1 Protocol Architecture 1.Protocols 2.Connection-Oriented and Connectionless Protocols 3.OSI...

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Protocol Architecture

1. Protocols

2. Connection-Oriented and Connectionless Protocols

3. OSI Standard Architecture

4. TCP/IP Protocol Architecture

5. Vertical Communication Between Layer Processes

1. Protocols

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Key Elements of a Protocol

• Syntax

– Data formats

– Signal levels

• Semantics

– Control information

– Error handling

• Timing

– Speed matching

– Sequencing

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Standards

Standards are rules of operationthat allow two hardware or software processes

to work together

Even if they are from different vendors

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Figure 2-1: Standards Govern the Exchange of Messages

• Standards Govern the Exchange of Messages

– Messages must be governed by strict rules

– Because computers are not intelligent

Message

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Figure 2-1: Standards Govern the Exchange of Messages (Continued)

• Standards Govern Syntax– Syntax: the organization of the message

– Human example: “Susan thanked Tom”

– This sentence has a subject-verb-object syntax

• Standards Govern Semantics– Semantics: The meaning of the message

– Human example: “Susan thanked Tom”

– Humans understand this message easily

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Figure 2-1: Standards Govern the Exchange of Messages, Continued

• General Message Syntax (Organization)

– General Message Organization (Figure 2-4)

– Primary parts of messages

• Data Field (content to be delivered)

• Header (everything before the data field)

• Trailer (everything after the data field)

– The header and trailer act like a delivery envelope for the data field.

HeaderData FieldTrailer

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Figure 2-1: Standards Govern the Exchange of Messages, Continued

• General Message Syntax (Organization)– Header and trailer are further divided into fields

Trailer Data Field Header

OtherHeader

FieldDestination

AddressField is

Used by Switches and RoutersLike the Address on an Envelope

Message withall three parts

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Figure 2-4: General Message Organization, Continued

Data Field Header

OtherHeader

Field

DestinationAddress

Field

Message withouta trailer

Usually only data linklayer messages have trailers

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Figure 2-4: General Message Organization, Continued

Header

OtherHeader

Field

DestinationAddress

Field

Message withonly a header

e.g.TCP supervisory

messages arepure headers

(there is no data field content to deliver)

2.Connection-Oriented andConnectionless Protocols

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Figure 2-6: Connection-Oriented and Connectionless Protocols

Message(No Sequence Number)

Connectionless Protocol

A B

Message 1 (Seq. Num = A1)

Message 2 (Seq. Num = A2)

Close Connection

Connection-Oriented Protocol

Open ConnectionA B

Message 3 (Seq. Num B1)

Connection-oriented protocolsFormal openings and closings

Also have sequence numbersso that the receiver can putmessages in order

And so the receiver can sendAcknowledgments for specificmessages

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Figure 2-6: Connection-Oriented and Connectionless Protocols, Continued

Client PCBrowser

WebserverApplication

HTTP Request

HTTP is connectionless

No OpeningsNo Closings

No Sequence NumbersNo Acknowledgments

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Figure 2-6: Connection-Oriented and Connectionless Protocols, Continued

Client PCTCP Process

WebserverTCP Process

Connection-Opening Messages

Time

Connection-Closing Messages

Messages During the Connection

In TCP

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Figure 2-7: Advantages and Disadvantages or Connection-Oriented Protocols

• Advantages

– Thanks to sequence numbers, the parties can tell if a message is lost.

– Error messages, such as ACKs can refer to specific messages.

– Long messages can be fragmented into many smaller messages that can fit inside packets.

• Fragmentation followed by reassembly on the destination host is an important concept in networking.

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Figure 2-7: Advantages and Disadvantages or Connection-Oriented Protocols, Cont.

• Disadvantages

– The presence of many supervisory messages consumes existing bandwidth

– The processing of connection information places a heavy processing load on computers connected to the network

3. OSI Standard Architecture

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Standards Architecture

• A Standards Architecture is a Broad Plan for Creating Standards

– Break the problem of effective communication into smaller pieces for ease of development

– Develop standards for the individual pieces

– Just as a building architect creating a general plan for a house before designing the individual rooms in detail

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OSI

• Open Systems Interconnection

• Developed by the International Organization for Standardization (ISO)

• Seven layers

• A theoretical system delivered too late!

• TCP/IP is the de facto standard

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OSI - The Model

• A layer model

• Each layer performs a subset of the required communication functions

• Each layer relies on the next lower layer to perform more primitive functions

• Each layer provides services to the next higher layer

• Changes in one layer should not require changes in other layers

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Why Layer?

• Breaking up large tasks into smaller tasks and assigning tasks to different individuals is common in all fields

• Specialization in standards design (EEs for physical layer, application specialists for application layer, etc.)

• Simplification in standards design for individual standards

• If you change a standard at one layer, you do not have to change standards at other layers

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OSI Layers

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The OSI Environment

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Protocol Data Units (PDU)

• At each layer, protocols are used to communicate

• Control information is added to user data at each layer (PDU = Control + Data)

• Transport layer may fragment user data

• Each fragment has a transport header added

– Destination SAP

– Sequence number

– Error detection code

• This gives a transport protocol data unit

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Protocol Data Units

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OSI as Framework for Standardization

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Figure 2.9Layer Specific Standards

4. TCP/IP Protocol Architecture

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TCP/IP Protocol Architecture

• Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)

• Used by the global Internet

• No official model but a working one.

Application layer

Transport layer

Internet layer

Data Link layer (Network Access)

Physical layer

(host-to-host)

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Hybrid TCP/IP-OSI Architecture

General Purpose Layer Specific Layer Purpose

Application-application communication

Application (5) Application-application interworking

Transmission across an internet

Transport (4) Host-host communication

Internet (3) Packet delivery across an internet

Transmission across a single network (LAN or WAN)

Data Link (2) Frame delivery across a network

Physical (1) Device-device connection

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Figure 2-8: Hybrid TCP/IP-OSI Architecture, Continued

• Physical and Data Link Layer Standards

– Govern Communication Through a Single Network

– LAN or WAN

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Physical Layer

• Physical interface between data transmission device (e.g. computer) and transmission medium or network

• Characteristics of transmission medium

• Signal levels

• Data rates

• etc.

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Figure 2-9: Physical and Data Link Layer Standards in a Single Network

• Physical Layer

– Physical layer standards govern transmission between adjacent devices connected by a transmission medium

Switch X1

Physical LinkA-X1

Host A

Switch X2Physical LinkX1-X2

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Figure 2-9: Physical and Data Link Layer Standards in a Single Network, Continued

• Data Link Layer

– Data link layer standards govern the transmission of frames across a single network—typically by sending them through several switches along the data link

Switch X1Host A

Switch X2

Host BData LinkA-B

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• Data Link Layer

– Data link layer standards also govern

• Frame organization

• Switch operation

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Host A

Mobile ClientStation

ServerStation

Switch

SwitchX2

Switch X1

Switch

Data LinkA-R1

Physical LinkA-X1

PhysicalLink

X1-X2

Router R1

PhysicalLink

X2-R1

3 Physical Links1 Data Link2 Switches

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Figure 2-10: Internet and Data Link Layers in an Internet

• Internet and Transport Layers

– An internet is a group of networks connected by routers so that any application on any host on any network can communicate with any application on any other host on any other network

– Internet and transport layer standards govern communication across an internet composed of two or more single networks

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Figure 2-10: Internet and Data Link Layers in an Internet, Continued

• Internet Layer

– Internet layer standards govern the transmission of packets across an internet—typically by sending them through several routers along the route

– Messages at the internet layer are called packets

– Internet layer standards also govern packet organization and router operation

Router 1 Router 2

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Host B

Host A

Network XNetwork Y

Network Z

R1

R2

Data Link A-R1

Data Link R3-B

DataLink

R1-R2Route A-B

3 Data Links: One per Network1 Route per Internet

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Host A

Mobile ClientStation

ServerStation

Switch

SwitchX2

SwitchX1

Switch

Data LinkA-R1

Router R1

Packet

Frame X

Network X

RouteA-B

In Network X:Two Destination Addresses:

Packet: Host B (Destination Host)Frame: Router R1

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Router R1

Router R2

Packet

Frame Y

ToNetwork X

ToNetwork Z

Network Y

Data LinkR1-R2

RouteA-B

In Network Y:Two Destination Addresses:

Packet: Host B (Destination Host)Frame: Router R2

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Host B

Mobile ClientStations

SwitchZ1

SwitchX2

SwitchZ2

PacketFrame Z

Network Z

Router R2

Router

Data LinkR2-B

In Network Z:Two Destination Addresses:

Packet: Host B (Destination Host)Frame: Host B

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Frames and Packets

• In an internet with hosts separated by N networks, there will be:– 2 hosts

– One packet (going all the way between hosts)

– One route (between the two hosts)

– N frames (one in each network)

– N-1 routers (change frames between each pair of networks)

– There usually are many switches within single networks

– There usually are many physical links within networks

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Figure 2-11: Internet and Transport Layer Standards

• Transport Layer

– Transport layer standards govern aspects of end-to-end communication between two end hosts that are not handled by the internet layer

– These standards allow hosts to work together even if the two computers are from different vendors and have different internal designs

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Figure 2-11: Internet and Transport Layer Standards, Continued

Transport Layerend-to-end (host-to-host)

TCP is connection-oriented, reliableUDP is connectionless and unreliable

Internet Layer(usually IP)

hop-by-hop (host-router or router-router)connectionless, unreliable

Router 1 Router 2 Router 3

Client PCServer

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Figure 2-12: Application Layer Standards

• Application Layer

– The application layer governs how two applications work with each other, even if they are from different vendors

Webserver

Browser WebserverApplication

Client PC

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Figure 2-12: Application Layer Standards

• There are more application layer standards than any other type of standard because there are many applications

– HTTP

– E-Mail

– Database

– Instant Messaging

– FTP

– Etc.

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Some Protocols in TCP/IP Suite

5.Vertical Communication Between Layer Processes

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Figure 2-18: Layered Communication on the Source Host

ApplicationProcess

HTTPMessage

TransportProcess

HTTPMessage

TCPHdr

Encapsulation of HTTP Messagein Data Field of TCP Segment

Passes MessageDown to Transport Process

The process begins when a browser creates an HTTP request message

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Figure 2-18: Layered Communication on the Source Host, Continued

• When a layer process (N) creates a message, it passes it down to the next-lower-layer process (N-1) immediately

• The receiving process (N-1) will encapsulate the Layer N message, that is, place it in the data field of its own (N-1) message

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TransportProcess

HTTPMessage

InternetProcess

HTTPMessage

TCPHdr

TCPHdr

IPHdr

Encapsulation of TCP Segmentin Data Field of IP Packet

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InternetProcess

HTTPMessage

TCPHdr

IPHdr

Data LinkProcess

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

Encapsulation of IP Packetin Data Field of Ethernet Frame

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Data LinkProcess

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

Physical Process

Physical Layer converts the bits of the frame into signals.

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The following is the final frame for aan HTTP message on an Ethernet LAN

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

L5 L4 L3 L2L2

Notice the Pattern: From Right to Left: L2, L3, L4, L5, maybe L2

This makes it easier to remember the order of headers and messages

Don’t forget the possible trailing L2 trailer

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Figure 2-19: Decapsulation on the Destination Host

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

Data LinkProcess

Physical Process

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Figure 2-19: Decapsulation on the Destination Host, Continued

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

Data LinkProcess

InternetProcess

HTTPMessage

TCPHdr

IPHdr

Decapsulation of IP Packetfrom Data Field of Ethernet Frame

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InternetProcess

HTTPMessage

TCPHdr

IPHdr

TransportProcess

HTTPMessage

TCPHdr

Decapsulation of TCP Segmentfrom Data Field of IP Packet

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TransportProcess

HTTPMessage

TCPHdr

ApplicationProcess

HTTPMessage

Decapsulation of HTTP Messagefrom Data Field of TCP Segment

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PDUs in TCP/IP

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Figure 2-20: Layered End-to-End Communication

Int

App

DL

Trans

Phy

SourceHost

DestinationHost

Switch1

Switch2

Router1

Switch3

Router2

Source andDestinationHosts Have

5 Layers

SwitchesHave Two

Layers---

Each SwitchPort

Has OneLayer (1)

RoutersHave Three

Layers---

Each RouterPort

Has TwoLayers (1&2)

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Figure 2-21: Combining Horizontal and Vertical Communication

Int

App

DL

Trans

Phy

SourceHost

DestinationHost

Switch1

Switch2

Router1

Switch3

Router2

Hypertext Transfer Protocol

Transmission Control Protocol

Internet Protocol

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TCP Header + Telnet Data

Telnet Data

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IP Header + TCP Header + Telnet Data

Ethernet Frame Header + IP Header + TCP Header + Telnet Data

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Example Header Information

• Destination port

• Sequence number

• Checksum

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Figure 2-23: OSI and TCP/IP

OSI TCP/IP

StandardsAgency or Agencies

ISO (InternationalOrganization for Standardization)

ITU-T (InternationalTelecommunicationsUnion—TelecommunicationsStandards Sector)

IETF (InternetEngineering TaskForce)

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Figure 2-23: OSI and TCP/IP, Continued

OSI TCP/IP

Dominance Nearly 100% dominant at physical and datalink layers

70%-80% dominantat the internet and transportlayers.

Documents areCalled

Various Mostly RFCs (requestsfor comments)

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Figure 2-26: Characteristics of Protocols Discussed in the Chapter

Layer Protocol Connection-Oriented/Connectionless

Reliable/Unreliable

5 (App) HTTP Connectionless Unreliable

4 (Transport) TCPConnection-oriented

Reliable

3 (Internet) IP Connectionless Unreliable

2 (Data Link) Ethernet Connectionless Unreliable

Note: Only TCP is connection-oriented and reliable

4 (Transport) UDP Connectionless Unreliable

1 Protocol Architecture 1.Protocols 2.Connection-Oriented and Connectionless Protocols 3.OSI...

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