ccna lihkg

ccna lihkg.High-Level Data Link Control (HDLC) is a bit-oriented, synchronous data link layer protocol developed by the International Organization for Standardization (ISO). HDLC uses synchronous serial transmission to provide error-free communication between two points. Cisco's HDLC protocol extends the standard HDLC protocol to include a field to identify the encapsulated network protocol, thus solving the problem of not being able to support multiple protocols and the resulting incompatibility between Cisco's HDLC encapsulation and the standard HDLC encapsulation. If both ends of the link are Cisco devices, there is no problem using HDLC encapsulation, but if a Cisco device is connecting to a non-Cisco device, the PPP protocol should be used. HDLC does not provide authentication and lacks the security of the link. Cisco HDLC is the default encapsulation method used by Cisco devices on synchronous serial lines. The standard HDLC and CiscoHDLC frame formats are shown in Figure 18-1, and the meanings of the fields are described below.Figure 18-1 Standard HDLC and Cisco HDLC Frame Format Flags: frame delimiter that identifies the start and end positions of the frame with 01111110. Address: Contains the HDLC address of the slave. The address can be a specific address, a group address, or a broadcast address, such as OxOf, 0x8f.Control: There are 3 different formats, depending on whether the type of HDLC frame used is an information frame, a monitor frame, or an unnumbered frame. Protocol: for CiscoHDLC only, this field specifies the type of protocol encapsulated within the frame, e.g. use 0x0800 for IP protocol and 0x86dd for IPv6 protocol. Data: Can be any binary bit string. Frame CheckSequence (FCS): precedes the termination delimiter and is usually cyclic redundant.340.Cisco Networking Lab CCNA Lab Guide (Release 2) Checksum ( CyclicRedundancy Check, CRC) The remainder of the result of the calculation.18.1.2 PPP Components and Session ProcessesLike HDLC, PointtoPointProtocol (PPP) is a frame encapsulation protocol on a serial line (synchronous or asynchronous circuits), but PPP can provide support for multiple network layer protocols. PPP offers the possibility of interconnecting devices from different vendors and supports features such as link authentication, multi-link bundling, callback, compression and link quality management. PPP contains the following 3 main components.For transmitting packets of a protocol type over a point-to-point link, similar to the way HDLC is framed.Extensible Link Control Protocol (LinkControlProtocol, LCP) for establishing, configuring, and testing data link connections. oA series of network control protocols ( Network Control Protocol.) used to establish and configure various network layer protocols,NCP)O The most common NCPs are the IPv4 control protocol and the IPv6 control protocol.The PPP layered architecture is shown in Figure 18.2 and consists of a physical layer (either synchronous or asynchronous media can be used), an LCP, and an NCP.