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

Network Types LAN – Local Area Network Computer network that spans a relatively small area. WAN – Wide Access Network Geographically dispersed computer network

Open Systems Interconnection Model Physical defines all the electrical and physical specifications for devices Data Link functional and procedural means to transfer data between network entities Network means of transferring variable length data sequences from a source to a destination Transport provides transparent transfer of data between end users Session mechanism for managing the dialogue between end-user application processes Presentation formats information for the application layer Application facilitates communication between software applications and lower-layer network services

OSI: Physical Layer 10BASE-T 100BASE-TX 1000BASE-T ISDN DSL 802.11b 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 Ethernet 802.11 Frame Relay Token Ring X.25 PPP Logical Link Control (LLC) the functions required to establish and control a network link Media Access Control (MAC) Separate devices on a network Addressing Address Resolution Protocol used to convert an IP to MAC address is performed at this level Data Framing encapsulates messages Error Detection and Handling ensures 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 bytes Destination MAC Address – 6 bytes Source MAC Address – 6 bytes Ether Type – 2 bytes Data – 46 to 1500 bytes CRC Checksum – 4 bytes

OSI: Network Layer IP IPSec NetBEUI IPX Heirarchal Addressing address to specify a machine. Independent of hardware and unique across a network. Routing this level handles transferring data across interconnected networks while maintaining the transportation layers specified QoS. Datagram Encapsulation places data into datagrams to send Fragmentation and Reassembly The size of a packet is determined by software at this level Error Handling Find 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 TCP UDP ICMP SPX SCTP Fragmentation Responsible for breaking large groups of data up into chunks for transmission. Assembly Keep track of where data is coming from for each application, and combine it into one stream of data Connection Services Define if it's a Connectionless or Connection-Oriented protocol. Transmission Quality optional assurance that a packet is received TCP UDP ICMP SPX SCTP

Transmission Control Protocol Connection oriented both client and server must open a connection before data is sent End to end reliability acknowledge packets are sent to confirm packet reception, or the packet is resent Data packet re-sequencing reorders packets when received out of order Flow Control determines the rate that data is sent between the sender and receiver

TCP Packet

User Datagram Protocol Connectionless Protocol there's no check to ensure that the receiving computer is ready or accepting of a packet(s) No reliability, flow control, or error recovery they'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 Layer RPC = 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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