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MD – Mediation Devices or Connecting Devices
(repeater, bridge, …)

heterogeneous MD

Token Ring

Ethernet

homogeneous MD

LAN interconnection

LAN interconnection by analog telephone lines

LAN 1

Modem

LAN 2

Analog

telephone line

NT 2

NT 1

LAN A

A 1

NT 1

NT 2

LAN B

A 1

LAN C

A 1

NT 2

NT 1

LAN D

A 1

NT 2

NT 1

ISDN

LAN interconnection by N-ISDN

LAN interconnection by B-ISDN (ATM)

N – ATM Node (switch)
NT1 – Network
Termination

LAN A

NNI

NT1

NT1

UNI

LAN B

LAN C

LAN D

Connecting devices

Networking

Devices

Internetworking

Devices

Hub/Repeater

Bridge/

Switch L2

Router/

Switch L3

Gateway

•

Repeater is a low-level devices that amplify or regenerate

weak signals

•  Repeater is used to join network segments together
    to increase the total length of the network
•  Act at the physical layer and allow all traffic to cross LAN

segments

What is a Repeater ?

Repeater

(HUB)

• Hub is a repeater with fault detection functionality

• It connects nodes (stations/computers) to LAN

(Ethernet) in star topology

What is a Hub?

  Two pairs (emission and reception)
  Node (station, computer, server,…)
  RJ-45 jack

Hub (10 BASE T)

Node
(host)

Nod

(hos

t
)

Hub

• It connects LAN (segment) to another LAN

(segment)

that uses the same protocol (for example, Ethernet

or Token Ring)

• A bridge works at the data-link level of a network,
copying a data frame from one network to the next

network

along the communications path.

• Bridges can make minor changes to the frame

before forwarding it

(such as adding and deleting some fields from the

frame header)

What is a Bridge ?

Bridge

Bridges

Bridges are

intermediate systems
    (Data Link Layer)
- Operate on Ethernet
frames,
   examining MAC
addresses
   and selectively
forwarding frame
   based on its destination
- Bridge isolates

collision

domains

since it buffers frames.

INTERNETWORKING

Remote bridges

can be used to interconnect distant LANs.

Point-to-point line

Remote bridge

LAN C

LAN B

LAN A

•

A network device that selects a path or circuit

    for sending a unit of data to its next destination.
•  A network device processing packets at layer 2 and 3
    – Layer 2 Switch:
        • Switches frames at the Data Link Layer
        • Uses MAC addresses to determine where frames will be

sended.

     – Layer 3 Switch:
        • Switches packets at the Network Layer
        • Uses IP addresses to determine where packets will be

sended.

What is a Switch?

Switch seperates collision domains

Switch

Collisi

Domai

Switch

Coolision Domains

– LAN with collision detection

Broadcating Domain

– max. size of the network, in which frame can be transmit

LAN Switch

 Multiport switching devices

 Distribute broadcating domain into collision domains

Collisi

Domai

Collisi

Domai

Collisi

Domai

Collisi

Domai

Collisi

Domai

Fast Link

Hub sending a packet form F to C Switch sending a packet from F to C

Switch sending a frame from F
to a broadcast address

With multicast filtering.
The multicast traffic form F
is only forwarded to selected interfaces.
In this case, only E and H.

Hub vs. Switch functionality

Cut-through vs. Store-and-Forward Switching

PAYLOAD

CRC

incoming
frame

PAYLOAD

CRC

PAYLOAD

CRC

outgoing
frame

48 bit Destination Address + Switching Delay
~30us at 10 Mbit/s

Frame Length + Store-and-Forward Delay
~ 2ms at 10 Mbit/s

outgoing
frame

Frame Switching

Three methods of switching:
- Cut –Through (C-T),
- Store-and-Forward (S-F),
- Inteligent (IS) – hybrid uses C-T or S-F switching.

•  Routers determine the next network point
     to which a packet should be forwarded
     on the way to its final destination

• Routers use the Network Layer Protocol Information
within each packet to "route" it from one destination or

LAN to another.

This means that a router must be able to recognize all

the different devices

that may be used on the networks it is linking together

• Routers communicate with one another
to determine the best route through the complex

connections of many LANs

to increase speed and cut down on network traffic

What is a Router?

Router

TRANSPORT GATEWAYS AND GATEWAYS

 TRANSPORT GATEWAYS

– Operate at Transport Layer
– Connect two or more station

that use different connection-oriented transport layer

protocols

 GATEWAYS

– Operate at Application Layer
– Translate one format into another

Why VLAN ?

What is VLAN?



Virtual LAN (VLAN) is a group of devices that can be located anywhere on a network,

but which communicate as if they are on the same physical segment.


With VLANs, we can easily segment your network logically without being restricted

by physical connection

 VLANs ease network changes
It

allow you to group devices as if they are connected by

physical connections.

You do not need to do anyre-cabling.

 VLANs enhance network security

Devices within each VLAN can only communicate with

other devices

on the same VLAN.

 VLANs help control traffic

Increases efficiency by separating traffic from different

groups to prevent

wasting unwanted broadcast/multicast packets.

Benefits of a VLAN

Virtual LANs



VLANs are a logically-independent LANs (which co-exist on

a switch).

It consists of a number of station (computers) that behave

as if they are

      in the same collision domain.
   One of the biggest advantages of VLANs
      - physically moving a computer to another location:
        it can stay on the same VLAN without the need for any

hardware reconfig.

 IEEE 802.1Q is the major protocol for the VLAN.
(Several other proprietary protocols such as Cisco's ISL and

3Com VLT exist)

   Nowadays VLAN configuration tends to reducing the size
       of the broadcast domain at the MAC layer.
   Virtual LANs operate at layer 2.
      However, administrators often configure a VLAN to map

directly

to an IP network or subnet - involving to layer 3.

A Layer-2 VLANs can be implemented in three ways:

   - Open VLANs (use a single MAC address database for all VLANs)
   - Closed VLANs (use a separate MAC address database for each VLAN)
   - Mixed-Mode VLANs (can be configured as Open or Closed on a VLAN basis)

VLAN - Virtual LAN

LAN  VLAN

  Keep the advantages of Layer 2 interconnection
      (addresses, topology - Spanning Tree, switching)
  Enhance with functionalities of Layer 3
      (spanning large distances, traffic filtering)
  Limit broadcast domains
  Security (separate sub-networks)
  VLANs build on bridges or switches

explicit & implicit VLAN ID mechanisms

explicit

implicit

tag

headers

MAC

address

switch

port

protocol

type

subnet

Virtual LANs

VLAN can be configured in various ways:

Two methods of establishing a VLAN:



Frame-tagging

It changes the information contained within the layer-2 frame,
so that switches may forward the VLAN traffic to its correct VLAN

destination

and return the frame to its normal format.



Frame-filtering

Frame-filtering involves the switch looking for certain criteria in

the layer-2 frame

and using this matching system to forward the traffic to its

correct VLAN and destination.

Virtual LANs

VLAN Red

= Ports 1,2,7,8

VLAN Blue

= Ports 3,4,5,6

A. VLAN based on ports
(called port-grouped

VLAN)

140.113.200.xxx

Layer 3

switch

140.113.200.xxx

140.113.225.xxx

B. VLAN based on IP subnet

VLAN Red

- Subnet 140.113.200.xxx

VLAN Blue

- Subnet 140.113.225.xxx

Layer 2
Switch

Virtual LANs



In a switched network, it is difficult to determine the broadcast domain.

   A station may belong to the same or multiple broadcast domain.
   We have to examine configuration files in a VLAN environment to determine
      the boundaries of the broadcast domain.

Switched Network

Broadcast Domain 2

Broadcast Domain 1



Although VLANs

and

are in the same switch,

traffic from VLAN

(

)

cannot pass directly to VLAN

(

) within the switch.



Two VLANs will become one large VLAN if a bridge is used to connect them.

 Layer 3 internetworking devices must be used to connect these two VLANs

Virtual LANs

VLAN A

VLAN B

Bridge

According to IEEE definition, VLAN is a group of devices
participating in the same Layer 2 domain. All devices in the
domain can communicate with each other without needing to
go through a router.
  Layer 2 switching VLANs
     It is based on source / destination MAC address.
  Layer 3 switching VLANs
     It is based on both source / destination MAC addresses
     and source / destination IP addresses - Multi-Layer
Switching (MLS)
  Layer 4 switching VLANs
     It is based on Layer 3 criteria and Layer 4 source /
destination port values.

Virtual LANs

IEEE 802.1Q VLAN Model

Mapping

Redistribution

/resolution

Configuration

Management

information base

VLAN mapping

protocol

request/response

Explicit tagging

Implicit tagging

• special config files in station

• specialised config server

• use of distribution protocol

• frames associated with VLAN

• associations distributed to all

• VLAN Mapping Protocol (VLMP)

• implicit tagging by frame content

• explicit tagging adds new header

IEEE 802.1Q VLAN Frame

Since there are various approaches to create VLANs,
administrators must be carefully handle multi-vendor VLAN.
Due to this deficiency, IEEE develop a vendor-independent method in 802.1Q
to create interoperable VLANs.

802.1Q Frame over Ethernet

TPID - 8 bits, Tag Protocol Identifier (802.1Q Tag Type which is
set to 0x8100)
PRI

- 3 bits, User Priority Field

(8 priorities are defined in

802.1p)
CFI         - 1 bit, Canonical Format Indicator
                            (indicates presence of a Routing Information
Field)
VID         - 12 bits, VLAN Identifier (identifies the VLAN)

Tag Len/Type Data

FCS

TPID

PRI

VID

Single-switch VLAN architecture

Computers can be assigned to VLANs in four ways:

- Port-based VLANs assign computers according to the VLAN switch port
to which they are attached (layer 1)
- MAC-based VLANs assign computers according to each computer’s
data link layer address (layer 2)
- IP-based VLANs assign computers using their IP-address (layer 3)

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