Network Communication Network Communication is the process by which two or more computers transfer information to each other.

Network Communication

Network Communication is the process by which two or more computers transfer information to

each other.

Network Types

● LAN – Local Area NetworkComputer network that spans a relatively small area.

● WAN – Wide Access NetworkGeographically dispersed computer network

Open Systems Interconnection Model

● Physicaldefines all the electrical and physical specifications for devices

● Data Linkfunctional and procedural means to transfer data between network entities

● Networkmeans of transferring variable length data sequences from a source to a destination

● Transportprovides transparent transfer of data between end users

● Sessionmechanism for managing the dialogue between end-user application processes

● Presentationformats information for the application layer

● Applicationfacilitates communication between software applications and lower-layer network services

OSI: Physical Layer

Defines the electrical and physical specifications for a networking card

● 10BASE-T● 100BASE-TX● 1000BASE-T● ISDN● DSL● 802.11b● 802.11g

OSI: Data Link Layer

Logical Link Control (LLC) the functions required to establish and control a network link

Media Access Control (MAC)Separate devices on a network

AddressingAddress Resolution Protocol used to convert an IP to MAC address is performed at this level

Data Framing encapsulates messages

Error Detection and Handlingensures data was received correctly using Cyclic Redundancy Checking

● Ethernet● 802.11● Frame Relay● Token Ring● X.25● PPP● PPTP

Ethernet Topologies

Ethernet Frame Transmission

● Frame ready for transmission

● If medium is not idle, wait until it is

● Start transmission

● Check for collision

Finish transmission

If at max transmission attempts, abort

otherwise, calculate and wait random back off period

Restart Process

● End successful transmission

Ethernet II Frame

● MAC Header – 14 bytesDestination MAC Address – 6 bytesSource MAC Address – 6 bytesEther Type – 2 bytes

● Data – 46 to 1500 bytes● CRC Checksum – 4 bytes

OSI: Network Layer

Heirarchal Addressingaddress to specify a machine. Independent of hardware and unique across a network.

Routingthis level handles transferring data across interconnected networks while maintaining the transportation layers specified QoS.

Datagram Encapsulationplaces data into datagrams to send

Fragmentation and ReassemblyThe size of a packet is determined by software at this level

Error HandlingFind status of the host on a network, or the device itself

● IP● IPSec● NetBEUI● IPX

Internet Protocol

● Developed by DARPA in the early 1970's

● IPv4 and IPv6

● ICMP, UDP, and TCP are based on IP

● Deals with transferring packets of data from a source to a destination

IP Versions

● IPv4 uses 32-bit addresses, giving 4,294,967,269 possible unique addresses. Of that, 18 million addresses are reserved for special purposes.

Addresses are written as four 3 digit base10 numbers separated by decimals

● IPv6 uses 128-bit addresses, giving ~3.403 x 1032 unique addresses.

Addresses are written as eight 4 digit hex numbers separated by colons

IPv4 Packet

IPv6 Packet

NetBEUI Protocol

● Unrouted networking strategy used in Microsoft networks

● Can only communicate with devices on the same network segment

● NetBIOS (Session Level) applications register a name to distinguish it on a network

● Must be encapsulated in another protocol to be used over a WAN

Internetwork Packet eXchange Protocol

● Supported by Novell's NetWare OS

● Logical networks are assigned a unique 32-bit hex address

● Hosts have a 48-bit node address which is set to it's MAC address by default. This is appended to the network address to create a unique identifier.

● Very similar to IP in terms of addresses and routing

● ARP not required since it uses MAC address

OSI: Transport Layer

FragmentationResponsible for breaking large groups of data up into chunks for transmission.

AssemblyKeep track of where data is coming from for each application, and combine it into one stream of data

Connection ServicesDefine if it's a Connectionless or Connection-Oriented protocol.

Transmission Qualityoptional assurance that a packet is received

● TCP● UDP● ICMP● SPX● SCTP

Transmission Control Protocol

● Connection orientedboth client and server must open a connection before data is sent

● End to end reliabilityacknowledge packets are sent to confirm packet reception, or the packet is resent

● Data packet re-sequencingreorders packets when received out of order

● Flow Controldetermines the rate that data is sent between the sender and receiver

TCP Packet

User Datagram Protocol

● Connectionless Protocolthere's no check to ensure that the receiving computer is ready or accepting of a packet(s)

● No reliability, flow control, or error recoverythey're either not used, or implemented by a higher level protocol

UDP Packet

Sequence Packet eXchange

● It is a datagram protocol similar to UDP

● Provides connection-oriented service

● Primarily used on LAN's, and is very efficient here

Typical Internet Transaction

Packet Sending

● TCP software adds the port number to the packet

● IP software adds a header with the sender's and recipient's IP addresses

● Ethernet header is added to the packet with the hardware address of the network card. Packet is then sent. This happens in the Ethernet layer

Packet Receiving

● Machine detects it's address in a packet, and retrieves the data. Header data is stripped, and sent to the IP layer

● IP layer looks at the IP header, and determines if the sender's address is accepted to provide service to. If it is, the IP header is stripped and sent to the TCP layer

● TCP layer reads the port number in the header, and determines if service is provided on that port and what application is servicing that port. Strips the TCP header, and passes the rest to application.

Distributed Computing

Also known as 'Distributed Networking'

Includes parallel processing

Fall under different OSI Layers

SOAP = Presentation LayerRPC = Session Layer

● RPC● CORBA● DCOM● SOAP● Named Pipes

Remote Procedural Call

● Sometimes called Remote Method Invocation

● Allows a computer to call a subroutine on another computer, and fetch the results.

● Object Oriented● Many different, incompatible variations● In order to allow different clients to access a

server, standardized Interface Description Languages have been developed

Simple Object Access Protocol

● Protocol for exchanging XML based messages, normally using HTTP

● Easy to read. Open, standardized structure.● Can be complex, and slow to process

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <someFunctionTag xmlns="http://some.example.com/"> <variableName> variable </variableName> </someFunctionTag> </soap:Body> </soap:Envelope>

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