Chapter 11 ATM

Switching and Teletraffic TheoryLecture 8TCP/IP Concepts

IPv4 Header

Header Fields (1)VersionCurrently 4IP v6 - see laterInternet header lengthIn 32 bit wordsIncluding optionsType of serviceTotal lengthOf datagram, in octets

Header Fields (2)IdentificationSequence numberUsed with addresses and user protocol to identify datagram uniquelyFlagsMore bitDont fragmentFragmentation offsetTime to liveProtocolNext higher layer to receive data field at destinationHeader Fields (3)Header checksumReverified and recomputed at each routerSet to zero during calculationSource addressDestination addressOptionsPaddingTo fill to multiple of 32 bits longOptionsSecuritySource routingRoute recordingStream identificationTimestampingData FieldCarries user data from next layer upInteger multiple of 8 bits long (octet)Max length of datagram (header plus data) 65,535 octets

IPv4 Address Formats

Subnets and Subnet MasksAllow arbitrary complexity of internetworked LANs within organizationInsulate overall internet from growth of network numbers and routing complexitySite looks to rest of internet like single networkEach LAN assigned subnet numberHost portion of address partitioned into subnet number and host numberLocal routers route within subnetted networkSubnet mask indicates which bits are subnet number and which are host numberIP v6 - Version NumberIP v 1-3 defined and replacedIP v4 - current versionIP v5 - streams protocolIP v6 - replacement for IP v4During development it was called IPngWhy Change IP?Address space exhaustionTwo level addressing (network and host) wastes spaceNetwork addresses used even if not connected to InternetGrowth of networks and the InternetExtended use of TCP/IPSingle address per hostRequirements for new types of service

IPv6 Enhancements (1)Expanded address space128 bitImproved option mechanismSeparate optional headers between IPv6 header and transport layer headerMost are not examined by intermediate routesImproved speed and simplified router processingEasier to extend optionsIPv6 Enhancements (2)Increased addressing flexibilityAnycast - delivered to one of a set of nodesImproved scalability of multicast addressesSupport for resource allocationReplaces type of serviceLabeling of packets to particular traffic flowAllows special handlinge.g. real time video

IPv6StructureExtension HeadersHop-by-Hop OptionsRequire processing at each routerRoutingSimilar to v4 source routingFragmentAuthenticationEncapsulating security payloadDestination optionsFor destination node

IP v6 Header

IP v6 Header Fields (1)Version6Traffic ClassClasses or priorities of packetFlow LabelUsed by hosts requesting special handlingPayload lengthIncludes all extension headers plus user dataIP v6 Header Fields (2)Next HeaderIdentifies type of headerExtension or next layer upSource AddressDestination addressIPv6 Addresses128 bits longAssigned to interfaceSingle interface may have multiple unicast addressesThree types of address

Types of addressUnicastSingle interfaceAnycastSet of interfaces (typically different nodes)Delivered to any one interfacethe nearestMulticastSet of interfacesDelivered to all interfaces identifiedAsynchronous Transfer Mode (ATM)Protocol ArchitectureSimilarities between ATM and packet switchingTransfer of data in discrete chunksMultiple logical connections over single physical interfaceIn ATM, data flow on each logical connection is sent in fixed sized packets called cellsMinimal error and flow controlReduced overheadData rates (physical layer) 25.6Mbps to 622.08MbpsProtocol Architecture

Reference Model PlanesUser planeProvides for user information transferControl planeCall and connection controlManagement planePlane managementWhole system functionsLayer managementResources and parameters in protocol entitiesATM Logical ConnectionsVirtual channel connections (VCC)Basic unit of switchingBetween two end usersFull duplexTypesUser-User (data)User-network exchange (control)Network-network exchange (network management and routing)Virtual path connection (VPC)Bundle of VCC with same end pointsATM Connection Relationships

Advantages of Virtual PathsSimplified network architectureIncreased network performance and reliabilityReduced processingShort connection setup timeEnhanced network servicesCall Establishment Using VPs

Virtual Channel Connection UsesBetween end usersEnd to end user dataControl signalsVPC provides overall capacity (e.g. to connect branch with main office)VCC organization done by usersBetween end user and networkControl signalingBetween network entitiesNetwork traffic managementRoutingControl Signaling - VCCSignaling sent on a separate connectionSemi-permanent VCCUser to network signaling virtual channelFor control signalingUsed to set up VCCs to carry user dataUser to user signaling virtual channelWithin pre-established VPCUsed by two end users without network intervention to establish and release user to user VCCATM CellsFixed size5-octets header48-octets information fieldSmall cells reduce queuing delay for high priority cellsSmall cells can be switched more efficientlyEasier to implement switching of small cells in hardwareATM Cell Format

Header FormatGeneric flow controlOnly at user to network interfaceControls flow only at this pointVirtual path identifierVirtual channel identifierPayload typee.g. user info or network managementCell loss priorityHeader error controlATM Service CategoriesReal timeConstant bit rate (CBR)Real time variable bit rate (rt-VBR)Non-real timeNon-real time variable bit rate (nrt-VBR)Available bit rate (ABR)Unspecified bit rate (UBR)Guaranteed frame rate (GFR)UBRMay be additional capacity over and above that used by CBR and VBR trafficNot all resources dedicatedBursty nature of VBRFor application that can tolerate some cell loss or variable delayse.g. TCP based trafficCells forwarded on FIFO basisBest effort service

ABRApplication specifies peak cell rate (PCR) and minimum cell rate (MCR)Resources allocated to give at least MCRSpare capacity shared among all ABR sourcese.g. LAN interconnection

Guaranteed Frame Rate (GFR)Designed to support IP backbone subnetworksBetter service than UBR for frame based trafficIncluding IP and EthernetOptimized handling of frame based traffic passing from LAN through router to ATM backboneABR difficult to implement between routers over ATM networkGFR better alternative for traffic originating on EthernetNetwork aware of frame/packet boundariesWhen congested, all cells from frame discardedGuaranteed minimum capacityAdditional frames carried if not congestedATM Bit Rate Services

Adaptation Layer ServicesHandle transmission errorsSegmentation and re-assemblyHandle lost and misinserted cellsFlow control and timing

Wireless SystemsWireless SystemsIn wired systems, there is a permanent link between the subscriber and the networkSuch a link does not exist in wireless systemsSubscribers must compete to get a linkSubscribers can lose the link during the connection (mobility)This user-network link/channel is the main issue in wireless systemsOther stuff is similar to wired networksUser-Network ChannelsAll data must travel through the airMore than one transmitter will cause interference and hence no data will be receivedAccess to the air (spectrum) must be organizedBetween operators-> governmentBetween users-> operator

Spectrum OrganizationOperator must rent part of the spectrum for his sole use (license)The allocated spectrum is expensive and limitedIt is divided into 2 partsUplink (mobile-> basestation)Downlink (basestation-> mobile)Each part is further divided into two (unequal) partsControl (signaling)Voice (data)Wireless ChannelsControl (and voice) channels are organized in pairsOne channel in the uplink (reverse channel) has a corresponding channel in the downlink (forward channel)Channels are assigned to terminals/basestations in pairsTerminals always listen to the basestation control channel (forward control channel)If they want to call, they send in basestation reverse control channelMobile Switching CenterA large central officeConnected to other operators networksAll basestations are connected to the MSC via permanent linksAll calls are relayed by the switching centerBasestations forward data from the terminal to the switching centerCall Setup-Landline to MobileMSCReceive call request from PSTN, forward to all BSsVerify MS infoRequest BS to move MS to VCConnect call to PSTNBasestationFCCTX MINInstruct MS to move to VCRCCRX Ack, forward to MSC

FVCBegin TXRVCBegin RXMobileFCCRX MIN, compare with ownRX InstructionRCCAck, send MS infoFVCBegin RXRVCBegin TXCall Setup-Mobile to LandlineMSCVerify MS infoRequest BS to move MS to VCConnect call to PSTNBasestationFCCInstruct MS to move to VCRCCRX info, forward to MSC

FVCBegin TXRVCBegin RXMobileFCCRX InstructionRCCSend call request with number and MS infoFVCBegin RXRVCBegin TX