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Home , Network packet, Virtual circuit

Chapter 4 Introduction to

Kyung Hee University 1 4.1 Introduction

At the conceptual level, we can think of the global Internet as a black box network that connects millions of computers

Application Application Transport Transport Network Network Data link Physical Physical Internet A B

Kyung Hee University 2 Internet as a combination of LAN and WANs

 Internet is made of many networks (or links) connected together through the connecting device

 Internet is a internetwork, a combination of LANs and WANs

Kyung Hee University 3 4.2 Switching  A physical circuit is established between the source and destination of the message before the delivery of the message The source informs the network that transmission is complete The network opens all switched for another devices A good example of circuit-switched network  early telephone system

The network layer in the Internet today : packet-switched network A message from the upper layer is divided into the packets The source sends packets to destination one-by-one The packet switched network decides the route of the message from source to final destination Classification : , Virtual Circuit Kyung Hee University 4 4.2 Switching (con’t)

In circuit switching, the whole message is sent from the source to the destination without being divided into packets.

In packet switching, the message is first divided into manageable packets at the source before being transmitted. The packets are assembled at the destination.

Kyung Hee University 5 4.3 Packet Switching

 The network layer is designed as a packet-switched network

 The packet at the source is divided into manageable packets, called datagram

 Individual are transferred from source to the destination

 The received datagrams are assembled at the destination before recreating original message

 Provided services

Connectionless service Connection-oriented service

Kyung Hee University 6 Connectionless Packet-Switched Network

Each packet is routed based on the information contained in its header

There is no relationship between packets The switches in this type of network are called routers

Network A connectionless packet-swtiched network R1 R2 4 3 2 1 2

Sender 1 Network 4 2 3 R4 1 3 3 4 1 3 4 2 R3 R5 Out of order Kyung Hee Receiver University 7 Forwarding Process in Connectionless Network

The routes the packet based only on the destination address Legend SA: Source address table DA: Destination address Destination Output address interface A 1 B 2

H Send the packet 3 out of interface 2 Destination address

SA DA Data 1 2 SA DA Data

3 4

Kyung Hee University 8 Delay in a Connectionless network

Destination Souce

1

2 d e l a y T o t a l

3

Time Time Time Time

Kyung Hee University 9 Connection-Oriented Service

 Connection setup, data delivery, teardown processes are used to provide the service

 There is a relationship between all packets belonging to a message

 A virtual connection should be set up to defines the virtual path the packet should follow

 After connection setup, the datagrams can follow the same path

 The packet must contain a flow label, a virtual circuit identifier Each packet is forwarded based on the label in the packet

Kyung Hee University 10 Connection-Oriented Packet Switched Network

 Each packet is forwarded through virtual path

Legend

4 3 2 1 Packets Network Virtual circuit A connection-oriented packet-switched network R1 R2 4 3 2 1 Sender 4 R5 3 Network 2 1 4 3 2 1 4 3 2 1 R3 R4 Receiver

Kyung Hee University 11 Setup Phase of Connection-Oriented Service

 Setup Phase

A router creates an entry for virtual circuit A request packet carries the source and destination address An acknowledgement packet complete the entries in the switching tables  Data Transfer Phase : the network-layer packets belonging to one message can be sent one after another

 Teardown Phase

After sending all packets to destination, source sends a special packet called a teardown packet A destination responds with a confirmation packet All routers delete the corresponding entry from their tables

Kyung Hee University 12 Forwarding Process in Connection-Oriented Network

Forwarding decision is based on the label in the packet

Routing Table Legend Incoming Outgoing SA: Source address Port Label Port Label DA: Destination address 1 L1 2 L2 L1, L2: Labels

L1 SA DA Data L2 SA DA Data 1 2

3 4 Incoming Outgoing label label

Kyung Hee University 13 Sending Request Packet in a Virtual-Circuit Network

A to B Legend Incoming Outgoing A to B Request packet Port Label Port Label Network Virtual circuit 1 14 3

1 R2 R1 2 A to B 1 4 A 3 R5 Network 2 A to B

1 2 3 2 3 4 A to B A to B 3 1 4 R3 R4 B

Incoming Outgoing Incoming Outgoing Port Label Port Label Port Label Port Label 1 66 3 1 22 4 A to B A to B Kyung Hee University 14 Setup Acknowledgment in a Virtual-Circuit Network

A to B Legend Incoming Outgoing Acknowledge packet Label Label Network Port Port Virtual circuit 1 14 3

4 R1 R2 2 14 1 4 3 A R5 Network 3 66 66

2 1 2 2 3 1 22 77 3 1 4 R3 22 R4 77 B

Incoming Outgoing Incoming Outgoing Port Label Port Label Port Label Port Label 1 66 3 1 22 4 A to B A to B

Kyung Hee University 15 Flow of One Packet in an Established Virtual Circuit

A to B Legend Incoming Outgoing A B Data Datagram Port Label Port Label Network 1 14 3 66 Virtual circuit

R1 R2 2 14 A B Data 1 4 A 3 R5 Network 66 A B Data

1 2 2 3 22 A B Data 77 A B Data 3 1 4 R3 R4

Incoming Outgoing Incoming Outgoing Port Label Port Label Port Label Port Label 1 66 3 22 1 22 4 77 A to B A to B Kyung Hee University 16 Delay in a Connection-Oriented Network

Source Destination

1

S e t u p 2

3 Transmission time d e l a y 4

T o t a l 5

6

7 T e a r d o w n

Time Time Time Time

Kyung Hee University 17 4.4 Network Layer Services

Connectionless services are the dominant service in today’s Internet

Example : Alice, who working in a publishing company, Wonderful Publishing, needs to send a message to Bob, the manager of a flower shop, Just Flower, to inform him that the advertising brochure for the shop has been printed and is ready to be shipped

Logical Addressing

Identification provided in the network-layer through a uniform and global addressing mechanism

Kyung Hee University 18 An Imaginary part of the Internet Legend Alice Wonderful Publishing Application layer Alice Cable modem Network layer DSL modem Point-to-point WAN

Cable

Regional ISP R1 T3 BestNet R1 R2 To other ISPs SONET R3 National ISP SONET SONET R3 R4 To other ISPs

I II

III ATM

R5

R5 SONET ServeNet R7 Just R6 Flowers T3 T3

R6 T3 R8 DSL Regional ISP Bob R8 Bob Kyung Hee University 19 Service Provided at the Source Computer

 Packetizing

Encapsulate the data coming from the upper layer in a datagram  Finding Logical Address of Next Hop

Consult a routing table to find the logical address of the next hop  Finding MAC Address of Next Hop

Using ARP(Address Resolution Protocol)  Fragmentation

When the datagram is bigger then MTU(Maximum Transmission Unit) datagram needs to be fragmented to smaller units before being passed to the data link layer

Kyung Hee University 20 Services Provided at the Source Computer

Kyung Hee University 21 Services Provided at Each Router  A router is involved with two interface (the incoming interface and the outgoing interface)

 Finding next-hop logical address

 Finding next-hop MAC address

 Fragmentation

Kyung Hee University 22 Processing at Each Router

Kyung Hee University 23 Services Provided at the Destination Computer  Reassemble the fragment (Validating each datagram)

 Deliver the data to upper layer

 Set a reassembly timer, if the timer is expired, all data fragments are destroyed and an error message is sent that all the fragmented datagram need to be resent

Kyung Hee University 24 Processing at the Destination Computer

Kyung Hee University 25 4.5 Other Network Layer Issues

 Error Control Mechanism for detecting corrupted, lost or duplicate datagram Checksum, ICMP  Flow Control Regulate the amount of data a source can send without overwhelming the receiver  Congestion Control Congestion in the network layer is a situation in which too many datagrams are present in an area of the internet Choke protocol in connectionless network and ICMP Advanced negotiation during connection setup in connection-oriented network  QoS () For Multimedia communication(real-time communication of audio and video)  Routing - How a router creates its routing table  Security IPSec

Kyung Hee University 26 Error Checking at the Data Link Layer

The case of that there are some areas in the path of the datagram that some errors may occurs but never checked

Kyung Hee University 27 Note

No flow control is provided for the current version of Internet network layer

Kyung Hee University 28 Summary(1)

 At the conceptual level. We can think of the global Internet as a black box network. The Internet, however, is not one single network; it is made of many networks (or links) connected together through the connecting devices.

 In this Internet, a connecting device such as a router acts as a switch. Two types of switching are traditionally used in networking: circuit switching and packet switching.

 The network layer is designed as a packet-switched network. Packet- switched network can provide either a connectionless service or a connection-oriented service. When the network layer provides a connectionless service, each packet traveling in the Internet is an independent entity; there is no relationship between packets belonging to the same message. In a connection-oriented service, there is a virtual connection between all packets belonging to a message.

Kyung Hee University 29 Summary(2)

 In a connectionless service, the packets are forwarded to the next hop using the destination address in the packet. In a connection-oriented service, the packets are forwarded to the next hop using a label in the packet.

 In a connection-oriented network, communication occurs in three phases: setup, data transfer, and teardown. After connection setup, a virtual circuit is established between the sender and the receiver in which all packets belonging to the same message are sent through that circuit.

 We discussed existing services at the network layer in the Internet including addressing, services provided at the source computer, services provided at the destination computer, and services provided at the each router.

 We also discussed some issues related to the network layer, services that are normally discussed for the network layer, but they are either partially implemented at the network layer or not implemented at all. Some of these services, such as routing and security are provided by other protocols in the Internet. Kyung Hee University 30 Q and A

Kyung Hee University 31