<Li> Similarly, bit stuffing replaces these start and end marks with flag 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 . Note that this 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 . </Li> <Ul> <Li> Encapsulation of network layer data packets into frames </Li> <Li> Frame synchronization </Li> <Li> Logical link control (LLC) sublayer: <Ul> <Li> 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 . Data - link - layer error control (i.e. retransmission of erroneous packets) is provided in wireless networks and V. 42 telephone network modems, but not in LAN protocols such as Ethernet, since bit errors are so uncommon in short wires . In that case, only error detection and canceling of erroneous packets are provided . </Li> <Li> Flow control, in addition to the one provided on the transport layer . Data - link - layer flow control is not used in LAN protocols such as Ethernet, but in modems and wireless networks . </Li> </Ul> </Li> <Li> Media access control (MAC) sublayer: <Ul> <Li> Multiple access protocols for channel - access control, for example CSMA / CD protocols for collision detection and re-transmission in Ethernet bus networks and hub networks, or the CSMA / CA protocol for collision avoidance in wireless networks . </Li> <Li> Physical addressing (MAC addressing) </Li> <Li> LAN switching (packet switching), including MAC filtering, Spanning Tree Protocol (STP) and Shortest Path Bridging (SPB) </Li> <Li> Data packet queuing or scheduling </Li> <Li> Store - and - forward switching or cut - through switching </Li> <Li> Quality of Service (QoS) control </Li> <Li> Virtual LANs (VLAN) </Li> </Ul> </Li> </Ul> <Li> Encapsulation of network layer data packets into frames </Li> <Li> Logical link control (LLC) sublayer: <Ul> <Li> 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 . Data - link - layer error control (i.e. retransmission of erroneous packets) is provided in wireless networks and V. 42 telephone network modems, but not in LAN protocols such as Ethernet, since bit errors are so uncommon in short wires . In that case, only error detection and canceling of erroneous packets are provided . </Li> <Li> Flow control, in addition to the one provided on the transport layer . Data - link - layer flow control is not used in LAN protocols such as Ethernet, but in modems and wireless networks . </Li> </Ul> </Li>

At which layer do the ultimate sender and receiver of data make contact