1. Protocols and Protocol Suit Review
Lecture 14

2. Overview Network Access Layer Transport Layer Protocols
Protocol Data Unit
Protocol Architecture
TCP/IP Stack
Layered Approach and its Advantages
Router

3. What is a Protocol ?
Q:- What is a protocol?

4. Communication Protocols
Definition
Protocol is a set of rules that govern all aspect of data communication between computers on a network.
These rules include guidelines that regulate the following characteristics of a network: access method, allowed physical topologies, types of cabling, and speed of data transfer.
A protocol defines what, how, when it communicated.
The key elements of a protocol are syntax, semantics and timing.
Protocols are to computers what language is to humans. Since this article is in English, to understand it you must be able to read English. Similarly, for two devices on a network to successfully communicate, they must both understand the same protocols.

5. Key Elements of protocol
Syntax
The structure or format of the data.
Eg. A simple protocol;

6. Elements of protocol ii) Semantics
- Refers to the meaning of each section of bits.
- how is a particular pattern to be interpreted, and what action is to be taken based on that interpretation.
Eg. Does an address identify the route to be taken or the final of the message?

7. Elements of protocol iii) Timing Refers to two characteristics:
When data to be sent
How fast it can be sent
Eg. If a sender produces data at 100 Mbps but the receiver can process data at only 1 Mbps, the transmission will overload the receiver and data will be largely lost.

8. Characteristics of protocol
Direct / indirect
communication between two entities maybe direct or indirect.
i) point-to-point link
- connection provides a dedicated link between two devices
- the entities in these systems may
communicate directly that is data and
control information pass directly
between entities with no intervening
active agent.

9. Characteristics of protocol
ii) multipoint link
- connection more than two devices can share a single link
- The entities must be concerned with the issue of access control and making the protocol more complex.

10. Common protocol used Remarks Protocol Acronym Point To Point PPP
Used to manage network communication over a modem
Transfer/Transmission Control Protocol
TCP / IP
Backbone protocol. The most widely used protocol.
Internetwork package exchange
IPX
Standard protocol for Novell NOS
NetBIOS extended user interface
NetBEUI
Microsoft protocol that doesn’t support routing to other network. Running only Windows-based clients.
File transfer Protocol
FTP
used to send and received file from a remote host
Simple mail Transfer protocol
SMTP
Used to send over a network
Hyper text transfer protocol
HTTP
Used for Internet to send document that encoded in HTML
Apple Talk
Protocol suite to network Macintosh computer and a peer-to-peer network protocol
OSI Model
OSI Layers
A way of illustrating how information functions travels through network of its 7 layers.

11. What is a Protocol ? Q:- What is a protocol?
Protocols are a set of rules and conventions. By enforcing that communicating parties adhere to a common protocol, communication is made possible. Protocol Architecture The “Common Language”
Ans:- A protocol is the set of rules or conventions governing the way in which two entities cooperate to exchange data.

13. PDU
What is a protocol data unit (PDU)?

14. 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 (port)
Sequence number
Error detection code
This gives a transport protocol data unit

15. Network PDU Adds network header, network address for destination computer and Facilities requests
Protocol Data Units

16. PDU What is a protocol data unit (PDU)?
Ans:- A PDU is the combination of data from the next higher communications layer and control information.

18. Protocol Architecture
Q:- What is a protocol architecture?

19. Need For Protocol Architecture
There are lots of network applications
Building each application from scratch is very time-consuming and challenging
What commands should be supported?
How to respond to each command?
How to identify the two peer applications?
Each computer may run multiple applications!
How to identify the two computers?
How to convert the data into bit stream?
How to convert the bit stream into signals?
How to detect and handle data loss and data error?
The network is not perfect!
Etc.

20. Need For Protocol Architecture
Data exchange can involve complex procedures, cf. file transfer example
Better if task broken into subtasks
Implemented separately in layers in stack
each layer provides functions needed to perform communication for layers above
using functions provided by layers below
Peer layers communicate with a protocol
When computers, terminals, and/or other data processing devices exchange data, the procedures involved can be quite complex. eg. file transfer. There must be a data path between the two computers. But also need:
Source to activate communications Path or inform network of destination
Source must check destination is prepared to receive
File transfer application on source must check destination file management system will accept and store file for his user
May need file format translation
Instead of implementing the complex logic for this as a single module, the task is broken up into subtasks, implemented separately. In a protocol architecture, the modules are arranged in a vertical stack, each layer in the stack performs a related subset of the functions. It relies on the next lower layer to perform more primitive functions. It provides services to the next higher layer. The peer layers communicate using a set of rules or conventions known as a protocol.

21. Key Elements of a Protocol
Syntax – data block format
Semantics - control info. & error handling
Timing - speed matching & sequencing
Communication is achieved by having the corresponding, or peer, layers in two systems communicate. The peer layers communicate by means of formatted blocks of data that obey a set of rules or conventions known as a protocol. The key features of a protocol are:
• Syntax: Concerns the format of the data blocks
• Semantics: Includes control information for coordination and error handling
• Timing: Includes speed matching and sequencing

22. (Cont.) Most of the network apps share some common modules Module A
Application A
Application B
Application C
Module A
Module B
Module C
Module T
Module T
Module T
Module I
Module I
Module I
Common modules
Module N
Module N
Module N
Module P
Module P
Module P

23. (Cont.) A complex task is broken into subtasks: modular design
Each subtask is implemented separately as a layer, arranged in a vertical stack
Each layer performs a related subset of the functions required to communicate with another system.
It relies on the next lower layer to perform more primitive functions and to conceal the details of those functions.
It provides services to the next higher layer.
Layers should be defined so that changes in one layer do not require changes in other layers.
So, instead of using a single complex protocol, it’s more flexible to implement a stack of protocols!
Reduce the design and development workload significantly!

24. Vertical Stack Module A Module B Module C Module T Module I Module N
Application developers
Application A
Application B
Application C
Module A
Module B
Module C
Operating System
Module T
Module I
Hardware
Module N
Module W
can be replaced by other modules
Module P

25. Example
E.g., A can only speak Chinese, B can only speak Spanish, how can A communicate with B?
A finds a translator C, who can speak Chinese and English
B finds a translator D, who can speak Spanish and English
Two layers:
Higher layer: A and B
Lower layer: C and D

26. Lower layer provides services to the next higher layer.
A Two-layer example
How to communicate?
Higher Layer B A
messages in Spanish
messages in Chinese
Lower Layer
messages in English D C
Lower layer provides services to the next higher layer.

27. Protocol Architecture
Tasks of communications are broken up into modules
Each module (or layer) can have its own protocol
In very general terms, communications can be said to involve three components: applications, computers, and networks.
For example, file transfer could use three modules (or layers)
File transfer application
Communications service module
Network access module
The stack of protocols is called “Protocol Stack”
Or Protocol Architecture

28. 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
It consists of a large collection of protocols that have been issued as Internet standard by the Internet Architecture Board (IAB).
Check
The TCP/IP protocol architecture organizes the communication task into five relatively independent layers:
Layer 5: Application layer
Layer 4: Transport layer, or Host to host (TCP belongs to this layer)
Layer 3: Internet layer, or Network layer (IP belongs to this layer)
Layer 2: Network access layer, or Link layer
Layer 1: Physical layer
Remark: Each layer can have lots of different protocols!

29. Example World Wide Web HTTP HTTP TCP TCP IP IP
Replies on the HTTP protocol
Web browser
Web server
HTTP
HTTP
Layer 5
Layer 4
TCP
TCP IP IP
Layer 3
Layer 2
IEEE
IEEE 802.3
IEEE g
IEEE BASE-SX
Layer 1

30. Standardized Protocol Architectures
Required for devices to communicate
Vendors have more marketable products
Customers can insist on standards based equipment
Two standards:
OSI Reference model
Never lived up to early promises
TCP/IP protocol suite
Most widely used

31. Protocol Architecture
Q:- What is a protocol architecture?
Ans:- The software structure that implements the communications function. Typically, the protocol architecture consists of a layered set of protocols, with one or more protocols at each layer.

33. Lower level vendor implementations
TCP/IP
Q:- What is TCP/IP?
OSI layers
TCP/IP layers
Application
Presentation
Session
FTP,
Telnet,
SMTP
DNS
Transport
TCP
UDP
Network
Data link
Physical
Lower level vendor implementations IP
OSPF
IGMP
DHCP
ICMP

34. Postal System
To: Mr. Jacky Chan
No. 123, XX Road,
XXX, USA

35. Inside Postal System
Central Post Office (New York)
Central Post Office (Beijing)
The delivery of your package depends on the postal address.
Central Post Office (Hong Kong)
Local Post Office (Kowloon Tong)
Local Post Office (Tseung Kwan O)

36. TCP/IP Protocol Architecture
Developed by US Defense Advanced Research Project Agency (DARPA)
ARPANET packet switched network reuired
Now popular all over the world used by the global Internet
Protocol suite comprises a large collection of standardized protocols
The TCP/IP protocol architecture is a result of protocol research and development conducted on the experimental packet-switched network, ARPANET, funded by the Defense Advanced Research Projects Agency (DARPA), and is generally referred to as the TCP/IP protocol suite. This protocol suite consists of a large collection of protocols that have been issued as Internet standards by the Internet Activities Board (IAB).

37. TCP/IP Q:- What is TCP/IP?
Ans:- Transmission Control Protocol/Internet Protocol (TCP/IP) are two protocols originally designed to provide low level support for internetworking. The term is also used generically to refer to a more comprehensive collection of protocols developed by the U.S. Department of Defense and the Internet community.

39. Layers
Q:- What are some advantages to layering as seen in the TCP/IP architecture?

40. TCP/IP Layers
Because TCP/IP was developed earlier than the OSI 7-layer mode, it does not have 7 layers but only 4 layers
TCP/IP Protocol Suite
OSI 7-layer
FTP, SMTP, Telnet, HTTP,…
TCP, UDP
IP, ARP, ICMP
Network Interface

41. Benefit of layering
The most challenging problem: how to provide a reliable data transfer service on top of an unreliable data network?
This problem is so important that today’s Operating Systems all provide such reliable service.
The burden of network application developers has been reduced significantly!
Hence the application developers can simply focus on the application layer issues.
We can easily develop thousands of network applications.

42. TCP/IP Layers
Q:- What are some advantages to layering as seen in the TCP/IP architecture? Ans:- Layering decomposes the overall communications problem into a number of more manageable subproblems
TCP/IP Protocol Suite
OSI 7-layer
FTP, SMTP, Telnet, HTTP,…
TCP, UDP
IP, ARP, ICMP
Network Interface

44. Router Q:- What is a router? Router Functions Linking WANs and LANs
Interconnecting communication lines
Path determination and packet switching
Application of security rules (ACLs)
Protocol conversion (encapsulation)
E.g. HDLC, PPP etc.

45. Routers
Internetworking among dissimilar subnetworks is achieved by using routers to interconnect the subnetworks. Essential functions that the router must perform include the following:
Provide a link between networks.
Provide for the routing and delivery of data between processes on end systems attached to different networks.
Provide these functions in such a way as not to require modifications of the networking architecture of any of the attached subnetworks.

46. Routers
Addressing schemes: The networks may use different schemes for assigning addresses to devices. For example, an IEEE 802 LAN uses 48-bit binary addresses for each attached device; an ATM network typically uses 15-digit decimal addresses (encoded as 4 bits per digit for a 60-bit address). Some form of global network addressing must be provided, as well as a directory service.
Maximum packet sizes: Packets from one network may have to be broken into smaller pieces to be transmitted on another network, a process known as segmentation or fragmentation. For example, Ethernet imposes a maximum packet size of 1500 bytes; a maximum packet size of 1000 bytes is common on X.25 packet-switching networks. A packet that is transmitted on an Ethernet system and picked up by a router for retransmission on an X.25 network may have to be fragmented into two smaller ones.

47. Router

48. TCP/IP (Sender)
Preparing the data. The application protocol prepares a block of data for transmission. For example, an message (SMTP), a file (FTP), or a block of user input (TELNET)
Using a common syntax. If necessary, the data are converted to a form expected by the destination. This may include a different character code, the use of encryption, and/or compression.
Segmenting the data. TCP may break the data block into a number of segments, keeping track of their sequence. Each TCP segment includes a header containing a sequence number and a frame check sequence to detect errors.
Duplicating segments. A copy is made of each TCP segment, in case the loss or damage of a segment necessitates retransmission. When an acknowledgment is received from the other TCP entity, a segment is erased.

49. Operation of TCP/IP(Action at Router)
Arriving at router. The incoming signal is received over the transmission medium and interpreted as a cell of bits.
Processing the cell. The ATM layer removes the cell header and processes it. The header error control is used for error detection. The connection number identifies the source.
Routing the packet. IP examines the IP header and makes a routing decision. It determines which outgoing link is to be used and then passes the datagram back to the link layer for transmission on that link
Forming LLC PDU. An LLC header is added to each IP datagram to form an LLC PDU. The header contains sequence number and address information.
Framing. A MAC header and trailer is added to each LLC PDU, forming a MAC frame. The header contains address information and the trailer contains a frame check sequence.
Transmission. Each frame is transmitted over the medium as a sequence of bits.

50. Router Components Hardware components of a router: Network interfaces
Interconnection network
Processor with a memory and CPU
PC router:
interconnection network is the (PCI) bus and interface cards are NICs
All forwarding and routing is done on central processor
Commercial routers:
Interconnection network and interface cards are sophisticated
Processor is only responsible for control functions (route processor)
Almost all forwarding is done on interface cards

51. Functional Components
Control
Datapath:
per-packet
processing

52. Routing and Forwarding
Routing functions include:
route calculation
maintenance of the routing table
execution of routing protocols
On commercial routers handled by a single general purpose processor, called route processor
IP forwarding is per-packet processing
On high-end commercial routers, IP forwarding is distributed
Most work is done on the interface cards

53. Basic Architectural Components Per-packet processing
Output
Scheduling
Routing
Table
Switch Fabric
Routing
Decision
Routing
Table
Forwarding
Decision
Routing
Table
Forwarding
Decision

54. Router Components On a PC router:
interconnection network is the (PCI) bus
Interface cards are NICs (e.g., Ethernet cards)
All forwarding and routing is done on central processor
On Commercial routers:
Interconnection network and interface cards can be sophisticated
Central processor is the route processor (only responsible for control functions)

55. Router Q:- What is a router? Router Operations Layer 3 device
Accepts PDUs on incoming network
Examines PDU data
Makes decision(s) for next stage of PDU journey
May modify PDU contents (not payload)
Passes PDU on to outgoing network

56. Router
Q:- What is a router? Ans:-A router is a device that operates at the Network layer of the OSI model to connect dissimilar networks.

57. Summary Network Layer Functionality Task performed @ Transport Layer
Protocol and Protocol Stack
Protocol Data Unit
Protocol Architecture
TCP/IP Stack
Layering Advantages in TCP/IP
Router Architecture and Functionality

59. Question
Q:- A broadcast network is one in which a transmission from any one attached station is received by all other attached stations over a shared medium. Examples are a bustopology local area network, such as Ethernet, and a wireless radio network. Discuss the need or lack of need for a network layer (OSI layer 3) in a broadcast network.

60. Routing in Case of Broadcast
A case could be made either way. First, look at the functions performed at the network layer to deal with the communications network (hiding the details from the upper layers). The network layer is responsible for routing data through the network, but with a broadcast network, routing is not needed. Other functions, such as sequencing, flow control, error control between end systems, can be accomplished at layer 2, because the link layer will be a protocol directly between the two end systems, with no intervening switches. So it would seem that a network layer is not needed. Second, consider the network layer from the point of view of the upper layer using it. The upper layer sees itself attached to an access point into a network supporting communication with multiple devices. The layer for assuring that data sent across a network is delivered to one of a number of other end systems is the network layer. This argues for inclusion of a network layer. In fact, the OSI layer 2 is split into two sublayers. The lower sublayer is concerned with medium access control (MAC), assuring that only one end system at a time transmits; the MAC sublayer is also responsible for addressing other end systems across the LAN. The upper sublayer is called Logical Link Control (LLC). LLC performs traditional link control functions. With the MAC/LLC combination, no network layer is needed (but an internet layer may be needed).

62. Question:
Q:- A TCP segment consisting of 1500 bits of data and 160 bits of header is sent to the IP layer, which appends another 160 bits of header. This is then transmitted through two networks, each of which uses a 24-bit packet header. The destination network has a maximum packet size of 800 bits. How many bits, including headers, are delivered to the network layer protocol at the destination? Sol:- Data plus transport header plus internet header equals 1820 bits. This data is delivered in a sequence of packets, each of which contains 24 bits of network header and up to 776 bits of higher-layer headers and/or data. Three network packets are needed. Total bits delivered = (3 x 24) = 1892 bits.

64. UDP Requirement
Q:- Why is UDP needed? Why can't a user program directly access IP? Ans:- UDP provides the source and destination port addresses and a checksum that covers the data field. These functions would not normally be performed by protocols above the transport layer. Thus UDP provides a useful, though limited, service.

66. IP, TCP and UDP Error Checksum
Q:- IP, TCP, and UDP all discard a packet that arrives with a checksum error and do not attempt to notify the source. Why?
Ans:- In the case of IP and UDP, these are unreliable protocols that do not guarantee delivery, so they do not notify the source. TCP does guarantee delivery. However, the technique that is used is a timeout. If the source does not receive an acknowledgment to data within a given period of time, the source retransmits.

68. TCP UDP Header Length
Q:- Why does the TCP header have a header length field while the UDP header does not? Ans:- UDP has a fixed-sized header. The header in TCP is of variable length.

69. Summary Network Layer Functionality Task performed @ Transport Layer
Protocol and Protocol Stack
Protocol Data Unit
Protocol Architecture
TCP/IP Stack
Layering Advantages in TCP/IP
Router Architecture and Functionality