1. A quick intro to networking

2. However, a SEECSNET cannot access a node outside this network
Framing
Encoding
Error detection
Reliable delivery
Access Mediation
SEECSNET
All nodes on SEECSNET implement and understand the SEECSNET protocol consistently allowing any arbitrary node to contact any other node.
However, a SEECSNET cannot access a node outside this network

3. The problem of internetworking:
how can a SEECSNET connect to any arbitrary node connected to an arbitrary network (other than its own)?
Ethernet
SEECSNET
Token Ring
By using a router/ gateway having an interface connected to each network.

4. The problem of flat addressing:
Even if we have a router, how does a SEECSNET node identify an Ethernet node? (or, any other node on a different network)
Ethernet
Destination
SEECSNET
Source
Token Ring
We need a hierarchical address that can identify a host while also identifying its network. This is the commonly used IP address.

5. The problem of incompatible heterogeneity:
Even with a hierarchical address to identify a node on another network, a SEECSNET node can only transmit using its own packet/ addressing format.
Ethernet
Destination
SEECSNET
Source
Token Ring
Encapsulation and Virtual addressing

6. Design the frame format
[ class activity ]
How do we modify the SEECSNET packet to enable internetworking using concepts of encapsulation and virtual addressing
Design the frame format
SEECSNET
Higher-layer data IP

7. Class Activity
Problem: Even if we have a hierarchical address through which we can identify a node on another network, for actual transmission, SEECSNET node can only use its own format.
Ethernet
Destination
SEECSNET
Source
Token Ring
The router receives the SEECSNET frame and removes the SEECSNET header to recover the IP packet.
SEECSNET IP
Higher-layer data

8. Class Activity
Problem: Even if we have a hierarchical address through which we can identify a node on another network, for actual transmission, SEECSNET node can only use its own format.
Ethernet
Destination
SEECSNET
Source
Token Ring
The router forwards the IP packet on the appropriate Ethernet interface after making a routing decision and adding appropriate header.
Ethernet IP
Higher-layer data

9. Destination: HTTP server
Class Activity
Problem: While using IP address and MAC address has allowed node to node communicate, how can we identify the end-to-end communicating processes?
Ethernet
Destination: HTTP server
SEECSNET
Source: HTTP client
Token Ring
APP data IP
SEECSNET
TRANSPORT
APP data IP
SEECSNET

10. Transport layer header
SEECSNET packet (sending)
SEECSNET IP
TRANSPORT
APP data
SEECSNET ®
Source Host
Application
Transport
Network
Data Link
Bits
IP header
Contains destination and source IP addresses
(and some other fields)
Transport layer header
(TCP for reliable data and UDP for unreliable data)
Contains source and destination port info which identifies the source/ destination process (and some other info)
HTTP message
(application layer data)

11. Transport layer header
SEECSNET packet (receiving)
SEECSNET IP
TRANSPORT
APP data
SEECSNET ®
Application
Transport
Network
Data Link
Bits
IP header
Contains destination and source IP addresses
(and some other fields)
Transport layer header
(TCP for reliable data and UDP for unreliable data)
Contains source and destination port info which identifies the source/ destination process (and some other info)
HTTP message
(application layer data)
Destination Host

12. History of internetworking
Vint Cerf
Bob Kahn
Proposed TCP/IP as a single integrated protocol in 1974 for internetworking
APP data IP
SEECSNET
TRANSPORT
Internetworking functionality
TCP/IP initially had the following format (Cerf and Kahn, 74)
Local header
Source
Dest.
Sequence number
Byte Count
Flag Field
Text
Checksum
This functionality has now been broken down into two distinct layers
(IP is another protocol and TCP is another protocol)

13. References Chapter 1: Computer Networks and the Internet [K&R]
Direct Link Networks [P&D]

14. [ End of lecture ]