• Introduction• Types of network• Network principles• Internet protocols• Network case studies:

Ethernet, wireless LAN and ATM• Summary

Chapter 3: Networking and Internetworking

Network performance measures• l = length of signal path in communication medium (metres)• v = signal propagation speed in the medium (metres/second)• L = average length of frame or packet (bits)• C = transmission rate (bits/second)• Propagation delay = l / v , in seconds• shows how long a bit takes to propagate along the path• Transmission time = L / C , in seconds• shows how long it takes to get packet onto the medium• Throughput: how fast data can pass a certain point• can be measured in bits/second, packets/second, …• Efficiency is related to throughput, e.g.• efficiency = throughput (in packets/sec) * packet transmission

time

Revision on Networking

Consider an optical fibre 3000 km long with transmitter transmitting at 1.5 Gbps (1 Gbps = 1 000 000 000 bps). The signal propagation speed in optical fibre is approximately 200 000 km/sec. Suppose packet switching is being used with a packet length of 2000 bits.

• What is the bit propagation delay along the fibre ?• What is the packet transmission time here ?• How many packets have been transmitted and are propagating over the fibre when the first bit reaches the destination ?

Ex1

• Consider a route in a store-and-forward network goingthrough 8 intermediate nodes. The packets contain 1000 bits and are transmitted at 64 kbps. Assume propagation delays over the links are negligible. As a packet travels along the route, it encounters an average of 5 packets when it arrives at each node. How long does it take forthe packet to get to the receiver if the nodes transmit on a “first come first served” basis ?

• At each intermediate node, 6 packets must be transmitted in order for “our” packet to be transmitted: our packet finds 5 packets ahead of it, which will be transmitted first due to the “first come first served” policy.

• What is the bit propagation delay along the fibre ?• What is the packet transmission time here ?• How many packets have been transmitted and are propagating over the fibre when the first bit reaches the destination ?

Ex2

150 nodes are connected to a 1000 metre length of coaxialcable. Using some (unspecified) protocol, each node cantransmit 70 frames/second, where each frame is 1000 bitslong. The transmission rate at each node is 100 Mbps.• What is the per-node throughput ?• What is the total throughput (of the 150 nodes) ?• What is the efficiency of this protocol ?

Ex3

• Internetwork – integrate many subnets that use different network

technologies

• Requirements– Unified internetwork addressing scheme that enables packets

to be addressed to any host connected to any subnet– A protocol defining the format of internetwork packets and

giving rules according to which they are handled– Interconnecting components that route packets to their

destinations in terms of internetwork addresses, transmitting the packets using subnets with a variety of network technologies

Internetworking

• Internetwork – integrate many subnets that use different network

technologies

• Requirements– Unified internetwork addressing scheme that enables packets

to be addressed to any host connected to any subnet– A protocol defining the format of internetwork packets and

giving rules according to which they are handled– Interconnecting components that route packets to their

destinations in terms of internetwork addresses, transmitting the packets using subnets with a variety of network technologies

Internetworking

• Router– Conduct routing, additionally link networks of different types

• Bridge– link networks of different types, but not conduct routing

• Hub– Connect hosts and extend segments of Ethernet and other

broadcast local network

• Switch– Perform similar function to router, but for LANs only

Internetworking components

• Introduction• Types of network• Network principles• Internet protocols• Network case studies: Ethernet, wireless

LAN and ATM• Summary

Chapter 3: Networking and Internetworking

• Protocol layers (n1)– TCP(UDP)/IP,(n2) web [HTTP], Email [SMTP,POP], news

[NNTP], FTP, SSL, etc

• Exceptions to the universal adoption of TCP/IP– The use of WAP for wireless applications on portable

devices– Special protocols to support multimedia streaming

applications• Heterogeneous underlying networks support

– The success of TCP/IP: independence of the underlying transmission technology (n3)

– E.g., IP over ATM, IP over Ethernet, IP over PPP, etc

Internet protocols

Internet protocol layers

Messages (UDP) or Streams (TCP)

Application

Transport

Internet

UDP or TCP packets

IP datagrams

Network-specific frames

MessageLayers

Underlying network

Network interface

• Schemes for naming and addressing hosts and for routing IP packets to their destination is challenging.

• Requirement:– It must be universal– It must be efficient– The addressing scheme must lend itself to the development of

routing scheme• The scheme

– A 32-bit numeric identifier containing a network identifier and a host identifier

– There are four allocated classed of Internet address-A,B,C,D

IP addressing

Internet address structure

7 24

Class A: 0 Network ID Host ID

14 16

Class B: 1 0 Network ID Host ID

21 8

Class C: 1 1 0 Network ID Host ID

28

Class D (multicast): 1 1 1 0 Multicast address

27

Class E (reserved): 1 1 1 1 unused0

28

Decimal representation of Internet addresses

octet 1 octet 2 octet 3

Class A: 1 to 127

0 to 255 0 to 255 1 to 254

Class B: 128 to 191

Class C: 192 to 223

224 to 239 Class D (multicast):

Network ID

Network ID

Network ID

Host ID

Host ID

Host ID

Multicast address

0 to 255 0 to 255 1 to 254

0 to 255 0 to 255 0 to 255

0 to 255 0 to 255 0 to 255

Multicast address

0 to 255 0 to 255 1 to 254240 to 255 Class E (reserved):

1.0.0.0 to 127.255.255.255

128.0.0.0 to 191.255.255.255

192.0.0.0 to 223.255.255.255

224.0.0.0 to 239.255.255.255

240.0.0.0 to 255.255.255.255

Range of addresses

Two steps were taken: IPv6, Classless interdomain routing (CIDR)

• Transmits datagrams from one host to another, if necessary via intermediate routers– Unreliable (best-effort) delivery semantics

• packets can be lost, duplicated, delayed or delivered out of order

– Address resolution: Address Resolution Module(ARP)• IP address -> Ethernet address mapping, (IP address,

Ethernet address) pairs cache on each host

IP protocol

dataIP address of destinationIP address of source

header

up to 64 kilobytes

[1] Addressing• [1] How to find if destination is in the same

network ?– IP address = network ID + host ID.

• Source and destination network IDs match => same network (I.e. direct connectivity)

– Splitting address into multiple parts is called hierarchical addressing

Network Host

Boundary

IP Forwarding: Example Scenario

IP datagram:

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE

miscfields

sourceIP addr

destIP addr data

datagram remains unchanged, as it travels source to destinationaddr fields of interest here

routing table in ADest. Net. next router Nhops223.1.1 1223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2

IP Forwarding (Direct)

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE

Starting at A, given IP datagram addressed to B:look up net. address of Bfind B is on same net. as Alink layer will send datagram directly to B inside link-layer frame

B and A are directly connected

Dest. Net. next router Nhops223.1.1 1223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2

miscfields 223.1.1.1 223.1.1.3 data

IP Forwarding (Indirect): Step 1

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE

Dest. Net. next router Nhops223.1.1 1223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2Starting at A, dest. E:

look up network address of EE on different network

A, E not directly attached

routing table: next hop router to E is 223.1.1.4 link layer sends datagram to router 223.1.1.4 inside link-layer framedatagram arrives at 223.1.1.4 continued…..

miscfields 223.1.1.1 223.1.2.2 data

IP Forwarding (Indirect): Step 2

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE

Arriving at 223.1.1.4, destined for 223.1.2.2look up network address of EE on same network as router’s interface 223.1.2.9

router, E directly attached

link layer sends datagram to 223.1.2.2 inside link-layer frame via interface 223.1.2.9 datagram arrives at 223.1.2.2

miscfields 223.1.1.1 223.1.2.2 data network router Nhops interface

223.1.1 - 1 223.1.1.4 223.1.2 - 1 223.1.2.9223.1.3 - 1 223.1.3.27

Dest. next

The Internet Network layer

routingtable

Host, router network layer functions:

Routing protocols•path selection•RIP, OSPF, BGP

IP protocol•addressing conventions•datagram format•packet handling conventions

ICMP protocol•error reporting•router “signaling”

Transport layer: TCP, UDP

Link layer

physical layer

Networklayer

IP Addressing: introduction• IP address: 32-bit identifier

for host, router interface • Interface: connection

between host, router and physical link– router’s typically have

multiple interfaces– host may have multiple

interfaces– IP addresses associated with

interface, not host, router• Hosts in the same network have

same network ID

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

223.1.1.1 = 11011111 00000001 00000001 00000001

223 1 11

IP Address Formats• Class A: Network Host0

71 24 bits

Network Host10142 16 bits

Class B:

Network Host110213 8 bits

Class C:

Router Router

Multicast Group addresses1110284 bits

Class D:

Class E: Reserved.

Subnet Addressing• Classful addressing inefficient: Everyone

wants class B addresses • Can we split class A, B addresses spaces and

accommodate more networks ?– Need another level of hierarchy. Defined by

“subnet mask”, which in general specifies the sets of bits belonging to the network address and host address respectively

Network Host

Boundary is flexible, and defined by subnet mask

• Routs packets from source to destination– Internet topology: Autonomous System, Areas(n1)– Routing algorithms:

• RIP -1• RIP-2• Open Short Path First (OSPF)

– Default routes: trade routing efficiency for table size– Classless interdomain routing (CIDR): create subnet

by means of subdividing address or aggregating addresses by mask field, e.g. 162.105.203.0/24

IP routing

• IPv6(n1)– 2128 (3*1038) addresses, 1000 IP addresses per square meter of

the Earth’s surface– Routing speed : no checksum, no fragmentation– Real time : priority and flow label which is used to reserve

resources– Extension header ( information of router, authentication, etc),– multicast and anycast– Security through extension header type

• Migration from IPv4: – IPv6 router island, – depend on economics

Future of IP

IPv6 header layout

Source address(128 bits)

Destination address(128 bits)

Version (4 bits) Priority (4 bits) Flow label (24 bits)

Payload length (16 bits) Hop limit (8 bits)Next header (8 bits)

The MobileIP routing mechanism

Sender

Home

Mobile host MH

Foreign agent FAInternet

agent

First IP packet addressed to MH

Address of FAreturned to sender

First IP packettunnelled to FA

Subsequent IP packetstunnelled to FA

• Use of ports– Provide process-to-process communication

• UDP features• TCP features

TCP and UDP

• Connectionless• Datagram delivery

– A UDP datagram is encapsulated inside an IP packet, up to 64kb in size

• Con– unreliable delivery due to unreliable IP

• Pro– minimal additional cost and transmission delays

UDP features

• Connection oriented– two side must shake hands to establish a bi-directional communication

channel

• Message delivery– Deliver arbitrary long sequences of bytes via stream-based programming

abstraction– Sequencing: divide stream into data segments, sequence number on each

segment– Checksum: cover the header and the data in the segment

• Flow control– Receiver send the highest number of received segment and window size to

sender by acknowledge message– Buffering: receiver buffer and sender buffer used for flow control– In interactive application, receiver inform sender when timeout or the buffer

reaches the MTU limit – Retransmission: retransmit the segment when no acknowledgement within a

specified timeout

TCP

• Symbolic names for hosts and networks– upm.edu.my

• The DNS would not workable without the extensive use of caching.

Domain names

• The purpose of a firewall is to monitor and control all communication into and out of an intranet– including service control, – behavior control – and user control

• Filter approaches (n1)– IP packet filtering, e.g. router/filter– TCP gateway, e.g. bastion– Application level gateway, e.g. telnet proxy process

• Virtual private networks (VPN)– Secure connections located at different sites using public Internet links– By the use of cryptographically protected secure channels at the IP level

Firewall

Firewall configurations

Internet

Router/ Protected intraneta) Filtering router

Internet

b) Filtering router and bastion

filter

Internet

R/filterc) Screened subnet for bastion R/filter Bastion

R/filter Bastion

web/ftpserver

web/ftpserver

web/ftpserver

• Introduction• Types of network• Network principles• Internet protocols• Network case studies: Ethernet, wireless

LAN and ATM• Summary

Chapter 3: Networking and Internetworking

• IEEE 802.3[Xerox 1973]– Carrier sensing, multiple access with collision detection – Frame broadcasting– Bandwidth: 3m -> 10m -> 100m -> 1000m

• Ethernet packet layout (n1)– 248 different addresses

• Packet collisions– Carrier sensing

• wait until no signal is present then transmit– Collision detection

• When transmit through output port, also listen on the input port, and compare the two signals, If differ, send jamming signal

– Back-off • wait a time n before retransmitting, n: a random integer

Ethernet

Ethernet frame layout

Destinationaddress

Sourceaddress

Length

of data

Data for transmission Frame checksequence

7bytes 1byte 6 bytes 6 bytes 2 bytes 46 bytes ≤ length ≤ 1500bytes 4 bytes

Spreamble

• Ethernet efficiency– Efficiency = number of packets transmitted successfully /

theoretical maximum number without collision– Affected by

• A finite time for a signal inserted at a point in the media to reach all other points

• number of stations on the network• stations’ level of activity

Ethernet … continued

• Wireless LAN types– Infrastructure network, e.g. IEEE 802.11 (n1)– Ad hoc network: network built on the fly

• Collision detection failures in 802.11– Hidden stations: carrier sensing fail to detect that

another station on the network is transmitting, lead to collision at base station

– Fading: the strength of radio signals diminishes rapidly with the distance from the transmitter, so that defeating both carrier sensing and collision detection

– Collision masking

Wireless LAN

Wireless LAN configuration

LAN

Server

WirelessLAN

Laptops

Base station/access point

Palmtop

radio obstruction

A B C

D E

• Slot reservation added to the MAC protocol in 802.11 1. Firstly, sense the medium, if no carrier signal, then

• medium is available• an out-of-range station is in the process of requesting a slot• an out-of-range station is using a slot

2. Sender send a RTS (Request To Send) frame to receiver; Receiver reply a CTS (Clear To Send) frame to sender. The effect of the exchange is

• the station within range of sender will pick up the RTS frame and take note of the duration

• the station within range of receiver will pick up the CTS frame and take note of the duration

3. Begin to transmit

802.11 introduction

• 802.11 avoid collisions in ways– CTS frames avoid the hidden station and fading problem – If RTS/CTS is corrupted, then a back-off period is used– When RTS/CTS exchange correctly, there is no collisions in the

following communication except intermittent fading prevents a third party from receiving either of them

• Security in 802.11– Shared-key authentication mechanism– XOR operation on the base of shared key to prevent from

eavesdropping

802.11 introduction … continued

Asynchronous Transfer Mode networks (ATM)• Deploy ATM on top of other networks

– Can be implemented over existing digital telephony networks, Bandwidth from 32 kbps (voice) to 622mbps

– Native mode: Over optical fiber, copper and other transmission media, bandwidth up to several gigabits per seconds

• ATM layers (n1)– Adaptation layer

• end-to-end layer implemented at the sending and receiving host– ATM layer

• connection-oriented service that transmits fixed length packets called cells, avoid flow control and error checking at the switching, provide bandwidth and latency guarantees

• VC (virtual channel): a logical unidirectional association between two endpoints of a link in the physical path from source to destination

• VP (virtual path): a bundle of virtual channel that are associated with a physical path between two switching nodes

ATM protocol layers

Physical

Application

ATM layer

Higher-layer protocols

ATM cells

ATM virtual channels

MessageLayers

ATM adaption layer

ATM… continued

• The nodes in a ATM network can play three distinct roles (n1)– Hosts: send and receive messages– VP switches: hold tables showing the correspondence

information between incoming and outgoing VPs– VP/VC switches: correspondence information for both VPs

and VCs• ATM cell: 5-bytes header and a 48-byte data field

Flags DataVirtual channel idVirtual path id

53 bytes

Header: 5 bytes

Switching virtual paths in an ATM network

VPI in VPI out

23

45

VPI = 3

VPI = 5

VPI = 4

Virtual path Virtual channels

VPI = 2

VPI : virtual path identifier

VP switch VP/VCswitch

VP switch

Host

Host

• Introduction• Types of network• Network principles• Internet protocols• Network case studies: Ethernet, wireless

LAN and ATM• Summary

Chapter 3: Networking and Internetworking

• Layered protocols– 7 layers in OSI model / 5 layers in the Internet

• Delivery approach– Packet switch, frame relay

• Routing mechanism– distance vector / link state

• Congestion control• The Internet

– TCP/IP• Network cases

– Ethernet, WLAN, ATM

Summary

OSI protocol summary

Layer Description Examples

Application Protocols that are designed to meet the communication requirements ofspecific applications, often defining the interface to a service.

HTTP, FTP, SMTP,CORBA IIOP

Presentation Protocols at this level transmit data in a network representation that isindependent of the representations used in individual computers, which maydiffer. Encryption is also performed in this layer, if required.

Secure Sockets(SSL),CORBA DataRep.

Session At this level reliability and adaptation are performed, such as detection offailures and automatic recovery.

Transport This is the lowest level at which messages (rather than packets) are handled.Messages are addressed to communication ports attached to processes,Protocols in this layer may be connection-oriented or connectionless.

TCP, UDP

Network Transfers data packets between computers in a specific network. In a WANor an internetwork this involves the generation of a route passing throughrouters. In a single LAN no routing is required.

IP, ATM virtualcircuits

Data link Responsible for transmission of packets between nodes that are directlyconnected by a physical link. In a WAN transmission is between pairs ofrouters or between routers and hosts. In a LAN it is between any pair of hosts.

Ethernet MAC,ATM cell transfer,PPP

Physical The circuits and hardware that drive the network. It transmits sequences ofbinary data by analogue signalling, using amplitude or frequency modulationof electrical signals (on cable circuits), light signals (on fibre optic circuits)or other electromagnetic signals (on radio and microwave circuits).

Ethernet base- bandsignalling, ISDN

EJB

Distance-Vector Routing table for the network

Routings from DTo Link CostABCDE

336

local6

12201

Routings from ETo Link CostABCDE

4456

local

21110

Routings from A Routings from B Routings from CTo Link Cost To Link Cost To Link CostABCDE

local1131

01212

ABCDE

1local

214

10121

ABCDE

22

local55

21021

Hosts Linksor local networks

A

D E

B

C

12

5

43

6

Routers

Psudo-code for RIP routing algorithm

Send: Each t seconds or when Tl changes, send Tl on each non-faulty outgoing link.Receive: Whenever a routing table Tr is received on link n:

for all rows Rr in Tr {if (Rr.link <> n) {

Rr.cost = Rr.cost + 1;Rr.link = n;if (Rr.destination is not in Tl) add Rr to Tl; // add new destination to Tlelse for all rows Rl in Tl {

if (Rr.destination = Rl.destination and (Rr.cost < Rl.cost or Rl.link = n))

Rl = Rr;// Rr.cost < Rl.cost : remote node has better route// Rl.link = n : remote node is more authoritative

}}

}

Simplified view of the QMW Computer Science network

file

compute

dialup

hammer

henry

hotpoint

138.37.88.230

138.37.88.162

bruno138.37.88.249

router/sickle

138.37.95.241138.37.95.240/29

138.37.95.249

copper138.37.88.248

firewall

web

138.37.95.248/29

server

desktop computers 138.37.88.xx

subnet

subnet

Eswitch

138.37.88

server

server

server

138.37.88.251

custard138.37.94.246

desktop computers

Eswitch

138.37.94

hubhub

Student subnetStaff subnet

otherservers

router/firewall

138.37.94.251

1000 Mbps EthernetEswitch: Ethernet switch

100 Mbps Ethernet

file server/gateway

printers

Campusrouter

Campusrouter

138.37.94.xx

Tunnelling

A BIPv6 IPv6

IPv6 encapsulated in IPv4 packets

Encapsulators

IPv4 network

A BIP IP

IP encapsulated in PPP packets

Encapsulators

PPP network

ATM cell layout

Flags DataVirtual channel idVirtual path id

53 bytes

Header: 5 bytes