1. Protocol Architecture
Protocols
Connection-Oriented and Connectionless Protocols
OSI Standard Architecture
TCP/IP Protocol Architecture
Vertical Communication Between Layer Processes

2. 1. Protocols We will look first at standards that govern messages.
Such standards are called protocols. In fact, many standards have “protocol” in their names.
We will use the terms “standards” and “protocols” interchangeably in this book.

3. Key Elements of a Protocol
Syntax
Data formats
Signal levels
Semantics
Control information
Error handling
Timing
Speed matching
Sequencing

4. Standards Standards are rules of operation
that allow two hardware or software processes
to work together
Even if they are from different vendors
<Read the definition.>
Because standards allow products from different vendors to work together, standards create competition. You can buy products from any standards-compliant vendor.
This produces all of the usual benefits of competition: more competitors, lower costs, and more rapid feature development.

5. Figure 2-1: Standards Govern the Exchange of Messages
Messages must be governed by strict rules
Because computers are not intelligent
What do standards govern in networking? They govern the exchange of messages.
As long as two communicating parties send messages in a way dictated by the standard they are using, they don’t care what vendor produced the other product.
In the play “My Fair Lady,” Professor Henry Higgens says that. “The French don’t care what you do, as long as you pronounce it correctly!” Roughly speaking, this is how standards work.
In this textbook, the “standard” language is English. However, it can be read by someone who has a different native language if they can follow the standard by reading English.
Message

6. 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
Humans understand this message easily
<Read through the slide.>

7. 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.
Moving from the specific syntax of HTTP messages to the syntax of messages in general, we see that in general a message can have three parts.
The most important part is the data field, which contains the content to be delivered.
This is like the letter in an envelope.
The data field is usually by far the longest part of the message.
The header is everything that comes before the data field, and the trailer is everything that comes after the data field.
The header and trailer act like a delivery envelope for the data field.
Trailer
Data Field
Header

8. 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
Other
Header
Field
Destination
Address
Field is
Used by Switches and Routers
Like the Address on an Envelope
Message with
all three parts
Now that we have seen the three basic parts, we will look more closely at the header and trailer.
This figure shows that the header is divided into smaller sections called fields.
The most important header field is the destination address field.
This is like the address on a postal letter.
Switches and routers use this field to decide how to forward an incoming message back out.
Trailers can also be divided into fields.

9. Figure 2-4: General Message Organization, Continued
Data Field
Header
Other
Header
Field
Destination
Address
Field
Message without
a trailer
Usually only data link
layer messages have trailers
Not all messages have all three parts.
For example, trailers are only found at something called the data link layer, which we will see later in this chapter.
Most messages DO NOT have trailers!

10. Figure 2-4: General Message Organization, Continued
Header
Message with
only a header
e.g.
TCP supervisory
messages are
pure headers
(there is no data field content to deliver)
Other
Header
Field
Destination
Address
Field
Some messages only have a header.
This is true of supervisory messages in TCP—a standard we will see alter in this chapter.
There is no data field in TCP because there is no content to be delivered other than the supervisory information in the header.
Some other protocols, including the Internet Protocol, carry supervisory messages in their data fields. We will see this in Chapter 8.

11. 2. Connection-Oriented and Connectionless Protocols
In addition to being either reliable or unreliable, protocols are either connection-oriented or connectionless.

12. Figure 2-6: Connection-Oriented and Connectionless Protocols
Connection-Oriented Protocol
Connectionless Protocol
Open Connection A B A B
Message
(No Sequence Number)
Message 1 (Seq. Num = A1)
Connection-oriented protocols
Formal openings and closings
Also have sequence numbers
so that the receiver can put
messages in order
And so the receiver can send
Acknowledgments for specific
messages
Message 3 (Seq. Num B1)
Message 2 (Seq. Num = A2)
Connection-oriented protocols require the communicating partners to have formal openings and closings. Both sides must agree to open the communication, and. generally speaking, both sides must agree to close the communication.
Telephone conversations are like this. At the beginning of the cal, therel is at least a tacit negotiation that this is a good time to talk. At the end, simply hanging up is rude.
With formal connections, the two parties can keep track of all communication in the communication.
Message have sequence numbers, so if messages arrive out of order, they can be put into order.
Also, acknowledgements can refer to specific messages, so there is no need to stop an wait for an acknowledgement before sending the next message.
Close Connection

13. HTTP is connectionless
Figure 2-6: Connection-Oriented and Connectionless Protocols, Continued
Client PC
Browser
Webserver
Application
HTTP Request
HTTP is connectionless
No Openings
No Closings
No Sequence Numbers
No Acknowledgments
HTTP is a connectionless protocol
There is no formal connection opening or closing in HTTP.
There are no sequence numbers or acknowledgements.
In connectionless protocols, the sender simply sends the message. works this way.
<Ask whether a postal letter is connectionless or connection-oriented. Answer: It is connectionless.>
[Advanced note: Because HTTP is connectionless, if there is a series of HTTP exchanges, as in e-commerce transactions, the protocol cannot keep the messages in order or remember what happened in an earlier message. To get around this problem, the webserver can place small text files on your computer to remind it what happened in the last step or steps. These small files are called cookies.]

14. Figure 2-6: Connection-Oriented and Connectionless Protocols, Continued
In TCP
Client PC
TCP Process
Webserver
TCP Process
Connection-Opening Messages
Messages During the Connection
Time
In addition to being reliable, TCP, is connection-oriented.
There are formal openings and closings to TCP sessions. We will see these in detail in Chapter 8.
Connection-Closing Messages

15. Figure 2-7: Advantages and Disadvantages or Connection-Oriented Protocols
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.
<Read the slide.>

16. Figure 2-7: Advantages and Disadvantages or Connection-Oriented Protocols, Cont.
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
<Read the slide.>

17. 3. OSI Standard Architecture
We are switching topics again, this time to look at something called a standards architecture.

18. 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
<Read the slide.>

19. 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

20. 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

21. 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
<This is not essential material. If you want to cover it, read the slide.>

22. OSI Layers

23. The OSI Environment

24. 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

25. Protocol Data Units

26. OSI as Framework for Standardization

27. Figure 2.9 Layer Specific Standards

28. 4. TCP/IP Protocol Architecture

29. 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)

30. 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
<Note to teacher, not to be read: Almost no companies use the pure OSI or pure TCP/IP architectures in practice. What they use is a hybrid of OSI at Layers 1 and 2 and TCP/IP or another standards architecture at Layers 3 and 4.>
Now let’s look at the most widely used standards architecture, the hybrid TCP/IP-OSI standards architecture. We will see later why it has this rather long name.
the architecture has three general purposes. <Read the first column.>
These general purposes are further subdivided into specific standards layers. <Go through the second and third columns.>

31. Figure 2-8: Hybrid TCP/IP-OSI Architecture, Continued
Physical and Data Link Layer Standards
Govern Communication Through a Single Network
LAN or WAN
We will begin by discussing the architecture at its two bottom layers: the physical and data link layers.
As noted in the previous slide, these two layers together govern communication in a single network—a single LAN or a single WAN.

32. 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.

33. 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
Physical Link
A-X1
Switch X1
<Read the bullet point.>
<Then point out the two physical links—A-X1 and X1-X2.>
Host A
Switch X2
Physical Link
X1-X2

34. Figure 2-9: Physical and Data Link Layer Standards in a Single Network, Continued
Data link layer standards govern the transmission of frames across a single network—typically by sending them through several switches along the data link
Data Link
A-B
Host B
<Read the slide.>
<As a check on their understanding, ask, “How many data links are there in the figure?” Answer: 1 (HostA—Host B).>
<Then ask, “How many physical links there are in the figure?” Answer: 3
Host A to Switch X1,
Switch X1 to Switch X2, and
Switch X2 to Host B.>
Switch X1
Host A
Switch X2

35. Figure 2-9: Physical and Data Link Layer Standards in a Single Network, Continued
Data link layer standards also govern
Frame organization
Switch operation
<Read the Slide.>
<Tell students that a message at the data link layer is called a frame.>

36. Figure 2-9: Physical and Data Link Layer Standards in a Single Network, Continued
3 Physical Links
1 Data Link
2 Switches
Host A
Switch
Data Link
A-R1
Switch
Physical Link
A-X1
Server
Station
Switch X1
<This is a wrap-up slide for the physical and data link layers.>
<Note the box in the upper-right quadrant. Show the three physical links, the one data link, and the two switches.>
<Point out that the number of switches is always one LESS than the number of physical links.>
<Note that the destination host is a router, which will communicate outside the network. The router is the destination host within this single network>
Physical
Link
X1-X2
Physical
Link
X2-R1
Switch X2
Mobile Client
Station
Router R1

37. 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
<Note that we have been looking at single networks, which are governed by the physical and data link layers.>
<Now, we will look at the next two layers, the internet and transport layers, which govern transmission through an internet.>
<Read the slide.>

38. 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
We will look first at the internet layer.
<Read the slide.>
Note that messages at the data link layer are called frames, while messages at the internet layer are called packets.
Router 1
Router 2

39. Figure 2-10: Internet and Data Link Layers in an Internet, Continued
Host A
Data Link A-R1 R1
Network X
3 Data Links: One per Network
1 Route per Internet
Network Y
Data
Link
R1-R2
Network Z
Route A-B
This figure compares data links at the data link layer and routes at the internet layer.
A route is the packet’s path through the internet. There is only one route in an internet. <Show it.>
A data link is the frame’s path through a single network. There are as many data links as there are single networks (3 in this case). <Show it.> R2
Host B
Data Link R3-B

40. Figure 2-10: Internet and Data Link Layers in an Internet, Continued
Frame X
Packet
Data Link
A-R1
Switch
In Network X:
Two Destination Addresses:
Packet: Host B (Destination Host)
Frame: Router R1
Host A
Switch
Server
Station
Switch X1
<Hand out a copy of Figure 2-10 so that students can see the entire figure.>
<Point out that this slide shows the top network, Network X>
<Go through the box in the upper-right>
<Note that the packet’s destination address is that of Host B, the destination host at the end of the route.>
<Note that the frame only goes as far as Router R1. Therefore, the frame’s destination address is that of Router R1.>
Mobile Client
Station
Switch X2
Route
A-B
Router R1
Network X

41. Figure 2-10: Internet and Data Link Layers in an Internet, ContinuedTo
Network X
Route
A-B
Router R1
Frame Y
Data Link
R1-R2
In Network Y:
Two Destination Addresses:
Packet: Host B (Destination Host)
Frame: Router R2
Packet
<Point out that this slide shows the middle network, Network Y.>
<Go through the box in the left middle of the screen.>
<Note that the packet’s destination address is still that of Host B, the destination host at the end of the route. This never changes.>
<Note that the frame carrying the packet only goes as far as Router R2. Therefore, the frame’s destination address is that of Router R2.> To
Network Z
Router R2
Network Y

42. Figure 2-10: Internet and Data Link Layers in an Internet, Continued
Frame Z
Packet
Data Link
R2-B
Switch Z1
Host B
Router R2
In Network Z:
Two Destination Addresses:
Packet: Host B (Destination Host)
Frame: Host B
Switch Z2
<Point out that this slide shows the bottom network, Network Z.>
<Go through the box in the left middle.>
<Note that the packet’s destination address is still that of Host B, the destination host at the end of the route. Again, the packet’s address never changes.>
<Note that the frame goes all the way to the destination host. Therefore, the frame’s destination address is that of the destination host, Host B.>
<Point out that Host B has two addresses—an internet layer address and a data link layer address.>
Mobile Client
Stations
Switch X2
Router
Network Z

43. In an internet with hosts separated by N networks, there will be:
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
<Go through the slide.>

44. Figure 2-11: Internet and Transport Layer Standards
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
Now we are moving to Layer 4—the transport layer.
<Go through the slide.>

45. Figure 2-11: Internet and Transport Layer Standards, Continued
end-to-end (host-to-host)
TCP is connection-oriented, reliable
UDP is connectionless and unreliable
Server
Client PC
Internet Layer
(usually IP)
hop-by-hop (host-router or router-router)
connectionless, unreliable
This slide shows how the internet and transport layers are related.
At the internet layer, the standard usually is the Internet Protocol (IP).
IP operates on a hop-by-hop basis from the source host to the first router, between each router, and from the last router to the destination host.
IP is unreliable and connectionless, so uncorrected errors will occur, and packets may arrive out of order.
The transport layer is an end-to-end layer. It only operates on the two hosts.
There are two transport layer standards. TCP, which we saw earlier, is connection-oriented and reliable. It fixes errors and makes sure that packets arrive in order.
There also is a second transport layer standard, UDP. UDP is connectionless and unreliable. As we will see later, not all applications need a reliable transport layer to fix problems, and UDP places a lighter burden on the network and the two computers.
Note that making IP reliable would require error checking on each hop between routers. This would make routers very expensive and would be overkill because errors are fairly rare.
However, making TCP reliable only requires error correction to be done on two devices—the two hosts
In addition, if the transport layer is reliable, it will fix errors that occurred at lower layers as well
Router 1
Router 2
Router 3

46. Figure 2-12: Application Layer Standards
The application layer governs how two applications work with each other, even if they are from different vendors
Now we are moving to the top layer in the hybrid TCP/IP-OSI architecture” the application layer.
<Read the bullet point, then note that the two application programs in this example are the browser on the client PC and the webserver application program on the webserver.>
Browser
Webserver
Application
Client PC
Webserver

47. 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.
<Read the slide.>
<Ask how many students do music downloading.
Ask if they think the communication between their device and the music source is governed by a standard. (It must be.).
Ask at what layer the standard works. (It’s an application, so it MUST be an application layer standard.)>

48. Some Protocols in TCP/IP Suite

49. 5. Vertical Communication Between Layer Processes
We have talked about standards at various layers.
On hosts, switches, and routers, there is a hardware or software process that implements each layer.
We will look at how the processes at different layers interact on a single computer, switch, or router.

50. Figure 2-18: Layered Communication on the Source Host
The process begins when a browser creates an HTTP request message
Application
Process
HTTP
Message
Passes Message
Down to Transport Process
Transport
Process
HTTP
Message
TCP
Hdr
Let’s see what happens when a browser creates an HTTP request message.
The application process is the browser on the client PC. It creates the HTTP request message.
The application process then passes the application layer message—the HTTP request message—down to the next-lower-layer process, the transport layer process.
HTTP requires TCP at the transport layer.
The transport process encapsulates the application layer message in the data field of a TCP message. The transport process does this by adding a TCP header to the HTTP request message.
Encapsulation of HTTP Message
in Data Field of TCP Segment

51. 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
Let’s look at the vertical communication process more abstractly.
<Read the slide.>
<Ask: In the previous slide, what was layer N? Answer: The application layer.>
<Ask: In the previous slide, what was layer N-1? Answer: The transport layer.>

52. Figure 2-18: Layered Communication on the Source Host, Continued
Transport
Process
HTTP
Message
TCP
Hdr
Internet
Process
HTTP
Message
TCP
Hdr IP
Hdr
Now let’s look at what the transport layer process does with the TCP message.
The transport layer is now Layer N. It passes the message down to Layer N-1 – the internet layer process.
The internet layer process encapsulates the TCP message in the data field of an IP packet by adding an IP header.
We now have an IP packet consisting of the HTTP message, a TCP header, and an IP header.
Encapsulation of TCP Segment
in Data Field of IP Packet

53. Figure 2-18: Layered Communication on the Source Host, Continued
Internet
Process
HTTP
Message
TCP
Hdr IP
Hdr
Data Link
Process
Eth
Trlr
HTTP
Message
TCP
Hdr IP
Hdr
Eth
Hdr
Now we will look at what the internet layer process does.
Now, the internet layer is now Layer N.
The internet process passes the IP packet down to the N-1 layer, the data link layer.
The data link layer encapsulates the IP packet in a frame. In this case, the frame is an Ethernet frame, so the layer process adds both an Ethernet header and an Ethernet trailer.
Encapsulation of IP Packet
in Data Field of Ethernet Frame

54. Figure 2-18: Layered Communication on the Source Host, Continued
Data Link
Process
Eth
Trlr
HTTP
Message
TCP
Hdr IP
Hdr
Eth
Hdr
Physical
Process
Things are a little different at the data link layer.
The data link layer, Layer N, still passes the message down to the next-lower layer, the physical layer.
However, the physical layer does not do encapsulation. It merely converts the bits of the frame into electrical or radio signals and sends the signal on to the next device.
Physical Layer converts the bits of the frame into signals.

55. Figure 2-18: Layered Communication on the Source Host, Continued
The following is the final frame for a
an HTTP message on an Ethernet LAN
Eth
Trlr
HTTP
Message
TCP
Hdr IP
Hdr
Eth
Hdr L2 L5 L4 L3 L2
Although the vertical layering process on the source host is simple, many students have trouble with it.
Here’s a trick. It helps to draw the messages, headers, and trailers with layer indications under them.
Notice that the message starts with a Layer 2 header, then has a Layer 3 (IP) header, an L4 header, and an L5 message.
Don’t forget the L2 trailer.
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

56. Figure 2-19: Decapsulation on the Destination Host
Eth
Trlr
HTTP
Message
TCP
Hdr IP
Hdr
Eth
Hdr
Data Link
Process
Physical
Process
So far, we have been looking at vertical communication on the source host.
Now we will see what happens on the destination host.
The signal comes into the computer at the physical layer.
The physical layer process converts the signal into the bits of the data link layer frame. It then passes this frame up to the data link layer process.

57. Figure 2-19: Decapsulation on the Destination Host, Continued
HTTP
Message
TCP
Hdr IP
Hdr
Internet
Process
Eth
Trlr
HTTP
Message
TCP
Hdr IP
Hdr
Eth
Hdr
Data Link
Process
The data link layer process DECAPSULATES the IP packet from the frame’s data field.
It then passes the packet up to the next higher layer (N+1) – the internet layer process.
Decapsulation of IP Packet
from Data Field of Ethernet Frame

58. Figure 2-19: Decapsulation on the Destination Host, Continued
HTTP
Message
TCP
Hdr
Transport
Process
HTTP
Message
TCP
Hdr IP
Hdr
Internet
Process
Now it’s the internet layer process’s turn.
The internet layer process decapsulates the transport layer message from the IP packet and passes this message up to the transport layer process.
Decapsulation of TCP Segment
from Data Field of IP Packet

59. Figure 2-19: Decapsulation on the Destination Host, Continued
HTTP
Message
Application
Process
HTTP
Message
TCP
Hdr
Transport
Process
Finally, the transport layer process decapsulates the application layer message from the TCP message.
It passes the HTTP request message up to the application layer process—the webserver application program on the webserver.
Decapsulation of HTTP Message
from Data Field of TCP Segment

60. PDUs in TCP/IP

61. Figure 2-20: Layered End-to-End Communication
Routers
Have Three
Layers
---
Each Router
Port
Has Two
Layers (1&2)
Switches
Have Two
Layers
---
Each Switch
Port
Has One
Layer (1)
Source and
Destination
Hosts Have
5 Layers
Int
App DL
Trans
Phy
What happens on the switches and routers between the source and destination hosts?
Switches only have two layers.
Each switch port has a physical layer process.
There is one data link process to decide which port to use to send the frame back out.
Switches are Layer 2 devices.
Routers are Layer 3 devices.
Each router port has both a physical layer process and a data link layer process.
There is a single internet process to decide which port to use to send the packet back out.
Note that switches and routers receiver first, then send.
So they first decapsulate, then encapsulate.
Source
Host
Switch 1
Switch 2
Router 1
Switch 3
Router 2
Destination
Host

62. Figure 2-21: Combining Horizontal and Vertical Communication
Hypertext Transfer Protocol
Int
App DL
Trans
Phy
Transmission Control Protocol
Internet Protocol
Standards (protocols) are designed to govern communication between processes at the same layer but on different computers. This is horizontal communication.
There also is vertical communication on each device.
This figure brings the two pictures together.
Source
Host
Switch 1
Switch 2
Router 1
Switch 3
Router 2
Destination
Host

63. Telnet Data
TCP Header + Telnet Data

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

65. Example Header Information
Destination port
Sequence number
Checksum

66. Figure 2-23: OSI and TCP/IP
Standards
Agency or
Agencies
ISO (International
Organization for
Standardization)
ITU-T (International
Telecommunications
Union—
Standards Sector)
IETF (Internet
Engineering Task
Force)
Standards architectures are governed by standards agencies.
OSI is governed by two standards agencies that work together.
<Read the names.>
ISO specializes in computer and LAN standards.
ITU-T specializes in WAN standards.
TCP/IP is governed by the Internet Engineering Task Force (IETF).
The IETF creates all standards for the Internet.

67. Figure 2-23: OSI and TCP/IP, Continued
Dominance
Nearly 100%
dominant at
physical and data
link layers
70%-80% dominant
at the internet and
transport
layers.
Documents are
Called
Various
Mostly RFCs (requests
for comments)
Note that OSI is nearly completely dominant for standards at the physical and internet layers. All other standards agencies say, “Use OSI standards at the physical and data link layers.”
At the internet and transport layers, TCP/IP is almost as dominant but not quite. However, its dominance is growing.
Most IETF documents are called Requests for Comment (RFCs).

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)
TCP
Connection-
oriented
Reliable
4 (Transport)
UDP
Connectionless
Unreliable
This slide recaps the main standards that we saw in this chapter.
3 (Internet) IP
Connectionless
Unreliable
2 (Data Link)
Ethernet
Connectionless
Unreliable
Note: Only TCP is connection-oriented and reliable