1. Cisco – Chapters 12-14 Layers 4, 5, and 6 More Details

2. Transport Layer - 4 Assures data reliably travels end-to-end across the often vast network path Performs multiple functions to provide "quality of service” Guarantees Flow control Provides End-to-end control using sliding windows Provides reliability through sequencing numbers and acknowledgements

3. Layer 4 Protocols TCP - supplies a virtual circuit between end-user applications –connection-oriented –reliable –divides outgoing messages into segments –reassembles messages at the destination station –re-sends anything not received –reassembles messages from incoming segments.

4. Layer 4 Protocols UDP -- transports data unreliably between hosts. *unreliable *connectionless *transmits messages (called user datagrams) *provides no software checking for message delivery (unreliable) *does not reassemble incoming messages *uses no acknowledgements *provides no flow control

5. TCP/IP Combination of two individual protocols - TCP and IP –IP is a Layer 3 protocol - a connectionless service that provides best-effort delivery across a network –TCP is a Layer 4 protocol - a connection- oriented service that provides flow control as well as reliability

6. TCP Protocols HTTP – internet transmission rules FTP – file transfer SMTP -- mail DNS – domain name

7. UPD Protocols TFTP – trivial file transfer DNS – domain name SNMP - monitor and control network devices, and manage configurations, statistics collection, performance, and security. DHCP – assigns IP addresses

8. TCP Segment Fields Source and destination ports Sequence number Acknowledgement number Window – number of octets willing to accept Code bits Check Sum Others Data

9. UDP Segment Fields Source and destination address Length Check Sum Data –Note: No acknowledgements, no guaranteed delivery, no error control; used for tasks that do not require assembling segments in sequence

10. Port (Socket) Numbers 21FTP 23Telnet 25SMTP 53 DNS 69TFTP 161 SNMP

11. Port Ranges Numbers below 255 - for public applications Numbers from 255-1023 - assigned to companies for marketable applications Numbers above 1023 - are unregulated

12. TCP Three-way Handshake segments are encapsulated in packets Packets travel connectionless paths through internetworks Sequence and acknowledgement numbers necessary for TCP to track segments Synchronizes a connection at both ends before data is transferred.

13. PAR the source sends a packet, starts a timer, and waits for an acknowledgement before sending the next packet. If the timer expires before the source receives an acknowledgement, the source retransmits the packet and starts the timer over again.

14. Windows Size (number of windows determines the amount of data that you can transmit at one time before receiving an acknowledgment from the destination. After a host transmits the window-sized number of bytes, the host must receive an acknowledgment before it can transmit again

15. Windowing Expectational acknowledgments –the acknowledgment number refers to the octet that is next expected. The "sliding" part, of sliding window – the window size is negotiated dynamically during the TCP session. This results in inefficient use of bandwidth by the hosts.

16. Chapter 13 Layer 5 -- Session

17. Session Layer Tasks Accounting Conversation control, that is, determining who can talk when Session parameter negotiation.

18. Interhost Communications Establishes, manages and terminates communications between applications – two-way alternate communication - TWA Taking turns – uses a data token –two-way simultaneous communication - TWS Both can transmit at same time – collisions result –Checkpoints orderly initiation and termination of the conversation.

19. Dual Roles Server and Client Dialogue Control –Determining which role host is playing at any given moment Dialogue Separation –orderly initiation, termination, and managing of communication Major and minor synchronizations – see slide

20. Layer 5 Protocols Network File System (NFS) Structured Query Language (SQL) Remote Procedure Call (RPC) X-Window System AppleTalk Session Protocol (ASP) Digital Network Architecture Session Control Protocol (DNA SCP)

21. Chapter 14 – Layer 6 Presentation Layer

22. Layer 6 Tasks Pass-through protocol for information from adjacent layers Allows communication between applications on diverse computer systems in transparent manner Concerned with the format and representation of data Concerned with data structures

23. Layer 6 Responsible for presenting data in a form that the receiving device can understand –data formatting (presentation) EBCDIC – mainframe text ASCII – PC text –Layer 6 translates between two formats – data encryption (coding) – data compression (bit substitution)

24. Layer 6 Graphic Formats PICT - a picture format used to transfer QuickDraw graphics between programs on the MAC operating system TIFF (Tagged Image File Format) - a format for high-resolution, bit-mapped images JPEG (Joint Photographic Experts Group) - graphic format used most often to compress still images of complex pictures and photographs GIF (Graphic Image Format) – still images

25. Layer 6 Movie and Sound Formats MIDI (Musical Instrument Digital Interface) - for digitized music MPEG (Motion Picture Experts Group) - standard for the compression and coding of motion video for CDs and digital storage QuickTime - a standard that handles audio and video for programs on a MAC operating system

26. More Formats HTML – displays web pages – uses tags

27. Data Encryption & Compression Encryption - Protects information during its transmission –encryption key is used to encrypt the data at its source and then to decrypt the data at its destination Compression – Uses algorithms (complex mathematical formulas) to shrink the size of the files. –The algorithm searches each file for repeating bit patterns, and then replaces them with a token. A token is a much shorter bit pattern that represents the long pattern.