special material 3

BASIC DATA NETWORKS

Bandwidth

Narrowband0 - 64 kbps

Wideband64 Kbps - 45 Mbps

Broadband45 Mbps and Beyond

X.25 Frame Relay ATMSMDS

Token Ring

x xT-1,PRI

Backbone

Network Access

Network Hierarchy and Protocols

Ethernet

Definition: Topology

The Physical and Logical Way theNetwork Elements are Connected

Legend

Device on LAN=

Bus Star Ring

Local Area Network (LAN) Topologies

LAN Topologies

Legend

Device on LAN=

BusExample: Ethernet

CSM/CD: Carrier Sense Multiple Access/Collision Detection

Send Data Units out unless you detect another data unit.

LAN Topologies

RingExample: Token Ring

Send data units when youpossess the token

Token: Special Type of Data Unit

LAN Standards

IEEE 802.1 INTERNETWORKING

OSILAYERS3-7

OSILAYER 2

OSILAYER 1

IEEE 802.2TYPE 1 - UNACKNOWLEDGED CONNECTIONLESS SERVICETYPE 2 - CONNECTION MODE SERVICETYPE 3 - ACKNOWLEDGED CONNECTIONLESS SERVICE

802.3CSMA/CD(ETHERNET)

802.4TOKEN BUS

802.5 TOKEN RING

802.6DQDB(MAN)

BASEBANDCOAXIALAND UNSHIELDEDTWISTED PAIR

BROADBANDCOAXIAL

OPTICALFIBER

SHIELDED OR UNSHIELDEDTWISTED PAIR

OPTICALFIBERORCOAXIALCABLE

Access Networks: Entry to Wide Area Network (WAN)

CustomerPremises

Bridge-Router

Access NetworkEnter via port on LAN router

Data Flow in an X.25 Network

Protocol LayersInvolvedin DataTransfer

Switch A Switch CX.25 Network

Switch B

Data Flow in a Frame Relay Network

Frame Relay Network

Protocol LayersInvolvedin DataTransfer

Switch A Switch CSwitch B

Backbone Networks

High Speed Interconnection of Networks

ATM Cell Structure

Header Payload

48 Octets5 Octets

Octet 8 7 6 5 4 3 2 1

Bit Position

GFC VPIVPI VCI

VCIVCI PTI

VCI = Virtual Channel IDVPI = Virtual Path IDPTI = Payload Type IdentifierGFC = Generic Flow ControlCLP = Cell Loss PriorityHEC = Header Error Control

Backbone Example: Asynchronous Transfer Mode (ATM)

ATM Users Receive as Much Bandwidth as They Require

PYTHON WITHEXPANDABLE

SKIN (BANDWIDTH)

User 1

User 2

User 3

125 sec 250 sec 375 sec 500 sec

Asynchronous means data units (cells) areplaced on the network as the application requires

User 1 User 1 User 1

User 2 User 2User 2

User 3

OPEN SYSTEMS INTERFACE (OSI) MODEL

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Network

Data Link Data Link

NetworkNode

Wireless OSI Model

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Network

Data Link Data Link

NetworkNode

MESSAGES USE

BOTTOM 3 LAYERS

OSI Protocol “Stack”

What are We Doing?7

Are We Speaking the Same Language (Code)?6

How Long Can Both Sides Talk?

How do We Control Info Flows andand Keep Messages in the Right Order?

How do We Put Together and Move Chunks of InformationAcross a Whole Network?

What Signals and Timing Are We Using?How Are We Going to Recognize Errors between Two Points?2

What Hardware Are We Using?1

The OSI Model

Application

Presentation

Session

Transport

Network

Datalink

Physical Header

User Info

A Set of Rules

Layer Details – Layer 1

Network

Data Link

Physical

Application

Presentation

Session

Transport

Transmits bits received from the Data Link layer across the transmission medium

Data Link

Physical

Sequences messages and checks for errors between adjacent link stations

Network

Application

Presentation

Session

Transport

Network

Data Link

Physical

Fragments or “packetizes” messages, and routes them to the proper destination

Application

Presentation

Session

Transport

Network

Data Link

Physical

Transport

Fragments or “packetizes” messages, and routes them to the proper destination

Provides multiplexing, network connection management, quality of service, etc.

Application

Presentation

Session

Header Information

Packet Format

•Header•User Data

•Perhaps a Trailer•Store and Forward

Packet Switched Routing

Header Information

Packet Format

Layer 2 Info Layer 3-5 Info Layer 2 InfoFlag Flag

Message Format

Types of Protocol Data UnitBeing Sent Through a Packet Switched Network

Protocol Data Units

Header TrailerUser Data

Protocol Data Unit

Routing Fields

ROUTERNODE B

DATAC CDATAB C

NODE A NODE C

Destination NodeWon’t Change

Address of NextNode on Route

Router Stores Packet, Reads Destination Information And Forwards

To The Next Node

Routers Routing Packets

Final Path

Data Switch Routing Example

• Ethernet Switch

– Receives Ethernet frame

– Looks up 6-byte Destination Address in a

Forwarding Table

– Sends frame out only the port associated with

the Destination Address

Ethernet Switch

10Base-T Switch

MAC #11 MAC #14MAC #13MAC #12

10Base-T Hub

MAC #21 MAC #24MAC #23MAC #22

Address Port UpdateTime

# 11 D 6:05.1441 PM # 12 C 6:04.1523 PM # 13 B 6:04.8722 PM # 14 A 6:05.1422 PM # 21 E 6:04.6623 PM # 22 E 6:04.2355 PM # 23 E 6:05.0233 PM # 24 E 6:04.9722 PM

FORWARDING TABLE

AE D C B

ROUTINGCONSIDERATION

WHAT’S INCLUDED

Performance Number of hops Cost Delay Throughput

Decision Time Packet (Datagram) Session (Virtual Circuit)

Decision Place Each node (Distributed) Central node (Centralized) Originating node

Source of Information onNetwork Status

None Local Adjacent Nodes Nodes along route All nodes

Routing Strategy Fixed Flooding Random Adaptive

Adaptive Routing UpdateTime

Continuous Periodic Major load change Topology change

Packet Switched Network Routing

Data Network Devices & the OSI Reference Model

•Gateways•Routers•Switches•Hubs•Bridges•Repeaters

REPEATER

• LAYER 1 PHYSICAL

• I PHYSICALLY REPEAT AND REGENERATE BITS FOR MY OWN LAN

BRIDGE

• LAYER 2 DATA LINK LAYER

• I LINK DATA FRAMES BY BRIDGING BETWEEN ISLANDS.

LAN 1 LAN 2

• LAYER 2 DATA LINK LAYER• I ROUTE PACKETS BETWEEN ISLANDS

WITH COMMON PROTOCOLS

DATA SWITCH

• LAYER 2 DATA LINK LAYER• I ROUTE PACKETS BETWEEN PORTS• PACKETS ARE NOT SENT TO EVERY PORT

(ONLY TO THE DESTINATION PORT)

USER USER

ROUTER

• LAYER 3 NETWORK LAYER• I ROUTE PACKETS BETWEEN ISLANDS

WITH COMMON PROTOCOLS

GATEWAY

• LAYER 3+• I CONVERT PROTOCOLS BETWEEN ISLANDS • SYNCHRONOUS TO ASYNCHRONOUS

SYNC ASYNC

Data Network Devices in Data Network Applications

Router

Carrier Network

Router

ChicagoRouter

LAN Hub

Client

DetroitRouter

LAN Hub

Server

CustomerNetwork

AccessLine

Typical Packet Data Services

• Routers modify layer 2 frame headers & trailers so packet can travel end-to-end over many links. They provide Gateways into and out of the PSTN.

IP packets / TR frames

IP packets / PPP frames

Router or Gateway modifies frame

IP packets / TR frames

Router RouterCSU CSUC.O .

T1T1TokenRing

TokenRing

Packets, Routers and the PSTN

Combined Network

MSC TELCO

NIU NIU

HostDigital

Terminal

SS7 SS7

Internet

Intranet orPublic Data Network

Average ResidencePower ResidenceCorporate A Corporate B

Trunks toTelco

Switch

Gateway

IP Telephony Using a Computer as the Terminal

PSTN Internet

Gateway

Router Cable Modem

Microphone

PSTN Internet

Gateway

Router

IP TelephonyGenerates Mobile Like Traffic

Cable Modem

TelephoneAdapter

•Committed Information Rate (CIR)

•Data Collisions

•Protocol Analyzers

Detecting and Fixing Errors

0 1 0 0 1 1 0 1 11 1 1 0 0 1 0 0 10 0 0 1 0 0 1 1 01 1 0 1 0 1 1 0 00 1 0 1 1 0 0 1 11 1 0 1 0 1 1 1 10 0 0 1 0 1 1 0 00 0 0 0 1 0 1 1 0

Block Parity Bits

BitPosition

1234567

CharacterParity

BlockParityCharacter

•Longitudinal Redundancy Check (LRC)

•Block Parity Character •Checksum

•XMODEM Checksum

New Terms

DATACRCResult

Figure AA

•Automatic Repeat Request (ARQ)

•Acceptance (ACK)

•Reject (NAK)

Forward Error Correction (FEC)

Types of Digital Error Measurement

•Bit Error Rate (BER)

•Block Error Rate (BLER)

•Errored Seconds

•Severely Errored Seconds

Bit Error Rate Tester

Shift Register

InterfaceCoder

Itemundertest

InterfaceDecoder

ErrorCounter

Shift Register

Illustration Courtesy of Hewlett PackardSource: Application Note 387

Summary

•Types of Data Networks•OSI Reference Model•Packet Structures•Routing•Devices•Applications•Detecting And Fixing Errors

special material 3

data link layer

data network devices

data flow

header user data

network routing

network elements

network switch b

layer details layer

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