Chapter 3Protocols and the TCP/IP Suite

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3.1 The Need for a Protocol Architecture

need for a standard communication tasks by layers architecture peer protocol: a set of rules or conventions to

exchange data syntax semantics timing

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3.2 TCP/IP Protocol Architecture

architecture for ARPANET packet switching network funded by DARPA Internet standards by Internet Activities

Board (IAB)

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TCP/IP Layers three agents of communication

applications: distributed applications, e.g., e-mail and file transfer

computers: supports multiple applications at a time

networks

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communication tasks organized into five layers physical layer network access layer internet layer host-to-host (or transport) layer application layer

physical layer physical interface between computer and

network

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network access layer data exchange between a computer (end

system) and the network from source to destination computer within

a network requires destination address and possibly

priority internet layer

transfer of data over multiple interconnected networks

routing across multiple networks internet protocol (IP)

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host-to-host or transport layer independent of the network type and the

application type collection of functions for reliable data exchange assurance of delivery, correctness, and correct

order transmission control protocol (TCP)

application layer to support the various user applications a separate module needed for each different

type of application

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Operations of TCP and IP network comprised of subnetworks

network access protocol: sending data within a subnetwork or to routers

IP: moving data to a destination via routers TCP: reliable data transfer from source to

destination

two levels of addressing

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TCP segment segmented user data + control information

(TCP header: port, sequence number, checksum)

IP datagram TCP segment + control information (IP header:

host address) packet or frame

IP datagram + control information (network header: subnetwork address, priority)

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router stripping network header checking destination host address sending it as another datagram

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TCP/IP Applications simple mail transfer protocol (SMTP) file transfer protocol (FTP)

two connections: control and data transfer control connection for user access

TELNET remote logon

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3.3 The OSI Model

International Standardization Organization (ISO) Open Systems Interconnection (OSI)

reference model open denotes the ability of connecting two

systems conforming to the standards

Overall Architecture layering issues of layering

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OSI model as a framework for standardization

TCP/IP as a de facto standard

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Physical Layer: physical interface between devices and

the rules for passing bits from one to another RS-232-C

Data Link Layer: make the physical link reliable

provide means to activate, maintain, and deactivate the link

error detection and control HDLC (High-level Data Link Control)

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Network Layer: transfer of information between end

systems across some type of network relieving higher layers of the need to know

what types of switching and data transmission are used

specification of destination address and request for network facilities such as priority

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a direct point-to-point link between stations

stations connected across a single network such as a circuit-switching or packet-switching network

X.25 covering the lower three layers

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Transport Layer: reliable information exchange between

end systems error-free, in sequence, no loss, no

duplication duplication of layer 2

size and complexity depends on the type of the layer 3

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Session Layer: controlling dialogue between two end

systems little or no need for session layer service in

many cases dialogue discipline

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Presentation Layer: define the format of the data to be

exchanged data compression data encryption

Application Layer: provide means for applications to

access the OSI environment management functions support for distributed applications general-purpose applications

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3.4 Internetworking

internet

interconnected set of different subnetworks

the Internet

intranet

end system (ES)

intermediate system (IS)

bridge: interconnection at OSI layer 2

router: interconnection at OSI layer 3

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