1. Protocols Used for communications between entities in a system Used for communications between entities in a system Must speak the same language Must speak the same language Entities Entities User applications User applications E-mail facilities E-mail facilities Terminals Terminals Systems Systems Computer Computer Terminal Terminal Remote sensor Remote sensor

2. Protocol Cont Protocol: Protocol: A set of rules and conventions A set of rules and conventions Governs how computers exchange information over a shared/network medium. Governs how computers exchange information over a shared/network medium. Used for communications between entities in a system Used for communications between entities in a system Defines : Defines : What is communicated What is communicated How it is communicated How it is communicated When it is communicated When it is communicated Varieties of communication protocols exist. Varieties of communication protocols exist. LAN protocols, WAN protocols, Network protocols, Routing protocols etc. LAN protocols, WAN protocols, Network protocols, Routing protocols etc.

3. Key Elements of Protocol Syntax: Syntax: Refers to structure or format of the data (the order they are presented) Refers to structure or format of the data (the order they are presented) Example - data format, coding Example - data format, coding Semantics: Semantics: Refers to the meaning of each section of the bits Refers to the meaning of each section of the bits Example - data information, control information Example - data information, control information Timing: Timing: Refer to synchronous Refer to synchronous When data should be sent When data should be sent How fast they can be sent How fast they can be sent Example sequencing, speed/delay matching Example sequencing, speed/delay matching

4. Protocol Architecture Protocols in networking follows ‘layered’ architecture Protocols in networking follows ‘layered’ architecture Purpose of this layered architecture: Purpose of this layered architecture: functions necessary for transfer of data are grouped into layers. functions necessary for transfer of data are grouped into layers. a set of/each task(s) is separated from others. a set of/each task(s) is separated from others. several protocols at each layer, each suitable for a different situation. several protocols at each layer, each suitable for a different situation. work that must be done in networking is broken down into manageable units. work that must be done in networking is broken down into manageable units.

5. Protocol Architecture Task of communication broken up into modules, for example file transfer could use three modules Task of communication broken up into modules, for example file transfer could use three modules File transfer application File transfer application Communication service module Communication service module Network access module Network access module

6. A simplified architecture for file transfer

7. Three-layered Model Network Access Layer Network Access Layer Exchange of data between the computer and the network Exchange of data between the computer and the network Sending computer provides address of destination computer. Sending computer provides address of destination computer. May invoke levels of service May invoke levels of service Dependent on type of network used (LAN, packet switched etc.) Dependent on type of network used (LAN, packet switched etc.)

8. Cont… Transport Layer Transport Layer Reliable data exchange Reliable data exchange Independent of network being used Independent of network being used Independent of application Independent of application Application Layer Application Layer Support for different user applications Support for different user applications E.g. e-mail, file transfer E.g. e-mail, file transfer

9. Protocols in simplified architecture

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

11. Protocol Data Unit At each layer, protocols are used to communicate At each layer, protocols are used to communicate Control information is added to user data at each layer Control information is added to user data at each layer Transport layer may fragment user data Transport layer may fragment user data Each fragment has a transport header added Each fragment has a transport header added Destination SAP Destination SAP Sequence number Sequence number Error detection code Error detection code This gives a transport protocol data unit This gives a transport protocol data unit

12. Protocol Data Units

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

14. Standardized Protocol Architectures Required for devices to communicate Required for devices to communicate Vendors have more marketable products Vendors have more marketable products Customers can insist on standards based equipment Customers can insist on standards based equipment Two standards: Two standards: OSI Reference model OSI Reference model Never lived up to early promises Never lived up to early promises TCP/IP protocol suite TCP/IP protocol suite Most widely used Most widely used Also: IBM Systems Network Architecture (SNA) Also: IBM Systems Network Architecture (SNA)

15. OSI Model The OSI Model The OSI Model A layered framework for network systems design A layered framework for network systems design allows for communication across all types of computer systems allows for communication across all types of computer systems consists of 7 layers consists of 7 layers each layer defines a segment of process of moving information each layer defines a segment of process of moving information

16. Layered Architecture Please Do Not Touch Steve’s Pet Alligator Application Presentation Session Transport Network Data Link Physical

17. Peer-to-Peer Processes Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical machine A machine B provides services for uses services provide d by

18. The OSI Environment

19. Functions of the Layers Physical Layer Physical Layer Transmits a bit stream over a physical link Transmits a bit stream over a physical link Deals with the mechanical and electrical specifications of the interface and transmission medium Deals with the mechanical and electrical specifications of the interface and transmission medium Specification Responsibilities : defines Specification Responsibilities : defines interface the devices and the transmission medium interface the devices and the transmission medium data rates : # of bits sent each second data rates : # of bits sent each second synchronisation of bits : synchronises both side clocks synchronisation of bits : synchronises both side clocks

20. Physical Layer (Cont.) Specification Responsibilities : defines (cont.) Specification Responsibilities : defines (cont.) Line configuaration : Line configuaration : concerns with the connection of devices to the medium concerns with the connection of devices to the medium point-to-point configuration point-to-point configuration 2 devices are connected together through a link 2 devices are connected together through a link multipoint configuaration multipoint configuaration a link is shared between several devices a link is shared between several devices physical topology, defines physical topology, defines how devices are connected (mesh, star, etc.) how devices are connected (mesh, star, etc.)

21. Physical Layer (Cont.) Specification Responsibilities : defines (cont.) Specification Responsibilities : defines (cont.) Transmission mode, defines Transmission mode, defines direction of transmission between 2 devices direction of transmission between 2 devices simplex, half-duplex, full-duplex simplex, half-duplex, full-duplex

22. Data Link Layer node-to-node delivery node-to-node delivery fix the errors for the next layer fix the errors for the next layer Specification Responsibility Specification Responsibility framing framing devides the stream of bits into frames devides the stream of bits into frames physical addressing physical addressing add headers (souce address, destination address) add headers (souce address, destination address) flow control flow control prevent overflow transmission prevent overflow transmission error control error control add mechanism for detecting damages add mechanism for detecting damages

23. Data Link Layer Specification Responsibility (cont.) Specification Responsibility (cont.) access control access control for multipoint configuaration for multipoint configuaration determines which device has control over the link at any given time determines which device has control over the link at any given time Responsible the delivery of packets between 2 systems on the same network link Responsible the delivery of packets between 2 systems on the same network link

24. Network Layer Responsible for the source-to-destination delivery of packet across mulitple network links Responsible for the source-to-destination delivery of packet across mulitple network links ensures that a packet gets from it origin to destination ensures that a packet gets from it origin to destination Specification Responsibilities Specification Responsibilities logicall addressing logicall addressing add source/destination addresses add source/destination addresses routing routing

25. Network Layer (cont.) Responsible for end-to-end delivery of individual packet Responsible for end-to-end delivery of individual packet each packet is treated independently each packet is treated independently gets the packet to the correct computer gets the packet to the correct computer

26. Transport Layer Responsible for source-to-destination (end-to- end) delivery of entire message Responsible for source-to-destination (end-to- end) delivery of entire message ensure that the whole message arrives intact and in order ensure that the whole message arrives intact and in order Specification Responsibilities Specification Responsibilities service-point addressing service-point addressing port address port address gets the entire message to the correct program on the computer gets the entire message to the correct program on the computer

27. Transport Layer (cont.) Specification Responsibilities (cont.) Specification Responsibilities (cont.) segmentation and reassembly segmentation and reassembly devides message into segment (packet) devides message into segment (packet) addes a sequence number to each segment addes a sequence number to each segment flow control flow control similar to the data link flow control similar to the data link flow control perform end to end (machine) rather than across a link perform end to end (machine) rather than across a link error control error control makes sure that the entire message arrives at the receiver without error (damage, loss, etc.) makes sure that the entire message arrives at the receiver without error (damage, loss, etc.) retransmission mechanism retransmission mechanism

28. Session Layer The network dialog controller The network dialog controller Establishes, maintains, synchronise the interaction between communication systems Establishes, maintains, synchronise the interaction between communication systems Specification Responsibilities Specification Responsibilities dialog control dialog control agree to take either simplex, half-duplex, full-duplex mode agree to take either simplex, half-duplex, full-duplex mode synchronisation synchronisation allows a process to add checkpoints (synchronisation points in to a data stream) allows a process to add checkpoints (synchronisation points in to a data stream)

29. Session Layer (Cont.) a message of 1320 bytes 10 0 …... checkpo int synchronisation

30. Presentation Layer Concerns with the syntax and semantics of information exchanged between 2 systems Concerns with the syntax and semantics of information exchanged between 2 systems Specification Responsibilities Specification Responsibilities translation translation character string character string numbers, etc. numbers, etc. different computers use different encoding systems different computers use different encoding systems

31. Presentation Layer (Cont.) Specification Responsibilities (cont.) Specification Responsibilities (cont.) responsible for interoperability between these different encoding methods responsible for interoperability between these different encoding methods encryption encryption for sensitive information for sensitive information encode/decode information encode/decode information compression compression reduce the number of bits to be transmitted reduce the number of bits to be transmitted

32. Application Layer Enables the user (human/software) to access the network Enables the user (human/software) to access the network Specification Responsibilities Specification Responsibilities Applications : examples Applications : examples network virtual terminal network virtual terminal to remote login to a remote machine to remote login to a remote machine file transfer file transfer mail services mail services

33. TCP/IP Protocol Suite Used in the Internet Used in the Internet Developed before the OSI Model Developed before the OSI Model do not match exactly with OSI Model do not match exactly with OSI Model 5 layers 5 layers Application Application Transport Transport Internetworking Internetworking Network Network Physical Physical

34. TCP/IP Protocol Suite (Cont.) Two main protocols Two main protocols Transmission Control Protocol Transmission Control Protocol Internetworking Protocol Internetworking Protocol Many other protocols Many other protocols Hierarchical protocol architecture made up for interactive modules Hierarchical protocol architecture made up for interactive modules each upper-level protocol is supported by one or more lower-level protocols each upper-level protocol is supported by one or more lower-level protocols

35. TCP/IP Protocol Suite (Cont.) At the Transport layer, TCP/IP defines two protocols At the Transport layer, TCP/IP defines two protocols TCP TCP UDP (User Datagram Protocol) UDP (User Datagram Protocol) At the Network layer At the Network layer IP IP

36. OSI vs TCP/IP

37. TCP/IP and the OSI Model Physical Data Link Protocols defined by the underlying networks Networ k ICM P IP RAR P IGM P AR P Transport UDP TCP Applicat ion Present ation Session Applicat ion SMTP TELNET NFS FTP DNS SNMP

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

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

40. PDUs in TCP/IP

41. Standard Organizations ISOITU IEEE ANSI EIA State Department Carriers Other org.