The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking.This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors. SCITEX DOLEV 400 PSM L2 DRIVERS FOR WINDOWS 8. Dolev400 psm l2 driver. Find scitex dolev. Ps l2 driver assist. Choose operation system. Scitex dolev 800 psm l2 download drivers. Colors view nagesh. Creo scitex dolev, download official hp. Mp3 player drivers pps, creo scitex brisque, mac g4 preps, interface cable two. Dvd used creo scitex dolev.
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer.[1] The data link layer provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the physical layer.
L2 Form California Medical Board
The data link layer is concerned with local delivery of frames between nodes on the same level of the network..
The Media Access Control sublayer also performs frame synchronization, which determines the start and end of each frame of data in the transmission bitstream. It entails one of several methods: timing-based detection, character counting, byte stuffing, and bit stuffing.
The time-based approach expects a specified amount of time between frames.
Character counting tracks the count of remaining characters in the frame header. This method, however, is easily disturbed if this field is corrupted.
Byte stuffing precedes the frame with a special byte sequence such as DLESTX and succeeds it with DLE ETX. Appearances of DLE (byte value 0x10) have to be escaped with another DLE. The start and stop marks are detected at the receiver and removed as well as the inserted DLE characters.
Similarly, bit stuffing replaces these start and end marks with flags consisting of a special bit pattern (e.g. a 0, six 1 bits and a 0). Occurrences of this bit pattern in the data to be transmitted are avoided by inserting a bit. To use the example where the flag is 01111110, a 0 is inserted after 5 consecutive 1's in the data stream. The flags and the inserted 0's are removed at the receiving end. This makes for arbitrary long frames and easy synchronization for the recipient. The stuffed bit is added even if the following data bit is 0, which could not be mistaken for a sync sequence, so that the receiver can unambiguously distinguish stuffed bits from normal bits.
Services[edit]
The services provided by the data link layer are:
Encapsulation of network layer data packets into frames
In the logical link control (LLC) sublayer:
Error control (automatic repeat request, ARQ), in addition to ARQ provided by some transport-layer protocols, to forward error correction (FEC) techniques provided on the physical layer, and to error-detection and packet canceling provided at all layers, including the network layer., by encoding each letter as its position in the alphabet. Thus, the letter A is coded as 1, B as 2, and so on as shown in the table on the right. Adding up the resulting numbers yields 8 + 5 + 12 + 12 + 15 = 52, and 5 + 2 = 7 calculates the metadata. Finally, the '8 5 12 12 15 7' numbers sequence is transmitted, which the receiver will see on its end if there are no transmission errors. The receiver knows that the last number received is the error-detecting metadata and that all data before is the message, so the receiver can recalculate the above math and if the metadata matches it can be concluded that the data has been received error-free. Though, if the receiver sees something like a '7 5 12 12 15 7' sequence (first element altered by some error), it can run the check by calculating 7 + 5 + 12 + 12 + 15 = 51 and 5 + 1 = 6, and discard the received data as defective since 6 does not equal 7.
More sophisticated error detection and correction algorithms are designed to reduce the risk that multiple transmission errors in the data would cancel each other out and go undetected. An algorithm that can even detect if the correct bytes are received but out of order is the cyclic redundancy check or CRC. This algorithm is often used in the data link layer.
Protocol examples[edit]
Cisco Discovery Protocol (CDP)
Controller Area Network (CAN)
Ethernet Automatic Protection Switching (EAPS)
Fiber Distributed Data Interface (FDDI)
High-Level Data Link Control (HDLC)
IEEE 802.2 (provides LLC functions to IEEE 802 MAC layers)
Link Layer Discovery Protocol (LLDP)
Multiprotocol Label Switching (MPLS)
Nortel Discovery Protocol (NDP)
Point-to-Point Protocol (PPP)
Serial Line Internet Protocol (SLIP) (obsolete)
Split multi-link trunking (SMLT)
IEEE 802.1aq - Shortest Path Bridging
Unidirectional Link Detection (UDLD)
and most forms of serial communication.
Relation to the TCP/IP model[edit]
Internet protocol suite
Application layer
Transport layer
Internet layer
IP
Link layer
Tunnels
MAC
In the Internet Protocol Suite (TCP/IP), OSI's data link layer functionality is contained within its lowest layer, the link layer. The TCP/IP link layer has the operating scope of the link a host is connected to, and only concerns itself with hardware issues to the point of obtaining hardware (MAC) addresses for locating hosts on the link and transmitting data frames onto the link. The link-layer functionality was described in RFC 1122 and is defined differently than the data link layer of OSI, and encompasses all methods that affect the local link.
The TCP/IP model is not a top-down comprehensive design reference for networks. It was formulated for the purpose of illustrating the logical groups and scopes of functions needed in the design of the suite of internetworking protocols of TCP/IP, as needed for the operation of the Internet. In general, direct or strict comparisons of the OSI and TCP/IP models should be avoided, because the layering in TCP/IP is not a principal design criterion and in general, considered to be 'harmful' (RFC 3439). In particular, TCP/IP does not dictate a strict hierarchical sequence of encapsulation requirements, as is attributed to OSI protocols.
See also[edit]
SANA-II – Standard Amiga Networking Architecture, version 2
References[edit]
^'What is layer 2, and Why Should You Care?'. accel-networks.com. Archived from the original on February 18, 2010. Retrieved September 29, 2009.
^Regis J. Bates and Donald W. Gregory (2007). Voice & data communications handbook (5th ed.). McGraw-Hill Professional. p. 45. ISBN978-0-07-226335-0.
^Guowang Miao; Guocong Song (2014). Energy and spectrum efficient wireless network design. Cambridge University Press. ISBN978-1107039889.
S. Tanenbaum, Andrew (2005). Computer Networks (4th ed.). 482,F.I.E., Patparganj, Delhi 110 092: Dorling Kindersley(India)Pvt. Ltd.,licenses of Pearson Education in South Asia. ISBN81-7758-165-1.CS1 maint: location (link)
Odom, Wendel (2013). CCENT/CCNA ICND1 100-101, CCENT Official cert guide. Paul Boger, cisco press. ISBN978-1-58714-385-4.
External links[edit]
Wikimedia Commons has media related to Data link layer.
L2 Format
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