TDC 461: Session 9

DePaul University

Spring Quarter, 2001

Agenda

• FDDI

• ATM

• Internetworking

• IPv6

FDDI (Fiber Data Distributed Interface)

FDDI Ring

ATM

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.

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).

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.

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)

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.

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.

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).

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) •

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.

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.

Three ways ATM controls congestion:

• 1. Admission control -

• 2. Resource reservation -

• 3. Rate-based congestion control -

ATM Cells

• 53 byte cell - small so switching can be performed in hardware. – Generic flow control -

– Virtual path identifier -

– Virtual channel identifier –

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 -

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.

ATM Adaptation Layer (AAL)

• The AAL is the transport layer of ATM.

• AAL can provide the following services:– 1. – 2. – 3. – 4.

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.

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

Connection-Mode Operations

• Intermediate Systems

• For data transmission

• End-to-end connections

Connection-Oriented Routers

• Intermediate internetworking systems that operate at Layer 3 of the OSI model.

• Relaying=>

• Routing=>

Connectionless-Mode Operations

• Different routes

• Independent routing decisions

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)

Bridges

Why Use Bridges• Reliability=>

• Performance=>

Why Use Bridges, cont.

• Security=>

• Geography=>

Bridge Functions

•

Requirements of Internetworking

•

•

•

•

Connectionless Internetworking (IP)

• Advantages– Flexibility=> – Highly robust=> – Connectionless Transport Protocols=>

ICMP

• =>internet control message protocol

•

•

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

ICMP Messages, cont.

• Timestamp and timestamp reply=>

• Address mask request/reply=>

Routing Protocols

• Routing information=>

• Routing algorithm=>

Different Types of Routing

• Routing between End Systems and routers

• Routing between routers

Border Gateway Protocol (BGP)

• =>

•

•

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

IPv6 New Developments

• 128-bit address space

• Better options management=>

• Address AutoConfiguration=>

• Addressing flexibility=>

IPv6 New Developments, cont.

• Support for resource allocation=>

• Security capabilities=>