1. Chapter 3 Review of Protocols And Packet Formats

2. Outline
Protocol Layering
Ethernet IP
TCP / IP
ARP

3. Protocol Layering (1 / 2) OSI 7-layers Internet 5-layer
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
Application
Transport
Internet
Network Interface
Physical

4. Protocol Layering (2 / 2) Multiple protocols can occur at each layer
The resulting software is known as a stack
Outgoing data must pass down through all layers of the stack between the application and the physical network
Incoming data must pass up through all layers of the stack
We will learn that optimizing communication among layers is an important aspect of building high-speed networks system

5. Layer 1 And 2 (Physical And Network Interface)
Two protocols are important
Ethernet
ATM
We will concentrate on Ethernet

6. Ethernet
Layer 1 standards specify details such as the voltage used on copper wires
Carrier Sense Multiple Access with Collision Detection (CSMA / CD)
Layer 2 standards specify details such as the format of frames and addresses
Variable-size frames

7. Ethernet Frame Processing
Dest. Address
Source Address
Frame Type
Dedicated physical layer hardware
Checks and removes preamble and CRC on input
Computes and appends CRC and preamble on output
Layer 2 systems use source, destination and (possibly) type fields
Data In Frame 6 2
Header
Payload

8. Ethernet Addressing (1 / 2)
48-bit addressing
Unique address assigned to each station (NIC)
Destination address in each packet can specify delivery to
A single computer (unicast)
All computers in broadcast domain (broadcast)
Some computers in broadcast domain (multicast)

9. Ethernet Addressing (2 / 2)
Broadcast address is all 1s
Single bit determines whether remaining addresses are unicast or multicast
multicast bit
x x x x x x x m
x x x x x x x x

10. Internet Protocols Of Interest
Layer 2
Address Resolution Protocol (ARP)
Layer 3
Internet Protocol (IP)
Layer 4
User Datagram Protocol (UDP)
Transmission Control Protocol (TCP)

11. IP OPTION (MAY BE OMITTED)
IP Datagram Format
Format of each packet sent across Internet
Fixed-size fields make parsing efficient 4 8 16 19 24 31
VERS
HLEN
SERVICE
TOTAL LENGTH ID
FLAGS
F.OFFSET
TTL
TYPE
HDR CHECKSUM
SOURCE
DESTINATION
IP OPTION (MAY BE OMITTED)
PADDING
BEGINNING OF PAYLOAD

12. IP Datagram Fields Field Meaning
VERS Version number of IP being used (4)
HLEN Header length measured in 32-bit units
SERVICE Level of service desired
TOTAL LENGTH Datagram length in octets including header
ID Unique value for this datagram
FLAGS Bits to control fragmentation
F. OFFSET Position of fragment in original datagram
TTL Time to live (hop countdown)
TYPE Contents of payload area
HDR CHECKSUM One’s-complement checksum over header
SOURCE IP address of original sender
DESTINATION IP address of ultimate destination
IP OPTIONS Special handling parameters
PADDING To make options a 32-bit multiple

13. IP addressing 32-bit Internet address assigned to each computer
Virtual, hardware independent value
Prefix identifies network; suffix identifies host
Network systems use address mask to specify boundary between prefix and suffix
The address remain unchanged as the datagram passes across the Internet

14. Next-Hop Forwarding Routing table Route lookup
Found in both hosts and routers
Stores ( destination, mask, next_hop ) tuples
Route lookup
Takes destination address as argument
Finds next hop
Uses longest-prefix match

15. UDP Datagram Format 16 31 SOURCE PORT DESTINATION PORT MESSAGE LENGTH16 31
SOURCE PORT
DESTINATION PORT
MESSAGE LENGTH
CHECKSUM
BEGINNING OF PAYLOAD
Field Meaning
SOURCE PORT ID of sending application
DESTINATION PORT ID of receiving application
MESSAGE LENGTH Length of datagram including the header
CHECKSUM One’s-complement checksum over entire datagram

16. OPTIONS (MAY BE OMITTED)
TCP Segment Format
Sent end-to-end
Fixed-size fields make parsing efficient 4 10 16 24 31
SOURCE PORT
DESTINATION PORT
SEQUENCE
ACKNOWLEDGEMENT
HLEN
NOT USED
CODE BITS
WINDOW
CHECKSUM
URGENT PRT
OPTIONS (MAY BE OMITTED)
PADDING
BEGINNING OF PAYLOAD

17. TCP Segment Fields Field Meaning SOURCE PORT ID of sending application
DESTINATION PORT ID of receiving application
SEQUENCE Sequence number for data in payload
ACKNOWLEDGEMENT Acknowledgement of data received
HLEN Header length measured in 32-bit units
NOT USED Currently unassigned
CODE BITS URGENT, ACK, PUSH, RESET, SYN, FIN
WINDOW Receiver’s buffer size for additional data
CHECKSUM One’s-complement checksum over entire segment
URGENT PTR Pointer to urgent data in segment
OPTIONS Special handling
PADDING To make options a 32-bit multiple

18. Destination IP Address Destination IP Address
Protocol Port Numbers
16-bits values knows as protocol port numbers
Each UDP user datagram and each TCP segment carries the port numbers :
SOURCE PORT
DESTINATION PORT
The port spaces of the two protocols are completely independent
UDP demultiplex packets (each application)
TCP demultiplex packets (each application)
Destination IP Address
Destination Port NO.
Destination IP Address
Destination Port NO.
Source IP Address
Source Port NO.

19. Encapsulation And Transmission
Field in each header specifies type of encapsulated packet
UDP HEADER
UDP PAYLOAD
IP HEADER
IP PAYLOAD
ETHERNET HEADER
ETHERNET PAYLOAD

20. Address Resolution Protocol (ARP)8 16 24 31
ETHERNET ADDRESS TYPE (1)
IP ADDRESS TYPE (0800)
ETH ADDRLEN(6)
IP ADDRLEN(4)
OPERATION
SENDER’S ETH ADDR (first 4 octets)
SENDER’S ETH ADDR (last 2 octets)
SENDER’S IP ADDR (first 2 octets)
SENDER’S IP ADDR (last 2 octets)
TARGET’S ETH ADDR (first 2 octets)
TARGET’S ETH ADDR (last 4 octets)
TARGET’S IP ADDR (all 4 octets)
Format when ARP used with Ethernet and IP
Each Ethernet address is six octets
Each IP address is four octets

21. QUESTION？