What methods / approaches do you know, to realize a CSMA / CA access?

(1)

CDS Wt

Chapter 2.3

Layer 3

e r

Layer 3

Network Layer

3.3 N e tw ork Lay e 1 CDS Wt

Warm up !

• What methods / approaches do you know, to realize

a CSMA / CA access ?

e

r

• Explain the difference between an adressed based

and an Information based Layer 2 addressing.

• consider a data sequence (1 1 0 0 1 1 0 0 1 1) and the Generatorpolynom, given as (1 0 0 1 1).

C l l t th CRC F h k 3.3 N e tw ork Lay e 2

(2)

CDS Wt • Introduction Layer 3

Content

e r • IP Protocol

– IP-Header: www.ietf.org and RFC-760 – Addressing schemes

– Subnetting – Routing

Layer 3 Solution in Trains

3.3 N e tw ork Lay e 3

• Layer 3 Solution in Trains

• Communication Matrix

(Information Based Communication)

CDS

Wt

Protocol aspect of the OSI-Model

7 7 Endsystem 2 Endsystem 1 Layer 7 protocol Layer 6 protocol e r 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 Transit-system Layer 6 protocol 3.3 N e tw ork Lay e transmission-system

Protocols are defined between the same layers of two systems. They define rules and formats of message/information exchange.

(3)

CDS

Wt

Why network layer (1) ?

e r 3.3 N e tw ork Lay e 5 CDS Wt

Why network layer (2) ?

Vehicle bus

Locomotive _{Wagon: Trainset:} _{Control-Wagon}

e

r

Redundant nodes Single node Multiple Wagons reduntand Nodes

Gateway WTB/MVB

C

C WTB trainbus (UIC 556) Standard!

MVB vehicle bus 3.3 N e tw ork Lay e 6 Türen Türen dez. I/O dez. I/O Brake control Main Control Climate control Multi-media Doors Hilfs- betriebe-Umrichter Dezentrale I/O Dezentrale I/O Dezentrale I/O Dezentrale I/O MMI Subsystemes Motorr Subsysteme, Motor Sub-systeme Antriebs-steuerung

Vehicle Bus (CAN, FIP,...)

Brake Control Main Control Climate Control Multi-media Doors Hilfs- betriebe-Umrichter Dezentrale I/O Dezentrale I/O Dezentrale I/O Dezentrale I/O MMI Subsysteme, motor Subsysteme, Motor Sub-systeme Antriebs-steuerung ONIX Umrichter ONIX Umrichter Display Display

(4)

CDS

Wt

Why network layer (3) ?

Network-Layer

The Network Layer...

• segment network and control flow of traffic.

• provides the functional and procedural means of transferring variable length data sequences from a source to a destination

e

r

variable length data sequences from a source to a destination via one or more networks

• transfers packetsfrom one network to another

• maintains the quality of service requested by the Transport layer.

• performs network routing functions and might also perform fragmentation and reassembly, and report delivery errors. • Is based on a logical addressing scheme

3.3 N e tw ork Lay e

Internet Protocol (IP) is the best known layer 3 protocol • connectionless transfer of data

• fragmenting data into sufficiently small packets that the Layer 2 can accept it

(5)

CDS

Wt

Network segmentation

• Control network traffics and reduce broadcast traffics.

• Separate computer networks are managed by

e

r

Separate computer networks are managed by a single administration - Autonomous

systems. 3.3 N e tw ork Lay e 9 CDS Wt

Communication among networks

• Networks operate in much the same manner.

e r 3.3 N e tw ork Lay e 10

(6)

CDS

Wt

Router

• Routers connect separate networks.

• Routers make best path decisions based on

Layer 3 information.

e

r

Layer 3 information.

• Routers actually switch packets from

incoming ports to appropriate outgoing ports.

• Routers can change the media and Layer 2

b h i 3.3 N e tw ork Lay e 11 behaviour CDS Wt

Data relaying

e r 3.3 N e tw ork Lay e

(7)

CDS

Wt

Path determination

• Path determination is the process that the router uses to choose the next hop in the path for the packet to travel to its destination

e

r

based on the link bandwidth, hop, delay ...

Network layer addressing

• Network address + Host address: Hierarchical

Addressing Schemes. e r 3.3 N e tw ork Lay e 14

(8)

CDS

Wt

Flat Addressing Scheme

e r 1 2 4 5 A B 1 – A₁ 1 – A 3.3 N e tw ork Lay e 15 2 3 5 6 2 – A2 3 – A₃ 2 – A 3 – A 4 – B 5 – B 6 – B CDS Wt

MAC Addressing (Layer 2)

e r 3.3 N e tw ork Lay e

(9)

CDS

Wt

Hierarchical Addressing Scheme

e r A1 A2 B1 B2 A B 1 – A₁ 3.3 N e tw ork Lay e 17 A2 A3 B2 B3 2 – A2 3 – A₃ A – Local B – Switch to B CDS Wt

Hierarchical Addressing Scheme

International Gateway e r Domestic Switch Local 3.3 N e tw ork Lay e 18 Local Switch 84 8 9321044

(10)

CDS

Wt

Network address

• The network address helps the router to identify a path within the network cloud.

• The router uses the network address to

e

r

The router uses the network address to identify the destination network of a packet within an internetwork.

• Network address is assigned by higher-level

administrator. Host address is assigned manually or automatically by manager of that network. 3.3 N e tw ork Lay e 19 CDS Wt • Introduction Layer 3

Content

3.3 N e tw ork Lay e

• Communication Matrix (Information Based

(11)

CDS

Wt

Network layer datagram

• At the network layer, the data is encapsulated within packets(also known as datagrams).

• Packet includes header - addressing and

e

r

Packet includes header addressing and other control information and actual data -whatever is passed down from the higher layers. 3.3 N e tw ork Lay e 21 CDS Wt

IP header format

e r 3.3 N e tw ork Lay e 22

(12)

CDS

Wt

IP header format:

Version

e

r

• 4 bits.

• Indicates the version of

IP currently used.

3.3 N e tw ork Lay e 23

IP currently used.

– IPv4 : 0100 – IPv6 : 0110 CDS Wt

IP header format: Header length

e

r

• 4 bits.

• IP header length : Indicates the

datagram header length in 32 bit

3.3 N e tw ork Lay e

datagram header length in 32 bit

words (4 bits), and thus points to

the beginning of the data.

(13)

CDS

Wt

IP header format: Service type

e

r

• 8 bits.

• Specifies the level of importance

that has been assigned by a

particular upper-layer protocol

3.3 N e tw ork Lay e 25

particular upper-layer protocol.

• Precedence.

• Reliability.

• Speed.

CDS

Wt

IP header format: Total length

e r

• 16 bits.

3.3 N e tw ork Lay e 26

• Specifies the length of the

entire IP packet, including

data and header, in bytes.

(14)

CDS

Wt

IP header format: Identification

e

r

• 16 bits.

• Identification contains an integer

that identifies the current datagram.

3.3 N e tw ork Lay e 27

g

• Assigned by the sender to aid in

assembling the fragments of a

datagram.

CDS

Wt

IP header format: Flags

e

r

• 3 bits.

• The second bit specifying whether the

packet can be fragmented .

3.3 N e tw ork Lay e

p

g

• The last bit specifying whether the packet

is the last fragment in a series of

(15)

CDS

Wt

IP header format: Fragment

offset

e

r

• 13 bits.

• The field that is used to help piece together

datagram fragments

3.3 N e tw ork Lay e 29

datagram fragments.

• The fragment offset is measured in units of

8 octets (64 bits).

• The first fragment has offset zero.

CDS

Wt

IP header format: Time to Live

e r

_•

_{8 bits.}

3.3 N e tw ork Lay e 30

8 bits.

• Time-to-Live maintains a counter that

gradually decreases to zero, at which point

the datagram is discarded, keeping the

packets from looping endlessly.

(16)

CDS

Wt

IP header format: Protocol

e

r

• 8 bits.

• Indicates which upper layer protocol receives

3.3 N e tw ork Lay e 31

• Indicates which upper-layer protocol receives incoming packets after IP processing has been completed

• 06 : TCP

• 17 : UDP

CDS

Wt

IP header format: Header

checksum

e r

16 bit

3.3 N e tw ork Lay e

• 16 bits.

• A checksum on the header only,

helps ensure IP header integrity.

(17)

CDS

Wt

IP header format: Addresses

• 32 bits each.

e r

• Source IP Address

• Destination IP Address

IP header format: Options

e

r

• Variable length.

• Allows IP to support various options,

such as security, route, error report ...

3.3 N e tw ork Lay e 34

(18)

CDS

Wt

IP header format: Padding

e

r

• The header padding is used to ensure

that the internet header ends on a 32 bit

boundary.

3.3 N e tw ork Lay e 35 CDS Wt • Introduction Layer 3

Content

– IP-Header: www.ietf.org and RFC-760 – Addressing Schemes

3.3 N e tw ork Lay e

(19)

CDS

Wt

IP network address

• Network layer addresses are 32 bits long.

• The are presented as four octets in dotted decimal format.

e

r

decimal format.

• The IP address has two components:

Network ID and Host ID.

Network ID and host ID

• Network ID :

– Assigned by Internet Network Information Center. – Assigned by upper organization.

e

r

– Identifies the network to which a devices is attached.

• Host ID :

– Assigned by a network administrator.

– Identifies the specific device on that network.

3.3 N e tw ork Lay e 38

(20)

CDS

Wt

Bits on the IP address

• Network Bits : – Identifies network ID

– Identifies class of the IP address

e

r

– All of bits are 0: not allowed

• Host Bits : – Identifies host ID

– All of bits are 0: reserved for network address – All of bits are 1: reserved for broadcast address

IP address classes

• Different class addresses reserve different amounts of bits for the Network and Host portions of the address

e

r

• Provide the flexibility required to support different size networks

3.3 N e tw ork Lay e

(21)

CDS

Wt

IP address classes: Class A

• The first bit of a Class A address is always 0.

• The first 8 bits to identify the network part of the address.

e

r

the address.

• Possible network address from 1.0.0.0 to 127.0.0.0.

• The remaining three octets can be used for the host portion of the address.

• Each class A network have up to 16,777,214

possible IP addresses 3.3 N e tw ork Lay e 42 possible IP addresses.

(22)

CDS

Wt

IP address classes: Class B

• The first 2 bits of a Class B address is always 10.

• The first two octets to identify the network

e

r

The first two octets to identify the network part of the address.

• The remaining two octets can be used for the host portion of the address.

• Class B network have up to 65 534 possible

3.3 N e tw ork Lay e

• Class B network have up to 65.534 possible IP addresses.

(23)

CDS

Wt

IP address classes: Class C

• The first 3 bits of a Class C address is always 110.

• The first three octets to identify the network

e

r

The first three octets to identify the network part of the address.

• The remaining last octet can be used for the host portion of the address.

• Class C network have up to 254 possible IP

3.3 N e tw ork Lay e 46

• Class C network have up to 254 possible IP addresses.

(24)

CDS

Wt

IP address classes: Summary

• 1.0.0.0 - 126.0.0.0 : Class A. • 127.0.0.0 : Loopback network. • 128 0 0 0 - 191 255 0 0 : Class B e r • 128.0.0.0 - 191.255.0.0 : Class B. • 192.0.0.0 - 223.255.255.0 : Class C. • 224.0.0.0 < 240.0.0.0 : Class D, multicast. • >= 240.0.0.0 : Class E, reserved. 3.3 N e tw ork Lay e 47 CDS Wt

Network address

• Network address provide a convenient way to

refer to all of the addresses on a particular network or subnetwork.

e

r

• Two hosts with differing network address require a device, typically a router, in order to communicate.

• An IP address that ends with binary 0s in all host bits is reserved for the network address.

3.3 N e tw ork Lay e

(25)

CDS

Wt

Broadcast address

• Broadcast goes to every host with a particular network ID number.

• An IP address that ends with binary 1s in all

e

r

An IP address that ends with binary 1s in all host bits is reserved for the directed

broadcast address.

• An IP address with binary 1s in all network bits and host bits is reserved for the local broadcast address. 3.3 N e tw ork Lay e 49 CDS Wt

Local broadcast address

e r

STOP

3.3 N e tw ork Lay e 50

STOP

255.255.255.255

(26)

CDS

Wt

Directed broadcast address

e r

192.168.20.0

3.3 N e tw ork Lay e 51

Broadcast address

192.168.20.255

CDS Wt

Example: 172.16.20.200

• 172.16.20.200 is Class B address • Network portion: 172.16 • Host portion: 20 200 e r • Host portion: 20.200 • Network address: 172.16.0.0 • Broadcast address: 172.16.255.255 3.3 N e tw ork Lay e

(27)

CDS

Wt

Private addresses

• According to RFC-1918.

• Organizations make use of the private

Internet address space for hosts that require

e

r

Internet address space for hosts that require IP connectivity within their enterprise

network, but do not require external connections to the global Internet.

• Class A: 10.0.0.0. • Class B: 172.16.0.0 - 172.31.0.0. • Class C: 192 168 0 0 192 168 255 0 3.3 N e tw ork Lay e 53 • Class C: 192.168.0.0 - 192.168.255.0. CDS Wt • Introduction Layer 3

Content

– IP-Header: www.ietf.org and RFC-760 – Addressing Schemes

3.3 N e tw ork Lay e 54

(28)

CDS

Wt

Why we need to divide network?

• Network administrators sometimes need to

divide networks, especially large ones, into smaller networks:

e

r

– Reduce the size of a broadcast domain. – Improve network security.

– Implement the hierarchical managements.

• So we need more network addresses for your

network. But I want the outside networks see our network as a single network.

Divide network by three

e r 3.3 N e tw ork Lay e

(29)

CDS

Wt

Subnetting

• Subnetworks are smaller divisions of network.

• Subnet addresses include the Class A, Class

e

r

Subnet addresses include the Class A, Class B, or Class C network portion, plus a subnet field and a host field.

• To create a subnet address, a network administrator borrows bits from the original host portion and designates them as the subnet field. 3.3 N e tw ork Lay e 57

• Subnet addresses are assigned locally, usually by a network administrator.

CDS Wt

Subnetting

e r 3.3 N e tw ork Lay e 58

(30)

CDS

Wt

Subnet mask

• “Extended Network Prefix”.

• Determines which part of an IP address is the network field and which part is the host field.

e

r

network field and which part is the host field.

• 32 bits long.

• Divided into four octets.

• Network and Subnet portions all 1’s.

• Host portions all 0’s.

Default subnet mask: Example

• 192.168.2.100 / 255.255.255.0. • 11000000.10101000.00000010.01100100. • 11111111 11111111 11111111 00000000 e r • 11111111.11111111.11111111.00000000. • 11000000.10101000.00000010.01100100. • Class C network:

– 24 bits for network portion. – 0 bits for subnet portion. – 8 bits for host portion.

S b t dd 192 168 2 0 3.3 N e tw ork Lay e • Subnet address: 192.168.2.0.

(31)

CDS

Wt

Subnet mask: Example

• 172.16.65.100 / 255.255.240.0. • 10101100.00010000.01000001.01100100. • 11111111 11111111 11110000 00000000 e r • 11111111.11111111.11110000.00000000. • 10101100.00010000.01000000.00000000. • Class B network:

– 16 bits for network portion. – 4 bits for subnet portion. – 12 bits for host portion.

S b t dd 172 16 64 0 3.3 N e tw ork Lay e 61 • Subnet address: 172.16.64.0. CDS Wt

How many bits can I borrow?

• All of subnet bits are:

– 0 : reserved for network address. – 1 : reserved for broadcast address.

e

r

• The minimum bits you can borrow is: 2 bits.

• The maximum bits you can borrow is:

• A: 22 bits ~ 222 - 2 = 4.194.302 subnets. • B: 14 bits ~ 214 - 2 = 16.382 subnets. • C: 06 bits ~ 206 - 2 = 62 subnets. 3.3 N e tw ork Lay e 62

(32)

CDS

Wt

Why we need to know Boolean

ops?

IP

AND

Subnet

=

Network and

e

r

• Network layer performs the Boolean

operations in order to find the network ID of a subnet

Example:

Address

AND

Mask

Subnet address

3.3 N e tw ork Lay e 63 • Example: – 172.16.65.100 AND 255.255.240.0 – Network address: 172.16.64.0 CDS Wt

ARP to find a MAC Address

e r 3.3 N e tw ork Lay e

(33)

CDS

Wt _{Broadcasting messages are}

intended to be seen by every host on a network.

Address all nodes (braodcast)

e

r

The broadcast address is formed by using all 1s within a portion of the IP address

Two kinds of broadcasts -directed broadcasts and flooded broadcasts. 3.3 N e tw ork Lay e 65

Broadcasts directed into a specific network/subnet are allowed and are forwarded by the router. These directed broadcasts contain all 1s in the host portion of the address.

Flooded broadcasts (255.255.255.255) are not propagated, but are considered local broadcasts. CDS Wt • Introduction Layer 3

Content

3.3 N e tw ork Lay e 66

(34)

CDS

Wt

Initially, a router must refer

Routing: Forward IP-Packets

e

r

to entries about networks or subnets that are directly connected to it.

Each interface must be configured with an IP address and a mask.

3.3 N e tw ork Lay e 67

The initial source of addressing is a user who types it into a configuration file.

CDS

Wt

•static routes- manually defined by the system administrator as the next hop to a destination; useful

Routing: types of routes

e

r

hop to a destination; useful for security and traffic reduction

•default routes- manually defined by the system administrator as the path to take when there is no known route to the

3.3 N e tw ork Lay e destination

•dynamic routing- the router learns of paths to destinations by receiving periodic updates from other

(35)

CDS

Wt

Default route

• A default network must exist in a routing table. Default routes keep routing tables shorter. When an entry for a destination network does not exist in a routing table the

e

r

network does not exist in a routing table, the packet is sent to the default network.

• Because a router does not have complete

knowledge about all destination networks, it can use a default network number to indicate

th di ti t t k f k t k 3.3 N e tw ork Lay e 69

the direction to take for unknown network numbers. Use the default network number when you need to locate a route, but have only partial information about the destination network.

CDS

Wt

a router can use an IP routing protocol to accomplish routing through the implementation of a

Different routing protocols

e

r

specific routing algorithm. Examples of IP routing protocols include:

• RIP - a distance-vector

routing protocol

• IGRP - Cisco’s

distance-3.3 N e tw ork Lay e 70

• IGRP - Cisco s

distance-vector routing protocol

• OSPF - a link-state routing

protocol

• EIGRP - a balanced hybrid

(36)

CDS

Wt

RIP was originally specified in RFC 1058.

Its key characteristics include

Routing: RIP

e

r

Its key characteristics include the following:

•It is a distance-vector routing protocol.

•Hop count is used as the metric for path selection.

•The maximum allowable

3.3 N e tw ork Lay e 71 hop count is 15. •By default, routing updates are broadcast every 30 seconds CDS Wt

Routing Table

e r 3.3 N e tw ork Lay e

The show ip routecommand displays the contents of the IP routing table, which contains entries for all known networks and subnetworks, along with a

(37)

Content

3.3 N e tw ork Lay e 73

Communication)

CDS

Wt

Train Network Structure

e r 3.3 N e tw ork Lay e 74 Sources: IEC 61375

(38)

CDS Wt

WTB Data-Frame

Routing in a train

• The network layer routes packets from an Origin station to a Final station.

e

r

• To this effect, the network layer uses the mapping provided by several directories:

• a) the station directory,

• b) the function directory,

• c) the group directory, and d) the node directory

3.3 N e tw ork Lay e

• d) the node directory.

(39)

CDS Wt

Network-Layer / Routing

Routing Situations

e r 3.3 N e tw ork Lay e 78

(40)

CDS Wt

Frame Structure

e r 3.3 N e tw ork Lay e

(41)

Content

3.3 N e tw ork Lay e 81

• Communication Matrix