1. 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”
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Digital System Architecture : Networks

2. 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
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Digital System Architecture : Networks

3. 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
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Digital System Architecture : Networks

4. Increasing Bandwidth with Bridges
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Digital System Architecture : Networks

5. Packet Format for CM-5, Ethernet and ATM
Data size/header size
- CM-5: 4-20/4
- Ethernet: /26
- ATM: 48/5
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Digital System Architecture : Networks

6. 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
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Digital System Architecture : Networks

7. 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
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Digital System Architecture : Networks

8. Standford--Berkeley Connection
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Digital System Architecture : Networks

9. 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)
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Digital System Architecture : Networks

10. 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, ...
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Digital System Architecture : Networks

11. An ATM Network of Workstations
Why not use ATM as LAN?
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Digital System Architecture : Networks

12. Relationship between TCP, IP and AAL-5 layers
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Digital System Architecture : Networks

13. 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
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Digital System Architecture : Networks

14. 240-530 Digital System Architecture : Networks
Homework
Exercises: 7.1, , 7.3, 7.8, 7.13
This homework will be counted as two homeworks
Due date: July, 20, 2001
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Digital System Architecture : Networks

15. 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
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Digital System Architecture : Networks

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