1. Point to Point Protocol
PRESENTER: PHAN DINH VUONG
INSTRUCTOR: PROF.DR.FRIEDBERT KASPAR

2. Agenda
What is PPP?
Design Requirements
Data frame format
Byte stuffing
Control Protocol
Wireshark Demo
Q&A

3. OSI Model

4. What is Point-to-Point Protocol ?
What is the difference between point to point and peer to peer?
Answer:
- Point to point is a protocol for communication between two
computers using a serial interface (phone).
- Peep to peer (P2P) is a communication model in which each
party has the same capabilities and either party can initiate a
communication session (BitTorrent).

5. What is Point-to-Point Protocol ?
The Point-to-Point Protocol (PPP) provides a standard method for transporting
multi-protocol datagrams over point-to-point links. PPP is comprised of three
main components:
• A method for encapsulating multi-protocol datagrams.
• A Link Control Protocol (LCP) for establishing, configuring, and testing the
data-link connection.
• A family of Network Control Protocols (NCPs) for establishing and configuring
different network-layer protocols.

6. Design requirements?
• Packet framing: Packet (from network-layer)  Frames (start & end of frame)
• Transparency.To network layer packet (headers or data).
• Multiple network layer protocols. Able to support multiple network layer protocols (e.g., IP, RIP,
ICMP) running over the same physical link at the same time.
• Multiple types of links. Operate over a wide variety of link types: serial or parallel, synchronous or
asynchronous, low speed or high speed, electrical or optical.
• Error detection. Able to detect bit errors in the received frame.
• Connection liveness: detect a failure at the link level (e.g., the inability to transfer data from the
sending side of the link to the receiving side of this link) and signal this error condition to the
network layer.
• Network Layer Address Negotiation. mechanism for the communicating network layers (e.g., IP)
to learn or configure each other's network layer address.
• Simplicity.The first and foremost among all requirements . RFC 1547 states "the watchword for a
point-to-point protocol should be simplicity."

7. Design Non-requirements?
• Error correction. Required to detect bit errors but
is NOT required to correct
• Flow control. receive frames at the full rate of the underlying
physical layer .NO need to control for upper layers
• Sequencing. NOT required to deliver frames in the same order
• Multipoint links. Only a single sender and a single receiver.

8. Data frame format
01111110 11111111 00000011 Protocol Info Padding Check 01111110
• Flag: delimiter (framing)
• Address: not used in PPP as no support addressing(used in HDLC broadcast address)
• Control: always 00000011, transmission not sequenced, connectionless link.
• Protocol: upper layer protocol to which frame delivered (eg,IP 0x0021, IPX 0x002B)
• Info: upper layer data being carried
• Padding: In some cases, additional dummy bytes may be added to pad out the size
of the PPP frame.
• Check: cyclic redundancy check for error detection (2 0r 4 bytes, default 2 bytes)
Flag FlagAddress Control
1 byte 1 byte 1 byte 1 or 2 byte
Variable
length 2 or 4 bytes 1 byte
Variable
length

9. Stuffing
• Question: if receive <01111110> => It is data or flag?
• Sender: adds (“stuffs”) extra < 01111110> byte after
each < 01111110> data byte
• Receiver:
- two 01111110 bytes in a row:  discard first byte,
continue data reception
- single 01111110: flag byte
PPP PPP
A5
BB
01111110
B4
B4
01111110
BB
A5
A5 BB 01111110 01111110 B4

10. Control Protocol

11. Authentication
Value (in hex) Protocol
• c023 Password Authentication Protocol (PAP)
• c223 Challenge Handshake Authentication Protocol (CHAP)

12. Password Authentication Protocol (PAP)

13. Challenge Handshake Authentication Protocol(CHAP)

14. Wireshark Demo

15. Frame format

18. Q&A

19. Thank you!

20. References
• http://www-ee.uta.edu/online/wang/ppp.pdf
• Wikipedia: http://en.wikipedia.org/wiki/PPP
• RFC 1661: http://www.ietf.org/rfc/rfc1661.txt