Peer-to-peer relationship?
Layer 7 | Application |
User Interface: - Identifies & establishes the availability of intended communications partners. - Synchronizes cooperating applications. - Establishes agreement on procedure for error recovery. - Controls data integrity |
Direct Network Applications: - Client / Server relationship: -- FTP,TFTP, HTTP, SMTP, Web browsers, Email / Web Server / Email Server. Indirect Network Support: - Redirectors work with operating systems and network clients. Protocols that use redirectors: -- Apple Talk Filing Protocol. -- NetBIOS Extended User Interface. -- Network File System (NFS) of the TCP/IP suite. - DNS - Domain Name System: -- .edu / .com /.gov /.org /.net / .biz / .info -- http://www.celticrover.com --- becomes: -- http://64.224.39.150 -Network applications: - Telnet, HTTP, POP3, FTP. - Clients: -- Outlook, Internet Explorer, Eudora, Netscape Navigator. |
Data: Email message - web page - download / upload file. |
Layer 6 | Presentation |
- How data is presented to the Application Layer. - Format, syntax, compression, encryption. |
-ASCII / EBCDIC / JPEG / GIF / AVI / TIFF / MP3 / MIDI / HTML | Data: Specific format - ASCII ..... |
Layer 5 | Session |
Interhost Communication: - Establishes, manages, and terminates sessions. - Mini-conversations occur between applications located on different networks. - Decides whether to use full-duplex (2-way simultaneous communication or half-duplex (two-way alternate) communication using Dialog Control. - Dialog separation is used to initial, terminate and manage communication in an orderly fashion. |
- Remote Procedure Call - RPC - X-Window System - Apple Talk Session Protocol (ASP) - Zone Information Protocol (ZIP) - Digital Network Architecture Session Control Protocol (DNA SCP) - SQL |
Data |
Layer 4 | Transport |
- Reliable transport of data between source and destination. - Logical connection between end-points on a network. - End-to-end control is provided by sliding windows and reliability in sequencing numbers and acknowledgements. - TCP and UDP use port numbers to keep track of different conversation that cross the network at the same time. - Error correction before retransmission. Flow control: - Avoids overflowing buffers. - Ensures the segments delivered will be acknowledged. - Provides for retransmission of any segments that are not acknowledged. - Puts segments back into their correct sequence at the destination. - Provides congestion avoidance and control. |
TCP, UDP, SPX | PDU: Segments |
Layer 3 | Network |
- Logical addresses associated with the source and destination stations. - Paths through the network to reach desired destination. - Encapsulates data & attaches header. The packets or datagrams include the logical addresses Routers operate on Layer 3: - Tie together, or interconnect, network segments or entire networks. - Make logical decision regarding best path for the delivery. - Forward packets through the network. IP (logical) Addresses: - Class A, Class B, Class C, Class D, Class E. - 32 bit (4-octets) binary number. - Static - Dynamic Addressing. Subnetting: - Network, Subnet, Host. - Subnet Mask - Broadcast Address. |
IP (routed protocol), IPX, RARP, ARP, RIP, DHCP. | PDU: Packets |
Layer 2 | Data Link |
- Physical (Hexadecimal) addresses used by smart devices: -- Bridges and Switches. - Access to media using MAC (physical) addresses. - Combines bits into frames. - Error detection -- not correction. Important Note: A NIC (Network Interface Card) is considered both a Layer 1 & Layer 2 interface. (serial communication) |
- LLC Sublayer* - Logical Link Control (IEEE 802.2) -- Identifies different protocols. -- Supports connectionless and connection-oriented services. -- Encapsulates the network information into frames which includes physical addresses. -- Ethernet (Non-Deterministic) * IEEE defined - MAC Sublayer - Media Access Control: -- Defines how to xmit 802.3 frames on physical media. -- Physical addressing, network topology. -- Line discipline. -- Ethernet (Non-Deterministic - first come, first served) (spans both sublayers) - CSMA/CD -- IEEE 802.3 (spans Layer 1 and 2) -- CSMA/CD -- 10BaseT -- Token Ring (Deterministic - taking turns)/IEEE 802.5 (spans Layer 1 and 2) -- FDDI - Logical Ring / physical dual ring. |
PDU: Frames |
Layer 1 | Physical |
- Moves bits between devices. - Specifies voltage, wire speed and pin-out cables. - Combines bits into frames. - Error detection -- not correction. - Passive devices: Modem/CSU/Hub/Repeater. Important Note: A NIC (Network Interface Card) is considered both a Layer 1 & Layer 2 interface. |
EIA/TIA-232 - 449 IEEE 802.3 (spans Layer 1 and 2) - IEEE 802.5 (spans Layer 1 and 2) |
PDU: Bits 0s / 1s |
DNS - Domain Name System: | Top
The system used in the Internet for translating names of network nodes into addresses.
Encapsulation: | Top
Wrapping of data in a particular protocol header. For example, upper-layer data is wrapped in a specific Ethernet header before network
transit. Also, when bridging dissimilar networks, the entire frame from one network can simply be placed in the header used by the data link
layer protocol of the other network.
Ethernet: | Top
A baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox, Intel, and Digital Equipment Corporation. Ethernet
networks use CSMA/CD and run over a variety of cable types at 10,100, and 1000 Mbps. Ethernet is similar to the IEEE 802.3 series of
standards. (Deterministic - first come, first served.)
File Transfer Protocol: | Top
An application layer protocol used for transferring files between network nodes.
Flow Control: | Top
A technique for ensuring that a transmitting entity does not overwhelm a receiving entity with data. When 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.
Frame - Protocol Data Unit: | Top
A logical grouping of information sent a as data link-layer unit over transmission media Often refers to header and trailer, and used for
synchronization and error control, that surround the data contained in the unit. The terms cell, datagram message, packet, and segment are
also used to describe logical information groupings within the various layers of the OSI model.
Hop: | Top
The passage of a data packet from one network node, typically a router, to another.
HTML - Hypertext Markup Language: | Top
A simple hypertext document formatting language that uses tags to indicate how a given part of a document should be interpreted by a viewing
application, such as a web browser.
HTTP - Hypertext Transfer Protocol: | Top
Used by Web browsers and Web servers to transfer files, such as text and graphics files.
LLC - Logical Link Control: | Top
The higher of two data link-layer sublayers defined by IEEE. LLC handles error control, flow control, frame and MAC sublayer addressing. The
most common LLC protocol is IEEE 802.2 which incorporates both connectionless and connection-orientated variants.
IEEE - Institute of Electrical and Electronic Engineers (I-triple E) 802.2: | Top
A LAN protocol that specifies an implementation of the Logical Link Control sublayer of the data link layer (Layer 2). 802.2 handles errors,
framing, flow control and the network layer (Layer 3) service interface.
IEEE (I-triple E) 802.3: | Top
A LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. 802.3 uses CSMA/CD access
at a variety of speeds over a variety of physical media. Extensions of the IEEE 802.3 specification include 10Base2, 10Base5,10BaseF,
10BaseT, and 10Broad36. Physical variations for Fast Ethernet include 100BaseTX and 100BaseFX.
IEEE (I-triple E) 802.5: | Top
A LAN protocol that specifies an implementation of the physical layer and MAC sublayer of the data link layer. 802.5 users token passing
access at 4 or 16 Mbps over Shielded Twisted-Pair or Unshielded Twisted-Pair cabling and is functionally and operationally equivalent to IBM
Token Ring.
PDU - Protocol Data Unit: | Top