A quick intro to networking

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

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.

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.

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

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

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

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

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

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)

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

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)

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

[ End of lecture ]