Iam john berkmans

1. Chapter 10:
Ethernet and Fibre Cable
Business Data Communications, 5e

2. Business Data Communications, 5e 2
Increase in High-Speed LANs
• Extraordinary growth in speed, power, and
storage capacity of PCs
• Increasing use of LANs as computing
platforms
• Examples
– Server farms
– Workgroups with “power” requirements
– High-speed backbones

3. Business Data Communications, 5e 3
Increase in High-Speed LANs
• Fast Ethernet and Gigabit Ethernet
• Fibre Channel
• High-speed Wireless LANs

4. Business Data Communications, 5e 4
Characteristics of
Some High-Speed LANS

5. Business Data Communications, 5e 5
Trends Influencing Emergence
of High-Speed LANs
• Explosive growth of speed and computing
power of PCs
• Recognition by MIS organizations of the
value and importance of networked
computing
– Centralized server farms
– Power workgroups
– High-speed local backbone

6. Business Data Communications, 5e 6
Traditional Ethernet
• Ethernet and CSMA/CD (IEEE 802.3)
• Carrier sense multiple access with collision
detection
• Four step procedure
– If medium is idle, transmit
– If medium is busy, listen until idle and then transmit
– If collision is detected, cease transmitting
– After a collision, wait a random amount of time before
retransmitting

7. Business Data Communications, 5e 7
Ethernet MAC Frame Format
• Preamble: 7-octet pattern of 0s &1s used to establish bit
synchronization.
• Start Frame Delimiter (SFD): Indicates actual start of frame.
• Destination Address (DA): Specifies the station(s) for which the
frame is intended
• Source Address (SA): Specifies the station that sent the frame.
• Length: Length of LLC data field in octets.
• LLC Data: Data unit supplied by LLC.
• Pad: Octets added to ensure that the frame is long enough for proper
CD operation.
• Frame Check Sequence (FCS): A 32-bit CRC, based on all fields
except preamble, SFD, and FCS.

8. Business Data Communications, 5e 8
Ethernet MAC Frame

9. Business Data Communications, 5e 9
802.3 Medium Notation
• Notation format:
<data rate in Mbps><signaling
method><maximum segment length in
hundreds of meters>
• e.g 10Base5 provides 10Mbps baseband,
up to 500 meters
• T and F are used in place of segment
length for twisted pair and fiber

10. Business Data Communications, 5e 10
802.3 10BaseX Media Options

11. Business Data Communications, 5e 11
Bridges
• Allow connections between LANs and to WANs
• Used between networks using identical
physical and link layer protocols
• Provide a number of advantages
– Reliability: Creates self-contained units
– Performance: Less contention
– Security: Not all data broadcast to all users
– Geography: Allows long-distance links

12. Business Data Communications, 5e 12
Bridge Functions
• Read all frames from each network
• Accept frames from sender on one network that are
addressed to a receiver on the other network
• Retransmit frames from sender using MAC protocol
for receiver
• Must have some routing information stored in order
to know which frames to pass

13. Business Data Communications, 5e 13
Bridge Operation

14. Business Data Communications, 5e 14
Key Aspects of Bridge Function
• Makes no modification to content or format of
frames it receives; simply copies from one LAN
and repeats with exactly the same bit pattern as
the other LAN.
• Should contain enough buffer space to meet peak
demands.
• Must contain addressing and routing intelligence.
• May connect more than two LANs.

15. Business Data Communications, 5e 15
Hubs
• Alternative to bus topology
• Each station is connected to the hub by two lines
(transmit and receive)
• When a single station transmits, the hub repeats
the signal on the outgoing line to each station.
• Physically a star; logically a bus.
• Hubs can be cascaded in a hierarchical
configuration.

16. Business Data Communications, 5e 16
Two-Level Hub Topology

17. Business Data Communications, 5e 17
Layer 2 Switches
• Also called a “switching hub”
• Has replaced hub in popularity, particularly for
high-speed LANs
• Provides greater performance than a hub
• Incoming frame from a particular station is
switched to the appropriate output line to be
delivered to the intended destination
• At the same time, other unused lines can be used
for switching other traffic

18. Business Data Communications, 5e 18
Ethernet Hubs and Switches
• Shared
medium
hubs
• Switched
LAN hubs
x

19. Business Data Communications, 5e 19
Advantages of Switched Hubs
• No modifications needed to workstations
when replacing shared-medium hub
• Each device has a dedicated capacity
equivalent to entire LAN
• Easy to attach additional devices to the
network

20. Business Data Communications, 5e 20
Types of Switched Hubs
• Store and forward switch
– Accepts a frame on input line
– Buffers it briefly
– Routes it to appropriate output line
• Cut-through switch
– Begins repeating the frame as soon as it
recognizes the destination MAC address
– Higher throughput, increased chance of error

21. Business Data Communications, 5e 21
Differences Between
Switched Hubs and Bridges
• Bridge frame handling is done in software. A layer 2
switch performs the address recognition and frame
forwarding functions in hardware.
• Bridges typically only analyze and forward one frame at
a time; a layer 2 switch can handle multiple frames at a
time.
• Bridges uses store-and-forward operation; layer 2
switches use cut-through instead of store-and-forward
operation
• New installations typically include layer 2 switches with
bridge functionality rather than bridges.

22. Business Data Communications, 5e 22
Problems With Layer 2 Switches
• Broadcast overload
• Lack of multiple links
• Can be solved with subnetworks connected by
routers
• However, high-speed LANs layer 2 switches
process millions of packets per second whereas a
software-based router may only be able to handle
well under a million packets per second

23. Business Data Communications, 5e 23
Layer 3 Switches
• Implement the packet-forwarding logic of the router in
hardware.
• Packet-by-packet switch operates like a traditional router
– Forwarding logic is in hardware
– Achieves an order of magnitude increase in performance
compared to software-based routers
• Flow-based switch identifies flows of IP packets that
have the same source and destination
– Once flow is identified, a predefined route can be established to
speed up the forwarding process
– Again, huge performance increases over a pure software-based
router are achieved

24. Business Data Communications, 5e 24
Why Use Ethernet for
High-Speed Networks?
• Negative
– CSMA/CD is not an ideal choice for high-speed LAN
design due to scaling issues, but there are reasons for
retaining Ethernet protocols
• Positive
– Use of switched Ethernet hubs in effect eliminates
collisions
– CSMA/CD protocol is well understood; vendors have
experience building the hardware, firmware, and
software
– Easy for customers to integrate with existing systems

25. Business Data Communications, 5e 25
Fast Ethernet
• Refers to low-cost, Ethernet-compatible
LANs operating at 100 Mbps
• 802.3 committee defined a number of
alternatives to be used with different
transmission media

26. Business Data Communications, 5e 26
802.3 100Base-T Options

27. Business Data Communications, 5e 27
802.3 100BaseX Media Options

28. Business Data Communications, 5e 28
Gigabit Ethernet
• Retains CSMA/CD protocol and Ethernet
format, ensuring smooth upgrade path
• Uses optical fiber over short distances
• 1-gbps switching hub provides backbone
connectivity

29. Business Data Communications, 5e 29
Gigabit Ethernet Media Options

30. Business Data Communications, 5e 30
10-Gbps Ethernet
• Driven by increased network traffic
– Increased number of network connections
– Increased connection speed of each end-station (e.g.,
10 Mbps users moving to 100 Mbps, analog 56k users
moving to DSL and cable modems)
– Increased deployment of bandwidth-intensive
applications such as high-quality video
– Increased Web hosting and application hosting traffic

31. Business Data Communications, 5e 31
10-Gbps Ethernet vs ATM
• No expensive, bandwidth-consuming conversion
between Ethernet packets and ATM cells is
required
• Combination of IP and Ethernet offers quality of
service and traffic policing capabilities that
approach those provided by ATM
• A wide variety of standard optical interfaces have
been specified for 10-Gbps Ethernet, optimizing
its operation and cost for LAN, MAN, or WAN
applications

32. Business Data Communications, 5e 32
Physical Layer Options
for 10-Gbps Ethernet

33. Business Data Communications, 5e 33
Example 100-Mbps Ethernet
Backbone Strategy

34. Business Data Communications, 5e 34
Fibre Channel
• Combine the best features of channel and
protocol-based technologies
– the simplicity and speed of channel communications
– the flexibility and inter-connectivity that characterize
protocol-based network communications.
• More like a traditional circuit-switched or packet-
switched network, in contrast to the typical
shared-medium LAN

35. Business Data Communications, 5e 35
Fibre Channel Goals
• Full-duplex links with
two fibers per link
• Performance from 100
Mbps to 800 Mbps on a
single link (200 Mbps
to1600 Mbps per link)
• Support for distances up
to 10 km
• Small connectors
• High-capacity utilization
with distance insensitivity
• Greater connectivity than
existing multidrop
channels
• Broad availability (i.e.,
standard components)
• Support for multiple
cost/performance levels,
from small systems to
supercomputers
• Ability to carry multiple
existing interface
command sets for existing
channel and network
protocols

36. Business Data Communications, 5e 36
Fibre Channel Elements
• Nodes
– The end systems
– Includes one or more N_ ports for interconnection
• Fabric
– Collection of switching elements s between systems
– Each element includes multiple F_ ports
– Responsible for buffering and for routing frames
between source and destination nodes

37. Business Data Communications, 5e 37
Fibre Channel
Protocol Architecture
• FC-0 Physical Media: Includes optical fiber,
coaxial cable, and shielded twisted pair, based on
distance requirements
• FC-1 Transmission Protocol: Defines the signal
encoding scheme
• FC-2 Framing Protocol: Defines topologies,
frame format, flow/error control, and grouping of
frames
• FC-3 Common Services: Includes multicasting
• FC-4 Mapping: Defines the mapping of various
channel and network protocols to Fibre Channel

38. Business Data Communications, 5e 38
Fibre Channel Media
• Media options include shielded twisted
pair, video coaxial cable, and optical fiber
• Data rates range from 100 Mbps to 3.2
Gbps
• Point-to-point link distances range from 33
m to 10 km

39. Business Data Communications, 5e 39
Fibre Channel Topologies
• Fabric/Switched Topology
– includes at least 1 switch to interconnect end systems.
– may also use multiple switches for a switched network, with
switches also supporting end nodes
• Point-to-point topology
– only two ports, directly connected, with no intervening fabric
switches
• Arbitrated loop topology
– Simple, low-cost topology for connecting up to 126 nodes in a
loop.
– Operates in a manner roughly equivalent to token ring protocols