Protocols

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

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

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

4. Protocol Architecture • Protocols in networking follows ‘layered’ architecture • Purpose of this layered architecture: • functions necessary for transfer of data are grouped into layers. • a set of/each task(s) is separated from others. • several protocols at each layer, each suitable for a different situation. • 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 • File transfer application • Communication service module • Network access module

6. A simplified architecture for file transfer

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

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

9. Protocols in simplified architecture

10. 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

11. Protocol Data Unit • 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

12. Protocol Data Units

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

14. 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 • Also: IBM Systems Network Architecture (SNA)

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

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

17. Application Application Presentation Presentation Session Session Transport Transport Network Network Data Link Data Link Physical Physical Peer-to-Peer Processes <---peer-to-peer process ---> provides services for uses services provided by machine A machine B

18. The OSI Environment

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

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

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

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

23. Data Link Layer • Specification Responsibility (cont.) • access control • for multipoint configuaration • 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

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

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

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

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

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

29. Session Layer (Cont.) • synchronisation a message of 1320 bytes 100 100 100 100 …... checkpoint

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

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

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

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

34. TCP/IP Protocol Suite (Cont.) • Two main protocols • Transmission Control Protocol • Internetworking Protocol • Many other protocols • Hierarchical protocol architecture made up for interactive modules • 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 • TCP • UDP (User Datagram Protocol) • At the Network layer • IP

36. OSI vs TCP/IP

37. TCP/IP and the OSI Model Application Application Presentation SMTP TELNET NFS SNMP FTP DNS Session TCP UDP Transport ICMP IGMP IP Network ARP RARP Data Link Protocols defined by the underlying networks Physical

38. 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)

39. 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

40. PDUs in TCP/IP

41. ISO ITU ANSI StateDepartment IEEE EIA Carriers Otherorg. Standard Organizations