Chapter6 - LAN Hardware

Chapter 6-Local Area Network Hardware

1

Necessary to connect LAN to LAN or WAN

LAN to LAN connections are often performed with bridge-like device.

LAN to WAN connections are usually performed with router.

Third device, switch, can be used to interconnect segments of LAN.

Introduction


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Local Area Network Hardware

Focus on hardware technologyTransition from shared media network architectures to hardware based switched network architectures


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To connect one division with another.

To connect two LANs with different protocols.

To connect LAN to Internet.

To break LAN into segments to relieve traffic congestion.

To provide security between different users.

Why Interconnect


4

LAN Requirements

LAN requires following components Central wiring concentrator (Hub) Media - cable or wireless NIC - internal or external Other – switch, repeater, etc.

NIC drivers - programs that interface between NIC and NOS.


5

Network interface card driver software bridges the hardware/software gap between the Network Interface Card (NIC) and the installed Network Operating System (NOS)

SERVER

WIRING CENTER of some type -

CLIENT PC

media

hub MAU LAN switch

Logical Diagram

NIC (network interface card)

NIC (network interface card)

NIC driver software

Network Operating System

GOLDMAN & RAWLES: ADC3e FIG. 06-01

LAN Architecture


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Implications of LAN Technology Choices

Choosing particular technology in one LAN technology category has significant implications/limitations on available technology choices in other LAN technology categories


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Architecture choices - Peer-to-Peer vs. Client/Server

Server Function choices

Network Operating System choices Network Operating System choices

Adapter Card Driver choices

Adapter Card Driver choices

Operating System choices

Operating System choices

Access Methodology choices

Logical and Physical Topology choices

Network Architecture choices

Wiring System choices

Wiring Center choices

Network Adapter Card choices

CPU choices

Media choices

BUS Type choices

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Representative Server PC Representative Client PC

Wiring System choices

Media choices Network Adapter

Card choicesCPU

choices

BUS Type choices


Implications of LAN Technology Choices


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Media Sharing vs. Switched

Client/server systems and distributed computing has put increasing demands on LAN infrastructure with demands for amount of data traffic to be transferred One solution to bandwidth problem is to offer higher speed shared media network architectures


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Media Sharing vs. Switched cont’d

LAN switches resolve one at time limitation of shared-media LAN architectures by offering attached workstations access to switching matrix that provided point-to-point connections between any two ports.Each port on LAN switch is dedicated LAN segment with dedicated bandwidth


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Media Sharing vs. Switched cont’d

Limiting factor in switch-based LAN architecture is number of simultaneous point-to-point connections that switch can support.Coming slide contrasts differences in wiring center functionality between media sharing and switch based LAN architecture.


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serversclient workstations

Shared Media Hubshared, single 10Mbps LAN

segment

only one 10Mbps connection at a

time

Shared Media LAN Architecture

10 Mbps

"10 Mbps for ALL"

Switching Hubmultiple dedicated

10Mbps LAN segments

Workgroup with shared connection

Workgroup with shared connection

servers with dedicated connections

shared media hub

shared media hub

Workstations with dedicated connections

Multiple, simultaneous

10Mbps connections

All connections at 10Mbps

switching matrix

Switch-Based LAN Architecture

"10 Mbps for EACH"


Switched LAN Architectures vs. Media-Sharing LAN Architectures Wiring Center

Functionality


12GOLDMAN & RAWLES: ADC 3e FIG: 06-04

LAN Switch

1 Gigabit per second network

LAN Switch

LAN Switch

10 Mbps network10 Mbps network

100 Mbps network

Servers

workstations

workstations

Building Bandwidth Hierarchy with Switched LAN Architecture


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Workstation Connected to LAN


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ADVANTAGES of SWITCHED LAN

ARCHITECTURES

Switched LAN architecture only change wiring center technology and manner in which workstations set up point to point communication to each other.Installing LAN switch is often easiest alternative chosen when network bandwidth demands exceed current supply.


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Implementation Scenarios for Switched LAN

Architectures

Stand-alone workgroup/departmental LAN switches Backbone attached workgroup/departmental LAN switches Backbone/data center switches Switches offer switched connectivity to

other workgroup switches, media sharing hubs, and corporate servers that must be accessed by multiple departments/groups


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GOLDMAN & RAWLES: ADC 3e FIG: 06-05

shared media hub

Stand-Alone Workgroup/Departmental LAN Switches

Dedicated switched connections for all clients and servers.

Dedicated switched connections for servers, shared switched connections for clients.

Standard Server front-end variation

LAN Switch

Backbone-Attached Workgroup/Departmental LAN Switches

100Mbps backbone connection to backbone network.

10Mbps local switched connections

Backbone/Data Center Switches

Corporate shared servers

Corporate backbone network

Backbone/data center switch

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Backbone attached workgroup/departmental LAN switches with locally attached clients and servers.

LAN Switch

LAN Switch

shared media hub

Implementation Scenarios for Switched LAN Architectures


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Network Interface Card

NIC - Physical link between client and server PC and media of network NIC have ability to adhere to access methodology (CSMA/CD or token passing) of network architectureSoftware rules, implemented by NIC, control access to shared network media and are known as media access control (MAC) protocols


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Network Interface Card, cont’d

NIC cards determine network architecture and constituent protocols more than any other componentNIC act like mediator or translator Has demands of client/server PC Has network architecture with rules

for accessing network media or LAN switch.


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Technology Analysis

Bus into which network adapter card allows different types of cards to be attached in pathway leading to CPU and RAM memory.PCI bus offers clocking signaling and low CPU utilization and seems to be bus of choice for high performance NICs.


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Technology Analysis, cont’d

Important choice related to bus architecture is that network adapter card chosen is compatible with installed bus and takes advantage of data transfer capability bus may offer.Key job of NIC is to transfer data between local PC and shared network media.


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Hardware related network adapter characteristics that bare on data transfer efficiency are Amount of on board memory Processing power of onboard CPU

contained on network adapter card


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Coming figure summarizes NIC to PC memory data transfer techniques.Techniques are: Programmed I/O Direct Memory Access (DMA) Shared memory Bus mastering DMA


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CPU

RAM

RAMCPU

network interface card

Motherboard

BUS

Shared I/O address

NIC connector

network media (cable)

Programmed I/OSteps

Data enters network interface card through the network media and connector. Adapter card CPU loads network data into a specific I/O address on the motherboard. Main CPU checks I/O area for data If data exists, it is transferred to main memory, RAM, by main CPU.

Keynote The motherboard's CPU has the ultimate responsibility of data transfer into RAM.

1. 2. 3. 4.

CPU

RAM

CPU


Motherboard

BUS

NIC connector


DMA (Direct Memory Access)Steps

Data enters network interface card through the network media and connector. Adapter card CPU interrupts the motherboard CPU. Main CPU stops other processing and transfers the data to RAM.


1. 2. 3.

CPU

RAM

RAMCPU


Motherboard

BUS

NIC connector


Shared MemorySteps

Data enters network interface card through the network media and connector. Adapter card CPU stores data on its RAM. Adapter card CPU interrupts the motherboard CPU. Main CPU stops other processing and transfers data into RAM.


1. 2. 3. 4.

RAM

RAMCPU


Motherboard

BUS

NIC connector


Bus Mastering DMASteps

Data enters network interface card through the network media and connector. Adapter card CPU temporarily stores data on its RAM. Adapter card CPU sends data directly to motherboard RAM when network transmission completes (it does NOT interrupt the main CPU.)

Keynote The adapter card's CPU has the ultimate responsibility of data transfer into RAM.

1. 2. 3.

1

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1

1

1

2

2

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Network Interface Cards Data Transfer Methods


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Only bus mastering DMA data transfer technique leaves system CPU alone to process other applicationsIn bus mastering DMA, CPU on network adapter card manages movement of data directly into PC’s RAM without interrupting system CPU by taking control of PC’s expansion bus


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Bus mastering DMA on adapter cards requires expansion bus in PC to support being “mastered” by CPU on network adapter card.CPU and operating system must have capability to relinquish control of expansion bus for bus mastering network adapter cards to function correctly


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NIC must be properly configured to interact successfully with that computerNIC configuration issues: IRQ (Interrupt request) – IRQ must not

be used by other device and must be supported by NIC

Base I/O port address – defines memory location through which data will flow between NIC and CPU


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Base Memory Address – Some NICs require base memory address to indicate starting location in computer’s memory to be used by NIC as buffer memory


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NIC must worry about hardware compatibility in two directions NIC must be compatible with expansion

bus into which it will be inserted NIC must be compatible with media of

network architecture

Some NICs come with interfaces for more than one media type.Jumpers on NIC enable one media type or another


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8 pin RJ-45 jack for 10Base-T

BNC connector for 10Base-2 (thin coax Ethernet)

DB-15 AUI connector for 10Base-5 (thick coax Ethernet)

Jumpers to enable/disable media interfaces

Transceiverthick coax Ethernet

DB-15 AUI

AUI or transceiver cable

DB-15 AUI


Ethernet Media Interfaces


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Possible for NIC to be connected externally to PC via PC’s parallel port USB NICs communicate with PC at speeds greater than 12 Mbps Actual USB performance depends

on number of devices sharing bus


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Network Interface Card Trends

Dual speed cards – 10/100 Ethernet cards feature auto sensing, automatically determine whether traffic is being transmitted and received at 10 or 100 Mbps through single media interface card.Integrated or on board NICs – Build Ethernet NIC onto motherboardMultiport NICS – Ability of PCI bus allows multiport NICs to be manufactured on single card.


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Network Interface Card Trends, cont’d

On-NIC virus protection and security – Some NICS now offer encryption, virus protection, or both

Integrated repeater modules – allow up to seven additional devices to be cascaded from NIC and attached to network via single 10BaseT hub port.

Full duplex mode – Some Ethernet NICs have full duplex capability that can be enabled.


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Network Interface Card Trends, cont’d

Performance improvements – Mfg of Ethernet NICs implemented fast packet forwarding technologyNext packet of information is forwarded as soon as start of frame is detected rather than waiting for previous frame to be totally on network media before beginning transmission of next packet.


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NIC Drivers

Interoperability depends on compatibility between NIC and NOS installed in given computer, and is delivered by network interface card driversIt was to an adapter card vendor ‘s advantage to ship drivers for as many operating systems as possible.


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Approaches for NIC Drivers

Supply drivers that could interact successfully with either NetBIOS or TCP/IP.Emulate adapter interface specifications of market leading network interface cards for which drivers are most commonly available.


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Multiprotocol NIC Drivers

By allowing adapter card vendors to develop one file called IPX.COM which was linked with Novell file called IPX.OBJ through process known as WSGEN, unique drivers could be more easily created and updated.


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Network Driver Interface Specification (NDIS)

NDIS - driver specification offering standard commands for communication between NDIS compliant NOS protocol stacks (NDIS protected driver) and NDIS compliant network adapter card drivers (NDIS MAC drivers).NDIS specifies binding operation managed by protocol managerNDIS specifies standard commands for communication between protocol manager program and protocol or MAC drivers.


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Open Datalink Interface (ODI)

ODI allows users to load several protocol stacks simultaneously for operation with single network adapter card and supports independent development with subsequent linking of protocol drivers and adapter drivers.


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PCMCIA Drivers

When NICs are PCMCIA based, two levels of driver software are required: Drivers to interface to OS and

NOS. Drivers to interface PCMCIA

controller to PCMCIA card and on client software drivers.


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PCMCIA Drivers, cont’d

PCMCIA version 2.1 has Card and Socket Service (CSS) driver specifications.CSS is split into two logical sub layers:1. Card services sub layer is hardware independent and interfaces to NOS driver software.2. Socket services sub layer is written specifically for type of PCMCIA controller included in laptop.


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PCMCIA Drivers, cont’d

If compatible card and socket service (CSS) drivers are not available for particular PC card/controller combination or if amount of memory CSS drivers requires is unacceptable, then lower level drivers known as direct enablers must be configured and installed.


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LAN Wiring Centers

Most common network physical topology employed today is star topology Token ring wiring centers are known as MAUs (Multistation Access Units)Wiring centers for other networks are known as hubs. Hubs and MAUs are multiport digital signal repeaters


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Hubs

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


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Types of Wiring Center Categories

Repeaters Hubs

Stackable Hubs

Multistation Access Units

Enterprise Hubs

Management Hubs


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Wiring Center Categories

Wiring centers can be separated into three broad categories.1. Stand-alone hubs - Offers limited number of ports of particular type of network architecture and media.2. Stackable hubs - add expandability and manageability. Stackable hubs can be linked together to form one larger virtual hub of single type of network architecture and media.


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Wiring Center Categories, cont’d

3. Enterprise hubs - modular by design and offer chassis based architecture to which variety of different modules can be inserted.



10 Base-T

Stand-alone hubs

all RJ-45 connections for UTP

Network Interface Card in

workstation Fixed number of ports Single network architecture Hubs are cascadable Single media type

Stackable hubsserial

connection into management

console

management console port(s)

Each hub has a fixed number of ports Hubs are stackable Single network architecture and media Provides management software and link to network management console Logically one large hub/switch

management console

Enterprise hubs

10Base-T

Token Ring

FDDI

multiple redundant cooling fans

management module

multiple redundant power supplies

Modular chassis-based design Supports multiple network architectures and media types Integrated management module May include internetworking or WAN modules

stacking port(s)

Major Categories of Hubs


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Repeaters

Stand-alone hubs

Stackable hubs

MAUsstand-alone

stackable

Enterprise hubs

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Network Architectures


Wiring Center Functional Comparison


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Repeater

Repeater - repeats each bit of digital data that it receives. Repeating action cleans up digital signal by retiming and regenerating signal before passing this repeated data from one attached device or LAN segment to next.


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Hub

Hubs - are subnet of repeaters that allow attachment of single devices rather than LAN segments to each hub port.Terms hub and concentrator or intelligent concentrator are often used interchangeably.


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Hub interconnects two or more workstations into local area network.

When workstation transmits, hub resends data frame out all connecting links.

Hub can be managed or unmanaged. managed hub possesses enough processing power that it can be managed from remote location.

Hubs, cont’d


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Multistation Access Unit (MAU)

MAU (Multistation Access Unit) is IBM’s name for token ring hub.MAUs offer varying degrees of management capability.Active management MAUs – send alerts to management consoles regarding malfunctioning token ring adapters and forcibly remove misbehaving adapters from ring.


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Enterprise Hubs

Hub allows concentrator to mix cards Cards could be added for connections with Ethernet modules, Token ring adapters, PCs, workstations with FDDI adapters, or dumb asynchronous terminalsAdditional modules available for some concentrators may allow data traffic to travel to other local LANs via bridge or router add-on modules


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Enterprise Hubs, cont’d

Local network traffic travels through single enterprise hub; ideal location for security modules to be added for either encryption or authorization functionality


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Hub Management Hub - ideal place for installation of management software to monitor and manage network trafficIn stackable and enterprise hubs, two layers of management software may be found 1. Software is supplied by hub vendor.

Allows monitoring and management of hub.

2. Hubs - capable of sharing MIS with enterprise network management systems.


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Hub Management, cont’d

Standards that govern network management communication is part of TCP/IP family of protocols, more correctly known as Internet suite of protocols.Network management information is formatted according to simple network management protocol (SNMP)



Agent

Management Information Base

Enterprise Network Management System

Enterprise Hub

Stackable Hubs

SNMP protocol

Stackable HubsAgentAgent

Standards-Based Network Management Communications

Protocols


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LAN Switches

LAN switch - seeks to overcome this “one at time” broadcast scheme, which can lead to data collisions, retransmissions, and reduced throughput between high bandwidth demanding devicesSwitched LAN Architectures vs. Media-Sharing LAN Architectures Wiring Center Functionality


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LAN Switches, cont’d

Many high-end LAN switches support ATM (Asynchronous Transfer Mode), which is type of switching that not only allow previously mentioned LAN architectures to be switched extremely quickly, but also allows similarly quick switching of voice, video, and image traffic


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Switch is combination of hub and bridge.

It can interconnect two or more workstations, but like bridge, it observes traffic flow and learns.

When frame arrives at switch, switch examines destination address and forwards frame out one necessary connection.

Switches, cont’d


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Switches, cont’d

Workstations that connect to hub are on shared segment.

Workstations that connect to switch are on switched segment.


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Backplane of switch is fast enough to support multiple data transfers at one time.

Switch that employs cut-through architecture is passing on frame before entire frame has arrived at switch.

Switches, cont’d


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Switches, cont’d

Multiple workstations connected to switch use dedicated segments. Very efficient way to isolate heavy users from network.

Switch can allow simultaneous access to multiple servers, or multiple simultaneous connections to single server.


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Full duplex switch allows for simultaneous transmission and reception of data to and from workstation.

Full duplex connection helps to eliminate collisions.

To support full duplex connection to switch, two sets of wires are necessary - one for receive operation and one for transmit operation.

Full Duplex Switches


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Types of Switches – Cut Through Switch

Cut through switches - read only address information in MAC layer head before beginning processing. After reading destination address, switch consults an address look up table to determine which port on switch this frame should be forwarded to. Once address look up is completed, point-to-point connection is created and frame is immediately forwarded.


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Types of Switches- Store and Forward

Store and Forward switches – read entire frame into shared memory area in switch. Contents of transmitted Frame Check Sequence (FCS) field is read and compared to locally recalculated frame check sequence. If results match, switch consults address look up table, builds appropriate point-to-point connection, and forwards frame.


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Types of Switches- Error free cut through

switches Error free cut through switches – read both addresses and frame check sequences for every frame. Frames are forwarded immediately to destination nodes in an identical fashion to cut through switches.


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Types of Switches - Error free cut through switches,

cont’d

Should bad frames be forwarded, error free cut through switch is able to reconfigure those individual ports producing bad frames to use store and forward switching. As errors diminish to preset thresholds, port is set back to cut through switching for higher performance throughput.


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Ethernet Hubs and Switches

Shared medium hubs

Switched LAN hubs

x


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Advantages of Switched Hubs

No modifications needed to workstations when replacing shared-medium hubEach device has dedicated capacity equivalent to entire LANEasy to attach additional devices to network


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Types of Switched Hubs

Store and forward switch Accepts frame on input line Buffers it briefly Routes it to appropriate output line

Cut-through switch Begins repeating frame as soon as it

recognizes destination MAC address Higher throughput, increased chance

of error


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Layer 3 Switches

Problems With Layer 2 Switches Broadcast overload Lack of multiple links Can be solved with subnetworks

connected by routers

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


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More on Switches

Circuit-switched Packet-switched


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Circuit-SwitchingDefinition: Communication in which dedicated communications path is established between two devices through one or more intermediate switching nodesDominant in both voice and data communications today e.g. PSTN is circuit-switched network

Relatively inefficient (100% dedication even without 100% utilization)


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Circuit-Switching Stages

Circuit establishmentTransfer of information point-to-point from endpoints to node internal switching/multiplexing among

nodes

Circuit disconnect


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Circuit Establishment

Station requests connection from nodeNode determines best route, sends message to next linkEach subsequent node continues establishment of pathOnce nodes have established connection, test message is sent to determine if receiver is ready/able to accept message


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Information Transfer

Point-to-point transfer from source to nodeInternal switching and multiplexed transfer from node to nodePoint-to-point transfer from node to receiverUsually full-duplex connection throughout


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Circuit Disconnect

When transfer is complete, one station initiates terminationSignals must be propagated to all nodes used in transit in order to free up resources


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Public Switched Telephone Network

(PSTN)

SubscribersLocal loop Connects

subscriber to local telco exchange

Exchanges Telco switching

centers Also known as end

office

Trunks Connections

between exchanges

Carry multiple voice circuits using FDM or synchronous TDM

Managed by IXCs (inter-exchange carriers)


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Digital Circuit-Switching Node


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Circuit Switching Node:Digital Switch

Provides transparent signal path between any pair of attached devicesTypically full-duplex


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Circuit-Switching Node:Network Interface

Provides hardware and functions to connect digital devices to switchAnalog devices can be connected if interface includes CODEC functionsTypically full-duplex


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Circuit-Switching Node:Control Unit

Establishes on-demand connectionsMaintains connection while neededBreaks down connection on completion


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Blocking/Nonblocking Networks

Blocking: network is unable to connect two stations because all possible paths are already in useNonblocking: permits all possible connection requests because any two stations can be connected


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Switching Techniques

Space-Division Switching Developed for analog

environment, but has been carried over into digital communication

Requires separate physical paths for each signal connection

Time-Division Switching Used in digital

transmission Utilizes multiplexing

to place all signals onto common transmission path

Bus must have higher data rate than individual I/O lines


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Routing in Circuit-Switched Networks

Requires balancing efficiency and resiliencyTraditional circuit-switched model is hierarchical, sometimes supplemented with peer-to-peer trunksNewer circuit-switched networks are dynamically routed: all nodes are peer-to-peer, making routing more complex


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Alternate Routing

Possible routes between two end offices are predefinedOriginating switch selects best route for each callRouting paths can be fixed (1 route) or dynamic (multiple routes, selected based on current and historical traffic)


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Control Signaling

Manage establishment, maintenance, and termination of signal pathsIncludes signaling from subscriber to network, and signals within networkIn-channel signaling uses same channel for control signals and callsCommon-channel signaling uses independent channels for controls (SS7)


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ISDN1st generation: narrowband ISDN Basic Rate Interface (BRI) Two 64Kbps bearer channels + 16Kbps data

channel (2B+D) = 144 Kbps Circuit-switched

2nd generation: broadband ISDN (B-ISDN) Primary Rate Interface (PRI) Twenty-three 64Kbps bearer channels + 64

data channel (23B+D) = 1.536 Mbps Packet-switched network Development effort led to ATM/cell relay


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Packet-Switching Networks

Includes X.25, ISDN, ATM and frame-relay technologiesData is broken into packets, each of which can be routed separatelyAdvantages: better line efficiency, signals can always be routed, prioritization optionDisadvantages: transmission delay in nodes, variable delays can cause jitter, extra overhead for packet addresses


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Packet-Switching Techniques

Datagram each packet treated independently and

referred to as datagram packets may take different routes, arrive

out of sequence

Virtual Circuit preplanned route established for all packets similar to circuit switching, but circuit is not

dedicated


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Packet-Switched Routing

Adaptive routing changes based on network conditionsFactors influencing routing are failure and congestionNodes must exchange information on network statusTradeoff between quality and amount of overhead


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Packet-Switched Congestion Control

When line utilization is >80%, queue length grows too quicklyCongestion control limits queue length to avoid throughput problemsStatus information exchanged among nodesControl signals regulate data flow using interface protocols (usually X.25)


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X.25 Interface Standard

ITU-T standard for interface between host and packet-switched networkPhysical level handles physical connection between host and link to node Technically X.21, but other standards can be

substituted, including RS-232

Link level provides for reliable data transfer Uses LAPB, which is subset of HDLC

Packet level provides virtual circuits between subscribers


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Virtual-Circuit Service

External virtual circuit: logical connection between two stations on networkInternal virtual circuit: specific preplanned route through networkX.25 usually has 1:1 relationship between external and internal circuitsIn some cases, X.25 can be implemented as packet-switched network


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Bridges

Allow connections between LANs and WANsOperates at Layer 2 (Data Link Layer) of OSIUsed between networks using identical physical and link layer protocolsProvide number of advantages Reliability: Creates self-contained units Performance: Less contention Security: Not all data broadcast to all users Geography: Allows long-distance links


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Bridge Functions

Read all frames from each networkAccept frames from sender on one network that are addressed to receiver on 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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Bridge (or bridge-like device) can be used to connect two similar LANs, such as two CSMA/CD LANs.

Bridge can connect two closely similar LANs, such as CSMA/CD LAN and token ring LAN.

Bridges


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Bridges, cont’d

Bridge examines destination address in frame and either forwards this frame onto next LAN or does not.

Bridge examines source address in frame and places this address in routing table, to be used for future routing decisions.


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Bridge Interconnecting


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Bridge – Similar LANs


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Bridge Operation


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Transparent bridge does not need programming but observes all traffic and builds routing tables from this observation.

This observation is called backward learning.

Each bridge has two connections (ports) and there is routing table associated with each port.

Transparent Bridges


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Transparent Bridges, cont’d

Bridge observes each frame that arrives at port, extracts source address from frame, and places that address in port’s routing table.

Transparent bridge is CSMA/CD LANs.


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Bridge – CSMA/CD LANs


113

Transparent bridge can also convert one frame format to another.

Note that some people/manufacturers call bridge such as this gateway or sometimes router.

Bridge removes headers and trailers from one frame format and inserts (encapsulates) headers and trailers for second frame format.

Transparent Bridge


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Data Frame – CSMA/CD to Token


115

Source-routing bridge used with token ring networks.

Source-routing bridges do not learn from watching tables.

When workstation wants to send frame, it must know exact path of network / bridge …

Source-Routing Bridge


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Source-Routing Bridge, cont’d

If workstation does not know exact path, it sends out discovery frame.

Discovery frame makes its way to final destination, as it returns, it records path.


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Remote bridge is capable of passing data frame from LAN to LAN when LANs are separated by long distance and there is WAN connecting two LANs.

Remote bridge takes frame before it leaves first LAN and encapsulates WAN headers and trailers.

When packet arrives at destination remote bridge, bridge removes WAN headers and trailers leaving original frame.

Remote Bridge


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LAN with Frame Relay Network


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Device that connects LAN to WAN or WAN to WAN.

Router accepts an outgoing packet, removes any LAN headers and trailers, and encapsulates necessary WAN headers and trailers.

Routers


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Because router has to make WAN routing decisions, router has to dig down into network layer of packet to retrieve network destination address.

Routers operate at third layer, or OSI network layer, of packet.

Routers often incorporate firewall functions.

Routers, cont’d


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Asynchronous Transfer Mode

Connection oriented switched transmission methodology ATM characteristics is capability of delivering variety of traffic over both local and wide area networksATM has fixed length 53-byte cellUniform length allows timed, dependable delivery for streaming traffic (voice, video), and simplifies troubleshooting, administration, setup, and design


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Migration Strategies to ATM

IP over ATM – Known as classical IP, adapts CP/IP protocol stack to employ ATM services as native transport protocol directlyLAN emulation - allows all current upper layer LAN protocols to be transported by ATM services in an unmodified fashion. Provides translation between ATM addressing scheme and scheme native to particular emulated LAN.


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Migration Strategies to ATM, cont’d

Multi-Protocol Over ATM (MPOA), provides support for multiple local area network protocols running on top of ATM cell switched network


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ATM switch

ATM switch connections running at 155Mbps, upgradeable to 2.4 Gbps or higher.

ATM Backbone Network

Bridge or Router with ATM module - also known as an

ATM Access Switch

10 Mbps 16 Mbps

100 or 155 Mbps

155 Mbps

155 Mbps

Corporate Servers or High Speed Workstations with

155 Mbps NICs

25 Mbps ATM workgroup

concentrator

Local Clients and Servers with 25Mbps ATM NICs

25 Mbps

100 Mbps or 155 Mbps connection from workgroup concentrator to

ATM switch.

ATM WAN

Services

10Mbps Token Ring

MAU

Token Ring LAN (16Mbps)

10Base-T hub

Ethernet LAN (10Mbps)

ATM switch

ATM switch

155 Mbps

155 Mbps


ATM Implementation

Documents

Chapter6 - LAN Hardware