1. Connection-Based vs. Connectionless
Telephone: operator sets up connection between the caller and the receiver
Once the connection is established, conversation can continue for hours
(i.e this is connection-based)
Share transmission lines over long distances by using switches to multiplex several conversations on the same lines
Problem: lines busy based on number of conversations, not amount of information sent
Advantage: reserved bandwidth
Before computers
How share lines for multiple conversation
Works until today;
Continuous

2. Connection-Based vs. Connectionless
Connectionless: every package of information must have an address => packets
Each package is routed to its destination by looking at its address
Analogy, the postal system (sending a letter)
also called “Statistical multiplexing”
Analogy: post

3. Protocol Family Concept
Message
Logical
Message
Actual
Actual
Logical H
Message T H
Message T
Actual
Actual H H
Message T T H H
Message T T
Physical

4. What is a Minimal Protocol
Bridge application’s notion of “message” to the network’s notion of a packet
(i.e. how does an application’s notion of a message relate to a networks notion of a message?)
1. Application layer
Hands over application program’s message to the transport layer

5. What is a Minimal Protocol
2. Transport layer
At sending end
Takes a message from the application layer and breaks it into packets commensurate with the network characteristics
Attaches headers to the packets that contain information for use at the destination
Handles retransmissions if necessary for overcoming network errors
At receiving end
Use the header info to assemble a message destined for an application program at this node
Keeps track of packets of message(s) being assembled
Negotiate with the sender (using ACKS/NACKS) to complete the message assembly
Hand over assembled message to the application layer

6. What is a Minimal Protocol
3. Network layer
Implements the network driver to deal with the physical characteristics of the network
e.g.
CSMA/CD for Ethernet
token re-generation for token ring
Routing packets on the available network links
Filtering packets on the network and snarfing those intended for this node

7. ISO Model 7 Application 6 Presentation 5 Session 4 Transport 3 Network
Interact with user: e.g. mail, telnet, ftp 6
Presentation
Char conv., echoing, format diffs: endian-ness 5
Session
Process to process comm.: e.g. Unix sockets 4
Transport
Packetizing, seq-num, retrans.: e.g. TCP, UDP 3
Network
Routing, routing tables: e.g. IP
Interface to physical media, error recovery: e.g. retransmit on collision in Ethernet 2
Data Link 1
Electrical and mechanical characteristics of physical media: e.g. Ethernet
Physical

8. ISO Model Examples 7 Application 6 Presentation 5 Session 4 Transport
User
program
FTP 6
Presentation 5
Session
Sockets: open/close/read/write interface
Kernel
Software 4
Transport
TCP: reliable infinite-length stream 3
Network
IP: unreliable datagrams anywhere in world
Ethernet: unreliable datagrams on local segment 2
Data Link
Hardware 1
10baseT ethernet spec: twisted pair w/RJ45s
Physical

9. Techniques Protocols Use
Sequencing for Out-of-Order Delivery
Sequencing to Eliminate Duplicate Packets
Retransmitting Lost Packets
Avoiding Replay Caused by Excessive Delay
Flow Control to Prevent Data Overrun
Mechanism to Avoid Network Congestion
Name Resolution (external to protocol really)

10. the address of computer
Today IP
One protocol to rule them all
Address assignment
IP Routing (layer-3 switching)
What exactly do we mean by this???
Name Resolution
ARP: IP -> ethernet MAC (media access control)
DNS: name -> IP
TCP
Reliable in-order streams
Built atop IP
(i.e. how do we find
the address of computer
we want to go to?
is more like
a VA…)

11. TCP/IP
A number of different protocols have been developed to permit internetworking
TCP/IP (actually a suite of protocols) was the first developed.
Work began in 1970 (same time as LAN's were developed)
Most of the development of TCP/IP was funded by the US Government (ARPA)

12. Layered Model Application Transport Internet Network Interface
TCP/IP Model
Application 5
Transport 4
Internet 3
Network Interface 2
Physical 1

13. Layer upon layer upon layer...
Layer 1: Physical
Basic network hardware (same as ISO model Layer 1)
Layer 2: Network Interface
How to organize data into frames and how to transmit over network (similar to ISO model Layer 2)
Layer 3: Internet
Specify format of packets sent across the internet as well as forwarding mechanisms used by routers
Layer 4: Transport
Like ISO Layer 4 specifies how to ensure reliable transfer
Layer 5: Application
Corresponds to ISO Layers 6 and 7. Each Layer 5 protocol specifies how one application uses an internet

14. IP Addresses

15. IP: Internet Protocol Addresses
The various networking schemes (LAN's and WAN's) used physical addresses
To achieve a seamless network with universal connectivity we need addresses for the virtual internet
The internet is an abstraction created in software which can use addresses, packet format and delivery techniques independent of the physical hardware
(sound familiar???)

16. IP Addressing Each host in the internet must have a unique address
Users, application programs and software operating in the higher layers of the protocol stack use these addresses
In the IP protocol each host is assigned a unique 32 bit address. Any packet destined for a host on the internet will contain the destination IP address.

17. IP Address Hierarchy
Addresses are broken into a prefix and a suffix for routing efficiency
The Prefix is uniquely assigned to an individual network.
The Suffix is uniquely assigned to a host within a given network 1 1
Network 1
Network 2 2 3 3 5

18. Guarantee Each computer has a unique address
The full address contains both a prefix and a suffix assigned to guarantee uniqueness.
Although network numbers must be assigned globally, suffixes can be assigned locally without global coordination

19. How many bits? How should the 32 bit address be divided?
In other words how many bits for prefix, how many for suffix?
Example 1:
16 bits for each
65536 max networks, max hosts/network
Example 2:
24 bits for prefix, 8 bits for suffix
8,388,608 max networks, 256 max hosts/network
Other possibilities?

20. More Flexible System
Create system with different classes of address. Each class has different size for the prefix and the suffix
(Up to) the first 4 bits determine the class
Five classes are defined

21. Five Classes of IP Address
Prefix
Suffix
Class A 1
Prefix
Suffix
Class B 1
Prefix
Suffix
Class C 1
Multicast Address
Class D 1
Reserved for future use
Class E

22. Five Classes of IP Address
Primary Classes
Prefix
Suffix
Class A 1
Prefix
Suffix
Class B 1
Prefix
Suffix
Class C 1
Multicast Address
Class D 1
Reserved for future use
Class E

23. Dotted Decimal Notation
Conventionally 32 bit IP addresses are expressed in dotted decimal notation
Each byte is expressed as a decimal number (0-255). The bytes are separated by decimal points
Addresses range from to 28 28 28 28

24. Classes and Dotted DecimalB C D E
Range of Values
0 through 127
128 through 191
192 through 223
224 through 239
240 through 255
Does this mean there are
64 Class B networks?
Does this mean there are
32 Class C networks?
(on the board)

25. Division of the Address Space
Class
Bits in
Prefix
Maximum Number
of Networks
Bits in
Suffix
Maximum Number of
Hosts per Network A B C 7 14 21
128
16384 24 16 8
65536
256
(on the board)

26. Special IP Addresses Network Address Directed Broadcast Address
Limited Broadcast Address
This Computer Address
Loopback Address
Berkeley Broadcast Address Form

27. Network Address Useful to have an address which represents a network
Formed by adding a 0 suffix
Example   
A network address should never appear as a destination in a packet
(quiz question)

28. Directed Broadcast Address
Often convenient to send a message to all hosts on a single network
Directed broadcast address formed by adding a suffix containing all 1 bits
Once the direct broadcast message arrives in the destination network it is sent to all host on the network via
The local networks hardware broadcast facility or if none present
Individual messages sent to each host

29. Limited Broadcast Address
Typically used on startup by a computer that doesn't yet know the network number
Message must contain all 1 bits
Message remains on local net
(quiz question)

30. This Computer Address
A computer needs to know its IP address to send or receive internet packets
TCP/IP contains protocols which allow a computer to obtain its IP address automatically when it boots
These startup protocols use IP to communicate
Sending an IP packet requires a source address
Address means "this computer"

31. Loopback Address
During testing it is often convenient to have two applications which will eventually communicate run on the same computer.
A message can travel down the stack from one application and back up the stack to the other application
IP reserves class A network prefix 127 for this purpose (the suffix doesn't matter)
By convention is most often used

32. Berkeley Broadcast Address Form
UC Berkeley developed and distributed an early version of TCP/IP as part of BSD UNIX
Instead of a directed broadcast address suffix of all 1 bits they used a suffix of all 0 bits. This is known as a Berkley Broadcast
Many early computer manufacturers derived their software from the Berkeley Implementation
Some can accept either, some both

33. Special IP Address Summary
Prefix
Suffix
Type of Address
Purpose
All-0's
All-0's
This computer
Used during bootstarp
Network
All-0's
Network
Identifies a network
Network
all-1's
Directed broadcast
Broadcast on specified net
All-1's
All-1's
Limited broadcast
Broadcast on local net
127
Any
Loopback
Testing
Network
All-0's
Directed broadcast
Berkley broadcast

34. TCP: Reliable Transport Service
TCP must use an inherently unreliable service, IP, to provide reliable service
TCP = Transmission Control Protocol
TCP must supply a service that guarantees
Prompt, reliable communication
Data delivery in the same order sent
No loss
No duplication

35. Services Provided by TCP
Connection Orientation
Point-To-Point Communication
Complete Reliability
Full Duplex Communication
Stream Interface
Reliable Connection Startup
Graceful Connection Shutdown

36. End to End Services
TCP provides a connection from one application on a computer to an application on a remote computer
Connection is virtual - provided by software passing messages
TCP messages are encapsulated in IP Datagrams
Upon arrival IP passes the TCP message on to the TCP layer.
TCP exists at both end of the connection but not at intermediate points (routers).

37. Achieving Reliability
Causes of problems
Failure of the IP system to deliver information reliably
Messages may be duplicated, lost, delayed or delivered out of order
Reboot of a host computer
Two programs make a connection
One computer reboots
New connection is formed
Messages from first session now arrive

38. Packet Loss and Retransmission

39. Adaptive Retransmission
Whenever TCP sends a message it records the time and then the time when a response is received
A statistical function is used to maintain a current estimate of expected delay
Timer can be set to a value depending on
Stable conditions
Increasing delay
Decreasing delay

40. Buffers and Windows Receiving host can have a buffer
Acknowledgements can contain amount of free buffer space available (Window)
Sender will not send more data than buffer will hold
As buffer space increases (i.e. application consumes data from buffer) additional acks can be sent updating buffer space available