| A | B |
|---|
| required protocol for the District WAN (in your final project)? | PPP |
| LCPPPP addresses the problems of Internet connectivity by employing three main components: | 1. 1) A method for encapsulating datagrams over serial links. PPP uses High-Level Data Link Control (HDLC) as a basis for encapsulating datagrams over point-to-point links; 2) A Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection. 3) A family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols. PPP is designed to allow the simultaneous use of multiple network-layer protocols. Today, PPP supports other protocols besides IP, including Internetwork Packet Exchange (IPX) and Appletalk |
| High-Level Data Link Control (HDLC) | for encapsulating datagrams over point-to-point links. |
| Link Control Protocol (LCP) | establishing, configuring, and testing the data-link connection |
| family of Network Control Protocols (NCPs) | establishing and configuring different network-layer protocols. |
| PPP lower level functions | 1) Synchronous physical media, such as those that connect Integrated Services Digital Network (ISDN) networks; 2) Asynchronous physical media, such as those that use basic telephone service for modem dialup connections. |
| PPP higher level functions | encapsulates several network-layer protocols with NCPs such as 1) BCP -- Bridge Control Protocol ; 2) IPCP -- Internet Protocol Control Protocol; 3) IPXCP -- Internetwork Packet Exchange Control Protocol |
| PPP frame fields | Flag; Address; Control; Protocol; Data; FCS |
| PPP frame Flag | Indicates the beginning or end of a frame and consists of the binary sequence 01111110 |
| PPP frame Address | Consists of the standard broadcast address, which is the binary sequence 11111111. PPP does not assign individual station addresses |
| PPP frame Control | 1 byte that consists of the binary sequence 00000011, which calls for transmission of user data in an unsequenced frame. A connection-less link service similar to that of Logical Link Control (LLC) Type 1 is provided. |
| PPP frame Protocol | 2 bytes that identify the protocol encapsulated in the data field of the frame |
| PPP frame Data | 0 or more bytes that contain the datagram for the protocol specified in the protocol field. The end of the data field is found by locating the closing flag sequence and allowing 2 bytes for the frame check sequence (FCS) field. The default maximum length of the data field is 1,500 bytes. |
| PPP frame FCS | Normally 16 bits (2 bytes). Refers to the extra characters added to a frame for error control purposes. |
| four phases through which PPP establishes a point-to-point connection | 1) Link establishment and configuration negotiation; 2) Link-quality determination; 3) Network-layer protocol configuration negotiation; 4) Link termination |
| Link establishment and configuration negotiation | An originating PPP node sends LCP frames to configure and establish the data link |
| Link-quality determination | The link is tested to determine whether the link quality is sufficient to bring up network-layer protocols. Note that this is an optional phase |
| Network-layer protocol configuration negotiation | The originating PPP node sends NCP frames to choose and configure network-layer protocols |
| Link termination | The link remains configured for communications until LCP or NCP frames close the link or until some external event occurs (for example, an inactivity timer expires or a user intervenes). |
| three classes of LCP frames | Link establishment; Link termination; Link maintenance |
| Link establishment frames | establish and configure a link |
| Link termination frames | terminate a link |
| Link maintenance frames | manage and debug a link |
| 2 methods of PPP authentication | PAP and CHAP |
| PAP | Password Authentication Protocol, PAP, is considered a weak authentication subject to hacking. Passwords are sent across the link in clear text, and there is no protection from playback or repeated trial-and-error attacks |
| CHAP | Challenge Handshake Authentication Protocol (CHAP), conducts periodic, unannounced challenges to make sure the remote node still has a valid variable password value. |
