1 protocol architecture 1.protocols 2.connection-oriented and connectionless protocols 3.osi...
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1
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
3
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
23
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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Figure 2-9: Physical and Data Link Layer Standards in a Single Network, Continued
• Data Link Layer
– Data link layer standards also govern
• Frame organization
• Switch operation
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Figure 2-9: Physical and Data Link Layer Standards in a Single Network, Continued
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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Figure 2-10: Internet and Data Link Layers in an Internet, Continued
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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Figure 2-10: Internet and Data Link Layers in an Internet, Continued
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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Figure 2-10: Internet and Data Link Layers in an Internet, Continued
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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Figure 2-10: Internet and Data Link Layers in an Internet, Continued
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
45
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
– 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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Figure 2-18: Layered Communication on the Source Host, Continued
TransportProcess
HTTPMessage
InternetProcess
HTTPMessage
TCPHdr
TCPHdr
IPHdr
Encapsulation of TCP Segmentin Data Field of IP Packet
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Figure 2-18: Layered Communication on the Source Host, Continued
InternetProcess
HTTPMessage
TCPHdr
IPHdr
Data LinkProcess
HTTPMessage
TCPHdr
IPHdr
EthHdr
EthTrlr
Encapsulation of IP Packetin Data Field of Ethernet Frame
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Figure 2-18: Layered Communication on the Source Host, Continued
Data LinkProcess
HTTPMessage
TCPHdr
IPHdr
EthHdr
EthTrlr
Physical Process
Physical Layer converts the bits of the frame into signals.
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Figure 2-18: Layered Communication on the Source Host, Continued
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
58
Figure 2-19: Decapsulation on the Destination Host, Continued
InternetProcess
HTTPMessage
TCPHdr
IPHdr
TransportProcess
HTTPMessage
TCPHdr
Decapsulation of TCP Segmentfrom Data Field of IP Packet
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Figure 2-19: Decapsulation on the Destination Host, Continued
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)
67
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)
68
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
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