COP 4930COP 4930Computer Network Computer Network

ProjectsProjects

Summer C 2004Summer C 2004

Prof. Roy B. LevowProf. Roy B. Levow

Lecture 3Lecture 3

Network AnalyzerNetwork Analyzer

Captures, analyses, and reports on all Captures, analyses, and reports on all packets at point of attachment to the packets at point of attachment to the networknetwork

Decodes packets to reveal contentsDecodes packets to reveal contents Can capture all packets or only selected Can capture all packets or only selected

onesones Also known asAlso known as

– Network monitorNetwork monitor– Packet analyzerPacket analyzer– Network sniffer ™Network sniffer ™

Network Analyzer.2Network Analyzer.2

Interface operates in Interface operates in promiscuouspromiscuous modemode

Can also be implemented in softwareCan also be implemented in software– EtherealEthereal

http://www.ethereal.comhttp://www.ethereal.com

Packet SwitchingPacket Switching

Packet switch is basic switching Packet switch is basic switching element of wide-area networks element of wide-area networks (WAN)(WAN)

Has multiple network interfacesHas multiple network interfaces Connects toConnects to

– Communication linesCommunication lines– NetworksNetworks– LANsLANs– ComputersComputers

Packet Switching.2Packet Switching.2

Processing at switchProcessing at switch– Arriving packet is stored in bufferArriving packet is stored in buffer– Destination address is readDestination address is read– Packet is placed on output queue for Packet is placed on output queue for

next hop to destinationnext hop to destination– Packet is sentPacket is sent

Packet RoutingPacket Routing

Hierarchical AddressingHierarchical Addressing– Address is split into two partsAddress is split into two parts

Network identifierNetwork identifierHost identifierHost identifier

– In tcp/ip, net mask indicated bits in In tcp/ip, net mask indicated bits in network portion of addressnetwork portion of address

– Packet switching uses only network Packet switching uses only network address except at destinationaddress except at destination

Packet RoutingPacket Routing

Next-Hop ForwardingNext-Hop Forwarding– Switch only needs to know next step to Switch only needs to know next step to

destinationdestination Routing tableRouting table

– Matches network with outgoing linkMatches network with outgoing link– Many different ways table can be set Many different ways table can be set

and updatedand updated

ProtocolsProtocols

Protocol defines an interaction Protocol defines an interaction between two entitiesbetween two entities

Specifies the format and meaning of Specifies the format and meaning of messagesmessages

Application program interacts with Application program interacts with software that implements a protocolsoftware that implements a protocol

Protocol SuitesProtocol Suites

Totality of issues are divided into Totality of issues are divided into component protocols that work component protocols that work togethertogether

Conventional design is layeredConventional design is layered– Each protocol communicates directly Each protocol communicates directly

only with those directly above and only with those directly above and belowbelow

– TCP/IP layers (fig. TCP/IP layers (fig. 17.417.4))

TCP/IP LayersTCP/IP Layers

1: Physical – network hardware1: Physical – network hardware2: Network Interface – how frames are 2: Network Interface – how frames are

formatted and transmitted over the formatted and transmitted over the networknetwork

3: Internet – how packets are sent 3: Internet – how packets are sent across an internetacross an internet

4: Transport – assures reliable transport4: Transport – assures reliable transport5: Application – interface to applications5: Application – interface to applications

Protocol StackProtocol Stack

Software at each layer interacts only Software at each layer interacts only with adjacent layers (with adjacent layers (fig. 16.2fig. 16.2))

Each frame is nested in next one, Each frame is nested in next one, from lower layer of stack (from lower layer of stack (fig. 16.4fig. 16.4))

Each layer at destination receives Each layer at destination receives frame sent from corresponding layer frame sent from corresponding layer at origin (at origin (fig. 16.5fig. 16.5))

SequencingSequencing

Adding sequencing numbers to Adding sequencing numbers to frames allows detection and handling frames allows detection and handling of a variety of error situationsof a variety of error situations– Out-of-order deliveryOut-of-order delivery– Duplicate detection and deletionDuplicate detection and deletion– Recognizing packet loss and prompting Recognizing packet loss and prompting

retransmissionretransmission Send positive acknowledgement Send positive acknowledgement

(ACK) or negative ack (NAK) with (ACK) or negative ack (NAK) with frame numberframe number

ReplayReplay

Delayed, duplicated packets arrive Delayed, duplicated packets arrive after end of sessionafter end of session– Include session IDInclude session ID

Flow ControlFlow Control

Data Overrun occurs if data arrives Data Overrun occurs if data arrives faster than it can be processedfaster than it can be processed

Sliding windowSliding window– Allows only a limited number of Allows only a limited number of

unacknowledged frames in transmissionunacknowledged frames in transmission– Sender and receiver agree on a window Sender and receiver agree on a window

size, which may be changed by receiver size, which may be changed by receiver during sessionduring session

Network CongestionNetwork Congestion

Problem of routers when incoming Problem of routers when incoming data, usually from several sources, data, usually from several sources, exceeds outgoing capacityexceeds outgoing capacity

Congested node sends control Congested node sends control messages back requesting that data messages back requesting that data be sent at a slower ratebe sent at a slower rate

InternetworkingInternetworking

Provides the ability a collection of Provides the ability a collection of different networks as a single different networks as a single networknetwork

The networks can run different The networks can run different protocols at the network interface protocols at the network interface and physical layersand physical layers

Internally they can be structured Internally they can be structured entirely differentlyentirely differently

IP AddressingIP Addressing

Unique 32-bit (4-octet) address for Unique 32-bit (4-octet) address for each nodeeach node

Address space was partitioned into Address space was partitioned into networks of various classesnetworks of various classes– Class defines the number of nodes the Class defines the number of nodes the

network can supportnetwork can support

SubnetworksSubnetworks

Network differentiation is enhanced Network differentiation is enhanced by the use of netmasksby the use of netmasks

Each network has a network address Each network has a network address and netmask that specifies the bits and netmask that specifies the bits of the IP address that identify that of the IP address that identify that networknetwork

Classless Internet-Domain RoutingClassless Internet-Domain RoutingCIDRCIDR

Uses netmask to define networkUses netmask to define network