1. Protocols; TCP/IP and OSI Model
ECE 4321 Computer Networks
Protocols; TCP/IP and
OSI Model

2. Need For Protocol Architecture
Data exchange can be complex, e.g. file transfer
Source must activate communication path or inform network the destination
Source must check if destination is prepared to receive
File transfer application on source must check if destination file management system will accept and store the file for his user
May need file format translation
Better if tasks are broken into subtasks
Implemented separately in layers in a stack
Communication of peer layers is required

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

4. Protocol Architectures and Networks

5. Addressing Requirements
Two levels of addressing required
Each computer needs unique network address
Each application on a (multi-tasking) computer needs a unique address within the computer
The service access point or SAP
The port on TCP/IP stacks

6. Protocols in Simplified Architecture

7. Protocol Data Units (PDU)
At each layer, protocols are used to communicate
Control information is added to user data at each layer
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

8. Protocol Data Units

9. Network PDU Adds network header
network address for destination computer
Facilities requests

10. Operation of a Protocol Architecture

11. 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
Used as a reference model (not for implementation)
TCP/IP protocol suite
Most widely used

12. David Clark’s Theory of Standards
Billion Dollars of Investments
Research
Activity
Standards
Time
Apocalypse of two elephants

13. OSI Open Systems Interconnection (OSI) Model
Developed by the International Organization for Standardization (ISO)
Seven layers
Adopted in 1984 as ISO 7498
A theoretical system delivered too late!
Presently not an actual working model, but serves as a model for network layers
TCP/IP is the de facto standard

14. 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
Solves communication problem in heterogeneous computers

15. OSI Layers

16. The OSI Environment

17. OSI as Framework for Standardization

18. Layer Specific Standards

19. Elements of Standardization
Protocol specification
Operates between the same layer on two systems
May involve different operating systems
Protocol specification must be precise
Format of data units
Semantics of all fields
allowable sequence of PCUs
Service definition
Functional description of what is provided
Addressing
Referenced by SAPs

20. Service Primitives and Parameters
Services between adjacent layers expressed in terms of primitives and parameters
Primitives specify function to be performed
Parameters pass data and control info

21. Primitive Types REQUEST
A primitive issued by a service user to invoke some service and to pass the parameters needed to specify fully the requested service
INDICATION
A primitive issued by a service provider either to:
indicate that a procedure has been invoked by the peer service user on the connection and to provide the associated parameters, or
notify the service user of a provider-initiated action
RESPONSE
A primitive issued by a service user to acknowledge or complete some procedure previously invoked by an indication to that user
CONFIRM
A primitive issued by a service provider to acknowledge or complete some procedure previously invoked by a request by the service user

22. Timing Sequence for Service Primitives

23. OSI Layers (1) Physical Data Link Physical interface between devices
Mechanical—specifications of pluggable connectors
Electrical--- representation of bits (e.g. voltage) and bit rates
Functional--- specifies the functions of each individual circuits
Procedural ---specifies the sequence of events by which bit streams are exchanged
Example) EIA-232-F, ISDN and LAN connectors
Data Link
Means of activating, maintaining and deactivating a reliable link
Error detection and control
Higher layers may assume error free transmission
Synchronization and flow control
Example) HDLC, LAPB, LLC, LAPD

24. OSI Layers (2) Network Transport
Transport of information between end systems across communication networks
Higher layers do not need to know about underlying technology
Provides route decision, addressing and priorities
Transport
Provides reliable transfer of data between end systems
Error free, in sequence, no losses, no duplications
Provides quality of services to session entities
Example) TCP (connection oriented), UDP (connectionless datagram)

25. OSI Layers (3) Session Presentation Application
Control structure for communication between applications
Dialogue discipline --- full duplex, half duplex
Grouping--- flow of data can be marked to define group, e.g, sales data, inventory data, etc
Recovery --- check point recovery
Presentation
Data formats and coding
Data compression
Encryption
Application
Means for applications to access OSI environment

26. 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
Host to host or transport layer
Internet layer
Network access layer
Physical layer

27. Internet Standards and internet Society
Internet Society (ISOC) --- Coordinating committee for Internet design, engineering, and management. Participated by over 100 countries.
IAB (Internet Architecture Board)
IETF (Internet Engineering Task Force)
IESG (Internet Engineering Steering Group)

28. ISOC
Internet Architecture Board (IAB): Defines the overall architecture of the Internet and sets directions for IETF.
Internet Engineering Task Force (IETF): Responsible for protocol engineering and developments. Comprise many working groups.
Internet Engineering Steering Group (IESG): Responsible for technical management of IETF and Internet standards process.
Standard Track: At each step, IETF must make a recommendation for advancement of the protocol, and the IESG ratifies it.

29. Internet RFC Publication Process: RFC 2026
Internet Draft
If the draft is not progressed as RFC by IESG, it is withdrawn.
Proposed Standard
Experimental
Informational
RFC
6mo
Protocols and specifications that are not ready for standardization.
Draft Standard
RFC
4mo
Internet Standard
RFC, STD
Each step is proposed by IETF and ratified by IESG
Historic

30. OSI v TCP/IP

31. TCP/IP Concepts

32. Trace of Simple Operation
Process associated with port 1 in host A sends message to port 2 in host B
Process at A hands down message to TCP to send to port 2
TCP hands down to IP to send to host B
IP hands down to network layer (e.g. Ethernet) to send to router J
Generates a set of encapsulated PDUs

33. PDUs in TCP/IP

34. Addressing level Level in architecture at which entity is named
Unique address for each end system (computer) and router
Network level address
IP or internet address (TCP/IP)
Network service access point or NSAP (OSI)
Process within the system
Port number (TCP/IP)
Service access point or SAP (OSI)

35. Internet Layer (IP)
Concerns with routing data across one or more networks connected by routers.
Addressing of computers and fragmentation of packets
Best effort to forward packets to the next destination
Implemented in end systems (Internet connected computers) and routers
RFC 791, MIL-STD 1777

36. Transport Layer (TCP)
Establishes reliable host-host data transportation
Ordering of delivery
RFC 793 and MIL-STD 1778

37. TCP Provides a full-duplex bi-directional virtual circuit
As seen by the user, data is transmitted as a stream.
Reliable data transmission using sequence numbers, checksums, acknowledgements, etc.
Utilizes a sliding window principle for greater efficiency
Includes urgent data and push functions
Transport user addressing 16-bit port number
Graceful connection/disconnection, shutdown

38. UDP Alternative to TCP is User Datagram Protocol
Not guaranteed delivery
No preservation of sequence
No protection against duplication
Minimum overhead
Adds port addressing to IP

39. TCP Well-Known Ports Service Port No Protocol Telnet 23 TCP FTP 21
SMTP 25
rlogin
513
rsh
514
Portmap
111
TCP. UDP
rwhod
UDP
HTTP 80
TCP (rfc 1945)

40. Some Protocols in TCP/IP Suite