| A | B |
|---|
| "quality of service" | describes the purpose of Layer 4 - the transport layer |
| TCP properties | connection-oriented , reliable , divides outgoing messages into segments , reassembles messages at the destination station , re-sends anything not received , reassembles messages from incoming segments. |
| UDP properties | connectionless , unreliable , transmit messages (called user datagrams) , provides no software checking for message delivery (unreliable) , does not reassemble incoming messages , uses no acknowledgments , provides no flow control |
| TCP/IP | a combination of two individual protocols - TCP and IP |
| Transmission Control Protocol (TCP) protocol fields | source port -- number of the calling port , destination port -- number of the called port , sequence number -- number used to ensure correct sequencing of the arriving data , acknowledgment number - next expected TCP octet , HLEN -- number of 32-bit words in the header , reserved -- set to zero , code bits -- control functions (such as setup and termination of a session) , window-- number of octets that the sender is willing to accept , checksum -- calculated checksum of the header and data fields , urgent pointer -- indicates the end of the urgent data , option-one option -- maximum TCP segment size , data -- upper-layer protocol data |
| Protocols that use UDP | TFTP (Trivial File Transfer Protocol) , SNMP (Simple Network Management Protocol) , DHCP (Dynamic Host Control Protocol) , DNS (Domain Name System) |
| port (or socket) numbers | Port numbers are used to keep track of different conversations that cross the network at the same time |
| expectational acknowledgments | meaning that the acknowledgment number refers to the octet that is next expected |
| sliding window | the window size is negotiated dynamically during the TCP session |
| three-way handshake | synchronizes a logical connection between the endpoints of a network |
| flow control | Technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving entity with data. When the buffers on the receiving device are full, a message is sent to the sending device to suspend the transmission until the data in the buffers has been processed. In IBM networks, this technique is called pacing. |
| sliding window flow control | Method of flow control in which a receiver gives transmitter permission to transmit data until a window is full. When the window is full, the transmitter must stop transmitting until the receiver advertises a larger window. TCP, other transport protocols, and several data link layer protocols use this method of flow control. |
| Common TCP ports | 21- FTP; 23 - Telenet; 25 - SMTP |
| Common UDP ports | 53 - DNS; 69 - TFTP; 161 - SNMP |
| two-way alternate communication | taking turns sending messages to avoid interrupting each other |
| two-way simultaneous communication. | each person would type whenever he/she wishes, regardless of who is transmitting, and you would assume that more information is always on the way |
| synchronization | Establishment of common timing between sender and receiver. |
| orderly initiation | how sessions begins |
| termination of the conversation | how session ends |
| session layer | establishes, manages, and terminates sessions between applications. This includes starting, stopping, and re-synchronizing two computers that are having a "rap session". The session layer coordinates applications as they interact on two communicating hosts |
| dialogue control | each host plays dual roles: requesting service - like a client; and, replying with service - like a server. Determining which role they are playing at any given moment |
| Dialogue separation | the orderly initiation, termination, and managing of communication |
| Checkpointing | similar to the way a word processor on a stand-alone computer pauses for a second when it performs an AutoSave of the current document. However, these checkpoints are used, instead, to separate parts of a session previously referred to as dialogues |
| 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) ; |
| The presentation layer | concerned with the format and representation of data. If necessary, this layer can translate between different data formats |
| 3 function of Presentation Layer | ยท 1) data formatting (presentation); 2) data encryption 3) data compression |
| Graphic Image Standards | 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 |
| Sound & Movie Standards | 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 both MAC and PC operating system |
| Text Standards | ASCII and EBCDIC are used to format text |
| Data encryption | protects information during its transmission |
| Data compression | Compression works by using algorithms (complex mathematical formulas) to shrink the size of the files |
| application layer | closest to you as an end-user, when you are interacting with software applications such as sending and receiving e-mail over a network |
| client-server applications | constantly repeating the following looped routine: client-request, server-response; client-request, server-response; etc. |
| Redirector | a protocol that works with computer operating systems and network clients instead of specific application programs |
| Redirector Process | 1) The client requests that the network file server allow the data file to be stored. ; 2) The server responds by saving the file to its disk, or by rejecting the client's request. ; 3) If the client requests that the network print server allow the data file to be printed by a remote (network) printer, the server processes the request by printing the file on one of its print devices, or by rejecting the request. |
| Examples of top level domains | .us - United States & .uk - United Kingdom |
| Examples of generic domain names | .edu - educational sites; .com - commercial sites; .gov - government sites; .org - non-profit sites; .net - network service |
| domain name server (DNS) | responds to requests from clients to translate a domain name into the associated IP address. The DNS system is set up in a hierarchy that creates different levels of DNS servers. |
| application protocols | The World Wide Web uses the HTTP protocol; Remote access programs use the Telnet protocol for directly connecting to remote resources; E-mail programs support the POP3 application layer protocol for electronic mail; File utility programs use the FTP protocol for copying and moving files between remote sites; Network data gathering and monitoring use the SNMP protocol. |
