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A quick intro to networking 1. Framing SEECSNET 2. Encoding 3. Error detection 4. Reliable delivery 5. Access Mediation 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 SEECSNET Destination Token Ring Source 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 SEECSNET Destination Token Ring Source Encapsulation and Virtual addressing [ class activity ] How do we modify the SEECSNET packet to enable internetworking using concepts of encapsulation and virtual addressing Design the frame format 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 SEECSNET Destination 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 SEECSNET Destination 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 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 SEECSNET Destination: HTTP server Source: HTTP client Token Ring IP SEECSNET IP SEECSNET TRANSPORT APP data SEECSNET packet (sending) SEECSNET IP TRANSPORT APP data Application Transport HTTP message Network (application layer data) Data Link Bits Source Host SEECSNET packet (receiving) SEECSNET IP TRANSPORT APP data Application Transport HTTP message Network (application layer data) Data Link Bits Destination Host History of internetworking SEECSNET IP TRANSPORT APP data 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 Vint Cerf This functionality has now been broken down into two distinct layers (IP is another protocol and TCP is another protocol) Bob Kahn Proposed TCP/IP as a single integrated protocol in 1974 for internetworking Chapter 1: Computer Networks and the Internet [K&R] Chapter 2: Direct Link Networks [P&D] [ End of lecture ]