Transcript PPP

Link Layer
2
Ethernet and IEEE 802 Encapsulation

MUST be able to send and receive Ethernet

SHOULD be able to receive IEEE 802

MAY be able to send Ethernet and IEEE 802

configurable

default Ethernet
2
SLIP - Serial Line IP

A way to encapsulate IP-datagrams on a serial link

Simple - END + ESC character

no address negotiation

no type field - 1 protocol

Error prone - no CRC

CSLIP

Old fashioned
2
SLIP - Framing
IP datagram
c0
END
ESC
c0
db
dc
db
ESC
END
db dd
c0
SLIP encapsulation
2
PPP - Point to Point Protocol

A way to encapsulate IP-datagrams on a serial link

Asynchronous AND synchronous communication

Link Control Protocol (LCP)


negotiation for datalink options

Conf-req * Conf-ack * Conf-nack * Conf-rej
Network Control Protocol (NCP)

negotiation for network protocol options
2
PPP Framing
flag
addr
contol
1
protocol
information
CRC
flag
protocol Network control data
Link setup
2
protocol Link control data
3
protocol
IP datagram
2
PPP - LCP Negotiation options

Maximum Receive Unit (MRU)

Asynchronous Control Character Map

Authentication Protocol

Address and Control field compression

Multi-link procedure

Call-back
2
PAP Authentication
 Password
authentication protocol
 Snooping
gets you the password
 Not
compatible with
bidirectional authorization
2
CHAP Authentication

Challenge authentication protocol

Follows establishment of LCP

Identifies user

Random number challenge,
crypto response

Snooping does not discover password
2
CHAP Authentication
Challenge
CHAP
Response
CHAP
LCP
LCP
Link (Async, ISDN)
Link (Async, ISDN)
2
Multilink PPP
IPCP
IPXCP
MLP Bundle
LCP
LCP
LCP
Link
Link
Link
2
PPP - IPCP options

IP-Address

IP-Compression-Protocol

Unnumbered mode

Primary-DNS-Address

Secondary-DNS-Address
2
PPP summary

Multiple protocols on one link

CRC for every frame

Dynamic IP address negotiation (LCP)

TCP and IP header compression

Negotiation of datalink options (NCP)
2
Serial line troughput calculation

33.6 kbps - 8 bits / byte - 1 start - 1 stop = 3360 bytes
/sec

1024-byte + 20(TCP) + 20(IP) + 8(PPP) --> 319 msec

RTT = 638 ms

> 100 - 200 ms is bad for interactive response

for multiple sessions use small frames or better use
queuing
2