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ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 1 K. Suresh Sub Divisional Engineer(DX) Telephones: +91-120-2728412(O) +91-120-2728434(O) +91-120- 2728839(R) E-mail: [email protected]
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Page 1: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 1

K. SureshSub Divisional Engineer(DX)Telephones: +91-120-2728412(O)

+91-120-2728434(O) +91-120-2728839(R)E-mail: [email protected]

Page 2: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 2

LAN Topology

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ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 3

Inter working Devices

Local Area Network (LAN)Works in a single office, building or campusMost common LAN topologies are bus, ring & starEthernet was early network introduced in 1980

Wide Area Network (WAN)Provides long distance transmission over large geographical area

Metropolitan Area Network (MAN)Connecting number of LANs into a larger network using WAN circuits

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Network Topologies (Mesh & Star)

Dedicated point-to-point link between devices.Advantages: Dedicated link & fault isolation is easyDisadvantages: More Space/Hardware requirement

Topology is the geometric representation of all the links and linking devices

Mesh Topology

• Each device has a dedicated point-to-point link to a central controller, called a hub.

• Advantages :Less expensive, fault isolation is easy & each device needs only one link

• Disadvantage : If hub fails, whole network will be down

HUB

Star Topology

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Network Topologies (Tree & Bus)

The central hub in the tree is an active hub.An active hub contains a repeater.The secondary hubs can be active or passive.

HUB

HUB

HUB

Tree Topology

Tap

Tap

Tap

Tap

Cable End

Cable End

Drop line

Drop line

Drop line

Drop line

Advantages : Multi point, Ease of installation & Uses less cables than mesh/star/tree topologies

Disadvantage: Difficult to add new devices & A fault in the bus cable stops all transmission000

Bus Topology

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Network Topologies (Ring & Hybrid)Each device is connected with the two devices on either side of it. Advantages: To add or delete a device, requires moving only two connections & Fault isolation is simplifiedDisadvantage : A break in ring can disable the entire network. Ring Topology

HUB

HUB

Star

Bus

Ring

Star

• Mixed topology using Star/Mesh & Ring according to the need

Hybrid Topology

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Inter-working Devices

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Inter-working Devices

HubBridgesLAN SwitchesRoutersGateways

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Hub

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HubsHubs are essentially physical-layer repeaters:

bits coming from one link go out all other links at the same rateno frame bufferingno CSMA/CD at hub: adapters detect collisions

twisted pair

hub

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Hubs

The active central element of the star layout.When a single station transmits, the hub repeats the signal on the outgoing line to each station.Physically a star; logically a bus.Hubs can be cascaded in a hierarchical configuration.

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Hubs

Operating at the physical layer, hubs are very simple devices that pass all traffic in both directions between the LAN sections they link. They may connect different types of cable, but use the same data link and network protocol.Strictly speaking, hubs are not considered part of a backbone network, but are usually repeaters or amplifiers.

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Hub/Switch uses Star topologyBus topology popular through mid 90sNow star topology prevailsConnection choices:

hub or switch

hub orswitch

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Interconnecting with hubsBackbone hub interconnects LAN segmentsExtends max distance between nodesBut individual segment collision domains become one large collision domainCan’t interconnect 10BaseT & 100BaseT

hub

hub hub

hub

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Bridges

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Bridges

Allow connections between LANs and to WANsOperates at Layer 2 (Data Link Layer) of OSIUsed between networks using identical physical and link layer protocolsProvide a number of advantages

Reliability: Creates self-contained unitsPerformance: Less contentionSecurity: Not all data broadcast to all usersGeography: Allows long-distance links

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Bridges

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Bridge Functions

Read all frames from each networkAccept frames from sender on one network that are addressed to a receiver on the other networkRetransmit frames from sender using MAC protocol for receiverMust have some routing information stored in order to know which frames to pass

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Bridges

If a bridge receives a packet with a destination address that is not in the address table, it forwards the packet to all networks or network segments except the one on which it was received.Bridges are a combination of both hardware and software, typically a “black box” that sits between the two networks, but can also be a computer with two NICs and special software.

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Bridge Operation

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LAN Switch

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Switch: Forwarding

hub

hub hub

switch1

2 3

How do determine onto which LAN segment to forward frame?Looks like a routing problem...

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Switch: Self learning

A switch has a switch tableEntry in switch table:

(MAC Address, Interface, Time Stamp)stale entries in table dropped (TTL can be 60 min)

Switch learns which hosts can be reached through which interfaces

when frame received, switch “learns” location of sender: incoming LAN segmentrecords sender/location pair in switch table

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Switch: Filtering/ForwardingWhen switch receives a frame:

Searches the switch table using MAC destination addressIf entry found for destinationthen forward the frame on interface indicated, if it has not come from the same segmentElse drop the frameIf no match found in the switch table, flood on all the other interfaces

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Switch example

Suppose C sends frame to DSwitch receives frame from from C

notes in bridge table that C is on interface 1because D is not in table, switch forwards frame into interfaces 2 and 3

Frame received by D

hub

hub hub

switch

A

B C DE

F G H

I

address interfaceABEG

1123

12 3

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Switch example

Suppose D replies back with frame to C.Switch receives frame from D

notes in bridge table that D is on interface 2because C is in table, switch forwards frame only to interface 1

Frame received by C

hub

hub hub

switch

A

B C DE

F G H

I

address interfaceABEGC

11231

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Switch: traffic isolationSwitch filters packets:

same-LAN-segment frames not usually forwarded onto other LAN segmentssegments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

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Switches: dedicated accessSwitch with many interfacesHosts have direct connection to switchNo collisions; full duplex

Switching: A-to-A’ and B-to-B’ simultaneously, no collisions

switch

A

A’

B

B’

C

C’

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Switches

Like bridges, switches operate at the data link layer. Switches connect two or more computers or network segments that use the same data link and network protocol. They may connect the same or different types of cable.

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Switches

Switches operate at the same layers as bridges but differ from them in two ways:

First, most switches enable all ports to be in use simultaneously, making them faster than bridges.Second, unlike bridges, switches don’t learn addresses, and need to have addresses defined.

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Ethernet Hubs and Switches

Shared medium hubs

Switched LAN hubs

x

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Switched Ethernet

A simple concept behind switched Ethernet - replace the LAN hub with a switch. Each computer now has its own dedicated point-to-point circuit.By increasing the number of connections from the server to the switch, the throughput of the server will be improved because of more circuits.

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Switched Ethernet

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Types of Switches

Switch establishes a connection between two segments just long enough to send the current packetIncoming packets (part of an Ethernet frame) are saved to a temporary memory area (buffer)MAC address contained in the header is read and then compared to a list of addresses maintained in the switch's lookup table

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Types of Switches

Routes the packet using one of the following methods:

Cut-throughStore-and-forward Fragment-free

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Cut-through Switching

After storing the MAC Address (6 bytes) immediately begin sending the packet to the destination node, even as the rest of the packet is coming into the switch.

No CRC Checking (disadvantage)Fast switching (advantage)

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Store-and-forward Switching Switch will save the entire packet to the buffer and check it for CRC errors or other problems before sending. Otherwise, the switch looks up the MAC address and sends the packet on to the destination node.

Slow (disadvantage)Error free operation (advantage)

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Fragment-free SwitchingWorks like cut-through except that it stores the first 64 bytes of the packet before sending it on. The reason for this is that most errors, and all collisions, occur during the initial 64 bytes of a packet.

Still CRC cannot be checked (disadvantage)faster (advantage)

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Layer 3 Switches

Problems With Layer 2 SwitchesBroadcast overload because of the single MAC broadcast address (e.g. using ARP for Data Link Layer address resolution)Lack of multiple links - only one path

Normally, the above problems can be solved with several subnets connected by routers. However,

A MAC broadcast frame is then limited to only the devices and switches contained in a single subnet.A router does all IP-level processing, some of which could be not necessary.It is implemented in software and slow.

Layer 3 switches implement the packet-forwarding logic of the router in hardware.

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Transparent Bridging &

Broadcast storm

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Transparent Bridging

A Technology that allows a switch to learn everything it needs to know about the location of nodes on the network without the network administrator having to do anything.Transparent bridging has five parts:

LearningFlooding Filtering ForwardingAging

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Transparent Bridging

HUB

HUB

Switch A

Switch CSwitch B

Node C

Node A

Node B

Segment-A

Segment-B

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Transparent Bridging: LearningA computer (Node A) on the first segment (Segment A) sends data to a computer (Node B) on another segment (Segment B). The switch gets the first packet of data from Node A. It reads the MAC address and saves it to the lookup table for Segment A. The switch now knows where to find Node A anytime a packet is addressed to it. This process is called learning.

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Transparent Bridging: Flooding

Since the switch does not know where Node B is, it sends the packet to all of the segments except the one that it arrived on (Segment A). When a switch sends a packet out to all segments to find a specific node, it is called flooding.

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Transparent Bridging: Forwarding

Node B gets the packet and sends a packet back to Node A in acknowledgement. The packet from Node B arrives at the switch. Now the switch can add the MAC address of Node B to the lookup table for Segment B. Since the switch already knows the address of Node A, it sends the packet directly to it. Because Node A is on a different segment than Node B, the switch must connect the two segments to send the packet. This is known as forwarding.

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Transparent Bridging: FilteringThe next packet from Node A to Node B arrives at the switch.The switch now has the address of Node B, too, so it forwards the packet directly to Node B. Node C sends information to the switch for Node A. The switch looks at the MAC address for Node C and adds it to the lookup table for Segment A.

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Transparent Bridging: FilteringThe switch already has the address for Node A and determines that both nodes are on the same segment, so it does not need to connect Segment A to another segment for the data to travel from Node C to Node A. Therefore, the switch will ignore packets traveling between nodes on the same segment. This is filtering.

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Transparent Bridging: AgingLearning and flooding continue as the switch adds nodes to the lookup tables. Most switches have plenty of memory in a switch for maintaining the lookup tables; but to optimize the use of this memory, they still remove older information so that the switch doesn't waste time searching through stale addresses. To do this, switches use a technique called aging.

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Broadcast Storms

HUB

Switch A

Switch CSwitch B

Node B

Node A

Segment-A

Segment-B

Segment-C

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Broadcast Storms When switches are connected in a loop, a packet from a node could quite possibly come to a switch from two different segments. In this scenario, imagine that Node B is connected to Switch A, and needs to communicate with Node A on Segment B. Switch A does not know who the destination Node A is, so it floods the packet.Packet travels via Segment A or Segment C to the other two switches (B and C).

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Broadcast Storms Switch B will add Node B to the lookup table it maintains for Segment A, while Switch C will add it to the lookup table for Segment C.Each switch will take the packet sent by the other switch and flood it back out again immediately, since they still don't know who the destination Node A is. Switch A will receive the packet from each segment and flood it back out on the other segment. This causes a broadcast storm as the packets are broadcast, received and re-broadcasted by each switch.

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Spanning Tree Protocol

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Spanning TreePrevents broadcast stormsStandardized as the 802.1d specification by IEEE.Spanning Tree uses the spanning-tree algorithm (STA) that:

senses that the switch has more than one way to communicate with a nodedetermines which way is bestand blocks out the other duplicate path(s)

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Spanning Tree Protocol

Each switch is assigned a group of IDs, one for the switch itself and one for each port on the switch. The switch's identifier, called the bridge ID (BID), is 8 bytes long and contains a bridge priority (2 bytes) along with one of the switch's MAC addresses (6 bytes). Each port ID is 16 bits long with two parts: a 6-bit priority setting and a 10-bit port number.

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Spanning Tree Protocol

A path cost value is given to each port. The cost is typically based on a guideline established as part of 802.1d. According to the original specification, cost is 1,000 Mbps (1 gigabit per second) divided by the bandwidth of the segment connected to the port. Therefore, a 10 Mbps connection would have a cost of (1,000/10) 100.

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Spanning Tree ProtocolEach switch begins a discovery process to choose which network paths it should use for each segment. This information is shared between all the switches by way of special network frames called bridge protocol data units (BPDU).

The parts of a BPDU are: Root BID - This is the BID of the current root bridge. Path cost to root bridge - This determines how far away the root bridge is.Sender BID - This is the BID of the switch that sends the BPDU. Port ID - This is the actual port on the switch that the BPDU was sent from.

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Spanning Tree ProtocolAll switches constantly send BPDUs to each other. When a switch receives a BPDU (from another switch):

Checks if it is better than the one it is broadcasting for the same segmentIf yes, then it will stop broadcasting its BPDU out that segmentIt will store the other switch's BPDU for reference and for broadcasting out to inferior segments, such as those that are farther away from the root bridge

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Spanning Tree Protocol

A root bridge is chosen based on the results of the BPDU process between the switches.Initially, every switch considers itself the root bridge. When a switch first powers up on the network, it sends out a BPDU with its own BID as the root BID.When the other switches receive the BPDU, they compare the BID to the one they already have stored as the root BID.

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Spanning Tree ProtocolIf the new root BID has a lower value, they replace the saved one.If the saved root BID is lower, a BPDU is sent to the new switch with this BID as the root BID. When the new switch receives the BPDU, it realizes that it is not the root bridge and replaces the root BID in its table with the one it just received.The result is that the switch that has the lowest BID is elected by the other switches as the root bridge.

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Spanning Tree Protocol

Based on the location of the root bridge, the other switches determine which of their ports has the lowest path cost to the root bridge. These ports are called root ports, and each switch (other than the current root bridge) must have one. The switches determine who will have designated ports.

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Spanning Tree ProtocolA designated port is the connection used to send and receive packets on a specific segment. By having only one designated port per segment, all looping issues are resolved.Once the designated port for a network segment has been chosen, any other ports that connect to that segment become non-designated ports. They block network traffic from taking that path so it can only access that segment through the designated port.

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Routers & Gateways

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Routers

Routers operate at the network layer. Routers connect two or more LANs that use the same or different data link protocols, but the same network protocol. Routers may be “black boxes,” computers with several NICs, or special network modules in computers.In general they perform more processing on each message than bridges and therefore operate more slowly.

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Routers

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Routers

Segments LANs into distinct networks and subnetworks;

e.g. the distinct red, green and blue LANs with distinct network numbers.

Segments LANs into broadcast domains

3rd floor

2nd floor

1st floor

Ethernet switch

router

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Routers

Provides interface to the WAN.

Intranet, commercial Internet and Internet2 connections.WAN

Campus Backbone

intranet Internet2intranetInternet2Commercial

Internet

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Routers vs Bridges

Routers can choose the best route.Routers also only process messages specifically addressed to it.Routers can connect networks using different data link layer protocols. Therefore, routers are able to change data link layer packets.Routers may split a message into several smaller messages for transmission.

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Switches vs. RoutersBoth store-and-forward devices

routers: network layer devices (examine network layer headers)switches are link layer devices

Routers maintain routing tables, implement routing algorithmsSwitches maintain switch tables, implement filtering, learning algorithms

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LAN: Switches vs. Repeaters

Repeaters (hubs) are old technology.A repeater sends (repeats) packets that are incoming on one port, out all other ports (I know you’re out there somewhere!). Can only operate in half duplex mode.Bandwidth and jitter provided to any single device is highly dependent on the LAN traffic.

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LAN: Switches vs. Repeaters

A switch learns the MAC addresses of the devices connected to it, and sends packets directly and only to the target end-point.Provides much more consistent bandwidth and latency (low jitter).A well-designed switched LAN is important for videoconferencing. Repeater-based LANs should be upgraded to switched for videoconferencing!

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Campus LAN example

hub

hub hub

switch

to externalnetwork

router

IP subnet

mail server

web server

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Gateways

Gateways operate at the network layer and use network layer addresses in processing messages.Gateways connect two or more LANs that use the same or different (usually different) data link and network protocols. The may connect the same or different kinds of cable.Gateways process only those messages explicitly addressed to them.

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GatewaysGateways translate one network protocol into another, translate data formats, and open sessions between application programs, thus overcoming both hardware and software incompatibilities.A gateway may be a stand-alone microcomputer with several NICs and special software, a FEP connected to a mainframe computer, or even a special circuit card in the network server.

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Gateways

One of the most common uses of gateways is to enable LANs that use TCP/IP and ethernet to communicate with IBM mainframes that use SNA.The gateway provides both the basic system interconnection and the necessary translation between the protocols in both directions.

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Gateways

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Backbone Architecture

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Backbone Architecture Layers

Network designs are made up of three technology layers:

The access layer which is the technology used in LANsThe distribution layer connects LANs togetherThe core layer connects different backbone networks together

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Backbone network design layers

LAN

LAN

LAN

LAN

LAN

LAN

Access LayerDistributionLayerCore Layer

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Routed Backbones

Routed backbones move packets using network layer addressesEach LAN is a separate and isolated network.LANs can use different data link layer protocols.Main advantage:

LAN segmentation.Main disadvantages:

Routers introduce more delay and require more mgmt. compared to bridging/ switching

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Routed Backbones

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Bridged Backbones

Forwards the packet based on their data link layer addresses. The entire bridged backbone falls under one subnet.Bridged backbones are cheaperPerformance

performs well For small networksfor large networks broadcast messages lower performance.

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Bridged Backbones

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Collapsed Backbones

Collapsed backbones use a star topologyThe backbone has fewer devices. Advantages are:

simultaneous access and much higher performance a simpler & more easily managed network.

Disadvantages are:use more cableif the central switch fails, the network goes down.

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Collapsed Backbones

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Rack-based Collapsed Backbones

Rack-based backbones collapse the into a single room using

Main Distribution Facility (MDF) Devices are connected using short patch cables.Moving computers between LANs is relatively simple

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Rack-based Collapsed Backbones

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Chassis-based Collapsed Backbones

Uses a large chassis switch that has slots into which modules can be inserted.Chassis switch designs include a number of open slots and have an internal capacity capable of supporting all active modules.

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Chassis-based Collapsed Backbones

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Ethernet Technology

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Background of Ethernet (First LAN)

Digital, Intel & Xerox (DIX) consortium created original Ethernet 1980 (originally known as Alto Aloha Network)The first network to provide Carrier Sense Multiple Access / Collision Detection (CSMA/CD)Ethernet_II to followed in 1984 (ver-2)IEEE termed this as 802 project

Initially IEEE 802 Project divided into three groups

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High level interface (HILI) became 802.1 committee

Responsible for High level interworking protocols and management

LLC group became 802.2 committee, for end to end link connectivity between higher layer and media access dependent layers

DL & MAC (DLMAC) group became responsible medium access protocols

DL MAC has been split into three sub committees

Initial IEEE 802 Project

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802.3 for Ethernet Came of with Ethernet physical layer spec. MAC addressing is same as Ethernet_II but length field replaced type filed Bus topology LAN at 10 Mbps with collision detection (CSMA/CD)

10base 2/ thinnet – 185 meters segment without repeater over RG58 coaxial cable at 50 ohms 10base 5/ thicknet – 500 meters segment without repeater over RG8/11 coaxial cable at 50 ohms10base T/UTP – cat 3 UTP(Unshielded Twisted Pair) to support 10 Mbps

DL MAC committees – 802.3

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802.4 for Token BusBurroughs, concord data systems, Honeywell, western digital, general motors & Boeing took over 802.4802.5 for Token RingIBM worked on 802.5

DL MAC committees – 802.4/802.5

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Ethernet Standards (802.3)

Ethernet (10 Mbps)Ethernet_II - (DIX- Ethernet)IEEE 802.3 - Ethernet

Fast Ethernet (100 Mbps)IEEE 802.12 - 100VG AnyLANIEEE 802.3u - Fast Ethernet

Gigabit Ethernet (1000 Mbps or 1 Gbps)

IEEE 802.3z - Gigabit EthernetIEEE 802.ab - Gigabit Ethernet

10 Gigabit Ethernet (10 Gbps)IEEE 802.3ae - 10 Gigabit Ethernet

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Ethernet_II

Upper Layers

Network

Ethernet_II

Other LayersNetworkData LinkPhysical

OSI model

Media Access Control(MAC)

DIX-Ethernet Layers

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Ethernet Frame Structure

Sending Network Adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble: 7 bytes with pattern 10101010 followed by one byte with pattern 10101011 Used to synchronize receiver, sender clock rates

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Ethernet Frame Structure

Addresses:matching destination address or broadcast address are passed to network-layer protocolrest discardedType: indicates the higher layer protocol CRC: checked at receiver, if error is detected, the frame is simply dropped

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Ethernet CSMA/CD algorithm

Adaptor receives datagram from Layer3 & creates frameIf adapter senses channel idle, it starts to transmit frame. If it senses channel busy, waits until channel idle and then transmitsIf adapter transmits entire frame without detecting another transmission, the adapter is done with frame !

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Ethernet CSMA/CD algorithmIf adapter detects another transmission while transmitting, aborts and sends jam signalAfter aborting, adapter enters exponential backoff after mth collision

first collision: choose K from {0,1} i.e.{0, 22-1}; delay is K x 512 bit transmission timesafter second collision: choose K from {0,1,2,3}…ie. {0,1,..22-1}after ten collisions, choose K from {0,1,2,3,4,…,1023}I.e. {0,1,..210-1}

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Ethernet_II- Frame

8B 6B 6B 2B 46~1500B 4B

SOURCEHARDWAREADDRESS

CRCLAYER 3 DATATYPE

DESTINATIONHARDWAREADDRESS

PREAMBLE

64~1518B72~1526B

Eg. Of Type Fields: 0800- IP 0806- ARP 8035- RARP

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Ethernet_II Frame - DetailsPreamble: 8 bytes of alternating 0s and 1s to synchronise the receiverDestination Address (DA): 6 bytes (48 bits) unique physical address of destination machine encoded in NICSource Address (SA): 6 bytes (48 bits) unique physical address of source machine encoded in NICType : 2 bytes (16 bits) indicates the type of Layer 3 protocol being used Eg. IP, ARP or RARP (uses RFC 1700 Ethernet Type Values)Layer 3 Data: Between 46-1500 bytesCRC : 4 bytes (32 bits) for error detection information

Page 102: LAN Technology

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MAC Address structure (for all Ethernet)

Destination address : (LS Bit first and MS bit Last in each byte - Little-Endian style) I/G Individual / group address:

0 - Individual address.1 - Group address.

U/L Universal /local address:0 - Universally administered.1- Locally administered.

Source address (LS Bit first and MS bit Last in each byte - Little-Endian style)

I/G bit is always 0. U/L Universal/local address may be 0/1

U/L I/G

Organisationally Unique Identifier (OUI)

(3 bytes)

LSB MSB LSB MSB LSB MSB LSB MSB LSB MSB LSB MSB

Vendor Assingned No. (Serial No.)

(3 bytes)

Most Significant Byte Least Significant Byte

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CSMA/CDEthernet Uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) as access methodAny station wishing to transmit must listen for Carrier on the lineIf no carrier is detected, the line is idle and transmission can be initiated Two or more stations transmits at the same time, when there was no carrier, results in collision which is indicated by high voltage on the line After collision retry is done at staggered time by different devicesCSMA/CD reduces the number of collision but does not eliminate them

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Category 3 – (Cat 3)for speed 10 MbpsCategory 4 – (Cat 4) for speed 16 MbpsCategory 5 – Cat 5) for speed 100 MbpsCategory 6 – (Cat 6) for speed 1Gbps

also known as Category 5ECategory 7 – Cat 7) for speed 10 Gbps

Cabling Spec. for UTP Standard

Page 105: LAN Technology

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IEEE Project 802

IEEE Project 802 sets standard to enable interworking between devices of various vendors.

Logical Link Control (LLC) sub-layer has been added to achieve the above objective

Other LayersNetwork

IEEE Project 802

Other LayersNetworkData LinkPhysical

OSI model

Logical Link ControlMedia Access Control

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Initial IEEE Project 802

Other LayersNetwork

IEEE Project 802

802.2 - Logical Link Control802.4

Token Bus802.5

Token RingANSIFDDI

802.3CSMA/CD

• IEEE 802.2 LLC deals with logical address, control information and data

• MAC sub layer resolves contention for shared media

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802.3 MAC Frame/802.2 LLC without SNAP

802.2 LLC LAYER ENCAPSULATION DATA

43~1497B3B

7B 1B 6B 6B 2B 46~1500B 4B

SOURCEHARDWAREADDRESS

CRC802.2 PDULENGTH

DESTINATION

HARDWAREADDRESS

SFD

PREAMBLE

64~1518B72~1526B

DSAP SSAP Control1B 1B 1–2 B

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802.3 MAC FramePreamble

7 bytes of alternating 0s and 1s that alert the receiving system and enable it to synchronise its input timing

Start Frame Delimiter (SFD)I byte (10101011) signals the beginning of the frame

Destination Address (DA)6 bytes (48 bits) unique physical address of destination machine encoded in NIC

Source Address (SA)6 bytes (48 bits) unique physical address of source machine encoded in NIC

Page 109: LAN Technology

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802.3 MAC Frame

Length (2 bytes)Indicate number of bytes in the frame

802.2 PDUUpper layer information between 46-1500 bytes

CRC (4 bytes)for error detection information

Page 110: LAN Technology

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802.2 LLC Header

DSAP:Destination service access point structure I/G - Individual/group address

0 - Individual DSAP.1 - Group DSAP.

SSAP:Source service access point structure C/R - Command/response:

0 - Command.1 - Response.

Control: The structure of the control field is same as HDLC . For IP Network value is (03)

DSAP SSAP ControlI/G C/R

802.2 LLC Header

Page 111: LAN Technology

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802.3 MAC Frame/802.2 LLC with SNAP

802.2 LLC / SNAP ENCAPSULATION DATA

38~1492B8B

7B 1B 6B 6B 2B 46~1500B 4B

SOURCEHARDWAREADDRESS

CRC802.2 PDULENGTH

DESTINATION

HARDWAREADDRESS

SFD

PREAMBLE

64~1518B72~1526B

DSAP SSAP Control1B 1B 1–2 B

OUI Ether Type

SNAP5B

2B3B

OUI- Organisationally Unique IdentifierSNAP- Sub Network Access Point

Page 112: LAN Technology

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Ethernet Encapsulations Methods

On Ethernet you have four encapsulation formats:

Ethernet version II Novell-specific framing Ethernet 802.3/802.2 without SNAP Ethernet 802.3/802.2 with SNAP Ethernet 802.3/802.2 with SNAP

Page 113: LAN Technology

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Ethernet Encapsulations Methods

Ethernet 802.3/802.2 uses the type field to determine the packet protocol. 802.3/802.2 use the DSAP and SSAP fields.Because there are only 256 possible SAP values, they are fairly hard to get. The special SAP number of AA was assigned to indicate that there are further headers after the 802.2 header that must be seen to determine the network-level protocol.

Page 114: LAN Technology

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Ethernet Encapsulations Methods

This is the SNAP (Sub Network Access point) header that uses the same type field used by Ethernet_II.IP on an Ethernet can be indicated by

Ethernet V2 type 0x0800;802.2 SAP code 0x06;or a SAP code of 0xAA followed by a SNAP type code of 0x0800.

AppleTalk can be indicated by either Ethernet V2 type 0x809B (Phase I), or a SAP code of 0xAA followed by a SNAP type code of 0x809B (Phase II).

AppleTalk is currently never sent as an 802.3/802.2 packet with a unique SAP code.

Page 115: LAN Technology

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Ethernet Encapsulations MethodsNovell can be found as either

Ethernet type 0x8137, or a raw 802.3 packet. It is not sent as an 802.3/802.2 packet with a unique SAP code (0xE0).

There are only a few SAP values that you are likely to run across. They are:

04 - IBM SNA 06 - IP 80 - 3Com AA - SNAP BC - Banyan E0 - Novell (TR)

Page 116: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 116

Ethernet (Cabling Spec.)

Three main Cabling specifications are available in Ethernet:10 Base 5

Uses Thick co-axial Cable10 Base 2

Uses Thin Coaxial Cable10 Base T

Uses Unshielded Twisted pair cable

Page 117: LAN Technology

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10Base5; Thick Ethernet; Thicknet

The nickname derives from the size of the cableEach station on Ethernet network has its own Network Interface Card (NIC) which provides the station with a unique 6 bytes physical addressEach frame is transmitted to every station on the link but will be read only by the station to which it is addressedTransceiver performs the CSMA/CD for checking voltages and collisions on the line

Page 118: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 118

10Base5; Thick Ethernet; Thicknet

5 Segments; 2500 M; 1000 Stations

R RSegment 1 Segment

1500 M; 200

Stations

2.5 M

50 M

1-NIC(Network Interface Card)

1

2-RG-8 Thick Coaxial Cable

2

3-Cable Terminator

3

5-Attachment Unit Interface (AUI);Transceiver Cable (15 Wires)

5

6-Media Attachment unit (MAU);commonly known as Transceiver

6

4

4-Transceiver Vampire Tap

Page 119: LAN Technology

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10Base2; Thin Ethernet; ThinnetAlso known as cheapnet or cheapernetProvides same data rate as 10Base5 but with distance limitation of 185 meters and lesser number of work stationsTransceiver circuitry has moved into the NICTransceiver tap has been replaced by a connector that splices the station directly into the cableBNC-T connector is with 3 ports; one for NIC, one each for input and output ends of the cable

Page 120: LAN Technology

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10Base2; Thin Ethernet; Thinnet

185 M

2-RG-58 Thin Coaxial Cable

2

4

4-Cable Terminator1-NIC(Network Interface Card)

1

3-BNC-T Connector

3

Page 121: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 121

10BaseT

A star topology LANAll individual transceiver functions and networking operations are placed in an intelligent hub with a port for each stationHub fans out any transmitted frame to all its connected stationsFrame will be read by all, but will only be processed by the station to which it is addressed

Page 122: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 122

Manchester encoding

Used in 10BaseTEach bit has a transitionAllows clocks in sending and receiving nodes to synchronize to each other

Page 123: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 123

10BaseT

100 M

10Base-T Hub

100 M

1-10 Base-T Hub

1

2-RJ-45 Connector Male

2 5

5-RJ-45; Four Pairs UTP (Unshielded Twisted Pair) Cable4-Network Interface Card

4

3-RJ-45 Connector Female

3

Page 124: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 124

Fast Ethernet Standards

Two standards are approved by IEEE in June 1995

802.12 802.3u

Page 125: LAN Technology

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Fast Ethernet Standards- 802.12/802.3u

802.12 Uses even efficient signaling techniques than CSMA/CD known as Demand Priority Access Method (DPAM) Also known as 100VG-AnyLANis similar to the other standard however utilizes a different type of Ethernet frame to send its data. Not popular and eventually disappeared from the market

802.3u Most popular spec. in 100Mbps over cat 5 UTP or cat 5 plus

Page 126: LAN Technology

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Need for Media Independent Interface (MII)

Fast Ethernet requires faster interface than 10 Mbps Ethernet 10 Mbps Ethernet uses Attachment Unit Interface (AUI) to connect Ethernet segment MAC is to remain constant for any physical layer technologiesAUI cannot support 100 Mbps Ethernet because of high frequencies( AUI Uses 2.5 MHz clock in Ethernet- 10 Mbps) 100 base T needed new interface- media Independent Interface (MII)

Page 127: LAN Technology

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Media Independent Interface (MII)

100 base T created new Sub interface between physical/data link layer called reconciliation sub layer (RS) RS maps is 1s and 0s to MII. MII transfers one nibble which is 4 bits MII has 25MHz clock and and one nibble (4 bits) are transferred to Physical Layer every clock cycle

Page 128: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 128

Fast Ethernet MII/Physical Layers

Page 129: LAN Technology

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100 Base T (Cabling Spec.)

100Base-T is available in three different types of cable technologies:

100Base-T4 = Utilizes four pairs of telephone-grade twisted-pair wire and is used for networks that need a low quality twisted-pair on a 100-Mbps Ethernet100Base-TX = Developed by ANSI 100Base-TX is also known as 100Base-X, 100Base-TX uses two wire data grade twisted-pair wire100Base-FX = Developed by ANSI, 100Base-FX utilizes 2 stands of fiber cable

Page 130: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 130

Fast Ethernet

100 Base-TXUses 2 pairs (1 pair towards hub and other pair from hub) of CAT-5 UTP or STPEncoding used is 4B/5BDistance between hub & station be < 100 M

100 Base-FXUses 2 optical Fibers (1 fibre towards hub and other fibre from hub) Encoding used is 4B/5BDistance between hub & station be < 2000 M

Page 131: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 131

Fast Ethernet

100 Base-T4Makes use of already exiting telephone cablesUses 4 pairs of voice grade UTP CAT-32 pairs are bi-directional and the other 2 are uni-directionalAt a time 3 pairs are used to carry data in each direction at a data rate of 33.33 Mbps i.e. 2 pairs carry data bi-directionallyEncoding used is 8B/6T (8Binary/6Ternary)Distance between hub & station be < 100 M

Page 132: LAN Technology

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Auto Negotiation in Fast Ethernet

Auto negotiatiation uses a priority scheme to decide more preferred option for 100/10 Mbps Ethernet Lower the functioning value more the preferred one Auto negotiatiation uses fast link pulses (FLPs) for negotiatiationLowest functioning option is chosenAuto negotiation may fail sometimesImportant connection are configured manually

Page 133: LAN Technology

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Auto Negotiation Priorities

Standard full/half Auto negotiation priority

100 base T2 full 1100 base T2 half 2100 base Tx full 3100 base Tx half 4100 base T4 half 510 base T full 610 base T half 7

Page 134: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 134

10BaseT and 100BaseT10/100 Mbps rate; latter called “fast ethernet”‘T’ stands for Twisted PairNodes connect to a hub: “star topology”; 100 m max distance between nodes and hub

twisted pair

hub

Page 135: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 135

Gigabit Eth MAC/Phy Layer

1000 base T created new Sub interface between physical/data link layer known as GMII ( Gigabit Media Independent Interface). GMII transfers one byte (8 bits) at a time to physical layer GMII has 125MHz clock and and one byte (8 bits) is transferred to Physical Layer every clock cycle

Page 136: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 136

Gigabit Ethernet MAC/Phy Layer

Page 137: LAN Technology

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Gigabit Ethernet

4 implements have been designed:1000 Base-LX1000 Base-SX1000 Base-CX1000 Base-T

FEATURE 1000Base-LX 1000Base-SX 1000Base-CX

1000Base-T

MEDIUMOptical Fiber(Multi mode;Single mode)

Optical Fiber(Multi mode) STP UTP

SIGNAL Long-Wave Laser

Short-Wave Laser Electrical Electrical

MAXIMUM

DISTANCE

550 MetersMulti mode;5000 MetersSingle mode

550 Meters 25M 25M

Page 138: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 138

Ethernet Cabling Spec for UTP

Page 139: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 139

IEEE 802.4 (Token Bus)

Combines physical configuration of Ethernet (a bus topology) and the collision free feature of Token RingToken bus is a physical bus that operates as logical ring using tokens (Round Robin)

T

Page 140: LAN Technology

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IEEE 802.5 (Token Ring)Each transmits only one frame during its turnAccess method is token passingStation keeps the token and sends the frame in the ring Each station in the ring regenerates the frameThe intended recipient copies the frame and send the frame back to senderThe sender receives the frame back, discards the frame and releases the token for others

Page 141: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 141

Ring Topology & Token Ring Hub

Page 142: LAN Technology

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Token Ring Media Access Control

Token ring uses a controlled-access technique called token passing.The “token” is a series of bits, travels between the computers in a predetermined sequence. A computer with a message waits to transmit until it receives a free token. The computer changes the free token to a busy token and attaches its message to it. Then it retransmits it on the circuit to the next computer in the sequence. The computer receiving the message, changes the acknowledgement to ACK (or NAK) and sends the message back to the sender, who creates a new free token.

Page 143: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 143

Token Ring Media Access Control

Page 144: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 144

Token Ring Media Access Control

Page 145: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 145

Token Ring Media Access Control

Token loss:The token crashes before being transmitted - lost a free token A computer in the ring crashes - lost a busy tokenA token is always busy.

A solution for the “lost” token problem: Designate one computer to be the token monitor and another computer to be a backup token monitor. If no token circulated through the network for a certain length of time or if a busy token circulates too often, the token monitor will create a new free token (and destroy the busy token if necessary.)

Page 146: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 146

IEEE 802.5 (Token Ring)

TT T

T T

Page 147: LAN Technology

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FDDIFiber Distributed Data Interface, standardised by ANSI and the ITU-THigh speed alternative to Ethernet and Token RingCopper version of FDDI is known as CDDIUses Token passing as access methodImplemented in dual ringIn most cases, data transmission is confined to the primary ringThe secondary ring is provided in case the primary ring fails

Page 148: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 148

MAC Address structure- Token Ring/FDDI

I/G U/L

Organisationally Unique Identifier (OUI)

(3 bytes)

MSB LSB MSB LSB MSB LSB MSB LSB MSB LSB MSB LSB

Vendor Assingned No. (Serial No.)

(3 bytes)

Most Significant Byte Least Significant Byte

Destination address (LS Bit first and MS bit Lastin each byte - Big-Endian style) I/G Individual / group address

0 - Individual address.1 - Group address.

U/L Universal /local address0 - Universally administered.1- Locally administered.

Source address (LS Bit first and MS bit Last in each byte - Big-Endian style)

I/G bit is always 0. U/L Universal/local address may be 0/1

Page 149: LAN Technology

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FDDI-Self Healing Ring

Primary Ring

Secondary Ring

Fault

Page 150: LAN Technology

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Fiber Distributed Data Interface

Fiber Distributed Data Interface (FDDI) is a set of standards originally designed in the late 1980s, but has since made its way into backbone networks.

FDDI is a token-passing ring network that operates at 100 Mbps over two-counter-rotating fiber optic cable rings.

Page 151: LAN Technology

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Topology

The FDDI standard assumes a maximum of 1000 stations and a 200-kilometers (120 miles) path that requires a repeater every 2-kilometers. The second ring is for backup.Single attachment stations (SAS) and dual-attachment stations (DAS) are both computer that can connect to one or both of the rings, respectively.If the cable in the FDDI ring is broken, the ring can still operate in a limited fashion.

Page 152: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 152

Topology

Page 153: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 153

Topology

Page 154: LAN Technology

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Media Access Control

The FDDI-MAC scheme uses a variation of the IEEE 802.5 token-passing standard.

Messages and the token are sent in different frames separately in a FDDI LAN. A computer can send data only when it captures the token. When a computer on an FDDI network waiting for transmission receives the token, it holds the token and then transmits all messages that were attached to it. The computer then transmits whatever messages its wants before transmitting the token. When receiver receives the data frame it simply copy the data frame leaving it to be absorbed by the sender.

Page 155: LAN Technology

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Fiber Distributed Data Interface

FDDI (standardized as ANSI X3T9.5) backbone protocol was developed in the 1980s and popular during the 80s and 90s.FDDI operates at 100 Mbps over a fiber optic cable. Copper Distributed Data Interface (CDDI) is a related protocol using cat 5 twisted wire pairs.FDDI’s future looks limited, as it is now losing market share to Gigabit Ethernet and ATM.

Page 156: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 156

FDDI Topology (Figure 7-15)FDDI uses both a physical and logical ring topology capable of attaching a maximum of 1000 stations over a maximum path of 200 km. A repeater is need every 2 km.FDDI uses dual counter-rotating rings (called the primary and secondary). Data normally travels on the primary ring.Stations can be attached to the primary ring as single attachment stations (SAS) or both rings as dual attachment stations (DAS).

Page 157: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 157Figure 7-15 FDDI Topology

Page 158: LAN Technology

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FDDI’s Self Healing Rings

One important feature of FDDI is its ability to handle a break in the ring to form a temporary ring out of the pieces of the two rings.Figure 7-16, show an example of a cable break between two dual-attachment stations. After the cable break is detected, a single ring is formed out of the primary and secondary rings until the cable break can be repaired.

Page 159: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 159Figure 7-16 FDDI’s Self-healing Rings

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ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 160

Page 161: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 161

Gigabit Ethernet

Still under developmentRetains CSMA/CD protocol and Ethernet format, ensuring smooth upgrade pathUses optical fiber over short distances1-Gbps switching hub provides backbone connectivityMay not be good for LAN (explain why) and has been used in backbone networks for point-to-point connections.

Page 162: LAN Technology

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Gigabit Ethernet

1000BASE-LX: Long-wavelength, supports up to 550m (m-mode fiber) or 5km (single-mode fiber)1000BASE-SX: Short-wavelength, supports up to 275 - 550 m(m-mode fiber)1000BASE-CX: uses copper jumpers in a single room or equipment rack1000BASE-T: uses 4 pairs of Cat-5 UTP

Page 163: LAN Technology

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Gigabit Ethernet Media Options

Page 164: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 164

Fast Ethernet Backbone

Page 165: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 165

Fibre Channel

combine the best features of channel and protocol-based technologies

the simplicity and speed of channel communicationsthe flexibility and inter-connectivity that characterize protocol-based network communications.

more like a traditional circuit-switched or packet-switched network, in contrast to the typical shared-medium LAN

Page 166: LAN Technology

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Fiber Channel Network

N_portF_port

Page 167: LAN Technology

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Fibre Channel Elements

NodesThe end systemsIncludes one or more N_ ports for interconnection

FabricCollection of switching elements between systemsEach element includes multiple F_ portsResponsible for buffering and for routing frames between source and destination nodes

Page 168: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 168

Fibre Channel Goals

Full-duplex links with two fibers per linkPerformance from 100 Mbps to 800 Mbps on a single link (200 Mbps to1600 Mbps per link)Support for distances up to 10 kmSmall connectorsHigh-capacity utilization with distance insensitivity

Greater connectivity than existing multidrop channelsBroad availability (i.e., standard components)Support for multiple cost/performance levels, from small systems to supercomputersAbility to carry multiple existing interface command sets for existing channel and network protocols

Page 169: LAN Technology

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*Fibre ChannelProtocol Architecture

FC-0 Physical Media: Includes optical fiber, coaxial cable, and shielded twisted pair, based on distance requirementsFC-1 Transmission Protocol: Defines the signal encoding schemeFC-2 Framing Protocol: Defines topologies, frame format, flow/error control, and grouping of framesFC-3 Common Services: Includes multicastingFC-4 Mapping: Defines the mapping of various channel and network protocols to Fibre Channel

Page 170: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 170

Fibre Channel - Maximum Distance

800Mbps 400Mbps 200Mbps 100Mbps

SingleMode 10,000m 10,000m 10,000m 10,000m

M-mode 500m 1,000m 2,000m --

CoaxialCable 50m 71m 100m 100m

STP 28m 46m 57m 80m

Page 171: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 171

Present IEEE 802 Project Working Groups

802.1 Higher Layer LAN Protocols Working Group 802.2 Logical Link Control Working Group802.3 Ethernet Working Group802.4 Token Bus Working Group802.5 Token Ring Working Group802.6 Metropolitan Area Network Working Group 802.7 Broadband TAG802.8 Fiber Optic TAG802.9 Isochronous LAN Working Group802.10 Security Working Group

• 802.11 Wireless LAN Working Group

• 802.12 Demand Priority Working Group

• 802.14 Cable Modem Working Group

• 802.15 Wireless Personal Area Network (WPAN) Working Group

• 802.16 Broadband Wireless Access Working Group

• 802.17 Resilient Packet Ring Working Group

Page 172: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 172

Virtual LAN (VLAN)

Virtual Local Area Networks (VLANs) are a collection of nodes that are grouped together in a single broadcast domain that is based on something other than physical location. A broadcast domain is a network (or portion of a network) that will receive a broadcast packet from any node located within that network.In a typical network, everything on the same side of the router is all part of the same broadcast domain. A switch, with the implemented VLANs on, has multiple broadcast domains, similar to a router. However, a router is still needed (or Layer 3 Switch) to route from one VLAN to another -- the switch can't do this by itself.

Page 173: LAN Technology

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Virtual LAN (VLAN)

VLANs can be created simply by logging into the switch via TELNET and then entering the parameters for the VLAN (name, domain and port assignments).Once the VLAN is created, any network segments connected to the assigned ports will become part of that VLAN. While you can have more than one VLAN on a switch, they cannot communicate directly with one another on that switch. Communication between VLANs requires the use of a router. VLANs can span multiple switches, and you can have more than one VLAN on each switch.

Page 174: LAN Technology

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VLAN Trunking Protocol

VLAN trunking protocol (VTP) is the protocol that switches use to communicate among themselves about VLAN configuration

Page 175: LAN Technology

ALTTC/ DX Faculty/ KSK/ LAN Technology/ Nov 2004 175

VLAN Trunking ProtocolIn the example:Each switch has two VLANs. On the first switch, VLAN A and VLAN B are sent through a single port (trunked) to the router and through another port to the second switch. VLAN C and VLAN D are trunked from the second switch to the first switch, and through the first switch to the router. This trunk can carry traffic from all four VLANs. The trunk link from the first switch to the router can also carry all four VLANs. In that case, this one connection to the router allows the router to appear on all four VLANsThe VLANs can communicate with each other via the trunking connection between the two switches using the router. For example, data from a computer on VLAN A that needs to get to a computer on VLAN B (or VLAN C or VLAN D) must travel from the switch to the router and back again to the switch.