UNIT - I

Frame Relay Networks

Asynchronous transfer mode
ATM protocol architecture
ATM logical connection
ATM cell and service categories AAL
High speed LANs: Fast, Gigabit ethernet, Fiber
channel
Wireless LANs
 Introduction

Packet-Switching Networks
Switching Technique
Routing
X.25
Frame Relay Networks
Architecture
User Data Transfer
Call Control

3
 Packet-Switching Networks

Basic technology the same as in the 1970s

One of the few effective technologies for long
distance data communications
Frame relay and ATM are variants of packet-
switching
Advantages:
- flexibility, resource sharing, robust, responsive
Disadvantages:
Time delays in distributed network, overhead penalties
Need for routing and congestion control

4
 Circuit-Switching

Long-haul telecom network designed for voice

Network resources dedicated to one call
Shortcomings when used for data:
Inefficient (high idle time)
Constant data rate

5
 Packet-Switching

Data transmitted in short blocks, or packets

Packet length < 1000 octets
Each packet contains user data plus control
info (routing)
Store and forward

6
Figure 4.1 The Use of Packets

Chapter 4 Frame Relay 7

 Figure 4.2 Packet
Switching: Datagram
Approach

Chapter 4 Frame Relay 8

Advantages over Circuit-Switching

Greater line efficiency (many packets can go

over shared link)
Data rate conversions
Non-blocking under heavy traffic (but
increased delays)

9
Disadvantages relative to Circuit-Switching

Packets incur additional delay with every node

they pass through
Jitter: variation in packet delay
Data overhead in every packet for routing
information, etc
Processing overhead for every packet at every
node traversed

10
Figure 4.3 Simple Switching Network

Chapter 4 Frame Relay 11

 Switching Technique

Large messages broken up into smaller packets

Datagram
Each packet sent independently of the others
No call setup
More reliable (can route around failed nodes or
congestion)
Virtual circuit
Fixed route established before any packets sent
No need for routing decision for each packet at
each node

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Figure 4.4 Packet
Switching: Virtual-
Circuit Approach

Chapter 4 Frame Relay 13

 Routing

Adaptive routing
Node/trunk failure
Congestion

14
 X.25

3 levels
Physical level (X.21)
Link level (LAPB, a subset of HDLC)
Packet level (provides virtual circuit
service)

15
Figure 4.5 The Use of Virtual Circuits

Chapter 4 Frame Relay 16

Figure 4.6 User Data and X.25
Protocol Control Information

Chapter 4 Frame Relay 17

 Frame Relay Networks

Designed to eliminate much of the overhead in X.25

Call control signaling on separate logical connection
from user data
Multiplexing/switching of logical connections at layer
2 (not layer 3)
No hop-by-hop flow control and error control
Throughput an order of magnitude higher than X.25

18
Figure 4.7 Comparison of X.25 and
Frame Relay Protocol Stacks

Chapter 4 Frame Relay 19

Figure 4.8 Virtual Circuits and Frame
Relay Virtual Connections

Chapter 4 Frame Relay 20

 Frame Relay Architecture

X.25 has 3 layers: physical, link, network

Frame Relay has 2 layers: physical and data link (or
LAPF)
LAPF core: minimal data link control
Preservation of order for frames
Small probability of frame loss
LAPF control: additional data link or network layer
end-to-end functions

21
 LAPF Core

Frame delimiting, alignment and transparency

Frame multiplexing/demultiplexing
Inspection of frame for length constraints
Detection of transmission errors
Congestion control

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LAPF-core Formats

23
 User Data Transfer

No control field, which is normally used for:

Identify frame type (data or control)
Sequence numbers
Implication:
Connection setup/teardown carried on separate
channel
Cannot do flow and error control

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 Frame Relay Call Control

Frame Relay Call Control

Data transfer involves:
Establish logical connection and DLCI
Exchange data frames
Release logical connection

25
 Frame Relay Call Control

4 message types needed

SETUP
CONNECT
RELEASE
RELEASE COMPLETE

26
 ATM Protocol Architecture

Fixed-size packets called cells

Streamlined: minimal error and flow control
2 protocol layers relate to ATM functions:
Common layer providing packet transfers
Service dependent ATM adaptation layer (AAL)
AAL maps other protocols to ATM

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 Protocol Model has 3 planes

User
Control
management

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29
 Logical Connections

VCC (Virtual Channel Connection): a logical

connection analogous to virtual circuit in X.25

VPC (Virtual Path Connection): a bundle of VCCs

with same endpoints

30
 Figure 5.2

Chapter 2 Protocols and the TCP/IP Suite 31

 Advantages of Virtual Paths

Simplified network architecture

Increased network performance and reliability
Reduced processing and short connection setup time
Enhanced network services

32
33
 VCC Uses

Between end users

Between an end user and a network entity
Between 2 network entities

34
 Figure 5.3

Chapter 2 Protocols and the TCP/IP Suite 35

 VPC/VCC Characteristics

Quality of Service (QoS)

Switched and semi-permanent virtual channel
connections
Cell sequence integrity
Traffic parameter negotiation and usage monitoring
(VPC only) virtual channel identifier restriction
within a VPC

36
 Control Signaling

A mechanism to establish and release VPCs

and VCCs
4 methods for VCCs:
Semi-permanent VCCs
Meta-signaling channel
User-to-network signaling virtual channel
User-to-user signaling virtual channel

37
 Control Signaling

3 methods for VPCs

Semi-permanent
Customer controlled
Network controlled

38
 ATM Cells

Fixed size
5-octet header
48-octet information field
Small cells reduce delay for high-priority cells
Fixed size facilitate switching in hardware

39
 Header Format

Generic flow control

Virtual path identifier (VPI)
Virtual channel identifier (VCI)
Payload type
Cell loss priority
Header error control

40
 Figure 5.4

Chapter 2 Protocols and the TCP/IP Suite 41

 Generic Flow Control

Control traffic flow at user-network interface (UNI)

to alleviate short-term overload conditions
When GFC enabled at UNI, 2 procedures used:
Uncontrolled transmission
Controlled transmission

42
43
 Header Error Control

8-bit field calculated based on remaining 32 bits of

header
error detection
in some cases, error correction of single-bit errors in
header
2 modes:
error detection
Error correction

44
 Figure 5.5

Chapter 2 Protocols and the TCP/IP Suite 45

 Figure 5.6

Chapter 2 Protocols and the TCP/IP Suite 46

 Figure 5.7

Chapter 2 Protocols and the TCP/IP Suite 47

 Service Categories

Real-time service
Constant bit rate (CBR)
Real-time variable bit rate (rt-VBR)
Non-real-time service
Non-real-time variable bit rate (nrt-VBR)
Available bit rate (ABR)
Unspecified bit rate (UBR)
Guaranteed frame rate (GFR)

48
 Figure 5.8

Chapter 2 Protocols and the TCP/IP Suite 49

 ATM Adaptation Layer (ATM)

Support non-ATM protocols

e.g., PCM voice, LAPF
AAL Services
Handle transmission errors
Segmentation/reassembly (SAR)
Handle lost and misinserted cell conditions
Flow control and timing control

50
 Applications of AAL and ATM

Circuit emulation (e.g., T-1 synchronous TDM

circuits)
VBR voice and video
General data services
IP over ATM
Multiprotocol encapsulation over ATM (MPOA)
LAN emulation (LANE)

51
 AAL Protocols

AAL layer has 2 sublayers:

Convergence Sublayer (CS)
Supports specific applications using AAL
Segmentation and Reassembly Layer (SAR)
Packages data from CS into cells and unpacks at
other end

52
 Figure 5.9

Chapter 2 Protocols and the TCP/IP Suite 53

 Figure 5.10

Chapter 2 Protocols and the TCP/IP Suite 54

 AAL Type 1

Constant-bit-rate source
SAR simply packs bits into cells and unpacks
them at destination
One-octet header contains 3-bit SC field to
provide an 8-cell frame structure
No CS PDU since CS sublayer primarily for
clocking and synchronization

55
 AAL Type 3/4

May be connectionless or connection oriented

May be message mode or streaming mode

56
57
 Figure 5.12

Chapter 2 Protocols and the TCP/IP Suite 58

 AAL Type 5

Streamlined transport for connection oriented

protocols
Reduce protocol processing overhead
Reduce transmission overhead
Ensure adaptability to existing transport protocols

59
 Figure 5.13

Chapter 2 Protocols and the TCP/IP Suite 60

61
Emergence of High-Speed LANs

2 Significant trends
Computing power of PCs continues to grow
rapidly
Network computing
Examples of requirements
Centralized server farms
Power workgroups
High-speed local backbone

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 Classical Ethernet

Bus topology LAN

10 Mbps
CSMA/CD medium access control protocol
2 problems:
A transmission from any station can be received by
all stations
How to regulate transmission

63
 Solution to First Problem

Data transmitted in blocks called frames:

User data
Frame header containing unique address of
destination station

64
 Figure 6.1

Chapter 6 High-Speed LANs 65

 CSMA/CD

Carrier Sense Multiple Access/ Carrier Detection

If the medium is idle, transmit.

If the medium is busy, continue to listen until the
channel is idle, then transmit immediately.
If a collision is detected during transmission,
immediately cease transmitting.
After a collision, wait a random amount of time, then
attempt to transmit again (repeat from step 1).

66
 Figure 6.2

Chapter 6 High-Speed LANs 67

Figure 6.3

Chapter 6 High-Speed LANs 68

 Medium Options at 10Mbps
<data rate> <signaling method> <max length>
10Base5
10 Mbps
50-ohm coaxial cable bus
Maximum segment length 500 meters
10Base-T
Twisted pair, maximum length 100 meters
Star topology (hub or multipoint repeater at central
point)

69
Figure 6.4

Chapter 6 High-Speed LANs 70

 Hubs and Switches

Hub
Transmission from a station received by central hub
and retransmitted on all outgoing lines
Only one transmission at a time

Layer 2 Switch
Incoming frame switched to one outgoing line
Many transmissions at same time

71
 Figure 6.5

Chapter 6 High-Speed LANs 72

Bridge Layer 2 Switch

Frame handling done Frame handling done

in software in hardware
Analyze and forward Multiple data paths
one frame at a time and can handle
Store-and-forward multiple frames at a
time
Can do cut-through

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 Layer 2 Switches

Flat address space

Broadcast storm
Only one path between any 2 devices

Solution 1: subnetworks connected by routers

Solution 2: layer 3 switching, packet-
forwarding logic in hardware

74
 Figure 6.6

Chapter 6 High-Speed LANs 75

Figure 6.7

Chapter 6 High-Speed LANs 76

Figure 6.8

Chapter 6 High-Speed LANs 77

 Figure 6.9

Chapter 6 High-Speed LANs 78

Figure 6.10

Chapter 6 High-Speed LANs 79

Figure 6.11

Chapter 6 High-Speed LANs 80

Benefits of 10 Gbps Ethernet over ATM

No expensive, bandwidth consuming conversion

between Ethernet packets and ATM cells
Network is Ethernet, end to end
IP plus Ethernet offers QoS and traffic policing
capabilities approach that of ATM
Wide variety of standard optical interfaces for 10
Gbps Ethernet

81
 Fibre Channel

2 methods of communication with processor:

I/O channel
Network communications

Fibre channel combines both

Simplicity and speed of channel communications
Flexibility and interconnectivity of network
communications

82
Figure 6.12

Chapter 6 High-Speed LANs 83

 I/O channel

Hardware based, high-speed, short distance

Direct point-to-point or multipoint communications
link
Data type qualifiers for routing payload
Link-level constructs for individual I/O operations
Protocol specific specifications to support e.g.
SCSI

84
Fibre Channel Network-Oriented Facilities

Full multiplexing between multiple destinations

Peer-to-peer connectivity between any pair of ports
Internetworking with other connection technologies

85
 Fibre Channel Requirements

Full duplex links with 2 fibres/link

100 Mbps 800 Mbps
Distances up to 10 km
Small connectors
high-capacity
Greater connectivity than existing multidrop channels
Broad availability
Support for multiple cost/performance levels
Support for multiple existing interface command sets

86
Figure 6.13

Chapter 6 High-Speed LANs 87

Fibre Channel Protocol Architecture

FC-0 Physical Media

FC-1 Transmission Protocol
FC-2 Framing Protocol
FC-3 Common Services
FC-4 Mapping

88
 Wireless LAN Requirements
Throughput
Number of nodes
Connection to backbone
Service area
Battery power consumption
Transmission robustness and security
Collocated network operation
License-free operation
Handoff/roaming
Dynamic configuration
89
Figure 6.14

Chapter 6 High-Speed LANs 90

 IEEE 802.11 Services

Association
Reassociation
Disassociation
Authentication
Privacy

91
Figure 6.15

Chapter 6 High-Speed LANs 92

 Figure 6.16

Chapter 6 High-Speed LANs 93