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Jozef Goetz, 2012
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expanded by Jozef Goetz, 2012
The McGraw-Hill Companies, Inc., 2006
Jozef Goetz, 2012
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13-1 IEEE STANDARDS13-1 IEEE STANDARDS
•In In 19851985, the Computer Society of the , the Computer Society of the IEEEIEEE started a started a project, called project, called Project 802Project 802, to set , to set standardsstandards to enable to enable intercommunication among equipment from a variety of intercommunication among equipment from a variety of manufacturers. manufacturers.
•Standard 802Standard 802 adopted by adopted by ANSIANSI and approved by and approved by ISOISO is is a way of a way of specifying functions of the physical layerspecifying functions of the physical layer and and the the data link layer data link layer ofof major LAN protocols major LAN protocols..
Data Link LayerPhysical Layer
Topics discussed in this section:Topics discussed in this section:
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INTRODUCTION
The key technology ingredients that determine the nature of a LAN are:
[1] Topology
[2] Transmission medium
[3] Medium access control technique
LANs usually are owned by the organization that is using the network to interconnect equipment.
LANs have much greater capacity than WAN.
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4LAN ARCHITECTURE
•In OSI terms, higher-layer protocols (layer 3/4 & above) are independent of
network architecture and are applicable to LANs & WANs.
SCOPESCOPE OF OF IEEE 802 STANDARDS IEEE 802 STANDARDS
[1] LOGICAL LINK CONTROL ([1] LOGICAL LINK CONTROL (LLCLLC))
[2] MEDIUM ACCESS CONTROL [2] MEDIUM ACCESS CONTROL ((MACMAC))
[3] PHYSICAL LAYER[3] PHYSICAL LAYER
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Figure 13.1 IEEE standard for LANs
Note: there is one LLC sublayer for all IEEE LANs
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6LAN ARCHITECTURE
Physical Layer
[1] Encoding/decoding of signals
[2] Preamble generation/removal (synch)
[3] Bit transmission/reception
Medium Access Layer (MAC)
[1] On transmission, assemble data into a frame with address and error-detection fields.
[2] On reception, disassemble frame, and perform recognition and error detection.
[3] Govern access to the LAN transmission medium
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7LAN ARCHITECTURE
Logical Link Control (LLC)
[1] Provide an interface to higher layers and perform flow and error control.
LAN Protocols in LAN Protocols in ContextContext
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Figure 13.2 HDLC (typical DLL protocol) frame compared with LLC and MAC frames in the 803 IEEE standard
PDU – protocol data unit
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9LOGICAL LINK CONTROL
3 services are provided by LLC:
[1] Connection-mode service
A logical connection is set up between users. Flow/error control.
Extended HDLC format.
[2] Acknowledged connectionless service
No connection is setup up, but datagrams are acknowledged.
[3] Unacknowledged connection service
Simple, the delivery of data is not guaranteed.
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10LOGICAL LINK CONTROL
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11LOGICAL LINK CONTROL
Most upper-layer protocols such as IP don’t use the services of LLC
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Ethernet Cabling
(a) Linear – from room to room, (b) Vertical Spine – from the basement to the roof
with cables on each floor connected by repeaters, (c) Tree, (d) Segmented – see max in the previous slide
repeaters are the physical layer device – amplifies signals in both directions
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Gigabit Ethernet
(a) A two-station Ethernet. (b) A multistation Ethernet.
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14LAN TOPOLOGIES
The common topologies for LANs are bus, tree, ring, and star.
STARSTARRINGRINGTREETREE
BUSBUS
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Three generations of Ethernet
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13-2 STANDARD ETHERNET13-2 STANDARD ETHERNET
•The The original Ethernetoriginal Ethernet was created in was created in 1976 at Xerox’s 1976 at Xerox’s Palo Alto Research Center (PARC).Palo Alto Research Center (PARC). •Since then, it has gone through four generations. Since then, it has gone through four generations. •We briefly discuss the We briefly discuss the Standard (or traditional) EthernetStandard (or traditional) Ethernet in in this section.this section.
MAC SublayerPhysical Layer
Topics discussed in this section:Topics discussed in this section:
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Figure 13.3 Ethernet evolution through four generations
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Ethernet • A thick coax cable was used for data
transmission.
• The coax could be up to 2.5km long (with repeaters every 500 meters).
• 256 machines could connect to the cable.
• A cable with multiple machines is called a multidrop cable.
• The original throughput was 2.94 Mbps
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IEEE 802.3 Based on 1-persistent CSMA/CD with some
extra features.
More commonly (but incorrectly) referred to as Ethernet.
Ethernet is the original product designed by Xerox PARC based on Bob Metcalfe's idea
It was later upgraded to 10 Mbps by Xerox, Intel and DEC.
This formed the basis for the IEEE 802.3 standard.
Which then became an ISO standard.
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Ethernet – IEEE 802.3 in ’83.
LAN Architecture of the original Ethernet. A multidrop cabel A computer first listened to the cable to see if
someone was already transmitting. If so, then back off and wait a random time before retrying If a 2nd collision happen, the random waiting time is doubled
Other standards a token bus (IEEE 802.4) and a token ring (IEEE 802.5)
Ethernet (most popular LAN) won a war between Ethernet, token bus, token ring
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Ethernet
• What happens when there is a collision on Ethernet?
• The terminals listen while transmitting,
and if they don’t hear the same thing that they transmitted, they jam the cable to alert the other terminals that a collision has happened.
• They then back off and wait a random time before trying again.
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22Ethernet Cabling
4 kinds of Ethernet cabling. 10Base5 => 1st one =10 means 10 Mbps – the speed in Mbps; Base = baseband transmission, 3rd one is its length rounded to 100 m(a) 10Base5, (b) 10Base2 – much cheaper and easier to install, (c) 10Base-T – cheapest, no share cable.(d) 10Base-F – fiber optic, excellent noise immunity, good security
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23IEEE 802.3 10-Mbps Specs
(ETHERNET)
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24MAC FRAME FORMAT
The MAC layer receives a block of data from the LLC layer and is responsible for performing functions related to medium access and for transmitting the data.
MAC controlMAC control
ex. Priority levelex. Priority level
PDU – protocol data unit
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802.3 MAC frameMinimum and maximum length
•Ethernet does not provide any mechanism for acknowledging received frames, making it what is known as an unreliable medium. •Acknowledgments must be implemented at the higher layers.
Start Frame Delimiter
physicalnext length
or PDU (protocol data unit) packetphysicalPreamble is addedat the physical layer
Data encapsulated from the upper-layer
protocols
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802.3 MAC frameMinimum and maximum length
Start Frame Delimiter
physical next lengthor PDU packetphysical
Preamble is addedat the physical layer
DSAP = Destination Service Access Point Defines a number to which a higher layer protocol or
application is bound to at the destination, e.g. IP SSAP = Source Service Access Point
Tells the destination which SAP to send back the response to, e.g. IP
Control information depends on the service type Type 1 – no other information required Type 2 – full sliding window protocol implementation with
extensions Type 3 – basic stop and wait protocol information
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Each station on an Ethernet network (such as a PC, workstation, or printer) has its own Network Interface Card (NIC).
The NIC fits inside the station and provides the station with a 6-byte physical address.
written in hexadecimal notation using a hyphen to separate bytes from each other
Ethernet addresses in hexadecimal notation
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Figure 13.6 Example of an Ethernet address in hexadecimal notation
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Unicast and multicast addresses
•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.
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The broadcast destination address is a special case of the multicast address in which all bits are 1s.
FF:FF:FF:FF:FF:FF
Note
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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
Solution•To 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.
Solution•The address is sent left-to-right, byte by byte;
•for each byte, it is sent right-to-left, bit by bit, as shown below:
e.g. 47 = 0100 0111 => 1110 0010
Example 13.2
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33Physical layer
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AUI
NIC – Network Interface Card
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35Function of MAU (transceiver)
AUI – Attachment Unit InterfaceMAU – Medium Attachment UnitMDI – Medium Dependent InterfacePLS – Physical Layer Signaling
NIC – Network Interface Card
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Function of MAU (transceiver)
MDI – Medium Dependent InterfacePLS – Physical Layer Signaling
•It creates the appropriate signal for each particular medium. •There is a MAU for each type of medium used in 10-Mbps Ethernet.
•the coaxial cable needs its own type of MAU,
• the twisted-pair medium needs a twisted-pair MAU, and• •fiber-optic cable needs a fiber optic MAU.
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NIC Evolution
Volumes for Ethernets NICs became huge
NIC becomes cheaper than the AUI cable!
Moved from 3 separate components to one integral NIC card
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38Categories of traditional Ethernet cables
Thick coaxialone segmentis 500m long max
Thin coaxialone segmentis 185m long max
UTP category 5100m max P2P
Optical Fiber2km max P2P
P2P = point-to-pointUnshielded Twisted-Pair
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39BUS LANs
4 media that can be used for a bus LAN:
[1] Twisted pair,
[2] Baseband coaxial cable,
[3] Broadband coaxial cable,
[4] Optical fiber.
10BASE 5 - thick cable10BASE 5 - thick cable
10BASE2 - thin cable10BASE2 - thin cable
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Figure 13.10 10Base5 implementation
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Connection of a station to the medium using 10Base5
the size of the cable, which is roughly the size of a garden hose and too stiff to bend with your hands
AIU cable
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Figure 13.11 10Base2 implementation
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43Connection of stations to the medium using 10Base2
uses a bus topology with 1. an internal transceiver
• Note that if the station uses an internal transceiver, there is no need for an AUI cable.
2. a point-to-point connection via an external transceiver• If the station lacks a transceiver, then an external transceiver can be used in
conjunction with the AUI - Attachment Unit Interface.
AIU cableConnection of stations to the medium using 10Base5
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Figure 13.12 10Base-T implementation
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45Connection of stations to the medium using 10Base-T
uses a physical star topology. The stations are connected to a repeater hub with 1. an internal transceiver
• Note that if the station uses an internal transceiver, there is no need for an AUI cable. 2. a point-to-point connection via an external transceiver
• If the station lacks a transceiver, then an external transceiver can be used in conjunction with the AUI - Attachment Unit Interface.
Each UTP (Unshielded Twisted-Pair) cable can be up to 100m long (max network size = 200m)
A repeater hub connects segments of a LAN.A repeater forwards every frame; it has no filtering capability.
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Ethernet
Ethernet now looks like a star network from a physical perspective
Hub is a half duplex device – “effectively a small piece of coaxial cable”
Collisions on a hub can still take place
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Figure 13.13 10Base-F implementation
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48Connection of stations to the medium using 10Base-FL
uses a star topology. The stations are connected to a repeater hub with 1. an external transceiver (a point-to-point connection)
• The standard is normally implemented using an external transceiver called fiber-optic MAU.
• The station is connected to the external transceiver by an AUI cable.• The transceiver is connected to the hub by using two pairs of fiber-optic cables
AUI cabel
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49Comparison of Connection of stations to the medium
10Base5 10Base2
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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 The 10-Mbps Standard Ethernet10-Mbps Standard Ethernet has gone through has gone through several changesseveral changes before moving to the before moving to the higher data rateshigher data rates..
•These These changeschanges actually actually openedopened the road to the the road to the evolutionevolution of the Ethernetof the Ethernet to become to become compatiblecompatible with with other high-other high-data-rate LANs.data-rate LANs.
Bridged EthernetSwitched EthernetFull-Duplex Ethernet
Topics discussed in this section:Topics discussed in this section:
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53A network with and without a bridge
•The first step in the Ethernet evolution was the division of a LAN by bridges. •Bridges have two effects on an Ethernet LAN: •They raise the bandwidth and separate collision domains.
•Without bridging, 12 stations contend for access to the medium; •with bridging only 6 stations contend for access to the medium.
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Sharing bandwidth
•In an unbridged Ethernet network, the total capacity (10 Mbps) is shared between all stations with a frame to send; •If only one station has frames to send, it benefits from the total capacity (10 Mbps).
•But if more than one station needs to use the network, the capacity is shared. •For example, if 2 stations have a lot of frames to send, they probably alternate in usage.
•When one station is sending, the other one refrains from sending (a and b). •We can say that, on average, each station sends at the rate of 5 Mbps.
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55A network with and without a bridge
A bridge divides the network into two or more networks. Bandwidthwise, each network is independent.
a network with 12 stations is divided into two networks, each with 6 stations.
Now each network has a capacity of 10 Mbps. The 10-Mbps capacity in each segment is now shared between 6
stations (actually 7 because the bridge acts as a station in each segment), not 12 stations.
In a network with a heavy load, each station theoretically is offered 10/6 Mbps instead of 10/12 Mbps, assuming that the traffic is not going through the bridge.
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56Collision domains in a nonbridged and bridged network
each station is now offered 10/3 Mbps, which is 4 times more than a nonbridged network.
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HubIn an Ethernet network there are 4 devices that from the outside
look very similar.
A hub is the simplest of these devices. Any data packet coming from one port is sent to all other
ports. It is then up to the receiving computer to decide if the packet
is for it.
Imagine packets going through a hub as messages going into a mailing list.
The mail is sent out to everyone and it is up to the receiving party to decide if it is of interest.
The biggest problem with hubs is their simplicity. Since every packet is sent out to every computer on the network, there is a
lot of wasted transmission. This means that the network can easily become bogged down.
Hubs are typically used on small networks where the amount of data going across the network is never very high.
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Bridge Bridge
A bridge goes one step up on a hub in that it looks at the destination of the packet before sending.
If the destination address is not on the other side of the bridge it will not transmit the data.
A bridge only has one incoming and one outgoing port.
To build on the email analogy above, the bridge is allowed to decide if the message should continue on.
It reads the address [email protected] and decides if there is a [email protected] on the other side.
If there isn’t, the message will not be transmitted.
Bridges are typically used to separate parts of a network that do not need to communicate regularly, but still need to be connected.
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59Bridges BasicFiltering_
Detect which frames need to go from one LAN to another
Forwarding_
Send those frames from the incoming LAN to the outgoing LAN_
“Drop” those frames that don’t need to be forwarded
Loop Prevention_
Avoid issues with networks where a frame can keep going round and round
Types of Bridges
Static
Dynamic – called learning bridges
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60BRIDGES
In virtually all cases, there is a need to expand beyond the confines of a single LAN, to provide interconnection to other LANs and to WAN.
The The bridgebridge is a simpler is a simpler device than a router and device than a router and provides a means of provides a means of interconnecting interconnecting similarsimilar LANs.LANs.
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61BRIDGES
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62BRIDGES - FIXED ROUTING
Each bridge must make a decision whether or not to retransmit the frame on its other LAN, in order to move it closer to its intended destination.
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Switch A switch steps up on a bridge in that it has
multiple ports. When a packet comes through a switch it is read to
determine which computer to send the data to.
This leads to increased efficiency in that packets are not going to computers that do not require them.
Now the email analogy has multiple people able to send email to multiple users.
The switch can decide where to send the mail based on the address.
Most large networks use switches rather than hubs to connect computers within the same subnet.
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ROUTER A router is similar in a switch in that it forwards
packets based on address. But, instead of the MAC address that a switch
uses, a router can use the IP address. This allows the network to go across different
protocols.
The most common home use for routers is to share a broadband internet connection.
The router has a public IP address and that address is shared with the network.
When data comes through the router it is forwarded to the correct computer.
This comparison to email gets a little off base. This would be similar to the router being able to receive
a packet as email and sending it to the user as a fax.
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Switched Ethernet•The idea of a bridged LAN can be extended to a switched LAN. •Instead of having two to four networks, why not have N networks,
where N is the number of stations on the LAN?
•A layer 2 switch is an N-port bridge with additional sophistication that allows faster handling of the packets
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66HUBs & SWITCHES
HUBHUB SWITCHSWITCH
•Hubs are commonly used to connect segments of a LAN. •A hub contains multiple ports. •When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.
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Full-duplex switched Ethernet
One of the limitations of 1OBase5 and 1OBase2 is that communication is half-duplex (1OBase-T is always full-duplex);
The next step in the evolution was to move from switched Ethernet to full duplex switched Ethernet = to 20 Mbps
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No Need for CSMA/CD In full-duplex switched Ethernet, there is
no need for the Carrier Sense Multiple Access with Collision Detection - CSMA/CD method. Each station or switch can send and receive independently
without worrying about collision. Each link is a point-to-point separate dedicated path between
the station and the switch. There is no more need for carrier sensing; there is no more need for
collision detection.
-’s: There is no explicit flow control or error control to inform the sender that the frame has arrived at the destination without error. .
To provide it, a new sublayer, called the MAC control, is added between the LLC sublayer and the MAC sublayer.
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13-4 FAST ETHERNET – IEEE 13-4 FAST ETHERNET – IEEE 802.3u802.3u
•Fast Ethernet was designed to Fast Ethernet was designed to competecompete with LAN with LAN protocols such as protocols such as FDDIFDDI or or Fiber ChannelFiber Channel. . •IEEEIEEE created created Fast EthernetFast Ethernet under the under the name 802.3uname 802.3u. . •Fast EthernetFast Ethernet is is backward-compatiblebackward-compatible with with Standard Standard EthernetEthernet, but it can , but it can transmit data 10 times fastertransmit data 10 times faster at a rate at a rate of of 100 Mbps100 Mbps. .
MAC SublayerPhysical Layer
Topics discussed in this section:Topics discussed in this section:
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13-4 FAST ETHERNET CONCEPT13-4 FAST ETHERNET CONCEPT
- The whole idea in the evolution of Ethernet from 10 to 100 Mbps is to keep the MAC sublayer untouched.
-The access method is the same (CSMA/CD). -for full-duplex there is no need for CSMA/CD.
-Backward compatibility with traditional Ethernet.
-Frame format, minimum and maximum frame lengths,
and addressing are the same for 10- and 100-Mbps Ethernet.
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Figure 13.19 Fast Ethernet topology
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autonegotiation A new feature added to Fast Ethernet
It allows to have : a station or a hub a range of capabilities a station to check a hub's capabilities. to negotiate the mode or data rate of
operation.
purposes: to allow incompatible devices to connect
to one another. For example, a device with a maximum capacity of 10
Mbps can communicate with a device that is designed for 100 Mbps (but can work at a lower rate).
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Fast Ethernet implementations
Fast Ethernet can be categorized as either a two-wire or a four-wire implementation.
The two-wire implementation is called 100Base-X, which can be either twisted-pair cable (100Base-TX) or fiber-optic cable (100Base-FX).
The four-wire implementation is designed only for twisted-pair cable (100Base-T4).
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IEEE 802.3 100-Mbps Specs (ETHERNET)
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Fast Ethernet 802.3u
The original fast Ethernet cabling.
• People needed to go faster than 10Mbps, so we needed a faster Ethernet.• Instead of going with a new protocol, it was decided to just make regular Ethernetgo faster – IEEE 802.3u.
•This was done by reducing the bit time from 100nsec to 10 nsec•and keeping backward compatible – frame formats, interfaces and rules
• Note: that 10Base2 and 10Base5 were not included – it was based only on 10BaseT
• Only two lines are used – one wire in and one wire out of the station.• This makes 100BaseTX full-duplex – able to handle 100 Mbps in either direction atthe same time.
•all switches can handle a mix of 10- and 100 Mbps stations• The (slower) 100BaseT4 and 100BaseTX are collectively referred to as “100BaseT”
Uses “Category 5 UTP” clock @ 125 MHz
or 100mhubs not permitted
Uses “Category 3 UTP” clock @ 25 MHz
2 twisted pairs per station
4 twisted pairs per station
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Fast Ethernet physical layer
•RS in Fast Ethernet replaces the PLS sublayer in 10-Mbps Ethernet. •Encoding and decoding, which were performed by the PLS, are moved to the PHY sublayer (transceiver) because encoding in Fast Ethernet is medium-dependent.
•The reconciliation sublayer RS is responsible
for the passing of data in 4-bit format (nibble) to the MII
The MII is an improved interface
that can be used with both a 10- and 100.
the AUI was replaced with (MII)
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MII
transceiver in Fast Ethernet is responsible for encoding and decoding.
can be external or internal. An external transceiver is installed
close to the medium and is connected via an MII cable to the station.
An internal transceiver is installed inside the station (on the interface card) and does not need an MII cable.
transceiver is medium-dependent, a medium dependent interface (MDI) is
just a piece of hardware that is implementation specific.
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100Base-TX implementation
The transceiver is responsible for •transmitting, •sending, •detecting the collision, and •encoding/decoding.
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Encoding and decoding in 100Base-TX
•To maintain synchronization, the encoder first performs block encoding. •The 4 parallel bits received from the NIC is encoded into 5 serial bits using 4B/5B. •This requires a bandwidth of 125 MHz (125 Mbps).•The data at the 125-Mbps rate are then encoded into a signal using MLT-3
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100Base-FX implementation
100Base-TX implementation
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Encoding and decoding in 100Base-FXEncoding and Decoding 100Base-FX uses two levels of encoding
•To maintain synchronization, the encoder first performs block encoding. •The 4 parallel bits received from the NIC is encoded into 5 serial bits using 4B/SB. •This requires a bandwidth of 125 MHz (125 Mbps).•The data at the 125-Mbps rate are then encoded into a signal using NRZ-I
Encoding and decoding in 100Base-TX
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100Base-T4 implementation
•it requires the use of category 5 UTP or STP (shielded twisted-pair) cable. •A new standard, called 100Base T4, was designed to use category 3 or higher UTP.•The implementation uses four pairs of UTP for transmitting 100 Mbps.
100Base-FX implementation
100Base-TX implementation
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Using four wires in 100Base-T4
•Transmission Using Four Wires The 8B/6T encoding reduces the bandwidth from 100 to 75 Mbaud (ratio of 8/6).
•However, a voice-grade UTP is not capable of handling even this bandwidth. •100Base-T4 is designed to operate on 25-Mbaud bandwidths. •It cuts to 4 pairs – see the picture
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13.84
Summary of Encoding for Fast Ethernet implementation
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85Table 13.2 Summary of Fast Ethernet implementations
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13-5 GIGABIT ETHERNET – IEEE 13-5 GIGABIT ETHERNET – IEEE 802.3z802.3z
The need for an The need for an even higher data rateeven higher data rate resulted in the resulted in the design of the design of the Gigabit Ethernet protocol (1000 Mbps).Gigabit Ethernet protocol (1000 Mbps). The IEEE committee calls the standard The IEEE committee calls the standard 802.3z. 802.3z.
It It allowsallows the internet the internet interconnectioninterconnection of of existing existing LANsLANs into a into a Metropolitan Area Network (Metropolitan Area Network (MANMAN) ) or a or a Wide Wide Area Network (Area Network (WANWAN))
MAC SublayerPhysical LayerTen-Gigabit Ethernet
Topics discussed in this section:Topics discussed in this section:
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Gigabit Ethernet
(a) A two-station Ethernet. (b) A multistation Ethernet.
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Figure 13.22 Topologies of Gigabit Ethernet
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Gigabit Ethernet implementations
•Gigabit Ethernet can be categorized as either a two-wire or a four-wire implementation. •The two-wire implementation is called 1000Base-X, which can use shortwave optical fiber (1000Base-SX), •long-wave optical fiber (1000Base-LX), or •short copper jumpers (1000Base-CX). •The four-wire version uses twisted-pair cable (1000Base-T).
Unshielded Twisted-PairShielded Twisted-Pair
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90Gigabit Ethernet Gigabit Ethernet cabling.
• 10 times faster than fast Ethernet and still is backwards compatible. •supports both copper and fiber cabling• All configurations are point-to-point.
•Compatible with technologies: FrameRelay and ATM• It supports two modes – full-duplex and half-duplex.
• Full-duplex– no collisions– uses a switch
• Half-duplex– has collisions– uses a hub
Encoding rules called 8B/10B•each 8-bit byte is encoded on the fiber as 10 bits hence the name 8B/10B•Manchester encoding required a 2 Gbaud at 1 Gbps, so
>> too wasteful of bandwidth
1.3 micron laser
0.85 and 1.3 micron laser
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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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92IEEE 802.2: LLC Logical Link Control
(a) Position of LLC. Hides the differences between various kind of 802 networks by providing a single format
and interface to the network layer(b) Protocol formats.
LLC header contains: a destination access point, a source access point and a control field which contains a seq and acknowledgement numbers
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Physical layer in Gigabit Ethernet
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1000Base-X implementation
•Both 1000Base-SX and 1000Base-LX use two fiber-optic cables. •The only difference between them is that the former uses shortwave laser and the latter uses long-wave laser. • designed with an internal transceiver, so there is no external GMII cable or connector.
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1000Base-T implementation
1000Base-X implementation
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•5 levels of pulse amplitude modulation are used. •The technique is very complicated and beyond the scope of this book.
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Summary: Encoding/decoding in Gigabit Ethernet implementations
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Standard IEEE IEEE 802.3z802.3z
Table 13.4 Summary of Ten-Gigabit Ethernet implementationsStandard IEEE 802.3ae
•Ten-Gigabit Ethernet uses fiber optic cable over long distances and operates in full duplex mode which means there is no need for contention;
•CSMA/CD is not used in Ten-Gigabit Ethernet.•Make it compatible with Standard, Fast, and Gigabit Ethernet
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Ethernet advantages1. simple and flexible2. reliable3. cheap
twisted pair wiring is relatively inexpensive interface cards are low cost
4. easy to maintain no software to install (other than drivers) no configuration table to manage
5. interworks easily with TCP/IP IP is a connectionless protocol, so fits perfectly
with Ethernet IP fits much less well with ATM, which is connection
oriented
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UTP - unshielded twisted-pair cable
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Table 13.3 Summary of Gigabit Ethernet implementations
Table 13.4 Summary of Ten-Gigabit Ethernet implementations Standard IEEE 802.3ae
SummaryTable 13.1 Summary of Standard Ethernet implementations
Table 13.2 Summary of Fast Ethernet implementations
