1. Multiplexing

2. 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

3. Stream of Arriving or Outgoing IP Packets
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

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

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

6. 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

7. 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)
Total Length in bytes (16)
Indication (16 bits)
Flags (3)
Fragment Offset (13)
Time to Live (8)
Protocol (8)
Header Checksum (16)
Source IP Address
Destination IP Address …

8. Multiplexing Other Messages have Analogous Fields TCP and UDP
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
(4)
Reserved (6)
Flags (6)
Window Size (16)

9. Multiplexing Other Messages have Analogous Fields PPP
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