【计算机网络课程课件@中科大】3The Data Link Layer.pdfVIP

COMPUTER NETWORKS Chapter 03 The Data Link Layer Shoubao Yang Tel: 3601540 syang@ 1/~syang September 2006 2012-8-18 Computer Networks -03 1/77 Chapter 3 The Data Link Layer  Physical: Describes the transmission of raw bits in terms of mechanical and electrical issues.  Data Link: Describes how a shared communication channel can be accessed, and how a data frame can be reliably transmitted.  Network: Describes how routing is to be done. Mostly needed in subnets. 2012-8-18 Computer Networks -03 2/77  Transport: The hardest one, generally offers connection-oriented as well as connectionless services, and varying degrees of reliability. This layer provides the actual network interface to applications.  Application: Contains the stuff that users see: e-mail, remote logins, the Web’s exchange protocol, etc.  Note: We’ll just concentrate on transmission issues. Channel access is discussed in Chapter 4 2012-8-18 Computer Networks -03 3/77 3.1 Data Link Layer Design Issues  Basic Services Network layer passes a number of bits (frame) to the data link layer. Data link layer is responsible for transmitting the frame to the destination machine. Receiving layer passes received frame to its network layer.  Functions of the Data Link Layer • Providing a well-defined service interface to the network layer • Dealing with transmission errors • Regulating data flow so that slow receivers are not swamp