresses

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The least significant bit of the first byte defines the type of address.

If the bit is 0, the address is unicast;otherwise, it is multicast.

Note

13.24

The broadcast destination address is a special case of the multicast address in

which all bits are 1s.

Note

13.25

Define the type of the following destination addresses:a. 4A:30:10:21:10:1A b. 47:20:1B:2E:08:EEc. FF:FF:FF:FF:FF:FF

SolutionTo find the type of the address, we need to look at the second hexadecimal digit from the left. If it is even, the address is unicast. If it is odd, the address is multicast. If all digits are F’s, the address is broadcast. Therefore, we have the following:a. This is a unicast address because A in binary is 1010.b. This is a multicast address because 7 in binary is 0111.c. This is a broadcast address because all digits are F’s.

Example 13.1

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Show how the address 47:20:1B:2E:08:EE is sent out on line.

SolutionThe address is sent left-to-right, byte by byte; for each byte, it is sent right-to-left, bit by bit, as shown below:

Example 13.2

13.27

Figure 13.8 Categories of Standard Ethernet

13.28

Figure 13.9 Encoding in a Standard Ethernet implementation

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Figure 13.10 10Base5 implementation

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Figure 13.11 10Base2 implementation

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StarLAN (1BaseT) Problem with 10Base5 and 10Base2: poor

cabling plant What is the problem?

Need: a cabling plant like telephone system

1983: AT&T and NCR, running Ethernet on UTP

Speed: 1M bps (This is the major issue) Importance: a market failure but a

technology milestone We have a structured cabling plant now

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StarLAN

Ethernet hub or repeater

• Network topology: now a star topology• A structured cabling plant similar to telephone network.Q: Why is star topology better than bus topology?

13.33

Figure 13.12 10Base-T implementation

Ethernet Encoding Schemes Manchester (10BaseT)

0-bit = + voltage, - voltage 1-bit = - voltage, + voltage

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Figure 13.13 10Base-F implementation

NRZ-I Encoding (100Base-FX)

0: no change 1: inverse

Medium idle? Transmit. Not ready? Wait until it becomes ready then wait interframe gap (9.6 microseconds) or use p-persistent algorithm

Collision detected? Continue transmission until min packet time reached (jam signal)

Increment retransmission counter

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CSMA/CD Basic Algorithm

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CSMA/CD ProcedureStation is ready to send

SenseChannel

Transmit data andsense channel

Wait (backoff strategy)

Sendjam signal

collision detected

channelbusy

try again

successful transmission

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802.3 Parameters (Table 3.2)

Slot time 512 bit times (51.2 s)

InterFrameGap

96 bit times (9.6 s)

AttemptLimit 16 (tries)

BackoffLimit 10 (exponent)

JamSize 32 bits

MaxFrameSize

1518 bytes

MinFrameSize

64 bytes

AddressSize 48 bits (6 bytes)

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Ethernet Performance

Why do large frames have better performance?

Collisions are the killer!! Network throughput typically 20-

30%, 40% was max! Need a way to eliminate collisions What about token ring and token

bus? What about bridges and switches?

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CSMA/CD Basic Algorithm

How long does it take to hear a collision?

Signals travel at 2/3 speed of light thru copper

Propagation time = distance / velocity How many bits can you transmit during

that time? Data transfer time = length of frame

(bits) / data rate (bps)

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CSMA/CD Collisions

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Table 13.1 Summary of Standard Ethernet implementations

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13-3 CHANGES IN THE STANDARD13-3 CHANGES IN THE STANDARD

The 10-Mbps Standard Ethernet has gone through The 10-Mbps Standard Ethernet has gone through several changes before moving to the higher data several changes before moving to the higher data rates. These changes actually opened the road to the rates. These changes actually opened the road to the evolution of the Ethernet to become compatible with evolution of the Ethernet to become compatible with other high-data-rate LANs. other high-data-rate LANs.

Bridged EthernetSwitched EthernetFull-Duplex Ethernet

Topics discussed in this section:Topics discussed in this section:

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Figure 13.14 Sharing bandwidth

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Figure 13.15 A network with and without a bridge

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Figure 13.16 Collision domains in an unbridged network and a bridged network

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Figure 13.17 Switched Ethernet

How Switches Learn Host Addresses and Locations

• Initial MAC forwarding table is empty

MAC forwarding table

0260.8c01.1111

0260.8c01.2222

0260.8c01.3333

0260.8c01.4444

E0 E1

E2 E3

A B

C D

How Switches Learn Host Addresses and Locations

MAC forwarding table

0260.8c01.1111

0260.8c01.2222

0260.8c01.3333

0260.8c01.4444

E0 E1

E2 E3

A B

C D

• Station A sends a frame to Station C

• Switch caches station A MAC address to port E0 by learning the source address of data frames

• The frame from station A to station C is flooded out to all ports except port E0 (unknown unicasts are flooded)

E0: 0260.8c01.1111

MAC forwarding table

0260.8c01.1111

0260.8c01.2222

0260.8c01.3333

0260.8c01.4444

E0 E1

E2 E3

A B

C D

Station A sends a frame to station C Destination is known, frame is not flooded

How Switches Filter Frames

E0: 0260.8c01.1111

E2: 0260.8c01.2222E1: 0260.8c01.3333E3: 0260.8c01.4444

Broadcast FramesBroadcast Frames

• Station D sends a broadcast frame

• Broadcast frames are flooded to all ports other than the originating port

0260.8c01.1111

0260.8c01.2222

0260.8c01.3333

0260.8c01.4444

E0 E1

E2 E3 DC

A B

E0: 0260.8c01.1111

E2: 0260.8c01.2222E1: 0260.8c01.3333E3: 0260.8c01.4444

MAC Forwarding Table

Unlike IP address, MAC address is local. MAC forwarding table is also local, within

the single broadcast domain (which is an IP subnet).

MAC address learning stops at the router, and a switch does not learn the MAC addresses at the other side of the router. The switch learns one MAC address of the

router.

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Figure 13.18 Full-duplex switched Ethernet

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5-4-3 Rule (10BaseX) 5 segments, 4 repeaters, 3 populated segments hub/repeater

13.56

13-4 FAST ETHERNET13-4 FAST ETHERNET

Fast Ethernet was designed to compete with LAN Fast Ethernet was designed to compete with LAN protocols such as FDDI or Fiber Channel. IEEE protocols such as FDDI or Fiber Channel. IEEE created Fast Ethernet under the name 802.3u. Fast created Fast Ethernet under the name 802.3u. Fast Ethernet is backward-compatible with Standard Ethernet is backward-compatible with Standard Ethernet, but it can transmit data 10 times faster at a Ethernet, but it can transmit data 10 times faster at a rate of 100 Mbps. rate of 100 Mbps.

MAC SublayerPhysical Layer

Topics discussed in this section:Topics discussed in this section:

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Figure 13.19 Fast Ethernet topology

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Figure 13.20 Fast Ethernet implementations

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Figure 13.21 Encoding for Fast Ethernet implementation

MLT-3 Signal (100Base-TX)

three levels: +1, 0, -1transition (at 1’s only): +1 => 0 = -1 => 0 => +1

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Table 13.2 Summary of Fast Ethernet implementations

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13-5 GIGABIT ETHERNET13-5 GIGABIT ETHERNET

The need for an even higher data rate resulted in the The need for an even higher data rate resulted in the design of the Gigabit Ethernet protocol (1000 Mbps). design of the Gigabit Ethernet protocol (1000 Mbps). The IEEE committee calls the standard 802.3z.The IEEE committee calls the standard 802.3z.

MAC SublayerPhysical LayerTen-Gigabit Ethernet

Topics discussed in this section:Topics discussed in this section:

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In the full-duplex mode of Gigabit Ethernet, there is no collision;

the maximum length of the cable is determined by the signal attenuation

in the cable.

Note

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Figure 13.22 Topologies of Gigabit Ethernet

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Figure 13.23 Gigabit Ethernet implementations

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Figure 13.24 Encoding in Gigabit Ethernet implementations

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Table 13.3 Summary of Gigabit Ethernet implementations

1G to 10G (802.3ae)

10GbE Full-duplex only (no CSMA/CD) Fiber only (802.3ae) WAN (SONET-friendly) PHY Mapping to OC-192 carrier

Rate adaptation to SONET payload capacity New line coding (64b/66b) Standard for copper 10GBase-CX (802.3ak) - 2004

dual coax cable <20m (for data center use only)

Standard for copper 10GBase-T (802.3an) - 2006 UTP cable (~50m for Cat-6 and ~100m for Cat-6a)

IEEE P802.3ba

100G physical layer specifications for operation up to: 40 km on single-mode fiber (SMF) using wavelength division

multiplexing (WDM) 10 km on SMF using WDM 100 m on parallel OM3 multimode fiber (MMF) 10 m over a copper cable assembly

40G physical layer specifications for operation up to: 10 km on SMF using WDM 100 m on parallel OM3 MMF 10 m over a copper cable assembly

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Other High Speed LANTechnologies

Token Ring Fiber Distributed Data Interface

(FDDI) 100VG-AnyLAN ATM LAN

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Continuous Improvement 10M => 100M (802.3u) => 1G (802.3z and

802.3ab) 10G (802.3ae, 802.3ak, 802.3an) Now 40 G and 100G (approved in 2010) Virtual LAN (802.1Q) Quality of Service (802.1p) Fault tolerance

Spanning Tree Algorithm and Protocol 802.1D Rapid STP 802.1w and per VLAN STP 802.1s Link aggregation 802.1ad

Port based network access control: 802.1X Wireless LAN: 802.11

13.73

Power Over Ethernet (PoE)

Power over Ethernet (PoE)PoE delivers low-voltage power over Cat 5 cable.

Ideal for applications such as wireless access points, access-card readers, IP telephones, IP video cameras,and may even be useful with cell phones, PDAs, and laptops.

Once a proprietary technology, now it is an IEEE standard802.3af.

For small scale systems, installing PoE may be as simpleas installing a new line card in a switch or hub.

13.74

Power Over Ethernet (PoE)

Power over Ethernet (PoE)Installing PoE in a large network may create physicalpower infrastructure problems.

For example, each powered device (PD) can draw up to15 watts from the switch/hub (power sourcing equipment,or PSE). If you have a 100-port hub, that’s 1500 wattsto support the PDs, plus another 1000 watts normallyneeded to drive the switch. The total is 2500 watts, or roughly 25 amps. Does your wiring closet have a 25 ampcircuit? What if the switch has 300 ports?

PoE can deliver this 48 volt 15 watt power over theunused spare pair of wires in an Ethernet connection,or over the transmit/receive pairs.