This PPT contains Network Layer , Virtual Circuit, etc.

2.  Network layer is responsible for source to destination
delivery of the packets.
 The network layer must know the topology of the subnet
and choose appropriate paths through it.
 When source and destination are in different networks,
the network layer (IP) must deal with these differences.
 If two system are connected to the same link, there is
usually no need for a network layer.

3. H3 H3Data Data
From Transport layer
From data link layer
To Transport layer
To data link layer

4. WAN
LAN
LAN
LAN
LAN
F1
F1
F3
F2
F1
F2
F2
There is no provision in the data link(or physical layer) to make the
routing decision as the frame does not carry any routing information. To
solve the problem of delivery through several link, the network layer was
designed. The network layer is responsible for host to host delivery and for
routing the packets through routers and switches.

5. LOGICAL ADDRESSING
 Logical addressing are necessary for universal
communication that are independent of underlying physical
network.
 The logical address in the Internet is a 32 bit address
ROUTING
 When independent network or link are connected to create
internetwork or a large network, the connecting devices(router
or switch) routes the packet to their final destination.

6. Physical
layer
Data link
layer
Physical
layer
Data link
layer
End
system
a
Network
layer
Physical
layer
Data link
layer
Physical
layer
Data link
layer
Transport
layer
Transport
layer
Messages Messages
Segments
End
system
b
Network
service
Network
service
Network
layer
Network
layer
Network
layer

7. Routing table
IP packet and
routing
information
To data link layer
Data from another
protocol
Processing
Network layer
The network layer at the source is responsible for creating a packet from
data coming from another protocol such as transport layer protocol. It is
responsible for checking its routing table to find the routing information.
NETWORK LAYER AT THE SOURCE
Source

8. Routing table
IP packet and
routing
information
To data link layer
Processing
Network layer
From data link
layer
Router
The network layer at the switch or router is responsible for routing the
packet. When a packet arrives, the router or switch consults its routing
table and find the interface from which the packet must be send. After
some changes in the header with the routing information is passed to the
data link layer again.
NETWORK LAYER AT THE SWITCH

9. IP packet
Fromdata link layer
Data to another
protocol
Processing
Network layer
The network layer at the destination is responsible for address verification,
it make sure that the destination address on the packet is the same as the
address of the host.
NETWORK LAYER AT THE DESTINATION
Destination

10. At the network layer, TCP/IP supports the Internetworking
Protocol i.e. IP with four supporting protocol: ARP, RARP, ICMP,
and IGMP.
LOGICAL ADDRESSING
 Transmission mechanism used by the TCP/IP protocol.
 It is unreliable and connectionless protocol.
 It does not provide error checking or tracking.
 IP transport data in packets called datagram.
 IP does not keep track of the routes and has no facility of
reordering datagram.
ADDRESS RESOLUTION PROTOCOL
 Used to associate a logical address with a physical address.
 ARP is used to find the physical address of the node when its
internet address is known.

11. REVERSE ADDRESS RESOLUTION PROTOCOL
 Its allows a host to discover its Internet address when its
knows only its physical address.
 It is used when a computer is connected to a network for the
first time.
INTERNET CONTROL MESSAGE PROTOCOL
 ICMP is used by hosts or gateways to send notification of
datagram problems back to the sender.
 Its send query and error reporting messages.
INTERNET GROUP MESSAGE PROTOCOL
 IGMP is used to facilitate the simultaneous transmission of a
message to a group of recipients.

12.  The internet at the network layer is a packet switched
network.
 Packet switching uses either the virtual circuit approach or
the datagram approach.
 The internet is chosen the datagram approach to switching
in the network layer.
 It uses the universal address defined in the network layer to
route packets from the source to the destination.

13. DATAGRAM
 Packets in the IPv4 layer are called datagram.
 A datagram is a variable-length packet consisting of two
parts : header and data.
 The header is 20 to 60 bytes in length and contains
information essential to routing and delivery.

15. 1. VERSION(VER) : This 4-bit field defines the version of the
IPv4 protocol. This field tells the IPv4 software running in
the processing machine that the datagram has the format
of version 4.
2. HEADER LENGTH(HLEN) :This 4 bit field defines the total
length of the datagram header in 4 byte word. This field is
needed because the length of the header is variable. When
there are no option the header length is 20 bytes and value
of this field is 5. When the option field is at its max. size the
value is 15.

16. 3. SERVICES : This is a 8 bit field previously called service type
is now called differentiated service.
 SERVICE TYPE : In this interpretation the first 3 bit are
called the precedence bits and the next 4 bits are called type
of service(TOS) bits
Precedence TOS Bits
D T R C
D : Minimize delay, T: Maximize Throughput
R: Maximize reliability, C: Minimize Cost
1. PRECEDENCE : This is a 3 bit field ranging from 0(000 in
binary) to 7(111 in binary). The precedence defines the
priority of the datagram in issue such as congestion. If a
router is congested then the lower precedence datagram
are discarded.

17. TOS BITS Description
0000 Normal(default)
0001 Minimize Cost
0010 Maximize Reliability
0100 Maximize Throughput
1000 Minimize delay

18.  DIFFERENTIATED SERVICES : In this interpretation the first 6
bits make up the code point subfield and the last 2 bits are not
used. It can be used in two different ways:
a) When the 3 rightmost bits are 0’s, the 3 leftmost bits are
interpreted the same as the precedence bits in the service type
interpretation. In other word it is compatible with the old
interpretation.
b) When the three rightmost bits are not all 0’s , the 6 bits define 64
services based on the priority assignment by the internet or local
authorities.
Category Code point Assigning authority
1 XXXXX0 Internet
2 XXXX11 Local
3 XXXX01 Temporary or
experimental
The first category contain 32 services type, the second and
third contain 16 services types

19. 4. TOTAL LENTH : This is a 16 bit field that defines the total
length (header plus data) of the IPv4 datagram in bytes. To find the
length of the data coming from the upper layer from the total length.
Length of data= Total length – Header length
Encapsulation of a small datagram in an Ethernet frame
One of the reason why “total length” field is required.

20. Protocol field and encapsulated data
5. PROTOCOL : This 8 bit field defines the higher level
protocol that uses the services of the Ipv4 layer. An IPv4
datagram can encapsulated data from several higher level
protocol such as TCP, UDP, ICMP, and IGMP. This specifies the
final destination protocol to which the IPv4 datagram is
delivered.

21. 6. CHECKSUM
• IPv4 checksum use the 1’s compliment method.
• Checksum only computes for IP header, not data
• Upper layer has checksum for data portion
• Header always changes in each router
• Header is chunked to 16-bit sections for computing
7. OPTION
• Option as the name implies, are not required for a
datagram.
• They can be used for network testing and debugging.
• Option process is required for IPv4 software.

22. 7. OPTION(contd..)
Record route
End of option
No operation
Multiple byte
Single byte
Option
Time Stamp
Loose source route
Strict source route
Taxonomy of option in IPv4
NO OPERATION : A no operation is a 1 byte option used as a filler between
option
END OF OPTION: An end of option is a 1 byte option used for padding at the
end of the option field. It however can only be used as the past location.
RECORD ROUTE: An record route is used to record the internet router that
handle the datagram. It can list up to nine router

23. 7. OPTION(contd..)
STRICT SOURCE ROUTE: A strict route option is used by the source to
predetermine a route for the datagram as its travel through the internet.
LOOSE SOURCE ROUTE : A loose source route option is similar to the
strict source route, but it is less rigid. Each router in the list must be visited , but
the datagram can visit other router as well.
TIMESTAMP: A timestamp option is used to record the time of datagram
processing by a router. The time is expressed in million seconds from midnight

24.  Datagram can travel through different network.
 Each router decapsulates the IPv4 datagram from the frame it
receives, and then encapsulate it in another protocol.
 The format and size of the received and sent frame depends on the
protocol used by the physical through which the frame has just traveled
 Dividing the datagram which make it possible to pass through the
other physical network is called fragmentation.
 For example, if a router connects a LAN or WAN, its receives a frame
in the LAN format and sends a frame in the WAN format.

25. Application may request a specific type of service
Protocol TOS bits Description
ICMP 0000 normal
BOOTP 0000 normal
NNTP 0001 Minimize cost
IGP 0010 Maximize reliability
SNMP 0010 Maximize reliability
TELNET 1000 Minimize delay
FTP(data) 0100 Maximize
throughput
FTP(control) 1000 Minimize delay
TFTP 1000 Minimize delay
SMTP(command) 1000 Minimize delay
SMTP(data) 0100 Maximize
throughput
DNS(UDP query) 1000 Minimize delay
DNS(TCP query) 0000 normal
DNS(zone) 0100 Maximize
throughput

26. MAXIMUM TRANSFER UNIT
 Each data link layer protocol has its own frame format in most
protocol.
 When a datagram is encapsulated in a frame, the total size of
the datagram must be less than its maximum size which is
defined by the restriction imposed by the hardware and
software used in the network
 To make the IPv4 protocol independent of the physical network, the
designers to make the maximum length of the IPv4 datagram equal to
65,535 bytes.

27. MTU’s FOR SOME NETWORKS

28.  When a datagram is fragmented, each fragment has its own
header with most of the field repeated, but with some changed.
 A fragmented datagram may itself be fragmented if it
encounter a network with an even smaller MTU
 The reassembly of the datagram is done by the destination
host because each fragment becomes an independent
datagram.
 The host or router that fragments a datagram must change the
values of three fields : flags, fragmentation offset, total length. The
rest of the field must be copied.

29. 7. IDENTIFICATION
This is a 16 bit field that identifies a datagram originating from the
source host.
 The combination of the identification and source IPv4 address must
uniquely define a datagram as it leaves the source host.
 When a datagram is fragmented, the value in the identification
field is copied to all the fragment.
 The identification number helps the destination in reassembling the
datagram
8. FLAG
This is 3 bit field. The first bit is reversed. The second bit is called the
donot fragment bit.
 If its value is 1, the machine must not fragment the datagram.
 If its value is 0, the datagram can be fragmented if necessary.
 The third bit is called the “more fragment bit”

30. 9. FLAG(contd..)
 If its value is 1, it means the datagram is not the last fragment, there
are more fragment after this one.
 If its value is 0, it means this is the last or only fragment.
10.FRAGMENTATION OFFSET
 This is a 13 bit field that shows the relative position of this fragment
with respect to the whole datagram.
 It is the offset of the data in the original datagram measured in units
of 8 bytes.
Fragmentation Example

31. IPv6 PACKET FORMAT
 Each packet is composed of a mandatory base header followed
by the payload.
 The payload consist of two parts: optional extension header and
data from an upper layer.
 The base header occupies 40 bytes , whereas the extension
header and data from the upper layer contains up to 65,535 byte of
information

32. FORMAT OF IPv6 DATAGRAM

33. FORMAT OF IPv6
DATAGRAM(contd..)
 VERSION: This 4 bit field defines the version number of the IP. For IPv6, the
value is 6.
 PRIORITY: The 4 bit priority field defines the priority of the packet with
respect to the traffic congestion.
 FLOW LABEL: The flow label is a 3 byte(24 bit) field that is designed to
provide special handling for the particular flow of the data.
 PAYLOAD LENGTH: The 2 byte payload length field defines the length of
the IP datagram excluding in the base header.
 NEXT HEADER: The next header is an 8 bit field defining the header that
follows the base header in the datagram. The next header is either one of the
optional extension header used by the IP or header of an encapsulated packet such
as UDP or TDP.
 HOP LIMIT: This HOP limit is a 8 bit field that serves the same purpose as the
TTL field in the Ipv4.
 SOURCE ADDRESS: The source address field is a 16 byte Internet address
that identifies the original source of the datagram.
 DESTINATION ADDRESS: The destination address is a 16 byte Internet
address that usually identifies the final destination of the datagram

34. Value for higher level protocol

36. VIRTUAL CIRCUIT NETWORK
 Virtual circuit network is a cross between a circuit switched network
and a datagram network.
 As in a circuit switch network there is a setup and a tear down phase in
addition to the data-transfer phase.
 The resources can be allocated during the setup phase as in a circuit
switched network or on a demand as in a datagram network.
 As in a circuit switched network, all packets follow the same path
established during the connection.
 A virtual circuit is normally implemented in a data link layer.

37. VIRTUAL CIRCUIT APPROACH IN
A WAN
• FRAME RELAY : A frame relay is a relatively high-
speed protocol that can provide some service not
available in other WAN technologies such as DSL,
cable TV, and T lines.
• ATM : ATM, as a high speed protocol, can be the
superhighway of communication when it deploys
physical layer carriers such as SONET.

38.  Frame Relay is a virtual circuit wide –area network that was designed in
response to demands for a new type of WAN in the late 1980s and early 1990s.
 Frame Relay operates at a higher speed(1.544 Mbps & recently 44.376 Mbps)
 Frame Relay operates in just the physical and data link layer. This means it can
be easily used as a backbone network to provide services to protocol that
already have a network layer protocol such as the internet.
 Frame relay allows bursty data.
 Frame Relay allows a frame size of 9000 bytes, which can accommodate all
local area network frame sizes.
 Frame Relay is less expensive than other traditional WANs.
 Frame Relay has error detection at the data link layer only. There is no floe
control or error control.

39. WHY USE FRAME RELAY?
 Prior to Frame Relay, some organization were using a virtual-circuit
switching network called X.25 that perform switching at the network layer.
 X.25 has a low 64-kbps data rate. By the 1990s, there was a need for
higher data rate WANs.
 X.25 has extensive flow and error control at both the data link layer and
the network layer.
 Originally X.25 was designed for private use, not for the Internet.
 X.25 has its own network layer. This means that the user’s data are
encapsulated in the network layer packets of X.25. This doubles the
overhead.
 Disappointed with X.25, some organization started their own private
WAN by leasing T-1 or T-2 lines from public service providers. This
approach has some drawback which are as:

40.  If an organization has n branches spread over an area , it needs n(n-1)/2 T-
1 or T-3 lines. The organization pays for all these lines although it may use
the lines only 10 percent of the time. This can be very costly.
The service provided by T-1 and T-3 lines assumes that the user has fixed
rate data all the time. So this type of service is not suitable for the many users
today that need to send bursty data
CONTD…..

41. FRAME RELAY ARCHITECTURE
• FR provides permanent virtual circuits and
switched virtual circuits.
• The FR WAN is used as one link in the global
Internet.
Switch Table matches an
incoming port-DLCI
combination with an outgoing
port-DLCI combination.
A virtual circuit in Frame Relay is identified by a number called a “DATA
LINK CONNECTION IDENTIFIER(DLCI)”

42. PERMANENT VS. SWITCHED
VIRTUAL CIRCUITS
 In PVC the connection setup is very simple. The corresponding table
entry is recorded for all switches by the administrator (remotely and
electronically). An outgoing DLCI is given to the source, and an
incoming DLCI is given to the destination.
 PVCs have 2 drawbacks:
 Costly…pay for connection all the time
 A connection is created from one source to one single destination. If
a source needs connections with several destinations, it needs a
PVC for each connection.
 SVC creates a temporary, short connection that exists only when the
data are being transferred between source and destination. SVC
requires establishing and terminating phases (Chapter 8).

43. FRAME RELAY LAYER
Data link
Simplified core function
of data link layer
Physical
ANSI Standard
“Frame Relay operates only at the physical layer and data link layer”
PHYSICAL LAYER :
No specific protocol is defined for the physical layer in Frame Relay.
Instead, it is left to the implementer to use whatever is available.
Frame relay supports any of the protocol recognized by ANSI

44. FRAME RELAY LAYER(contd.)
DATA LINK LAYER :
At the data link layer, Frame Relay uses a simple protocol that does
not support flow or error control. It has only an error detection
mechanism

45. FRAME RELAY AND IP
The TCP/IP protocol suite has become a widely accepted standard for
network communications.
IP, the Internet Protocol, is the component of the TCP/IP suite that is
responsible for routing data to its destination. IP operates at layer 3, the
network layer
 Frame relay is very well-suited to carrying IP datagram traffic, which typically
is bursty in nature.
 Frame relay and IP are a well-matched team—they work well together to
make efficient use of wide area bandwidth.
IP
NETWORK LAYER
FRAME RELAY
DATA LINK LAYER
PHYSICAL LAYER
IP and frame relay
layering

46. USING FRAME RELAY IN AN IP
NETWORK
 A frame relay circuit can simply be used as a replacement for a point-to-
point leased line in an IP network.
“Replacing a leased line with a frame relay circuit”

47. VIRTUAL IP SUBNET
 Multiple IP routers can be connected into a frame relay
configuration that behaves like a virtual LAN—or in IP terminology,
a virtual IP subnet.
 An IP subnet is a set of systems (usually located on a LAN) that
have some special characteristics:
a. Their IP addresses start with the same network and subnet
numbers.
b. Any system can communicate directly with any other system in
the subnet. Data will not flow through an intermediate router

48. VIRTUAL IP SUBNET(contd.)
 This is a fully meshed set of connections—that is, each system has
direct connections to the other systems and hence can communicate
directly with the other systems.

49. FRAME RELAY FRAME
 ADDRESS (DLCI) FIELD: 10-bit DLCI field represents the address of the frame
and corresponds to a PVC.The first 6 bits of the first byte makes up the first part of
the DLCI. The second part of the DLCI uses the first 4 bits of the second byte.
These are the parts of the 10 bits DLCI defined by the Standard.
 COMMAND/RESPONSE(C/R) : The command/response(C/R) bit is provided to
allow upper layer to identify a frame as either a command or a response. It is not
used by the frame relay protocol.

50. FRAME RELAY FRAME(contd.)
 EXTENDED ADDRESS(EA) : The extended address (EA) bit indicates whether
the current byte is the final byte of the address. An EA of 0 means that another
address byte is to follow. An EA of 1 means that the current byte is the final one.
 FORWARD EXPLICIT CONGESTION NOTIFICATION(FECN) : The FECN bit can
be set by any switch to indicate that traffic is congested. This bit inform the
destination that congestion has occurred.
 BACKWARD EXPLICIT CONGESTION NOTIFICATION(BECN) : The BECN bit is
set (in frame that travel in the other direction) to indicate a congestion problem in
the network. This bit inform the sender that congestion has occurred.
 DISCARD ELIGIBILITY(DE) : The discard eligibility bit indicates the priority level
of the frame. In emergency situation, switches may have to discard frames to
relieve bottleneck and keep the network from collapsing due to overload.

51. THREE ADDRESS FORMAT
(EXTENDED ADDRESS)

52. FRAME RELAY
ASSEMBLER/DISASSEMBLER(FRAD)
To handle frames arriving from other protocol, frame relay uses a device called
a Frame Relay assembler/dissasembler(FRAD).
A FRAD assembles and disassembles frame coming from other protocol to
allow to be carried by Frame Relay frames.
A FRAD can be implemented as a separate device or as part of a switch.

53. VOICE OVER FRAME RELAY(VOFR)
 VOFR is offered by the Frame Relay Network that sends voice through the
network.
 Voice is digitized using PCM and then compressed. The result is sent as data
frames over the network.
 VOFR allows the inexpensive sending of voice over long distances.
 The quality of voice is not as good as voice over a circuit switched network
such as the telephone network

54. PRO’S AND CONS OF FRAME RELAY
PRO’S :
 In many scenario's involving long haul, high speed connections, it is cheaper
than dedicated lines.
 There is a cheap solution to incorporate redundancy in the network.
 Less hardware is needed to for the same amount of connections
CONS :
There may be jams; no guaranteed bandwidth.
 In a point-to-point scenario it is not economically feasible.
 In short haul, it is not economically feasible.

55. ASYNCHRONOUS TRANSFER
MODE(ATM)
 Asynchronous Transfer Mode, a network technology based on
transferring data in cells or packets of a fixed size.
 ATM was developed to meet the need of the “Broadband Integrated
service digital network” as defined in the late 1980’s and designed to unify
telecommunication and computer network.
 Asynchronous transfer mode(ATM) is the cell relay protocol designed by
the ATM Forum and adopted by the ITU-T.
 The cell used with ATM is relatively small compared to units used with
older technologies.
 The small, constant cell size allows ATM equipment to transmit video,
audio, and computer data over the same network, and assure that no
single type of data hogs the line.

56. DESIGN GOALS
 A technology is needed for the transmission system to optimize the use of high-
data rate transmission media.
 The system must interface with existing system and provide wide area
interconnectivity between them without lowering their effectiveness or requiring
their replacement.
 The design must be implemented inexpensively so that cost would not be a
barrier to adoption.
 The new system must be able to work with and support the existing
telecommunications hierarchies.
 The new system must be connection oriented to ensure accurate and
predictable delivery.

57. PROBLEM WITH THE EXISTING
SYSTEM
FRAME NETWORK :
 Before ATM, data communication at the data link layer had been based on
frame switching and frame network.
 Different protocol uses frames of varying size.
 As the network become more complex, the information in the header
become more extensive and this result in larger header.
 Due to large header some protocol have enlarge the size of the data unit
to make use header more efficient by sending more data with same size
header.
 If there is not much more information to transmit, much of the field goes
unused.

58. MULTIPLEXING USING DIFFERENT FRAME SIZES
 If line 1’s frame X arrives at the multiplexer even a moment earlier than line 2’s
frames, the multiplexer puts frame X onto the new path first.
 The multiplexer will first process the arrived frame X before considering the frame
of line 2’s.
 Therefore frame A must wait for the entire X bit stream to move into place before
it can follow.
 The sheer size of X creates an unfair delay for frame A.
MIXED FRAME NETWORK :

59. CELL NETWORK :
 Many of the problems associated with frame internetworking are solved by
adopting a concept called cell networking.
 A cell is a small data unit of fixed size.
 In a cell network , all data which are to be transmitted are loaded into the
identical cells that are transmitted with complete predictability and uniformity.
 When a frames of different sizes and formats reaches the cell network from a
tributary network, they are split into the multiple small data unit of equal length and
are loaded into cells.

60. MULTIPLEXING USING CELLS
CELL NETWORK(contd.) :
 Here the Frame X has been divided into three cells: X,Y and Z. Only the first
cell from line 1 gets put on the link before the first cell from line 2.
 The high speed of the links coupled with the small size of the cells mean that,
despite interleaving, cells from each line arrive at their respective destination in
an continuous stream.
 A cell network can handle real transmission such as phone call.

61. ATM MULTIPLEXING
 ATM use asynchronous time division multiplexing- that is why it is called
Asynchronous Transfer Mode- to multiplex cells coming from different channels.
 It uses a fixed size slot(size of a cell).
 ATM multiplexer fill a slot with a cell from any input channel that has a cell, the slot
is empty if none of the channels has cell to send.
 At the first tick of the clock, channel 2 has no cell, so the multiplexer fills the slot
with a cell from the third channel.
 When all the cells from all the channels are multiplexed, the output slots are
empty..

62. ARCHITECTURE OF AN ATM
NETWORK
 ATM is a cell switched network.
 The user access device is called the end-points, are connected through a
“user-to-network interface(UNI)” to the switches inside the network.
 The switches are connected through “network-to-network interface(NNIs)”

63. VIRTUAL CONNECTION
Connection between two endpoints is accomplished through
transmission paths(TPs), virtual paths, and virtual circuits(VCs)
TRANSMISSION PATH(TP) : A transmission path (TP) is the physical
connection wire(wire, cable etc) between an endpoints and a switch.
Think of two switches as two cities. A transmission path is the set of all
highways that directly connect the two cities.

64. VIRTUAL PATHS(VP) : A virtual Paths (VP) provides a connection or a set of
connection between two switches. A highway between two cities is a virtual
path.
VIRTUAL CIRCUITS(VCs) : Cell network are based on virtual circuits(VCs) .
All cells belonging to a single message follow the same virtual circuit and remain
in their original order until they reach their destination. Think of a virtual circuits
as a lane of a highway
Fig. : Example of VPs and VCs

65. VIRTUAL CONNECTION IDENTIFIER
 In virtual circuit network, to route data from one end-point to another, the
virtual connection need to be identified.
 The designer of the ATM creates a hierarchal with two level : Virtual path
identifier(VPI) and Virtual circuit identifier(VCI)

66. VIRTUAL CONNECTION IDENTIFIER
IN UNIs AND NNIs
 In a UNI, the VPI is 8 bits whereas in an NNI, the VPI is 12 bits. The length of
the VCI is the same in both interface(16 bits).
 The whole idea behind dividing a virtual circuit identifier into two parts is to allow
hierarchal routing.
 Most of the switches in a typical ATM network are routed using VPIs.
 The switches at the boundary of the network, those that interact directly with the
endpoints use both VPIs and VCIs

67. ATM CELL
 The basic data unit in an ATM network is called a cell.
 A cell is only 53 bytes long with 5 bytes allocated to the header and 48 bytes
carrying the payload(user data may be less than 48 bytes).

68. CONNECTION IN ATM
ATM uses two type of connection : PVC and SVC
PVC : A permanent virtual circuit connection is established between two
endpoints by the network provider. The VPI and VCI are defined for the
permanent connection and the values are entered for the table of each switch.
SVC :
 In a switched virtual circuit connection, each time an end points wants to make
a connection with another endpoints, a new virtual circuit must be established.
 ATM cannot do the job by itself, but needs the network layer addresses and the
services of another protocol such as IP.

69. ROUTING WITH A SWITCH
 ATM uses switches to route the cell from a source endpoint to the destination
endpoints.
 A switch routes the cell using both the VPIs and the VCIs
 The switch checks it switching table which stores six pieces of information per
row: arrival interface number, incoming VPI & VCI, corresponding output ports,
Outgoing VPI & VCI.

70. ATM LAYER
PHYSICAL LAYER :
Like ethernet and wireless LANs, ATM cells can be carried by
any physical layer carrier.

71. PHYSICAL LAYER(contd..):
 SONET: The design of ATM was based on SONET.
 SONET is preferred for two reasons.
 First, the high rate of SONET’s carrier reflects the design
and philosophy of ATM.
 Second, In SONET the boundaries of cells can be clearly
defined.
ATM LAYER:
 The ATM layer provides routing, traffic management,
switching, and multiplexing service.
 It process outgoing traffic by accepting 48 byte segments
from AAL sub layer and transforming into 53- byte cells by the
addition of a 5 byte header

72. ATM LAYER(contd..):

73. ATM HEADER

74. ATM HEADER(contd..)
 ATM uses two format for this header, one for user-to-network
interface(UNI) cells and another for network to network interface(NNI)
cells
 Generic flow control(GFC): The 4 bit GFC field provides floe
control at the UNI level. In the NNI header, these bits are added to
the VPI. The longer VPI allows more virtual path to be defined at the
NNI level.
 Virtual path identifier(VPI): The VPI is an 8 bit field in a UNI cells
and a 12 bit field in an NNI cells.
 Payload type(PT): In the 3 bit PT field, the first bit defines the
payload as user data or managerial. The interpretation of the last 2
bits depend on the first bit.
 Cell loss priority(CLP): The 1 bit CLP field is provided for
congestion control.
 Header error correction(HEC): The HEC is a code computed for
the first 4 bytes header

75. APPLICATION ADAPTION LAYER:
 The application adaption layer (AAL) was designed to enable two
ATM concept.
 ATM must accept any type of payload, both data frames and
streams of bits.
 To accept continuous bits streams and break them into chunks to
be encapsulated into a cells at the ATM layer , it uses two sub layer.
 The payload must be segmented into 48- bytes segment carried by
the cells. At the destination these segment need to be reassembled
to recreate the original payload. The AAL defines a sub layer called
“segmentation and reassemble(SAR)” sub layer to do so.
 Before data are segmented by SAR, they must be prepared to
guarantee the integrity of the data. This is done by the sub layer
called convergence sub layer(CS)

76. APPLICATION ADAPTION LAYER(contd..) :
 ATM defines four versions of AAL : AAL1, AAL2, AAL3/4, AAL5
AAL1:
 AAL1 supports application that transfer information at constant bit
rates such as video and voice.
 It allows ATM to connect existing digital telephone networks such as
voice channels and T- channels.

77. AAL1(contd..):
 The CS sub layer divides the bit stream into 47 bytes segment and passes
them to SAR sub layer.
 The SAR sub layer adds 1 byte of header and passes the 48 byte segment
to the ATM layer. The Header has two field:
Sequence number(SN) : This 4 bit field defines a sequence number to
order the bits.
 Sequence number protection(SNP): The second 4 bit field protects the
first field. The first 3 bit automatically corrects the SN field. The last bit is a
parity bit that detects error over all 8 bits.
AAL2:
 Originally AAL2 was intended to support a variable data rate bit stream
but it has been redesigned.
 It is now used for low-bit-rate traffic and short – frame traffic such as
audio(compressed or uncompressed ) , video, fax.
 A good example of AAL2 uses is in mobile telephony.

78. AAL2(contd):
The CS layer overhead consists of five layer
 Channel identifier(CID) : The 8 bit field defines the channel of the short
packet.
 Length indicator(LI): The 6 bit LI field indicates how much of the final
packet is data.

79. AAL2(contd..):
 User-to-user indicator(UUI): The UUI field can be used by end to end users.
 Header error control(HEC): The last 5 bits is used to correct errors in the
header
AAL3/4:

80. AAL3/4I(contd..):
 Common part identifier(CPI): The CPI defines how the subsequent field are
to be interpreted.
 Begin Tag(Btag): The value of this field is repeated in each cell to identify all
the cells belonging to the same packet.
 Buffer allocation size(BA size): The 2 byte BA field tells the receiver what size
buffer is needed for the coming data.
 Alignment(AL): The 1 byte AL field is included to make the rest of the trailer 4
byte long.
 Ending tag(Etag): The 1 byte ET field serves as an ending flag. Its value is the
same as that of the beginning tag.
Length (L): The 2 byte L field indicates the length of the data unit.
The CS layer header and trailer consist of six field:
The SAR header and trailer consist of five fields:
 Segment Type (ST): The 2 bit ST identifier specifies the position of the segment
in the message: beginning(0), middle(01), or end(10).
 Sequence Number(SN): This field is the same as defined previously.
 Multiplexing Identifier(MID): The 10 Bit MID field identifies cells coming from
different data flows and multiplexed on the same virtual connection.,
 CRC: The last 10 bit of the trailer is a CRC for the entire data unit.

81. AAL5:
The four trailer fields in the CS layer are:
 User – to user(UU): This field is used by end users.
Common part identifier(CPI): This defines how the subsequent fields are to
be interpreted.
Length(L): The 2 byte L fields indicates the length of the original data.
CRC: The last 4 byte is for error control on the entire data unit

82. ATM LANS
 The ATM technology can be adapted to local area network called ATM
LANs.
 The high data rate of technology (155 to 622 Mbps) has attracted the
attention of designer who are looking for greater and greater speed of
LAN.
 ATM technology supports different type of connection between two
end user. Its support permanent and temporary connection.
 ATM technology supports multimedia communication with a wide
variety of bandwidth for different application.
 An ATM LAN can be easily expanded in an organization

83. ATM LANs ARCHITECTURE

84. PURE ATM ARCHITECTURE
 In a pure ATM LAN, an ATM switch is used to connect stations in the LAN.
 Stations can exchange data at one of two standard rates of ATM technology(155
and 652 Mbps)
 Station uses a virtual path identifier (VPI) and a virtual circuit identifier (VCI)
instead of a source and a destination address.

85. LEGACY ATM ARCHITECTURE
 In a legacy ATM LAN, stations on the same LAN can exchange data at the rate and
format of traditional LANs.
 The advantage here is that output from several LAN can be multiplexed together
to create a high data rate input to the ATM switch.

86. MIXED ARCHITECTURE
 In a mixed architecture LAN, it allows the gradual migration of legacy LANs onto
ATM LANs by adding more and more directly connected stations to the switch.
 The station is one specific LAN can exchange data using the format and data rate
of that particular LAN.
 The stations directly connected to the ATM switch can use an ATM frame to
exchange data

87. LAN Emulation(LANE)
 Connectionless versus connection-oriented :
 Traditional LANs are connectionless protocols . A station sends data packets to
another station whenever the packets are ready. There is no connection
establishment or connection termination phase.
 ATM is a connection oriented protocol . A station that wishes to send cells to
another station must first establish a connection and after all the cells are sent ,
connection is terminated.
 Physical addresses versus virtual-circuit identifiers:
 A connectionless protocol defines the route of a packet through source and
destination addresses.
 A connection-oriented protocol defines the route of a cell through virtual
connection identifiers(VPIs and VCIs).
 Multicasting and broadcasting delivery :
 Traditional LANs can cast both multicast and broadcast packets. A station can
send packets to a group of stations or to all stations.
 In ATM network , there is no easy way to multicasts or broadcast , although point-
to-multipoint connections are available.
 Interoperability : In a mixed architecture, a station connected to a legacy LAN
must be able to communicate with a station directly connected to an ATM switch.

88. Client/Server Model
LEC
BUS
LES
LECS
ATM LAN

89.  LAN Emulation Client
 All ATM stations have LAN emulation client(LEC) software installed on the
three ATM protocols.
The upper-layer protocols are unaware of the existence of the ATM technology.
These protocols send their request to LEC for a LAN service such as
connectionless delivery using MAC unicast , multicast, or broadcast addresses.
The LEC just interprets the request and passes the result on to the servers.
 LAN Emulation Configuration Server
 The LAN emulation configuration server(LECS) is used for the initial connection
between the client and LANE. This server is always waiting to receive the initial
contact.
 It has a well-know ATM address that is known to every client in the system.

90.  Broadcast/Unknown Server
 Multicasting and broadcasting require the use of another server called the
Broadcast/Unknown server(BUS).
 If a station needs to send a frame to a group of stations or to every station, the
frame first goes to the BUS. The server has permanent virtual connection to every
station.
 The server creates copies of the received frame and sends a copy to a group of
stations or to all stations, simulating a multicasting or broadcasting process.
 The server can also deliver a unicast frame by sending frame to every station. In
this case , the address is unknown and it is sometimes more efficient than getting
the connection identifier from the LES.