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Chapter 6. Networking Protocols. Introduction. Topics Protocol Basics Protocol Characteristics Transmission Control Protocol/Internet Protocol Network Access Layer Protocols Internet Layer Protocols Transport Layer Protocols Application Layer Protocols. Protocol Basics.

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Chapter 6 l.jpg

Chapter 6

Networking Protocols

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  • Topics

    • Protocol Basics

    • Protocol Characteristics

    • Transmission Control Protocol/Internet Protocol

    • Network Access Layer Protocols

    • Internet Layer Protocols

    • Transport Layer Protocols

    • Application Layer Protocols

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Protocol Basics

  • A protocol is a set of rules that determines how computers exchange information over a network medium

  • A wide variety of communication protocols exist, and many of them rely on others for operation

  • Groups of related protocols are often called stacksorprotocol stacks

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Protocol Characteristics

  • Data packets can be sent over a medium using any one of a number of protocols

  • Protocols can be either standard or proprietary

  • Standard protocols

    • Support universal communication so equipment from different manufacturers can interact

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Proprietary Protocols

  • Proprietary protocols are vendor specific and are usually protected by patents or other legal stipulations

  • Proprietary protocols include

    • XNS

    • NetBIOS

    • IPX/SPX

    • AppleTalk

    • DECNet

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Xerox Network System (XNS)

  • XNS is a suite of protocols created by Xerox in the late 1970s for Ethernet networks

  • XNS is rarely used in new networks today

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  • The Network Basic Input/Output System (NetBIOS) interface was developed in 1983 for IBM

  • The intention was to allow applications on different computers to communicate within a local area network

  • NetBIOS was not designed for large networks

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  • Novell introduced Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) in the early 80s

  • This stack was based on the XNS network protocol family

  • IPX is the Network layer protocol

  • SPX is the Transport layer protocol

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  • AppleTalk is Macintosh’s networking protocol

  • It is designed to be a flexible, simple, and inexpensive network means for connecting computers, peripherals, and servers

  • Newer versions of Macintosh operating systems use TCP/IP and SMB as default protocols rather than AppleTalk

  • AppleTalk is a protocol and LocalTalk is a media type

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  • DECnetis a proprietary network protocol designed by Digital Equipment Corporation

  • Currently two versions of DECnet are in use:

    • DECnet Phase IV which is based on the Phase IV Digital Network Architecture (DNA)

    • DECnet/OSI also called DECnet Phase V is a layered model

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Transmission Control Protocol/Internet Protocol

  • TCP/IP is considered the language of the Internet

  • It is the most widely used protocol today

  • It is a suite, or stack, of small, specialized protocols

  • Because of its routing ability, TCP/IP has become the standard for many LANs, as well as for the Internet

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Transmission Control Protocol/Internet Protocol

  • In the early 1970s, the Department of Defense funded ARPA to design a new set of computer communication protocols that would allow multiple networks to be interconnected in a flexible and dynamic way

  • The protocol developed was originally called Network Control Protocol

  • This success led to the implementation of the two main Internet protocols

  • These are Transmission Control Protocol and Internet Protocol (TCP/IP)

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Transmission Control Protocol/Internet Protocol

  • The TCP/IP suite maps the seven layers of the OSI model to a four-layer model

  • The TCP/IP model focuses more on interconnectivity than on functional layers

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Transmission Control Protocol/Internet Protocol

  • The TCP/IP model is also called the Internet reference model

  • Layers

    • Network Access

    • Internet

    • Transport

    • Application

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Network Access Layer Protocols

  • The Network Access layer is the lowest layer in the model

  • It Maps to Layers 1 (Physical) and 2 (Data Link) of the OSI model

  • It is responsible for the framing (DL) and physical delivery of datagrams

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Network Access Layer Protocols

  • Access Layer Protocols deliver data to computers and devices on the network

  • These include Serial Line Interface Protocol (SLIP) and Point-to-Point Protocol (PPP)

  • These protocols support serial data transmission over a modem

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Network Access Layer Protocols

  • Other Network Access protocols

    • the Address Resolution Protocol (ARP)

    • the Reverse Address Resolution Protocol (RARP)

  • Provide a means of mapping IP addresses to MAC addresses

  • These protocols provide a means for last hop message delivery

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Internet Layer Protocols

  • The layer above the Network Access layer is called the Internet layer

  • It manages the routing of packets that are to be forwarded on to different networks

  • It relies on routable protocols for delivery

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Internet Layer Protocols

  • The Internet Protocol (IP) is responsible addressing and routing of data packets

  • Routing tables created by routing protocols are used to forward messages from one network to another

  • It is a low overhead, best effort delivery protocol

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IP Message Format

  • IP Packets or datagrams consist of a header, data (payload), and a trailer

  • The header contains routing information

  • Trailers contain a checksum value, which is used to determine if data was corrupted during transmission

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Packet Delivery

  • IP compares the destination address in the packet header to router table addresses

  • If the address corresponds to a local network, the datagram is delivered to the appropriate computer

  • If the address corresponds to a remote network, the packet is passed to a router for delivery

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Routing Controls

  • Time to Live (TTL)

    • prevents packets from circulating on the network forever

    • The TTL value is decremented by one each time the packet traverses a router (each hop)

    • Default value is usually 120

  • Fragmentation – Routers may break oversize packets into fragments, then route the individual fragments, which are reassembled at the destination computer

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  • Each subnetwork has a maximum transmission unit (MTU), which is the largest packet it can transfer

  • A datagram received from one network may be too large to be transmitted as a single packet on another network

  • Fragmentation is the process of dividing a packet into smaller pieces

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Internet Control Message Protocol

  • ICMP

    • Internet layer protocol

    • uses IP to send its messages

    • uses IP as if it was higher-level protocol

    • used as an aid for other protocols

    • used to test for connectivity and search for configuration errors in a network

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ICMP Error Messages

  • Destination Unreachable – message returned to sender if a router cannot forward an IP datagram

  • Buffer Full – message returned until congestion due to full buffer has abated

  • Hops – an IP datagram has passed through its allotted number of routers

  • Ping – ICMP echo messages are returned to sender if destination exists and is reachable

  • Traceroute – ICMP timeouts used to discover path a packet takes as it traverses an internetwork

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  • Used to test connectivity

  • uses the ICMP echo function

  • A small packet containing an ICMPecho message is sent through the network to a particular IP address

  • The computer that sent the packet then waits for a return packet

  • If the connections are good and the target computer is up, an echo message is returned to the sender

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  • Originally developed for the Unix operating system

  • used to track the path a packet takes from sender to destination

  • Calculates travel time for each hop

  • uses an ICMP echo request packet to determine the path

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Transport Layer Protocols

  • The protocol layer above the Internet layer

  • provides a reliable communication service so that extended two-way conversations may take place

  • responsible for providing end-to-end data integrity

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Transport Layer Protocols

  • Transmits data as a stream of characters

  • initiates and terminates the connections between sender and receiver

  • Two main protocols

    • Transmission Control Protocol (TCP)

    • User Datagram Protocol (UDP)

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Transmission Control Protocol (TCP)

  • provides connection-oriented data transmission

  • supports multiple data streams

  • provides for flow and error control

  • uses sequence numbers and acknowledgements to guarantee delivery

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TCP Connections

  • TCP communications are port to port

  • A socket is an IP address plus a port number

  • Well-defined port numbers have been assigned to common applications

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Port Numbers

  • Used to communicate with upper layers by keeping track of conversations with different services (applications)

  • Well-Known port numbers define different application locations on the server that hosts the applications

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User Datagram Protocol (UDP)

  • a connectionless protocol

  • Low overhead - does not provide either sequencing or acknowledgements

  • used a lot in telephony traffic and the Remote Procedure Call (RPC)

  • UDP does not provide the reliability that TCP provides

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Application Layer Protocols

  • The top layer in the Internet reference model

  • Provides applications access to network services

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ApplicationLayer Protocols

  • Telnet – remote client access to resources on a Telnet server

  • FTP – reliable file transport using TCP; requires authentication

  • TFTP – Unreliable file transport using UDP

  • NFS – allows file sharing on different platforms

  • SMTP – delivers mail to a server; use POP or IMAP to retrieve mail

  • LPD – for printer sharing

  • X Window – graphical interface for client/server applications

  • SNMP –Provides network management by polling capable devices

  • DNS –maps host names to IP addresses

  • DHCP – provides IP address configuration to workstations

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File Transfer and Remote Access

  • File Transfer Protocol (FTP) which allows files to be uploaded and downloaded on port 21

  • Telnet which uses terminal emulation for access to remote hosts using port 23

  • Both FTP and Telnet use TCP as their Transport layer protocol

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Mail and Internet

  • Simple Mail Transfer Protocol (SMTP) which supports basic message delivery services to mail servers on port 25

  • HyperText Transfer Protocol (HTTP) which is a low-overhead Web browser service protocol that uses port 80

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Management and News

  • Simple Network Management Protocol (SNMP) which uses UDP port 161 to collect information from network devices.

  • Network News Transfer Protocol (NNTP): handles distribution and posting of news articles using port 119

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Address Assignment and Name Mapping

  • Dynamic Host Configuration Protocol (DHCP) allows for automatic IP addressing

  • Domain Name Service (DNS) uses UDP port 53 for resolving domain names to IP addresses