Topics:

-Network layer design issues

-Routing Algorithm

Chapter 5

Network Layer Part 1

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

Store-and-Forward Packet Switching

The environment of the network layer protocols.

fig 5-1

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 :1.The services should be independent of the router technology.2.The transport layer should be shielded from the number, type, and

topology of the routers present.3.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

Implementation of Connectionless Service

The algorithm that manages the tables and makes the routing decisions is called the routing algorithm

Implementation of Connection-Oriented Service

Routing within a virtual-circuit subnet.

Comparison of Virtual-Circuit and Datagram Subnets

5-4

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

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.

Routing Algorithms

Routing algorithms can be grouped into two major classes:

a)a) NNonon--adaptive adaptive (static)(static)

b)b) AdaptiveAdaptive (dynamic) (dynamic)

In the following sections we will discuss a variety of routing algorithms, both static and dynamic.

The Optimality Principle

(a) A subnet. (b) A sink tree for router B.

Tujuan dari semua algoritma routing adalah untuk menemukan dan menggunakan sink tree bagi seluruh router

• 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

Static Routing

1. Shortest Path Routing

2. Flooding

1. Shortest Path Routing

The first 5 steps used in computing the shortest path from A to D. The arrows indicate the working node.

Dijkstra’s Algorithm

Dijkstra's algorithm to compute the shortest path through a graph.

5-8 top

Dijkstra’s Algorithm (2)

Dijkstra's algorithm to compute the shortest path through a graph.

5-8 bottom

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

Dynamic routing

1. Distance Vector Routing

2. Link State Routing

1. Distance Vector Routing

(a) A subnet. (b) Input from A, I, H, K, and the new routing table for J.

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

Distance Vector Routing (2)

The count-to-infinity problem.

Routing bereaksi cepat untuk berita baikRouting bereaksi sgt lambat utk berita buruk

Solusi: menetapkan nilai tertinggi

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:

1.Discover its neighbors, learn their network address.

2.Measure the delay or cost to each of its neighbors.

3.Construct a packet telling all it has just learned.

4.Send this packet to all other routers.

5.Compute the shortest path to every other router.

1-Learning about the Neighbors

(a) Nine routers and a LAN. (b) A graph model of (a).

- Ketika router di boot !- Paket “hello” via P2P-Nama router harus unik

2-Measuring Line Cost

A subnet in which the East and West parts are connected by two lines.

Lintasan yg tdk berbeban sbg rute --> unjuk kerja meningkat

Memperhitungkan delay?

Routing berosilasi scr tdk teratur, routing mjd tdk menentu

3-Building Link State Packets

(a) A subnet. (b) The link state packets for this subnet.

Kapan membuatnya?

4-Distributing the Link State Packets

The packet buffer for router B in the previous slide (Fig. 5-13).

Tumpang tindih?

32 bit !

-Router tabrakan/ duplikat-Nmr urut rusak

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?

Hierarchical Routing

Hierarchical routing.

Tabel routing bertambah:-Konsumsi memori router-Waktu penulusuran

720 Router = Berapa entry?- Tanpa hirarki- 24 wilayah @ 30 router- 8 cluster@ 9 wilyh @10 rou

Broadcast Routing

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

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.

Routing for Mobile Hosts

A WAN to which LANs, MANs, and wireless cells are attached.

Routing for Mobile Hosts (2)

Packet routing for mobile users.