Alternative metrics
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This document discusses several routing metrics that can be used for wireless networks beyond traditional hop count. It describes least interference routing (LIR) which calculates path cost based on the number of stations that can receive a transmission. It also mentions max-min residual capacity routing (MMRCR) and least resistance routing (LRR) which take interference into account. An example is provided to show how LIR can find a path with the lowest cost between two nodes by factoring interference, even if the paths have the same hop count.
![Sender S1 wants to send a packet to receiver R1,& S2 to R2.
Using the hop count as metric S1 could choose three different paths with three
hops which is also the minimum.
S1 to R1
Possible paths are (S1,N3,N4,R1)
(S1,N3,N2,R1)
(S1,N!,N2,R1)]
S2 to R2
Possible paths are ( S2,N5,N6,R2)
Taking Interference into account . To calculate the possible interference of a path
each node calculates its possible interference
Interference:-
The number of neighbors that can overhear a transmission .
Every node only needs local information to compute its interference
In this example the Interference of node N3 is 6 and for node N4 is 5 etc.
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Alternative metrics
- 1. ALTERNATIVE METRICS In a fixed networks e.g. Bandwidth can also be a factor for the routing metric. Due to the varying link quality and the fact that different transmissions can interface other metrics can be more useful. One other metric called least interference routing (LIR) • LIR ( Least Interference Routing) :- • LIR is very simple to implement only information from direct neighbors • necessary. • Takes possible interference into account. • Calculate the cost of path based on the No. of stations that can receive a • transmission. 1
- 2. • MMRCR:- (Max-Min Residual Capacity routing) • • Calculate the cost of path based on a probability function of successful; • transmissions and interference. LRR (Least Resistance Routing) • Calculate the cost of path based on interference, jamming & other • transmissions. 2
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- 4. Sender S1 wants to send a packet to receiver R1,& S2 to R2. Using the hop count as metric S1 could choose three different paths with three hops which is also the minimum. S1 to R1 Possible paths are (S1,N3,N4,R1) (S1,N3,N2,R1) (S1,N!,N2,R1)] S2 to R2 Possible paths are ( S2,N5,N6,R2) Taking Interference into account . To calculate the possible interference of a path each node calculates its possible interference Interference:- The number of neighbors that can overhear a transmission . Every node only needs local information to compute its interference In this example the Interference of node N3 is 6 and for node N4 is 5 etc. 4
- 5. Calculating the costs of possible path between S1 and R1 results in the following C1 = cost(S1,N3,N4,R1) = 16 C2=cost(S1,N3,N2,R1) = 15 C3 = cost(S1,N1,N2,R1) = 12 All three paths have the same number of hops but the last path has the lowest cost due to interference. S1 chooses (S1,N1,N2,R1) S2 also computes the cost of different paths C4=cost(S2,N5,N6,R2) = 16 C5=cost(S2,N7,N8,N9,R2)=15 S2 chooses the path (S2,N2,N8,N9,R2). 5
- 6. - Routing can take place several metrics into account at the same time and weigh them. Metrics could be the Number of hops h interference i reliability r error rate e 6
- 7. ACTIVITY-1 : POGIL – Random Groups (7) – With the understanding of Routing, the students will be made to discuss the concepts of IP Routing Protocols like, OSPF (Open Shortest Path First) IS-IS (Intermediate System-to-Intermediate System) BGP (Border Gateway Protocol Representative of the groups will summarize the points and share in class. 7
- 8. 8 Protocol support for mobility IPV4, DHCP, HTTP,SMTP,TCP/IP,FTP , etc.. Changes in IPv6 for Mobile IPv6 • A set of mobility options to include in mobility messages • A new Home Address option for the Destination Options header • A new Type 2 Routing header • New Internet Control Message Protocol for IPv6 (ICMPv6) messages to discover the set of home agents and to obtain the prefix of the home link • Changes to router discovery messages and options and additional Neighbor Discovery options • Foreign Agents are no longer needed
- 9. File systems – Motivation Goal • efficient and transparent access to shared files within a mobile environment while maintaining data consistency. Problems • limited resources of mobile computers (memory, CPU, ...) • low bandwidth, variable bandwidth, temporary disconnection • high heterogeneity of hardware and software components (no standard PC architecture) • wireless network resources and mobile computer are not very reliable • standard file systems (e.g., NFS, network file system) are very inefficient, almost unusable Solutions • replication of data (copying, cloning, caching) • data collection in advance (hoarding, pre-fetching) 9
- 10. File systems - consistency problems • THE big problem of distributed, loosely coupled systems • are all views on data the same? • how and when should changes be propagated to what users? Weak Consistency • many algorithms offering strong consistency (e.g., via atomic updates) cannot be used in mobile environments • invalidation of data located in caches through a server is very problematic if the mobile computer is currently not connected to the network • occasional inconsistencies have to be tolerated, but conflict resolution strategies must be applied afterwards to reach consistency again • Conflict detection • content independent: version numbering, time-stamps • content dependent: dependency graphs 10
- 11. 8.11 Database systems in mobile environments • Request processing – power conserving, location dependent, cost efficient – example: find the fastest way to a hospital • Replication management – similar to file systems • Location management – tracking of mobile users to provide replicated or location dependent data in time at the right place (minimize access delays) – example: with the help of the HLR (Home Location Register) in GSM a mobile user can find a local towing service • Transaction processing – “mobile” transactions can not necessarily rely on the same models as transactions over fixed networks (ACID: atomicity, consistency, isolation, durability) – therefore models for “weak” transaction
- 12. 12 ACTIVITY-2 : JIGSAW – Column wise groups (5) – Students will be motivated to make a discussion on Features and Various Versions of NFS. Conclude points in each group and share among the fellow-mates
- 13. 8.13 World Wide Web and mobility • Protocol (HTTP, Hypertext Transfer Protocol) and language (HTML, Hypertext Markup Language) of the Web have not been designed for mobile applications and mobile devices, thus creating many problems! • Typical transfer sizes – HTTP request: 100-350 byte – responses avg. <10 kbyte, header 160 byte, GIF 4.1kByte, JPEG 12.8 kbyte, HTML 5.6 kbyte – but also many large files that cannot be ignored • The Web is no file system – Web pages are not simple files to download – static and dynamic content, interaction with servers via forms, content transformation, push technologies etc. – many hyperlinks, automatic loading and reloading, redirecting – a single click might have big consequences!
- 14. 8.14 HTTP 1.0 and mobility I • Characteristics – stateless, client/server, request/response – needs a connection oriented protocol (TCP), one connection per request (some enhancements in HTTP 1.1) – primitive caching and security • Problems – designed for large bandwidth (compared to wireless access) and low delay – large and redundant protocol headers (readable for humans, stateless, therefore large headers in ASCII) – uncompressed content transfer – using TCP • huge overhead per request (3-way-handshake) compared with the content, e.g., of a GET request • slow-start problematic as is without having to deal with the wireless problem – DNS lookup by client causes additional traffic and delays
- 15. 8.15 HTTP 1.0 and mobility II • Caching – quite often disabled by information providers to be able to create user profiles, usage statistics etc. – dynamic objects cannot be cached • numerous counters, time, date, personalization, ... – mobility quite often inhibits caches – security problems • caches cannot work with authentication mechanisms that are contracts between client and server and not the cache – today: many user customized pages, dynamically generated on request via CGI, ASP, ... • POSTing (i.e., sending to a server) – can typically not be buffered, very problematic if currently disconnected • Many unsolved problems!
- 16. 8.16 HTML and mobile devices • HTML – designed for computers with “high” performance, color high-resolution display, mouse, hard disk – typically, web pages optimized for design, not for communication • Mobile devices – often only small, low-resolution displays, very limited input interfaces (small touch-pads, soft-keyboards) • Additional “features” – animated GIF, Java AWT, Frames, ActiveX Controls, Shockwave, movie clips, audio, ... – many web pages assume true color, multimedia support, high-resolution and many plug-ins • Web pages ignore the heterogeneity of end-systems! – e.g., without additional mechanisms, large high-resolution pictures would be transferred to a mobile phone with a low- resolution display causing high costs
- 17. 8.17 Approaches toward a WWW for mobile devices • Application gateways, enhanced servers – simple clients, pre-calculations in the fixed network – Compression, transcoding, filtering, content extraction – automatic adaptation to network characteristics • Examples – picture scaling, color reduction, transformation of the document format (e.g., PS to TXT) – Present only parts of the image: detail studies, clipping, zooming – headline extraction, automatic abstract generation – HDML (handheld device markup language): simple language similar to HTML requiring a special browser, developed by Unwired Planet – HDTP (handheld device transport protocol): transport protocol for HDML, developed by Unwired Planet • Problems – proprietary approaches, require special enhancements for browsers – heterogeneous devices make approaches more complicated
- 18. 8.18 mobile client browser integrated enhancement System support for WWW in a mobile world I • Enhanced browsers – Pre-fetching, caching, off-line use – e.g. Internet Explorer web server
- 19. 8.19 System support for WWW in a mobile world II • Client Proxy – Pre-fetching, caching, off-line use – e.g., Caubweb, TeleWeb, Weblicator, WebWhacker, WebEx, WebMirror, ... mobile client browser client proxy web server
- 20. 8.20 System support for WWW in a mobile world III • Client and network proxy – combination of benefits plus simplified protocols – e.g., MobiScape, WebExpress • Special network subsystem – adaptive content transformation for bad connections, pre-fetching, caching – e.g., Mowgli • Additional many proprietary server extensions possible – “channels”, content negotiation, ... mobile client browser web server mobile client browser client proxy web server network proxy client proxy network proxy
- 21. • ACTIVITY-3 – ROLEPLAY – Students assuming them as the protocols of WWW and its mobility services and enact the functionalities of them. (HTTP,FTP, SMTP) 21