Multiplexing Multiplexing IP packets can carry different things

Multiplexing

Multiplexing • IP packets can carry different things in their data fields – TCP segments – UDP datagrams – ICMP supervisory messages (later) – RIP messages (later) IP Data Field IP Header

Multiplexing • We say that IP can multiplex (mix) different types of traffic in a stream of IP packets Single IP Packet Carrying UDP Datagram UDP IP-H TCP IP-H UDP IP-H ICMP IP-H Stream of Arriving or Outgoing IP Packets

Multiplexing • IP process must pass contents of arriving IP packets to the correct process for subsequent handling TCP UDP IP-H Arriving Packets UDP IP IP Process ICMP

Multiplexing • IP process must also accept messages from multiple processes and multiplex them on an outgoing stream TCP IP-H UDP Outgoing Packets UDP IP IP Process ICMP

Multiplexing • Need a Way for Receiving IP Process to Know What is in the Data Field – So it can pass the contents to the appropriate process IP Data Field IP Header

Multiplexing • IP Header has an 8 -bit Protocol field – Identifies the contents of the data field • 1=ICMP (later), 8=TCP, 17=UDP, etc. Version (4) Hdr Len (4) TOS (8) Indication (16 bits) Time to Live (8) Total Length in bytes (16) Flags (3) Protocol (8) Fragment Offset (13) Header Checksum (16) Source IP Address Destination IP Address …

Multiplexing • Other Messages have Analogous Fields – Identify contents of data field • TCP and UDP – Have Port number fields – Identify the application process (80=HTTP) Source Port # (16) Destination Port # (16) Sequence Number (32 bits) Acknowledgement Number (32 bits) Hdr Len Reserved (6) (4) Flags (6) Window Size (16)

Multiplexing • Other Messages have Analogous Fields – Identify contents of data field • PPP – Protocol field identifies contents of information field as IP, IPX, a supervisory message, etc. Flag Addr Ctrl Prot Info CRC Flag