Download ICSA 745 Transmission Systems Foundations

ICSA 745 Transmission Systems
Foundations for Emerging
Technologies
Nirmala Shenoy
Dept. of Information Technology
Rochester Institute of Technology
Scope
• Virtual circuits
• Connection oriented and connectionless
services
• Variable and constant bit rate services
• Flow control and congestion management
Scope
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User payload integrity management
Address and identification schemes
Multiplexing methodologies
Switching, routing and relaying
Virtual Circuits
• Physical circuit
– two users communicate directly with each
other through a circuit
• Virtual circuit
– User unaware of sharing
– Intermediate systems relay information as
they arrive
Types of Virtual Circuits
• Permanent Virtual Circuit - PVC
Allocated by contract
• Switched Virtual Circuits - SVC
allocated on demand
• Semi-Permanent Virtual Circuits – SPVC
– Not guaranteed continuous service
Permanent Virtual Circuits
• Requires a contract agreement
• Provisioned on a continuous basis
• Entries stored at intermediate nodes for
appropriate handling
• Payloads should carry assigned identifier
• Quality of service - throughput, delay,
security, error-rates, etc. specified
Switched Virtual Circuit
• Not pre-provisioned
• Call setup essential
• Connection request -virtual circuit number
allocation, connection tear down
• Virtual circuit number is used during the
session to route information –
• Resources released when session is over
Semi-permanent Virtual Circuits
• Pre-provisioned similar to PVC
• Does not guarantee that users will obtain
level of requested service
Connection-Oriented System
• Systems using virtual circuits
• Connection setup, connection tear down
• Forwarding nodes maintain connection
information for packet handling
• Processing overheads
• Normally in-sequence delivery
Connectionless Systems
• Does not employ virtual circuits
• No information maintained by intermediate
nodes
• Ad hoc processing
• Known as datagram networks
Comparison
• Connection-Oriented
• Connectionless
– more control over
traffic and servicing
user’s QOS
– Faster payload
processing
– Low end-to-end
delays
Foundation
updated 12/2001
– No Qos guarantees
– Robust
– forwarding decisions
to be made
11
Coexistence
• Telephone networks – throughout
connection oriented
• TCP/IP based transfers – end-to-end
connection oriented, within the network
connection less
• UDP/IP – connectionless throughout
• Protocol Layer based
Traffic Characteristics
• Different applications have different
patterns of traffic
– Continuous
– Bursty
– Highly Bursty
Variable Bit Rate
• Service preferred by bursty traffic
– Periods of lull and periods of heavy traffic
• Transmit and receive traffic asynchronously
• Loose timing and synchronisation between
sender and receiver
• Traffic may be queued during bursts
• Non-real-time, Real time
• Example: email, client-server apps, video(?)
Constant Bit Rate
• Can be used by services requiring
continuous bandwidth
– Predictable and bound delay, low jitter
• Normally preferred by real-time services
• Example: voice, video, video-conferencing
(?)
Virtual Multiple Networks
• Integrated VBR and CBR service support
• All traffic is digitized
• Manage the different traffic and provide fair
and suitable service for all traffic
• User perspective – one network
Flow Control
• Network QoS Requirement –
– traffic should not saturate a network
– Should not exceed the network’s capacity
• Methods of flow control
– Explicit
– Implicit
– None
Explicit Flow Control
• Network explicitly informs end systems via
“explicit messages” on the amount of traffic
the end systems can send
• Users can increase traffic on congestion
clearance
Implicit Flow Control
• Informs user about congestion
– Packet dropping, messages
• User should reduce traffic, else data will be
dropped
• Control messages
– user is violating service contract
– network is congested
No Flow Control
• Network discards any traffic that is creating
congestion
– Simple for network to implement
– User service requirements not met
• Connectionless networks have traffic regulation
mechanisms
– carrier-sense collision
– issuance of tokens
User Payload Integrity Mgmt
• All payload correctly received
– Network responsibility?
– End system responsibility?
• Do all applications need this feature?
– EFT, voice, video, data – service based?
Addresses & Labels
• Connectionless systems – Explicit Address
– each PDU uses explicit addresses for routing
– IP address - network/subnetwork/device
• Connection-oriented systems - Labels
– uses a short label or Virtual Circuit Identifier
– label used to index into state tables to determine the
explicit location or forwarding information
Multiplexing
• Frequency Division Multiplexing (FDM)
– each user has fixed portion of freq. spectrum
• Time Division Multiplexing (TDM)
– each user is given a slot
– slots are rotated among the attached users
• Statistical TDM (STDM)
– dynamically allocate time slots
• Code Division Multiplexing
– Usage of codes
Network Interface
• User-to-Network Interface - UNI or SNI
– protocol that governs the interface between
the user and the network
• Network-to-Network Interface - NNI or ICI
– protocol that governs the interface between
networks
Switching, Routing and Relaying
• Relaying – forward data as it comes
• Switching – comes in at one input is
switched on to another
• Routing – decision made on which path to
take
– Source routing
– Non-source routing
Network Interfaces
• UNI or SNI
– User network interface, subscriber network interface
• NNI or INSI – within network
– Network- network interface, intra-network switching
interface
• NNI or ICI – between networks
– inter-carrier interface
Convergence Operations
• Performed at UNI
– Add synchronization and accommodate
different transfer rates
• Convergence Sublayer - CS
• Application specific
• Example: error detection, synchronization
Segmentation and Reassembly
• Segmentation is performed on the user
traffic before it enters the network
• Reassembly is performed before data
reaches end user