Networks: OverviewNetwork typesConceptual layering of protocol softwareEncapsulation as it is applied in layered protocolsProtocol layers in the ISO Open Systems Interconnection (OSI) modelOSI protocol summaryInternetwork layersRouting in a wide area networkTCP/IP layersEncapsulation in a message transmitted via TCP over an EthernetThe programmer's conceptual view of a TCP/IP InternetInternet address structure, showing field sizes in bitsDecimal representation of Internet addressesDNS: Domain Name SystemDNS name serversDNS: Root name serversSimple DNS example1Networks: Overview2Network typesRange Bandwidth (Mbps) Latency (ms)LAN 1-2 kms 10-1000 1-10WAN worldwide 0.010-600 100-500MAN 2-50 kms 1-150 10Wireless LAN 0.15-1.5 km 2-11 5-20Wireless WAN worldwide 0.010-2 100-500Internet worldwide 0.010-2 100-50023Conceptual layering of protocol softwareLayer nLayer 2Layer 1Message sentMessage receivedCommunicationmediumSender Recipient4Encapsulation as it is applied in layered protocolsPresentation headerApplication-layer messageSession headerTransport headerNetwork header35Protocol layers in the ISO Open Systems Interconnection (OSI) modelApplicationPresentationSessionTransportNetworkData linkPhysicalMessage sentMessage receivedSender RecipientLayersCommunicationmedium6OSI protocol summaryLayer Description ExamplesApplication Protocols that are designed to meet the communication requirements ofspecific applications, often defining the interface to a service.HTTP, FTP, SMTP,CORBA IIOPPresentation Protocols at this level transmit data in a network representation that isindependent of the representations used in individual computers, which maydiffer. Encryption is also performed in this layer, if required.Secure Sockets(SSL),CORBA DataRep.Session At this level reliability and adaptation are performed, such as detection offailures and automatic recovery.Transport This is the lowest level at which messages (rather than packets) are handled.Messages are addressed to communication ports attached to processes,Protocols in this layer may be connection-oriented or connectionless.TCP, UDPNetwork Transfers data packets between computers in a specific network. In a WANor an internetwork this involves the generation of a route passing throughrouters. In a single LAN no routing is required.IP, ATM virtualcircuitsData link Responsible for transmission of packets between nodes that are directlyconnected by a physical link. In a WAN transmission is between pairs ofrouters or between routers and hosts. In a LAN it is between any pair of hosts.Ethernet MAC,ATM cell transfer,PPPPhysical The circuits and hardware that drive the network. It transmits sequences ofbinary data by analogue signalling, using amplitude or frequency modulationof electrical signals (on cable circuits), light signals (on fibre optic circuits)or other electromagnetic signals (on radio and microwave circuits).Ethernet base- bandsignalling, ISDN47Internetwork layersUnderlying networkApplicationNetwork interfaceTransportInternetworkInternetwork packetsNetwork-specific packetsMessageLayersInternetworkprotocolsUnderlyingnetworkprotocols8Routing in a wide area networkHostsLinksor local networksADEBC125436Routers59TCP/IP layersMessages (UDP) or Streams (TCP)ApplicationTransportInternetUDP or TCP packetsIP datagramsNetwork-specific framesMessageLayersUnderlying networkNetwork interface10Encapsulation in a message transmitted via TCP over an EthernetApplication messageTCP headerIP headerEthernet headerEthernet frameportTCPIP611The programmer's conceptual view of a TCP/IP InternetIPApplication ApplicationTCP UDP12Internet address structure, showing field sizes in bits724Class A: 0 Network ID Host ID14 16Class B: 1 0 Network ID Host ID21 8Class C: 1 1 0 Network ID Host ID28Class D (multicast): 1 1 1 0 Multicast address27Class E (reserved): 1 1 1 1 unused0713Decimal representation of Internet addressesoctet 1 octet 2 octet 3Class A:1 to 1270 to 255 0 to 255 1 to 254Class B:128 to 191Class C:192 to 223 224 to 239 Class D (multicast):Network IDNetwork IDNetwork IDHost IDHost IDHost IDMulticast address0 to 255 0 to 255 1 to 2540 to 255 0 to 255 0 to 2550 to 255 0 to 255 0 to 255Multicast address0 to 255 0 to 255 1 to 254240 to 255 Class E (reserved):1.0.0.0 to 127.255.255.255128.0.0.0 to 191.255.255.255192.0.0.0 to 223.255.255.255224.0.0.0 to 239.255.255.255128.0.0.0 to 247.255.255.255Range of addresses14DNS: Domain Name SystemPeople: many identifiers:❍ SSN, name, Passport #Internet hosts, routers:❍ IP address (32 bit) -used for addressing datagrams❍ “name”, e.g., gaia.cs.umass.edu - used by humansQ: map between IP addresses and name ?Domain Name System:❒distributed databaseimplemented in hierarchy of many name servers❒application-layer protocolhost, routers, name servers to communicate to resolvenames (address/name translation)815DNS name servers❒ no server has all name-to-IP address mappingslocal name servers:❍ each ISP, company has local (default) name server❍ host DNS query first goes to local name serverauthoritative name server:❍ for a host: stores that host’s IP address, name❍ can perform name/address translation for that host’s name Why not centralize DNS?❒ single point of failure❒ traffic volume❒ distant centralized database❒ maintenancedoesn’t scale!16DNS: Root name servers❒ contacted by local name server that can not resolve name❒ root name server:❍ contacts authoritative name server if name mapping not known❍ gets mapping❍ returns mapping to local name server❒ ~ dozen root name servers worldwide917Simple DNS examplehost surf.eurecom.frwants IP address of gaia.cs.umass.edu1. Contacts its local DNS server, dns.eurecom.fr2. dns.eurecom.fr contacts root name server, if necessary3. root name server contacts authoritative name server, dns.umass.edu, if necessaryrequesting hostsurf.eurecom.frgaia.cs.umass.eduroot name serverauthorititive name serverdns.umass.edulocal name