1. Lecture (2)

2. 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

3. Physical Layer
Physical interface between data transmission device (e.g. workstation/computer) and transmission medium or network
Characteristics of transmission medium
Signal levels
Data rates
etc.

4. Network Access Layer
Exchange of data between end system (e.g. workstation) and network
Providing the network with Destination address
Concerned with access to and routing data across a network for two end systems attached to the same network.
Invoking services (like priority).
Different standards have been developed
e.g. frame relay  circuit switching, packet switching
e.g. Ethernet  LANs

5. Internet Layer (IP)
Concerned with cases where two devises (end systems) are attached to different networks
Routing functions across multiple networks
Implemented in end systems and routers
Router: a processor that connects two networks and whose primary function is to relay data from one network to the other on its route from the source to the destination end system.

6. Transport Layer (TCP) Application Layer Reliable delivery of data
Data arrive at the destination application
Data id delivered, in the same order in which they sent, to a certain SAP (port)
Application Layer
Support for user applications
e.g. http, SMTP

7. TCP/IP Protocol Architecture Model

8. Operation of TCP/IP

9. OSI Model Open Systems Interconnection (OSI)
Developed by the International Organization for Standardization (ISO)
Seven layers
A theoretical system delivered too late!
TCP/IP is the real standard

10. OSI Layers Application Presentation Session Transport Network
Data Link
Physical

12. OSI v TCP/IP

13. Standards Required to allow for interoperability between equipment
Advantages
Ensures a large market for equipment and software
Allows products from different vendors to communicate
Disadvantages
Freeze technology
May be multiple standards for the same thing

14. William Stallings Data and Computer Communications
Chapter 2
Protocols and Architecture

15. Protocols Characteristics
Direct or indirect
Monolithic or structured
Symmetric or asymmetric
Standard or nonstandard

16. Direct or Indirect Direct Indirect
Systems share a point to point link or
Systems share a multi-point link
Data can pass without intervening active agent
Indirect
Switched networks or
Internetworks or internets
Data transfer depend on other entities

17. Monolithic or Structured
Communications is a complex task
Too complex for single unit
Structured design breaks down problem into smaller units
Layered structure

18. Symmetric or Asymmetric
Communication between peer entities
Asymmetric
Client/server

19. Standard or Nonstandard
Nonstandard protocols built for specific computers and tasks
K sources and L receivers leads to K*L protocols and 2*K*L implementations
If common protocol used, K + L implementations needed

20. Use of Standard Protocols

21. Functions A. Encapsulation B. Segmentation and reassembly
C. Connection control
D. Ordered delivery
E. Flow control
F. Error control
G. Addressing
H. Multiplexing
I. Transmission services

22. A.Encapsulation Addition of control information to data
Address information (sender/receiver)
Error-detecting code
Protocol control information
The queries and replies among communications equipment to determine the respective capabilities of each end of the communications link.
Information exchanged between entities of a given layer, via the service provided by the next lower layer, to coordinate their joint operation.

23. A.Encapsulation (cont’d)

24. B. Segmentation (Fragmentation)
Data blocks (PDUs) are of bounded size
Application layer messages (continuous stream) may be large
Network packets may be smaller
Splitting larger blocks into smaller ones is segmentation (or fragmentation in TCP/IP)
ATM blocks (cells) are 53 octets long
Ethernet blocks (frames) are up to 1526 octets long
Smaller PDU blocks result in more interrupts
Checkpoints and restart/recovery

25. Why Fragment? Advantages Disadvantages More efficient error control
More equitable access to network facilities
Shorter delays
Smaller buffers needed
Disadvantages
Overheads
Increased interrupts at receiver
More processing time

26. Reassembly
The segmented data must be reassembled into messages appropriate to the application level
If PDU arrive out of order, the task is complicated

27. C. Connection Control Connection Establishment Data transfer
Connection termination
May be connection interruption and recovery
Conectionless data transfer (datagram): an entity may transfer data to another entity in a way that each PDU is treated independently of all prior PDUs.

28. Connection Oriented Data Transfer

29. C. Connection Control (cont’d)
Sequence numbers used for
Ordered delivery
Flow control (managing the rate of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver)  congestion avoidance
Error control
Sequencing is not found in all connection oriented protocols (e.g. Frame relay and ATM)

30. D. Ordered Delivery PDUs may traverse different paths through network
PDUs may arrive out of order
Sequentially number PDUs to allow for ordering

31. E. Flow Control Done by receiving entity Limit amount or rate of data
The simplest procedure is (Stop and wait)
Each PDU must be acknowledged before the next can be sent
Credit systems for transmitter
Sliding window (determines the amount of data that can be sent without an ACK)
Needed at application as well as transport and network access layers

32. F. Error Control Guard against loss or damage
Implemented as two separate functions:
Error detection
Sender inserts error detecting bits
Receiver checks these bits
If OK, acknowledge
If error, discard packet
Retransmission
If no acknowledge in given time, re-transmit
Some protocols employ an error correction code
Performed at various layers

33. End of Lecture (2)