Performance Metrics & Network Architectures Professor Jinhua Guo CIS 427 Winter 2003

Performance Metrics Bandwidth (throughput) –data transmitted per time unit –Ex: 10 million bits per second, 10Mbp –Bandwidth related to “bit width” –link versus end-to-end –notation KB = 2 10 bytes Mbps = 10 6 bits per second Propagation delay –Amount of time it takes a signal to propagate from one end of a link to another –Propagation = Distance / c –one-way versus round-trip time (RTT)

Latency –time to send message from point A to point B –components Latency = Propagation Delay + Insertion Delay + Queue Propagation Delay = Distance / c Insertion Delay (transmit) = Size / Bandwidth Note: –No queuing delays in direct link –Bandwidth not relevant if size = 1 bit –Process-to-process latency includes software overhead –Software overhead can dominate when distance is small

Bandwidth versus RTT Relative importance –1-byte: 1ms vs 100ms dominates 1Mbps vs 100Mbps –25MB: 1Mbps vs 100Mbps dominates 1ms vs 100ms Infinite bandwidth –RTT dominates Effective Throughput = TransferSize / TransferTime TransferTime = RTT + 1/Bandwidth x TransferSize –1-MB file to 1-Gbps link as 1-KB packet to 1-Mbps link

Delay x Bandwidth Product –Amount of data “in flight” or “in the pipe” –Example: 100ms x 45Mbps = 560KB Application Needs –Bandwidth requirement: constant rate, burst and perk rate –Jitter: Variance in latency (inter-packet gap)

Layering Use abstractions to hide complexity Abstraction naturally lead to layering Application programs Hardware Host-to-host connectivity Process-to-process channels

Alternative abstractions at each layer Request/reply channel Message stream channel Application programs Hardware Host-to-host connectivity

Protocols Building blocks of a network architecture Each protocol object has two different interfaces –service interface: operations on this protocol –peer-to-peer interface: messages exchanged with peer Term “protocol” is overloaded –specification of peer-to-peer interface –module that implements this interface

Host 1 Protocol Host 2 Protocol High-level object High-level object Service interface Peer-to-peer interface Interfaces

Protocol Graph –collection of protocols and their dependencies –most peer-to-peer communication is indirect –peer-to-peer is direct only at hardware level File application Digital library application Video application RRPMSP HHP Host 1 File application Digital library application Video application RRPMSP HHP Host 2

Multiplexing and Demultiplexing (demux key) Encapsulation (header/body) RRPDataHHP Application program Application program Host 1Host 2 Data RRP Data HHP Data RRP Data HHP

Standard Architecture Open Systems Interconnection (OSI) Architecture –International Standards Organization (ISO) –International Telecommunication Union (ITU) formerly CCITT –“X dot” series: X.25, X.400, X.500, … –Reference Model

ISO Architecture Application Presentation Session Transport End host One or more nodes within the network Network Data link Physical Network Data link Physical Network Data link Physical Application Presentation Session Transport End host Network Data link Physical

Internet Architecture Defined by Internet Engineering Task Force (IETF) Application vs Application Protocol (FTP, HTTP) … FTPHTTPNV TFTP TCP UDP IP NET 1 2 n

TCPUDP IP Network Application Does not imply strict layering Hourglass shape Implement as you go Features of Internet Architecture