Module 7/- Data Link Layer _JIIlllllÍllIIIIlll((lIIIIUIl((lIIIUIIllIIIUUIIIlIIIIIUIIIIIIUUIUIII CCNA Exploration 4.0 s1[t1ostj1, Cisco BACHKHOA NETWORKING ACADEMY Overview | | / BACHKHOA NETWORKING ACADEMY Application | Predentation |S | I4 Spssion = ậnspori 13 Nebtwork | Data Link | | Network | _ Pica > The Data Link layer prepares network data for the physical network Hoc vién mang Bach khoa - Website: www.bkacad.com Overview Em Tnn0n000104I1 SACHIKHOA NETWORKING ACADEMY Upon completion of this chapter, you will be able to: Explain the role of Data Link layer protocols in data transmission Describe how the Data Link layer prepares data for transmission on network media Describe the different types of media access control methods Identify several common logical network topologies and describe how the logical topology determines the media access control method for that network Explain the purpose of encapsulating packets into frames to.faeilitate media access Describe the Layer frame structure and identify generic fields Explain the role of key frame header and trailertfields,»including addressing, QoS, type of protocol, and Frame Check Sequence Hoc vién mang Bach khoa - Website: www.bkacad.com IS l [111 TT BACHKHOA NETWORKING ACADEMY Data Link Layer — Accessing the Media Hoc vién mang Bach khoa - Website: www.bkacad.com Supporting & Connecting to Upper Layer Services ,lI(lllllllllllllllIIlIlIIIIIIIIIIIIIIIlI BACHKHOA NETWORKING ACADEMY Data Link Layer Terms Frame A PDU PDU at the Data Link layer is called a frame Application A node is a device on a network Presentation Session Transport Media Network Qo Data Link Physical koef aaa a The media are the physical means used to carry data signals A network is two or more devices connected to a common medium Hoc vién mang Bach khoa - Website: www.bkacad.com The Data Link layer provides a means for exchanging data over a common local media The Data Link layer performs two basic services: — Allows the upper layers to access the media using techniques such as framing — Controls how data Is.olaced ơnto the fnedia and Is received from the media using techniques such as media access control and error detection Supporting & Connecting to Upper Layer Services BACHKHOA NETWORKING ACADEMY FT) The Data Link Layer Data link layer protocols Different protocols may be govern how to format a in use for different media frame for use on different media, At each hop along the path, an intermediary device accepts frames from one medium, decapsulates the rame and then forwards the packets in a new frame The headers of each frame are formatted for the specific medium that it will cross e The Data Link layer effectively insulates the communhication*processes at the higher layers from the media transitions that mayoccurend-to-end ° A packet is received from and directed to an upper layer protocol, in this case IPv4 or IPv6, that does not need to be aware of which media the communication will use Hoc vién mang Bach khoa - Website: www.bkacad.com Controlling Transfer across Local Media BACHKHOA NETWORKING ACADEMY _,Ill(I(IlllllllIlllIIlIIIUIIlIIIIIlIIIIU( ‘ WAN Header l ‹ WAN Treiber HUỘ ee ee ¬Y — wAN Header ——ễễễ WAN Trailer ————— ` Serial Connection Ethernet Connection The Data Link layer is responsible for controlling the transfer of frames across the media e The media access control methods described by:the Data Link layer protocols define the processes by which network devices can-access the network media and transmit frames in diverse network environments Hoc vién mang Bach khoa - Website: www.bkacad.com Creating a Frame BACHKHOA NETWORKING ACADEMY _/IÌl(llllIIlllIIIlIlllIIIIIIII((IlIIIIlIIIlIlIlIlI Data Link Layer Services Network Layer Packet (Data) HEADER TRAILER Y \ Frame Physical Layer ° Control information may tell: — Which nodes are in communication — — Which Which errors occurred while the nodes communicated nodes will communicate next — with each other: When communication between individual nodes begins and when it ends Hoc vién mang Bach khoa - Website: www.bkacad.com Creating a Frame EMMWs BACHKHOA NETWORKING ACADEMY [II Formatting Data for Transmission ( Ầ Packet Frame Start Addressina ressing | 1010 ÍT lype A specific bit pattern denotes the start of the frame Quality DATA Ki 41 0 L 14 0 rror D : E Detection 1 rame 0.1 S Stop 0 Another specific bit pattern denotes the end of the frame e Framing breaks the stream into decipherable greupings, with control information inserted in the header and trailer as values in different fields ° This format gives the physical signals a structure that can be received by nodes and decoded into packets at the destination Hoc vién mang Bach khoa - Website: www.bkacad.com Connecting Upper Layer Services to the Media BACHKHOA NETWORKING ACADEY EMWEEETTITIIIIITT Connecting Upper Layer Services to the Media The Data Link layer links the software and hardware layers l Physical devices devoted to the Data Link layer have both hardware and software components Application _