CS 5565 Network Architecture and Protocols Lecture 16 Godmar Back

Announcements Midterm April 1 (Wednesday) Project 2A due Apr 8 Required Reading: DCCP by Koehler et al, SIGCOMM 2006 CS 5565 Spring 2009 2/23/2019

Handling multiple clients using multiple execution contexts A/B: # grows & shrinks A B C/D: fixed # C D Q.: When would you use which? CS 5565 Spring 2009 2/23/2019

Network Layer

The Network Layer transports segment from sending to receiving host on sending side encapsulates segments into datagrams on receiving side, delivers segments to transport layer network layer protocols in every host, router router examines header fields in all IP datagrams passing through it network data link physical application transport CS 5565 Spring 2009 2/23/2019

Key Network-Layer Functions forwarding: move packets from router’s input to appropriate router output routing: determine route taken by packets from source to dest. Routing algorithms analogy: routing: process of planning trip from source to dest forwarding: process of getting through single interchange CS 5565 Spring 2009 2/23/2019

Interplay between Routing and Forwarding 1 2 3 0111 value in arriving packet’s header routing algorithm local forwarding table header value output link 0100 0101 1001 CS 5565 Spring 2009 2/23/2019

Network Service Model Q: What service model for “channel” transporting datagrams from sender to receiver? Example services for individual datagrams: Guaranteed delivery Guaranteed delivery with less than 40 msec delay Example services for a flow of datagrams: In-order datagram delivery Guaranteed minimum bandwidth to flow Restrictions on changes in inter-packet spacing CS 5565 Spring 2009 2/23/2019

Network Layer Service Models: Guarantees ? Network Architecture Internet ATM Service Model best effort CBR VBR ABR UBR Congestion feedback no (inferred via loss) no congestion yes Bandwidth none constant rate guaranteed minimum Loss no yes Order no yes Timing no yes CS 5565 Spring 2009 2/23/2019

Datagram vs VC Networks Datagram network provides network-layer connectionless service VC network provides network-layer connection service Analogous to the transport-layer services, but different in: Service: host-to-host No choice: network provides one or the other Implementation: in the core CS 5565 Spring 2009 2/23/2019

Virtual Circuits “source-to-dest path behaves much like telephone circuit” performance-wise network actions along source-to-dest path call setup, teardown for each call before data can flow each packet carries VC identifier (not destination host address) every router on source-dest path maintains “state” for each passing connection link, router resources (bandwidth, buffers) may be allocated to VC CS 5565 Spring 2009 2/23/2019

Virtual Circuits: Signaling Protocols used to setup, maintain teardown VC used in ATM, frame-relay, X.25 not used in today’s Internet (at least not end-to-end) application transport network data link physical application transport network data link physical 5. Data flow begins 6. Receive data 4. Call connected 3. Accept call 1. Initiate call 2. incoming call CS 5565 Spring 2009 2/23/2019

VC Implementation A VC consists of: Path from source to destination VC numbers, one number for each link along path Entries in forwarding tables in routers along path Packet belonging to VC carries a VC number. VC number must be changed on each link. New VC number comes from forwarding table CS 5565 Spring 2009 2/23/2019

Forwarding Tables in VCN 12 22 32 1 2 3 VC number interface number Forwarding table in northwest router: Incoming interface Incoming VC # Outgoing interface Outgoing VC # 1 12 2 22 2 63 1 18 3 7 2 17 1 97 3 87 … … … … Routers maintain connection state information! CS 5565 Spring 2009 2/23/2019

Datagram Networks no call setup at network layer routers: no state about end-to-end connections no network-level concept of “connection” packets forwarded using destination host address packets between same source-dest pair may take different paths application transport network data link physical application transport network data link physical 1. Send data 2. Receive data CS 5565 Spring 2009 2/23/2019

Internet vs ATM Internet ATM data exchange among computers “elastic” service, no strict timing req. “smart” end systems (computers) can adapt, perform control, error recovery simple inside network, complexity at “edge” many link types different characteristics uniform service difficult ATM evolved from telephony human conversation: strict timing, reliability requirements need for guaranteed service “dumb” end systems telephones complexity inside network CS 5565 Spring 2009 2/23/2019

Router Architectures; Packet Forwarding & Classification

Router Architecture Overview Two key router functions: run routing algorithms/protocol (RIP, OSPF, BGP) forwarding datagrams from incoming to outgoing link CS 5565 Spring 2009 2/23/2019

Input Port Functions Decentralized switching: Physical layer: bit-level reception Decentralized switching: given datagram dest., lookup output port using forwarding table in input port memory goal: complete input port processing at ‘line speed’ queuing: if datagrams arrive faster than forwarding rate into switch fabric Data link layer: e.g., Ethernet CS 5565 Spring 2009 2/23/2019

Forwarding Tables Destination Address Range Link Interface 11001000 00010111 00010000 00000000 through 0 11001000 00010111 00010111 11111111 11001000 00010111 00011000 00000000 through 1 11001000 00010111 00011000 11111111 11001000 00010111 00011001 00000000 through 2 11001000 00010111 00011111 11111111 otherwise 3 CS 5565 Spring 2009 2/23/2019

Longest Prefix Matching Prefix Match Link Interface 11001000 00010111 00010 0 11001000 00010111 00011000 1 11001000 00010111 00011 2 otherwise 3 Examples DA: 11001000 00010111 00010110 10100001 Which interface? DA: 11001000 00010111 00011000 10101010 Which interface? DA: 11001000 00010111 00011010 00100101 Which interface? CS 5565 Spring 2009 2/23/2019

Packet Classification Service Example Packet Filtering Deny all traffic from ISP3(on interface X) destined to E2 Policy Routing Send all voice-over-IP traffic arriving from E1 (on interface Y) and destined to E2 via a separate ATM network. Accounting & Billing Treat all video traffic to E1(via interface Y) as highest priority and perform accounting for the traffic sent this way. Traffic Rate Limiting Ensure that ISP2 does not inject more than 10Mbps of email traffic and 50Mbps of total traffic on interface X Traffic Shaping Ensure that no more than 50Mbps of web traffic is injected into ISP2 on interface X. Source [Gupta & McKeown 2001] CS 5565 Spring 2009 2/23/2019

Performance Metrics for Packet Classification (Gupta/McKeown) Search speed 10 Gbps will have 31.25 Mp/s for min-TCP Low storage requirements The smaller, the faster (SRAM) Ability to handle large real-life classifiers Fast updates Scalability in number of header fields used for classification Flexibility in specification Not just prefixes: ranges, operators, wildcards, etc. CS 5565 Spring 2009 2/23/2019

Example for 2 Fields Priority Geometry problem: N number of regions, d number of dimensions; regions are prioritized Best worst case time O(log N) time with O(Nd) space Best worst case space O(N) with O((log N)d-1) time CS 5565 Spring 2009 2/23/2019

Packet Classification Solutions Basic data structures Linear search, caching, hierarchical tries, set-pruning tries Geometry-based structures Grid-of-tries, AQT (area-based quadtree), FIS (fat-inverted segment tree) Heuristics RFC (recursive flow classification), hierarchical cuttings, tuple-space search Hardware Ternary CAM (content-addressable memory), bitmap-intersection CS 5565 Spring 2009 2/23/2019

Three Types of Switching Fabrics CS 5565 Spring 2009 2/23/2019

Switching Via Memory First generation routers: traditional computers with switching under direct control of CPU packet copied to system’s memory speed limited by memory bandwidth (2 bus crossings per datagram) Newer routers: processing done via local processors on line cards Input Port Output Memory System Bus CS 5565 Spring 2009 2/23/2019

Switching Via a Bus datagram from input port memory to output port memory via a shared bus bus contention: switching speed limited by bus bandwidth 32 Gbps bus, Cisco 5600: sufficient speed for access and enterprise routers (not regional or backbone) CS 5565 Spring 2009 2/23/2019

Switching Via An Interconnection Network Overcome bus bandwidth limitations Banyan/Butterfly networks, other interconnection nets initially developed to connect processors in multiprocessor machines Advanced design: fragmenting datagram into fixed length cells, switch cells through the fabric. Cisco 12000: switches Gbps through the interconnection network See Cisco Whitepaper for more information & background CS 5565 Spring 2009 2/23/2019

Output Ports Buffering required when datagrams arrive from fabric faster than the transmission rate Possibility of queueing (delay) and loss due to output port buffer overflow! Scheduling discipline chooses among queued datagrams for transmission CS 5565 Spring 2009 2/23/2019

Scheduling Disciplines Single or multiple queues If multiple: Flow-based or Class-based FCFS, RR (Round-Robin), WRR Various priority schemes: expedited packets, assured forwarding WFQ (Weighted Fair Queuing) proportional sharing of link between queues HFSC (Hierarchical Fair Service Curve) hierarchical extension, better queuing delay bounds CS 5565 Spring 2009 2/23/2019

HFSC Decouple latency and bandwidth allocations Source: [Zhang] CS 5565 Spring 2009 2/23/2019

Active Queue Management (AQM) When should packets be dropped? Goal: avoid congestion Simplest policy: drop-tail If queue is full, drop new arrivals More sophisticated: Random Early Detection (RED) Before queue fills up, mark some packets randomly for drop Idea: force TCP congestion control to throttle rate Lots of research in this area CS 5565 Spring 2009 2/23/2019

Input Port Queuing Fabric slower than input ports combined  queueing may occur at input queues Head-of-the-Line (HOL) blocking: queued datagram at front of queue prevents others in queue from moving forward queueing delay and loss due to input buffer overflow! CS 5565 Spring 2009 2/23/2019

Summary Basics of Network Layer Next: Routing Algorithms Routing (path selection) vs Forwarding (switching) Service models Datagram Networks vs VC Networks Basics of routers Packet classification, Packet Scheduling, AQM Next: Routing Algorithms CS 5565 Spring 2009 2/23/2019