Practical Issues for Commercial Networks Standardization the goods

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” 12/26/2021 240 -530 Digital System Architecture : Networks 1

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 12/26/2021 240 -530 Digital System Architecture : Networks 2

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 12/26/2021 240 -530 Digital System Architecture : Networks 3

Increasing Bandwidth with Bridges 12/26/2021 240 -530 Digital System Architecture : Networks 4

Packet Format for CM-5, Ethernet and ATM Data size/header size -CM-5: 4 -20/4 -Ethernet: 0 -1500/26 -ATM: 48/5 12/26/2021 240 -530 Digital System Architecture : Networks 5

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 12/26/2021 240 -530 Digital System Architecture : Networks 6

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 12/26/2021 240 -530 Digital System Architecture : Networks 7

Standford--Berkeley Connection 12/26/2021 240 -530 Digital System Architecture : Networks 8

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) 12/26/2021 240 -530 Digital System Architecture : Networks 9

IP and TCP Headers • Application sends message • TCP breaks into 64 KB segments, adds 20 B header • IP adds 20 B header, sends to network • If Ethernet, broken into 1500 B packets with headers, trailers • Header, trailers have length field, destination, window number, version, . . . 12/26/2021 240 -530 Digital System Architecture : Networks 10

An ATM Network of Workstations • Why not use ATM as LAN? 12/26/2021 240 -530 Digital System Architecture : Networks 11

Relationship between TCP, IP and AAL-5 layers 12/26/2021 240 -530 Digital System Architecture : Networks 12

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 12/26/2021 240 -530 Digital System Architecture : Networks 13

Homework • Exercises: 7. 1, 7. 2, 7. 3, 7. 8, 7. 13 • This homework will be counted as two homeworks • Due date: July, 2001 12/26/2021 240 -530 Digital System Architecture : Networks 14

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 12/26/2021 240 -530 Digital System Architecture : Networks 15

240 -530 Midterm Exam. • Cover Chapter 6 and 7 • Date and time: will be discussed 12/26/2021 240 -530 Digital System Architecture : Networks 16