![a ppp frame includes fcs a ppp frame includes fcs](https://s8185.pcdn.co/wp-content/uploads/2014/01/12-5-1024x216.jpg)
Since the presence of the escape sequence itself, if transmitted in the frame payload, will trigger an erroneous “escape recovery” operation at the receiver, every occurrence of the escape sequence is itself escaped and modified. Upon each such occurrence, it discards the escape sequence and XORs the following octet with the same predetermined value (e.g., 0x20) to recover the value of the original octet. These are referred to herein as “substitution octets.” The receiver inspects each received octet, and recognizes occurrences of the escape sequence. The two octets (that is, the escape sequence and the XORed value) are then substituted in the frame for the original octet. The value of the original octet is then modified, such as by XOR with a predetermined value (e.g., 0x20). To escape octets (also known as character escaping), a unique bit sequence (e.g., 0x7D), referred to as the escape sequence, is inserted into the frame ahead of the problematic, original octet. To avoid this, the frame is made “transparent” by “escaping” the octets containing potentially troublesome bit sequences. Modems or other devices in the communication path may recognize other bit sequences, and erroneously interpret them as control signals, triggering undesired actions. For example, some interfaces recognize particular byte values as XON and/or XOFF control signals, which may signal the end of a frame or a communication session. Additionally, other unique bit sequences with the frame payload may be detected and cause undesired consequences. If an octet having the value of the HDLC flag is transmitted in the frame, the receiver will recognize the bit sequence, and erroneously demark a frame boundary. In general, data to be encapsulated in a PPP frame (referred to herein as “original octets”) may assume any value. The receiving device inspects each octet in the frame, and detects frame boundaries by recognizing the HDLC flag. Frames are separated by a HDLC flag, or a unique bit sequence that delimits the beginning and end of the HDLC-like frame. PPP uses a logical framing structure similar to the High-level Data Link Control (HDLC) specification, wherein higher layer data structures (such as IP packets) are encapsulated into data link layer frames. Data are transmitted between the mobile terminal and an attached peripheral device (such as a laptop computer) in a link level protocol, such as the Point to Point Protocol (PPP). Packet-switched data are transmitted over the air interface between the wireless communication network and the mobile terminal as Internet Protocol (IP) packets.
![a ppp frame includes fcs a ppp frame includes fcs](https://media.cheggcdn.com/media%2F6fd%2F6fd20fae-727a-4971-af77-333c63653839%2FphpE373hp.png)
![a ppp frame includes fcs a ppp frame includes fcs](https://image.slidesharecdn.com/chapter8-110404141453-phpapp02/85/chapter-8-27-320.jpg)
![a ppp frame includes fcs a ppp frame includes fcs](https://www.tech-faq.com/wp-content/uploads/Point-to-Point-Protocol.jpg)
In this case, the attached computer is considered a peripheral device, from the point of view of the mobile terminal.
#A ppp frame includes fcs serial#
For example, a mobile terminal may connect to a computer via a Universal Serial Bus (USB), Bluetooth link, infrared (IR) link, or other wired or wireless connection. In some cases, the mobile terminal may provide Internet connectivity to another device, such as a laptop computer that otherwise lacks convenient Internet access. These services include real-time streaming video and music, on-line interactive gaming, text messaging, email, web browsing, and the like. Many Internet applications and services, once available only to users at fixed terminals, are now being made available via wireless communication networks to mobile users. The 3rd Generation (3G) wireless communication networks provide mobile users wireless access to packet data networks, such as the Internet. The present invention relates generally to the field of wireless communications and in particular to hardware acceleration of PPP frame processing in conjunction with DMA transfers.