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2 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.

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Presentation on theme: "2 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."— Presentation transcript:

1 2 Link Layer

2 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

3 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

4 2 c0 db c0 db dc IP datagram SLIP encapsulation END db dd c0 ESC SLIP - Framing

5 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

6 2 PPP Framing flag addr contol protocol information CRC flag protocol IP datagram protocol Link control data protocol Network control data 1 2 3 Link setup

7 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

8 2 Password authentication protocol Snooping gets you the password Not compatible with bidirectional authorization PAP Authentication

9 2 Challenge authentication protocol Follows establishment of LCP Identifies user Random number challenge, crypto response Snooping does not discover password CHAP Authentication

10 2 CHAP LCP Link (Async, ISDN) CHAP LCP Link (Async, ISDN) Challenge Response CHAP Authentication

11 2 LCP Link LCP Link LCP Link MLP Bundle IPCPIPXCP Multilink PPP

12 2 PPP - IPCP options IP-Address IP-Compression-Protocol Unnumbered mode Primary-DNS-Address Secondary-DNS-Address

13 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)

14 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


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