ATM, PPP
ATM:
ATM stands for Asynchronous Transfer Mode and is a high-speed, packet-switching technique that uses short fixed length packets called cells which are about 53 bits in length. ATM can transmit voice, video, and data over a variable-speed LAN and WAN connections at speeds ranging from 1.544Mbps to as high as 622Mbps. I recently read that the new standard may be 2Gbps. ATM's speed is derived from the use of short fixed length cells, which reduce delays, and the variance of delay for delay-sensitive services such as voice and video. ATM is capable of supporting a wide range of traffic types such as voice, video, image and data.
PPP:As an improvement to Serial Line Internet Protocol (SLIP), Point-to-Point Protocol (PPP) was mainly for the transfer of data over slower serial interfaces. It is better than SLIP because it provides multiprotocol support, error correction as well as password protection. It is a Data Link Layer protocol used to encapsulate higher protocols to pass over synchronous or asynchronous communication lines. PPP is capable of operating across any DTE/DCE device, most commonly modems, as long as they support duplex circuits. There are 3 components to PPP:
• HDLC(High-level Data Link Control) - Encapsulates the data during transmission and is a link layer protocol which is also the default Cisco encapsulation protocol for synchronous serial links. HDLC is supposed to be an open standard, but Cisco's version is proprietary, meaning it can only function with Cisco routers.
• LCP(Link Control Protocol) - Establishes, tests and configures the data link connection.
• NCPs(Network Control Protocols) - Used to configure the different communication protocols, allowing them on the same line simultaneously. Microsoft uses 3 NCPs for the 3 protocols at the Network Layer (IP, IPX and NetBEUI)
PPP communication occurs in the following manner: PPP sends LCP frames to test and configure the data link. Next, authentication protocols are negotiated to determine what sort of validation is used for security. Below are 2 common authentication protocols:
• PAP is similar to a network login but passwords are sent as clear text. It is normally only used on FTP sites.
• CHAP uses encryption and is a more secure way of sending passwords.
Then NCP frames are used to setup the network layer protocols to be used. Finally, HDLC is used to encapsulate the data stream as it passes through the PPP connection.
Point-to-Point Tunneling Protocol(PPTP) provides for the secure transfer of data from a remote client to a private server by creating a multi-protocol Virtual Private Network(VPN) by encapsulating PPP packets into IP datagrams. There are 3 steps to setup a secure communication channel:
1. PPP connection and communication to the remote network are established.
2. PPTP creates a control connection between the client and remote PPTP server
3. PPTP creates the IP datagrams for PPP to send.
The packets are encrypted by PPP and sent through the tunnel to the PPTP server which decrypts the packets, disassembles the IP datagrams and routes them to the host. Setting Up PPTP requires a PPTP Client, PPTP Server and a Network Access Server(NAS).