CS-09 – Data Communications and Networks

AGENDA (Session 12)

Classless Internet Domain Routing

IPV6

ATM (Network Layer)

ATM Service Categories

Transport Layer

Transport Primitives

Transport Addressing

ATM Adaptation Layer

Network Performance Issues

CIDR (Classless Internet Domain Routing)

· Class ABC system of IPV4 wastes lot of Internet Addresses.

· Routers are supported to know at least all network addresses so there table sizes explode.

· CIDR (RFC 1519) allocates contiguous class C addresses instead of Class B.

· The world is partitioned as:

194.0.0.0 – 195.255.255.255 for Europe

198.0.0.0 – 199.255.255.255 for North America

200.0.0.0 – 201.255.255.255 for Central and South America

202.0.0.0 – 203.255.255.255 for Asia and pacific

204.0.0.0 – 223.255.255.255 for future use.

· Routing tables are now zonal.

· 32 bit masks are now used to route within class C addressing of a zone.

IPV6 (Internet Protocol Version 6)

· 16 Byte long addresses instead of 4 byte address.

· Header is simpler, less no. of fields.

· Options support is better.

· Security considerations improved.

IPV6 Header:

· Version – 4 bit (contains version 4 or 6).

· Priority – 4bits (Value 0-7 for non-real traffic, value 8-15 for real time traffic: this is defined in type of service field in ipv4).

· Flow Label – 24 bits (For setting pseudo connections with special requirements).

· Payload Length – 16 bits (How many bytes follow 40 bit header: header bytes not counted in IPV6 as in IPV4 data-length field).

· Next header – 8 bit (Next following header (optional) identification can also determine which protocol to handover (TCP, UDP etc.) when given in the last packet ).

· Hop limit – 8 bits (Time to live in terms of hops).

· Source – 16 bytes (128 bits)

· Destination – 16 bytes (128 bits)

Comparison to IPV4:

· IHL of IPV4 not required because of fixed header length.

· Protocol field handled by next header.

· Fragment fields are avoided by fixing ipv6 conformance of 576 bytes, otherwise extension headers can support it.

· Checksum is not done in IPV6 leaving it to D/L and Transport layer.

More Info:

· IPV4 packet on IPV4 start with 80 leading zeros and following 16 bits inform about how to use IPV6 over IPV4 routers.

· IPV6 addresses are written as 4 hexa-digits separated by colon (:) , double colon (::) shortcut can be used for a group of 0s.

ATM (Asynchronous Transfer Mode)

· Resembles more to network layer (Routing and switching algorithms).

· IP is put on top of ATM so sometimes considered as a part of data-link layer also.

· Connection Oriented (Virtual Channels).

· No Acks (designed for fiber channel).

· Guarantee of cells arrival in order (Along a virtual channel).

· Transmission path – Group of Virtual Paths.

· Virtual path – group of Virtual Channels.

UNI - User Network Interface (Between Host and ATM Switch):

40 Bit (5 bytes) header format

GFC (4)

VPI (8)

VCI (16)

PTI (3)

CLP (1)

HEC (8)

NNI – Network-Network Interface (Between ATM Switches):

40 Bit (5 bytes) header format

VPI (12)

VCI (16)

PTI (3)

CLP (1)

HEC (8)

GFC : General Flow Control (Flow control or priority, but not used)

VPI : Virtual Path Identifier

VCI : Virtual Channel Identifier

PTI : Payload Type Identifier (Data Type, Congestion status, Maintenance function etc.)

CLP: Cell Loss Priority (CLP=1 are discarded earlier)

HEC: Header Error Check (All Single bit error and 90% multi-bit errors are correctable)

ATM – Service Categories

CBR (Constant Bit Rate):

· Similar to copper circuits

· E.g. T1, E1 circuits.

VBR (Variable Bit rate):

· RT-VBR (Real Time VBR) e.g. Video Conferencing.

· NRT-VBR e.g. Video Email.

· Timely delivery is important.

ABR (Available Bit rate):

· No long term commitment to fixed bandwidth.

· E.g. web-surfing.

UBR (Unspecified Bit rate):

· Bit rate not known, data taken if capacity available else discarded.

· Could be cheaper service.

· E.g. Background File Transfer.

Transport Layer

· Efficient, Reliable and Cost Effective service to its users.

· Is mostly on Host systems-thus acts as the final interface point between application and the Physical media.

· Transport entity on the OS kernel or on the NIC.

· To improve situation either load is decreased to resources are increased (Using spare routers, Multiple Router splitting)

· Two peer Entities talk using TPDU (Transport protocol data unit)

· Connection oriented or Connectionless supported.

· Application programs are possible to write with a standard primitives and do not depend upon variations in the types of networks etc.

· TPDU header is put within network layer payload.

Simple Transport Primitives:

· LISTEN (Do nothing accept to wait for process trying to connect)

· CONNECT (Attempt to make connection)

· SEND (Send Info.)

· RECEIVE (Receive Info).

· DISCONNECT (wish to release)

BERKLEY SOCKETS:

· More feature packed transport primitives in UNIX.

· SOCKET (Communication end point creation).

· BIND (Attach a local address).

· LISTEN (Willingness to accept)

· ACCEPT (Block until a connection attempt)

· CONNECT (Attempt connection)

· SEND

· RECEIVE

· CLOSE (Release instruction)

· Allows port addressing flexibility

Transport Addressing

· Layer has multiple TSAP (Transport Service Access Points).

· Server process attaches itself to specific TSAP. Fixed by prior arrangement or dynamically found by calling a process server first (Initial Connection Protocol).

· Alternately A Name Server or Directory server process is used to find the requested process TSAP first)

· TSAP addresses are hierarchical addresses in order to determine which physical hardware the TSAP belong to.

· In case of Flat address space a second level mapping may be required to locate a proper machine.

ATM – AAL (ATM Adaptation) Layer Protocols

· Cannot be ideally defined as transport layer. TCP runs above it.

· Requirement defined on following parameters.

o Real-time vs. Non-real time.

o CBR versus VBR.

o CO (Connection oriented) versus CL (Connectionless).

· Part 1 - Convergence Sub-layer (Service specific and common)

· Part 2 – SAR (Segmentation – Reassembly sub-layer)

AAL 1:

· Real Time, CBR, Connection-Oriented.

· E.g. Uncompressed audio and video.

· Message boundary not preserved.

· No error protocols because delays are unacceptable.

AAL 2:

· Real Time, VBR, Connection Oriented.

· E.g. Compressed video (rate can vary).

· Message Boundary preserved.

AAL 3/4:

· Non real Time, VBR, CO or CL.

· Message Mode with preserved boundaries.

· Stream mode without boundaries.

· Multiplexing of several sessions allowed.

AAL 5

· Designed for computer traffic.

· SEAL (Simple efficient Adaptation Layer).

· Reliable service / Unreliable Service with flow and error control if required.

· Both Message and Stream mode supported.

· Uni-cast and Multicasting support.

Network Performance

Performance Problems:

· Congestion due to resource overload.

· Structural imbalance.

· Synchronous Overload (Error Broadcast).

· Address resolution after power failure.

· System Tuning Problem.

· Incorrectly set timeouts.

· Bandwidth delay Product is the Pipe capacity. Utilising it to maximum is the objective of performance enhancement.

Measuring Performance:

· Sample size is large and representative.

· Measured during expected and standard traffic situations.

· Avoid caching during measurement.

· Result extrapolations are not linear.

Designing for better performance:

· CPU speed is most important.

· Reduce packet count.

· Reduce switching between software contexts.

· Minimize copying data between various layers.

· Delay not improved by more bandwidth, so improve logic.

· Avoid congestion and timeouts.

· Faster TPDU processing. Replication in header information can be predicted and thus special shorter routines can be called when predictable data is coming.

· Better Timer and buffer management.