Chapter 5 Network Layer Part 1

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1 Chapter 5 Network Layer Part 1
Topics: Network layer design issues Routing Algorithm

2 1. Network Layer Design Isues
Store-and-Forward Packet Switching Services Provided to the Transport Layer Implementation of Connectionless Service Implementation of Connection-Oriented Service Comparison of Virtual-Circuit and Datagram Subnets

3 Store-and-Forward Packet Switching
fig 5-1 The environment of the network layer protocols.

4 Service Provided to Transport Layer
The network layer provides services to the transport layer at the network layer/transport layer interface The network layer services have been designed with the following goals : The services should be independent of the router technology. The transport layer should be shielded from the number, type, and topology of the routers present. The network addresses made available to the transport layer should use a uniform numbering plan, even across LANs and WANs. Thus, the designers of the network layer have a lot of freedom in writing detailed specifications of the services to be offered to the transport layer

5 Implementation of Connectionless Service
The algorithm that manages the tables and makes the routing decisions is called the routing algorithm

6 Implementation of Connection-Oriented Service
Routing within a virtual-circuit subnet.

7 Comparison of Virtual-Circuit and Datagram Subnets
5-4

8 2. Routing Algorithms The Optimality Principle Static Routing
Shortest Path Routing Flooding Dynamic Routing Distance Vector Routing Link State Routing Hierarchical Routing Broadcast Routing Multicast Routing Routing for Mobile Hosts Routing in Ad Hoc Networks

9 Routing Algorithms It is sometimes useful to make a distinction between : routing, which is making the decision which routes to use, and forwarding, which is what happens when a packet arrives.

10 Routing Algorithms Routing algorithms can be grouped into two major classes: Non-adaptive (static) Adaptive (dynamic) In the following sections we will discuss a variety of routing algorithms, both static and dynamic.

11 The Optimality Principle
If router J is on the optimal path from router I to router K, then the optimal path from J to K also falls along the same route Since a sink tree is indeed a tree, it does not contain any loops, so each packet will be delivered within a finite and bounded number of hops Tujuan dari semua algoritma routing adalah untuk menemukan dan menggunakan sink tree bagi seluruh router (a) A subnet. (b) A sink tree for router B.

12 Static Routing Shortest Path Routing Flooding

13 1. Shortest Path Routing The first 5 steps used in computing the shortest path from A to D. The arrows indicate the working node.

14 Dijkstra's algorithm to compute the shortest path through a graph.
5-8 top Dijkstra's algorithm to compute the shortest path through a graph.

15 Dijkstra’s Algorithm (2)
5-8 bottom Dijkstra's algorithm to compute the shortest path through a graph.

16 2. Flooding Setiap paket yang masuk dikirimkan melalui saluran keluar kecuali saluran tempat paket tersebut datang. Problems vs Solution Age  Hop counter More flood  Sequence number Duplication  Limit the sequence number, by augmenting with a counter Distributed database applications, wireless networks, a metric against which other routing algorithms can be compared

17 Dynamic routing Distance Vector Routing Link State Routing

18 1. Distance Vector Routing
Setiap router menjaga sebuah tabel routing yang di indeks oleh masing2 router pada subnet dan berisi sebuah entry bagi setiap router di dalam subnet. Entry ini berisi : Saluran keluar untuk mencapai tujuan Estimasi waktu atau jarak ke tujuan itu (a) A subnet. (b) Input from A, I, H, K, and the new routing table for J.

19 Distance Vector Routing (2)
Routing bereaksi cepat untuk berita baik Routing bereaksi sgt lambat utk berita buruk Solusi: menetapkan nilai tertinggi The count-to-infinity problem.

20 2. Link State Routing Pengembangan kapasitas saluran yg berbeda mengharuskan untuk memperhitungkan bandwidth sbg parameter. Solusinya : link state routing Each router must do the following: Discover its neighbors, learn their network address. Measure the delay or cost to each of its neighbors. Construct a packet telling all it has just learned. Send this packet to all other routers. Compute the shortest path to every other router.

21 1-Learning about the Neighbors
- Ketika router di boot ! - Paket “hello” via P2P Nama router harus unik (a) Nine routers and a LAN. (b) A graph model of (a).

22 2-Measuring Line Cost Lintasan yg tdk berbeban sbg rute --> unjuk kerja meningkat Memperhitungkan delay? Routing berosilasi scr tdk teratur, routing mjd tdk menentu A subnet in which the East and West parts are connected by two lines.

23 3-Building Link State Packets
Kapan membuatnya? (a) A subnet. (b) The link state packets for this subnet.

24 4-Distributing the Link State Packets
Tumpang tindih? 32 bit ! Router tabrakan/ duplikat Nmr urut rusak The packet buffer for router B in the previous slide (Fig ).

25 5-Computing the New Routes
Router membuat graf subnet keseluruhan Algoritma dijkstra dpt dioperasikan scr lokal utk menentukan lintasan terpendek. Memori yg dibutuhkan sebanding dengan kn, dg n= jumlah router, dan k= jumlah tetangga tiap router Bila subnet sangat besar? Memori?

26 Hierarchical Routing Hierarchical routing. Tabel routing bertambah:
Konsumsi memori router Waktu penulusuran 720 Router = Berapa entry? - Tanpa hirarki 24 30 router 8 9 rou Hierarchical routing.

27 Broadcast Routing Reverse path forwarding. (a) A subnet. (b) a Sink tree. (c) The tree built by reverse path forwarding.

28 Multicast Routing (a) A network. (b) A spanning tree for the leftmost router. (c) A multicast tree for group 1. (d) A multicast tree for group 2.

29 Routing for Mobile Hosts
A WAN to which LANs, MANs, and wireless cells are attached.

30 Routing for Mobile Hosts (2)
Packet routing for mobile users.