Datalink layer introduces the notion of a frame

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Unformatted text preview: te channel technology etc. Datalink layer Introduces the notion of a frame Introduces frame set of bits that belong together set Idle markers tell us that a link is not carrying a frame Idle markers Begin and end markers delimit a frame Begin and end markers On a broadcast link (such as Ethernet) On end-system must receive only bits meant for it end-system need datalink-layer address need also need to decide who gets to speak next also these functions are provided by Medium Access sublayer (MAC) these Medium Some data links also retransmit corrupted packets and pace the Some rate at which frames are placed on a link part of logical link control sublayer part logical layered over MAC sublayer layered Datalink layer (contd.) Datalink layer protocols are the first layer of software Datalink Very dependent on underlying physical link properties Very Usually bundle both physical and datalink layer on host adaptor Usually host card example: Ethernet example: Postal service Postal mail bag frames letters mail frames letters Internet Internet a variety of datalink layer protocols variety most common is Ethernet and PPP most others are FDDI, SONET, HDLC others Network layer Logically concatenates a set of links to form the abstraction of Logically an end-to-end link Allows an end-system to communicate with any other endAllows system by computing a route between them Hides idiosyncrasies of datalink layer Hides Provides unique network-wide addresses Provides Found both in end-syste...
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