Data Link Layer Issues Dealing with Different Types of Networks.

Data Link Layer IssuesDealing with Different Types of Networks

Types of Networks Network hardware can be categorized into:

Circuit-switched (e.g. telephone) Prior to communication, the hardware establishes a dedicated

end-to-end connection Since there is a dedicated connection, a continuous stream of bytes

can be sent Frequency or time-division multiplexing can be used to share

links in such a network Packet-switched (e.g. Ethernet, ATM)

Data is divided into packets of limited size, and each is forwarded through the network to the destination

This can be done by routers or switches

Types of Networks Disadvantages

Circuit-switched A dedicated connection that has no transmission means wasted

bandwidth A connection is time consuming if short, infrequent, or sporadic

communication is to occur

Packet-switched Forwarding each packet means that each router must decide the

next hop for every packet (even for the same destination) Routers are typically network slowdowns due to the amount of

processing, as well as input/output buffering

Types of Networks Circuit-switching is used in a telephone conversation

A connection to the receiver is established by the sender (the caller) The telephone company reserves a certain bandwidth (64 Kbps for voice

communication) for this call If the bandwidth is not used by the callers, it is wasted

Packet-switching is similar to the postal service Each message (envelope) is addressed to the recipient individually,

and the postal service delivers each message to the recipient The postal service may deliver these envelopes through different cities

and methods of transport (airplane, truck, …) It can be said that these messages can be delivered using different routes

Circuit-Switching

A BTelephone CompanySwitching System

Call: B

Disconnect

Talk Talk

Circuit-Switching

A BTelephone CompanySwitching System

Packet-Switching

A B

Postal Network

Buffalo, NYWindsor, ON

London, ON

Kitchener, ON

Toronto, ON

Ottawa, ON

Montreal, QC

Quebec, QC

Niagara Falls, ON

Types of Packet-Switching Virtual circuit-switching

A ‘virtual circuit’ is created between source and destination

This VC is used for all subsequent sending of packets

Datagram Each packet is routed individually

Virtual Circuit Packet-SwitchingAdvantages After the first message, routing is faster

A route must only be determined once, for the first message Once the route has been determined, the path used by the router is

reused for all messages As a result, routing tables are much smaller (and can be searched more

quickly) Because a connection is created, the connection identifier can

be used (alone) to address packets Typically, such as with ATM cells, this can reduce the size of a

cell/packet’s header Messages do not arrive out of order

As a result, receivers do not need to reorder the cells

Virtual Circuit Packet-SwitchingDisadvantages Connections take some time to create

Routers/switches must intercommunicate in order to create the connection

Infrequent messaging is not suitable for connection-based messaging The connection may be lost after a timeout, and will have to be

recreated again and again The time delay for creating the connection may outweigh the speed

benefits of using connection-based transport Routing tables will be dynamic, and routing algorithms are

more complex

Datagram Packet-SwitchingAdvantages Connections need not be created Infrequent messaging is perfect for connectionless messaging

Connectionless messaging can be resumed after any amount of delay, any number of times, without any delays due to the resumption of communication

Routing each message separately allows for load balancing Some messages may be sent through one route, but when that route

becomes saturated, messages may then be sent through a different route in order to achieve the most optimal communication possible

Datagram Packet-SwitchingDisadvantages Each message takes a certain amount of time to transmit

(including transmission, routing, reception, etc.) Nodes communicating large amounts of information in a short time

will: Use a lot of bandwidth for things such as header information Waste a lot of time routing messages to the same destination

Messages may arrive out of order Messages must be reordered by the recipient

Multiple Access StrategiesSchemes for Sharing a Communication Medium

Multiple Access Most networks are shared medium

This means that a single medium (e.g. radio frequency) is shared by all of a network’s hosts

We need a scheme to allow the hosts to share the medium, without collisions Collisions occur when two (or more) messages are

transmitted at the same time The result is constructive and destructive interference in

the carrier wave This causes the messages to be combined and scrambled

Contention In contention networks, any node that has a

packet to send, merely sends the packet It is clear that this type of network frequently

experiences collisions The more nodes trying to communicate, the

higher the chance of collisions Thus, contention networks are severely limited in

the number of hosts possible

Contention

Transmit

Contention

Contention

Transmit

Contention

Contention: Collisions

Transmit

Transmit

Contention: CollisionsScrambled

Signal

Contention No collision avoidance is present

Messages are just sent When collisions occur, the messages are simply

resent after some random (or pseudo-random) amount of time

Collisions can occur anytime

Carrier SensingTest the medium

for a signal

Carrier SensingTest the medium for a signal: Available

Transmit

Carrier Sensing

Test the mediumfor a signal

Carrier Sensing

Test the mediumfor a signal: In use

Carrier SensingTransmission

Complete

Carrier Sensing

Test the mediumfor a signal

Carrier Sensing

Test the mediumfor a signal: Available

Carrier Sensing: CollisionsTest the medium

for a signal: Available

Test the mediumfor a signal: Available

Carrier Sensing: Collisions

Transmit

Transmit


Scrambled data


Detect collision

Detect collisionTransmit

Transmit

Carrier Sensing (CSMA) 1

To reduce the number of collisions, the medium is tested for a signal before each transmission If a signal exists, the node waits Signal testing can be anything from detection of an

electrical signal, to testing for photons Collisions can still occur (although less often)

If a node tests for a signal before a transmission from another node, and transmits after, a collision occurs

1 CSMA/CA is short for: Carrier Sense Multiple Access with Collision Avoidance

Carrier Sensing Hardware

SignalDetector

Transmitter Receiver If the message isbroadcast or the address is this station’s address,the message isforwarded to thereceiver

When a signal is detected, transmissions areblocked by the signal detector

CSMA/CA CSMA/CA networks (such as wireless 802.11g) also

use carrier sensing and collision detect However, detecting collisions in wireless networks is

significantly more complicated Also, after detecting carrier and determining there is

no signal, a CSMA/CA network transmits a ‘Do not broadcast’ message If this message is sent without a collision, the host can

assume it is safe to transmit

Carrier Sensing NetworksAdvantages No tokens

Simple hardware No need for token transmission

Disadvantages Collisions

Wasted bandwidth for re-transmits Require complicated re-collision avoidance schemes

Token Passing

T

TransmitTransmitTransmitTransmit

Token Passing

T

TransferToken

Token Passing

T

Token Passing

T

Transmit

Token Passing A small packet (the token) is passed from

node to node When a node has the token, it has sole use of the

network medium There are no collisions

The nodes must have the token in order to transmit

The network hardware ensures that there is only one token at any given time

Token-Based NetworksAdvantages No collisions, so no bandwidth is wasted by

collisions and re-transmits No need for re-collision avoidance schemesDisadvantages Token transmission uses bandwidth More complicated hardware

Hardware must be built to use tokens, dynamically determine token sequence, etc.

Local Area Networks Networks which span a small geographic area They typically represent high bandwidth,

short delays, few errors They commonly support features such as

broadcasting, multicasting They are typically limited to hundreds of

network nodes (maximum)

Typical Local Area Networks A collection of computers in the same room

e.g. The basement of the computer centre All computers within an office building

e.g. The computers in the offices of the professors and staff in Lambton tower

Local Area Network TopologiesStructures of LANs

Token Bus Networks The token is passed in a specific sequence

Nodes must know the address if the next node in the sequence

The token sequence is not necessarily in the same order as the physical order of nodes on the communication medium

When a node has completed transmission, it forwards the token, addressed to the next node in the token sequence

The token sequence forms a ‘logical ring’

Common Token Bus Networks IEEE 802.4 networks

Nodes are share a communication medium similar to that of Ethernet (IEEE 802.3) Coaxial cable connection

Token Bus Operation

A

B

C

D

Token sequence: C,A,D,B

Transmit

Token Bus Operation

A

B

C

D


TransmitToken

Token Bus Operation

A

B

C

D


ReceiveToken

Token Bus Operation

A

B

C

D


Transmit

Token Bus Operation

A

B

C

D


TransmitToken

Token Bus Operation

A

B

C

D


ReceiveToken

Token Bus Operation

A

B

C

D


Transmit

Token Ring Networks The token is passed to each node, in the

physical order on the network The physical medium must be a closed loop

to meet this network category So the token can keep going around the network

Common Token Ring Networks IEEE 802.5 networks

Nodes are share a coaxial communication medium similar to that of Ethernet (IEEE 802.3)

FDDI networks (fibre distributed data interface) Nodes use 2 fibre optic rings as the communication

medium CDDI networks (copper dist. data interface)

Based on FDDI technology, but uses copper wiring similar to 802.4

However, CDDI uses 2 rings like FDDI

Token Ring Operation

D

C

B

A

Transmit


D

C

B

A

TransmitToken


D

C

B

A

ReceiveToken


D

C

B

A

Transmit


D

C

B

A

TransmitToken


D

C

B

A

ReceiveToken


D

C

B

A

Transmit

Bus and Ring NetworksAdvantages Less wiring is necessary

Disadvantages Node failure can mean partial (or complete)

LAN failure This can mean locating network problems is also

more difficult

Star Topology Star networks send all messages through a

central hub Each node on the network is wired separately

to the hub Star networks are not a shared bus

technology, but a private bus technology However, nodes still share the hub

Common Star Networks Twisted pair Ethernet (logical star):

All nodes connect to a central hub (an Ethernet hub) via Cat5 cables

The hub forwards messages to all wires, and the destination node keeps the message Other nodes ignore the message

An Ethernet switch (similar to an ATM switch) forwards only in the one correct direction (or not, if appropriate)

Star Network Operation

A B

C D

Hub

Transmit


A B

C D

Hub

Receive


A B

C D

Hub

Transmit


A B

C D

Hub

Receive

Twisted Pair Ethernet Physically, all Ethernet types are bus

networks However, the actual layout of the cables in

twisted pair Ethernet forms a star topology Twisted pair is called a logical star topology,

while still a physical bus topology

Twisted Pair Ethernet as a Bus

Hub

B C

F G

A D

E H

Long Private Lines

Short Shared Bus

Traditional Ethernet as a Bus

B C

F G

A D

E H

Long Shared Bus

Short Private Lines

Star TopologyAdvantages Simple installation and wiring Node failures do not affect the rest of the systemDisadvantages All traffic passes through same hub, so network bandwidth is

limited by hub speed This can be reduced with buffers inside hubs which store messages

that come in when the hub is busy Hub failure = LAN failure More wiring Duplication of messages

LAN Service Models In general, most LANs implement (in some sense)

the OSI reference model The IEEE committee on LAN technology (IEEE

802) chose to subdivide the Data Link Layer into 2 sub-layers:

1. MAC (Medium Access Control): Deals with issues specific to each type of LAN

Such as token passing, collision detection, error detection, etc.

2. LLC (Logical Link Control): Deals with issues common to all LAN types

Such as data transmission, etc.

Data Link Addressing The data link layer is represents the network

e.g. Ethernet Addressing, then, is specific to the network hardware

MAC addresses are typically used for this purpose These addresses are not used in routing

They are only used on a single network Thus, they are used for hop to hop delivery End-to-end delivery is the domain of the Network layer

MAC Addresses Officially the IEEE 802 committee standardized

addresses to be 16bit, 48bit, and even 60bit 48bit addresses (in use by most LANs covered by the 802

committee) allow for globally unique identifiers (GUIDs) to be assigned to each network card by the manufacturer As a result, each NIC can be uniquely identified on any network

These are called MAC addresses, due to the Data Link sub-layer that deals with them

e.g. 8D-F0-A6-75-9C-13

Data Link Flow Control Flow control is limiting the packet rate so that

both the source or destination can keep up At the data link layer, source and destination

are on the same LAN Thus, limiting the packet rate is relatively easy

Data Link Reliability Reliability:

Best effort: The network takes no steps to ensure packets arrive The majority of packets should be received without problems

Reliable: The network uses acknowledgements to ensure packets arrive When packets are lost (for whatever reason), they are handled

appropriately Error handling: Corrupt packets should be re-sent

Reliability at the Data Link layer is usually unnecessary, since the Transport layer will typically be able to do it more efficiently

Error Control Error control is achieved using one of the

following methods: Checksum: An n-bit sum is taken of the

binary stream In other words, a checksum counts the ones What if one 0 became a 1 and a 1 became a 0??

Cyclical redundancy check: Should generate different CRC values, despite the

same number of 0s and 1s

EthernetAn Early Incarnation of LANs

What Started It All

Robert Metcalfe (from Xerox PARC)

Ethernet History In 1973, Xerox PARC developed a packet-switched

LAN, called Ethernet In 1978, IEEE created a standard (802.3) based on

the research of Xerox, Intel, and DEC IEEE: Institute of Electrical and Electronics Engineers

802.3 Ethernet uses a coaxial cable to connect nodes (called 10Base5 or ThickNet)

Since then, several new forms of Ethernet have evolved

ThickNet (10Base5)Outer Insulating Jacket

BraidedMetalShield(Ground)

InnerInsulatingLayer

TransmissionWire

½ Inch Diameter10Base55 => 0.5”

ThickNet (10Base5)

Transceiver

•Each network node uses a transceiver•A transceiver ‘taps’ into the wire through holes•Maximum throughput is 10 million bits per second (10 Mbps)

10Base510 => 10 Mbps

ThinNet (10Base2) Create as an inexpensive alternative to ThickNet (or

10Base2) Called thin-wire Ethernet, because it uses a thin

cable with less shielding Less shielding means more interference, so cable

placement is important 10Base2 does not use transceivers, which are

expensive, which further reduces cost

ThinNet (10Base2)

Node A Node DNode B Node C

•The signal passes through each node•The network interface card (NIC) retransmits the signal, so transceivers are not required•Maximum throughput is 10 million bits per second (10 Mbps)

10Base22 => 0.2”

10Base210 => 10 Mbps

Twisted Pair Ethernet (10BaseT) Uses 4 pairs of twisted wires inside an

unshielded cable The twisting of the wires reduces interference The absence of shielding makes the cable

flexible and inexpensive The cable is capable of 10Mbps

Twisted Pair Ethernet Connectors on twisted pair Ethernet (RJ45) look

similar to telephone wire connectors (RJ11) This kind of Ethernet uses unshielded twisted pair

(UTP) UTP cable has various categories:

Cat3: Can only be used for 10BaseT Cat5: Can be used for 10BaseT, 100BaseT Cat5e, Cat6: Can be used for up to 1000BaseT

ThinNet Ethernet

011100110011100110

Twisted Pair Ethernet

011100110011100110accept

message

ignoreignore

ignore

011100110

011100110

011100110

10 Mbps Ethernet Overview 10Base2 and 10Base5 both used coaxial cable

which joined each node in a line 10BaseT uses UTP cabling, where each node

is directly connected with the hub The hub receives messages and forwards them to

all nodes The one that is connected to the recipient node

Fast Ethernet Using the same Cat5 cabling used for 10BaseT, an

Ethernet-based LAN that operates at 100 Mbps (100BaseT) is possible Standard: IEEE 802.3u

While using the same cable, network hubs and network interface cards (NICs) must be upgraded to transmit messages at 100 Mbps

Fast Ethernet While very few computers can handle 100 Mbps

throughput (bus speeds of computers are often slower than this), multiple computers can share this bandwidth

10/100 Ethernet (or 10/100 switched Ethernet) allows you to use the same NICs and hubs for both 10BaseT and 100BaseT If a NIC and hub can both handle 100BaseT, that speed is

used, otherwise 10BaseT is used 10/100 Ethernet allows you to slowly upgrade your

network with minimal downtime

Gigabit Ethernet

Gigabit Ethernet allows for 1000 Mbps throughput Gigabit Ethernet (Gig-E) can use Cat5 cabling

(1000BaseT) or shielded Cat5E cabling (1000BaseTX) Standard: IEEE 802.3ab

Gig-E pushes the limits of the speed capable with Cat5 cabling, due to interference with the electrical signal, Cat5E cabling results in better performance

Gigabit Ethernet is so fast, that it is sometimes used as a backbone for a Wide Area Network (WAN) instead of more expensive optical networks e.g. One of the backbones of the network here at the U

Ethernet Future

Another form of Gigabit Ethernet which uses fibre optic cabling has been proposed (802.3z) Using multimode (multiple channel – 1000BaseSX), or

single mode (1000BaseLH, 1000BaseZX) Research groups are in the process of developing

10 Gigabit Ethernet (802.3ae) This research is managed by the 10 Gigabit

Ethernet Alliancehttp://www.10gea.org

LAN Service Models LLC (Logical Link Control), for LANs, can

be one of two types:Type 1: A straight datagram scheme

The packet is delivered using best-effort service No acknowledgements are used to ensure packet

arrival

Type 2: A reliable scheme Packets are numbered Packets are acknowledged as they are received

IEEE 802 Committees Five 802 committees were developed to research

various technologies associated with LANs: 802.1: Issues common to all LANs

e.g. addressing, management, bridges 802.2: Issues related to the LLC sub-layer

e.g. reliability schemes, packet transmission 802.3: Issues related to CSMA/CD category LANs

e.g. Ethernet 802.4: Issues related to token bus category LANs 802.5: Issues related to token ring category LANs

LAN Addresses The 48 bit addresses (often called MAC

addresses) are the ones used by Ethernet LANs e.g. 02-60-8C-08-E1-0C

All Ethernet cards contain a globally unique MAC address

Ethernet Overview Ethernet is not a reliable service

There are no acknowledgements for packet receipt Ethernet uses best-effort delivery

Most Ethernet networks use broadcasting to achieve messaging Each message is received by each node

Ethernet is one network in a category of networks known as shared bus networks Each node shares a single communication medium

Ethernet Overview Ethernet is a carrier-sensing network

Carrier-sensing networks use distributed access control methods Each station determines whether it can access the

communication medium Each station senses whether or not the

transmission medium (wire) is charged If not, an attempt at transmission is made If so, the node will wait and sense again

Ethernet Overview Sometimes, more than one station will attempt to

transmit at roughly the same time This is called a collision Due to the finite speed of electrons traversing a wire

70% of the speed of light Or due to the finite speed of photons moving through

glass The speed of light

The two (or more) messages collide or interfere with one another, creating scrambled data packets

Collision Detection in Ethernet When scrambled messages are read by the

transmitting stations, it is determined to be a collision Both (or all) of the stations involved will detect

the collision This type of network is known as CSMA/CD

Carrier-sensing, multiple access with collision detection

Each station must retransmit their packets

Collision Avoidance in Ethernet After a collision occurs, if both stations tried

to transmit after the same period of time, another collision would occur

To combat this, Ethernet uses a binary exponential back-off policy Each subsequent collision would cause the station

to wait double the amount of time before reattempting transmission

Ethernet Packets (Frames) Size: 64 octets – 1518 octets

An octet is another term for an 8-bit byte The frame contains more than just data

The source and destination addresses An identifier, signifying that the frame is in fact

an Ethernet frame A Cyclical Redundancy Check (CRC) to ensure

data integrity upon arrival

Ethernet Frames

Preamble

Dest Address

Source Address

Frame Type

Data

CRC

Sequence of 01010101 used to synchronize the receiving stationThe MAC address of the destination nodeThe MAC address of the sender nodeThe identifier used to identify the frame as an Ethernet frameThe data to be sent to the destinationA cyclical redundancy check (CRC) used to determine if data has been corrupted

8 octets

6 octets

6 octets

2 octets

46-1500

4 octets

Ethernet Distance Limitations Coaxial Ethernet cables have a maximum length

Due to signal deterioration This length could be extended using repeaters

Machines that read signals through a port and recreate them (at full strength) out another port

The use of more than 2 repeaters between any 2 stations would interfere with times used in CSMA/CD schemes As a result, a maximum of 2 repeaters can be placed between

any 2 nodes

Ethernet Distance Limitations Ethernet LAN sizes could also be increased by using

Bridges to connect separate LANs into a single LAN Bridges filter out erroneous frames, as well as line noise Some bridges (adaptive bridges) are even intelligent

enough to know when a frame must be forwarded or not e.g. If the destination node is not on the other side of a Bridge,

the frame need not be forwarded

FDDIFiber Distributed Data Interconnect

FDDI Use optical fibre cabling as a shared communication

medium Optical fibre cables are made of glass Because they are so thin, they are fairly flexible

Capable of 100 Mbps Light is used to transmit data

Light is not susceptible to electrical interference Optical cabling can span longer distances Optical cabling does not need to be shielded near devices which

generate electromagnetic interference Light waves (photons) travel faster than electrons

FDDI Is a token-ring category network

A token is passed from station to station When a station receives the token, it may transmit data If a station has no data, it allows the token to pass to the next

station

FDDI uses 2 rings of cabling, moving in opposite directions The second ring is used to allow twice the flow of data The purpose of the second ring is to allow data to reach its

destination, even when one station has failed (and cannot forward messages)

FDDI Ring Technology

FDDI With Node Failure

FDDI Token Passing

11

12

10 9 8 7

6

5

1 2 3 4

T

S:12D:07 S:12

D:07

S:12D:07

S:12D:07

S:12D:07

S:12D:07

S:12D:07

S:12D:07

S:12D:07

S:12D:07

S:12D:07

S:12D:07

S:12D:07

S:12D:07

FDDI Token Passing

11

12

10 9 8 7

6

5

1 2 3 4T

T

FDDI Frames

PreambleStart DelimiterFrame ControlDest Address

Source AddressRouting Info

DataFCS

End DelimiterFrame Status

Data Used to Synchronize StationsIndicates Start of FrameIdentifies the Type of FrameAddress of the Destination NodeAddress of the Source NodeRouting InformationFrame DataFrame Check SequenceIndicates End of FrameStatus of Frame

octets: 2+11

2 or 62 or 6

0-300-4500

40.5

1.5+

Wireless NetworksRadio-Based LANs

Wireless LANs Contrary to one’s initial guess, wireless LANs

are very similar to ‘wired’ LANs Wireless LANs are a shared media network,

just like Ethernet However, in a wireless LAN, the shared medium

is not the air, but something called a base station or wireless access point

Wireless LANs (WLANs) The wireless access point, which is similar to a hub,

is the shared medium Despite the fact that radio waves using the same

frequency will cause mutual interference, the air is not generally considered a shared medium

Technically speaking, twisted pair Ethernet is similar to WLANs The cables themselves are just point-to-point connectors

and are not shared The hub/switch, however, is shared

Wireless LANs (WLAN) Wireless Access Point (WAP): A base station that

coordinates transmission between one or more wireless hosts Analogous to a cell tower in a mobile phone network Wireless hosts must be a certain distance away from a WAP to

participate on a WLAN The communicable area of all of the WAPs in a WLAN, define the

coverage area for the WLAN Some WLANs do without a WAP, but pass messages directly

to one another These are typically small (2-3 hosts) networks, and are called ad hoc

networks

802.11 Operation 802.11 networks (such as 802.11g) use CSMA/CA multiple

access scheme Hosts try to detect carrier before sending (CS)

This is not adequate, since there could be hidden hosts These are hosts out of range of this host, but in range of the same

base station:

802.11 Operation To avoid collisions with hidden hosts:

The host will send a ‘request to send’ (RTS) frame before transmitting

The base station will respond with a ‘clear to send’ (CTS) frame if the channel is clear Once a base station sends a CTS, it will reject any further RTS

requests until the data is received by the host who sent the first RTS

This is called collision avoidance (CA) Frames are acknowledged at the data link layer in

802.11 networks

802.11 Frame FormatFlagsMAC Address of sending hostMAC Address of receiving hostMAC Address of sender base stationFragment number, sequence numberMAC Address of receiver base station

Frame data

CRC for frame header and data

Frame Control (2 octets)

Source Address (6)

Destination Address (6)

Receiving Station Address (6)

Transmitting Station Address (6)

Sequence Control (2)

Data (0-2312)

Frame Check Sequence (2)

802.11 Frame Header: Frame Control

FlagsManagement, control or data frameType of management or control frameSent to an access point?Sent by an access point?

Protocol Version (2 bits)

Type (2)

Subtype (4)

To AP (1)

More Fragments (1)

From AP (1)

Order (1)

Retry (1)

Power Management (1)

More Data (1)

WEP (1)

Are there more fragments from this frame?Is this a retransmission of a previous frame?Power state of sender after transmissionIs there more data to come?Has WEP encryption been applied to frame?Are the packets strictly ordered?

Wireless Access Points

WAP1

WAP2

WAP3

Ad Hoc Networks In ad hoc networks, stations directly transmit

to one another Hosts are responsible for routing, addressing,

name translation, security, etc. Two ad hoc networks using the same

frequency, within range of one another will cause conflicts Thus, different frequencies should be used

Handoffs in WAPs For WLANs with WAPs, roaming hosts must be

considered If a host moves into the range of another WAP, then out

of range of their current WAP, a handoff takes place A handoff is when one WAP gives the responsibility for a

particular host to one of its neighbouring WAPs The two WAPs must communicate for this to happen, and thus

neighbouring WAPs must be within each other’s transmission range

Wireless LAN Standards Some of the main standardized WLANs:

802.11a, 802.11g: 54Mbps, comparable with 100BaseT Ethernet, under 100M range

802.11b: 11Mbps, comparable to 10BaseT Ethernet, under 100M range These technologies are intended for LANs within the same small

to medium-sized building

BlueTooth/802.15: 721 kbps, under 10M range This technology is intended for communicate within one room or

vehicle

Data Link Layer Issues Dealing with Different Types of Networks.

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Transcript of Data Link Layer Issues Dealing with Different Types of Networks.