Transcript 2-Network Architectures

Network Architectures :
 ISO-OSI
 TCP/IP
 SNA
 ISDN
 ADSL
 X.25
 FDDI
 ATM
ISO-OSI Model
TCP/IP and OSI model
System Network Architecture (SNA)
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IBM’s Networking architecture that has a layered
logical structure and common conventions for
communicating among wide variety of hardware and
software communication products.
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SNA defines standards, protocols and functions – from
mainframes to terminals - that are used for transmitting
information units through networks.
System Network Architecture (SNA)
• SNA was developed by IBM in mid-1970s.
• SNA’s objective was as follows:
– Reduce the cost of operating large number of terminals
and as well as difficulties using earlier communication
protocols in large networks
– This would induce customers to use terminal-based system
opposed to batch systems
• IBM’s goal was an expansion of interactive terminal based
systems that would increase sales of terminals including
mainframe computers and peripherals.
SNA Architecture
• SNA’s overall structure is parallel to OSI reference model.
• IBM SNA maps to all the 7 layers of OSI model
Integrated Services Digital Network (ISDN)
• ISDN allows multiplexing of devices over
single ISDN line
• Two interfaces
– Basic ISDN Interface
– Primary ISDN Interface
Basic ISDN Interface (1)
• Digital data exchanged between subscriber and NTE
- Full Duplex
• Separate physical line for each direction
• Pseudoternary coding scheme
– 1=no voltage, 0=positive or negative 750mV +/-10%
• Data rate 192kbps
• Basic access is two 64kbps B channels and one
16kbps D channel
• This gives 144kbps multiplexed over 192kbps
• Remaining capacity used for framing and sync
Basic ISDN Interface (2)
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B channel is basic user channel
Data
PCM voice
Separate logical 64kbps connections for different
destinations
• D channel used for control or data
– LAPD frames
• Each frame 48 bits long
• One frame every 250s
Frame Structure
Primary ISDN
• Point to point
• Typically supporting PBX
• 1.544Mbps
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Based on US DS-1
Used on T1 services
23 B channels plus one D channel
Line coding is AMI using B8ZS
• 2.048Mbps
– Based on European standards
– 30 B channels plus one D channel
– Line coding is AMI using HDB3
Conceptual View of ISDN Connection Features
Asymmetrical Digital Subscriber Line
• ADSL
• Link between subscriber and network
– Local loop
• Uses currently installed twisted pair cable
– Can carry broader spectrum
– 1 MHz or more
Use of Packets
Advantages
• Line efficiency
– Single node to node link can be shared by many packets
over time
– Packets queued and transmitted as fast as possible
• Data rate conversion
– Each station connects to the local node at its own speed
– Nodes buffer data if required to equalize rates
• Packets are accepted even when network is busy
– Delivery may slow down
• Priorities can be used
Switching Technique
• Station breaks long message into packets
• Packets sent one at a time to the network
• Packets handled in two ways
– Datagram
– Virtual circuit
Datagram
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Each packet treated independently
Packets can take any practical route
Packets may arrive out of order
Packets may go missing
Up to receiver to re-order packets and recover
from missing packets
Virtual Circuit
• Preplanned route established before any
packets sent
• Call request and call accept packets establish
connection (handshake)
• Each packet contains a virtual circuit identifier
instead of destination address
• No routing decisions required for each packet
• Clear request to drop circuit
• Not a dedicated path
Virtual Circuit vs Datagram
• Virtual circuits
– Network can provide sequencing and error control
– Packets are forwarded more quickly
• No routing decisions to make
– Less reliable
• Loss of a node looses all circuits through that node
• Datagram
– No call setup phase
• Better if few packets
– More flexible
• Routing can be used to avoid congested parts of the network
X.25
• 1976
• Interface between host and packet switched
network
• Almost universal on packet switched networks
and packet switching in ISDN
• Defines three layers
– Physical
– Link
– Packet
X.25 - Physical
• Interface between attached station and link to
node
• Data terminal equipment DTE (user
equipment)
• Data circuit terminating equipment DCE
(node)
• Reliable transfer across physical link
• Sequence of frames
X.25 - Link
• Link Access Protocol Balanced (LAPB)
– Subset of HDLC (High-Level Data Link Control)
X.25 - Packet
• External virtual circuits
• Logical connections (virtual circuits) between
subscribers
X.25 Use of Virtual Circuits
Virtual Circuit Service
• Virtual Call
– Dynamically established virtual circuit
• Permanent virtual circuit
– Fixed network assigned virtual circuit
Frame Relay
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Designed to be more efficient than X.25
Developed before ATM
Larger installed base than ATM
ATM now of more interest on high speed
networks
Frame Relay Background - X.25
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Call control packets, in band signaling
Multiplexing of virtual circuits at layer 3
Layer 2 and 3 include flow and error control
Considerable overhead
Not appropriate for modern digital systems
with high reliability
Frame Relay - Differences
• Call control carried in separate logical connection
• Multiplexing and switching at layer 2
– Eliminates one layer of processing
• No hop by hop error or flow control
• End to end flow and error control (if used) are done
by higher layer
• Single user data frame sent from source to
destination and ACK (from higher layer) sent back
Advantages and Disadvantages
• Lost link by link error and flow control
– Increased reliability makes this less of a problem
• Streamlined communications process
– Lower delay
– Higher throughput
• ITU-T recommend frame relay above 2Mbps
Frame Relay - Virtual Circuits
• Permanent virtual circuits (PVCs)
– Original standard, more commonly used
• Switched virtual circuits (SVCs)
– Getting popular now
Permanent Virtual Circuits
• Set up by a network operator
• Defined as a connection between two sites
• Fixed path, not to be set up on a call-by-call
basis
• Pre-configured by the provider or network
manager with given bandwidth allocated
packet-by-packet
Switched Virtual Circuits
• Available by a call-by-call basis
• User specifies a destination address similar to
a phone number
• Network dynamically establishes connections
based on requests by many users
• Network allocates bandwidth based on the
user’s request
Fiber Distributed Data Interface
(FDDI)
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ANSI X3T9.5
Topology - token-passing
2 counter-rotating rings
Each ring operates at 100 Mbps over fiber optic
cable
maximum of 1000 stations
distance 120 mile path (200k)
required repeaters to push transmission (2K)
data is usually carried on the primary ring
FDDI Station Types
• Dual-Attachment Station (DAS)
– connects to both primary and secondary rings
– requires 4 fibers to the desk
– allows the ring to continue to operate even if a
break occurs in the line by rerouting through the
secondary ring (backwards)
• Single-Attachment Station (SAS)
– connects only to the primary ring
– requires 2 fibers to the desk
Mainframe
FDDI Topology
DAS
DAS
Workstations
Primary Ring
DAS
Secondary Ring
Gateway
SAS
SAS
DAS
FDDI Hub
SAS
DAS
Bridge
FDDI - How does it work?
• Media accesss control
– variation of token-passing standard
– FDDI allows multiple messages to attach to the token increases throughput above 100 Mbps
• An FDDI-to-IEEE 802.x bridge is required to
connect to lower speed corporate LANs
• At each node the optical signal is:
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converted to an electrical signal
amplified
copied (if necessary)
converted back to light to send to the next node
Types of FDDI
• Basic FDDI previously discussed
• FDDI-C (FDDI on Copper)
– Copper Distributed Data Interface (CDDI)
– uses copper wire instead of fiber optic
• FDDI-II
– permits transmission of voice and video over the same
cable as FDDI token-passing data
– uses time division multiplexing
– 17 channels
• 1 - 768 Kbps channel (token-passing)
• 16 - 6.144 Mbps channels (wide band - voice/video or data)
Switched Networks
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Switched Ethernet
Full-Duplex Ethernet
Switched Token Ring
Switched FDDI
Asynchronous Transfer Mode (ATM)
Fibre Channel
Switched Ethernet
– the switch replaces the hub
– creates a point-to-point circuit to the switch
– allows multiple transmissions between
computers
– store-and-forward
– improves LAN performance
– circuit to the server is the network bottleneck
Other Ethernet Solutions
• Full-Duplex Ethernet
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uses the same cables as regular Ethernet
10BaseT but full-duplex
doubles the speed of connections to 20 Mbps
full-duplex only from the switch to the server
• may have several connections to one server
• 10/100 switched ethernet
– combines 10BaseT and 100BaseT to the server
– cheaper to install than 100Base-T
– maybe as fast as fast ethernet
Switched Token Ring
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token ring switch replaces the token ring hub
provides a series of point-to-point connections
star topology
no token to pass because of full duplex switch
called “token-ring” because it uses token ring
packet format and is compatible with 802.5
hardware
– dedicated token ring (DTR) full duplex
– 32 Mbps data rate due to full duplex (16 Mbps
each direction)
Switched FDDI
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FDDI witch replaces the FDDI hub
point-to-point connctions to computers
star topology
no token because all computers can transmit
and receive at will
• same packet format and is fully compatible
with other FDDI hardwar
Asynchronous Transfer Mode (ATM)
• Cell-based switching and multiplexing technology
• Asynchronous; transmitted cells need not be periodic
in times as in STM
• General purpose: for a wide range of services: voice,
packet data, video, imaging
• Applied to both LAN and private network
technologies
Asynchronous Transfer Mode (ATM)
• Support both constant bit rate (CBR) or variable bit
rate (VBR)
• Each cell contains addresses information that
establishes a virtual connection from source to
destination
• Support both permanent virtual connections or
switched virtual connections (PVCs or SVCs)
• Support multiple Quality of Service (QoS) classes for
different applications on delay and loss performance
Asynchronous Transfer Mode (ATM)
• Transmit text, voice, video, data traffic
ATM Cell
• Fixed size cell 53 octets, 5-octet header and
48-octet payload (1 octet = 8 bits)
Protocol Architecture
• Similarities between ATM and packet switching
– Transfer of data in discrete chunks
– Multiple logical connections over single physical interface
• In ATM flow on each logical connection is in fixed
sized packets called cells
• Minimal error and flow control
– Reduced overhead
• Data rates (physical layer) 25.6Mbps to 622.08Mbps
Protocol Architecture (Diagram)
Reference Model Planes
• User plane
– Provides for user information transfer
• Control plane
– Call and connection control
• Management plane
– Plane management
• whole system functions
– Layer management
• Resources and parameters in protocol entities
ATM Logical Connections
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Virtual channel connections (VCC)
Analogous to virtual circuit in X.25
Basic unit of switching
Between two end users
Full duplex
Fixed size cells
Data, user-network exchange (control) and networknetwork exchange (network management and routing)
• Virtual path connection (VPC)
– Bundle of VCC with same end points
ATM Connection Relationships
Advantages of Virtual Paths in ATM
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Simplified network architecture
Increased network performance and reliability
Reduced processing
Short connection setup time
Enhanced network services