3. ethernet and atmbillatnapier.com/cnds2002_03/cnds_unit03_2002_2003.pdftransmitting frames and...

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Author: W.Buchanan. Ethernet and ATM (1)

Unit 3


3. Ethernet and ATM

100/1000BaseSwitch

100/1000BaseSwitch

10/100BaseSwitch or Hub10/100Base

Switch or Hub

ServerServer ServerServer

10/100BaseSwitch or Hub10/100Base

Switch or Hub

External connection (uses store-and-forward for external connection)

Segment switch allows direct connectionof any of the connected segments

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Why Ethernet?

• Simplicity. Easy to plan and cheap to install. The introduction of network hubs and twisted-pair cables has made Ethernet networks easy to connect to. It also has cheap and well-supported network components, such as network interface cards (NICs) and connectors (BNC and RJ-45).

• Reliability. Well-proven technology, which is fairly robust and reliable.• Ease-of-use. It is simple to add and remove computers to/from the network.• Upgradeability and compatibility. Ethernet has evolved from 10Mbps, to

100Mbps (Fast Ethernet, in 1985) and now to 1Gbps (Gigabit Ethernet, in 1998). All three Ethernet speeds use the same basic data frame format (IEEE 802.3), have full-duplex operation and have the same flow control methods.

• Popularity. Supported by most software and hardware systems.


3.1 Ethernet (Advantages/Problems)

Advantages:Ethernet networks are easy to plan and cheap to install.Ethernet network components, such as network cards and connectors, are cheap and well supported.Uses coaxial, fibre or twisted-pair cables.It is a well-proven technology, which is fairly robust and reliable.It is simple to add and delete computers on the network.It is supported by most software and hardware systems.Available as 10Mbps (10BASE), 100Mbps (100BASE) and 1Gbps (1000BASE). Dual-speed networks can be used, such as mixed 10Mbps/100Mbps networks. Network hub negotiates the required speed.Easy upgrade for different network speed. A dual-speed network can be run, and gradually upgraded.Standardised as 1EEE 802.3.

Advantages:Ethernet networks are easy to plan and cheap to install.Ethernet network components, such as network cards and connectors, are cheap and well supported.Uses coaxial, fibre or twisted-pair cables.It is a well-proven technology, which is fairly robust and reliable.It is simple to add and delete computers on the network.It is supported by most software and hardware systems.Available as 10Mbps (10BASE), 100Mbps (100BASE) and 1Gbps (1000BASE). Dual-speed networks can be used, such as mixed 10Mbps/100Mbps networks. Network hub negotiates the required speed.Easy upgrade for different network speed. A dual-speed network can be run, and gradually upgraded.Standardised as 1EEE 802.3.

Common bus

All computers have access toa common bus at the same time

Ethernet hub

Problem:A major problem with Ethernet is that, because computers must contend to get access to the network, there is no guarantee that they will get access within a given time. This contention also causes problems when two computers try to communicate at the same time, they must both

back off and no data can be transmitted.

Problem:A major problem with Ethernet is that, because computers must contend to get access to the network, there is no guarantee that they will get access within a given time. This contention also causes problems when two computers try to communicate at the same time, they must both

back off and no data can be transmitted.

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3.2 CSMA/CDCSMA/CDEthernet uses carrier sense, multiple access with collision detection (CSMA/CD). Nodes monitor the bus (or Ether) to determine if it is busy. A node wishing to send data waits for an idle condition then transmits its message. Collisions can occur when two nodes transmit at the same time, thus nodes must monitor the cable when they transmit. When a collision occurs, both nodes stop transmitting frames and transmit a jamming signal. This informs all nodes on the network that a collision has occurred. Each of the nodes involved in the collision then waits a random period of time before attempting a re-transmission. As each node has a random delay time then there

can be a prioritisation of the nodes on the network.

CSMA/CDEthernet uses carrier sense, multiple access with collision detection (CSMA/CD). Nodes monitor the bus (or Ether) to determine if it is busy. A node wishing to send data waits for an idle condition then transmits its message. Collisions can occur when two nodes transmit at the same time, thus nodes must monitor the cable when they transmit. When a collision occurs, both nodes stop transmitting frames and transmit a jamming signal. This informs all nodes on the network that a collision has occurred. Each of the nodes involved in the collision then waits a random period of time before attempting a re-transmission. As each node has a random delay time then there

can be a prioritisation of the nodes on the network.

Two nodes transmitat the same time

1

Node detect therehas been a collision

2

Nodes transmit ajamming signal

3

Nodes wait a randomperiod before retransmitted

4

Common bus



3.3 CSMA/CD

Common bus

Two nodes transmitat the same time

1 Node detect therehas been a collision

2

Nodes transmit ajamming signal

3 Nodes wait a randomperiod before retransmitting

4


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3.4 IEEE 802 LANs (802.2/802.3)

PhysicalPhysical

Data linkData link

NetworkNetwork

TransportTransport

SessionSession

PresentationPresentation

ApplicationApplication

PhysicalPhysical

Data linkData link

NetworkNetwork

TransportTransport

SessionSession


ApplicationApplicationA

A

A

A

A

A

P

P

P

P

P

S

S

S

S

T

T

T

N

ND D

Virtualdata flow

Actual data flow

Sender Receiver

PhysicalPhysical

Data linkData link

NetworkNetwork

TransportTransport

SessionSession



PhysicalPhysical

Data linkData link

NetworkNetwork

TransportTransport

SessionSession



PhysicalPhysical

Data linkData link

NetworkNetwork

TransportTransport

SessionSession


ApplicationApplicationA

A

A

A

A

A

P

P

P

P

P

S

S

S

S

T

T

T

N

ND D

Virtualdata flow

Actual data flow

Sender Receiver

PhysicalPhysical

Data linkData link

PhysicalPhysical

Data linkData linkLLC (IEEE 802.2)

Media AccessControl (IEEE 802.3)


3.5 IEEE 802.3 data frameOthers:4 bytes for the CRC (32 bits) and 2 bytes for the LLC length (16 bits). The LLC part may be up to 1500 bytes long. The preamble and delay components define the start and end of the frame. The initial preamble and start delimiter are, in total, 8 bytes long and the delay component is a minimum of 96 bits long.

Others:4 bytes for the CRC (32 bits) and 2 bytes for the LLC length (16 bits). The LLC part may be up to 1500 bytes long. The preamble and delay components define the start and end of the frame. The initial preamble and start delimiter are, in total, 8 bytes long and the delay component is a minimum of 96 bits long.

Preamble (seven bytes) precedes the Ethernet 802.3 frame. Each byte of the preamble has a fixed binary pattern of 10101010 and each node on the network uses it to synchronise their clock and transmission timings. It also informs nodes that a frame is to be sent and for them to check the destination address in the frame.Start delimiter field (SDF) is a single byte (or octet) of 10101011. It follows the preamble and identifies that there is a valid frame being transmitted.

Preamble (seven bytes) precedes the Ethernet 802.3 frame. Each byte of the preamble has a fixed binary pattern of 10101010 and each node on the network uses it to synchronise their clock and transmission timings. It also informs nodes that a frame is to be sent and for them to check the destination address in the frame.Start delimiter field (SDF) is a single byte (or octet) of 10101011. It follows the preamble and identifies that there is a valid frame being transmitted.

Delay. The end of the frame there is a 96-bit delay period, which provides the minimum delay between two frames. This slot time delay allows for the worst-case network propagation delay.

Delay. The end of the frame there is a 96-bit delay period, which provides the minimum delay between two frames. This slot time delay allows for the worst-case network propagation delay.

Source/destination addresses (2 or 6 bytes, Most Ethernet systems use a 48-bit MAC address for the sending and receiving node. Each Ethernet node has a unique MAC address, which is normally defined as hexadecimal digits, such as:

4C-31-22-10-F1-32 (4C31 : 2210: F132)

A 48-bit address field allows 248

different addresses (or approximately 281474976710000 different addresses).

Source/destination addresses (2 or 6 bytes, Most Ethernet systems use a 48-bit MAC address for the sending and receiving node. Each Ethernet node has a unique MAC address, which is normally defined as hexadecimal digits, such as:

4C-31-22-10-F1-32 (4C31 : 2210: F132)

A 48-bit address field allows 248

different addresses (or approximately 281474976710000 different addresses).

IP TCP HTTP DataE.g.

Preamble(7B)

Startdelimiter (1B)

Dest.address (6B)

Src.Address (6B)

Len(2B)

FCS(4 B)

Delay(92bits)

Data field(Logical link control)

52 to 1500 bytes

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3.6 Ethernet Limitations

Parameter 10BASE5 10BASE2 10BASE-T Common name

Standard or thick-wire Ethernet

Thinnet or thin-wire Ethernet

Twisted-pair Ethernet

Data rate

10 Mbps 10 Mbps 10 Mbps

Maximum segment length

500 m 200 m 100 m

Maximum nodes on a segment

100 30 3

Maximum number of repeaters

2 4 4

Maximum nodes per network

1024 1024

Minimum node spac-ing

2.5 m 0.5 m No limit

Location of trans-ceiver electronics

located at the cable connection

integrated within the node

in a hub

Typical cable type

RG-50 (0.5” diameter)

RG-6 (0.25” diameter)

UTP cables

Connectors

N-type BNC RJ-45/ Telco

Cable impedance

50 Ω 50 Ω 100 Ω

10BASE510BASE5

RG-50 backbonecable

N-typeT-connector

9-pin D-typeconnector (AUI)

9-pin D-typeconnector (AUI)

Vampire(or bee-sting)tap

BNCT-connector

BNC connector

10BASE2

10BASE-T

Hub

RG-50 backbonecable

Twisted-paircable

RJ-45connector

10BASE5 10BASE2

10BASE210BASE-T


3.7 Ethernet types

• Standard, or thick-wire, Ethernet (10BASE5).• Thinnet, or thin-wire Ethernet, or Cheapernet (10BASE2).• Twisted-pair Ethernet (10BASE-T).• Optical fibre Ethernet (10BASE-FL).• Fast Ethernet (100BASE-TX and 100VG-Any LAN).• Gigabit Ethernet (1000BASE-SX, 1000BASE-T, 1000BASE-LX and 1000BASE-

CX).

New standards relating to 100Mbps Ethernet are now becoming popular:

• 100BASE-TX (twisted-pair) – which uses 100Mbps over two pairs of Cat-5 UTP cable or two pairs of Type 1 STP cable.

• 100BASE-T4 (twisted-pair) – which is the physical layer standard for 100Mbps over Cat-3, Cat-4 or Cat-5 UTP.

• 100VG-AnyLAN (twisted-pair) – which uses 100Mbps over two pairs of Cat-5 UTP cable or two pairs of Type 1 STP cable.

• 100BASE-FX (fibre-optic cable) – which is the physical layer standard for 100Mbps over fibre-optic cables.

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HubHubConnects to thehub to give a startopology

Internal connectioninside the hub isstill a bus network

3.8 Ethernet hubs


BridgeBridge

BridgeBridge

Port1

Port2

A1 A2 A3 A4

B1 B2 B3 B4

C1 C2 C3

A1A2A3A4

B1B2B3B4

Port1 Port2A1A2A3A4

C1C2C3

Port1 Port2

Address tables whichassign MAC addresseswith ports

3.13 Transparent bridges with address tables

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146.176.151.100 146.176.151.130

Destination SourceFF-FF-FF-FF-FF-FF 65-F1-21-10-05-01

Destination Source146.176.151.130 146.176.151.100

ARP Request

Frame headerIP header

Destination Source65-F1-21-10-05-01 21-10-11-AA-42-FF


ARP Reply


3.14 ARP request and reply


Destination Source21-10-11-AA-42-FF 65-F1-21-10-05-01

Destination Source146.176.151.255 ????????

RARP Request


Destination Source65-F1-21-10-05-01 21-10-11-AA-42-FF


RARP Reply


RARPserver

Disklessworkstation

65-F1-21-10-05-01 146.176.151.100

Physical address IP address

65-F1-21-34-CD-A1 146.176.151.10165-F1-21-FF-1D-EF 146.176.151.102

RARP table

3.15 RARP

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Router_2Router_2

Router_1Router_1

Dest MAC address = 00-80-55-43-FE-FF

Port_1 IP address = 146.176.151.1MAC address = 00-80-55-43-FE-FF

Dest IP address = 146.176.120.2

Port_2 IP address = 146.176.130.1MAC address = 00-60-DD-E0-12-34

Dest MAC address = 00-90-10-33-DE-EE

Dest IP address = 146.176.120.2

Port_1 IP address = 146.176.120.1MAC address = 00-10-32-11-BC-B1

Port_2 IP address = 146.176.130.2MAC address = 00-65-21-44-33-A1

Node_A

Node_B

3.16 Example ARP


ATM

44

66

77

11

22

55

33

User 1

User 3

User 2

VCI=12

VCI=06

VCI=22

VCI=10VCI=15

IN OUT12 06

Routing tableIN OUT06 22

Routing table

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3.17 ATM overview

00.10.20.30.40.50.60.70.80.9

1

Example traffic profile for speech signal

00.10.20.30.40.50.60.70.80.9

1

Example traffic profile for computer-type data

ATM copes with real-time traffic with:Analysing the type of connection to be made. The type of data dictates the type of connection; for example, computer data requires a reliable connection, whereas real-time sampled data requires a connection with a low propagation time. Analysing the type of data to be transmitted and knowing its traffic profile. Computer data tends to create bursts of trafficwhereas real-time data will be constant traffic.Reserving a virtual path for the data to allow the data profile to be transmitted within the required quality of service.Splitting the data into small packets which have the minimum overhead in the number of extra bits. These ‘fast-packets' traverse

the network using channels which have been reserved for them.

ATM copes with real-time traffic with:Analysing the type of connection to be made. The type of data dictates the type of connection; for example, computer data requires a reliable connection, whereas real-time sampled data requires a connection with a low propagation time. Analysing the type of data to be transmitted and knowing its traffic profile. Computer data tends to create bursts of trafficwhereas real-time data will be constant traffic.Reserving a virtual path for the data to allow the data profile to be transmitted within the required quality of service.Splitting the data into small packets which have the minimum overhead in the number of extra bits. These ‘fast-packets' traverse

the network using channels which have been reserved for them.

Ethernet/FDDI/Token Ring are not suited to real-time traffic as:There is no guarantee that the connection can support a given Quality of Service (for errors, time delay, and so on).There is no guarantee that they can transmit the data within a given time limit.They allow nodes to burst data onto the network which can swamp other network traffic.

Ethernet/FDDI/Token Ring are not suited to real-time traffic as:There is no guarantee that the connection can support a given Quality of Service (for errors, time delay, and so on).There is no guarantee that they can transmit the data within a given time limit.They allow nodes to burst data onto the network which can swamp other network traffic.

Real-timetraffic profile

Computer-typetraffic profile


3.18 Data types

Data type Error or loss sensitive Delay sensitiveReal-time control system yes yesTelephone/hi-fi music no yesFile transfer/application progs. yes noTeletex information no no

Real-timecontrol system

Telephone/hi-fimusic

File transfer/application programsTeletex information

Error sensitive

Delay sensitive

SensitiveNot sensitive

Sensitive

Not sensitiveATMATM

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3.19 ATM cells (small ‘fast packets’)

VCI Label(24 bits)

VCI Label(24 bits)

Control(8 bits)

Control(8 bits)

Checksum(8 bits)

Checksum(8 bits)

Optional(32 bits)

Optional(32 bits)

Data(44 or 48 bytes)

Data(44 or 48 bytes)

The control field also contains bits which specify whether this is a flow control cell or an ordinary data cell, a bit to indicate whether this packet can be deleted in a congested network, and so on.

The control field also contains bits which specify whether this is a flow control cell or an ordinary data cell, a bit to indicate whether this packet can be deleted in a congested network, and so on.

The ETSI definition of an ATM cell also contains 53 bytes with a 5-byte header and 48 bytes of data. The main differences between ETSI and ANSI T1S! are the number of bits in the VCI field, the number of bits in the header checksum, and the definitions and position of the control bits.

The ETSI definition of an ATM cell also contains 53 bytes with a 5-byte header and 48 bytes of data. The main differences between ETSI and ANSI T1S! are the number of bits in the VCI field, the number of bits in the header checksum, and the definitions and position of the control bits.

The VCI label identifies the route for the data.

The VCI label identifies the route for the data.

Simple checksum for error detection. It is the 2’s complement of the sum of all the bytes in the cell.

Simple checksum for error detection. It is the 2’s complement of the sum of all the bytes in the cell.

Cell header (with every little overhead)


3.20 ATM cell routing

44

66

77

11

22

55

33

User 1

User 3

User 2

VCI=12

VCI=06

VCI=22

VCI=10VCI=15

IN OUT

12 06

Routing tableIN OUT

06 22

Routing table

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3.21 ATM call setup

44

66

77

11

22

55

33

End system A

End system B

Connect to B

Connect to B

Connect to B

OkayOkay

Okay

Signaling request

Connection routed

Connect accept/reject

Dataflow

Connectiontear-down

Signaling packet:VCI=5; VPI=0

As the path is set up, two VCI/VPI labels are assigned for each of

the flows of traffic on the virtual circuit.

44

66

77

11

22

55

33

End system A

End system B

Connect to B

Connect to B

Connect to B

OkayOkay

Okay

Signaling request

Connection routed

Connect accept/reject

Dataflow

Connectiontear-down

Signaling packet:VCI=5; VPI=0

As the path is set up, two VCI/VPI labels are assigned for each of

the flows of traffic on the virtual circuit.


3.22 Virtual Channels and Virtual Paths

VC1VC2

VC3VC4

VC5

VC7VC8

VC6

VC9

VC1

VC3VC2

Transmissionchannel

Virtual path VP

Virtual path

Virtual path

VP

VP

Virtual pathsNetwork user groups or interconnected networks can be mapped to virtual paths and are thus easily administered.Simpler network architecture which consists of groups (virtual paths) with individual connections (virtual circuits).Less network administration and shorter connection times arise from fewer set-up connections.

Virtual pathsNetwork user groups or interconnected networks can be mapped to virtual paths and are thus easily administered.Simpler network architecture which consists of groups (virtual paths) with individual connections (virtual circuits).Less network administration and shorter connection times arise from fewer set-up connections.

Several virtual channels grouped together to create a virtual path

Several virtual channels grouped together to create a virtual path

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3.23 Example ATM network (EaStMAN)

FDDI

router

FDDI

router

FDDI

router

FDDIrouter

FDDI

router

FDDI

router

FDDI

router

FDDI

router

FDDI

router

FDDI

router

FDDI

routerNapier(Merchiston) UoE

(New College)

Moray House(Holyrood)

UoE(Old College)

UoE(Pollock Halls)

ECA(Grassmarket)

ECA(Lauriston)

Napier(Sighthill)

QMC(Corstorphine)

Moray House(Cramond)

Heriot Watt(Riccarton)

ATMswitch

ATM

switch

ATMswitch

FDDI

router

UoE(King’s Buildings)ATM

switch

ATM

switch

ATMswitch

ATM

switch

ATM

switch

UoE (Western General Hospital)

University ofStirling

SuperJANET

AbMAN, FatMAN, ClydeNET

QMC(Leith Links)

ATM

switch Napier(Craighouse)

ATM

switchNapier(Craig lockhart)

Heriot Watt(Riccarton Campus)

Napier(Sighthill)

QMC

Crammond

WesternGeneralHospital

QMC (Leith)

Napier(Merchiston )

Napier(Craighouse)Napier

(Craiglockhart)

UoE (King’s Buildings)

UoE (Pollock Halls)

UoE (New College)

City of Edinburgh

College ofArt UoE

(Old College)

Moray House ( Holyrood )

Connection toUniversity of Stirling


Napier (Merchiston)

UoE(New College)

Moray House (Holyrood)

UoE(Old College)

UoE(Pollock Halls)

ECA(Grassmarket)

ECA(Lauriston)

Napier(Sighthill)

QMC (Corstorphine)

Moray House(Cramond)

Heriot-Watt(Riccarton)

UoE(King’s Buildings)

UoE (WesternGeneral Hospital)

University ofStirling

SuperJANET

AbMAN, FatMAN, ClydeNET

QMC (Leith Links)

Napier (Craighouse)

Napier (Craiglockhart)

3.24 EaStMAN network

ATMswitchATM

switchATM

switchATM

switchATM

switchATM

switch

ATMswitchATM

switchATM

switchATM

switch

ATMswitchATM

switch

ATMswitchATM

switch

ATMswitchATM

switch

ATMswitchATM

switch

ATMswitchATM

switch

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouterFDDI

router

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

FDDIrouter

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3.25 SuperJanet Network

London

Bristol

Manchester

Leeds

London MAN(ATM 155Mbps)

ULCC(UoL ComputerCentre)

ULC(University College London)

Telehouse

University ofGreenwich

South BankUniversity

UoL,ImperialCollege

Bristol

Birmingham

Exeter

Cardiff

Belfast

Edinburgh

Nottingham

Newcastle

SuperJANET

III

UoE (King’sBuildings)

Napier

University

(Craighouse)

Napier

University

(Craiglockhart)

EaSt MAN(ATM 155Mbps)

Heriot-Watt(Riccarton)

Napier University(Sighthill)

Napier University(Merchiston)

UoE(Old College) QMC

34

155

155

34

2x155TEN-155

Europeantraffic

TeleglobeUS ISP traffic

LINX(London Internet Exchange)

UK ISP traffic

London

Interconnect toClydeNETFatMANAbMAN

G-MANMAN

South WalesMAN

BWE

155


So to conclude?

• For organisational connections: Ethernet 10/100Mbps.• For organisational backbones: Ethernet 100Mbps/1Gbps.• For remote connections: ADSL (10Mbps), IEEE

802.11b (11Mbps), GPRS (10Mbps), Modem (56kbps).

• For wide area connections: ATM (155Mbps upwards),Gigabit Ethernet (for short distances), Frame relay.

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