high speed networks

P13ITE05 High Speed Networks

UNIT - I

Dr.A.Kathirvel

Professor & Head/IT - VCEW

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

3

Introduction

Packet-Switching Networks

Switching Technique

Routing

X.25


Architecture

User Data Transfer

Call Control

4

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

5

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

6

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

Chapter 4 Frame Relay 7

Figure 4.1 The Use of Packets


Figure 4.2 Packet

Switching: Datagram

Approach

9

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)‏

10

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


Figure 4.3 Simple Switching Network

12

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


Figure 4.4 Packet

Switching: Virtual-

Circuit Approach

14

Routing

Adaptive routing

Node/trunk failure

Congestion

15

X.25

3 levels

Physical level (X.21)‏

Link level (LAPB, a subset of HDLC)‏

Packet level (provides virtual circuit

service)‏


Figure 4.5 The Use of Virtual Circuits


Figure 4.6 User Data and X.25

Protocol Control Information

18


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


Figure 4.7 Comparison of X.25 and

Frame Relay Protocol Stacks


Figure 4.8 Virtual Circuits and Frame

Relay Virtual Connections

21

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

22

LAPF Core

Frame delimiting, alignment and transparency

Frame multiplexing/demultiplexing

Inspection of frame for length constraints

Detection of transmission errors

Congestion control

23

LAPF-core Formats

24

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

25

Frame Relay Call Control


Data transfer involves:

Establish logical connection and DLCI

Exchange data frames

Release logical connection

26


4 message types needed

SETUP

CONNECT

RELEASE

RELEASE COMPLETE

27

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

28

Protocol Model has 3 planes

User

Control

management

30

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

Chapter 2 Protocols and the TCP/IP Suite 31

Figure 5.2

32

Advantages of Virtual Paths

Simplified network architecture

Increased network performance and reliability

Reduced processing and short connection setup time

Enhanced network services

34

VCC Uses

Between end users

Between an end user and a network entity

Between 2 network entities


Figure 5.3

36

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

37

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

38

Control Signaling

3 methods for VPCs

Semi-permanent

Customer controlled

Network controlled

39

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

40

Header Format

Generic flow control

Virtual path identifier (VPI)‏

Virtual channel identifier (VCI)‏

Payload type

Cell loss priority

Header error control


Figure 5.4

42

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

44

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


Figure 5.5


Figure 5.6


Figure 5.7

48

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)‏


Figure 5.8

50

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

51

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)‏

52

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


Figure 5.9


Figure 5.10

55

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

56

AAL Type 3/4

May be connectionless or connection oriented

May be message mode or streaming mode


Figure 5.12

59

AAL Type 5

Streamlined transport for connection oriented

protocols

Reduce protocol processing overhead

Reduce transmission overhead

Ensure adaptability to existing transport protocols


Figure 5.13

62

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

63

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

64

Solution to First Problem

Data transmitted in blocks called frames:

User data

Frame header containing unique address of

destination station

Chapter 6 High-Speed LANs 65

Figure 6.1

66

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).


Figure 6.2


Figure 6.3

69

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)‏


Figure 6.4

71

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


Figure 6.5

73

Bridge

Frame handling done

in software

Analyze and forward

one frame at a time

Store-and-forward

Layer 2 Switch

Frame handling done

in hardware

Multiple data paths

and can handle

multiple frames at a

time

Can do cut-through

74

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


Figure 6.6


Figure 6.7


Figure 6.8


Figure 6.9


Figure 6.10


Figure 6.11

81

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

82

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


Figure 6.12

84

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

85

Fibre Channel Network-Oriented Facilities

Full multiplexing between multiple destinations

Peer-to-peer connectivity between any pair of ports

Internetworking with other connection technologies

86

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


Figure 6.13

88

Fibre Channel Protocol Architecture

FC-0 Physical Media

FC-1 Transmission Protocol

FC-2 Framing Protocol

FC-3 Common Services

FC-4 Mapping

89

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


Figure 6.14

91

IEEE 802.11 Services

Association

Reassociation

Disassociation

Authentication

Privacy


Figure 6.15


Figure 6.16

94

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