Practical Issues for Commercial Networks Standardization the good’s: low cost, stability (many suppliers) the bad’s: time for committees to agree, innovation suppression if released too early MPP’s: use proprietary interconnecting networks LAN’s, WAN’s: follow standards Node failure tolerance A single software crash on one node can cause all nodes to stop working? LAN’s & WAN’s: can survive such failure, “hot insert” = “yes” MPP’s: not sure! (fault intolerance), “hot insert” = “no” 10-Dec-18 240-530 Digital System Architecture : Networks

Interconnection Networks Examples 10 Mbits/sec Ethernet (IEEE 802.3): appeared since 1978, still being used today! carrier sensing with exponential backoff on collision detection Multiple Ethernets with devices to allow Ethernets to operate in parallel! 10 Mbit/sec Ethernet successors? FDDI: shared media (too late) ATM (too late?) Switched Ethernet 100 Mbit Ethernet (Fast Ethernet) Gigabit Ethernet 10-Dec-18 240-530 Digital System Architecture : Networks

240-530 Digital System Architecture : Networks Connecting Networks Bridges: connect LANs together, passing traffic from one side to another depending on the addresses in the packet. operate at the Ethernet protocol level usually simpler and cheaper than routers Routers or Gateways: these devices connect LANs to WANs or WANs to WANs and resolve incompatible addressing. Generally slower than bridges, they operate at the internetworking protocol (IP) level Routers divide the interconnect into separate smaller subnets, which simplifies manageability and improves security 10-Dec-18 240-530 Digital System Architecture : Networks

Increasing Bandwidth with Bridges 10-Dec-18 240-530 Digital System Architecture : Networks

Packet Format for CM-5, Ethernet and ATM Data size/header size - CM-5: 4-20/4 - Ethernet: 0-1500/26 - ATM: 48/5 10-Dec-18 240-530 Digital System Architecture : Networks

240-530 Digital System Architecture : Networks Internetworking allows computers on independent and incompatible networks to communicate reliably and efficiently Enabling technologies: software standards that allow reliable communications without reliable networks Hierarchy of software layers, giving each layer responsibility for portion of overall communications task, called protocol families or protocol suites 10-Dec-18 240-530 Digital System Architecture : Networks

Transmission Control Protocol/Internet Protocol (TCP/IP) This protocol family is the basis of the Internet IP makes best effort to deliver; TCP guarantees delivery TCP/IP used even when communicating locally: NFS uses IP even though communicating across homogeneous LAN One of the most important innovations in the communication community Software standards enable internetworking technologies 10-Dec-18 240-530 Digital System Architecture : Networks

Standford--Berkeley Connection 10-Dec-18 240-530 Digital System Architecture : Networks

Generic Protocol Stack communication occurs logically at the same level of the protocol, called peer-to-peer, but is implemented via services at the lower level Danger is each level increases latency if implemented as hierarchy (e.g., multiple check sums) 10-Dec-18 240-530 Digital System Architecture : Networks

240-530 Digital System Architecture : Networks IP and TCP Headers Application sends message TCP breaks into 64KB segments, adds 20B header IP adds 20B header, sends to network If Ethernet, broken into 1500B packets with headers, trailers Header, trailers have length field, destination, window number, version, ... 10-Dec-18 240-530 Digital System Architecture : Networks

An ATM Network of Workstations Why not use ATM as LAN? 10-Dec-18 240-530 Digital System Architecture : Networks

Relationship between TCP, IP and AAL-5 layers 10-Dec-18 240-530 Digital System Architecture : Networks

240-530 Digital System Architecture : Networks Networking Summary Protocols allow heterogeneous networking Protocols allow operation in the presence of failures Standardization is key for LAN & WAN Internetworking protocols used as LAN protocols => large overhead for LAN Integrated circuit revolutionizing networks as well as processors Switch is a specialized computer Faster networks and high overheads violate of Amdahl’s Law 10-Dec-18 240-530 Digital System Architecture : Networks

240-530 Digital System Architecture : Networks Homework Exercises: 7.1, 7.2, 7.3, 7.8, 7.13 This homework will be counted as two homeworks Due date: July, 20, 2001 10-Dec-18 240-530 Digital System Architecture : Networks

240-530 Digital System Architecture : Networks Assignment II Describe TCP/IP protocol in detail Explain each field of the TCP and IP headers Write a report Due date: July, 27, 2001 10-Dec-18 240-530 Digital System Architecture : Networks

240-530 Digital System Architecture : Networks 240-530 Midterm Exam. Cover Chapter 6 and 7 Date and time: will be discussed 10-Dec-18 240-530 Digital System Architecture : Networks