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1

Ethernet and CSMA/CD Reviews

CSC488: Special Topic in Computer Networks

Supanit Angsirikul

Rangsit University

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Aloha Protocol: Pure Aloha

Pure Aloha: Max Utilization = 1/(2e) =18%

2

reschedule

B send

Channel

A send

Collision

A and B don’t hear

what they are sending

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Carrier Sense Multiple Access: CSMA

Listen Before Talk (LBT)

1-persistent CSMA:

If the channel is busy, wait until idle.
If the channel is idle, transmit

p-persistent CSMA:

If the channel is busy, wait until idle.
If the channel is idle, transmit with a probability p

Non persistent CSMA (p=0):

If the channel is busy, go away for a random period of time
At scheduled time send if idle, otherwise reschedule

3

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CSMA Operation

If the location where packet collision take place is too far from the transmitted station

The station cannot detect the collision
No retransmission

4

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CSMA with Collision Detection ( CSMA/CD)

CSMA (Carrier Sense Multiple Access)
In order to make the transmitted station be able to detect collision any where in the segment

Max. Round-Trip Time < Min. Frame Time

5

Max. Round-Trip time

Min. Frame time

150m

1000bit

2x10⁸ m/s

=300/2x10⁸ = 1.5 microsecond

1000x10⁶ bit/s

=1000/1000x10⁶ = 1 microsecond

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Ethernet Family

10 Mbps (Ethernet – IEEE802.3)
100 Mbps (Fast Ethernet – IEEE802.3u)
1,000 Mbps (Gigabit Ethernet – IEEE802.3z)
10,000 Mbps (10 Gigabit Ethernet – IEEE802.3ae)

6

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LAN Physical Layer Implementations

7

Physical

Data-Link

(MAC Layer)

Physical layer implementations vary.
Some implementations support multiple physical media.

Ethernet

100baseTX

10BaseT

802.3

10Base5

10Base2

100baseFX

802.3 Specifications for 10-Mbps Ethernet

802.3u Specifications for 100-Mbps (Fast) Ethernet

100baseT4

10BaseF

DIX

Standard

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Frame Format (IEEE 802.3)

Ethernet II

8

IEEE 802.3

Dest.�Address

Source�Address

Length

6

2

IP

IPX

AppleTalk

CRC

bytes

4

Pad

Length

Info

Min Frame length =round trip time =512 bits (64bytes)

Max Frame length=1518 bytes

PA

SFD

7

1

Dest.�Address

Source�Address

Type

6

2

IP

IPX

AppleTalk

CRC

4

Pad

Info

PA

8

LLC

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10BASE-5

9

Thick coax RG8

0.5” diameter, 50 ohm

AUI cable limited to 50 m
No more than 500 m/segment

🡪10Base5

No more than 100 stations/segment
2.5 m between stations

2.5m

500 m

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10BASE-2

10

Thin coax RG58

0.25” diameter, 50 ohm

No more than 185 m/segment 🡪 10BASE 2
No AUI Cable
No more than 30 stations/segment
No less than 0.5 m between stations

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10BASE-T

11

UTP Cat 3, Cat 5 -2 pairs
No more than 100 m per segment

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10BASE-FX

12

Multi-Mode Fiber cable (MMF)

core/cladding 62.5/125 mm
wavelength 850 nm,
4 - 5 dB loss / kms.

ST connector, "BFOC/2.5” standard

FOIRL

(Fiber Optic Inter-Repeater Link)

Repeater-Repeater
1000 m.

10 BASE FX

10 BASE-FL

Link (1000m., 2000m.)

10 BASE-FB

Backbone (2000 m.)

10BASE-FP

500 m.
Mixed (33 nodes)

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Fast Ethernet 100BASE-X

13

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Comparing Ethernet Media Requirements

14

10Base5

100BaseTX

10BaseT

100BaseFX

Media

Maximum

Segment

Length

Topology

Connector

50-ohm coax (thick)

500 meters

Bus

100 meters

Star

Point-to-point

EIA/TIA Cat

3, 4, 5 UTP

2 pair

EIA/TIA Cat

5 UTP

2 pair

62.5/125-micron multi-mode fiber

AUI

(DB-15)

ISO 8877

(RJ-45)

Duplex media

interface connector

(MIC) ST

ISO 8877

(RJ-45)

400 meters

100 meters

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802.3z and 802.3ab Physical Media

15

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10 Gigabit Ethernet

16

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1

LAN/WAN Cabling

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Objectives

LAN Cabling and Components -- Ethernet
WAN Cabling and Components -- Serial and ISDN BRI.
Console connections among routers, switches, and a terminal.

18

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Cabling the Campus

19

ISDN Cloud

Leased Line/

Frame Relay

Legend

Fast Ethernet/

Ethernet

ISDN

Dedicated

Core Server

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Differentiating Between Connections

20

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UTP Cable, Jack and Plug

21

UTP Cable

8 Position Jack

RJ45 Plug

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Modular Jack Pair Assignments for UTP

22

1

8

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Patch Panel

23

Front

Back

Cable terminator

Patch

cable

Wall

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Transmission System

24

R

T

R

NIC/

Router

HUB/

Switch

R

T

R

NIC/

Router

HUB/

Switch

HUB/

Switch

R

T

R

NIC/

Router

1

2

3

6

1

2

3

6

1

2

3

6

1

2

3

6

1

2

3

6

1

2

3

6

X

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UTP Implementation Straight-Through

25

�Wires on cable ends are in same order.

Pin Label

1 RD+

2 RD-

3 TD+

4 NC

5 NC

6 TD-

7 NC

8 NC

Cable 10BaseT/�100BaseTX Straight-Through

Pin Label

1 TD+

2 TD-

3 RD+

4 NC

5 NC

6 RD-

7 NC

8 NC

Server/Router

8

1

w

g

b

w

o

w

b

o

br

w

br

1

8

Straight-Through Cable

(EIA/568A)

8

1

Hub/Switch

8

1

w

g

b

w

o

w

b

o

br

w

br

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UTP Implementation Crossover

26

Some wires on cable ends are crossed.

Cable 10BaseT/�100BaseT Crossover

Pin Label

1 RD+

2 RD-

3 TD+

4 NC

5 NC

6 TD-

7 NC

8 NC

Pin Label

1 RD+

2 RD-

3 TD+

4 NC

5 NC

6 TD-

7 NC

8 NC

Crossover Cable

8

1

8

Hub/Switch

8

1

w

g

b

w

o

w

b

o

br

w

br

1

8

1

w

0

b

w

g

w

b

g

br

w

br

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UTP Implementation of Straight-Through Versus Crossover

27

Use a crossover cable when BOTH ports are designated with an “x” or neither port is designated with an “x.”

Use straight-through when only one port is designated with an “x.”

1x

2x

3x

4x

1x

2x

3x

4x

1x

2x

3x

4x

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Cabling the Campus

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Determine the physical media used: 10-Mbps or �100-Mbps.

Indicates what category of cable is required

Locating interfaces on the chassis, determine if one �or both ports have an “x.”

Indicates if you need crossover or straight-through cable

100-Mbps

Cat 5

Crossover

10-Mbps

Cat 3, 4, 5

Crossover

100-Mbps

Cat 5

Straight-Through

10-Mbps

Cat 3, 4, 5

Straight-Through

10-Mbps

Cat 3, 4, 5

Straight-Through

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WAN Physical Layer Implementations

29

Physical layer implementations vary.
Cable specifications define speed of link.

PPP

Frame

Relay

EIA/TIA-232

EIA/TIA-449

X.21 V.24 V.35

HSSI

ISDN BRI (with PPP)

RJ-45

NOTE: Pinouts are different from RJ-45 used in campus.

HDLC

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Serial Implementation of DTE Versus DCE

DTE/DCE—The point where responsibility passes

30

Data Terminal Equipment:

End of the user’s device �on the WAN link.

Data Communications Equipment:

End of the WAN provider’s �side of the communication facility.
Responsible for clocking.

S

DTE

DCE

(CSU/DSU)

Local Loop

Serial

Connection

(CSU/DSU)

Local Loop

Serial

Connection

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Differentiating Between WAN Serial Connectors

31

DCE

DTE

CSU/DSU

Local Loop

Service Provider

Serial

Connection

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Differentiating Between WAN Serial Connectors

32

Router Connections

Smart Serial/DB60

Network Connections at the CSU/DSU

EIA/TIA-232

EIA/TIA-449

EIA-530

V.35

X.21

CSU/�DSU

End-User Device

DTE

DCE

Service Provider

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WAN Connector

33

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Serial Connections

34

CSU/�DSU

Clock

DTE

SS/DB60

DCE

V.35

Service Provider

Clock

CSU/�DSU

Router

Typical Serial Connection

Router

Clock

Lab Serial Connection

DTE

SS/DB60

DCE

V.35

DTE

SS/DB60

DCE

V.35

DTE

V.35

DCE

SS/DB60

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Setting Up a Console Connection

PCs require an RJ-45-to-DB-9 or RJ-45-to-DB-25 adapter.
COM port settings are 9600 bps, 8 data bits, no parity, 1 stop bit, no flow control.
This provides out-of-band console access.
AUX switch port may be used for a modem-connected console.

35

Device with Console

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Computer or Terminal Console Connection

36

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Modem Connection to Console or Auxiliary Port

37