TDC 461: Session 9
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Transcript of TDC 461: Session 9
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TDC 461: Session 9
DePaul University
Spring Quarter, 2001
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Agenda
• FDDI
• ATM
• Internetworking
• IPv6
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FDDI (Fiber Data Distributed Interface)
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FDDI Ring
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ATM
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ATM Details
• Cell size fixed at 53 bytes (5 byte header and 48 byte payload).
• Multiple logical connections over a physical connection.
• Minimal error and flow control.
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ATM vs. OSI
• ATM layers do not map well onto the OSI layers
• The ATM Layer does many network functions (routing, switching, addressing) but also does a few data link functions (flow control and frame packaging).
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Logical Connections
• A logical connection is called a virtual channel connection (VCC). –
• Virtual path connection (VPC)=>
• VCCs are established for data transfer, control signaling, and network management and routing.
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Logical Connections, Cont.
• VCCs can be established:– Between two end users (data and control signals).
– Between end user and a network entity (user to network control signaling) (User-Network Interface)
– Between two network entities (network management and routing signals) (Network-Network Interface)
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Characteristics of VCCs:
• Quality of service
• Switched virtual channel(circuit) and semi-permanent virtual channel connections
• Cell sequence integrity
• Traffic parameter negotiation and usage monitoring, such as average rate, peak rate, burstiness, peak duration.
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Connection Setup of Switched Virtual Channels
• Connection setup actually handled by complex ITU protocol called Q.2931.
• Nonetheless, basic idea is as follows:
– 1. Must first acquire a virtual channel for signaling. To establish a channel, a request is sent over virtual path 0, virtual channel 5.
– 2. Host issues a SETUP message, saying "Please establish a circuit."
– 3. Network responds with a CALL PROCEEDING message. As the SETUP message propagates toward the destination, it is acknowledged at each hop by another CALL PROCEEDING.
– 4. SETUP arrives at destination, and if connection accepted, a CONNECT is returned. As CONNECT propagates back through network, CONNECT ACKs are returned.
– 5. Release of connection works similarly.
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Routing and Switching
• No particular routing algorithm specified.– However, routes are only established for virtual
path, not virtual channels. Once a path has been established, additional channels may be established over that path. This keeps routing table smaller (212 virtual paths, where each path can have 216 channels).
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Service Categories
• 4 Kinds of traffic an can ATM network carry– 1. Constant Bit Rate (CBR) – 2. Variable Bit Rate (VBR )– 3. Available Bit Rate (ABR)
•
– 4. Unspecified Bit Rate (UBR) •
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Quality of Service
• User at transport layer and network agree upon a certain level of service.
• This contract consists of three parts:– 1. – 2. – 3.
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Congestion Control
•
• But congestion in ATM is tricky, because:– 1. Stop and wait– 2. Small header– 3. One policy for all traffic types will not work– 4. The high switching speeds in ATM can
produce some serious bottlenecks REAL fast.
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Three ways ATM controls congestion:
• 1. Admission control -
• 2. Resource reservation -
• 3. Rate-based congestion control -
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ATM Cells
• 53 byte cell - small so switching can be performed in hardware. – Generic flow control -
– Virtual path identifier -
– Virtual channel identifier –
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Cell Payload Type
• Payload type - user data or management data, congestion experienced or not.– For example: 000 User data cell, no congestion,
cell type 0.– 001 User data cell, no congestion, cell type 1.– 010 User data cell, congestion experienced, cell
type 0.– Cell loss priority -
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Header Error Control
• Header error control - 8 bit CRC (x8 + x2 + x + 1) which error checks the first 4 bytes of the header (not the data!). ATM can perform single-bit error correction or multi-bit error detection. How? ATM uses an adaptation of the Hamming code technique known as Bose-Chadhuri-Hocquenghem (BCH) codes.
• A 40-bit field (the cell header) needs 8 protection bits of BCH code to achieve 89% detection of multiple bits, and correction of a single bit.
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ATM Adaptation Layer (AAL)
• The AAL is the transport layer of ATM.
• AAL can provide the following services:– 1. – 2. – 3. – 4.
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Making Networks Talk to Each Other
• Internetworking=> the process of enabling multiple and diverse networks to communicate with one another via bridges and/or routers.
• Subnetwork=> a constituent network of an internet.
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Internetworking Accommodation• Different addressing schemes• Different maximum packet size• Different network-access methods• Different timeouts• Error recovery• Status Reporting• Routing techniques• User-access control• Connection/Connectionless
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Connection-Mode Operations
• Intermediate Systems
• For data transmission
• End-to-end connections
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Connection-Oriented Routers
• Intermediate internetworking systems that operate at Layer 3 of the OSI model.
• Relaying=>
• Routing=>
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Connectionless-Mode Operations
• Different routes
• Independent routing decisions
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Bridge Operations
• aka MAC-level relay
• Connectionless operation, but at layer 2 rather than layer 3
• Works with only like-network technologies (e.g., ethernet to ethernet)
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Bridges
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Why Use Bridges• Reliability=>
• Performance=>
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Why Use Bridges, cont.
• Security=>
• Geography=>
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Bridge Functions
•
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Requirements of Internetworking
•
•
•
•
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Connectionless Internetworking (IP)
• Advantages– Flexibility=> – Highly robust=> – Connectionless Transport Protocols=>
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ICMP
• =>internet control message protocol
•
•
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ICMP Messages
• Destination unreachable=> router is unable to complete message delivery
• Time Exceeded=> lifetime of datagram has expired
• Source-Squench=> simple version of flow control• Redirect=> redirect the PDU onto a better
alternative route• Echo and echo-reply=> tests communication
viability
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ICMP Messages, cont.
• Timestamp and timestamp reply=>
• Address mask request/reply=>
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Routing Protocols
• Routing information=>
• Routing algorithm=>
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Different Types of Routing
• Routing between End Systems and routers
• Routing between routers
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Border Gateway Protocol (BGP)
• =>
•
•
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IPv6 (IP Next Generation)
• Motivations– limitation of the 32-bit address field
• 2-level address scheme wasteful (network number and host number)
• IP model requires a unique network address even if network isn’t connected
• Rapid growth in number of internets
• Demand for unique Ips will outstrip availability
• Desire to assign multiple Ips to a single host
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IPv6 New Developments
• 128-bit address space
• Better options management=>
• Address AutoConfiguration=>
• Addressing flexibility=>
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IPv6 New Developments, cont.
• Support for resource allocation=>
• Security capabilities=>